Adaptation and Self-Organizing SystemsAstrophysicsAstrophysics of GalaxiesAtomic, Molecular and Optical PhysicsAtomic PhysicsCondensed Matter PhysicsCosmology and Nongalactic AstrophysicsDisordered Systems and Neural NetworksEarth and Planetary Astrophysics
By: Ryo Asaka, Kazumitsu Sakai, Ryoko Yahagi
We propose an implementation of the algorithm for the fast Fourier transform
(FFT) as a quantum circuit consisting of a combination of some quantum gates.
In our implementation, a data sequence is expressed by a tensor product of
vector spaces. Namely, our FFT is defined as a transformation of the tensor
product of quantum states. It is essentially different from the so-called
quantum Fourier transform (QFT) defined to be a linear transform... more
We propose an implementation of the algorithm for the fast Fourier transform
(FFT) as a quantum circuit consisting of a combination of some quantum gates.
In our implementation, a data sequence is expressed by a tensor product of
vector spaces. Namely, our FFT is defined as a transformation of the tensor
product of quantum states. It is essentially different from the so-called
quantum Fourier transform (QFT) defined to be a linear transformation of the
amplitudes for the superposition of quantum states. The quantum circuit for the
FFT consists of several circuits for elementary arithmetic operations such as a
quantum adder, subtractor and shift operations, which are implemented as
effectively as possible. Namely, our circuit does not generate any garbage
bits. The advantages of our method compared to the QFT are its high
versatility, and data storage efficiency in terms, for instance, of the quantum
image processing.
less
By: Victor Gurarie
Logarithmic operators and logarithmic conformal field theories are reviewed.
Prominent examples considered here include c=-2 and c=0 logarithmic conformal
field theories. c=0 logarithmic conformal field theories are especially
interesting since they describe some of the critical points of a variety of
longstanding problems involving a two dimensional quantum particle moving in a
spatially random potential, as well as critical two dimensiona... more
Logarithmic operators and logarithmic conformal field theories are reviewed.
Prominent examples considered here include c=-2 and c=0 logarithmic conformal
field theories. c=0 logarithmic conformal field theories are especially
interesting since they describe some of the critical points of a variety of
longstanding problems involving a two dimensional quantum particle moving in a
spatially random potential, as well as critical two dimensional self avoiding
random walks and percolation. Lack of classification of logarithmic conformal
field theories remains a major impediment to progress towards finding complete
solutions to these problems.
less
By: Ya-Hui Zhang, Zheng Zhu, Ashvin Vishwanath
XY* transitions represent one of the simplest examples of unconventional quantum criticality, in which fractionally charged excitations condense into a superfluid, and display novel features that combine quantum criticality and fractionalization. Nevertheless their experimental realization is challenging. Here we propose to study the XY* transition in quantum Hall bilayers at filling $(\nu_1,\nu_2)=(\frac{1}{3},\frac{2}{3})$ where the exci... more
XY* transitions represent one of the simplest examples of unconventional quantum criticality, in which fractionally charged excitations condense into a superfluid, and display novel features that combine quantum criticality and fractionalization. Nevertheless their experimental realization is challenging. Here we propose to study the XY* transition in quantum Hall bilayers at filling $(\nu_1,\nu_2)=(\frac{1}{3},\frac{2}{3})$ where the exciton condensate (EC)
phase plays the role of the superfluid. Supported by exact diagonalization calculation, we argue that there is a continuous transition between an EC phase at small bilayer separation to a pair of decoupled fractional quantum Hall states, at large separation. The transition is driven by condensation of a fractional exciton, a bound state of Laughlin quasiparticle and quasihole, and is in the XY* universality class. The fractionalization is manifested by
unusual properties including a large anomalous exponent and fractional universal conductivity, which can be conveniently measured through inter-layer tunneling and counter-flow transport, respectively. We also show that the edge is likely to realize the newly predicted extra-ordinary boundary criticality. Our work highlights the promise of quantum Hall bilayers as an ideal platform for exploring exotic bulk and boundary critical behaviors, that are amenable to immediate experimental exploration in dual-gated bilayer systems.
less
By: Tommaso Cea, Pierre A. Pantaleón, Niels R. Walet, Francisco Guinea
The effects of the long range electrostatic interaction in twisted bilayer graphene are described using the Hartree-Fock approximation. The results show a significant dependence of the band widths and shapes on electron filling, and the existence of broken symmetry phases at many densities, either valley/spin polarized, with broken sublattice symmetry, or both.
The effects of the long range electrostatic interaction in twisted bilayer graphene are described using the Hartree-Fock approximation. The results show a significant dependence of the band widths and shapes on electron filling, and the existence of broken symmetry phases at many densities, either valley/spin polarized, with broken sublattice symmetry, or both.
less
By: Dina Genkina, Lauren M. Aycock, Hsin-I Lu, Alina M. Pineiro, Mingwu Lu, I. B. Spielman
Physical systems with non-trivial topological order find direct applications
in metrology[1] and promise future applications in quantum computing[2,3]. The
quantum Hall effect derives from transverse conductance, quantized to
unprecedented precision in accordance with the system's topology[4]. At
magnetic fields beyond the reach of current condensed matter experiment, around
10^4 Tesla, this conductance remains precisely quantized but takes... more
Physical systems with non-trivial topological order find direct applications
in metrology[1] and promise future applications in quantum computing[2,3]. The
quantum Hall effect derives from transverse conductance, quantized to
unprecedented precision in accordance with the system's topology[4]. At
magnetic fields beyond the reach of current condensed matter experiment, around
10^4 Tesla, this conductance remains precisely quantized but takes on different
values[5]. Hitherto, quantized conductance has only been measured in extended
2-D systems. Here, we engineered and experimentally studied narrow 2-D ribbons,
just 3 or 5 sites wide along one direction, using ultracold neutral atoms where
such large magnetic fields can be engineered[6-11]. We microscopically imaged
the transverse spatial motion underlying the quantized Hall effect. Our
measurements identify the topological Chern numbers with typical uncertainty of
5%, and show that although band topology is only properly defined in infinite
systems, its signatures are striking even in nearly vanishingly thin systems.
less
By: Abraham Loeb, Toby Adamson, Sophie Bergstrom, Richard Cloete, Shai Cohen, Kevin Conrad, Laura Domine, Hairuo Fu, Charles Hoskinson, Eugenia Hyung, Stein Jacobsen, Mike Kelly, Jason Kohn, Edwin Lard, Sebastian Lam, Frank Laukien, Jim Lem, Rob McCallum, Rob Millsap, Christopher Parendo, Michail Pataev, Chaitanya Peddeti, Jeff Pugh, Shmuel Samuha, Dimitar Sasselov, Max Schlereth, J.J. Siler, Amir Siraj, Peter Mark Smith, Roald Tagle, Jonathan Taylor, Ryan Weed, Art Wright, Jeff Wynn
We have conducted an extensive towed-magnetic-sled survey during the period 14-28 June, 2023, over the seafloor about 85 km north of Manus Island, Papua New Guinea, and found about 700 spherules of diameter 0.05-1.3 millimeters in our samples, of which 57 were analyzed so far. Approximately 0.26 km2 of seafloor was sampled in this survey, centered around the calculated path of the bolide CNEOS 2014-01-08 (IMI) with control areas north and sou... more
We have conducted an extensive towed-magnetic-sled survey during the period 14-28 June, 2023, over the seafloor about 85 km north of Manus Island, Papua New Guinea, and found about 700 spherules of diameter 0.05-1.3 millimeters in our samples, of which 57 were analyzed so far. Approximately 0.26 km2 of seafloor was sampled in this survey, centered around the calculated path of the bolide CNEOS 2014-01-08 (IMI) with control areas north and south of that path. The 5 spherules, significantly concentrated along the expected meteor path, were retrieved from seafloor depths ranging between 1.5-2.2 km. Mass spectrometry of 47 spherules near the high-yield regions along IMI's path reveals a distinct extra-solar abundance pattern for 5 of them, while background spherules have abundances consistent with a solar system origin. The unique spherules show an excess of Be, La and U, by up to three orders of magnitude relative to the solar system standard of CI chondrites. These "BeLaU"-type spherules, never seen before, also have very low refractory siderophile elements such 10 as Re. Volatile elements, such as Mn, Zn, Pb, are depleted as expected from evaporation losses during a meteor's airburst. In addition, the mass-dependent variations in 57Fe/54Fe and 56Fe/54Fe are also consistent with evaporative loss of the light isotopes during the spherules' travel in the atmosphere. The "BeLaU" abundance pattern is not found in control regions outside of IMI's path and does not match commonly manufactured alloys or natural meteorites in the solar system. This evidence points towards an association of "BeLaU"-type spherules with IM1, supporting its interstellar origin independently of the high 15 velocity and unusual material strength implied from the CNEOS data. We suggest that the "BeLaU" abundance pattern could have originated from a highly differentiated magma ocean of a planet with an iron core outside the solar system or from more exotic sources. less
By: A. Valli, T. Fabian, F. Libisch, R. Stadler
We investigate the stability of destructive quantum interference (DQI) in electron transport through graphene nanostructures connected to source and drain electrodes. The fingerprint of DQI is the presence of an antiresonance in the transmission function, and its origin is deeply connected to the topology of the atomic structure, which we discuss in terms of symmetry arguments supported by numerical simulations. A systematic analysis of the i... more
We investigate the stability of destructive quantum interference (DQI) in electron transport through graphene nanostructures connected to source and drain electrodes. The fingerprint of DQI is the presence of an antiresonance in the transmission function, and its origin is deeply connected to the topology of the atomic structure, which we discuss in terms of symmetry arguments supported by numerical simulations. A systematic analysis of the influence of system size on the transmission function reveals that the DQI antiresonance persists for large systems in the ballistic regime and establishes the quantum confinement gap as the intrinsic resolution limit to detect QI effects. Furthermore, we consider the influence of disorder, electron-electron and electron-phonon interactions, and provide quantitative criteria for the robustness of DQI in their presence. We find that the conductance is quite sensitive to perturbations, and its value alone may not be sufficient to characterize the QI properties of a junction. Instead, the characteristic behavior of the transmission function is more resilient, and we suggest it retains information on the presence of an antiresonance even if DQI is partially concealed or suppressed. At the same time, DQI results in a non-linear transport regime in the current-bias characteristics that can be possibly detected in transport experiments.
less
By: Tommaso Cea, Pierre A. Pantaleón, Vo Tien Phong, Francisco Guinea
We study the emergence of superconductivity in rhombohedral trilayer graphene due purely to the long-range Coulomb repulsion. This repulsive-interaction-driven phase in rhombohedral trilayer graphene is significantly different from those found in twisted bilayer and trilayer
graphenes. In the latter case, the nontrivial momentum-space geometry of the Bloch wavefunctions leads to an effective attractive electron-electron interaction; this all... more
We study the emergence of superconductivity in rhombohedral trilayer graphene due purely to the long-range Coulomb repulsion. This repulsive-interaction-driven phase in rhombohedral trilayer graphene is significantly different from those found in twisted bilayer and trilayer
graphenes. In the latter case, the nontrivial momentum-space geometry of the Bloch wavefunctions leads to an effective attractive electron-electron interaction; this allows for less modulated order parameters and for spin-singlet pairing. In rhombohedral trilayer graphene, we instead find spin-triplet superconductivity with critical temperatures up to 0.15 K. The critical temperatures strongly depend on electron filling and peak where the density of states diverge. The order parameter shows a significant modulation within each valley pocket of the Fermi surface.
less
By: Jostein N. Kløgetvedt, Alireza Qaiumzadeh
We study magnon-polaron hybrid states, mediated by Dzyaloshinskii-Moriya and
magnetoelastic interactions, in a two-dimensional ferromagnetic insulator. The
magnetic system consists of both in-plane and flexural acoustic and optical
phonon bands, as well as acoustic and optical magnon bands. Through
manipulation of the ground-state magnetization direction using a magnetic
field, we demonstrate the tunability of Chern numbers and (spin) Berry... more
We study magnon-polaron hybrid states, mediated by Dzyaloshinskii-Moriya and
magnetoelastic interactions, in a two-dimensional ferromagnetic insulator. The
magnetic system consists of both in-plane and flexural acoustic and optical
phonon bands, as well as acoustic and optical magnon bands. Through
manipulation of the ground-state magnetization direction using a magnetic
field, we demonstrate the tunability of Chern numbers and (spin) Berry
curvatures of magnon-polaron hybrid bands. This adjustment subsequently
modifies two anomalous Hall responses of the system, namely, thermal Hall and
spin Nernset signals. Notably, we find that by changing the magnetic field
direction in particular directions, it is possible to completely suppress the
thermal Hall signal while maintaining a finite spin Nernst signal. Our finding
reveals the intricate interplay between topological and quantum geometrical
phenomena and magnetic ordering, offering compelling avenues for on-demand
control over emergent quantum states in condensed matter systems.
less
By: Kaizhen Guo, Yuan Li, Shuang Jia
We successfully synthesized polycrystalline LK-99-like ceramic samples with a
solid-state-sintering method. Powder X-ray diffraction shows that the main
contents are $\mathrm{Pb_{10-x}Cu_x(PO_4)_6O}$ and $\mathrm{Cu_2S}$, consistent
with recent reports [arXiv:2307.12037; arXiv:2308.01192]. In some small flaky
fragments, we successfully observed ``half levitation'' atop a
$\mathrm{Nd_2Fe_{14}B}$ magnet. Using magnetization measurements on su... more
We successfully synthesized polycrystalline LK-99-like ceramic samples with a
solid-state-sintering method. Powder X-ray diffraction shows that the main
contents are $\mathrm{Pb_{10-x}Cu_x(PO_4)_6O}$ and $\mathrm{Cu_2S}$, consistent
with recent reports [arXiv:2307.12037; arXiv:2308.01192]. In some small flaky
fragments, we successfully observed ``half levitation'' atop a
$\mathrm{Nd_2Fe_{14}B}$ magnet. Using magnetization measurements on such small
pieces, as well as on a large piece which does not exhibit the half levitation,
we show that the samples ubiquitously contain weak yet definitive soft
ferromagnetic components. We argue that, together with the pronounced shape
anisotropy of the small fragments, the soft ferromagnetism is sufficient to
explain the observed half levitation in strong vertical magnetic fields. Our
measurements do not indicate the presence of the Meissner effect, nor zero
resistance, in our samples, leading us to believe that our samples do not
exhibit superconductivity.
less
By: Vo Tien Phong, Pierre A. Pantaleón, Tommaso Cea, Francisco Guinea
We study the symmetries of twisted trilayer graphene's band structure under various extrinsic perturbations, and analyze the role of long-range electron-electron interactions near the first magic angle. The electronic structure is modified by these interactions in a similar way to twisted bilayer graphene. We analyze electron pairing due to long-wavelength charge fluctuations, which are coupled among themselves via the Coulomb interaction and... more
We study the symmetries of twisted trilayer graphene's band structure under various extrinsic perturbations, and analyze the role of long-range electron-electron interactions near the first magic angle. The electronic structure is modified by these interactions in a similar way to twisted bilayer graphene. We analyze electron pairing due to long-wavelength charge fluctuations, which are coupled among themselves via the Coulomb interaction and additionally mediated by longitudinal acoustic phonons. We find superconducting phases with either spin singlet/valley triplet or spin triplet/valley singlet symmetry, with critical temperatures of up to a few Kelvin for realistic choices of parameters. less
By: Evan McKinney, Michael Hatridge, Alex K. Jones
Building efficient large-scale quantum computers is a significant challenge
due to limited qubit connectivities and noisy hardware operations.
Transpilation is critical to ensure that quantum gates are on physically linked
qubits, while minimizing $\texttt{SWAP}$ gates and simultaneously finding
efficient decomposition into native $\textit{basis gates}$. The goal of this
multifaceted optimization step is typically to minimize circuit depth ... more
Building efficient large-scale quantum computers is a significant challenge
due to limited qubit connectivities and noisy hardware operations.
Transpilation is critical to ensure that quantum gates are on physically linked
qubits, while minimizing $\texttt{SWAP}$ gates and simultaneously finding
efficient decomposition into native $\textit{basis gates}$. The goal of this
multifaceted optimization step is typically to minimize circuit depth and to
achieve the best possible execution fidelity. In this work, we propose
$\textit{MIRAGE}$, a collaborative design and transpilation approach to
minimize $\texttt{SWAP}$ gates while improving decomposition using
$\textit{mirror gates}$. Mirror gates utilize the same underlying physical
interactions, but when their outputs are reversed, they realize a different or
$\textit{mirrored}$ quantum operation. Given the recent attention to
$\sqrt{\texttt{iSWAP}}$ as a powerful basis gate with decomposition advantages
over $\texttt{CNOT}$, we show how systems that implement the $\texttt{iSWAP}$
family of gates can benefit from mirror gates. Further, $\textit{MIRAGE}$ uses
mirror gates to reduce routing pressure and reduce true circuit depth instead
of just minimizing $\texttt{SWAP}$s. We explore the benefits of decomposition
for $\sqrt{\texttt{iSWAP}}$ and $\sqrt[4]{\texttt{iSWAP}}$ using mirror gates,
including both expanding Haar coverage and conducting a detailed fault rate
analysis trading off circuit depth against approximate gate decomposition. We
also describe a novel greedy approach accepting mirror substitution at
different aggression levels within MIRAGE. Finally, for $\texttt{iSWAP}$
systems that use square-lattice topologies, $\textit{MIRAGE}$ provides an
average of 29.6\% reduction in circuit depth by eliminating an average of
59.9\% $\texttt{SWAP}$ gates, which ultimately improves the practical
applicability of our algorithm.
less
By: J. Talukdar, D. Blume
We consider an array of $N_e$ non-interacting qubits or emitters that are
coupled to a one-dimensional cavity array with tunneling energy $J$ and
non-linearity of strength $U$. The number of cavities is assumed to be larger
than the number of qubits. Working in the two-excitation manifold, we focus on
the bandgap regime where the energy of two excited qubits is off-resonant with
the two-photon bound state band. A two-step adiabatic eliminat... more
We consider an array of $N_e$ non-interacting qubits or emitters that are
coupled to a one-dimensional cavity array with tunneling energy $J$ and
non-linearity of strength $U$. The number of cavities is assumed to be larger
than the number of qubits. Working in the two-excitation manifold, we focus on
the bandgap regime where the energy of two excited qubits is off-resonant with
the two-photon bound state band. A two-step adiabatic elimination of the
photonic degrees of freedom gives rise to a one-dimensional spin Hamiltonian
with effective interactions; specifically, the Hamiltonian features constrained
single-qubit hopping and pair hopping interactions not only between nearest
neighbors but also between next-to-nearest and next-to-next-to-nearest spins.
For a regularly arranged qubit array, we identify parameter combinations for
which the system supports novel droplet-like bound states whose characteristics
depend critically on the pair hopping. The droplet-like states can be probed
dynamically. The bound states identified in our work for off-resonance
conditions are distinct from localized hybridized states that emerge for
on-resonance conditions.
less
By: Jonathan B. Curtis, Prineha Narang, Victor Galitski
The interplay between disorder and quantum interference leads to a wide
variety of physical phenomena including celebrated Anderson localization -- the
complete absence of diffusive transport due to quantum interference between
different particle trajectories. In two dimensions, any amount of disorder is
thought to induce localization of all states at long enough length scales,
though this may be prevented if bands are topological or have s... more
The interplay between disorder and quantum interference leads to a wide
variety of physical phenomena including celebrated Anderson localization -- the
complete absence of diffusive transport due to quantum interference between
different particle trajectories. In two dimensions, any amount of disorder is
thought to induce localization of all states at long enough length scales,
though this may be prevented if bands are topological or have strong spin-orbit
coupling. In this note, we present a simple argument providing another
mechanism for disrupting localization: by tuning the underlying curvature of
the manifold on which diffusion takes place. We show that negative curvature
manifolds contain a natural infrared cut off for the probability of self
returning paths. We provide explicit calculations of the Cooperon -- directly
related to the weak-localization corrections to the conductivity -- in
hyperbolic space. It is shown that constant negative curvature leads to a rapid
growth in the number of available trajectories a particle can coherently
traverse in a given time, reducing the importance of interference effects and
restoring classical diffusive behavior even in the absence of inelastic
collisions. We conclude by arguing that this result may be amenable to
experimental verification through the use of quantum simulators.
less
By: Andrew McCalip and collaborators
A material called LK-99, a modified-lead apatite crystal structure with the composition Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O ($0.9<x<1.1$), was reported to behave as a room-Tc superconductor.
Andrew McCalip and a "do-it-yourself" (DIY) team working in their off hours in El Segundo, CA area chronicled their journey to make and test LK-99 on their own. Demonstrated possible "Meissner effect" levitation with a magnet at room temperature.
A material called LK-99, a modified-lead apatite crystal structure with the composition Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O ($0.9<x<1.1$), was reported to behave as a room-Tc superconductor.
Andrew McCalip and a "do-it-yourself" (DIY) team working in their off hours in El Segundo, CA area chronicled their journey to make and test LK-99 on their own. Demonstrated possible "Meissner effect" levitation with a magnet at room temperature.
less
By: Keavin Moore, Nicolas B. Cowan, Charles-Édouard Boukaré
Earth-like planets orbiting M-dwarf stars, M-Earths, are currently the best
targets to search for signatures of life. Life as we know it requires water.
The habitability of M-Earths is jeopardized by water loss to space: high flux
from young M-dwarf stars can drive the loss of 3 to the power of 20 Earth oceans from
otherwise habitable planets. We develop a 0-D box model for Earth-mass
terrestrial exoplanets, orbiting within the habitable zo... more
Earth-like planets orbiting M-dwarf stars, M-Earths, are currently the best
targets to search for signatures of life. Life as we know it requires water.
The habitability of M-Earths is jeopardized by water loss to space: high flux
from young M-dwarf stars can drive the loss of 3 to the power of 20 Earth oceans from
otherwise habitable planets. We develop a 0-D box model for Earth-mass
terrestrial exoplanets, orbiting within the habitable zone, which tracks water
loss to space and exchange between reservoirs during an early surface magma
ocean phase and the longer deep-water cycling phase. A key feature is the
duration of the surface magma ocean, assumed concurrent with the runaway
greenhouse. This timescale can discriminate between desiccated planets, planets
with desiccated mantles but substantial surface water, and planets with
significant water sequestered in the mantle. A longer-lived surface magma ocean
helps M-Earths retain water: dissolution of water in the magma provides a
barrier against significant loss to space during the earliest, most active
stage of the host M-dwarf, depending on the water saturation limit of the
magma. Although a short-lived basal magma ocean can be beneficial to surface
habitability, a long-lived basal magma ocean may sequester significant water in
the mantle at the detriment of surface habitability. We find that magma oceans
and deep-water cycling can maintain or recover habitable surface conditions on
Earth-like planets at the inner edge of the habitable zone around late M-dwarf
stars -- these planets would otherwise be desiccated if they form with less
than 10 terrestrial oceans of water.
less
By: Harshit Sharma, Udaysinh T. Bhosale
Earlier studies have given enough evidence in support of the BGS conjecture,
with few exceptions violating it. Here, we provide one more counterexample
using a many-body system popularly known as the model of quantum kicked top
consisting of $N$ qubits with all-to-all interaction and kicking strength
$k=N\pi/2$. We show that it is quantum integrable even though the corresponding
semiclassical phase-space is chaotic, thus violating the BGS c... more
Earlier studies have given enough evidence in support of the BGS conjecture,
with few exceptions violating it. Here, we provide one more counterexample
using a many-body system popularly known as the model of quantum kicked top
consisting of $N$ qubits with all-to-all interaction and kicking strength
$k=N\pi/2$. We show that it is quantum integrable even though the corresponding
semiclassical phase-space is chaotic, thus violating the BGS conjecture. We
solve the cases of $N=5$ to $11$ qubits analytically, finding its eigensystem,
the dynamics of the entanglement, and the unitary evolution operator. For the
general case of $N>11$ qubits, we provide numerical evidence of integrability
using degenerate spectrum, and the exact periodic nature of the time-evolved
unitary evolution operator and the entanglement dynamics.
less
By: Hao Wu, Li Yang, Bichen Xiao, Haixin Chang
Recently, Sukbae Lee et al. reported inspiring experimental findings on the atmospheric superconductivity of a modified lead apatite crystal (LK-99) at room temperature (10.6111/JKCGCT.2023.33.2.061, arXiv: 2307.12008, arXiv:2307.12037). They claimed that the synthesized LK-99 materials exhibit the Meissner levitation phenomenon of superconductors and have a superconducting
transition temperature (Tc) higher than 400 K. Here, for the first ... more
Recently, Sukbae Lee et al. reported inspiring experimental findings on the atmospheric superconductivity of a modified lead apatite crystal (LK-99) at room temperature (10.6111/JKCGCT.2023.33.2.061, arXiv: 2307.12008, arXiv:2307.12037). They claimed that the synthesized LK-99 materials exhibit the Meissner levitation phenomenon of superconductors and have a superconducting
transition temperature (Tc) higher than 400 K. Here, for the first time, we successfully verify and synthesize the LK-99 crystals which can be magnetically levitated with larger levitated angle than Sukbae Lee's sample at room temperature. It is expected to realize the true potential of room temperature, non-contact superconducting magnetic levitation in near future.
less
By: Qiang Hou, Wei Wei, Xin Zhou, Yue Sun, Zhixiang Shi
Room-temperature superconductivity has always been regarded as the ultimate goal in the fields of solid-state physics and materials science, with its realization holding revolutionary significance, capable of triggering significant changes in energy transmission and storage. However, achieving it poses various challenges. Recent research revealed that material Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O displays room-temperature superconductivity under ... more
Room-temperature superconductivity has always been regarded as the ultimate goal in the fields of solid-state physics and materials science, with its realization holding revolutionary significance, capable of triggering significant changes in energy transmission and storage. However, achieving it poses various challenges. Recent research revealed that material Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O displays room-temperature superconductivity under atmospheric pressure, sparking global interest in further exploration. Here, we utilized solid-phase synthesis to obtain a polycrystalline sample of
Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O. X-ray diffraction confirmed its structural consistency with referenced literature. Zero resistance, which is important evidence for superconductivity, was observed above 100$^\circ$ K under ambient pressure in our experiment. Our finding indicates that Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O is a possible candidate for searching high-temperature superconductors.
less
By: Gerson J. Ferreira, Boyu Wang, Jiyong Fu, Roberto Raimondi
The reciprocal interconversion between spin polarization and charge current
(CSC) is the focus of intensive theoretical and experimental investigation in
spintronics research. Its physical origin stems from the Rashba spin-orbit
coupling (SOC) induced by the breaking of the structure inversion symmetry. The
steady-state interconversion efficiency is the result of the non-trivial spin
textures of the electric-field distorted Fermi surface. I... more
The reciprocal interconversion between spin polarization and charge current
(CSC) is the focus of intensive theoretical and experimental investigation in
spintronics research. Its physical origin stems from the Rashba spin-orbit
coupling (SOC) induced by the breaking of the structure inversion symmetry. The
steady-state interconversion efficiency is the result of the non-trivial spin
textures of the electric-field distorted Fermi surface. Its full understanding
and evaluation requires the consideration of disorder-induced relaxation
effects in the presence of spin-orbit induced band splitting. In this paper the
additional effect of the orbital degree of freedom is analyzed in a two-subband
quantum well with both conventional and unconventional Rashba SOC in the
presence of disorder impurity scattering. The latter is treated at the level of
the Born approximation in the Green's function self-energy and with the
inclusion of vertex corrections in the linear response functions for the charge
current and the spin polarization. By explicitly considering the symmetry
properties of the Hamiltonian the matrix structure of the correlation functions
is shown to decompose in independent blocks of symmetry-related physical
observables. We find that the inclusion of vertex corrections is important for
the correct estimate of the CSC efficiency, which also depends on the position
of the Fermi level. We also find that the relative sign of the Rashba SOC in
the two subbands plays a key role in determining the behavior of the CSC.
