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A geometric multimessenger consistency test of radiative and near-zone gravity with LISA and SKA
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By: Bhooshan Gadre
Compact binary pulsars observed both through precision radio timing and low-frequency gravitational waves offer a direct way to compare the same binary geometry with two independent messengers. We propose a multimessenger consistency test based on the orbital inclination, measured from the Shapiro-delay shape parameter in radio timing and from the tensor polarization amplitude ratio in the gravitational-wave signal. Defining the common-epoch ... more
Compact binary pulsars observed both through precision radio timing and low-frequency gravitational waves offer a direct way to compare the same binary geometry with two independent messengers. We propose a multimessenger consistency test based on the orbital inclination, measured from the Shapiro-delay shape parameter in radio timing and from the tensor polarization amplitude ratio in the gravitational-wave signal. Defining the common-epoch residual $\eps(t_0)=s_{\rm Shapiro}(t_0)-s_{\rm GW}(t_0)$, general relativity predicts $\eps=0$, while a nonzero value would indicate either an unmodeled systematic or a mismatch between the near-zone and radiative descriptions of gravity. We estimate the attainable precision on this quantity for representative LISA--SKA compact binary pulsars using a seven-parameter timing Fisher matrix and a sky-averaged LISA sensitivity curve including the Galactic foreground. We adopt a conservative radio baseline, $σ_{\rm TOA}=1\,μ{\rm s}$ and $N_{\rm eff}=10^4$, intended to summarize radiometer noise, jitter, residual dispersion-measure and scattering effects, profile evolution, and cadence losses after wideband timing. For systems at $d=5\,{\rm kpc}$ observed for four years, we find $σ_\eps\simeq4\times10^{-3}$ for a favorable double neutron star and $σ_\eps\simeq9\times10^{-4}$ for a hypothetical pulsar--black-hole system. The former is the more robust astrophysical benchmark; the latter illustrates the reach if such a high-SNR chirping source is discovered. The useful cases remain limited mainly by gravitational-wave polarimetry, while radio timing supplies the near-zone reference measurement of the inclination. These results define a quantitative target for future joint Bayesian analyses of compact binary pulsars observed in both radio and gravitational waves. less
By: Yichen Xu, Xiao Wang
We introduce a surface-code cultivation protocol for reusable logical catalyst states that implement exact fine dyadic phase gates $Z^{2^{-b}}$ by phase kickback. The catalyst is an eigenstate of a high-period Clifford circuit $U$, with a direct construction supported on $O(2^b)$ logical qubits. Once cultivated, each invocation implements the target phase through a controlled-$U$ gadget, removing Clifford+$T$ synthesis approximation error fro... more
We introduce a surface-code cultivation protocol for reusable logical catalyst states that implement exact fine dyadic phase gates $Z^{2^{-b}}$ by phase kickback. The catalyst is an eigenstate of a high-period Clifford circuit $U$, with a direct construction supported on $O(2^b)$ logical qubits. Once cultivated, each invocation implements the target phase through a controlled-$U$ gadget, removing Clifford+$T$ synthesis approximation error from the online gate and making the online non-Clifford depth independent of the target logical accuracy. As a concrete demonstration, we construct a catalyst for $\sqrt{T}=Z^{1/8}$, where $U$ is a nine-qubit brickwork Clifford circuit and controlled-$U$ consists of eight controlled-CNOTs. Starting from nine distance-three rotated-surface-code blocks, we cultivate the catalyst through logical-$U$ checks, syndrome extraction and postselection, code growth, and complementary-gap decoding. Due to the intrinsic fault tolerance of the phase read-out, a \emph{single} verification round already reaches the leading error-corrected scaling, in contrast to the repeated logical checks required when cultivating single-qubit magic states. A hybrid tensor-network and stabilizer simulation shows that, at physical error rate $p=10^{-3}$, the postselected catalyst can be grown to distance-seven rotated-surface-code blocks with logical leakage rate $\sim 10^{-6}$ using around seven expected attempts, and can be suppressed further with stronger postselection. Compared with existing protocols, our approach trades offline, phase-specific catalyst cultivation for exactness, reusability, and constant-depth online implementation of fixed fine dyadic phases in codes with restricted transversal gate sets. less
By: Benjamin F. Schiffer, Christopher Monroe, Peter Zoller, J. Ignacio Cirac
