Instrumentation and Methods for Astrophysics
FOSSIL's preliminary thermal architecture
Valentin Sauvage, Clémence de Jabrun, Anaïs Besnard et al. (+6 more)
FOSSIL (FTS fOr CMB Spectral diStortIon expLoration) is a proposed ESA M8 mission tailored to measure the spectral distortions monopole of the
Cosmic Microwave Background (CMB) with a sensitivity three orders of magnitude beyond the COBE/FIRAS legacy measurement. Achieving this sensitivity demands an extraordinarily challenging cryogenic architecture: the scientific instrument must be maintained at 4.5 K, while the detector focal plane assembly operates at 50 mK. This paper presents an overview of the preliminary thermal architecture of the FOSSIL payload, from the spacecraft service module at 293~K down to the sub-kelvin detector stage. The design draws on heritage from the Planck and ARIEL missions and relies on a staged passive cooling chain comprising a multi-layer insulation blanket, three V-groove radiators (operating at approximately 130 K, 90 K, and 50 K), and a 25 K actively cooled shield fed by an ESA-provided 4 K mechanical cryocooler. Sub-kelvin temperatures are achieved via a multi-stage adiabatic demagnetisation refrigerator (ADR) developed for NewAthena/X-IFU, providing continuous cooling at 1.8 K and 350 mK, and 50 mK with an 80% duty cycle. The Focal Plane Assembly (FPA), housing four Kinetic Inductance Detector (KID) arrays at 50 mK, is thermally isolated from the 4.5 K bench via a carbon-fibre reinforced
polymer (CFRP) hexapod with staged heat interception. We outline the staged cooling concept and show that the architecture closes with positive thermal margins at every stage; the detailed steady-state thermal budget will be presented in a forthcoming dedicated paper.
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All authors Valentin Sauvage, Clémence de Jabrun, Anaïs Besnard, Bruno Borgo, Ivan Charles, Jean-Marc Duval, Bruno Maffei, Sylvain Martin, Nabila Aghanim
Physics and Society
Beyond persuasion: Mobile electoral interfaces in polarized societies
Nuno Crokidakis and Celia Anteneodo
Many traditional models of electoral dynamics emphasize opinion change, social influence and persuasion mechanisms. In contrast, contemporary polarized societies often exhibit relatively stable partisan blocs coexisting with an electorally relevant mobile population. We propose a minimal dynamical model in which electoral competition is governed not by direct persuasion between opposing blocs, but by the dynamics and allocation of a mobile electoral interface. The electorate is partitioned into two stable partisan blocs and a mobile fraction, while direct transitions between the polarized blocs are strongly suppressed. Mobile voters are allocated between the competing blocs through a
Fermi-like probabilistic rule governed by rejection asymmetries. Analytical calculations show that the electoral susceptibility to political shocks is proportional to the stationary size of the mobile electoral interface, identifying electoral mobility as the key quantity controlling the macroscopic response of polarized systems to external perturbations. The model naturally predicts a continuum of mobility regimes, ranging from frozen polarization to highly responsive electoral states characterized by a broad mobile interface. These results suggest that, in strongly polarized elections, aggregate electoral changes may be governed primarily by fluctuations at the mobile electoral interface rather than by large-scale ideological conversion.
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Mathematical Physics
On Toeplitz determinants with slow Fourier decay
Nedialko Bradinoff and Maurice Duits
We study Toeplitz determinants $\det T_n(e^f)$ for $f$ whose
Fourier coefficients satisfy $f_k=O(|k|^{-1})$. This regime extends beyond $H^{1/2}$ and includes symbols with Fisher-Hartwig singularities. We develop an operator-theoretic approach based on the Baker-Campbell-Hausdorff formula that separates the quadratic term \[ \sum_{k=1}^{\infty}\min(k,n)f_kf_{-k} \] from the higher-order terms in the expansion of $\log\det T_n(e^{tf})$. We show that this quadratic term accounts for the possible growth with $n$, while every fixed higher-order coefficient remains bounded. For symbols with bounded positive and negative
Fourier parts, our estimates yield two-sided bounds for the determinant after removal of the quadratic contribution. For a broader admissible class, including Fisher-Hartwig-type symbols, we obtain uniform higher-order coefficient bounds and a central limit
theorem for the associated CUE linear statistics. We also obtain bounds on mixed exponential moments for CUE-derived random fields beyond the characteristic
polynomial.