Finally, we point out how the two-subband model compares with the standard
single-band two-dimensional electron gas.
less
By: Pierre A. Pantaleón, Y. Xian
We investigate the properties of magnon edge states in a ferromagnetic honeycomb spin lattice with a Dzyaloshinskii-Moriya interaction (DMI). We derive analytical expressions for the energy spectra and wavefunctions of the edge states localized on the boundaries. By introducing an external on-site potential at the outermost sites, we show that the bosonic band structure is
similar to that of the fermionic graphene. We investigate the region i... more
We investigate the properties of magnon edge states in a ferromagnetic honeycomb spin lattice with a Dzyaloshinskii-Moriya interaction (DMI). We derive analytical expressions for the energy spectra and wavefunctions of the edge states localized on the boundaries. By introducing an external on-site potential at the outermost sites, we show that the bosonic band structure is
similar to that of the fermionic graphene. We investigate the region in the momentum space where the bosonic edge states are well defined and we analyze the width of the edge state and their dependence with DMI strength. Our findings extend the predictions using topological arguments and they allow size-dependent confirmation from possible experiments
less
By: Cicy K Agnes, Akthar Naveed V, Anitha Mary M O Chacko
Exoplanet detection opens the door to the discovery of new habitable worlds
and helps us understand how planets were formed. With the objective of finding
earth-like habitable planets, NASA launched Kepler space telescope and its
follow up mission K2. The advancement of observation capabilities has increased
the range of fresh data available for research, and manually handling them is
both time-consuming and difficult. Machine learning and ... more
Exoplanet detection opens the door to the discovery of new habitable worlds
and helps us understand how planets were formed. With the objective of finding
earth-like habitable planets, NASA launched Kepler space telescope and its
follow up mission K2. The advancement of observation capabilities has increased
the range of fresh data available for research, and manually handling them is
both time-consuming and difficult. Machine learning and deep learning
techniques can greatly assist in lowering human efforts to process the vast
array of data produced by the modern instruments of these exoplanet programs in
an economical and unbiased manner. However, care should be taken to detect all
the exoplanets precisely while simultaneously minimizing the misclassification
of non-exoplanet stars. In this paper, we utilize two variations of generative
adversarial networks, namely semi-supervised generative adversarial networks
and auxiliary classifier generative adversarial networks, to detect transiting
exoplanets in K2 data. We find that the usage of these models can be helpful
for the classification of stars with exoplanets. Both of our techniques are
able to categorize the light curves with a recall and precision of 1.00 on the
test data. Our semi-supervised technique is beneficial to solve the cumbersome
task of creating a labeled dataset.
less
By: Eleni Tsaprazi, Nhat-Minh Nguyen, Jens Jasche, Fabian Schmidt, Guilhem Lavaux
As a large-scale overdensity collapses, it affects the orientation and shape
of galaxies that form, by exerting tidal shear along their axes. Therefore, the
shapes of elliptical galaxies align with the tidal field of cosmic structures.
This intrinsic alignment provides insights into galaxy formation and the
primordial universe, complements late-time cosmological probes and constitutes
a significant systematic effect for weak gravitational l... more
As a large-scale overdensity collapses, it affects the orientation and shape
of galaxies that form, by exerting tidal shear along their axes. Therefore, the
shapes of elliptical galaxies align with the tidal field of cosmic structures.
This intrinsic alignment provides insights into galaxy formation and the
primordial universe, complements late-time cosmological probes and constitutes
a significant systematic effect for weak gravitational lensing observations. In
the present study, we provide constraints on the linear alignment model using a
fully Bayesian field-level approach, using galaxy shape measurements from the
SDSS-III BOSS LOWZ sample and three-dimensional tidal fields constrained with
the LOWZ and CMASS galaxy samples of the SDSS-III BOSS survey. We find
4$\sigma$ evidence of intrinsic alignment, with an amplitude of $A_I=2.9 \pm
0.7$ at 20$h^{-1}\;\mathrm{Mpc}$.
less
By: Abolfazl Ziaeemehr, Mina Zarei, Aida Sheshbolouki
The collective behaviour of neural networks depends on the cellular and
synaptic properties of the neurons. The phase-response curve (PRC) is an
experimentally obtainable measure of cellular properties that quantifies the
shift in the next spike time of a neuron as a function of the phase at which
stimulus is delivered to that neuron. The neuronal PRCs can be classified as
having either purely positive values (type I) or distinct positive a... more
The collective behaviour of neural networks depends on the cellular and
synaptic properties of the neurons. The phase-response curve (PRC) is an
experimentally obtainable measure of cellular properties that quantifies the
shift in the next spike time of a neuron as a function of the phase at which
stimulus is delivered to that neuron. The neuronal PRCs can be classified as
having either purely positive values (type I) or distinct positive and negative
regions (type II). Networks of type 1 PRCs tend not to synchronize via mutual
excitatory synaptic connections. We study the synchronization properties of
identical type I and type II neurons, assuming unidirectional synapses.
Performing the linear stability analysis and the numerical simulation of the
extended Kuramoto model, we show that feedforward loop motifs favour
synchronization of type I excitatory and inhibitory neurons, while feedback
loop motifs destroy their synchronization tendency. Moreover, large directed
networks, either without feedback motifs or with many of them, have been
constructed from the same undirected backbones, and a high synchronization
level is observed for directed acyclic graphs with type I neurons. It has been
shown that, the synchronizability of type I neurons depends on both the
directionality of the network connectivity and the topology of its undirected
backbone. The abundance of feedforward motifs enhances the synchronizability of
the directed acyclic graphs.
less
By: Bianca Turini, Sedighe Salimian, Matteo Carrega, Andrea Iorio, Elia Strambini, Francesco Giazotto, Valentina Zannier, Lucia Sorba, Stefan Heun
We report evidence of non-reciprocal dissipation-less transport in single
ballistic InSb nanoflag Josephson junctions, owing to a strong spin-orbit
coupling. Applying an in-plane magnetic field, we observe an inequality in
supercurrent for the two opposite current propagation directions. This
demonstrates that these devices can work as Josephson diodes, with
dissipation-less current flowing in only one direction. For small fields, the
super... more
We report evidence of non-reciprocal dissipation-less transport in single
ballistic InSb nanoflag Josephson junctions, owing to a strong spin-orbit
coupling. Applying an in-plane magnetic field, we observe an inequality in
supercurrent for the two opposite current propagation directions. This
demonstrates that these devices can work as Josephson diodes, with
dissipation-less current flowing in only one direction. For small fields, the
supercurrent asymmetry increases linearly with the external field, then it
saturates as the Zeeman energy becomes relevant, before it finally decreases to
zero at higher fields. We show that the effect is maximum when the in-plane
field is perpendicular to the current vector, which identifies Rashba
spin-orbit coupling as the main symmetry-breaking mechanism. While a variation
in carrier concentration in these high-quality InSb nanoflags does not
significantly influence the diode effect, it is instead strongly suppressed by
an increase in temperature. Our experimental findings are consistent with a
model for ballistic short junctions and show that the diode effect is intrinsic
to this material. Our results establish InSb Josephson diodes as a useful
element in superconducting electronics.
less
By: Kai Guther, Werner Dobrautz, Olle Gunnarsson, Ali Alavi
We present a stochastic method for solving the time-dependent Schrödinger
equation, generalizing a ground-state full configuration interaction Quantum
Monte Carlo method. By performing the time-integration in the complex plane
close to the real time axis, the numerical effort is kept manageable and the
analytic continuation to real frequencies is efficient. This allows us to
perform ab initio calculation of electron spectra for strongly cor... more
We present a stochastic method for solving the time-dependent Schrödinger
equation, generalizing a ground-state full configuration interaction Quantum
Monte Carlo method. By performing the time-integration in the complex plane
close to the real time axis, the numerical effort is kept manageable and the
analytic continuation to real frequencies is efficient. This allows us to
perform ab initio calculation of electron spectra for strongly correlated
systems. The method can be used as cluster solver for embedding schemes.
less
Reducing the molecular electronic Hamiltonian encoding costs on quantum computers by symmetry shifts
2upvotes
By: Ignacio Loaiza, Artur F. Izmaylov
Computational cost of energy estimation for molecular electronic Hamiltonians via quantum phase estimation (QPE) grows with the spectral norm of the Hamiltonian. In this work we propose a preprocessing procedure that reduces the norm of the Hamiltonian without changing its eigen-spectrum for the target states of a particular symmetry. The new procedure, block-invariant symmetry shift (BLISS), builds an operator T such that the cost of imple... more
Computational cost of energy estimation for molecular electronic Hamiltonians via quantum phase estimation (QPE) grows with the spectral norm of the Hamiltonian. In this work we propose a preprocessing procedure that reduces the norm of the Hamiltonian without changing its eigen-spectrum for the target states of a particular symmetry. The new procedure, block-invariant symmetry shift (BLISS), builds an operator T such that the cost of implementing H-T is reduced compared to that of H, yet H-T acts on the symmetric subspaces of interest the same way as H does. BLISS performance is demonstrated for linear combination of unitaries (LCU)-based QPE approaches on a set of small molecules. Using the number of electrons as the symmetry specifying the target set of states, BLISS provided a factor of 2-3 reduction of 1-norm compared to that in a single Pauli product LCU decomposition.
less
By: Changsu Cao, Jinzhao Sun, Xiao Yuan, Han-Shi Hu, Hung Q. Pham, Dingshun Lv
Quantum computing has shown great potential in various quantum chemical
applications such as drug discovery, material design, and catalyst
optimization. Although significant progress has been made in quantum simulation
of simple molecules, ab initio simulation of solid-state materials on quantum
computers is still in its early stage, mostly owing to the fact that the system
size quickly becomes prohibitively large when approaching the therm... more
Quantum computing has shown great potential in various quantum chemical
applications such as drug discovery, material design, and catalyst
optimization. Although significant progress has been made in quantum simulation
of simple molecules, ab initio simulation of solid-state materials on quantum
computers is still in its early stage, mostly owing to the fact that the system
size quickly becomes prohibitively large when approaching the thermodynamic
limit. In this work, we introduce an orbital-based multi-fragment approach on
top of the periodic density matrix embedding theory, resulting in a
significantly smaller problem size for the current near-term quantum computer.
We demonstrate the accuracy and efficiency of our method compared with the
conventional methodologies and experiments on solid-state systems with complex
electronic structures. These include spin polarized states of a hydrogen chain
(1D-H), the equation of states of a boron nitride layer (h-BN) as well as the
magnetic ordering in nickel oxide (NiO), a prototypical strongly correlated
solid. Our results suggest that quantum embedding combined with a chemically
intuitive fragmentation can greatly advance quantum simulation of realistic
materials, thereby paving the way for solving important yet classically hard
industrial problems on near-term quantum devices.
less
By: Sukbae Lee, Jihoon Kim, Hyun-Tak Kim, Sungyeon Im, SooMin An, Keun Ho Auh
A material called LK-99, a modified-lead apatite crystal structure with the composition Pb$_{10-x}$Cu$_x$(PO$_4$)$_{6O}$ ($0.9<x<1.1$), has been synthesized using the solid-state method. The material exhibits the Ohmic metal characteristic of Pb(6s1) above its superconducting critical temperature, $T_c$, and the levitation phenomenon as Meissner effect of a superconductor at room temperature and atmospheric pressure below $T_c$. A LK-99 sam... more
A material called LK-99, a modified-lead apatite crystal structure with the composition Pb$_{10-x}$Cu$_x$(PO$_4$)$_{6O}$ ($0.9<x<1.1$), has been synthesized using the solid-state method. The material exhibits the Ohmic metal characteristic of Pb(6s1) above its superconducting critical temperature, $T_c$, and the levitation phenomenon as Meissner effect of a superconductor at room temperature and atmospheric pressure below $T_c$. A LK-99 sample shows $T_c$ above 126.85$^\circ$C (400 K). We analyze that the possibility of
room-temperature superconductivity in this material is attributed to two factors: the first being the volume contraction resulting from an insulator-metal transition achieved by substituting Pb with Cu, and the second being on-site repulsive Coulomb interaction enhanced by the structural deformation in the one-dimensional(D) chain (Pb2-O$_{1/2}$-Pb2 along the c-axis) structure owing to superconducting condensation at $T_c$. The mechanism of the room-temperature $T_c$ is discussed by 1-D BR-BCS theory.
less
By: Ze-Pei Cian, Hossein Dehghani, Andreas Elben, Benoît Vermersch, Guanyu Zhu, Maissam Barkeshli, Peter Zoller, Mohammad Hafezi
One of the main topological invariants that characterizes several topologically-ordered phases is the many-body Chern number (MBCN). Paradigmatic
examples include several fractional quantum Hall phases, which are expected to be realized in different atomic and photonic quantum platforms in the near
future. Experimental measurement and numerical computation of this invariant is conventionally based on the linear-response techniques which requi... more
One of the main topological invariants that characterizes several topologically-ordered phases is the many-body Chern number (MBCN). Paradigmatic
examples include several fractional quantum Hall phases, which are expected to be realized in different atomic and photonic quantum platforms in the near
future. Experimental measurement and numerical computation of this invariant is conventionally based on the linear-response techniques which require having access to a family of states, as a function of an external parameter, which is not suitable for many quantum simulators. Here, we propose an ancilla-free
experimental scheme for the measurement of this invariant, without requiring any knowledge of the Hamiltonian. Specifically, we use the statistical
correlations of randomized measurements to infer the MBCN of a wavefunction. Remarkably, our results apply to disk-like geometries that are more amenable to current quantum simulator architectures.
less
By: Alireza Seif, Mohammad Hafezi, Yi-Kai Liu
Long-range correlated errors can severely impact the performance of NISQ (noisy intermediate-scale quantum) devices, and fault-tolerant quantum
computation. Characterizing these errors is important for improving the performance of these devices, via calibration and error correction, and to ensure correct interpretation of the results. We propose a compressed sensing method for detecting two-qubit correlated dephasing errors, assuming only t... more
Long-range correlated errors can severely impact the performance of NISQ (noisy intermediate-scale quantum) devices, and fault-tolerant quantum
computation. Characterizing these errors is important for improving the performance of these devices, via calibration and error correction, and to ensure correct interpretation of the results. We propose a compressed sensing method for detecting two-qubit correlated dephasing errors, assuming only that the correlations are sparse (i.e., at most s pairs of qubits have correlated errors, where s << n(n-1)/2, and n is the total number of qubits). In particular, our method can detect long-range correlations between any two
qubits in the system (i.e., the correlations are not restricted to be geometrically local). Our method is highly scalable: it requires as few as m = O(s log n)
measurement settings, and efficient classical postprocessing based on convex optimization. In addition, when m = O(s log^4(n)), our method is highly robust to noise, and has sample complexity O(max(n,s)^2 log^4(n)), which can be compared to conventional methods that have sample complexity O(n^3). Thus, our method is advantageous when the correlations are sufficiently sparse, that is, when s < O(n^(3/2) / log^2(n)). Our method also performs well in numerical simulations on small system sizes, and has some resistance to state-preparation-and-measurement (SPAM) errors. The key ingredient in our method is a new type of compressed sensing measurement, which works by preparing entangled Greenberger-Horne-Zeilinger states (GHZ states) on random subsets of qubits, and measuring their decay rates with high precision.
less
By: Beini Gao, Daniel G. Suárez-Forero, Supratik Sarkar, Tsung-Sheng Huang, Deric Session, Mahmoud Jalali Mehrabad, Ruihao Ni, Ming Xie, Jonathan Vannucci, Sunil Mittal, Kenji Watanabe, Takashi Taniguchi, Atac Imamoglu, You Zhou, Mohammad Hafezi
Understanding the Hubbard model is crucial for investigating various quantum many-body states and its fermionic and bosonic versions have been largely realized separately. Recently, transition metal dichalcogenides heterobilayers have emerged as a promising platform for simulating the rich physics of the Hubbard model. In this work, we explore the interplay between fermionic and bosonic populations, using a $\rm{WS}_2$/$\rm{WSe}_2$ heterobila... more
Understanding the Hubbard model is crucial for investigating various quantum many-body states and its fermionic and bosonic versions have been largely realized separately. Recently, transition metal dichalcogenides heterobilayers have emerged as a promising platform for simulating the rich physics of the Hubbard model. In this work, we explore the interplay between fermionic and bosonic populations, using a $\rm{WS}_2$/$\rm{WSe}_2$ heterobilayer device that hosts this hybrid particle density. We independently tune the fermionic and bosonic populations by electronic doping and optical injection of electron-hole pairs, respectively. This enables us to form strongly interacting excitons that are manifested in a large energy gap in the photoluminescence spectrum. The incompressibility of excitons is further corroborated by measuring exciton diffusion, which remains constant upon increasing pumping intensity, as opposed to the expected behavior of a weakly interacting gas of bosons, suggesting the formation of a bosonic Mott insulator. We explain our observations using a two-band model including phase space filling. Our system provides a controllable approach to the exploration of quantum many-body effects in the generalized Bose-Fermi-Hubbard model.
less
By: Pierre A. Pantaleon, Tommaso Cea, Rory Brown, Niels R. Walet, Francisco Guinea
The occurrence of superconducting and insulating phases is well-established
in twisted graphene bilayers, and they have also been reported in other
arrangements of graphene layers. We investigate three such arrangements:
untwisted AB bilayer graphene on an hBN substrate, two graphene bilayers
twisted with respect to each other, and a single ABC stacked graphene trilayer
on an hBN substrate. Narrow bands with different topology occur in all ca... more
The occurrence of superconducting and insulating phases is well-established
in twisted graphene bilayers, and they have also been reported in other
arrangements of graphene layers. We investigate three such arrangements:
untwisted AB bilayer graphene on an hBN substrate, two graphene bilayers
twisted with respect to each other, and a single ABC stacked graphene trilayer
on an hBN substrate. Narrow bands with different topology occur in all cases,
producing a high density of states which enhances the role of interactions. We
investigate the effect of the long-range Coulomb interaction, treated within
the self-consistent Hartree-Fock approximation. We find that the on-site part
of the Fock potential strongly modifies the band structure at charge
neutrality. The Hartree part does not significantly modify the shape and width
of the bands in the three cases considered here, in contrast to the effect that
such a potential has in twisted bilayer graphene.
less
By: Richard Barney, Michael Winer, Christopher L. Baldwin, Brian Swingle, Victor Galitski
Glasses have the interesting feature of being neither integrable nor fully
chaotic. They thermalize quickly within a subspace but thermalize much more
slowly across the full space due to high free energy barriers which partition
the configuration space into sectors. Past works have examined the
Rosenzweig-Porter (RP) model as a minimal quantum model which transitions from
localized to chaotic behavior. In this work we generalize the RP mode... more
Glasses have the interesting feature of being neither integrable nor fully
chaotic. They thermalize quickly within a subspace but thermalize much more
slowly across the full space due to high free energy barriers which partition
the configuration space into sectors. Past works have examined the
Rosenzweig-Porter (RP) model as a minimal quantum model which transitions from
localized to chaotic behavior. In this work we generalize the RP model in such
a way that it becomes a minimal model which transitions from glassy to chaotic
behavior, which we term the "Block Rosenzweig-Porter" (BRP) model. We calculate
the spectral form factors of both models at all timescales. Whereas the RP
model exhibits a crossover from localized to ergodic behavior at the Thouless
timescale, the new BRP model instead crosses over from glassy to fully chaotic
behavior, as seen by a change in the slope of the ramp of the spectral form
factor.
less
By: Pranav Chandarana, Narendra N. Hegade, Iraitz Montalban, Enrique Solano, Xi Chen
We propose a hybrid classical-quantum digitized-counterdiabatic algorithm to
tackle the protein folding problem on a tetrahedral lattice.
Digitized-counterdiabatic quantum computing is a paradigm developed to compress
quantum algorithms via the digitization of the counterdiabatic acceleration of
a given adiabatic quantum computation. Finding the lowest energy configuration
of the amino acid sequence is an NP-hard optimization problem that p... more
We propose a hybrid classical-quantum digitized-counterdiabatic algorithm to
tackle the protein folding problem on a tetrahedral lattice.
Digitized-counterdiabatic quantum computing is a paradigm developed to compress
quantum algorithms via the digitization of the counterdiabatic acceleration of
a given adiabatic quantum computation. Finding the lowest energy configuration
of the amino acid sequence is an NP-hard optimization problem that plays a
prominent role in chemistry, biology, and drug design. We outperform
state-of-the-art quantum algorithms using problem-inspired and
hardware-efficient variational quantum circuits. We apply our method to
proteins with up to 9 amino acids, using up to 17 qubits on quantum hardware.
Specifically, we benchmark our quantum algorithm with Quantinuum's trapped
ions, Google's and IBM's superconducting circuits, obtaining high success
probabilities with low-depth circuits as required in the NISQ era.
less
By: George Japaridze, Anzor Khelashvili, Koba Turashvili
Based on the novel prescription for the power of a complex number, a new
expression for the eigenfunction of the operator of the third component of the
angular momentum is presented. These functions are normalizable, single valued
and are invariant under the rotations at 2\pi for any, not necessary integer m
- the eigenvalue of the operator of the third component of the angular
momentum. For any real m these functions form an orthonormal se... more
Based on the novel prescription for the power of a complex number, a new
expression for the eigenfunction of the operator of the third component of the
angular momentum is presented. These functions are normalizable, single valued
and are invariant under the rotations at 2\pi for any, not necessary integer m
- the eigenvalue of the operator of the third component of the angular
momentum. For any real m these functions form an orthonormal set, therefore
they may serve as a quantum mechanical eigenfunctions. The eigenfunctions and
eigenvalues of the operator of the angular momentum operator squared, derived
for the two different prescriptions for the square root are reported. The
normalizable eigenfunctions of the operator of the angular momentum operator
squared are presented in terms of hypergeometric functions, admitting integer
as well as non-integer eigenvalues. It is shown that the purely integer
spectrum is not the most general solution but is just the artifact of a
particular choice of the Legendre functions as the pair of linearly independent
solutions of the eigenvalue problem for the operator of the angular momentum
operator squared.
less
By: Andrija Kostić, Nhat-Minh Nguyen, Fabian Schmidt, Martin Reinecke
Analyzing the clustering of galaxies at the field level in principle promises
access to all the cosmological information available. Given this incentive, in
this paper we investigate the performance of field-based forward modeling
approach to galaxy clustering using the effective field theory (EFT) framework
of large-scale structure (LSS). We do so by applying this formalism to a set of
consistency and convergence tests on synthetic dataset... more
Analyzing the clustering of galaxies at the field level in principle promises
access to all the cosmological information available. Given this incentive, in
this paper we investigate the performance of field-based forward modeling
approach to galaxy clustering using the effective field theory (EFT) framework
of large-scale structure (LSS). We do so by applying this formalism to a set of
consistency and convergence tests on synthetic datasets. We explore the
high-dimensional joint posterior of LSS initial conditions by combining
Hamiltonian Monte Carlo sampling for the field of initial conditions, and slice
sampling for cosmology and model parameters. We adopt the Lagrangian
perturbation theory forward model from [1], up to second order, for the forward
model of biased tracers. We specifically include model mis-specifications in
our synthetic datasets within the EFT framework. We achieve this by generating
synthetic data at a higher cutoff scale $\Lambda_0$, which controls which
Fourier modes enter the EFT likelihood evaluation, than the cutoff $\Lambda$
used in the inference. In the presence of model mis-specifications, we find
that the EFT framework still allows for robust, unbiased joint inference of a)
cosmological parameters - specifically, the scaling amplitude of the initial
conditions - b) the initial conditions themselves, and c) the bias and noise
parameters. In addition, we show that in the purely linear case, where the
posterior is analytically tractable, our samplers fully explore the posterior
surface. We also demonstrate convergence in the cases of nonlinear forward
models. Our findings serve as a confirmation of the EFT field-based forward
model framework developed in [2-7], and as another step towards field-level
cosmological analyses of real galaxy surveys.
less
By: Alexis Coissard, Adolfo G. Grushin, Cécile Repellin, Louis Veyrat, Kenji Watanabe, Takashi Taniguchi, Frédéric Gay, Hervé Courtois, Hermann Sellier, Benjamin Sacépé
Electronic edge states in topological insulators have become a major paradigm
in physics. The oldest and primary example is that of quantum Hall (QH) edge
channels that propagate along the periphery of two-dimensional electron gases
(2DEGs) under perpendicular magnetic field. Yet, despite 40 years of intensive
studies using a variety of transport and scanning probe techniques, imaging the
real-space structure of QH edge channels has proven ... more
Electronic edge states in topological insulators have become a major paradigm
in physics. The oldest and primary example is that of quantum Hall (QH) edge
channels that propagate along the periphery of two-dimensional electron gases
(2DEGs) under perpendicular magnetic field. Yet, despite 40 years of intensive
studies using a variety of transport and scanning probe techniques, imaging the
real-space structure of QH edge channels has proven difficult, mainly due to
the buried nature of most 2DEGs in semiconductors. Here, we show that QH edge
states in graphene are confined to a few magnetic lengths at the crystal edges
by performing scanning tunneling spectroscopy up to the edge of a graphene
flake on hexagonal boron nitride. These findings indicate that QH edge states
are defined by boundary conditions of vanishing electronic wavefunctions at the
crystal edges, resulting in ideal one-dimensional chiral channels, free of
electrostatic reconstruction. We further evidence a uniform charge carrier
density at the edges, contrasting with conjectures on the existence of
non-topological upstream modes. The absence of electrostatic reconstruction of
quantum Hall edge states has profound implications for the universality of
electron and heat transport experiments in graphene-based systems and other 2D
crystalline materials.
less
Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2
2upvotes
By: Saisab Bhowmik, Bhaskar Ghawri, Youngju Park, Dongkyu Lee, Suvronil Datta, Radhika Soni, K. Watanabe, T. Taniguchi, Arindam Ghosh, Jeil Jung, U. Chandni
New phases of matter can be stabilized by a combination of diverging electronic density of states, strong interactions, and spin-orbit coupling. Recent experiments in magic-angle twisted bilayer graphene (TBG) have uncovered a wealth of novel phases as a result of interaction-driven spin-valley flavour polarization. In this work, we explore correlated phases appearing due to the
combined effect of spin-orbit coupling-enhanced valley polariz... more
New phases of matter can be stabilized by a combination of diverging electronic density of states, strong interactions, and spin-orbit coupling. Recent experiments in magic-angle twisted bilayer graphene (TBG) have uncovered a wealth of novel phases as a result of interaction-driven spin-valley flavour polarization. In this work, we explore correlated phases appearing due to the
combined effect of spin-orbit coupling-enhanced valley polarization and large density of states below half filling ($\nu \lesssim 2$) of the moir\'e band in a TBG coupled to tungsten diselenide. We observe anomalous Hall effect, accompanied by a series of Lifshitz transitions, that are highly tunable with carrier density and magnetic field. Strikingly, the magnetization shows an
abrupt sign change in the vicinity of half-filling, confirming its orbital nature. The coercive fields reported are about an order of magnitude higher than previous studies in graphene-based moir\'e systems, presumably aided by a Stoner instability favoured by the van Hove singularities in the malleable bands. While the Hall resistance is not quantized at zero magnetic fields, indicative of a ground state with partial valley polarization, perfect quantization and complete valley polarization are observed at finite fields.
Our findings illustrate that singularities in the flat bands in the presence of spin-orbit coupling can stabilize ordered phases even at non-integer moir\'e band fillings.
less
By: Haicheng Mei, Jingsong Gao, Kailu Wang, Jiahao Dong, Qihuang Gong, Chengyin Wu, Yunquan Liu, Hongbing Jiang, Yi Liu
Nitrogen ions pumped by intense femtosecond laser pulses give rise to optical
amplification in the ultraviolet range. Here, we demonstrated that a seed light
pulse carrying orbital angular momentum (OAM) can be significantly amplified in
nitrogen plasma excited by a Gaussian femtosecond laser pulse. With the
topological charge of +1 and -1, we observed an energy amplification of the
seed light pulse by two orders of magnitude, while the amp... more
Nitrogen ions pumped by intense femtosecond laser pulses give rise to optical
amplification in the ultraviolet range. Here, we demonstrated that a seed light
pulse carrying orbital angular momentum (OAM) can be significantly amplified in
nitrogen plasma excited by a Gaussian femtosecond laser pulse. With the
topological charge of +1 and -1, we observed an energy amplification of the
seed light pulse by two orders of magnitude, while the amplified pulse carries
the same OAM as the incident seed pulse. Moreover, we show that a spatial
misalignment of the plasma amplifier with the OAM seed beam leads to an
amplified emission of Gaussian mode without OAM, due to the special spatial
profile of the OAM seed pulse that presents a donut-shaped intensity
distribution. Utilizing this misalignment, we can implement an optical switch
that toggles the output signal between Gaussian mode and OAM mode. This work
not only certifies the phase transfer from the seed light to the amplified
signal, but also highlights the important role of spatial overlap of the
donut-shaped seed beam with the gain region of the nitrogen plasma for the
achievement of OAM beam amplification.
less
By: Héctor Sainz-Cruz, Tommaso Cea, Pierre A. Pantaleón, Francisco Guinea
Angle disorder is an intrinsic feature of twisted bilayer graphene and other moiré materials. Here, we discuss electron transport in twisted bilayer graphene in the presence of angle disorder. We compute the local density of states and the Landauer-Büttiker transmission through an angle disorder barrier of width comparable to the moiré period, using a decimation technique based on a real space description. We find that barriers which separate... more
Angle disorder is an intrinsic feature of twisted bilayer graphene and other moiré materials. Here, we discuss electron transport in twisted bilayer graphene in the presence of angle disorder. We compute the local density of states and the Landauer-Büttiker transmission through an angle disorder barrier of width comparable to the moiré period, using a decimation technique based on a real space description. We find that barriers which separate regions where the width of the bands differ by 50% or more lead to a minor suppression of the transmission, and that the transmission is close to one for normal incidence, which is reminiscent of Klein tunneling. These results suggest that transport in twisted bilayer graphene is weakly affected by twist angle disorder.
less
Structured air lasing of N2+
2upvotes
By: Jingsong Gao, Xiang Zhang, Yang Wang, Yiqi Fang, Qi Lu, Zheng Li, Yi Liu, Chengyin Wu, Qihuang Gong, Yunquan Liu, Hongbing Jiang
Structured light has attracted great interest in scientific and technical
fields. Here, we demonstrate the first generation of structured air lasing in
N2+ driven by 800 nm femtosecond laser pulses. By focusing a vortex pump beam
at 800 nm in N2 gas, we generate a vortex superfluorescent radiation of N2+ at
391 nm, which carries the same photon orbital angular momentum as the pump
beam. With the injection of a Gaussian seed beam at 391 nm, ... more
Structured light has attracted great interest in scientific and technical
fields. Here, we demonstrate the first generation of structured air lasing in
N2+ driven by 800 nm femtosecond laser pulses. By focusing a vortex pump beam
at 800 nm in N2 gas, we generate a vortex superfluorescent radiation of N2+ at
391 nm, which carries the same photon orbital angular momentum as the pump
beam. With the injection of a Gaussian seed beam at 391 nm, the coherent
radiation is amplified, but the vorticity is unchanged. A new physical
mechanism is revealed in the vortex N2+ superfluorescent radiation: the vortex
pump beam transfers the spatial spiral phase into the N2+ gain medium, and the
Gaussian seed beam picks up the spatial spiral phase and is then amplified into
a vortex beam. Moreover, when we employ a pump beam with a cylindrical vector
mode, the Gaussian seed beam is correspondingly amplified into a cylindrical
vector beam. Surprisingly, the spatial polarization state of the amplified
radiation is identical to that of the vector pump beam regardless of whether
the Gaussian seed beam is linearly, elliptically, or circularly polarized.
