Machine-learning surrogates in computational science often require not only accurate predictions but also expectations, variances, conserved integrals, and normalization constants. Conventional neural networks, including Kolmogorov--Arnold networks (KANs), generally evaluate these quantities through Monte Carlo sampling or multidimensional quadrature, making repeated inference costly, particularly in high dimensions. We introduce KANs with Tractable Operators for Uncertainty and Constraints (TOUCKANs), whose finite-degree polynomial outer functions yield a decomposable sum--product representation. Under factorizing input measures, expectations and higher moments then reduce algebraically to deterministic recursions over one-dimensional leaf integrals. Independent and shared inner-block variants form a parameter-efficiency hierarchy, and a universal-approximation proof for its most restricted member extends to the complete class. The same deterministic operators allow conserved integrals and normalization to be imposed throughout training. Across uniform and Gaussian benchmarks through 50 dimensions, deterministic mean and variance errors remained below the median fixed-budget Monte Carlo errors in every case. TOUCKANs also conserved Cahn--Hilliard mass to machine precision and imposed normalization and orthogonality through deterministic moments, enabling joint computation of the lowest four Schrödinger eigenpairs in two, three, and five dimensions. TOUCKANs therefore connect KAN approximation with tractable probabilistic circuits, making statistical operators and integral constraints directly available within an expressive neural surrogate. less

The unique underground location of the Einstein Telescope (ET) is expected to substantially suppress seismic and gravity-gradient noise, providing a favorable environment for gravitational-wave detection at low frequencies compared with surface-based observatories. The baseline ET design aims to achieve broadband sensitivity through a xylophone configuration, in which separate cryogenic and room-temperature interferometers are optimised for low- and high-frequency gravitational-wave detection. However, achieving the target low-frequency sensitivity introduces substantial technical complexity caused by vertical suspension thermal noise, vibrations of the cryocooler, and detuned optical configuration. In this paper, we demonstrate an alternative, entirely room-temperature, fully resonant, single-interferometer architecture that addresses these challenges and achieves broadband sensitivity superior to that of the conventional ET xylophone configuration. Using mature fused-silica suspension technology, recent advances in optical coatings, and novel inertial isolation, we show that 4-m-long fused-silica fibres can meet the required suspension thermal-noise performance. We further demonstrate that vibrations, optical rigidity, and quantum back-action noise can be controlled through appropriate design of the interferometer, test mass suspensions, optical seismometers, and quantum states. less

Next-generation gravitational-wave detectors, such as LISA, the Einstein Telescope, and Cosmic Explorer, will require accurate and efficient models of long-lived, eccentric black-hole binary signals. In previous work, we reduced the cost of evolving nonspinning eccentric effective-one-body dynamics by recasting the equations of motion in terms of osculating orbital elements and applying near-identity averaging transformations to remove the fast orbital-timescale structure during the inspiral. However, the parametrization in terms of the eccentricity and relativistic anomaly becomes singular in the circular-orbit limit, excluding quasicircular binaries and the late stages of eccentric inspirals. Moreover, the cost of generating the waveform from the averaged dynamics limited the overall speed-up to a factor of $1.5-8$. In this work, we replace the eccentricity and relativistic anomaly by the Cartesian components of the eccentricity vector, in which the averaged equations are regular for all eccentricities $0 \leq e < 1$. We also decompose the waveform modes into radial harmonics whose coefficients are tabulated as functions of the averaged variables, so that the waveform is assembled directly on the output time grid at a fixed cost per sample. We validate the method against the full effective-one-body evolution across the parameter space of binaries observable by ground-based detectors, now including circular orbits. At second postadiabatic order, the waveforms reach median mismatches of $\sim 10^{-8}$ with a maximum of $1.1 \times 10^{-5}$, while achieving speed-ups of $3-100 \times$ on a single core or up to $300 \times$ on eight cores against the serial EOB waveform. Given the speed-ups demonstrated here, we plan to apply these techniques to state-of-the-art SEOBNR models in future work. less