We propose a quantum computer architecture based on ions confined in optical tweezer arrays, combining the long coherence times of trapped-ion qubits with the reconfigurability and parallel operation enabled by tweezer platforms. Selected ions are transported to local interaction zones, where excitation to an auxiliary state with a displaced optical potential generates a controllable effective electric dipole. We develop and analyze entanglin... more
We propose a quantum computer architecture based on ions confined in optical tweezer arrays, combining the long coherence times of trapped-ion qubits with the reconfigurability and parallel operation enabled by tweezer platforms. Selected ions are transported to local interaction zones, where excitation to an auxiliary state with a displaced optical potential generates a controllable effective electric dipole. We develop and analyze entangling-gate mechanisms mediated by the Coulomb interaction between such effective dipoles, and show that they enable precise, temperature-robust closure of the center-of-mass and relative motional trajectories, leaving no residual entanglement between the qubits and the motion. We further outline a concrete implementation with barium ions based on state-selective polarizability, and study the suppression of cross-talk during parallel gate execution, with relevance to transversal gates in quantum error correction. Our results thereby establish a realistic route toward scalable ion-tweezer quantum processors. less
By: YingYe Huang, Wentao Chen, Guoyu Zou, Xuan Fan, Jing-Ning Zhang, Kihwan Kim
Trapped-ion systems have emerged as a leading platform for scalable quantum information processing owing to their high-fidelity operations and long-range entangling capabilities. As the number of ions in a trap increases, the growing density of collective motional modes makes the synthesis of multimode entangling gates increasingly challenging. Designing large-scale gates requires simultaneously realizing the desired spin-spin interactions, s... more
Trapped-ion systems have emerged as a leading platform for scalable quantum information processing owing to their high-fidelity operations and long-range entangling capabilities. As the number of ions in a trap increases, the growing density of collective motional modes makes the synthesis of multimode entangling gates increasingly challenging. Designing large-scale gates requires simultaneously realizing the desired spin-spin interactions, suppressing residual spin-motion entanglement, and limiting experimental control resources, leading to a high-dimensional non-convex optimization problem. Here we develop a numerical framework for multi-tone gate synthesis that directly searches for control fields satisfying these competing requirements. By employing an alternating-minimization strategy, the framework improves numerical stability and remains effective for large systems with many motional modes and target interactions. As representative demonstrations, we synthesize gates implementing all-to-all and nearest-neighbor interaction patterns in ion chains of up to N = 1000, using only global laser control. Across the parameter regimes explored here, the control resources required to maintain high-fidelity interactions do not exhibit rapid growth with system size. We extend the framework to individual addressing using a structured qLDPC target at N = 512 as an example. These results identify multimode gate synthesis as a viable route toward programmable interaction engineering in large-scale trapped-ion quantum processors. less
Time-domain evolution of Lorenz-gauge metric perturbations: taming the $\ell=m=1$ gauge instability
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By: Jonathan Thornburg
Calculating the spacetime metric perturbation (MP) sourced by a small "particle" of mass $μM$ (with $0 < μ\ll 1$) moving in a Schwarzschild or Kerr "background" black hole spacetime of mass $M$ is a longstanding research area in general relativity. This calculation also has an important astrophysical motivation as a major step in calculating the gravitational waves emitted by an extreme-mass-ratio inspiral system. Here I consider the specific... more
Calculating the spacetime metric perturbation (MP) sourced by a small "particle" of mass $μM$ (with $0 < μ\ll 1$) moving in a Schwarzschild or Kerr "background" black hole spacetime of mass $M$ is a longstanding research area in general relativity. This calculation also has an important astrophysical motivation as a major step in calculating the gravitational waves emitted by an extreme-mass-ratio inspiral system. Here I consider the specific problem of the time-domain calculation of the $\mathcal{O}(μ)$ Lorenz-gauge MP $h_{ab}$ sourced by the particle. Decomposing the Schwarzschild-background MP into $e^{imφ}$ modes, Dolan and Barack [Phys. Rev. D 87, 084066 (2013), arXiv:1211.4586] found that the $m=1$ time-domain Lorenz-gauge MP generically contains an \emph{unstable gauge mode} which grows linearly with time. Here I demonstrate a method for computing a Lorenz-gauge time-domain evolution which is mostly free of