Solving three-dimensional coupled wave equations, we show how a Gaussian beam
becomes a cylindrical vector beam in a cylindrically symmetric gain medium.
This study provides a novel approach to generating structured light via N2+ air
lasing.
less
By: Armin Tavakoli, Alejandro Pozas-Kerstjens, Peter Brown, Mateus Araújo
Semidefinite programs are convex optimisation problems involving a linear objective function and a domain of positive semidefinite matrices. Over the last two decades, they have become an indispensable tool in quantum information
science. Many otherwise intractable fundamental and applied problems can be successfully approached by means of relaxation to a semidefinite program. Here, we review such methodology in the context of quantum corre... more
Semidefinite programs are convex optimisation problems involving a linear objective function and a domain of positive semidefinite matrices. Over the last two decades, they have become an indispensable tool in quantum information
science. Many otherwise intractable fundamental and applied problems can be successfully approached by means of relaxation to a semidefinite program. Here, we review such methodology in the context of quantum correlations. We discuss how the core idea of semidefinite relaxations can be adapted for a variety of
research topics in quantum correlations, including nonlocality, quantum communication, quantum networks, entanglement, and quantum cryptography.
less
By: Abu Musa Patoary, Amit Vikram, Laura Shou, Victor Galitski
Shor's factoring algorithm, believed to provide an exponential speedup over classical computation, relies on finding the period of an exactly periodic quantum modular multiplication operator. This exact periodicity is the hallmark of an integrable system, which is paradoxical from the viewpoint of quantum chaos, given that the classical limit of the modular multiplication operator is a highly chaotic system that occupies the "maximally rand... more
Shor's factoring algorithm, believed to provide an exponential speedup over classical computation, relies on finding the period of an exactly periodic quantum modular multiplication operator. This exact periodicity is the hallmark of an integrable system, which is paradoxical from the viewpoint of quantum chaos, given that the classical limit of the modular multiplication operator is a highly chaotic system that occupies the "maximally random" Bernoulli level of the classical ergodic hierarchy. In this work, we approach this apparent paradox from a quantum dynamical systems viewpoint, and consider whether signatures of ergodicity and chaos may indeed be encoded in such an "integrable" quantization of a chaotic system. We show that Shor's modular
multiplication operator, in specific cases, can be written as a superposition of quantized A-baker's maps exhibiting more typical signatures of quantum chaos and ergodicity. This work suggests that the integrability of Shor's modular multiplication operator may stem from the interference of other "chaotic" quantizations of the same family of maps, and paves the way for deeper studies
on the interplay of integrability, ergodicity and chaos in and via quantum algorithms.
less
By: Pierre A. Pantaleón, Tony Low, Francisco Guinea
Recent experiments have measured local uniaxial strain fields in twisted
bilayer graphene (TBG). Our calculations found that the finite Berry curvature
generated by breaking the sublattice symmetry and the band proximity between
narrow bands in these TBG induces a giant Berry dipole of order 10\,nm or
larger. The large Berry dipole leads to transverse topological non-linear
charge currents which dominates over the linear bulk valley current... more
Recent experiments have measured local uniaxial strain fields in twisted
bilayer graphene (TBG). Our calculations found that the finite Berry curvature
generated by breaking the sublattice symmetry and the band proximity between
narrow bands in these TBG induces a giant Berry dipole of order 10\,nm or
larger. The large Berry dipole leads to transverse topological non-linear
charge currents which dominates over the linear bulk valley current at
experimentally accessible crossover in-plane electric field of $\sim 0.1 {\rm
mV} / \mu \rm{m}$. This anomalous Hall effect, due to Berry dipole, is strongly
tunable by the strain parameters, electron fillings, gap size, and temperature.
less
By: Nilesh P. Salke, Alexander C. Mark, Muhtar Ahart, Russell J. Hemley
The recent report of superconductivity in nitrogen-doped lutetium hydride at near-ambient pressures and temperatures has attracted great attention but also continuing controversy. Several experimental groups have reported no observation of superconductivity at these conditions in Lu-N-H samples they have prepared. To address this issue, we have carried out a series of studies of phases in the Lu-N-H system using a variety of techniques. We ... more
The recent report of superconductivity in nitrogen-doped lutetium hydride at near-ambient pressures and temperatures has attracted great attention but also continuing controversy. Several experimental groups have reported no observation of superconductivity at these conditions in Lu-N-H samples they have prepared. To address this issue, we have carried out a series of studies of phases in the Lu-N-H system using a variety of techniques. We report here
electrical resistance measurements on a Lu-N-H sample that are in very good agreement with both previously reported Tc and its pressure dependence in the vicinity of room temperature for nitrogen-doped lutetium hydride.
less
By: C. G. L. Bøttcher, N. R. Poniatowski, A. Grankin, M. E. Wesson, Z. Yan, U. Vool, V. M. Galitski, A. Yacoby
Hybrid systems represent one of the frontiers in the study of unconventional superconductivity and are a promising platform to realize topological superconducting states. Owing to their mesoscopic dimensions, these materials are challenging to probe using many conventional measurement techniques, and require new experimental probes to successfully characterize. In this work, we develop a probe that enables us to measure the superfluid densi... more
Hybrid systems represent one of the frontiers in the study of unconventional superconductivity and are a promising platform to realize topological superconducting states. Owing to their mesoscopic dimensions, these materials are challenging to probe using many conventional measurement techniques, and require new experimental probes to successfully characterize. In this work, we develop a probe that enables us to measure the superfluid density of
micron-size superconductors using microwave techniques drawn from circuit quantum electrodynamics (cQED). We apply this technique to a paradigmatic hybrid system, the superconductor/ferromagnet bilayer, and find that the proximity-induced superfluid density is two-fold anisotropic within the plane of the sample and exhibits power law temperature-scaling which is indicative of a nodal superconducting state. These experimental results are consistent with
the theoretically predicted signatures of induced triplet pairing with a nodal p-wave order parameter. Moreover, we unexpectedly observe drastic modifications to the microwave response at frequencies near the ferromagnetic resonance, suggesting a coupling between the spin dynamics and induced superconducting order in the ferromagnetic layer. Our results offer new
insights into the unconventional superconducting states induced in superconductor/ferromagnet heterostructures and simultaneously establish a new avenue for the study of fragile unconventional superconductivity in low-dimensional materials such as van der Waals heterostructures.
less
By: Tommaso Cea, Pierre A. Pantaleon, Francisco Guinea
The effect of an hexagonal boron nitride (hBN) layer close aligned with
twisted bilayer graphene (TBG) is studied. At sufficiently low angles between
twisted bilayer graphene and hBN, $\theta_{hBN} \lesssim 2^\circ$, the graphene
electronic structure is strongly disturbed. The width of the low energy peak in
the density of states changes from $W \sim 5 - 10$ meV for a decoupled system
to $\sim 20 - 30$ meV. Spikes in the density of states d... more
The effect of an hexagonal boron nitride (hBN) layer close aligned with
twisted bilayer graphene (TBG) is studied. At sufficiently low angles between
twisted bilayer graphene and hBN, $\theta_{hBN} \lesssim 2^\circ$, the graphene
electronic structure is strongly disturbed. The width of the low energy peak in
the density of states changes from $W \sim 5 - 10$ meV for a decoupled system
to $\sim 20 - 30$ meV. Spikes in the density of states due to van Hove
singularities are smoothed out. We find that for a realistic combination of the
twist angle in the TBG and the twist angle between the hBN and the graphene
layer the system can be described using a single moir\'e unit cell.
less
By: Thorvald M. Ballestad, Alberto Cortijo, María A. H. Vozmediano, Alireza Qaiumzadeh
We analyze the effect of the tilt on the transverse thermoelectric
coefficient of Weyl semimetals in the \emph{conformal} limit, i.e., zero
temperature and zero chemical potential. Using the Kubo formalism, we find a
nonmonotonic behavior of the thermoelectric conductivity as a function of the
tilt perpendicular to the magnetic field, and a linear behavior when the tilt
is aligned to the magnetic field. An ``axial Nernst" current (chiral cu... more
We analyze the effect of the tilt on the transverse thermoelectric
coefficient of Weyl semimetals in the \emph{conformal} limit, i.e., zero
temperature and zero chemical potential. Using the Kubo formalism, we find a
nonmonotonic behavior of the thermoelectric conductivity as a function of the
tilt perpendicular to the magnetic field, and a linear behavior when the tilt
is aligned to the magnetic field. An ``axial Nernst" current (chiral currents
counter propagating perpendicularly to the magnetic field and the temperature
gradient) is generated in inversion symmetric Weyl materials when the tilt
vector has a projection in the direction of the magnetic field. This analysis
will help in the design and interpretation of thermoelectric transport
experiments in recently discovered topological quantum materials.
less
By: Marion M. S. Barbeau, Mikhail Titov, Mikhail I. Katsnelson, Alireza Qaiumzadeh
We describe a \emph{nonthermal} magnon activation mechanism in
antiferromagnetic (AFM) systems via locally equilibrated
\emph{spin-unpolarized} hot electrons excited by an ultrafast intense laser
pulse. We employ a quantum kinetic equation that takes into account a direct
electron-magnon scattering channel in either bulk AFM metal or at the interface
of the AFM/normal-metal heterostructure. The mechanism is responsible for the
nonequilibriu... more
We describe a \emph{nonthermal} magnon activation mechanism in
antiferromagnetic (AFM) systems via locally equilibrated
\emph{spin-unpolarized} hot electrons excited by an ultrafast intense laser
pulse. We employ a quantum kinetic equation that takes into account a direct
electron-magnon scattering channel in either bulk AFM metal or at the interface
of the AFM/normal-metal heterostructure. The mechanism is responsible for the
nonequilibrium population of AFM magnon modes on a subnanosecond timescale,
which are formed shortly after the local thermalization of hot electrons by
Coulomb interactions. Nonequilibrium magnon populations can be additionally
manipulated by applying an external magnetic field. Our work paves the way
toward spin dynamics control in AFM systems via the ultrafast manipulation of
out-of-equilibrium magnon excitations.
less
By: Verena Brehm, Olena Gomonay, Serban Lepadatu, Mathias Kläui, Jairo Sinova, Arne Brataas, Alireza Qaiumzadeh
Magnon eigenmodes in easy-plane antiferromagnetic insulators are linearly
polarized and are not expected to carry any net spin angular momentum.
Motivated by recent nonlocal spin transport experiments in the easy-plane phase
of hematite, we perform a series of micromagnetic simulations in a nonlocal
geometry at finite temperatures. We show that by tuning an external magnetic
field, we can control the magnon eigenmodes and the polarization o... more
Magnon eigenmodes in easy-plane antiferromagnetic insulators are linearly
polarized and are not expected to carry any net spin angular momentum.
Motivated by recent nonlocal spin transport experiments in the easy-plane phase
of hematite, we perform a series of micromagnetic simulations in a nonlocal
geometry at finite temperatures. We show that by tuning an external magnetic
field, we can control the magnon eigenmodes and the polarization of the spin
transport signal in these systems. We argue that a coherent beating oscillation
between two orthogonal linearly polarized magnon eigenmodes is the mechanism
responsible for finite spin transport in easy-plane antiferromagnetic
insulators. The sign of the detected spin signal is also naturally explained by
the proposed coherent beating mechanism. Our finding opens a path for on-demand
control of the spin signal in a large class of easy-plane antiferromagnetic
insulators.
less
Non-volatile leaky integrate-and-fire neurons with domain walls in antiferromagnetic insulators
2upvotes
By: Johannes W. Austefjord, Verena Brehm, Serban Lepadatu, Alireza Qaiumzadeh
Despite the rapid development of powerful supercomputers in recent years, the
human brain still has some abilities that outperform modern computers which are
based on the von Neumann architecture. The human brain is much more energy
efficient than state-of-the-art digital computers and can at the same time
perform complex tasks such as pattern recognition. The brain-inspired
neuromorphic computing paradigm is a promising path towards next g... more
Despite the rapid development of powerful supercomputers in recent years, the
human brain still has some abilities that outperform modern computers which are
based on the von Neumann architecture. The human brain is much more energy
efficient than state-of-the-art digital computers and can at the same time
perform complex tasks such as pattern recognition. The brain-inspired
neuromorphic computing paradigm is a promising path towards next generation
analogue computers with fundamentally different architecture. The building
blocks of the human brain are neurons with leaky integrate-and-fire mechanisms.
In this work, using the advantage of antiferromagnetic insulators, we propose a
non-volatile spintronic-based neuron. In our proposal, an antiferromagnetic
domain wall in the presence of a magnetic anisotropy gradient mimics a
biological neuron with leaky and integrative properties. This single neuron is
controlled by polarized antiferromagnetic magnons, activated by either a
magnetic field pulse or a spin transfer torque mechanism. We propose that this
single neuron, based on antiferromagnetic insulators, is faster and more energy
efficient than other metallic ferromagnetic-based neurons.
less
By: Christian Moulsdale, Pierre A. Pantaleón, Ramon Carrillo-Bastos, Yang Xian
We present theoretically the thermal Hall effect of magnons in a
ferromagnetic lattice with a Kekulé-O coupling (KOC) modulation and a
Dzyaloshinskii-Moriya interaction (DMI). Through a strain-based mechanism for
inducing the KOC modulation, we identify four topological phases in terms of
the KOC parameter and DMI strength. We calculate the thermal magnon Hall
conductivity ${\kappa^{xy}}$ at low temperature in each of these phases. We
predi... more
We present theoretically the thermal Hall effect of magnons in a
ferromagnetic lattice with a Kekulé-O coupling (KOC) modulation and a
Dzyaloshinskii-Moriya interaction (DMI). Through a strain-based mechanism for
inducing the KOC modulation, we identify four topological phases in terms of
the KOC parameter and DMI strength. We calculate the thermal magnon Hall
conductivity ${\kappa^{xy}}$ at low temperature in each of these phases. We
predict an unconventional conductivity due to a non-zero Berry curvature
emerging from band proximity effects in the topologically trivial phase. We
find sign changes of ${\kappa^{xy}}$ as a function of the model parameters,
associated with the local Berry curvature and occupation probability of the
bulk bands. Throughout, ${\kappa^{xy}}$ can be easily tuned with external
parameters such as the magnetic field and temperature.
less
By: Arman Pour Tak Dost, Mischa P. Woods
When an atom is in an excited state, after some amount of time, it will decay
to a lower energy state emitting a photon in the process. This is known as
spontaneous emission. It is one of the three elementary light-matter
interactions. If it has not decayed at time $t$, then the probability that it
does so in the next infinitesimal time step $[t, t+\delta t]$, is
$t$-independent. So there is no preferred time at which to decay -- in this
se... more
When an atom is in an excited state, after some amount of time, it will decay
to a lower energy state emitting a photon in the process. This is known as
spontaneous emission. It is one of the three elementary light-matter
interactions. If it has not decayed at time $t$, then the probability that it
does so in the next infinitesimal time step $[t, t+\delta t]$, is
$t$-independent. So there is no preferred time at which to decay -- in this
sense it is a random process. Here we show, by carefully engineering this
light-matter interaction, that we can associate it with a clock, where the
matter constitutes the clockwork and the spontaneous emission constitutes the
ticking of the clock. In particular, we show how to realise the quasi-ideal
clock. Said clock has been proven -- in an abstract and theoretic sense -- to
be the most accurate clock permissible by quantum theory, with a polynomial
enhancement in precision over the best stochastic clock of the same size. Our
results thus demonstrate that the seemingly random process of spontaneous
emission can in actual fact, under the right circumstances, be the most regular
one permissible by quantum theory. To achieve this we use geometric features
and flux-loop insertions to induce symmetry and Berry phases into the
light-matter coupling. We also study the entropy the clock produces per tick
and show that it also possesses a quantum advantage over that generated from
the previously known semi-classical clocks in the literature.
less
By: Ali G. Moghaddam, Kim Pöyhönen, Teemu Ojanen
Recently discovered measurement-induced entanglement phase transitions in
monitored quantum circuits provide a novel example of far-from-equilibrium
quantum criticality. Here, we propose a highly efficient strategy for
experimentally accessing these transitions through fluctuations. Instead of
directly measuring entanglement entropy, which requires an exponential number
of measurements in the subsystem size, our method provides a scalable a... more
Recently discovered measurement-induced entanglement phase transitions in
monitored quantum circuits provide a novel example of far-from-equilibrium
quantum criticality. Here, we propose a highly efficient strategy for
experimentally accessing these transitions through fluctuations. Instead of
directly measuring entanglement entropy, which requires an exponential number
of measurements in the subsystem size, our method provides a scalable approach
to entanglement transitions in the presence of conserved quantities. In analogy
to entanglement entropy and mutual information, we illustrate how bipartite and
multipartite fluctuations can both be employed to analyze the
measurement-induced criticality. Remarkably, the phase transition can be
revealed by measuring fluctuations of only a handful of qubits.
less
By: Brian Greene, Daniel Kabat, Janna Levin, Massimo Porrati
Brane observers executing appropriate motion through a partially compactified Lorentz invariant bulk spacetime, such as M4xS1, can send signals along the brane that are instantaneous or even travel backward in time. Nevertheless, causality in the braneworld remains intact. We establish these results, which follow from superluminal signal propagation reported in arXiv:2206.13590, through classical analysis and then extend our reasoning by ex... more
Brane observers executing appropriate motion through a partially compactified Lorentz invariant bulk spacetime, such as M4xS1, can send signals along the brane that are instantaneous or even travel backward in time. Nevertheless, causality in the braneworld remains intact. We establish these results, which follow from superluminal signal propagation reported in arXiv:2206.13590, through classical analysis and then extend our reasoning by examining quantum mechanical microcausality. One implication is the capacity
for real time communication across arbitrarily large distances.
less
By: Elias Andrade, Ramon Carrillo-Bastos, Pierre A. Pantaleón, Francisco Mireles
The formation of a superlattice in graphene can serve as a way to modify its
electronic bandstructure and thus to engineer its electronic transport
properties. Recent experiments have discovered a Kekul\'e bond ordering in
graphene deposited on top of a Copper substrate, leading to the breaking of the
valley degeneracy while preserving the highly desirable feature of linearity
and gapless character of its band dispersion. In this paper we s... more
The formation of a superlattice in graphene can serve as a way to modify its
electronic bandstructure and thus to engineer its electronic transport
properties. Recent experiments have discovered a Kekul\'e bond ordering in
graphene deposited on top of a Copper substrate, leading to the breaking of the
valley degeneracy while preserving the highly desirable feature of linearity
and gapless character of its band dispersion. In this paper we study the
effects of a Kekul\'e distortion in zigzag graphene nanoribbons in both, the
subband spectrum and on its electronic transport properties. We extend our
study to investigate also the electronic conductance in graphene nanoribbons
composed of sequentially ordered Kek-Y superlattice. We find interesting
resonances in the conductance response emerging in the otherwise energy gap
regions, which scales with the number of Kek-Y interfaces minus one. Such
features resembles the physics of resonant tunneling behavior observed in
semiconductors heterostructures. Our findings provide a possible way to measure
the strenght of Kekul\'e parameter in graphene nanoribbons.
less
By: Christopher L Duston
In this paper we will detail an approach to generate metrics and matter
models on end-periodic manifolds, which are used extensively in the study of
the exotic smooth structures of $\mathbb{R}^4$. We will present three distinct
examples, discuss their associated matter models by solving the Einstein
equations, and determine their physical viability by examining the energy
conditions. We will also compare one of the models directly with exis... more
In this paper we will detail an approach to generate metrics and matter
models on end-periodic manifolds, which are used extensively in the study of
the exotic smooth structures of $\mathbb{R}^4$. We will present three distinct
examples, discuss their associated matter models by solving the Einstein
equations, and determine their physical viability by examining the energy
conditions. We will also compare one of the models directly with existing
models of matter distributions in extragalactic systems, to highlight the
viability of utilizing exotic smooth structures to understand the existence and
distribution of dark matter.
less
By: Bridget C. Andersen, Chitrang Patel, Charanjot Brar, P. J. Boyle, Emmanuel Fonseca, Victoria M. Kaspi, Kiyoshi W. Masui, Juan Mena-Parra, Marcus Merryfield, Bradley W. Meyers, Ketan R. Sand, Paul Scholz, Seth R. Siegel, Saurabh Singh
Fast radio bursts (FRBs) are bright radio transients of micro-to-millisecond
duration and unknown extragalactic origin. Central to the mystery of FRBs are
their extremely high characteristic energies, which surpass the typical
energies of other radio transients of similar duration, like Galactic pulsar
and magnetar bursts, by orders of magnitude. Calibration of FRB-detecting
telescopes for burst flux and fluence determination is crucial for... more
Fast radio bursts (FRBs) are bright radio transients of micro-to-millisecond
duration and unknown extragalactic origin. Central to the mystery of FRBs are
their extremely high characteristic energies, which surpass the typical
energies of other radio transients of similar duration, like Galactic pulsar
and magnetar bursts, by orders of magnitude. Calibration of FRB-detecting
telescopes for burst flux and fluence determination is crucial for FRB science,
as these measurements enable studies of the FRB energy and brightness
distribution in comparison to progenitor theories. The Canadian Hydrogen
Intensity Mapping Experiment (CHIME) is a radio interferometer of cylindrical
design. This design leads to a high FRB detection rate but also leads to
challenges for CHIME/FRB flux calibration. This paper presents a comprehensive
review of these challenges, as well as the automated flux calibration software
pipeline that was developed to calibrate bursts detected in the first CHIME/FRB
catalog, consisting of 536 events detected between July 25th, 2018 and July
1st, 2019. We emphasize that, due to limitations in the localization of
CHIME/FRB bursts, flux and fluence measurements produced by this pipeline are
best interpreted as lower limits, with uncertainties on the limiting value.
less
By: Hong Liu, James H. Cullen, Dimitrie Culcer
Spin currents driven by spin-orbit coupling are key to spin torque devices, but determining the proper spin current is highly non-trivial. Here we derive a general quantum-mechanical formula for the intrinsic proper spin current showing that it is a topological quantity, and can be finite even in the gap. We determine the spin-Hall current due to the bulk states of topological insulators both deep in the bulk, where the system is unmagnetiz... more
Spin currents driven by spin-orbit coupling are key to spin torque devices, but determining the proper spin current is highly non-trivial. Here we derive a general quantum-mechanical formula for the intrinsic proper spin current showing that it is a topological quantity, and can be finite even in the gap. We determine the spin-Hall current due to the bulk states of topological insulators both deep in the bulk, where the system is unmagnetized, and near the interface, where a proximity-induced magnetization is present, as well as
for low-dimensional spin-3/2 hole systems.
less
By: Christopher L Duston
In this paper we calculate the effect of the inclusion of exotic smooth
structures on typical observables in Euclidean quantum gravity. We do this in
the semiclassical regime for several gravitational free-field actions and find
that the results are similar, independent of the particular action that is
chosen. These are the first results of their kind in dimension four, which we
extend to include one-loop contributions as well. We find thes... more
In this paper we calculate the effect of the inclusion of exotic smooth
structures on typical observables in Euclidean quantum gravity. We do this in
the semiclassical regime for several gravitational free-field actions and find
that the results are similar, independent of the particular action that is
chosen. These are the first results of their kind in dimension four, which we
extend to include one-loop contributions as well. We find these topological
features can have physically significant results without the need for
additional exotic physics.
less
By: Pierre A. Pantaleon, Ramon Carrillo-Bastos, Y. Xian
We examine the combined effects of a Kekule coupling texture (KC) and a
Dzyaloshinskii-Moriya interaction (DMI) in a two-dimensional ferromagnetic
honeycomb lattice. By analyzing the gap closing conditions and the inversions
of the bulk bands, we identify the parameter range in which the system behaves
as a trivial or a nontrivial topological magnon insulator. We find four
topological phases in terms of the KC parameter and the DMI strength... more
We examine the combined effects of a Kekule coupling texture (KC) and a
Dzyaloshinskii-Moriya interaction (DMI) in a two-dimensional ferromagnetic
honeycomb lattice. By analyzing the gap closing conditions and the inversions
of the bulk bands, we identify the parameter range in which the system behaves
as a trivial or a nontrivial topological magnon insulator. We find four
topological phases in terms of the KC parameter and the DMI strength. We
present the bulk-edge correspondence for the magnons in a honeycomb lattice
with an armchair or a zigzag boundary. Furthermore, we find Tamm-like edge
states due to the intrinsic on-site interactions along the boundary sites. Our
results may have significant implications to magnon transport properties in the
2D magnets at low temperatures.
less
By: Jeongin Moon, David Valcin, Michael Rashkovetskyi, Christoph Saulder, Jessica Nicole Aguilar, Steven Ahlen, Shadab Alam, Stephen Bailey, Charles Baltay, Robert Blum, David Brooks, Etienne Burtin, Edmond Chaussidon, Kyle Dawson, Axel de la Macorra, Arnaud de Mattia, Govinda Dhungana, Daniel Eisenstein, Brenna Flaugher, Andreu Font-Ribera, Cristhian Garcia-Quintero, Julien Guy, Malik Muhammad Sikandar Hanif, Klaus Honscheid, Mustapha Ishak, Robert Kehoe, Sumi Kim, Theodore Kisner, Anthony Kremin, Martin Landriau, Laurent Le Guillou, Michael Levi, Paul Martini, Patrick McDonald, Aaron Meisner, Ramon Miquel, John Moustakas, Adam Myers, Seshadri Nadathur, Richard Neveux, Jeffrey A. Newman, Jundan Nie, Nikhil Padmanabhan, Nathalie Palanque-Delabrouille, Will Percival, Alejandro Pérez Fernández, Claire Poppett, Francisco Prada, Ashley J. Ross, Graziano Rossi, Hee-Jong Seo, Gregory Tarlé, Mariana Vargas Magana, Andrei Variu, Benjamin Alan Weaver, Martin J. White, Sihan Yuan, Cheng Zhao, Rongpu Zhou, Zhimin Zhou, Hu Zou
We present the first detection of the baryon acoustic oscillations (BAO)
signal obtained using unblinded data collected during the initial two months of
operations of the Stage-IV ground-based Dark Energy Spectroscopic Instrument
(DESI). From a selected sample of 261,291 Luminous Red Galaxies spanning the
redshift interval 0.4 < z < 1.1 and covering 1651 square degrees with a 57.9%
completeness level, we report a ~5 sigma level BAO detectio... more
We present the first detection of the baryon acoustic oscillations (BAO)
signal obtained using unblinded data collected during the initial two months of
operations of the Stage-IV ground-based Dark Energy Spectroscopic Instrument
(DESI). From a selected sample of 261,291 Luminous Red Galaxies spanning the
redshift interval 0.4 < z < 1.1 and covering 1651 square degrees with a 57.9%
completeness level, we report a ~5 sigma level BAO detection and the
measurement of the BAO location at a precision of 1.7%. Using a Bright Galaxy
Sample of 109,523 galaxies in the redshift range 0.1 < z < 0.5, over 3677
square degrees with a 50.0% completeness, we also detect the BAO feature at ~3
sigma significance with a 2.6% precision. These first BAO measurements
represent an important milestone, acting as a quality control on the optimal
performance of the complex robotically-actuated, fiber-fed DESI spectrograph,
as well as an early validation of the DESI spectroscopic pipeline and data
management system. Based on these first promising results, we forecast that
DESI is on target to achieve a high-significance BAO detection at sub-percent
precision with the completed 5-year survey data, meeting the top-level science
requirements on BAO measurements. This exquisite level of precision will set
new standards in cosmology and confirm DESI as the most competitive BAO
experiment for the remainder of this decade.
less
By: Ekaterina Vlasiuk, Valerii K. Kozin, Jelena Klinovaja, Daniel Loss, Ivan V. Iorsh, Ilya V. Tokatly
We develop a length-gauge formalism for treating one-dimensional periodic
lattice systems in the presence of a photon cavity inducing light-matter
interaction. The purpose of the formalism is to remove mathematical ambiguities
that occur when defining the position operator in the context of the
Power-Zienau-Woolley Hamiltonian. We then use a diagrammatic approach to
analyze perturbatively the interaction between an electronic quantum system... more
We develop a length-gauge formalism for treating one-dimensional periodic
lattice systems in the presence of a photon cavity inducing light-matter
interaction. The purpose of the formalism is to remove mathematical ambiguities
that occur when defining the position operator in the context of the
Power-Zienau-Woolley Hamiltonian. We then use a diagrammatic approach to
analyze perturbatively the interaction between an electronic quantum system and
a photonic cavity mode of long wavelength. We illustrate the versatility of the
formalism by studying the cavity-induced electric charge imbalance and
polarization in the Rice-Mele model with broken inversion symmetry.
less
By: Anirban Mukherjee
This paper reports a quantum algorithm for simulating quantum chemical
systems of N molecular orbitals(MOs) using $4\log N +2$ qubits. The number of
multi-electron configurations scales exponentially with the number of MOs and
is the primary bottleneck in calculating the energy of a many-electron system.