We prove a conjecture of Yu, Lai, and Oh: their rounded family of strengthened quantum Hamming bounds, which interpolates between Hamming-type bounds and the Singleton bound, holds for arbitrary exact quantum subspaces of dimension $K>1$. The result covers every integer local dimension $p\ge2$, every integer $t\ge1$, both distances $2t+1$ and $2t+2$, and every interpolation parameter $e\in\{0,\ldots,t\}$. Yu, Lai, and Oh proved these bounds for pure codes and for general codes of distance three or four; the case $e=0$ contains the ordinary quantum Hamming bound for general codes, recently proved by Zhang and Chen. More generally, for $p\ge3$, we prove the inequality $Kf(0)\le p^n\mathbb{E}f(X)$, where $X\sim\operatorname{Bin}(n,1-p^{-2})$, for every real polynomial $f$ of degree at most $D$, with $2\le D<d$, that is nonnegative on $\{0,\ldots,n\}$ and positive at zero; here $n$ and $d$ are the code length and distance. less

One of the major challenges of modern foundational physics is the combination of quantum physics and general relativity into a theory of quantum gravity. A severe obstacle are the required extremely high energy scales for direct tests of quantum gravity effects. In recent years, attention has shifted towards near-future experimental predictions of effective or phenomenological models, such as gravitationally induced entanglement or interactions of linearized gravity with non-relativistic measurement devices. These developments motivate us to study the coupling between the quantized metric perturbation and an anisotropic quantum rigid rotor. The intuitive motivation for our study is that a sufficiently heavy rotor consists of a very large number of component systems. Although quantum gravitational effects are completely negligible at the scale of a single atom or molecule, the effects can get amplified by the sheer number of constituents. The resulting effective model describes the gravitational analogue of the angulon quasiparticle excitations discussed in condensed matter physics, suggesting a pathway for future analogue experiments. As a first concrete test of our model, we derive the gravitational Lamb shift for the energy eigenstates of the rotor, which become dressed by a cloud of virtual gravitons. Although the effect is very small, it could provide a concrete test for whether gravity is truly quantum. less

A core mission of gravitational-wave astronomy is to test general relativity (GR) in the high-curvature, high-velocity regime. The field has already seen significant progress in this space, though a remaining challenge is how to combine data from a population of binary mergers. This can both boost the significance of potential GR violations, and develop a phenomenological picture of how deviations manifest in different mergers. We propose a framework to coherently combine gravitational-wave measurements to build a population-level test of physics beyond GR. We assume that deviations from GR are (i) strongest near the merger, (ii) vary smoothly with the total mass of the binary, and (iii) are most prominent in the $\ell=|m|=2$ mode. While these assumptions do not describe every possible deviation of GR, they provide us with a plausible starting point upon which a more general framework can be built. We apply our framework to 28 high signal-to-noise ratio binary black hole mergers from LIGO-Virgo-KAGRA's Fifth Gravitational-Wave Transient Catalog, finding no evidence for deviations from GR. Our framework allows one to show how deviations could vary as a function of total mass of the system. We argue that such a reconstruction can be used to convincingly distinguish between systematic waveform errors and genuine GR violations. less

We show that the photograph of a Schwarzschild black hole can be written in closed form. The image plane is embedded as a plane tangent to a sphere centred on the black hole, and the map between a point source and its image point, which we call the photograph function, is treated as the analytic object. Explicit expressions are obtained for sources on the celestial sphere at infinity and for sources in the equatorial plane, without solving for the intermediate null geodesics. The construction is exact, and it makes the multivalued branch structure, the relation to the photon sphere and to the shadow boundary, and the self-similar higher-order images directly readable. less

Calderbank--Shor--Steane (CSS) codes support decoding and fault-tolerant logical operations through separate pure $X$ and pure $Z$ stabilizer checks. Generator choices and single-qubit Clifford transformations can obscure this structure. We give a deterministic polynomial-time algorithm that decides whether an arbitrary stabilizer code is locally Clifford-equivalent to a CSS code and constructs the required transformation and CSS checks whenever such a form exists. For $m$ possibly redundant generator rows on $n$ qubits, the algorithm uses $O(mn^2+n^4)$ binary field operations. We reduce the problem to affine linear systems by characterizing local projectors that preserve the span of the binary stabilizer labels. The conversion preserves code parameters and check sparsity for quantum low-density parity-check (qLDPC) codes. We demonstrate CSS recovery and decoder reuse and resolve previously open LC-to-CSS classification questions for published code constructions. For graph states, LC-to-CSS equivalence corresponds to the existence of a bipartite graph in the local-complementation orbit. We derive a necessary-and-sufficient adjacency-matrix criterion for this property and construct such a graph whenever one exists. Our algorithm makes CSS decoding and fault-tolerant constructions accessible throughout the local Clifford equivalence classes of CSS codes. less