this gauge mode. This method computes an "orthogonalized" MP $h_{ab}^\text{ortho}$ as a linear combination of the sourced MP and a homogeneous MP $h_{ab}^\text{hom}$ (evolved in parallel with the sourced MP). The linear combination is updated "occasionally" to make $h_{ab}^\text{ortho}$ orthogonal to $h_{ab}^\text{hom}$ with respect to a chosen inner product on MPs. I show that, for a Schwarzschild-circular-orbit test case, the resulting $h_{ab}^\text{ortho}$ satisfies the $\mathcal{O}(μ)$ Einstein equations and Lorenz gauge conditions, remains bounded as $t \to \infty$, and at late (finite) times contains only a small component of the unstable gauge mode. These results hold both with the particle modelled via MP jump conditions and with particle modelled by a "effective source". My numerical code for obtaining all of these results is included with this paper, and will be deposited in the Black Hole Perturbation Toolkit. less
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By: Bo-Xuan Ge
We investigate whether gravitational waveforms from massive boson-star mergers can be used to diagnose the underlying merger outcome. Using an existing numerical-relativity catalogue, we construct a branch-conditioned neural reconstruction model and infer the outcome by comparing the reconstruction quality of candidate waveform hypotheses. This makes the diagnosis waveform-based rather than a direct classification in the initial parameter spa... more
We investigate whether gravitational waveforms from massive boson-star mergers can be used to diagnose the underlying merger outcome. Using an existing numerical-relativity catalogue, we construct a branch-conditioned neural reconstruction model and infer the outcome by comparing the reconstruction quality of candidate waveform hypotheses. This makes the diagnosis waveform-based rather than a direct classification in the initial parameter space. We compare a supervised baseline model with a distilled student model and find that the merger outcome is encoded in the waveform morphology and can be recovered through branch-conditioned reconstruction. Our results provide a first step toward waveform-based classification of exotic compact-object mergers with multiple possible final states. less
By: Geoffrey Compère, Sébastien Robert
Under assumptions compatible with generic gravitational scattering, the vacuum relativistic gravitational field is entirely determined at leading order in the large radius expansion at spatial infinity by its supermomentum, its dual supermomentum and its global supertranslation frame. At subleading order, the gravitational field is determined by three additional sets of charges: the super-Lorentz charges, the leading tail charges and the lead... more
Under assumptions compatible with generic gravitational scattering, the vacuum relativistic gravitational field is entirely determined at leading order in the large radius expansion at spatial infinity by its supermomentum, its dual supermomentum and its global supertranslation frame. At subleading order, the gravitational field is determined by three additional sets of charges: the super-Lorentz charges, the leading tail charges and the leading peeling-breaking charges. In this work we provide a supertranslation-invariant definition of these charges in terms of asymptotic Bondi-Sachs fields as well as a corresponding supertranslation and logarithmic translation invariant definition of these charges in terms of Beig-Schmidt fields. Using the properties of homogeneous and inhomogeneous solutions to relevant wave equations over the boundary de Sitter spacetime at spatial infinity, we derive the conservation law of super-Lorentz charges between the future and past of spatial infinity. We obtain that the super-Lorentz aspects are non-locally defined from the Bondi-Sachs fields. less
By: Nicola Bellomo, Philippa Cole
The Square Kilometre Array Observatory (SKAO) will be an important component of the global gravitational wave network. This article provides an overview of chapter eight of the Advancing Astrophysics with the SKA II (AASKAII) book, in which gravitational waves are a new addition, since the previous edition preceded the announcement of the first detection of gravitational waves in 2016. The chapter investigates the impact that this new observa... more
The Square Kilometre Array Observatory (SKAO) will be an important component of the global gravitational wave network. This article provides an overview of chapter eight of the Advancing Astrophysics with the SKA II (AASKAII) book, in which gravitational waves are a new addition, since the previous edition preceded the announcement of the first detection of gravitational waves in 2016. The chapter investigates the impact that this new observatory will have on numerous gravitational wave science cases. From testing General Relativity, to measuring the properties of the nanohertz gravitational wave background and exploiting new synergies with other upcoming experiments, the SKAO will play a key role in the next decades of gravitational wave science. less