This paper introduces qubitized Hamiltonian downfolding(QHD) by combining the
techniques of qubitized quantum walks and Hamiltonian downfo... more
This paper reports a quantum algorithm for simulating quantum chemical
systems of N molecular orbitals(MOs) using $4\log N +2$ qubits. The number of
multi-electron configurations scales exponentially with the number of MOs and
is the primary bottleneck in calculating the energy of a many-electron system.
This paper introduces qubitized Hamiltonian downfolding(QHD) by combining the
techniques of qubitized quantum walks and Hamiltonian downfolding to reduce the
active space dimension systematically. At each stage of QHD, the number of
many-electron configurations is reduced by $1/4$ by decoupling the molecular
orbital (MO) farthest from the highest occupied MO (HOMO). The sequence of such
downfolding steps enables us to scale towards the low-energy HOMO-LUMO window.
For each stage of downfolding, we map the \emph{decoupling condition} i.e., a
many-body normal-ordered Bloch equation to a system of quadratic polynomial
equations. These downfolding equations can be solved using a non-linear least
squares (NLLS) approach within error $\epsilon$. Each step of NLLS involves a
Hessian inversion and comprises a quantum linear system problem(QLSP). We
describe quantum circuits that block-encode the Hessian using qubitization
oracles. Subsequently, we implement the Chebyshev expansion for solving the
QLSP within error $\epsilon'$, utilizing a sequence of qubitized quantum walks.
Starting from an N-orbital system the gate complexity of each downfolding
circuit scales as $O(N^{2}\log^{2}(1/\epsilon'))$ and for downfolding all the
MOs involve $O(N^3/\epsilon^{2})$ oracle queries.
less
By: Thomas Kohlert, Sebastian Scherg, Pablo Sala, Frank Pollmann, Bharath Hebbe Madhusudhana, Immanuel Bloch, Monika Aidelsburger
Quantum many-body systems may defy thermalization even without disorder.
Intriguingly, non-ergodicity may be caused by a fragmentation of the many-body
Hilbert-space into dynamically disconnected subspaces. The tilted
one-dimensional Fermi-Hubbard model was proposed as a platform to realize
fragmented models perturbatively in the limit of large tilt. Here, we
demonstrate the validity of this effective description for the transient
dynamics ... more
Quantum many-body systems may defy thermalization even without disorder.
Intriguingly, non-ergodicity may be caused by a fragmentation of the many-body
Hilbert-space into dynamically disconnected subspaces. The tilted
one-dimensional Fermi-Hubbard model was proposed as a platform to realize
fragmented models perturbatively in the limit of large tilt. Here, we
demonstrate the validity of this effective description for the transient
dynamics using ultracold fermions. The effective analytic model allows for a
detailed understanding of the emergent microscopic processes, which in our case
exhibit a pronounced doublon-number dependence. We study this experimentally by
tuning the doublon fraction in the initial state.
less
By: Bharath Hebbe Madhusudhana, Sebastian Scherg, Thomas Kohlert, Immanuel Bloch, Monika Aidelsburger
Quantum simulators have made a remarkable progress towards exploring the
dynamics of many-body systems, many of which offer a formidable challenge to
both theoretical and numerical methods. While state-of-the-art quantum
simulators are in principle able to simulate quantum dynamics well outside the
domain of classical computers, they are noisy and limited in the variability of
the initial state of the dynamics and the observables that can b... more
Quantum simulators have made a remarkable progress towards exploring the
dynamics of many-body systems, many of which offer a formidable challenge to
both theoretical and numerical methods. While state-of-the-art quantum
simulators are in principle able to simulate quantum dynamics well outside the
domain of classical computers, they are noisy and limited in the variability of
the initial state of the dynamics and the observables that can be measured.
Despite these limitations, here we show that such a quantum simulator can be
used to in-effect solve for the dynamics of a many-body system. We develop an
efficient numerical technique that facilitates classical simulations in regimes
not accessible to exact calculations or other established numerical techniques.
The method is based on approximations that are well suited to describe
localized one-dimensional Fermi-Hubbard systems. Since this new method does not
have an error estimate and the approximations do not hold in general, we use a
neutral-atom Fermi-Hubbard quantum simulator with $L_{\text{exp}}\simeq290$
lattice sites to benchmark its performance in terms of accuracy and convergence
for evolution times up to $700$ tunnelling times. We then use these
approximations in order to derive a simple prediction of the behaviour of
interacting Bloch oscillations for spin-imbalanced Fermi-Hubbard systems, which
we show to be in quantitative agreement with experimental results. Finally, we
demonstrate that the convergence of our method is the slowest when the
entanglement depth developed in the many-body system we consider is neither too
small nor too large. This represents a promising regime for near-term
applications of quantum simulators.
less
By: Bharath Hebbe Madhusudhana
An important step in developing multi-qubit gates is to construct efficient
benchmarking protocols for them. In our previous paper (arXiv: 2210.04330), we
developed metrological protocols to measure the reduced Choi matrix i.e., the
completely positive (CP) maps induced on a subset S of the qubits, by the
multi-qubit gate. Here, we show a set of classically verifiable properties that
the Choi matrix satisfies if it is a reduction of a multi... more
An important step in developing multi-qubit gates is to construct efficient
benchmarking protocols for them. In our previous paper (arXiv: 2210.04330), we
developed metrological protocols to measure the reduced Choi matrix i.e., the
completely positive (CP) maps induced on a subset S of the qubits, by the
multi-qubit gate. Here, we show a set of classically verifiable properties that
the Choi matrix satisfies if it is a reduction of a multi-qubit unitary and use
them to develop benchmarks. We identify three types of errors that affect the
implementation of a multi-qubit unitary, based on their mathematical properties
and physical origin. Although a target multi-qubit gate is a unitary operator,
errors turn it into a general completely positive (CP) map. Errors due to
coupling to a thermal bath result in the multi-qubit gate being CP-divisible
(Markovian), deviating from a unitary. The reduced Choi matrix of a multi-qubit
gate has a property known as double stochasticity, which is violated in the
presence of Markovian errors. We construct a benchmark using
double-stochasticity violation and show that it is sensitive to coupling to any
thermal bath at a finite temperature. Further, errors due to shot-to-shot
fluctuations result in a non-markovian, i.e., CP-indivisible quantum process.
We prove a new property, which we call the \rank property of the reduced Choi
matrix, the violation of which implies a CP-indivisible error. A third category
of errors comes from systematics in the implementation of a multi-qubit gate,
resulting in no deviation from unitarity. We refer to this as unitary errors.
This corresponds to the most challenging type of error to benchmark. We develop
a partial-benchmarking protocol for such errors using symmetries of the
multi-qubit gate being applied.
less
By: Bharath Hebbe Madhusudhana
Accurate and precise control of large quantum systems is paramount to achieve
practical advantages on quantum devices. Therefore, benchmarking the hardware
errors in quantum computers has drawn significant attention lately. Existing
benchmarks for digital quantum computers involve averaging the global fidelity
over a large set of quantum circuits and are therefore unsuitable for specific
multi-qubit gates used in analog quantum operations. ... more
Accurate and precise control of large quantum systems is paramount to achieve
practical advantages on quantum devices. Therefore, benchmarking the hardware
errors in quantum computers has drawn significant attention lately. Existing
benchmarks for digital quantum computers involve averaging the global fidelity
over a large set of quantum circuits and are therefore unsuitable for specific
multi-qubit gates used in analog quantum operations. Moreover, average global
fidelity is not the optimal figure-of-merit for some of the applications
specific to multi-qubit gates and analog devices , such as the study of
many-body physics, which often use local observables. In this two-part paper,
we develop a new figure-of-merit suitable for multi-qubit quantum gates based
on the reduced Choi matrix of the operation. In the first part, we develop an
efficient, scalable protocol to completely characterize the reduced Choi
matrix. We identify two sources of sampling errors in measurements of the
reduced Choi matrix and we show that there are fundamental limits to the rate
of convergence of the sampling errors, analogous to the standard quantum limit
and Heisenberg limit. A slow convergence rate of sampling errors would mean
that we need a large number of experimental shots. We develop protocols using
quantum information scrambling, which has been observed in disordered systems
for e.g., to speed up the rate of convergence of the sampling error at state
preparation Moreover, we develop protocols using squeezed and entangled initial
states to enhance the convergence rate of the sampling error at measurement,
which results in a metrologically enhanced reduced process tomography protocol.
less
By: Diego García-Martín, Martin Larocca, M. Cerezo
It is well known that artificial neural networks initialized from independent
and identically distributed priors converge to Gaussian processes in the limit
of large number of neurons per hidden layer. In this work we prove an analogous
result for Quantum Neural Networks (QNNs). Namely, we show that the outputs of
certain models based on Haar random unitary or orthogonal deep QNNs converge to
Gaussian processes in the limit of large Hilbert... more
It is well known that artificial neural networks initialized from independent
and identically distributed priors converge to Gaussian processes in the limit
of large number of neurons per hidden layer. In this work we prove an analogous
result for Quantum Neural Networks (QNNs). Namely, we show that the outputs of
certain models based on Haar random unitary or orthogonal deep QNNs converge to
Gaussian processes in the limit of large Hilbert space dimension $d$. The
derivation of this result is more nuanced than in the classical case due the
role played by the input states, the measurement observable, and the fact that
the entries of unitary matrices are not independent. An important consequence
of our analysis is that the ensuing Gaussian processes cannot be used to
efficiently predict the outputs of the QNN via Bayesian statistics.
Furthermore, our theorems imply that the concentration of measure phenomenon in
Haar random QNNs is much worse than previously thought, as we prove that
expectation values and gradients concentrate as $\mathcal{O}\left(\frac{1}{e^d
\sqrt{d}}\right)$ -- exponentially in the Hilbert space dimension. Finally, we
discuss how our results improve our understanding of concentration in
$t$-designs.
less
By: Jonathan Wurtz, Anatoli Polkovnikov
This paper presents a method of computing approximate conservation laws and
eigenstates of integrability-broken models using the concept of adiabatic
continuation. Given some Hamiltonian, eigenstates and conserved operators may
be computed by using those of a simple Hamiltonian close by in parameter space,
dressed by some unitary rotation. However, most adiabatic continuation analyses
only use this unitary implicitly. In this work, approxim... more
This paper presents a method of computing approximate conservation laws and
eigenstates of integrability-broken models using the concept of adiabatic
continuation. Given some Hamiltonian, eigenstates and conserved operators may
be computed by using those of a simple Hamiltonian close by in parameter space,
dressed by some unitary rotation. However, most adiabatic continuation analyses
only use this unitary implicitly. In this work, approximate adiabatic gauge
potentials are used to construct a state dressing using variational methods, to
compute eigenstates via a rotated truncated spectrum approximation. These
methods allow construction of both low and high-energy approximate nonthermal
eigenstates, as well as quasi-local almost-conserved operators, in models where
integrability may be non-perturbatively broken. These concepts will be
demonstrated in the mixed-field Ising model.
less
By: Pierre A. Pantaleón, Vo Tien Phong, Gerardo G. Naumis, Francisco Guinea
We analyze the effects of the long-range Coulomb interaction on the
distribution of Berry curvature among the bands near charge neutrality of
twisted bilayer graphene (TBG) closely aligned with hexagonal boron nitride
(hBN). Due to the suppressed dispersion of the narrow bands, the band structure
is strongly renormalized by electron-electron interactions, and thus, the
associated topological properties of the bands are sensitive to filling.... more
We analyze the effects of the long-range Coulomb interaction on the
distribution of Berry curvature among the bands near charge neutrality of
twisted bilayer graphene (TBG) closely aligned with hexagonal boron nitride
(hBN). Due to the suppressed dispersion of the narrow bands, the band structure
is strongly renormalized by electron-electron interactions, and thus, the
associated topological properties of the bands are sensitive to filling. Using
a Hartree formalism, we calculate the linear and nonlinear Hall conductivities,
and find that for certain fillings, the remote bands contribute substantially
to the Hall currents while the contribution from the central bands is
suppressed. In particular, we find that these currents are generically
substantial near regions of energies where the bands are highly entangled with
each other, often featuring doping-induced band inversions. Our results
demonstrate that topological transport in TBG/hBN is substantially modified by
electron-electron interactions, which offer a simple explanation to recent
experimental results.
less
By: Xiao-Liang Qi
In this paper, we obtain some general results on information retrieval from
the black hole interior, based on the recent progress on quantum extremal
surface formula and entanglement island. We study an AdS black hole coupled to
a bath with generic dynamics, and ask whether it is possible to retrieve
information about a small perturbation in the interior from the bath system. We
derive a state reconstruction formula based on one norm. Howev... more
In this paper, we obtain some general results on information retrieval from
the black hole interior, based on the recent progress on quantum extremal
surface formula and entanglement island. We study an AdS black hole coupled to
a bath with generic dynamics, and ask whether it is possible to retrieve
information about a small perturbation in the interior from the bath system. We
derive a state reconstruction formula based on one norm. However, we show that
a contradiction arises if we apply this result to a special situation when the
bath dynamics includes a unitary operation that carries a particular
measurement to a region $A$ and send the result to another region $W$.
Physically, the contradiction arises between transferability of classical
information during the measurement, and non-transferability of quantum
information which determines the entanglement island. We propose that the
resolution of the contradiction is to realize that the state reconstruction
formula does not apply to the special situation involving
interior-information-retrieving measurements. This implies that the assumption
of smooth replica AdS geometry with boundary condition set by the flat space
bath has to break down when the particular measurement operator is applied to
the bath. Using replica trick, we introduce an explicitly construction of such
operator, which we name as "miracle operators". From this construction we see
that the smooth replica geometry assumption breaks down because we have to
introduce extra replica wormholes connecting with the "simulated blackholes"
introduced by the miracle operator. We study the implication of miracle
operators in understanding the firewall paradox.
less
By: Ville Bergholm, Josh Izaac, Maria Schuld, Christian Gogolin, Shahnawaz Ahmed, Vishnu Ajith, M. Sohaib Alam, Guillermo Alonso-Linaje, B. AkashNarayanan, Ali Asadi, Juan Miguel Arrazola, Utkarsh Azad, Sam Banning, Carsten Blank, Thomas R Bromley, Benjamin A. Cordier, Jack Ceroni, Alain Delgado, Olivia Di Matteo, Amintor Dusko, Tanya Garg, Diego Guala, Anthony Hayes, Ryan Hill, Aroosa Ijaz, Theodor Isacsson, David Ittah, Soran Jahangiri, Prateek Jain, Edward Jiang, Ankit Khandelwal, Korbinian Kottmann, Robert A. Lang, Christina Lee, Thomas Loke, Angus Lowe, Keri McKiernan, Johannes Jakob Meyer, J. A. Montañez-Barrera, Romain Moyard, Zeyue Niu, Lee James O'Riordan, Steven Oud, Ashish Panigrahi, Chae-Yeun Park, Daniel Polatajko, Nicolás Quesada, Chase Roberts, Nahum Sá, Isidor Schoch, Borun Shi, Shuli Shu, Sukin Sim, Arshpreet Singh, Ingrid Strandberg, Jay Soni, Antal Száva, Slimane Thabet, Rodrigo A. Vargas-Hernández, Trevor Vincent, Nicola Vitucci, Maurice Weber, David Wierichs, Roeland Wiersema, Moritz Willmann, Vincent Wong, Shaoming Zhang, Nathan Killoran
PennyLane is a Python 3 software framework for differentiable programming of
quantum computers. The library provides a unified architecture for near-term
quantum computing devices, supporting both qubit and continuous-variable
paradigms. PennyLane's core feature is the ability to compute gradients of
variational quantum circuits in a way that is compatible with classical
techniques such as backpropagation. PennyLane thus extends the automat... more
PennyLane is a Python 3 software framework for differentiable programming of
quantum computers. The library provides a unified architecture for near-term
quantum computing devices, supporting both qubit and continuous-variable
paradigms. PennyLane's core feature is the ability to compute gradients of
variational quantum circuits in a way that is compatible with classical
techniques such as backpropagation. PennyLane thus extends the automatic
differentiation algorithms common in optimization and machine learning to
include quantum and hybrid computations. A plugin system makes the framework
compatible with any gate-based quantum simulator or hardware. We provide
plugins for hardware providers including the Xanadu Cloud, Amazon Braket, and
IBM Quantum, allowing PennyLane optimizations to be run on publicly accessible
quantum devices. On the classical front, PennyLane interfaces with accelerated
machine learning libraries such as TensorFlow, PyTorch, JAX, and Autograd.
PennyLane can be used for the optimization of variational quantum eigensolvers,
quantum approximate optimization, quantum machine learning models, and many
other applications.
less
By: Prateek Jain, Srinjoy Ganguly
In molecular research, simulation \& design of molecules are key areas with
significant implications for drug development, material science, and other
fields. Current classical computational power falls inadequate to simulate any
more than small molecules, let alone protein chains on hundreds of peptide.
Therefore these experiment are done physically in wet-lab, but it takes a lot
of time \& not possible to examine every molecule due to the... more
In molecular research, simulation \& design of molecules are key areas with
significant implications for drug development, material science, and other
fields. Current classical computational power falls inadequate to simulate any
more than small molecules, let alone protein chains on hundreds of peptide.
Therefore these experiment are done physically in wet-lab, but it takes a lot
of time \& not possible to examine every molecule due to the size of the search
area, tens of billions of dollars are spent every year in these research
experiments. Molecule simulation \& design has lately advanced significantly by
machine learning models, A fresh perspective on the issue of chemical synthesis
is provided by deep generative models for graph-structured data. By optimising
differentiable models that produce molecular graphs directly, it is feasible to
avoid costly search techniques in the discrete and huge space of chemical
structures. But these models also suffer from computational limitations when
dimensions become huge and consume huge amount of resources. Quantum Generative
machine learning in recent years have shown some empirical results promising
significant advantages over classical counterparts.
less
By: Prateek Jain, Alberto Garcia Garcia
Within this decade, quantum computers are predicted to outperform
conventional computers in terms of processing power and have a disruptive
effect on a variety of business sectors. It is predicted that the financial
sector would be one of the first to benefit from quantum computing both in the
short and long terms. In this research work we use Hybrid Quantum Neural
networks to present a quantum machine learning approach for Continuous varia... more
Within this decade, quantum computers are predicted to outperform
conventional computers in terms of processing power and have a disruptive
effect on a variety of business sectors. It is predicted that the financial
sector would be one of the first to benefit from quantum computing both in the
short and long terms. In this research work we use Hybrid Quantum Neural
networks to present a quantum machine learning approach for Continuous variable
prediction.
less
By: Hasan Mustafa, Sai Nandan Morapakula, Prateek Jain, Srinjoy Ganguly
Quantum computing has gained a lot of attention recently, and scientists have
seen potential applications in this field using quantum computing for
Cryptography and Communication to Machine Learning and Healthcare. Protein
folding has been one of the most interesting areas to study, and it is also one
of the biggest problems of biochemistry. Each protein folds distinctively, and
the difficulty of finding its stable shape rapidly increases w... more
Quantum computing has gained a lot of attention recently, and scientists have
seen potential applications in this field using quantum computing for
Cryptography and Communication to Machine Learning and Healthcare. Protein
folding has been one of the most interesting areas to study, and it is also one
of the biggest problems of biochemistry. Each protein folds distinctively, and
the difficulty of finding its stable shape rapidly increases with an increase
in the number of amino acids in the chain. A moderate protein has about 100
amino acids, and the number of combinations one needs to verify to find the
stable structure is enormous. At some point, the number of these combinations
will be so vast that classical computers cannot even attempt to solve them. In
this paper, we examine how this problem can be solved with the help of quantum
computing using two different algorithms, Variational Quantum Eigensolver (VQE)
and Quantum Approximate Optimization Algorithm (QAOA), using Qiskit Nature. We
compare the results of different quantum hardware and simulators and check how
error mitigation affects the performance. Further, we make comparisons with
SoTA algorithms and evaluate the reliability of the method.
less
By: Ruizhi Pan Joint Quantum Institute, NIST/University of Maryland, College Park, MD, USA, Charles W. Clark Joint Quantum Institute, NIST/University of Maryland, College Park, MD, USA National Institute of Standards and Technology, Gaithersburg, Maryland, USA
Neural-network state representations of quantum many-body systems are
attracting great attention and more rigorous quantitative analysis about their
expressibility and complexity is warranted. Our analysis of the restricted
Boltzmann machine (RBM) state representation of one-dimensional (1D) quantum
spin systems provides new insight into their computational complexity. We
define a class of long-range-fast-decay (LRFD) RBM states with quanti... more
Neural-network state representations of quantum many-body systems are
attracting great attention and more rigorous quantitative analysis about their
expressibility and complexity is warranted. Our analysis of the restricted
Boltzmann machine (RBM) state representation of one-dimensional (1D) quantum
spin systems provides new insight into their computational complexity. We
define a class of long-range-fast-decay (LRFD) RBM states with quantifiable
upper bounds on truncation errors and provide numerical evidence for a large
class of 1D quantum systems that may be approximated by LRFD RBMs of at most
polynomial complexities. These results lead us to conjecture that the ground
states of a wide range of quantum systems may be exactly represented by LRFD
RBMs or a variant of them, even in cases where other state representations
become less efficient. At last, we provide the relations between multiple
typical state manifolds. Our work proposes a paradigm for doing complexity
analysis for generic long-range RBMs which naturally yields a further
classification of this manifold. This paradigm and our characterization of
their nonlocal structures may pave the way for understanding the natural
measure of complexity for quantum many-body states described by RBMs and are
generalizable for higher-dimensional systems and deep neural-network quantum
states.
less
By: Jonathan B. Curtis, Marios H. Michael, Eugene Demler
Control of quantum matter through resonant electromagnetic cavities is a
promising route towards establishing control over material phases and
functionalities. Quantum paraelectric insulators -- materials which are nearly
ferroelectric -- are particularly promising candidate systems for this purpose
since they have strongly fluctuating collective modes which directly couple to
the electric field. In this work we explore this possibility in ... more
Control of quantum matter through resonant electromagnetic cavities is a
promising route towards establishing control over material phases and
functionalities. Quantum paraelectric insulators -- materials which are nearly
ferroelectric -- are particularly promising candidate systems for this purpose
since they have strongly fluctuating collective modes which directly couple to
the electric field. In this work we explore this possibility in a system
comprised of a quantum paraelectric sandwiched between two high-quality metal
mirrors, realizing a Fabry-Perot type cavity. By developing a full multimode,
continuum description we are able to study the effect of the cavity in a
spatially resolved way for a variety of system sizes and temperatures.
Surprisingly, we find that once a continuum of transverse modes are included
the cavity ends up suppressing ferroelectric correlations. This effect arises
from the screening out of transverse photons at the cavity boundaries and as a
result is confined to the surface of the paraelectric sample. We also explore
the temperature dependence of this effect and find it vanishes at high
temperatures, indicating it is a purely quantum mechanical effect. We connect
our result to calculations of Casimir and Van der Waals forces, which we argue
are closely related to the dipolar fluctuations in the quantum paraelectric.