We present an error-controlled framework for the quantum simulation of non-Markovian open-system dynamics in Gaussian environments. For a system coupled linearly to a Gaussian environment with zero mean, the bath's influence on the reduced dynamics is completely determined by its two-time correlation kernel. This allows us to replace the microscopic environment with an equivalent bath that has the same kernel. On a finite simulation interval, a rank-$N$ approximation of the kernel yields an effective bath of $N$ bosonic modes with time-dependent couplings to the system. To encode these modes in qubits, we first truncate each mode to its lowest $d$ occupation levels. When stronger couplings lead to large occupations, we introduce coupling dilution, which replaces each mode with several more weakly coupled copies while preserving the bath correlation kernel. This distributes excitations across more modes and trades additional modes for smaller local dimensions. We derive explicit reduced-state error bounds and establish polynomial circuit width and depth in simulation time and inverse accuracy under stated spectral-decay and coupling-regularity assumptions, provided elementary unitaries admit polynomial-cost implementations. less

We present Pinndorama, a physics-informed neural network (PINN) code for solving the Hamiltonian constraint in the puncture formalism. The networks are trained solely on the governing equation and boundary conditions, without an analytical or perturbative guiding solution, with collocation points sampled in curvilinear coordinates. Training combines two optimization algorithms: an initial stage using adaptive moment estimation (Adam), followed by the self-scaled Broyden quasi-Newton method. We apply this approach to a spherically symmetric test problem with a known exact solution, axisymmetric binary punctures with unequal spins, and a fully three-dimensional GW150914-like configuration with unequal spins and orbital momenta. Comparisons with the NRPyElliptic solver yield relative $L^2$ errors of order $10^{-8}$ in axisymmetry and $10^{-5}$ in three dimensions. In addition, we reduce the hyperbolic-relaxation time in NRPyElliptic by a factor of approximately $4.6$ by training a parametric network that takes the puncture spin as input and provides a physics-informed initial guess to the solver. These results demonstrate that PINNs can provide accurate binary-puncture initial data and complement conventional elliptic solvers in numerical relativity. less

Black-hole perturbation theory remains remarkably accurate beyond its formal small-mass-ratio regime, but what limits this accuracy remains unclear. We develop a modular time-domain Teukolsky framework that isolates finite-mass-ratio corrections to the orbital dynamics while keeping the radiation at first perturbative order. Comparisons with numerical relativity show that the dominant source of discrepancy changes across the waveform. For nonspinning binaries, the available second-order dissipative flux removes $87\%$ of the inspiral rate discrepancy, bringing it to within $\sim1\%$ of numerical relativity. For precessing binaries, we identify a $ν^2\sin^2ι$ dependence in the inspiral time rescaling that is not explained by the leading orbit-averaged post-Newtonian terms, suggesting finite-mass-ratio corrections to precessional dynamics. Near merger, the same dissipative correction removes only $1$--$2\%$ of the discrepancy. We show instead that the merger offset is quantitatively accounted for by the difference between the initial Kerr background used in the perturbative evolution and the remnant black hole, with $96\%$ of the leading predicted frequency shift arising from the change in spin rather than mass. We release $1571$ time-domain waveforms for $348$ binaries as the Vishveshwara Catalog. less

We give a new rigorous construction of outer trapped surface formation in smooth vacuum spacetimes without symmetry assumptions. The outer trapped surface is produced by the collision of two transversely localized, nearly plane-fronted gravitational waves described by short pulse data. The outer trapped surface is obtained by joining two smooth pieces along a curve with their future-directed outer null normals matching continuously. The incompleteness of the maximal future development is then established by adapting Penrose's original argument. This construction is inspired by Penrose's argument in constructing a marginally outer trapped surface in the collision of two ultra-relativistic particles modeled by the Aichelburg--Sexl solution. less