By: Naoki Seto
We present a framework to probe intrinsic stochastic fluctuation in the orbital phase evolution of long-lived double white dwarf binaries through gravitational-wave observations with LISA. To capture the essential structure of the fluctuation, we introduce a minimal quadratic statistic that isolates its temporal correlation. We derive a simple analytic scaling relation for the signal-to-noise ratio of this correlation statistic, explicitly sh... more
We present a framework to probe intrinsic stochastic fluctuation in the orbital phase evolution of long-lived double white dwarf binaries through gravitational-wave observations with LISA. To capture the essential structure of the fluctuation, we introduce a minimal quadratic statistic that isolates its temporal correlation. We derive a simple analytic scaling relation for the signal-to-noise ratio of this correlation statistic, explicitly showing its dependence on the total observation time and the intrinsic phase correlation time. less
By: Christos Charmousis, Simon Iteanu, David Langlois, Karim Noui
We study radial perturbations of static black holes with primary hair in a subfamily of degenerate higher-order scalar-tensor (DHOST) theories. We recast the equation of motion for the monopole degree of freedom into a flat radial wave equation and show that the associated operator can be extended, through appropriate boundary conditions, to a positive self-adjoint operator which ensures the stability of the radial mode. Remarkably, the coord... more
We study radial perturbations of static black holes with primary hair in a subfamily of degenerate higher-order scalar-tensor (DHOST) theories. We recast the equation of motion for the monopole degree of freedom into a flat radial wave equation and show that the associated operator can be extended, through appropriate boundary conditions, to a positive self-adjoint operator which ensures the stability of the radial mode. Remarkably, the coordinate choice that leads to the flat wave equation corresponds to the unitary gauge, in which the scalar field is uniform. As a result, the radial coordinate extends beyond the event horizon, into the black hole interior, in contrast with the tortoise coordinate in General Relativity. The same wave equation with the same coordinate choice applies to all solutions that are connected by disformal transformations. We also examine stealth black hole solutions, with either a constant or non constant kinetic term. In the former case, we find, to linear order, the absence of a propagating degree of freedom. In the latter case, we identify a stable radial degree of freedom, except for special values of the theory coupling constants. less
By: Aishwarya Majumdar, John M. Martyn, Yuan Liu, Nathan Wiebe
Realizing coherent quantum computation requires precise and robust manipulation of quantum systems through quantum control protocols. Most quantum control techniques rely on heuristic methods for designing the driving pulses that steer the system towards a target state. Such methods are often based on brute-force optimization and offer limited understanding of the solution landscape. In contrast, quantum algorithms offer a rich body of analyt... more
Realizing coherent quantum computation requires precise and robust manipulation of quantum systems through quantum control protocols. Most quantum control techniques rely on heuristic methods for designing the driving pulses that steer the system towards a target state. Such methods are often based on brute-force optimization and offer limited understanding of the solution landscape. In contrast, quantum algorithms offer a rich body of analytical methods with rigorous error guarantees for implementing unitary and non-unitary transformations, which suggests a promising direction for developing new approaches to quantum control. Among various such algorithms, quantum signal processing (QSP) has emerged as a powerful framework for quantum algorithm design, implementation, and optimization. However, its potential for quantum control remains largely unexplored. In this work, we establish QSP-Control, an analytical framework for quantum control of qubit-oscillator dynamics. We focus on dispersively coupled qubit-oscillator systems and employ the QSP formalism to mitigate unwanted nonlinear effects arising from cross-Kerr interactions. In addition, we develop constructions for precise manipulation of Fock states by designing Fock-state-selective operators, based on structural parallels between the Jaynes-Cummings interaction and QSP. These findings demonstrate how several practically relevant problems in quantum control can be mapped to forms amenable to QSP, offering both a systematic design framework and an interpretable perspective on quantum control. less
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