Our results are based on a general formalism and are expected to be widely
applicable, paving the way towards studies of the quantum electrodynamics of
heterostructures featuring multiple materials and phases.
less
By: Sam Wilken, Ashley Z. Guo, Dov Levine, Paul M. Chaikin
A simple dynamical model, Biased Random Organization, BRO, appears to produce the ensemble of configurations known as Random Close Packed (RCP) as its critical endpoint in dimension d=3. We conjecture that BRO likewise produces RCP in any dimension and come to the following conclusions: there is no RCP in
d=1 or d=2 (where dynamics lead to crystalline order); in d=3, d=4, and d=5, we recover RCP behavior with previously estimated packing fr... more
A simple dynamical model, Biased Random Organization, BRO, appears to produce the ensemble of configurations known as Random Close Packed (RCP) as its critical endpoint in dimension d=3. We conjecture that BRO likewise produces RCP in any dimension and come to the following conclusions: there is no RCP in
d=1 or d=2 (where dynamics lead to crystalline order); in d=3, d=4, and d=5, we recover RCP behavior with previously estimated packing fractions 0.64, 0.45, and 0.30 respectively, and the systems are isostatic with average contact numbers 6, 8, and 10. BRO belongs to the Manna universality class of dynamical phase transitions, which has well-defined critical exponents and an upper critical dimension of 4. Exponents are mean field for $4 \le d \le \infty$, which we confirm in simulations. Further, a hyperscaling relation between the correlation function exponent and density fluctuations implies that when mean field exponents hold, density fluctuations are random and not hyperuniform. Hence, hyperuniformity in RCP is only observed in d=3.
less
By: Pankaj C. Bhambhani, Ivan. K. Baldry, Sarah Brough, Alexander D. Hill, M. A. Lara-Lopez, J. Loveday, B. W. Holwerda
Galaxy populations are known to exhibit a strong colour bimodality,
corresponding to blue star-forming and red quiescent subpopulations. The
relative abundance of the two populations has been found to vary with stellar
mass and cosmic environment. In this paper, we explore the effect of environment
considering different types of measurements. We choose a sample of 49, 91
galaxies in the redshift range 0.05 < z < 0.18 from the Galaxy And Mass ... more
Galaxy populations are known to exhibit a strong colour bimodality,
corresponding to blue star-forming and red quiescent subpopulations. The
relative abundance of the two populations has been found to vary with stellar
mass and cosmic environment. In this paper, we explore the effect of environment
considering different types of measurements. We choose a sample of 49, 91
galaxies in the redshift range 0.05 < z < 0.18 from the Galaxy And Mass Assembly survey. We
study the dependence of the fraction of red galaxies on different measures of
the local environment as well as the large-scale "geometric" environment
defined by density gradients in the surrounding cosmic web. We find that the
red galaxy fraction varies with the environment at fixed stellar mass. The red
fraction depends more strongly on local environmental measures than on
large-scale geometric environment measures. By comparing the different
environmental densities, we show that no density measurement fully explains the
observed environmental red fraction variation, suggesting the different
measures of environmental density contain different information. We test
whether the local environmental measures, when combined together, can explain
all the observed environmental red fraction variation. The geometric
environment has a small residual effect, and this effect is larger for voids
than any other type of geometric environment. This could provide a test of the
physics applied to cosmological-scale galaxy evolution simulations as it
combines large-scale effects with local environmental impact.
less
By: Andrey Grankin, Victor Galitski
The conventional Bardeen-Cooper-Schrieffer (BCS) model of superconductivity assumes a frequency-independent order parameter, which allows a relatively simple description of the superconducting state. In particular, its excitation spectrum readily follows from the Bogoliubov-de-Gennes (BdG) equations. A more
realistic description of a superconductor is the Migdal-Eliashberg theory, where the pairing interaction, the order parameter, and elec... more
The conventional Bardeen-Cooper-Schrieffer (BCS) model of superconductivity assumes a frequency-independent order parameter, which allows a relatively simple description of the superconducting state. In particular, its excitation spectrum readily follows from the Bogoliubov-de-Gennes (BdG) equations. A more
realistic description of a superconductor is the Migdal-Eliashberg theory, where the pairing interaction, the order parameter, and electronic self-energy are strongly frequency dependent. This work combines these ingredients of phonon-mediated superconductivity with the standard BdG approach. Surprisingly, we find qualitatively new features such as the emergence of a shadow superconducting gap in the quasiparticle spectrum at energies close to the
Debye energy. We show how these features reveal themselves in standard tunneling experiments. Finally, we also predict the existence of additional high-energy bound states, which we dub "dark Andreev states."
less
Temperature-dependent phonon-induced relaxation of the nitrogen-vacancy spin triplet in diamond
0upvotes
By: M. C. Cambria, A. Norambuena, H. T. Dinani, G. Thiering, A. Gardill, I. Kemeny, Y. Li, V. Lordi, A. Gali, J. R. Maze, S. Kolkowitz
Phonon-induced relaxation within the nitrogen-vacancy (NV) center's
electronic ground-state spin triplet limits its coherence times, and thereby impacts its performance in quantum applications. We report measurements of the relaxation rates on the NV center's transitions as a function of temperature from 9 to 474 K in high-purity samples. Informed by ab initio calculations, we demonstrate that NV spin-phonon relaxation can be completely exp... more
Phonon-induced relaxation within the nitrogen-vacancy (NV) center's
electronic ground-state spin triplet limits its coherence times, and thereby impacts its performance in quantum applications. We report measurements of the relaxation rates on the NV center's transitions as a function of temperature from 9 to 474 K in high-purity samples. Informed by ab initio calculations, we demonstrate that NV spin-phonon relaxation can be completely explained by the effect of second-order interactions with two distinct groups of quasilocalized phonons. Using a novel analytical model based on this understanding, we determine that the quasilocalized phonon groups are centered at 68.2(17) and 167(12) meV.
less
By: Gregory Gabadadze
The question of building a local diff-invariant effective gravitational action for the trace anomaly is reconsidered. General Relativity (GR) combined with the existing action for the trace anomaly is an inconsistent low energy effective field theory. This issue is addressed by extending GR into a certain scalar-tensor theory, which preserves the GR trace anomaly equation, up to higher order corrections. The extension introduces a new mass ... more
The question of building a local diff-invariant effective gravitational action for the trace anomaly is reconsidered. General Relativity (GR) combined with the existing action for the trace anomaly is an inconsistent low energy effective field theory. This issue is addressed by extending GR into a certain scalar-tensor theory, which preserves the GR trace anomaly equation, up to higher order corrections. The extension introduces a new mass scale -- assumed to be below the Planck scale -- that governs four high dimensional terms in a local diff-invariant trace anomaly action. Such terms can be kept, while an infinite number of Planck-suppressed invariants are neglected. The resulting theory maintains two derivative equations of motion. In a certain approximation it reduces to the conformal Gallileon, which could have physical consequences.
less
By: Pierre A. Pantaleón, Y. Xian
The difference between the edge on-site potential and the bulk values in a
magnonic topological honeycomb lattice leads to the formation of edge states in
a bearded boundary, and the same difference is found to be the responsible for
the absence of edge states in a zig-zag termination. In a finite lattice, the
intrinsic on-site interactions along the boundary sites generate an effective
defect and Tamm-like edge states appear for both zig-z... more
The difference between the edge on-site potential and the bulk values in a
magnonic topological honeycomb lattice leads to the formation of edge states in
a bearded boundary, and the same difference is found to be the responsible for
the absence of edge states in a zig-zag termination. In a finite lattice, the
intrinsic on-site interactions along the boundary sites generate an effective
defect and Tamm-like edge states appear for both zig-zag and bearded
terminations. If a non-trivial gap is induced, Tamm-like and topologically
protected edge states appear in the band structure. The effective defect can be
strengthened by an external on-site potential and the dispersion relation,
velocity and magnon-density of the edge states become tunable.
less
Bits join the Dark Side
0upvotes
By: Paul Gough
The amount of information energy in the universe is of the same order of magnitude as the total mc2 energy equivalence of all universe baryons. Information energy can contribute to both dark energy and dark matter attributed effects. It is a transitional dark energy: phantom with increasing energy density in the early universe, changing around a redshift, z~1.35, to a near constant energy density in the late universe. On the scale of the univ... more
The amount of information energy in the universe is of the same order of magnitude as the total mc2 energy equivalence of all universe baryons. Information energy can contribute to both dark energy and dark matter attributed effects. It is a transitional dark energy: phantom with increasing energy density in the early universe, changing around a redshift, z~1.35, to a near constant energy density in the late universe. On the scale of the universe, information energy is repulsive as a dark energy causing the accelerating expansion, but, on local scales, it is clumped and attractive like dark matter. The combined characteristics of information energy enable us to resolve many of the problems of the standard ΛCDM model: the cosmological constant problem; the dark matter problem; the Hubble tension; S8 matter fluctuation parameter tension; cosmological principle problem and the cosmological coincidence problem. In addition, the model satisfies the two ideal requirements of a cosmological model: simplicity and naturalness. Most importantly, the model predicts a measurable difference in the Hubble parameter around z~2 that provides a clear signature for the information energy model to be falsified. Journal citation: https://www.mdpi.com/1099-4300/24/3/385 less
By: Victor V. Albert
Bosonic or continuous-variable coding is a field concerned with robust
quantum information processing and communication with electromagnetic signals
or mechanical modes. I review bosonic quantum memories, characterizing them as
either bosonic stabilizer or bosonic Fock-state codes. I then enumerate various
applications of bosonic encodings, four of which circumvent no-go theorems due
to the intrinsic infinite-dimensionality of bosonic systems.
Bosonic or continuous-variable coding is a field concerned with robust
quantum information processing and communication with electromagnetic signals
or mechanical modes. I review bosonic quantum memories, characterizing them as
either bosonic stabilizer or bosonic Fock-state codes. I then enumerate various
applications of bosonic encodings, four of which circumvent no-go theorems due
to the intrinsic infinite-dimensionality of bosonic systems.
less
By: Eric Culf, Thomas Vidick, Victor V. Albert
We develop an extension of a recently introduced subspace coset state
monogamy-of-entanglement game [Coladangelo, Liu, Liu, and Zhandry; Crypto'21]
to general group coset states, which are uniform superpositions over elements
of a subgroup to which has been applied a group-theoretic generalization of the
quantum one-time pad. We give a general bound on the winning probability of a
monogamy game constructed from subgroup coset states that ap... more
We develop an extension of a recently introduced subspace coset state
monogamy-of-entanglement game [Coladangelo, Liu, Liu, and Zhandry; Crypto'21]
to general group coset states, which are uniform superpositions over elements
of a subgroup to which has been applied a group-theoretic generalization of the
quantum one-time pad. We give a general bound on the winning probability of a
monogamy game constructed from subgroup coset states that applies to a wide
range of finite and infinite groups. To study the infinite-group case, we use
and further develop a measure-theoretic formalism that allows us to express
continuous-variable measurements as operator-valued generalizations of
probability measures.
We apply the monogamy game bound to various physically relevant groups,
yielding realizations of the game in continuous-variable modes as well as in
rotational states of a polyatomic molecule. We obtain explicit strong bounds in
the case of specific group-space and subgroup combinations. As an application,
we provide the first proof of one sided-device independent security of a
squeezed-state continuous-variable quantum key distribution protocol against
general coherent attacks.
less
By: B. Nord, A. Amara, A. Refregier, La. Gamper, Lu. Gamper, B. Hambrecht, C. Chang, J. E. Forero-Romero, S. Serrano, C. Cunha, O. Coles, A. Nicola, M. Busha, A. Bauer, W. Saunders, S. Jouvel, D. Kirk, R. Wechsler
The nature of dark matter, dark energy and large-scale gravity pose some of
the most pressing questions in cosmology today. These fundamental questions
require highly precise measurements, and a number of wide-field spectroscopic
survey instruments are being designed to meet this requirement. A key component
in these experiments is the development of a simulation tool to forecast
science performance, define requirement flow-downs, optimize ... more
The nature of dark matter, dark energy and large-scale gravity pose some of
the most pressing questions in cosmology today. These fundamental questions
require highly precise measurements, and a number of wide-field spectroscopic
survey instruments are being designed to meet this requirement. A key component
in these experiments is the development of a simulation tool to forecast
science performance, define requirement flow-downs, optimize implementation,
demonstrate feasibility, and prepare for exploitation. We present SPOKES
(SPectrOscopic KEn Simulation), an end-to-end simulation facility for
spectroscopic cosmological surveys designed to address this challenge. SPOKES
is based on an integrated infrastructure, modular function organization,
coherent data handling and fast data access. These key features allow
reproducibility of pipeline runs, enable ease of use and provide flexibility to
update functions within the pipeline. The cyclic nature of the pipeline offers
the possibility to make the science output an efficient measure for design
optimization and feasibility testing. We present the architecture, first
science, and computational performance results of the simulation pipeline. The
framework is general, but for the benchmark tests, we use the Dark Energy
Spectrometer (DESpec), one of the early concepts for the upcoming project, the
Dark Energy Spectroscopic Instrument (DESI). We discuss how the SPOKES
framework enables a rigorous process to optimize and exploit spectroscopic
survey experiments in order to derive high-precision cosmological measurements
optimally.
less
By: Gabriel A. Durkin
It is known that secondary non-stoquastic drivers may offer speed-ups or
catalysis in some models of adiabatic quantum computation accompanying the more
typical transverse field driver. Their combined intent is to raze potential
barriers to zero during adiabatic evolution from a false vacuum to a true
minimum; first order phase transitions are softened into second order
transitions. We move beyond mean-field analysis to a fully quantum mode... more
It is known that secondary non-stoquastic drivers may offer speed-ups or
catalysis in some models of adiabatic quantum computation accompanying the more
typical transverse field driver. Their combined intent is to raze potential
barriers to zero during adiabatic evolution from a false vacuum to a true
minimum; first order phase transitions are softened into second order
transitions. We move beyond mean-field analysis to a fully quantum model of a
spin ensemble undergoing adiabatic evolution in which the spins are mapped to a
variable mass particle in a continuous one-dimensional potential. We
demonstrate the necessary criteria for enhanced mobility or `speed-up' across
potential barriers is actually a quantum form of the Rayleigh criterion.
Quantum catalysis is exhibited in models where previously thought not possible,
when barriers cannot be eliminated. For the $3$-spin model with secondary
anti-ferromagnetic driver, catalysed time complexity scales between linear and
quadratically with the number of qubits. As a corollary, we identify a useful
resonance criterion for quantum phase transition that differs from the
classical one, but converges on it, in the thermodynamic limit.
less
By: Pierre A. Pantaleón, Yang Xian
We investigate the properties of magnon edge states in a ferromagnetic
honeycomb lattice with armchair boundaries. In contrast with fermionic
graphene, we find novel edge states due to the missing bonds along the boundary
sites. After introducing an external on-site potential at the outermost sites
we find that the energy spectra of the edge states are tunable. Additionally,
when a non-trivial gap is induced, we find that some of the edge s... more
We investigate the properties of magnon edge states in a ferromagnetic
honeycomb lattice with armchair boundaries. In contrast with fermionic
graphene, we find novel edge states due to the missing bonds along the boundary
sites. After introducing an external on-site potential at the outermost sites
we find that the energy spectra of the edge states are tunable. Additionally,
when a non-trivial gap is induced, we find that some of the edge states are
topologically protected and also tunable. Our results may explain the origin of
the novel edge states recently observed in photonic lattices. We also discuss
the behavior of these edge states for further experimental confirmations
less
By: Alejandro Jimeno-Pozo, Zachary A. H. Goodwin, Pierre A. Pantaleón, Valerio Vitale, Lennart Klebl, Dante M. Kennes, Arash Mostofi, Johannes Lischner, Francisco Guinea
We discuss the effect of long-range interactions within the self-consistent Hartree-Fock (HF) approximation in comparison to short-range atomic Hubbard interactions on the band structure of twisted bilayer graphene (TBG) at charge neutrality for various twist angles. Starting from atomistic calculations, we determine the quasi-particle band structure of TBG with Hubbard interactions for various magnetic orderings: modulated anti-ferromagnetic... more
We discuss the effect of long-range interactions within the self-consistent Hartree-Fock (HF) approximation in comparison to short-range atomic Hubbard interactions on the band structure of twisted bilayer graphene (TBG) at charge neutrality for various twist angles. Starting from atomistic calculations, we determine the quasi-particle band structure of TBG with Hubbard interactions for various magnetic orderings: modulated anti-ferromagnetic (MAFM), nodal anti-ferromagnetic (NAFM) and hexagonal anti-ferromagnetic (HAFM). Then, we develop an approach to incorporate these magnetic orderings along with the HF potential in the continuum approximation. Away from the magic angle, we observe a drastic effect of the magnetic order on the band structure of TBG compared to the influence of the HF potential. Near the magic angle, however, the HF potential seems to play a major role on the band structure compared to the magnetic order. These findings suggest that the spin-valley degenerate broken symmetry state often found in HF calculations of charge neutral TBG near the magic angle should favour magnetic order, since the atomistic Hubbard interaction will break this symmetry in favour of spin polarization.
less
By: Alejandro Jimeno-Pozo, Héctor Sainz-Cruz, Tommaso Cea, Pierre A. Pantaleón, Francisco Guinea
We discuss a Kohn-Luttinger-like mechanism for superconductivity in Bernal bilayer graphene and rhombohedral trilayer graphene. Working within the continuum model description, we find that the screened long-range Coulomb interaction alone gives rise to superconductivity with critical temperatures that agree with experiments. We observe that the order parameter changes sign between valleys, which implies that both materials are valley-singlet,... more
We discuss a Kohn-Luttinger-like mechanism for superconductivity in Bernal bilayer graphene and rhombohedral trilayer graphene. Working within the continuum model description, we find that the screened long-range Coulomb interaction alone gives rise to superconductivity with critical temperatures that agree with experiments. We observe that the order parameter changes sign between valleys, which implies that both materials are valley-singlet, spin-triplet superconductors. Adding Ising spin-orbit coupling leads to a significant enhancement in the critical temperature, also in line with experiment, and the superconducting order parameter shows locking between the spin and valley degrees of freedom.
less
By: Laura Budewig, Sang-Kil Son, Robin Santra
We theoretically study orbital alignment in x-ray-ionized atoms and ions,
based on improved electronic-structure calculations starting from the
Hartree-Fock-Slater model. We employ first-order many-body perturbation theory
to improve the Hartree-Fock-Slater calculations and show that the use of
first-order-corrected energies yields significantly better transition energies
than originally obtained. The improved electronic-structure calculati... more
We theoretically study orbital alignment in x-ray-ionized atoms and ions,
based on improved electronic-structure calculations starting from the
Hartree-Fock-Slater model. We employ first-order many-body perturbation theory
to improve the Hartree-Fock-Slater calculations and show that the use of
first-order-corrected energies yields significantly better transition energies
than originally obtained. The improved electronic-structure calculations enable
us also to compute individual state-to-state cross sections and transition
rates and, thus, to investigate orbital alignment induced by linearly polarized
x rays. To explore the orbital alignment of transiently formed ions after
photoionization, we discuss alignment parameters and ratios of individual
state-resolved photoionization cross sections for initially neutral argon and
two exotic electronic configurations that may be formed during x-ray
multiphoton ionization dynamics induced by x-ray free-electron lasers. We also
present how the orbital alignment is affected by Auger-Meitner decay and
demonstrate how it evolves during a sequence of one photoionization and one
Auger-Meitner decay. Our present work establishes a step toward investigation
of orbital alignment in atomic ionization driven by high-intensity x rays.
less
By: Pierre A. Pantaleon, Alejandro Jimeno-Pozo, Hector Sainz-Cruz, Vo Tien Phong, Tommaso Cea, Francisco Guinea
Twisted bilayer graphene has a rich phase diagram, including superconductivity. Recently, an unexpected discovery has been the observation of superconductivity in non-twisted graphene bilayers and trilayers. In this Perspective, we give an overview of the search for uncommon phases in non-twisted graphene systems. We first contextualise these recent results within earlier work in the field, before examining the new experimental findings. Fina... more
Twisted bilayer graphene has a rich phase diagram, including superconductivity. Recently, an unexpected discovery has been the observation of superconductivity in non-twisted graphene bilayers and trilayers. In this Perspective, we give an overview of the search for uncommon phases in non-twisted graphene systems. We first contextualise these recent results within earlier work in the field, before examining the new experimental findings. Finally, we analyse the numerous theoretical models which study the underlying physical processes in these systems.
less
By: Héctor Sainz-Cruz, Pierre A. Pantaleón, Vo Tien Phong, Alejandro Jimeno-Pozo, Francisco Guinea
Junctions provide a wealth of information on the symmetry of the order
parameter of superconductors. We analyze junctions between a scanning tunneling
microscope (STM) tip and superconducting twisted bilayer graphene (TBG) and TBG
Josephson junctions (JJs). We compare superconducting phases that are even or
odd under valley exchange (s- or f-wave). The critical current in mixed (s- and
f-) JJs strongly depends on the angle between the junct... more
Junctions provide a wealth of information on the symmetry of the order
parameter of superconductors. We analyze junctions between a scanning tunneling
microscope (STM) tip and superconducting twisted bilayer graphene (TBG) and TBG
Josephson junctions (JJs). We compare superconducting phases that are even or
odd under valley exchange (s- or f-wave). The critical current in mixed (s- and
f-) JJs strongly depends on the angle between the junction and the lattice. In
STM-TBG junctions, due to Andreev reflection, f-wave leads to a prominent peak
in subgap conductance, as seen in experiments.
less
By: Raghu K. Moorthy, Serena D'Souza, P. Sunthar, Santosh B. Noronha
Stationary phase plays a crucial role in the operation of a protein
chromatography column. Conventional resins composed of acrylic polymers and
their derivatives contribute to heterogeneity of the packing of stationary
phase inside these columns. Alternative polymer combinations through customized
surface functionalization schemes which consist of multiple steps using static
coating techniques are well known. In comparison, it is hypothesiz... more
Stationary phase plays a crucial role in the operation of a protein
chromatography column. Conventional resins composed of acrylic polymers and
their derivatives contribute to heterogeneity of the packing of stationary
phase inside these columns. Alternative polymer combinations through customized
surface functionalization schemes which consist of multiple steps using static
coating techniques are well known. In comparison, it is hypothesized that a
single-step scheme is sufficient to obtain porous adsorbents as stationary
phase for tuning surface morphology and protein immobilization. To overcome the
challenge of heterogeneous packing and ease of fabrication at a laboratory
scale, a change in the form factor of separation materials has been proposed in
the form of functional copolymer surfaces. In the present work, an amphiphilic,
block copolymer, poly(methyl methacrylate-co-methacrylic acid) has been chosen
and fully characterized for its potential usage in protein chromatography.
Hydrophilicity of the acrylic copolymer and abundance of carboxyl groups
inherently on the copolymer surface have been successfully demonstrated through
contact angle measurements, Fourier transform infrared (FTIR) and X-ray
photoelectron spectroscopy (XPS) studies. Morphological studies indicate
presence of a microporous region (nearly 1 to 1.5 $\mu$m pore size) that could
be beneficial as a cation exchange media as part of the stationary phase in
protein chromatography.
less
By: Priyamvada Natarajan Department of Astronomy, Yale University, New Haven CT, USA, Kwok Sun Tang UIUC, Robert McGibbon, University of Edinburgh, Sadegh Khochfar University of Edinburgh, Brian Nord FNAL and KICP, Steinn Sigurdsson Penn State University, Joe Tricot Sandbox@Alphabet, Nico Cappelluti University of Miami, Daniel George Sandbox@Alphabet, Jack Hidary Sandbox@Alphabet
We present QUOTAS, a novel research platform for the data-driven
investigation of super-massive black hole populations. While supermassive black hole data
sets -- observations and simulations -- have grown rapidly in complexity and
abundance, our computational environments and analysis tools have not matured
commensurately to exhaust opportunities for discovery. Motivated to explore black hole
host galaxy and the parent dark matter halo conne... more
We present QUOTAS, a novel research platform for the data-driven
investigation of super-massive black hole populations. While supermassive black hole data
sets -- observations and simulations -- have grown rapidly in complexity and
abundance, our computational environments and analysis tools have not matured
commensurately to exhaust opportunities for discovery. Motivated to explore black hole
host galaxy and the parent dark matter halo connection, in this pilot version
of QUOTAS, we assemble and co-locate the high-redshift, luminous quasar
population at $z \geq 3$ alongside simulated data of the same epochs.
Leveraging machine learning algorithms we expand simulation volumes that
successfully replicate halo populations beyond the training set. Training machine learning algorithms on the Illustris-TNG300 simulation that includes baryonic physics, we populate the larger LEGACY Expanse dark matter-only box with quasars. Our first science
results comparing observational and machine learning simulated quasars at $z \sim 3$, reveal that while the recovered Black Hole Mass Functions and clustering are in good agreement, simulated supermassive black holes fail to accrete, shine and grow at high enough rates to match observed quasars. We conclude that sub-grid models of mass accretion and supermassive black hole feedback implemented in Illustris-TNG300 do not reproduce their observed mass growth. QUOTAS, demonstrates the power of machine learning, both for analyzing large complex datasets, and offering a unique opportunity to interrogate our theoretical model assumptions. We deploy machine learning again to derive and devise an optimal survey strategy for bringing the undetected lower luminosity quasar population into view. QUOTAS, and all related materials are publicly available
at the Google Kaggle platform. less
By: Min Long, Zhen Zhan, Pierre A. Pantaleón, Jose Ángel Silva-Guillén, Francisco Guinea, Shengjun Yuan
The recent observed anomalous Hall effect in magic angle twisted bilayer
graphene (TBG) aligned to hexagonal boron nitride (hBN) and unconventional
ferroelectricity in Bernal bilayer graphene sandwiched by hBN present a new
platform to tune the correlated properties in graphene systems. In these
graphene-based moir\'e superlattices, the aligned hBN substrate plays an
important role. In this paper, we analyze the effects of hBN substrate on ... more
The recent observed anomalous Hall effect in magic angle twisted bilayer
graphene (TBG) aligned to hexagonal boron nitride (hBN) and unconventional
ferroelectricity in Bernal bilayer graphene sandwiched by hBN present a new
platform to tune the correlated properties in graphene systems. In these
graphene-based moir\'e superlattices, the aligned hBN substrate plays an
important role. In this paper, we analyze the effects of hBN substrate on the
band structure of the TBG. By means of an atomistic tight-binding model we
calculate the electronic properties of TBG suspended and encapsulated with hBN.
Interestingly, we found that the physical properties of TBG are extremely
sensitive to the presence of hBN and they may be completely different if TBG is
suspended or encapsulated. We quantify these differences by analysing their
electronic properties, optical conductivity and band topology. We found that
the narrow bandwidth, band gap, local density of states and optical
conductivity are significantly modified by the aligned hBN substrates.
Interestingly, these electronic properties can be used as a signature of the
alignment in experiment. Moreover, the TBG/hBN superlattices in the presence or
absence of the two-fold rotation symmetry response differently to the external
electric field. For the TBG suspended in the hBN, application of an electric
field results in the charge unevenly distributed between graphene layers, which
can be used to tune the strength of the valley Hall effect or the anomalous
Hall effect. Such rich topological phase diagram in these systems may be useful
for experiments.
less
By: C. L. Tschirhart, Evgeny Redekop, Lizhong Li, Tingxin Li, Shengwei Jiang, T. Arp, O. Sheekey, Takashi Taniguchi, Kenji Watanabe, Kin Fai Mak, Jie Shan, A. F. Young
In spin torque magnetic memories, electrically actuated spin currents are
used to switch a magnetic bit. Typically, these require a multilayer geometry
including both a free ferromagnetic layer and a second layer providing spin
injection. For example, spin may be injected by a nonmagnetic layer exhibiting
a large spin Hall effect, a phenomenon known as spin-orbit torque. Here, we
demonstrate a spin-orbit torque magnetic bit in a single two-... more
In spin torque magnetic memories, electrically actuated spin currents are
used to switch a magnetic bit. Typically, these require a multilayer geometry
including both a free ferromagnetic layer and a second layer providing spin
injection. For example, spin may be injected by a nonmagnetic layer exhibiting
a large spin Hall effect, a phenomenon known as spin-orbit torque. Here, we
demonstrate a spin-orbit torque magnetic bit in a single two-dimensional system
with intrinsic magnetism and strong Berry curvature. We study AB-stacked
MoTe2/WSe2, which hosts a magnetic Chern insulator at a carrier density of one
hole per moire superlattice site. We observe hysteretic switching of the
resistivity as a function of applied current. Magnetic imaging using a
superconducting quantum interference device reveals that current switches
correspond to reversals of individual magnetic domains. The real space pattern
of domain reversals aligns precisely with spin accumulation measured near the
high-Berry curvature Hubbard band edges. This suggests that intrinsic spin- or
valley-Hall torques drive the observed current-driven magnetic switching in
both MoTe2/WSe2 and other moire materials. The switching current density of
10^3 Amps per square centimeter is significantly less than reported in other
platforms paving the way for efficient control of magnetic order.
less
By: Andreas Sinner, Pierre A. Pantaleón, Francisco Guinea
We study the effects of strain in moir\'e systems composed of honeycomb
lattices. We elucidate the formation of almost perfect one-dimensional moir\'e
patterns in twisted bilayer systems. The formation of such patterns is a
consequence of an interplay between twist and strain which gives rise to a
collapse of the reciprocal space unit cell. As a criterion for such collapse we
find a simple relation between the two quantities and the materia... more
We study the effects of strain in moir\'e systems composed of honeycomb
lattices. We elucidate the formation of almost perfect one-dimensional moir\'e
patterns in twisted bilayer systems. The formation of such patterns is a
consequence of an interplay between twist and strain which gives rise to a
collapse of the reciprocal space unit cell. As a criterion for such collapse we
find a simple relation between the two quantities and the material specific
Poisson ratio. The induced one dimensional behavior is characterized by two,
usually incommensurate, periodicities. Our results offer explanations for the
complex patterns of one-dimensional channels observed in low angle twisted
bilayer graphene systems and twisted bilayer dicalcogenides. Our findings can
be applied to any hexagonal twisted moir\'e pattern and can be easily extended
to other geometries.
less
Quantum spherical codes
5upvotes
By: Shubham P. Jain, Joseph T. Iosue, Alexander Barg, Victor V. Albert
We introduce a framework for constructing quantum codes defined on spheres by
recasting such codes as quantum analogues of the classical spherical codes. We
apply this framework to bosonic coding, obtaining multimode extensions of the
cat codes that can outperform previous constructions while requiring a similar
type of overhead. Our polytope-based cat codes consist of sets of points with
large separation that at the same time form averagin... more
We introduce a framework for constructing quantum codes defined on spheres by
recasting such codes as quantum analogues of the classical spherical codes. We
apply this framework to bosonic coding, obtaining multimode extensions of the
cat codes that can outperform previous constructions while requiring a similar
type of overhead. Our polytope-based cat codes consist of sets of points with
large separation that at the same time form averaging sets known as spherical
designs. We also recast concatenations of qubit CSS codes with cat codes as
quantum spherical codes.
less
By: Sijo K. Joseph
Alcubierre warp drive metric is coupled to quantum mechanical scalar matter
field. The requirement of the exotic matter for the warp drive is mapped into a
conformal wave equation. This result into a fourth order partial differential
equation in terms of the quantum mechanical density. Finding a proper quantum
mechanical density obeying the proposed partial differential equation will be a
resolution to the exotic matter problem of Alcubierr... more
Alcubierre warp drive metric is coupled to quantum mechanical scalar matter
field. The requirement of the exotic matter for the warp drive is mapped into a
conformal wave equation. This result into a fourth order partial differential
equation in terms of the quantum mechanical density. Finding a proper quantum
mechanical density obeying the proposed partial differential equation will be a
resolution to the exotic matter problem of Alcubierre warp drive in Bohmian
Quantum Gravity context.
less
By: Milan Kornjača, Rhine Samajdar, Tommaso Macrì, Nathan Gemelke, Sheng-Tao Wang, Fangli Liu
Quantum spin liquids are elusive but paradigmatic examples of strongly
correlated quantum states that are characterized by long-range quantum
entanglement. Recently, the direct signatures of a gapped topological
$\mathbb{Z}_2$ spin liquid have been observed in a system of Rydberg atoms
arrayed on the ruby lattice. Here, we illustrate the concrete realization of a
fundamentally different class of spin liquids in a honeycomb array of Rydberg
... more
Quantum spin liquids are elusive but paradigmatic examples of strongly
correlated quantum states that are characterized by long-range quantum
entanglement. Recently, the direct signatures of a gapped topological
$\mathbb{Z}_2$ spin liquid have been observed in a system of Rydberg atoms
arrayed on the ruby lattice. Here, we illustrate the concrete realization of a
fundamentally different class of spin liquids in a honeycomb array of Rydberg
atoms. Exploring the quantum phase diagram of this system using both
density-matrix renormalization group and exact diagonalization simulations,
several density-wave-ordered phases are characterized and their origins
explained. More interestingly, in the regime where third-nearest-neighbor atoms
lie within the Rydberg blockade radius, we find a novel ground state -- with an
emergent $\mathrm{U}(1)\times \mathrm{U}(1)$ local symmetry -- formed from
superpositions of classical {\it trimer} configurations on the dual triangular
lattice. The fidelity of this trimer spin liquid state can be enhanced via
dynamical preparation, which we explain by a Rydberg-blockade-based projection
mechanism associated with the smooth turnoff of the laser drive. Finally, we
discuss the robustness of the trimer spin liquid phase under realistic
experimental parameters and demonstrate that our proposal can be readily
implemented in current Rydberg atom quantum simulators.
less
By: Vivek Reddy Pininti, Gopal Bhatta, Sagarika Paul, Aman Kumar, Aayushi Rajgor, Rahul Barnwal, Sarvesh Gharat
We present a first systematic time series study of a sample of blazars
observed by the Transiting Exoplanet Survey Satellite $\textit{TESS}$
spacecraft. By cross matching the positions of the sources in the TESS
observations with those from Roma-BZCAT, 29 blazars including both BL Lacerate
objects and flat-spectrum radio quasars were identified. The observation
lengths of the 79 light curves of the sources, across all sectors on which the
t... more
We present a first systematic time series study of a sample of blazars
observed by the Transiting Exoplanet Survey Satellite $\textit{TESS}$
spacecraft. By cross matching the positions of the sources in the TESS
observations with those from Roma-BZCAT, 29 blazars including both BL Lacerate
objects and flat-spectrum radio quasars were identified. The observation
lengths of the 79 light curves of the sources, across all sectors on which the
targets of interest have been observed by $\textit{TESS}$, range between 21.25
and 28.2 days. The light curves were analyzed using various methods of time
series analysis. The results show that the sources exhibit significant
variability with fractional variability spanning between 1.41% and 53.84%. The
blazar flux distributions were studied by applying normal and lognormal
probability density function models. The results indicate that optical flux
histogram of the sources are consistent with normal probability density
function with most of them following bi-modal distribution as opposed to
uni-modal distribution. This suggests that the days-timescale optical
variability is contributed either by two different emission zones or two
distinct states of short-term activity in blazars. Power spectral density
analysis was performed by using the power spectral response method and the true
power spectra of unevenly sampled light curves were estimated. The power
spectral slopes of the light curves ranged from 1.7 to 3.2.
less
By: Bruno Mera, Tomoki Ozawa
Lowest Landau level wavefunctions are eigenstates of the Hamiltonian of a
charged particle in two dimensions under a uniform magnetic field. They are
known to be holomorphic both in real and momentum spaces, and also exhibit
uniform, translationally invariant, geometrical properties in momentum space.
In this paper, using the Stone-von Neumann theorem, we show that lowest Landau
level wavefunctions are indeed the only possible states with u... more
Lowest Landau level wavefunctions are eigenstates of the Hamiltonian of a
charged particle in two dimensions under a uniform magnetic field. They are
known to be holomorphic both in real and momentum spaces, and also exhibit
uniform, translationally invariant, geometrical properties in momentum space.
In this paper, using the Stone-von Neumann theorem, we show that lowest Landau
level wavefunctions are indeed the only possible states with unit Chern number
satisfying these conditions. We also prove the uniqueness of their direct
analogs with higher Chern numbers and provide their expressions.
less
By: Qiangqiang Gu, Shishir Kumar Pandey
Spin-orbit coupling (SOC) drives interesting and non-trivial phenomena in
solid state physics, ranging from topological to magnetic to transport
properties. Thorough study of such phenomena often require effective models
where SOC term is explicitly included. However, estimation of SOC strength for
such models mostly depend on the spectroscopy experiments which can only
provide a rough estimate. In this work, we provide a simple yet effecti... more
Spin-orbit coupling (SOC) drives interesting and non-trivial phenomena in
solid state physics, ranging from topological to magnetic to transport
properties. Thorough study of such phenomena often require effective models
where SOC term is explicitly included. However, estimation of SOC strength for
such models mostly depend on the spectroscopy experiments which can only
provide a rough estimate. In this work, we provide a simple yet effective
computational approach to estimate the on-site SOC strength using a combination
of the $ab$ $initio$ and tight-binding calculations. We demonstrate the wider
applicability and high sensitivity of our method considering materials with
varying SOC strengths and the number of SOC active ions. The estimated SOC
strengths agree well with the proposed values in literature lending support to
our methodology. This simplistic approach can readily be applied to a wide
range of materials.
less
By: Fedor K. Popov, Grigory Tarnopolsky
We consider a configuration of three stacked graphene monolayers with equal
consecutive twist angles $\theta$. Remarkably, in the chiral limit when
interlayer coupling terms between $\textrm{AA}$ sites of the moir\'{e} pattern
are neglected we find four perfectly flat bands (for each valley) at a sequence
of magic angles which are exactly equal to the twisted bilayer graphene (TBG)
magic angles divided by $\sqrt{2}$. Therefore, the first ma... more
We consider a configuration of three stacked graphene monolayers with equal
consecutive twist angles $\theta$. Remarkably, in the chiral limit when
interlayer coupling terms between $\textrm{AA}$ sites of the moir\'{e} pattern
are neglected we find four perfectly flat bands (for each valley) at a sequence
of magic angles which are exactly equal to the twisted bilayer graphene (TBG)
magic angles divided by $\sqrt{2}$. Therefore, the first magic angle for
equal-twist trilayer graphene (eTTG) in the chiral limit is $\theta_{*} \approx
1.05^{\circ}/\sqrt{2} \approx 0.74^{\circ}$. We prove this relation
analytically and show that the Bloch states of the eTTG's flat bands are
non-linearly related to those of TBG's. Additionally, we show that at the magic
angles, the upper and lower bands must touch the four exactly flat bands at the
Dirac point of the middle graphene layer. Finally, we explore the eTTG's
spectrum away from the chiral limit through numerical analysis.
less
By: Riya Barick, Indrajit Ghose, Amitabha Lahiri
Propagation of fermions in spacetime requires a spin connection, which can be
split into a universal gravitational part and a non-universal ``contorsion''
part. The latter is non-dynamical and can be eliminated from the theory,
leaving an effective four-fermion interaction with unknown coupling constants.
The generic form of the contorsion-fermion coupling, and thus the four-fermion
interaction, breaks chiral symmetry. This interaction affe... more
Propagation of fermions in spacetime requires a spin connection, which can be
split into a universal gravitational part and a non-universal ``contorsion''
part. The latter is non-dynamical and can be eliminated from the theory,
leaving an effective four-fermion interaction with unknown coupling constants.
The generic form of the contorsion-fermion coupling, and thus the four-fermion
interaction, breaks chiral symmetry. This interaction affects all fermions --
in particular neutrinos passing through matter will notice a contribution to
their effective Hamiltonian, just like the MSW effect coming from weak
interactions. Then there is a possibility that this geometrical contribution is
not negligible for neutrinos passing through normal matter, provided the
coupling constants are not too small. We calculate the matter potential due to
this interaction and thus write the conversion and survival probabilities
including its effect. We plot conversion probabilities of $\nu_\mu$ to $\nu_e$
and $\nu_\tau$ for a baseline of 1300 km (DUNE) with and without the
geometrical interaction. If the geometrical couplings are not too small, it
should be possible to observe this effect.
less
By: Shantonu Mukherjee, Amitabha Lahiri
The description of a system of vortices in terms of dual fields provides a
window to new phases of the system. It was found recently that dualizing a
3+1-d boson-fermion system leads to a system of fermions and vortices
interacting via a 2-form field through a non-local term. Here we explore some
consequences of such an interaction when the degrees of freedom of the system
are confined to a 2+1-d space-time. In particular, we show that the ... more
The description of a system of vortices in terms of dual fields provides a
window to new phases of the system. It was found recently that dualizing a
3+1-d boson-fermion system leads to a system of fermions and vortices
interacting via a 2-form field through a non-local term. Here we explore some
consequences of such an interaction when the degrees of freedom of the system
are confined to a 2+1-d space-time. In particular, we show that the vortices in
the 2+1-d system are attached to the fermions via their non-zero spin magnetic
moment in a way similar to the phenomenon of flux attachment in Chern-Simons
gauge theory coupled to matter. We also show that such flux attached particles
exhibit fractional statistical behaviour like anyons. Thus our model provides a
realization of anyons without Chern-Simons theory.
less
By: Rohit K Ramakrishnan, Aravinth Balaji Ravichandran, Arpita Mishra, Archana Kaushalram, Gopalkrishna Hegde, Srinivas Talabattula, Peter P Rohde
Quantum information processing has conceptually changed the way we process
and transmit information. Quantum physics, which explains the strange behaviour
of matter at the microscopic dimensions, has matured into a quantum technology
that can harness this strange behaviour for technological applications with
far-reaching consequences, which uses quantum bits (qubits) for information
processing. Experiments suggest that photons are the most ... more
Quantum information processing has conceptually changed the way we process
and transmit information. Quantum physics, which explains the strange behaviour
of matter at the microscopic dimensions, has matured into a quantum technology
that can harness this strange behaviour for technological applications with
far-reaching consequences, which uses quantum bits (qubits) for information
processing. Experiments suggest that photons are the most successful candidates
for realising qubits, which indicates that integrated photonic platforms will
play a crucial role in realising quantum technology. This paper surveys the
various photonic platforms based on different materials for quantum information
processing. The future of this technology depends on the successful materials
that can be used to universally realise quantum devices, similar to silicon,
which shaped the industry towards the end of the last century. Though a
prediction is implausible at this point, we provide an overview of the current
status of research on the platforms based on various materials.
less
By: Rohit K. Ramakrishnan, Aravinth Balaji Ravichandran, Ishwar Kaushik, Gopalkrishna Hegde, Srinivas Talabattula, Peter P. Rohde
In the century following its discovery, applications for quantum physics are
opening a new world of technological possibilities. With the current decade
witnessing quantum supremacy, quantum technologies are already starting to
change the ways information is generated, transmitted, stored and processed.
The next major milestone in quantum technology is already rapidly emerging --
the quantum internet. Since light is the most logical candidate... more
In the century following its discovery, applications for quantum physics are
opening a new world of technological possibilities. With the current decade
witnessing quantum supremacy, quantum technologies are already starting to
change the ways information is generated, transmitted, stored and processed.
The next major milestone in quantum technology is already rapidly emerging --
the quantum internet. Since light is the most logical candidate for quantum
communication, quantum photonics is a critical enabling technology. This paper
reviews the hardware aspects of the quantum internet, mainly from a photonics
perspective. Though a plethora of quantum technologies and devices have emerged
in recent years, we are more focused on devices or components that may enable
the quantum internet. Our approach is primarily qualitative, providing a broad
overview of the necessary technologies for a large-scale quantum internet.
less
Spin waves and high-frequency response in layered superconductors with helical magnetic structure
3upvotes
By: A. E. Koshelev
We evaluate the spin-wave spectrum and dynamic susceptibility in a layered superconductors with helical interlayer magnetic structure. We especially focus on the structure in which the moments rotate 90∘ from layer to layer realized in the iron pnictide RbEuFe4As4. The spin-wave spectrum in superconductors is strongly renormalized due to the long-range electromagnetic interactions between the oscillating magnetic moments. This leads to a stro... more
We evaluate the spin-wave spectrum and dynamic susceptibility in a layered superconductors with helical interlayer magnetic structure. We especially focus on the structure in which the moments rotate 90∘ from layer to layer realized in the iron pnictide RbEuFe4As4. The spin-wave spectrum in superconductors is strongly renormalized due to the long-range electromagnetic interactions between the oscillating magnetic moments. This leads to a strong enhancement of the frequency of the mode coupled with a uniform field and this enhancement exists only within a narrow range of the c-axis wave vectors of the order of the inverse London penetration depth. The key feature of materials like RbEuFe4As4 is that this uniform mode corresponds to the maximum frequency of the spin-wave spectrum with respect to the c-axis wave vector. As a consequence, the high-frequency surface resistance acquires a very distinct asymmetric feature spreading between the bare and renormalized frequencies. We also consider the excitation of spin waves with Josephson effect in a tunneling contact between helical-magnetic and conventional superconductors and study the interplay between the spin-wave features and geometrical cavity resonances in the current-voltage characteristics. less
By: A. E. Koshelev
We consider a clean layered magnetic superconductor in which a continuous magnetic transition takes place inside superconducting state and the exchange interaction between superconducting and magnetic subsystems is weak so that superconductivity is not destroyed at the magnetic transition. An example of such material is RbEuFe4As4. We investigate the suppression of the superconducting gap and superfluid density by correlated magnetic fluctuat... more
We consider a clean layered magnetic superconductor in which a continuous magnetic transition takes place inside superconducting state and the exchange interaction between superconducting and magnetic subsystems is weak so that superconductivity is not destroyed at the magnetic transition. An example of such material is RbEuFe4As4. We investigate the suppression of the superconducting gap and superfluid density by correlated magnetic fluctuations in the vicinity of the magnetic transition. The influence of nonuniform exchange field on superconducting parameters is sensitive to the relation between the magnetic correlation length, ξh, and superconducting coherence length ξs defining the 'scattering' (ξh<ξs) and 'smooth' (ξh>ξs) regimes. As a small uniform exchange field does not affect the superconducting gap and superfluid density at zero temperature, smoothening of the spatial variations of the exchange field reduces its effects on these parameters. We develop a quantitative description of this 'scattering-to-smooth' crossover for the case of quasi-two-dimensional magnetic fluctuations. Since the magnetic-scattering probability varies at the energy scale comparable with the gap, the quasiclassical approximation is not applicable in the crossover region and microscopic treatment is required. We find that the corrections to both the gap and superfluid density grow proportionally to ξh until it remains much smaller than ξs. When ξh exceeds ξs, both parameters have much weaker dependence on ξh. Moreover, the gap correction may decrease with increasing of ξh in the vicinity of the magnetic transition. We also find that the crossover is unexpectedly broad: the standard scattering approximation becomes sufficient only when ξh is substantially smaller than ξs. less
By: Ivar Martin, Kartiek Agarwal
We construct a dynamical decoupling protocol for accurately generating local and global symmetries in general many-body systems. Multiple commuting and non-commuting symmetries can be created by means of a self-similar-in-time ("polyfractal") drive. The result is an effective Floquet Hamiltonian that remains local and avoids heating over exponentially long times. This approach can be used to realize a wide variety of quantum models, and non-e... more
We construct a dynamical decoupling protocol for accurately generating local and global symmetries in general many-body systems. Multiple commuting and non-commuting symmetries can be created by means of a self-similar-in-time ("polyfractal") drive. The result is an effective Floquet Hamiltonian that remains local and avoids heating over exponentially long times. This approach can be used to realize a wide variety of quantum models, and non-equilibrium quantum phases.
less
By: Pei-Xin Shen, Vivien Perrin, Mircea Trif, Pascal Simon
A chain of magnetic impurities deposited on the surface of a superconductor can form a topological Shiba band that supports Majorana zero modes and hold a promise for topological quantum computing. Yet, most experiments scrutinizing these zero modes rely on transport measurements, which only capture local properties. Here we propose to leverage the intrinsic dynamics of the magnetic impurities to access their non-local character. We use linea... more
A chain of magnetic impurities deposited on the surface of a superconductor can form a topological Shiba band that supports Majorana zero modes and hold a promise for topological quantum computing. Yet, most experiments scrutinizing these zero modes rely on transport measurements, which only capture local properties. Here we propose to leverage the intrinsic dynamics of the magnetic impurities to access their non-local character. We use linear response theory to determine the dynamics of the uniform magnonic mode in the presence of external $ac$ magnetic fields and the coupling to the Shiba electrons. We demonstrate that this mode, which spreads over the entire chain of atoms, becomes imprinted with the parity of the ground state and, moreover, can discriminate between Majorana and trivial zero modes located at the ends of the chain. Our approach offers a non-invasive alternative to the scanning tunnelling microscopy techniques used to probe Majorana zero modes. Conversely, the magnons could facilitate the manipulation of Majorana zero modes in topological Shiba chains. less
By: Frederik Nathan, Ivar Martin, Gil Refael
We theoretically predict a new working principle for optical amplification,
based on Weyl semimetals: when a Weyl semimetal is suitably irradiated at two
frequencies, electrons close to the Weyl points convert energy between the
frequencies through the mechanism of topological frequency conversion from
[Martin et al, PRX 7 041008 (2017)]. Each electron converts energy at a
quantized rate given by an integer multiple of Planck's constant mul... more
We theoretically predict a new working principle for optical amplification,
based on Weyl semimetals: when a Weyl semimetal is suitably irradiated at two
frequencies, electrons close to the Weyl points convert energy between the
frequencies through the mechanism of topological frequency conversion from
[Martin et al, PRX 7 041008 (2017)]. Each electron converts energy at a
quantized rate given by an integer multiple of Planck's constant multiplied by
the product of the two frequencies. In simulations, we show that optimal, but
feasible band structures can support topological frequency conversion in the
"THz gap" at intensities down to $ 2{\rm W}/{\rm mm^2}$; the gain from the
effect can exceed the dissipative loss when the frequencies are larger than the
relaxation time of the system. Topological frequency conversion provides a new
paradigm for optical amplification, and further extends Weyl semimetals'
promise for technological applications.
less
Quantum simulation costs for Suzuki-Trotter decomposition of quantum many-body lattice models
2upvotes
By: Nathan M. Myers, Ryan Scott, Kwon Park, Vito W. Scarola
Quantum computers offer the potential to efficiently simulate the dynamics of quantum systems, a task whose difficulty scales exponentially with system size on classical devices. To assess the potential for near-term quantum computers to simulate many-body systems we develop a model-independent formalism to straightforwardly compute bounds on the number of Trotter steps needed to accurately simulate the system's time evolution based on the fi... more
Quantum computers offer the potential to efficiently simulate the dynamics of quantum systems, a task whose difficulty scales exponentially with system size on classical devices. To assess the potential for near-term quantum computers to simulate many-body systems we develop a model-independent formalism to straightforwardly compute bounds on the number of Trotter steps needed to accurately simulate the system's time evolution based on the first-order commutator scaling. We apply this formalism to two closely related many-body models prominent in condensed matter physics, the Hubbard and t-J models. We find that, while a naive comparison of the Trotter depth first seems to favor the Hubbard model, careful consideration of the model parameters and the
allowable error for accurate simulation leads to a substantial advantage in favor of the t-J model. These results and formalism set the stage for significant improvements in quantum simulation costs.
less
By: Derek B. Fox, Steinn Sigurdsson, Sarah Shandera, Peter Mészáros, Kohta Murase, Miguel Mostafá, Stephane Coutu (Penn State University)
The ANITA collaboration have reported observation of two anomalous events
that appear to be $\varepsilon_{\rm cr} \approx 0.6$ EeV cosmic ray showers
emerging from the Earth with exit angles of $27^\circ$ and $35^\circ$,
respectively. While EeV-scale upgoing showers have been anticipated as a result
of astrophysical tau neutrinos converting to tau leptons during Earth passage,
the observed exit angles are much steeper than expected in Stand... more
The ANITA collaboration have reported observation of two anomalous events
that appear to be $\varepsilon_{\rm cr} \approx 0.6$ EeV cosmic ray showers
emerging from the Earth with exit angles of $27^\circ$ and $35^\circ$,
respectively. While EeV-scale upgoing showers have been anticipated as a result
of astrophysical tau neutrinos converting to tau leptons during Earth passage,
the observed exit angles are much steeper than expected in Standard Model (SM)
scenarios. Indeed, under conservative extrapolations of the SM interactions,
there is no particle that can propagate through the Earth with probability $p >
10^{-6}$ at these energies and exit angles. We explore here whether "beyond the
Standard Model" (BSM) particles are required to explain the ANITA events, if
correctly interpreted, and conclude that they are. Seeking confirmation or
refutation of the physical phenomenon of sub-EeV Earth-emergent cosmic rays in
data from other facilities, we find support for the reality of the ANITA
events, and three candidate analog events, among the Extremely High Energy
Northern Track neutrinos of the IceCube Neutrino Observatory. Properties of the
implied BSM particle are anticipated, at least in part, by those predicted for
the "stau" slepton ($\tilde{\tau}_R$) in some supersymmetric models of the
fundamental interactions, wherein the stau manifests as the next-to-lowest mass
supersymmetric partner particle.
less
By: Nathan Dasenbrock-Gammon, Elliot Snider, Raymond McBride, Hiranya Pasan, Dylan Durkee, Nugzari Khalvashi-Sutter, Sasanka Munasinghe, Sachith E. Dissanayake, Keith V. Lawler, Ashkan Salamat & Ranga P. Dias
The absence of electrical resistance exhibited by superconducting materials would have enormous potential for applications if it existed at ambient temperature and pressure conditions. Despite decades of intense research efforts, such a state has yet to be realized. At ambient pressures, cuprates are the material class exhibiting superconductivity to the highest critical superconducting transition temperatures (Tc), up to about 133 K. Over th... more
The absence of electrical resistance exhibited by superconducting materials would have enormous potential for applications if it existed at ambient temperature and pressure conditions. Despite decades of intense research efforts, such a state has yet to be realized. At ambient pressures, cuprates are the material class exhibiting superconductivity to the highest critical superconducting transition temperatures (Tc), up to about 133 K. Over the past decade, high-pressure ‘chemical precompression of hydrogen-dominant alloys has led the search for high-temperature superconductivity, with demonstrated Tc approaching the freezing point of water in binary hydrides at megabar pressures. Ternary hydrogen-rich compounds, such as carbonaceous sulfur hydride, offer an even larger chemical space to potentially improve the properties of superconducting hydrides. Here we report evidence of superconductivity on a nitrogen-doped lutetium hydride with a maximum Tc of 294 K at 10 kbar, that is, superconductivity at room temperature and near-ambient pressures. The compound was synthesized under high-pressure high-temperature conditions and then—after full recoverability—its material and superconducting properties were examined along compression pathways. These include temperature-dependent resistance with and without an applied magnetic field, the magnetization (M) versus magnetic field (H) curve, a.c. and d.c. magnetic susceptibility, as well as heat-capacity measurements. X-ray diffraction (XRD), energy-dispersive X-ray (EDX) and theoretical simulations provide some insight into the stoichiometry of the synthesized material. Nevertheless, further experiments and simulations are needed to determine the exact stoichiometry of hydrogen and nitrogen, and their respective atomistic positions, in a greater effort to further understand the superconducting state of the material. less
By: Nhat-Minh Nguyen, Dragan Huterer, Yuewei Wen
We present evidence for a suppressed growth rate of large-scale structure during the dark-energy dominated era. Modeling the growth rate of perturbations with the ``growth index'' γ, we find that current cosmological data strongly prefer a higher growth index than the value γ=0.55 predicted by general relativity in a flat ΛCDM cosmology. Both the cosmic microwave background data from Planck and the large-scale structure data from weak lensing... more
We present evidence for a suppressed growth rate of large-scale structure during the dark-energy dominated era. Modeling the growth rate of perturbations with the ``growth index'' γ, we find that current cosmological data strongly prefer a higher growth index than the value γ=0.55 predicted by general relativity in a flat ΛCDM cosmology. Both the cosmic microwave background data from Planck and the large-scale structure data from weak lensing, galaxy clustering, and cosmic velocities separately favor growth suppression. When combined, they yield γ=0.633+0.025−0.024, excluding γ=0.55 at a statistical significance of 3.7σ. The combination of fσ8 and Planck measurements prefers an even higher growth index of γ=0.639+0.024−0.025, corresponding to a 4.2σ-tension with the concordance model. In Planck data, the suppressed growth rate offsets the preference for nonzero curvature and fits the data equally well as the latter model. A higher γ leads to a higher matter fluctuation amplitude S8 inferred from galaxy clustering and weak lensing measurements, and a lower S8 from Planck data, effectively resolving the S8 tension. less
By: Deepanshu Aggarwal, Rohit Narula, Sankalpa Ghosh
The recent discovery of superconductivity in magic-angle twisted bilayer graphene has sparked a renewed interest in the strongly-correlated physics of sp2 carbons, in stark contrast to preliminary investigations which were dominated by the one-body physics of the massless Dirac fermions. We thus provide a self-contained, theoretical perspective of the journey of graphene from its single-particle physics-dominated regime to the strongly-correl... more
The recent discovery of superconductivity in magic-angle twisted bilayer graphene has sparked a renewed interest in the strongly-correlated physics of sp2 carbons, in stark contrast to preliminary investigations which were dominated by the one-body physics of the massless Dirac fermions. We thus provide a self-contained, theoretical perspective of the journey of graphene from its single-particle physics-dominated regime to the strongly-correlated physics of the flat bands. Beginning from the origin of the Dirac points in condensed matter systems, we discuss the effect of the superlattice on the Fermi velocity and Van Hove singularities in graphene and how it leads naturally to investigations of the moiré pattern in van der Waals heterostructures exemplified by graphene-hexagonal boron-nitride and twisted bilayer graphene. Subsequently, we illuminate the origin of flat bands in twisted bilayer graphene at the magic angles by elaborating on a broad range of prominent theoretical works in a pedagogical way while linking them to available experimental support, where appropriate. We conclude by providing a list of topics in the study of the electronic properties of twisted bilayer graphene not covered by this review but may readily be approached with the help of this primer. less
By: Alessandro Sonnenfeld
Context. The number of known strong gravitational lenses is expected to grow substantially in the next few years. The combination of large samples of lenses has the potential to provide strong constraints on the inner structure of galaxies.
Aims: We investigate the extent to which we can calibrate stellar mass measurements and constrain the average dark matter density profile of galaxies by combining strong lensing data from thousands of lens... more
Context. The number of known strong gravitational lenses is expected to grow substantially in the next few years. The combination of large samples of lenses has the potential to provide strong constraints on the inner structure of galaxies.
Aims: We investigate the extent to which we can calibrate stellar mass measurements and constrain the average dark matter density profile of galaxies by combining strong lensing data from thousands of lenses.
Methods: We generated mock samples of axisymmetric lenses. We assume that, for each lens, we have measurements of two image positions of a strongly lensed background source, as well as magnification information from full surface brightness modelling, and a stellar-population-synthesis-based estimate of the lens stellar mass. We then fitted models describing the distribution of the stellar population synthesis mismatch parameter αsps (the ratio between the true stellar mass and the stellar-population-synthesis-based estimate) and the dark matter density profile of the population of lenses to an ensemble of 1000 mock lenses.
Results: We obtain the average αsps, projected dark matter mass, and dark matter density slope with greater precision and accuracy compared with current constraints. A flexible model and knowledge of the lens detection efficiency as a function of image configuration are required in order to avoid a biased inference.
Conclusions: Statistical strong lensing inferences from upcoming surveys provide a way to calibrate stellar mass measurements and to constrain the inner dark matter density profile of massive galaxies. less
By: Alessandro Sonnenfeld
Context. Time-delay lensing is a powerful tool for measuring the Hubble constant H0. However, in order to obtain an accurate estimate of H0 from a sample of time-delay lenses, very good knowledge of the mass structure of the lens galaxies is needed. Strong lensing data on their own are not sufficient to break the degeneracy between H0 and the lens model parameters on a single object basis.
Aims: The goal of this study is to determine whether ... more
Context. Time-delay lensing is a powerful tool for measuring the Hubble constant H0. However, in order to obtain an accurate estimate of H0 from a sample of time-delay lenses, very good knowledge of the mass structure of the lens galaxies is needed. Strong lensing data on their own are not sufficient to break the degeneracy between H0 and the lens model parameters on a single object basis.
Aims: The goal of this study is to determine whether it is possible to break the H0-lens structure degeneracy with the statistical combination of a large sample of time-delay lenses, relying purely on strong lensing data with no stellar kinematics information.
Methods: I simulated a set of 100 lenses with doubly imaged quasars and related time-delay measurements. I fitted these data with a Bayesian hierarchical method and a flexible model for the lens population, emulating the lens modelling step.
Results: The sample of 100 lenses on its own provides a measurement of H0 with 3% precision, but with a −4% bias. However, the addition of prior information on the lens structural parameters from a large sample of lenses with no time delays, such as that considered in Paper I, allows for a 1% level inference. Moreover, the 100 lenses allow for a 0.03 dex calibration of galaxy stellar masses, regardless of the level of prior knowledge of the Hubble constant.
Conclusions: Breaking the H0-lens model degeneracy with lensing data alone is possible, but 1% measurements of H0 require either many more than 100 time-delay lenses or knowledge of the structural parameter distribution of the lens population from a separate sample of lenses. less
By: Alessandro Sonnenfeld
Context. Existing samples of strong lenses have been assembled by giving priority to sample size, but this is often at the cost of a complex selection function. However, with the advent of the next generation of wide-field photometric surveys, it might become possible to identify subsets of the lens population with well-defined selection criteria, trading sample size for completeness.
Aims: There are two main advantages of working with a comp... more
Context. Existing samples of strong lenses have been assembled by giving priority to sample size, but this is often at the cost of a complex selection function. However, with the advent of the next generation of wide-field photometric surveys, it might become possible to identify subsets of the lens population with well-defined selection criteria, trading sample size for completeness.
Aims: There are two main advantages of working with a complete sample of lenses. First, such completeness makes possible to recover the properties of the general population of galaxies, of which strong lenses are a biased subset. Second, the relative number of lenses and non-detections can be used to further constrain models of galaxy structure. The present work illustrates how to carry out a statistical strong lensing analysis that takes advantage of these features.
Methods: I introduce a general formalism for the statistical analysis of a sample of strong lenses with known selection function, and then test it on simulated data. The simulation consists of a population of 105 galaxies with an axisymmetric power-law density profile, a population of background point sources, and a subset of ∼103 strong lenses, which form a complete sample above an observational cut.
Results: The method allows the user to recover the distribution of the galaxy population in Einstein radius and mass density slope in an unbiased way. The number of non-lenses helps to constrain the model when magnification data are not available.
Conclusions: Complete samples of lenses are a powerful asset with which to turn precise strong lensing measurements into accurate statements on the properties of the general galaxy population. less
By: Alessandro Sonnenfeld
Context. Strong lensing mass measurements require the knowledge of the redshift of both the lens and the source galaxy. Traditionally, spectroscopic redshifts are used for this purpose. Upcoming surveys, however, will lead to the discovery of ∼105 strong lenses, and it will be very difficult to obtain spectroscopic redshifts for most of them. Photometric redshift measurements will also be very challenging due to the blending between lens and ... more
Context. Strong lensing mass measurements require the knowledge of the redshift of both the lens and the source galaxy. Traditionally, spectroscopic redshifts are used for this purpose. Upcoming surveys, however, will lead to the discovery of ∼105 strong lenses, and it will be very difficult to obtain spectroscopic redshifts for most of them. Photometric redshift measurements will also be very challenging due to the blending between lens and source light.
Aims: The goal of this work is to demonstrate how to carry out an inference of the structural properties of the galaxy population from the analysis of a set of strong lenses with no individual source redshift measurements, and to assess the loss in precision compared to the case in which spectroscopic redshifts are available.
Methods: Building on the formalism introduced in Paper III, I developed a method that allows a statistical strong lensing inference to be carried out while marginalising over the source redshifts. This method, which relies on the knowledge of the properties of the unlensed background source population and of the selection function of the survey, generalises an approach known as photogeometric redshift, originally introduced by the Strong Lensing Legacy Survey collaboration. I tested the method on simulated data consisting of a subset of 137 strong lenses that is complete above a cut in observational space.
Results: The method recovers the properties of the galaxy population with a precision that is comparable to that attainable in the case in which individual source redshifts are known.
Conclusions: The photogeometric redshift method is a viable approach for the analysis of large sets of strong lenses provided that the background source population properties and lens selection function are well known. less
By: Alessandro Sonnenfeld, Crescenzo Tortora, Henk Hoekstra, Marika Asgari, Maciej Bilicki, Catherine Heymans, Hendrik Hildebrandt, Konrad Kuijken, Nicola R. Napolitano, Nivya Roy, Edwin Valentijn, Angus H. Wright
Context. The assembly history of the stellar component of a massive elliptical galaxy is closely related to that of its dark matter halo. Measuring how the properties of galaxies correlate with their halo mass can therefore help to understand their evolution.
Aims: We investigate how the dark matter halo mass of elliptical galaxies varies as a function of their properties, using weak gravitational lensing observations. To minimise the chances... more
Context. The assembly history of the stellar component of a massive elliptical galaxy is closely related to that of its dark matter halo. Measuring how the properties of galaxies correlate with their halo mass can therefore help to understand their evolution.
Aims: We investigate how the dark matter halo mass of elliptical galaxies varies as a function of their properties, using weak gravitational lensing observations. To minimise the chances of biases, we focus on the following galaxy properties that can be determined robustly: the surface brightness profile and the colour.
Methods: We selected 2409 central massive elliptical galaxies (log M*/M⊙ ≳ 11.4) from the Sloan Digital Sky Survey spectroscopic sample. We first measured their surface brightness profile and colours by fitting Sérsic models to photometric data from the Kilo-Degree Survey (KiDS). We fitted their halo mass distribution as a function of redshift, rest-frame r-band luminosity, half-light radius, and rest-frame u − g colour, using KiDS weak lensing measurements and a Bayesian hierarchical approach. For the sake of robustness with respect to assumptions on the large-radii behaviour of the surface brightness, we repeated the analysis replacing the total luminosity and half-light radius with the luminosity within a 10 kpc aperture, Lr, 10, and the light-weighted surface brightness slope, Γ10.
Results: We did not detect any correlation between the halo mass and either the half-light radius or colour at fixed redshift and luminosity. Using the robust surface brightness parameterisation, we found that the halo mass correlates weakly with Lr, 10 and anti-correlates with Γ10. At fixed redshift, Lr, 10 and Γ10, the difference in the average halo mass between galaxies at the 84th percentile and 16th percentile of the colour distribution is 0.00 ± 0.11 dex. Conclusion. Our results indicate that the average star formation efficiency of massive elliptical galaxies has little dependence on their final size or colour. This suggests that the origin of the diversity in the size and colour distribution of these objects lies with properties other than the halo mass. less
By: Alessandro Sonnenfeld
Context. The Sérsic profile is a widely used model for describing the surface brightness distribution of galaxies. Spiral galaxies, however, are qualitatively different from a Sérsic model.
Aims: The goal of this study is to assess how accurately the total flux and half-light radius of a galaxy with spiral arms can be recovered when fitted with a Sérsic profile.
Methods: I selected a sample of bulge-dominated galaxies with spiral arms. Using ... more
Context. The Sérsic profile is a widely used model for describing the surface brightness distribution of galaxies. Spiral galaxies, however, are qualitatively different from a Sérsic model.
Aims: The goal of this study is to assess how accurately the total flux and half-light radius of a galaxy with spiral arms can be recovered when fitted with a Sérsic profile.
Methods: I selected a sample of bulge-dominated galaxies with spiral arms. Using photometric data from the Hyper Suprime-Cam survey, I estimated the contribution of the spiral arms to their total flux. Then I generated simulated images of galaxies with similar characteristics, fitted them with a Sérsic model, and quantified the error on the determination of the total flux and half-light radius.
Results: Spiral arms can introduce biases on the photometry of galaxies in a way that depends on the underlying smooth surface brightness profile, the location of the arms, and the depth of the photometric data. A set of spiral arms accounting for 10% of the flux of a bulge-dominated galaxy typically causes the total flux and the half-light radius to be overestimated by 15% and 30%, respectively. This bias, however, is much smaller if the galaxy is disk-dominated.
Conclusions: Galaxies with a prominent bulge and a non-zero contribution from spiral arms are the most susceptible to biases in the total flux and half-light radius when fitted with a Sérsic profile. If photometric measurements with high accuracy are required, then measurements over finite apertures are to be preferred over global estimates of the flux. less
By: Alessandro Sonnenfeld, Shun-Sheng Li, Giulia Despali, Anowar J. Shajib, Edward N. Taylor
Context. Strong lenses are a biased subset of the general population of galaxies. Aims. The goal of this work is to quantify how lens galaxies and lensed sources differ from their parent distribution, namely the strong lensing bias. Methods. We first studied how the strong lensing cross-section varies as a function of lens and source properties. Then, we simulated strong lensing surveys with data similar to that expected for Euclid and measur... more
Context. Strong lenses are a biased subset of the general population of galaxies. Aims. The goal of this work is to quantify how lens galaxies and lensed sources differ from their parent distribution, namely the strong lensing bias. Methods. We first studied how the strong lensing cross-section varies as a function of lens and source properties. Then, we simulated strong lensing surveys with data similar to that expected for Euclid and measured the strong lensing bias in different scenarios. We focused particularly on two quantities: the stellar population synthesis mismatch parameter, αsps , defined as the ratio between the true stellar mass of a galaxy and the stellar mass obtained from photometry, and the central dark matter mass at fixed stellar mass and size. Results. Strong lens galaxies are biased towards larger stellar masses, smaller half-mass radii and larger dark matter masses. The amplitude of the bias depends on the intrinsic scatter in the mass-related parameters of the galaxy population and on the completeness in Einstein radius of the lens sample. For values of the scatter that are consistent with observed scaling relations and a minimum detectable Einstein radius of 0.5′′ , the strong lensing bias in αsps is 10% , while that in the central dark matter mass is 5% . The bias has little dependence on the properties of the source population: samples of galaxy-galaxy lenses and galaxy-quasar lenses that probe the same Einstein radius distribution are biased in a very similar way. Quadruply imaged quasar lenses, however, are biased towards higher ellipticity galaxies. Conclusions. Given current uncertainties, strong lensing observations can be used directly to improve our current knowledge of the inner structure of galaxies, without the need to correct for selection effects. less
By: Eiichiro Komatsu; Yi-Kuan Chiang; Ryu Makiya; Brice Ménard
How hot is the Universe today? How hot was it before? We report on the result of the observational determination of the mean temperature of hot gas in the Universe. We find that the mean gas temperature has increased ten times over the last 8 billion years, to reach about 2 million Kelvin today. As cosmic structures form, matter density fluctuations collapse gravitationally and baryonic matter is shock-heated and thermalized. We therefore exp... more
How hot is the Universe today? How hot was it before? We report on the result of the observational determination of the mean temperature of hot gas in the Universe. We find that the mean gas temperature has increased ten times over the last 8 billion years, to reach about 2 million Kelvin today. As cosmic structures form, matter density fluctuations collapse gravitationally and baryonic matter is shock-heated and thermalized. We therefore expect a connection between the mean gravitational potential energy of collapsed halos and the mean thermal energy of baryons. Our result provides quantitative verification of such a connection via cosmic shock-heating. less
Cosmic Birefringence in 2022
5upvotes
By: Patricia Diego-Palazuelos; Johannes R. Eskilt; Eiichiro Komatsu
The observed pattern of linear polarization of the cosmic microwave background (CMB) photons is a sensitive probe of physics violating parity symmetry under inversion of spatial coordinates. A new parity-violating interaction might have rotated the plane of linear polarization by an angle β as the CMB photons have been traveling for more than 13 billion years. This effect is known as "cosmic birefringence." In this paper, we present new measu... more
The observed pattern of linear polarization of the cosmic microwave background (CMB) photons is a sensitive probe of physics violating parity symmetry under inversion of spatial coordinates. A new parity-violating interaction might have rotated the plane of linear polarization by an angle β as the CMB photons have been traveling for more than 13 billion years. This effect is known as "cosmic birefringence." In this paper, we present new measurements of cosmic birefringence from a joint analysis of polarization data from two space missions, Planck and WMAP. This dataset covers a wide range of frequencies from 23 to 353 GHz. We measure β=0.342°+0.094°−0.091° (68% C.L.) for nearly full-sky data, which excludes β=0 at 99.987% C.L. This corresponds to the statistical significance of 3.6σ. There is no evidence for frequency dependence of β. We find a similar result, albeit with a larger uncertainty, when removing the Galactic plane from the analysis. less
By: Yuto Minami; Eiichiro Komatsu
We search for evidence of parity-violating physics in the Planck 2018 polarization data, and report on a new measurement of the cosmic birefringence angle, β. The previous measurements are limited by the systematic uncertainty in the absolute polarization angles of the Planck detectors. We mitigate this systematic uncertainty completely by simultaneously determining β and the angle miscalibration using the observed cross-correlation of the E-... more
We search for evidence of parity-violating physics in the Planck 2018 polarization data, and report on a new measurement of the cosmic birefringence angle, β. The previous measurements are limited by the systematic uncertainty in the absolute polarization angles of the Planck detectors. We mitigate this systematic uncertainty completely by simultaneously determining β and the angle miscalibration using the observed cross-correlation of the E- and B-mode polarization of the cosmic microwave background and the Galactic foreground emission. We show that the systematic errors are effectively mitigated and achieve a factor-of-2 smaller uncertainty than the previous measurement, finding β=0.35±0.14° (68% C.L.), which excludes β=0 at 99.2% C.L. This corresponds to the statistical significance of 2.4σ. less
By: Jeet Shah, Gautam Nambiar, Alexey V. Gorshkov, Victor Galitski
Quantum spin liquids are exotic phases of matter whose low-energy physics is described as the deconfined phase of an emergent gauge theory. With recent theory proposals and an experiment showing preliminary signs of Z2 topological order [G. Semeghini et al., Science 374, 1242 (2021)], Rydberg atom arrays have emerged as a promising platform to realize a quantum spin liquid. In this work, we propose a way to realize a U(1) quantum spin liquid ... more
Quantum spin liquids are exotic phases of matter whose low-energy physics is described as the deconfined phase of an emergent gauge theory. With recent theory proposals and an experiment showing preliminary signs of Z2 topological order [G. Semeghini et al., Science 374, 1242 (2021)], Rydberg atom arrays have emerged as a promising platform to realize a quantum spin liquid. In this work, we propose a way to realize a U(1) quantum spin liquid in three spatial dimensions, described by the deconfined phase of U(1) gauge theory in a pyrochlore lattice Rydberg atom array. We study the ground state phase diagram of the proposed Rydberg system as a function of experimentally relevant parameters. Within our calculation, we find that by tuning the Rabi frequency, one can access both the confinement-deconfinement transition driven by a proliferation of "magnetic" monopoles and the Higgs transition driven by a proliferation of "electric" charges of the emergent gauge theory. We suggest experimental probes for distinguishing the deconfined phase from ordered phases. This work serves as a proposal to access a confinement-deconfinement transition in three spatial dimensions on a Rydberg-based quantum simulator. less
By: Alireza Parhizkar, Victor Galitski
Mutually distorted layers of graphene give rise to a moiré pattern and a variety of non-trivial phenomena. We show that the continuum limit of this class of models is equivalent to a (2+1)-dimensional field theory of Dirac fermions coupled to two classical gauge fields. We further show that the existence of a flat band implies an effective dimensional reduction in the field theory, where the time dimension is ``removed.'' The resulting two-di... more
Mutually distorted layers of graphene give rise to a moiré pattern and a variety of non-trivial phenomena. We show that the continuum limit of this class of models is equivalent to a (2+1)-dimensional field theory of Dirac fermions coupled to two classical gauge fields. We further show that the existence of a flat band implies an effective dimensional reduction in the field theory, where the time dimension is ``removed.'' The resulting two-dimensional Euclidean theory contains the chiral anomaly. The associated Atiyah-Singer index theorem provides a self-consistency condition for the existence of flat bands. In particular, it reproduces a series of quantized magic angles known to exist in twisted bilayer graphene in the chiral limit where there is a particle-hole symmetry. We also use this criterion to prove that an external magnetic field splits this series into pairs of magnetic field-dependent magic angles associated with flat moiré-Landau bands. The topological criterion we derive provides a generic practical method for finding flat bands in a variety of material systems including but not limited to moiré bilayers. less
By: Seonghoon Choi, Tzu-Ching Yen, Ignacio Loaiza, Artur F. Izmaylov
On the order problem in construction of unitary operators for the Variational Quantum Eigensolver
0upvotes
By: Artur F. Izmaylov, Manuel Díaz-Tinoco, Robert A. Lang
One of the main challenges in the Variational Quantum Eigensolver (VQE) framework is construction of the unitary transformation. The dimensionality of the space for unitary rotations of N qubits is 4^N−1, which makes the choice of a polynomial subset of generators exponentially difficult process. Moreover, due to non-commutativity of generators, the order in which they are used strongly affects results. Choosing the optimal order in a particu... more
One of the main challenges in the Variational Quantum Eigensolver (VQE) framework is construction of the unitary transformation. The dimensionality of the space for unitary rotations of N qubits is 4^N−1, which makes the choice of a polynomial subset of generators exponentially difficult process. Moreover, due to non-commutativity of generators, the order in which they are used strongly affects results. Choosing the optimal order in a particular subset of generators requires testing the factorial number of combinations. We propose an approach based on the Lie algebra - Lie group connection and corresponding closure relations that systematically eliminates the order problem. less
By: Ilaria Maccari, Johan Carlström, Egor Babaev
We study the effective model for superconducting magic-angle twisted bilayer graphene beyond mean-field approximation by using Monte Carlo simulations. We consider the parameter regime where the low-temperature phase is a superconductor that spontaneously breaks time-reversal symmetry. When fluctuations are taken into account, it is shown that a fluctuations-induced phase with a fermion quadrupling order appears, where a different condensate,... more
We study the effective model for superconducting magic-angle twisted bilayer graphene beyond mean-field approximation by using Monte Carlo simulations. We consider the parameter regime where the low-temperature phase is a superconductor that spontaneously breaks time-reversal symmetry. When fluctuations are taken into account, it is shown that a fluctuations-induced phase with a fermion quadrupling order appears, where a different condensate, formed by four electrons, breaks time-reversal symmetry. less
By: Scott N. Genin, Ilya G. Ryabinkin, Artur F. Izmaylov
Quantum chemistry calculations for small molecules on quantum hardware have been demonstrated to date only on universal-gate quantum computers, not quantum annealers. The latter devices are limited to finding the lowest eigenstate of the Ising Hamiltonian whereas the electronic Hamiltonian could not be mapped to the Ising form without exponential growth of the Ising Hamiltonian with the size of the system [J. Phys. Chem. B 122, 3384 (2018)]. ... more
Quantum chemistry calculations for small molecules on quantum hardware have been demonstrated to date only on universal-gate quantum computers, not quantum annealers. The latter devices are limited to finding the lowest eigenstate of the Ising Hamiltonian whereas the electronic Hamiltonian could not be mapped to the Ising form without exponential growth of the Ising Hamiltonian with the size of the system [J. Phys. Chem. B 122, 3384 (2018)]. Here we propose a novel mixed discrete-continuous optimization algorithm, which finds the lowest eigenstate of the qubit coupled cluster (QCC) method using a quantum annealer for solving a discrete part of the problem. The QCC method is a potentially exact approach for constructing the electronic wave function in the qubit space. Therefore, our methodology allows for systematically improvable quantum chemistry calculations using quantum annealears. We illustrate capabilities of our approach by calculating QCC ground electronic states for the LiH, H2O, and C6H6 molecules. C6H6 calculations involve 36 qubits and are the largest quantum chemistry calculations made on a quantum annealer (the D-Wave 2000Q system) to date. Our findings opens up a new perspective for use quantum annealers in high-throughput material discovery. less
By: Tzu-Ching Yen and Artur F. Izmaylov
An arbitrary operator corresponding to a physical observable cannot be measured in a single measurement on currently available quantum hardware. To obtain the expectation value of the observable, one needs to partition its operator to measurable fragments. However, the observable and its fragments generally do not share any eigenstates, and thus the number of measurements needed to obtain the expectation value of the observable can grow rapid... more
An arbitrary operator corresponding to a physical observable cannot be measured in a single measurement on currently available quantum hardware. To obtain the expectation value of the observable, one needs to partition its operator to measurable fragments. However, the observable and its fragments generally do not share any eigenstates, and thus the number of measurements needed to obtain the expectation value of the observable can grow rapidly even when the wavefunction prepared is close to an eigenstate of the observable. We provide a unified Lie algebraic framework for developing efficient measurement schemes for quantum observables, it is based on two elements: 1) embedding the observable operator in a Lie algebra and 2) transforming Lie algebra elements into those of a Cartan sub-algebra (CSA) using unitary operators. The CSA plays the central role because all its elements are mutually commutative and thus can be measured simultaneously. We illustrate the framework on measuring expectation values of Hamiltonians appearing in the Variational Quantum Eigensolver approach to quantum chemistry. The CSA approach puts many recently proposed methods for the measurement optimization within a single framework, and allows one not only to reduce the number of measurable fragments but also the total number of measurements. less
By: Jacqueline Bloch et al
An important goal of modern condensed matter physics involves the search for states of matter with new emergent properties and desirable functionalities. Although the tools for material design remain relatively limited, notable advances have been recently achieved by controlling interactions at hetero-interfaces , precise alignment of low-dimensional materials and the use of extreme pressures . Here, we highlight a new paradigm, based on con... more
An important goal of modern condensed matter physics involves the search for states of matter with new emergent properties and desirable functionalities. Although the tools for material design remain relatively limited, notable advances have been recently achieved by controlling interactions at hetero-interfaces , precise alignment of low-dimensional materials and the use of extreme pressures . Here, we highlight a new paradigm, based on controlling light-matter interactions, which provides a new way to manipulate and synthesize strongly correlated quantum matter. We consider the case in which both electron-electron and electron-photon interactions are strong and give rise to a variety of novel phenomena. Photon-mediated superconductivity, cavity-fractional quantum Hall physics and optically driven topological phenomena in low dimensions are amongst the frontiers discussed in this perspective, which puts a spotlight on a new field that we term here “strongly-correlated electron-photon science.” less
By: A.F. Izmaylov and T.C. Yen
Necessary and sufficient conditions for quantum Hamiltonians to be exactly solvable within mean-field (MF) theories have not been formulated so far. To resolve this problem, first, we define what MF theory is, independently of a Hamiltonian realization in a particular set of operators. Second, using a Lie-algebraic framework we formulate a criterion for a Hamiltonian to be MF solvable. The criterion is applicable for both distinguishable and ... more
Necessary and sufficient conditions for quantum Hamiltonians to be exactly solvable within mean-field (MF) theories have not been formulated so far. To resolve this problem, first, we define what MF theory is, independently of a Hamiltonian realization in a particular set of operators. Second, using a Lie-algebraic framework we formulate a criterion for a Hamiltonian to be MF solvable. The criterion is applicable for both distinguishable and indistinguishable particle cases. For the electronic Hamiltonians, our approach reveals the existence of MF solvable Hamiltonians of higher fermionic operator powers than quadratic. Some of the MF solvable Hamiltonians require different sets of quasi-particle rotations for different eigenstates, which reflects a more complicated structure of such Hamiltonians. less
By: R. A. Lang, I. G. Ryabinkin, A. F. Izmaylov
Application of current and near-term quantum hardware to the electronic structure problem is highly limited by qubit counts, coherence times, and gate fidelities. To address these restrictions within the variational quantum eigensolver (VQE) framework, many recent contributions have suggested dressing the electronic Hamiltonian to include a part of electron correlation, leaving the rest to be accounted by VQE state preparation. We present a n... more
Application of current and near-term quantum hardware to the electronic structure problem is highly limited by qubit counts, coherence times, and gate fidelities. To address these restrictions within the variational quantum eigensolver (VQE) framework, many recent contributions have suggested dressing the electronic Hamiltonian to include a part of electron correlation, leaving the rest to be accounted by VQE state preparation. We present a new dressing scheme that combines preservation of the Hamiltonian hermiticity and an exact quadratic truncation of the Baker-Campbell-Hausdorff expansion. The new transformation is constructed as the exponent of an involutory linear combination (ILC) of anti-commuting Pauli products. It incorporates important strong correlation effects in the dressed Hamiltonian and can be viewed as a classical preprocessing step alleviating the resource requirements of the subsequent VQE application. The assessment of the new computational scheme for electronic structure of the LiH, H2O, and N2 molecules shows significant increase in efficiency compared to conventional qubit coupled cluster dressings. less
By: Artur F. Izmaylov, Robert A. Lang, Tzu-Ching Yen
Optimization of unitary transformations in Variational Quantum Algorithms benefits highly from efficient evaluation of cost function gradients with respect to amplitudes of unitary generators. We propose several extensions of the parametric-shift-rule to formulating these gradients as linear combinations of expectation values for generators with general eigen-spectrum (i.e. with more than two eigenvalues). Our approaches are exact and do not ... more
Optimization of unitary transformations in Variational Quantum Algorithms benefits highly from efficient evaluation of cost function gradients with respect to amplitudes of unitary generators. We propose several extensions of the parametric-shift-rule to formulating these gradients as linear combinations of expectation values for generators with general eigen-spectrum (i.e. with more than two eigenvalues). Our approaches are exact and do not use any auxiliary qubits, instead they rely on a generator eigen-spectrum analysis. Two main directions in the parametric-shift-rule extensions are 1) polynomial expansion of the exponential unitary operator based on a limited number of different eigenvalues in the generator and 2) decomposition of the generator as a linear combination of low-eigenvalue operators (e.g. operators with only 2 or 3 eigenvalues). These techniques have a range of scalings for the number of needed expectation values with the number of generator eigenvalues from quadratic (for polynomial expansion) to linear and even log2 (for generator decompositions). This allowed us to propose efficient differentiation schemes superior to previous approaches for commonly used 2-qubit transformations (e.g. match-gates, transmon and fSim gates) and Ŝ^2-conserving fermionic operators for the variational quantum eigensolver. less
By: Ignacio Loaiza, Alireza Marefat Khah, Nathan Wiebe, Artur F. Izmaylov
We consider different Linear Combination of Unitaries (LCU) decompositions for molecular electronic structure Hamiltonians. Using these LCU decompositions for Hamiltonian simulation on a quantum computer, the main figure of merit is the 1-norm of their coefficients, which is associated with the quantum circuit complexity. It is derived that the lowest possible LCU 1-norm for a given Hamiltonian is half of its spectral range. This lowest norm ... more
We consider different Linear Combination of Unitaries (LCU) decompositions for molecular electronic structure Hamiltonians. Using these LCU decompositions for Hamiltonian simulation on a quantum computer, the main figure of merit is the 1-norm of their coefficients, which is associated with the quantum circuit complexity. It is derived that the lowest possible LCU 1-norm for a given Hamiltonian is half of its spectral range. This lowest norm decomposition is practically unattainable for general Hamiltonians; therefore, multiple practical techniques to generate LCU decompositions are proposed and assessed. A technique using symmetries to reduce the 1-norm further is also introduced. In addition to considering LCU in the Schrödinger picture, we extend it to the interaction picture, which substantially further reduces the 1-norm. less
By: Luis A. Martínez-Martínez, Tzu-Ching Yen, Artur F. Izmaylov
Solving the electronic structure problem via unitary evolution of the electronic Hamiltonian is one of the promising applications of digital quantum computers. One of the practical strategies to implement the unitary evolution is via Trotterization, where a sequence of short-time evolutions of fast-forwardable (i.e. efficiently diagonalizable) Hamiltonian fragments is used. Given multiple choices of possible Hamiltonian decompositions to fast... more
Solving the electronic structure problem via unitary evolution of the electronic Hamiltonian is one of the promising applications of digital quantum computers. One of the practical strategies to implement the unitary evolution is via Trotterization, where a sequence of short-time evolutions of fast-forwardable (i.e. efficiently diagonalizable) Hamiltonian fragments is used. Given multiple choices of possible Hamiltonian decompositions to fast-forwardable fragments, the accuracy of the Hamiltonian evolution depends on the choice of the fragments. We assess efficiency of multiple Hamiltonian partitioning techniques using fermionic and qubit algebras for the Trotterization. Use of symmetries of the electronic Hamiltonian and its fragments significantly reduces the Trotter error. This reduction makes fermionic-based partitioning Trotter errors lower compared to those in qubit-based techniques. However, from the simulation-cost standpoint, fermionic methods tend to introduce quantum circuits with a greater number of T-gates at each Trotter step and thus are more computationally expensive compared to their qubit counterparts. less
By: Orazio Scarlatella, Rosario Fazio, Aashish Clerk and Marco Schirò
Several experimental platforms, such as superconducting circuits or ultracold atomic in optical lattices, nowadays allow to probe many-body physics in unprecedented regimes, such as in non-equilibrium conditions resulting from controlled dissipation and driving, but theoretical techniques for describing those regimes are limited.
In this work [1], we introduce an extension of the nonequilibrium dynamical mean-field theory (DMFT) for bosoni... more
Several experimental platforms, such as superconducting circuits or ultracold atomic in optical lattices, nowadays allow to probe many-body physics in unprecedented regimes, such as in non-equilibrium conditions resulting from controlled dissipation and driving, but theoretical techniques for describing those regimes are limited.
In this work [1], we introduce an extension of the nonequilibrium dynamical mean-field theory (DMFT) for bosonic lattice models described by Markovian master equations. DMFT maps these lattice problems onto a problem of a single site coupled to a classical field and to a non-interacting bath, accounting for leading corrections to Gutzwiller mean-field theory due to finite dimensionality. Our approach relies on a new method for solving the effective single-site problem based on a non-crossing approximation in the coupling to the DMFT bath, going beyond standard Born-Markov approximations [2].
We then discuss an application to a driven-dissipative Bose-Hubbard model with two-body losses and incoherent pump, computing its steady-state properties. DMFT captures hopping-induced processes that are completely missed by Gutzwiller mean-field theory, which are crucial to obtain the correct stationary-state, such as to describe its quantum-Zeno behaviour when the losses are strong, or to predict the critical hopping for a phase transition between an incoherent phase and a coherent, limit-cycle phase.
[1] O. Scarlatella, A. A. Clerk, R. Fazio, and M. Schiró, Dynamical Mean-Field Theory for Markovian Open Quantum Many-Body Systems, Phys. Rev. X 11, 031018 (2021).
[2] O. Scarlatella and M. Schiro, Self-Consistent Dynamical Maps for Open Quantum Systems, arXiv:2107.05553. less
By: Vadim Grinenko, Rajib Sarkar, K Kihou, CH Lee, I Morozov, S Aswartham, B Büchner, P Chekhonin, W Skrotzki, K Nenkov, R Hühne, K Nielsch, S-L Drechsler, VL Vadimov, MA Silaev, PA Volkov, I Eremin, H Luetkens, H-H Klauss
In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors in which superconductivity coexists with magnetism, and a few examples are known where the superconductivity itself induces spontaneous magnetism. The best-known of these compounds are Sr2RuO4 and some non-centrosymmetric superconductors. Here, we report the finding of a narrow dome of an s+is′ superconducting pha... more
In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors in which superconductivity coexists with magnetism, and a few examples are known where the superconductivity itself induces spontaneous magnetism. The best-known of these compounds are Sr2RuO4 and some non-centrosymmetric superconductors. Here, we report the finding of a narrow dome of an s+is′ superconducting phase with apparent broken time-reversal symmetry (BTRS) inside the broad s-wave superconducting region of the centrosymmetric multiband superconductor Ba1 − xKxFe2As2 (0.7 ≲ x ≲ 0.85). We observe spontaneous magnetic fields inside this dome using the muon spin relaxation (μSR) technique. Furthermore, our detailed specific heat study reveals that the BTRS dome appears very close to a change in the topology of the Fermi surface. With this, we experimentally demonstrate the likely emergence of a novel quantum state due to topological changes in the electronic system. less
By: Jonathan B. Curtis, Ankit Disa, Michael Fechner, Andrea Cavalleri, Prineha Narang
By using intense coherent electromagnetic radiation, it may be possible to manipulate the properties of quantum materials very quickly, or even induce new and potentially useful phases that are absent in equilibrium. For instance, ultrafast control of magnetic dynamics is crucial for a number of proposed spintronic devices and can also shed light on the possible dynamics of correlated phases out of equilibrium. Inspired by recent experiments ... more
By using intense coherent electromagnetic radiation, it may be possible to manipulate the properties of quantum materials very quickly, or even induce new and potentially useful phases that are absent in equilibrium. For instance, ultrafast control of magnetic dynamics is crucial for a number of proposed spintronic devices and can also shed light on the possible dynamics of correlated phases out of equilibrium. Inspired by recent experiments on spin-orbital ferromagnet YTiO3 we consider the nonequilibrium dynamics of Heisenberg ferromagnetic insulator with low-lying orbital excitations. We model the dynamics of the magnon excitations in this system following an optical pulse which resonantly excites infrared-active phonon modes. As the phonons ring down they can dynamically couple the orbitals with the low-lying magnons, leading to a dramatically modified effective bath for the magnons. We show this transient coupling can lead to a dynamical acceleration of the magnetization dynamics, which is otherwise bottlenecked by small anisotropy. Exploring the parameter space more we find that the magnon dynamics can also even completely reverse, leading to a negative relaxation rate when the pump is blue-detuned with respect to the orbital bath resonance. We therefore show that by using specially targeted optical pulses, one can exert a much greater degree of control over the magnetization dynamics, allowing one to optically steer magnetic order in this system. We conclude by discussing interesting parallels between the magnetization dynamics we find here and recent experiments on photo-induced superconductivity, where it is similarly observed that depending on the initial pump frequency, an apparent metastable superconducting phase emerges. less
By: En-Jui Kuo, Yijia Xu, Dominik Hangleiter, Andrey Grankin, and Mohammad Hafezi
We introduce the notion of "generalized bosons" whose exchange statistics resemble those of bosons, but the local bosonic commutator [ai,a†i]=1 is replaced by an arbitrary single-mode operator that is diagonal in the generalized Fock basis. Examples of generalized bosons include boson pairs and spins. We consider the analogue of the boson sampling task for these particles and observe that its output probabilities are still given by permanents... more
We introduce the notion of "generalized bosons" whose exchange statistics resemble those of bosons, but the local bosonic commutator [ai,a†i]=1 is replaced by an arbitrary single-mode operator that is diagonal in the generalized Fock basis. Examples of generalized bosons include boson pairs and spins. We consider the analogue of the boson sampling task for these particles and observe that its output probabilities are still given by permanents, so that the results regarding hardness of sampling directly carry over. Finally, we propose implementations of generalized boson sampling in circuit-QED and ion-trap platforms. less
By: Yunxiang Liao
We use field-theoretic methods to explore the statistics of eigenfunctions of the Floquet operator for a large family of Floquet random quantum circuits. The correlation function of the quasienergy eigenstates is calculated and shown to exhibit random matrix circular unitary ensemble statistics, which is consistent with the analogue of Berry's conjecture for quantum circuits. This quantity determines all key metrics of quantum chaos, such as ... more
We use field-theoretic methods to explore the statistics of eigenfunctions of the Floquet operator for a large family of Floquet random quantum circuits. The correlation function of the quasienergy eigenstates is calculated and shown to exhibit random matrix circular unitary ensemble statistics, which is consistent with the analogue of Berry's conjecture for quantum circuits. This quantity determines all key metrics of quantum chaos, such as the spectral form factor and thermalizing time-dependence of the expectation value of an arbitrary observable. It also allows us to explicitly show that the matrix elements of local operators satisfy the eigenstate thermalization hypothesis (ETH); i.e., the variance of the off-diagonal matrix elements of such operators is exponentially small in the system size. These results represent a proof of ETH for the family of Floquet random quantum circuits at a physical level of rigor. An outstanding open question for this and most of other sigma-model calculations is a mathematically rigorous proof of the validity of the saddle-point approximation in the large-N limit. less
By: AQC team
This presentation reviews basics of quantum mechanics, quantum computing, and quantum sensing with an eye on practical applications, if any, of various quantum technologies. It discusses a realistic roadmap, time scales, and challenges facing this space and is intended for a business audience, C-level executives, and investors considering strategic decisions about engaging with nascent quantum technology (or not).
P.S. Supporting video co... more
This presentation reviews basics of quantum mechanics, quantum computing, and quantum sensing with an eye on practical applications, if any, of various quantum technologies. It discusses a realistic roadmap, time scales, and challenges facing this space and is intended for a business audience, C-level executives, and investors considering strategic decisions about engaging with nascent quantum technology (or not).
P.S. Supporting video content, animation, and copies of the accompanying Nature article are available upon request (through the ScienceCast comment section below).
less
By: Woo-Ram Lee, Zhangjie Qin, Robert Raussendorf, Eran Sela, and V. W. Scarola
Quantum simulation using time evolution in phase-estimation-based quantum algorithms can yield unbiased solutions of classically intractable models. However, long runtimes open such algorithms to decoherence. We show how measurement-based quantum simulation uses effective time evolution via measurement to allow runtime advantages over conventional circuit-based algorithms that use real-time evolution with quantum gates. We construct a hybrid ... more
Quantum simulation using time evolution in phase-estimation-based quantum algorithms can yield unbiased solutions of classically intractable models. However, long runtimes open such algorithms to decoherence. We show how measurement-based quantum simulation uses effective time evolution via measurement to allow runtime advantages over conventional circuit-based algorithms that use real-time evolution with quantum gates. We construct a hybrid algorithm to find energy eigenvalues in fermionic models using only measurements on graph states. We apply the algorithm to the Kitaev and Hubbard chains. Resource estimates show a runtime advantage if measurements can be performed faster than gates, and graph states compactification is fully used. In this letter, we set the stage to allow advances in measurement precision to improve quantum simulation. less
By: Eliot Kapit and Vadim Oganesyan
Quantum annealing is a powerful alternative model of quantum computing, which can succeed in the presence of environmental noise even without error correction. However, despite great effort, no conclusive demonstration of a quantum speedup (relative to state of the art classical algorithms) has been shown for these systems, and rigorous theoretical proofs of a quantum advantage (such as the adiabatic formulation of Grover's search problem) ge... more
Quantum annealing is a powerful alternative model of quantum computing, which can succeed in the presence of environmental noise even without error correction. However, despite great effort, no conclusive demonstration of a quantum speedup (relative to state of the art classical algorithms) has been shown for these systems, and rigorous theoretical proofs of a quantum advantage (such as the adiabatic formulation of Grover's search problem) generally rely on exponential precision in at least some aspects of the system, an unphysical resource guaranteed to be scrambled by experimental uncertainties and random noise. In this work, we propose a new variant of quantum annealing, called RFQA, which can maintain a scalable quantum speedup in the face of noise and modest control precision. Specifically, we consider a modification of flux qubit-based quantum annealing which includes low-frequency oscillations in the directions of the transverse field terms as the system evolves. We show that this method produces a quantum speedup for finding ground states in the Grover problem and quantum random energy model, and thus should be widely applicable to other hard optimization problems which can be formulated as quantum spin glasses. Further, we explore three realistic noise channels and show that the speedup from RFQA is resilient to 1/f-like local potential fluctuations and local heating from interaction with a sufficiently low temperature bath. Another noise channel, bath-assisted quantum cooling transitions, actually accelerates the algorithm and may outweigh the negative effects of the others. We also detail how RFQA may be implemented experimentally with current technology. less
By: Andrey Grankin and all
This work reviews our recent theoretical ideas along with related experimental results related to engineering non-equilibrium protocols and electromagnetic environments to enhance superconductivity in solid-state materials. First, I'll discuss a generalization of the Kennes, Millis et al's protocol of using phonon squeezing to strongly enhance superconducting Tc, in particular close to the dynamical lattice instabilities caused by driving. Se... more
This work reviews our recent theoretical ideas along with related experimental results related to engineering non-equilibrium protocols and electromagnetic environments to enhance superconductivity in solid-state materials. First, I'll discuss a generalization of the Kennes, Millis et al's protocol of using phonon squeezing to strongly enhance superconducting Tc, in particular close to the dynamical lattice instabilities caused by driving. Second, I will briefly review recent ideas of using cavity structures to engineer electromagnetic environments more favorable to superconductivity compared to materials in free space. Finally, I will zero in on hyperbolic metamaterial structures, which have been experimentally shown to strongly enhance superconducting Tc and the critical magnetic field in various compounds. These effects are usually attributed to hyperbolic plasmons, but I will argue that the conventional theory is probably unreliable. Based on our work in progress, I will speculate that it is likely boundary phonons that help bootstrap superconductivity in such systems. However, at the moment the nature of enhancement of superconductivity in hyperbolic metamaterials remains a bit of a mystery. less
By: Mehdi Kargarian
Integer quantum Hall effect, Chern insulators, topological insulators, and
topological superconductors are famous examples of topological phases
in noninteracting or weakly correlated electron systems. In these states
the ground state is nondegenerate and the excitations carry the original quantum
numbers. Fractional quantum Hall effect (FQHE) and spin liquids, on the other hand, arise
in strongly correlated electron systems an... more
Integer quantum Hall effect, Chern insulators, topological insulators, and
topological superconductors are famous examples of topological phases
in noninteracting or weakly correlated electron systems. In these states
the ground state is nondegenerate and the excitations carry the original quantum
numbers. Fractional quantum Hall effect (FQHE) and spin liquids, on the other hand, arise
in strongly correlated electron systems and exhibit exotic properties such as
ground state degeneracy and fractionalized excitations, dubbed as topologically ordered states,
with potential applications in quantum computations. While there are many material candidates for noninteracting topological phases of matter, the topological orders usually arise in texteme conditions such as strong magnetic fields and low temperatures, e.g., in FQHE, and in spin liquids, usually the extra interactions between spins spoil the realization of true topological orders.
Here, we ask the following question: Can we design the topological orders in
more conventional systems by properly coupling the degrees of freedom together? we try to present an understanding of one of the simplest topological orders, the Wen plaquette model, in a superconducting lattice model. Then, we discuss how one may obtain more exotic topological orders. less
Spin-plasma waves
2upvotes
By: Dmitry Efimkin and Mehdi Kargarian
The surface of a topological insulator hosts Dirac electronic states with the spin-momentum locking, which constrains spin orientation perpendicular to electron momentum. As a result, collective plasma excitations in the interacting Dirac liquid manifest themselves as coupled charge- and spin-waves. Here we demonstrate that the presence of the spin component enables effective coupling between plasma waves and spin waves at interfaces between ... more
The surface of a topological insulator hosts Dirac electronic states with the spin-momentum locking, which constrains spin orientation perpendicular to electron momentum. As a result, collective plasma excitations in the interacting Dirac liquid manifest themselves as coupled charge- and spin-waves. Here we demonstrate that the presence of the spin component enables effective coupling between plasma waves and spin waves at interfaces between the surface of a topological insulator and insulating magnet. Moreover, the helical nature of spin-momentum locking textures provides the phase winding in the coupling between the spin and plasma waves that makes the spectrum of hybridized spin-plasma modes to be topologically nontrivial. We also show that such topological modes lead to a large thermal Hall response. less
Equatorial magnetoplasma waves
2upvotes
By: Cooper Finnigan, Mehdi Kargarian, Dmitry K. Efimkin
Due to its rotation, Earth traps a few equatorial ocean and atmospheric waves, including Kelvin, Yanai, Rossby, and Poincare modes. It has been recently demonstrated that the mathematical origin of equatorial waves is intricately related to the nontrivial topology of hydrodynamic equations describing oceans or the atmosphere. In the present work, we consider plasma oscillations supported by a two-dimensional electron gas confined at the surfa... more
Due to its rotation, Earth traps a few equatorial ocean and atmospheric waves, including Kelvin, Yanai, Rossby, and Poincare modes. It has been recently demonstrated that the mathematical origin of equatorial waves is intricately related to the nontrivial topology of hydrodynamic equations describing oceans or the atmosphere. In the present work, we consider plasma oscillations supported by a two-dimensional electron gas confined at the surface of a sphere or a cylinder. We argue that in the presence of a uniform magnetic field, these systems host a set of equatorial magnetoplasma waves that are counterparts to the equatorial waves trapped by Earth. For a spherical geometry, the equatorial modes are well developed only if their penetration length is smaller than the radius of the sphere. For a cylindrical geometry, the spectrum of equatorial modes is weakly dependent on the cylinder radius and overcomes finite-size effects. We argue that this exceptional robustness can be explained by destructive interference effects. We discuss possible experimental setups, including grains and rods composed of topological insulators (e.g., Bi2Se3) or metal-coated dielectrics (e.g., Au2S). less
By: Byungmin Kang, Vito W Scarola, Kwon Park
When studying strongly correlated systems using quantum circuits, it is important to prepare good initial states from which the target many-body states can easily be accessed. Here, we discuss an efficient quantum circuit preparation of the resonating valence bond (RVB) state, which plays an essential role in understanding the high-Tc superconductivity and the spin liquid physics. It is known that the RVB state is given by the Gutzwiller proj... more
When studying strongly correlated systems using quantum circuits, it is important to prepare good initial states from which the target many-body states can easily be accessed. Here, we discuss an efficient quantum circuit preparation of the resonating valence bond (RVB) state, which plays an essential role in understanding the high-Tc superconductivity and the spin liquid physics. It is known that the RVB state is given by the Gutzwiller projection of a Bardeen-Cooper-Schrieffer (BCS) state for which an efficient quantum circuit construction is known. However, since the overlap between the RVB state and the BCS state decays exponentially in the system size, naive implementation of the Gutzwiller projection as projective measurements in quantum circuit would require exponentially many repetitions in order to obtain the RVB state. In this talk, we discuss how to systematically amplify the amplitude associated with the RVB state in the BCS state using a recently developed amplitude amplification technique. Following our construction, one can construct a quantum circuit for the RVB state with an arbitrarily high success probability. less
By: Noam Schiller, Barak A. Katzir, Ady Stern, Erez Berg, Netanel H. Lindner, Yuval Oreg
Systems harboring parafermion zero-modes hold promise as platforms for topological quantum computation. Recent experimental work (Gül et al., arXiv:2009.07836) provided evidence for proximity-induced superconductivity in fractional quantum Hall edges, a prerequisite in proposed realizations of parafermion zero-modes. The main evidence was the observation of a crossed Andreev reflection signal, in which electrons enter the superconductor from ... more
Systems harboring parafermion zero-modes hold promise as platforms for topological quantum computation. Recent experimental work (Gül et al., arXiv:2009.07836) provided evidence for proximity-induced superconductivity in fractional quantum Hall edges, a prerequisite in proposed realizations of parafermion zero-modes. The main evidence was the observation of a crossed Andreev reflection signal, in which electrons enter the superconductor from one chiral mode and are reflected as holes to another, counter-propagating chiral mode. Remarkably, while the probability for cross Andreev reflection was much smaller than one, it was stronger for $\nu=1/3$ fractional quantum Hall edges than for integer ones. We theoretically explain these findings, including the relative strengths of the signals in the two cases and their qualitatively different temperature dependencies. Beyond the coupling of the two counter-propagating modes through Andreev reflection and back-scattering, an essential part of our model is the coupling of the edge modes to normal states in the cores of Abrikosov vortices located close to the edges. These vortices are made dense by the magnetic field needed to form the quantum Hall states, and provide a metallic bath to which the edges are tunnel-coupled. The stronger crossed Andreev reflection in the fractional case originates from the suppression of electronic tunneling between the bath and the fractional quantum Hall edges. Our theory shows that the mere observation of crossed Andreev reflection signal does not necessarily imply the presence of localized parafermion zero-modes, and suggests ways to identify their presence from the behavior of this signal in the low-temperature limit. less
By: I. Martin, K. A. Matveev
We study the nature of many-body eigenstates of a system of interacting chiral spinless fermions on a ring. We find a coexistence of fermionic and bosonic types of eigenstates in parts of the many-body spectrum. Some bosonic eigenstates, native to the strong interaction limit, persist at intermediate and weak couplings, enabling persistent density oscillations in the system, despite it being far from integrability.
We study the nature of many-body eigenstates of a system of interacting chiral spinless fermions on a ring. We find a coexistence of fermionic and bosonic types of eigenstates in parts of the many-body spectrum. Some bosonic eigenstates, native to the strong interaction limit, persist at intermediate and weak couplings, enabling persistent density oscillations in the system, despite it being far from integrability. less
By: Shankar Balasubramanian (MIT), Ashvin Vishwanath (Harvard) et al
We study a general class of easy-axis spin models on a lattice of corner sharing even-sided polygons with all-to-all interactions within a plaquette. The low energy description corresponds to a quantum dimer model on a dual lattice of even coordination number with a multi dimer constraint. At an appropriately constructed frustration-free Rokhsar-Kivelson (RK) point, the ground state wavefunction can be exactly mapped onto a classical vertex m... more
We study a general class of easy-axis spin models on a lattice of corner sharing even-sided polygons with all-to-all interactions within a plaquette. The low energy description corresponds to a quantum dimer model on a dual lattice of even coordination number with a multi dimer constraint. At an appropriately constructed frustration-free Rokhsar-Kivelson (RK) point, the ground state wavefunction can be exactly mapped onto a classical vertex model on the dual lattice. When the dual lattice is bipartite, the vertex models are bonded and are self dual under Wegner's duality, with the self dual point corresponding to the RK point of the original multi-dimer model. We argue that the self dual point is a critical point based on known exact solutions to some of the vertex models. When the dual lattice is non-bipartite, the vertex model is arrowed, and we use numerical methods to argue that there is no phase transition as a function of the vertex weights. Motivated by these wavefunction dualities, we construct two other distinct families of frustration-free Hamiltonians whose ground states can be mapped onto these vertex models. Many of these RK Hamiltonians provably host Z2 topologically ordered phases. less
By: David Weld (UCSB) et al
Quantum interference can terminate energy growth in a continually kicked system, via a single-particle ergodicity-breaking mechanism known as dynamical localization. The effect of many-body interactions on dynamically localized states, while important to a fundamental understanding of quantum decoherence, has remained unexplored despite a quarter-century of experimental studies. We report the experimental realization of a tunably-interacting ... more
Quantum interference can terminate energy growth in a continually kicked system, via a single-particle ergodicity-breaking mechanism known as dynamical localization. The effect of many-body interactions on dynamically localized states, while important to a fundamental understanding of quantum decoherence, has remained unexplored despite a quarter-century of experimental studies. We report the experimental realization of a tunably-interacting kicked quantum rotor ensemble using a Bose-Einstein condensate in a pulsed optical lattice. We observe signatures of a prethermal localized plateau, followed for interacting samples by interaction-induced anomalous diffusion with an exponent near one half. Echo-type time reversal experiments establish the role of interactions in destroying reversibility. These results quantitatively elucidate the dynamical transition to many-body quantum chaos, advance our understanding of quantum anomalous diffusion, and delimit some possibilities for protecting quantum information in interacting driven systems. less
By: Andrew Allocca (Cambridge, UK) et al
We propose the Casimir effect as a general method to observe Lifshitz transitions in electron systems. The concept is demonstrated with a planar spin-orbit coupled semiconductor in a magnetic field. We calculate the Casimir force between two such semiconductors and between the semiconductor and a metal as a function of the Zeeman splitting in the semiconductor. The Zeeman field causes a Fermi pocket in the semiconductor to form or collapse by... more
We propose the Casimir effect as a general method to observe Lifshitz transitions in electron systems. The concept is demonstrated with a planar spin-orbit coupled semiconductor in a magnetic field. We calculate the Casimir force between two such semiconductors and between the semiconductor and a metal as a function of the Zeeman splitting in the semiconductor. The Zeeman field causes a Fermi pocket in the semiconductor to form or collapse by tuning the system through a topological Lifshitz transition. We find that the Casimir force experiences a kink at the transition point and noticeably different behaviors on either side of the transition. The simplest experimental realization of the proposed effect would involve a metal-coated sphere suspended from a micro-cantilever above a thin layer of InSb (or another semiconductor with large g-factor). Numerical estimates are provided and indicate that the effect is well within experimental reach. less
Moiré Gravity and Cosmology
2upvotes
By: Alireza Parizhkar
The vacuum catastrophe is a fundamental puzzle, where the observed scales of the cosmological constant are many orders of magnitude smaller than the natural scales expected in the theory. This work proposes a new ``bi-world'' construction that may offer an insight into the cosmological constant problem. The model generally includes a $(3+1)$-dimensional manifold with two different geometries and matter fields residing on them. The diffeomorp... more
The vacuum catastrophe is a fundamental puzzle, where the observed scales of the cosmological constant are many orders of magnitude smaller than the natural scales expected in the theory. This work proposes a new ``bi-world'' construction that may offer an insight into the cosmological constant problem. The model generally includes a $(3+1)$-dimensional manifold with two different geometries and matter fields residing on them. The diffeomorphism invariance and causality highly constrain the two metrics to be conformally related, $\eta_{\mu \nu} = \phi^2 g_{\mu \nu}$. This reduces the theory to a standard single-world description, but introduces a new inherently geometrical ``moir{\'e} field,'' $\phi$. Interestingly, the moir{\'e} field has the character of both a dilaton and Higgs field familiar in the conventional theory. Integrating out the moir{\'e} field naturally gives rise to the Starobinsky action and inflationary dynamics. In the framework of the Friedmann-Lemaitre–Robertson–Walker solution, we reduce an effective action for the moir{\'e} field to that of a particle moving in a Mexican hat potential. The equations of motion are then solved numerically and the moir{\'e} field is shown to approach a Mexican-hat minimum in an oscillatory fashion, which is accompanied by the decay of the Hubble parameter. Under additional reasonable assumptions, the vacuum energy asymptotically approaches zero in the end of inflationary evolution. The physics presented here shares similarities with the moir{\'e} phenomena in condensed matter and elsewhere, where two similar structures superimposed upon give rise to a superstructure with low emergent energy scales compared to the native theories. less
By: Alireza Parhizkar et al
The chiral anomaly is a fundamental quantum mechanical phenomenon which is of great importance to both particle physics and condensed matter physics alike. In the context of QED, it manifests as the breaking of chiral symmetry in the presence of electromagnetic fields. It is also known that anomalous chiral symmetry breaking can occur through interactions alone, as is the case for interacting one-dimensional systems. In this Letter, we invest... more
The chiral anomaly is a fundamental quantum mechanical phenomenon which is of great importance to both particle physics and condensed matter physics alike. In the context of QED, it manifests as the breaking of chiral symmetry in the presence of electromagnetic fields. It is also known that anomalous chiral symmetry breaking can occur through interactions alone, as is the case for interacting one-dimensional systems. In this Letter, we investigate the interplay between these two modes of anomalous chiral symmetry breaking in the context of interacting Weyl semimetals. Using Fujikawa’s path integral method, we show that the chiral charge continuity equation is modified by the presence of interactions which can be viewed as including the effect of the electric and magnetic fields generated by the interacting quantum matter. This can be understood further using dimensional reduction and a Luttinger liquid description of the lowest Landau level. These effects manifest themselves in the nonlinear response of the system. In particular, we find an interaction-dependent density response due to a change in the magnetic field as well as a contribution to the nonequilibrium and inhomogeneous anomalous Hall response while preserving its equilibrium value. less
By: Amit Vikram, Victor Galitski
Ergodic theory provides a rigorous mathematical description of classical dynamical systems, including a formal definition of the ergodic hierarchy consisting of merely ergodic, weakly-, strongly-, and K-mixing systems. Closely related to this hierarchy is a less-known notion of cyclic approximate periodic transformations [see, e.g., I. Cornfield, S. Fomin, and Y. Sinai, Ergodic theory (Springer-Verlag New York, 1982)], which maps any "ergodic... more
Ergodic theory provides a rigorous mathematical description of classical dynamical systems, including a formal definition of the ergodic hierarchy consisting of merely ergodic, weakly-, strongly-, and K-mixing systems. Closely related to this hierarchy is a less-known notion of cyclic approximate periodic transformations [see, e.g., I. Cornfield, S. Fomin, and Y. Sinai, Ergodic theory (Springer-Verlag New York, 1982)], which maps any "ergodic" dynamical system to a cyclic permutation on a circle and arguably represents the most elementary notion of ergodicity. This paper shows that cyclic ergodicity generalizes to quantum dynamical systems, which is proposed here as the basic rigorous definition of quantum ergodicity. It implies the ability to construct an orthonormal basis, where quantum dynamics transports an initial basis vector to all other basis vectors one by one, while minimizing the error in the overlap between the time-evolved initial state and a given basis state with a certain precision. It is proven that the basis, optimizing the error over all cyclic permutations, is obtained via the discrete Fourier transform of the energy eigenstates. This relates quantum cyclic ergodicity to level statistics. We then show that Wigner-Dyson level statistics implies quantum cyclic ergodicity, but that the reverse is not necessarily true. For the latter, we study an irrational flow on a 2D torus and argue that both classical and quantum flows are cyclic ergodic, while the level statistics is non-universal. We use the cyclic construction to motivate a quantum ergodic hierarchy of operators and argue that under the additional assumption of Poincare recurrences, cyclic ergodicity is a necessary condition for such operators to satisfy eigenstate thermalization. This work provides a general framework for transplanting some rigorous results of ergodic theory to quantum dynamical systems.
less
By: Bloch et al
A new paradigm for materials design emerges when a concerted interaction between strongly correlated materials, photons and phonons is established. Here we present some new avenues for the design and control of materials in and out of equilibrium by exploring the formation of strongly hybridized light-matter hybrids that lead the relation of fundamentally new materials functionalities.
A new paradigm for materials design emerges when a concerted interaction between strongly correlated materials, photons and phonons is established. Here we present some new avenues for the design and control of materials in and out of equilibrium by exploring the formation of strongly hybridized light-matter hybrids that lead the relation of fundamentally new materials functionalities. less