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Quantum Physics
Mid-circuit ground-state cooling and ancilla readout in the $\textit{omg}$ architecture
Sean Brudney, Connor Burns, Gabriel J. Gregory et al. (+4 more)
The trapped-ion optical-metastable-ground ($\textit{omg}$) architecture for
quantum processors promises the full functionality of two-species experiments, including sympathetic cooling and non-destructive ancilla readout, without the corresponding hardware overhead. We confirm that we can cool a global motional mode of a mixed metastable-ground state Coulomb
crystal to the motional ground state via dissipative operations on the ground ($\textit{g}$)
qubit without disturbing coherence of the metastable ($\textit{m}$)
qubit. This enables
quantum logic spectroscopy to non-destructively readout the state of the $\textit{m}$
qubit using fluorescence detection of the $\textit{g}$
qubit. Extensions of these demonstrations to larger system sizes should enable the mitigation of motional heating after ion shuttling and syndrome extraction for
quantum error correction, both crucial primitives for future fault-tolerant
quantum computers based on trapped ions.
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All authors Sean Brudney, Connor Burns, Gabriel J. Gregory, Evan Ritchie, David J. Wineland, David T.C. Allcock, Jameson O'Reilly
Cosmology and Nongalactic Astrophysics
Cosmography with DESI-DR1 Cosmic Chronometers: Direct H(z) measurements from Luminous Red Galaxy ages
Carlos A. Álvarez, Marcos M. Cueli, Balakrishna S. Haridasu et al. (+6 more)
Providing robust
redshift estimates for almost 3 million luminous red
galaxies (LRGs), the Dark Energy Spectroscopic Instrument (DESI) offers a unique opportunity to test the expansion rate of the Universe with independent approaches. We apply the
cosmic chronometer method to derive new, independent constraints on the Hubble parameter at 0.3<z<1.2 from the differential age
evolution of DESI LRGs. We select spectra applying spectroscopic cuts to ensure sample purity and remove contamination by
star-forming objects, then build a robust sample of
cosmic chronometers (CCs) by stacking to obtain stable, high signal-to-noise (S/N) spectra, which also serves as a democratic binning choice for the $t-z$ plane. Ages are estimated by measuring Lick indices on the stacked spectra and fitting them with a theoretical
stellar population model. We obtain $t-z$ relations from which we derive $H(z)$ constraints via two independent approaches: a fit with a pivotal-
redshift cosmography, and a direct estimate from the original CC method. The cosmographic fit yields posteriors for the kinematic parameters $\{H_{z_0}, q_{z_0}, j_{z_0}\}$ compatible with currently considered cosmologies, giving a precision-level estimate of $H(z)$. We provide the maximum-a-posteriori (MAP) $H(z)$ estimate, an array of the median confidence region in the $H-z$ plane, and its covariance
matrix. We also leverage the
redshift distributions of the $t-z$ relation for different velocity dispersion groups to obtain two independent local measurements using the discrete approximation $H(z) \approx -\Delta z/[\Delta t (1+z)]$; the one from the reddest envelope of CCs gives $H(z \approx 0.61) = 88.5^{+6.7}_{-12.6}$ (stat.) $\pm 8.1$ (syst.) km s$^{-1}$ Mpc$^{-1}$. Systematic uncertainties for both the cosmographic and discrete $H(z)$ measurements come from a comprehensive analysis of all methodological choices in the data treatment.
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All authors Carlos A. Álvarez, Marcos M. Cueli, Balakrishna S. Haridasu, Michele Moresco, Martina Torsello, Alessandro Bressan, Lumen Boco, Luigi Danese, Andrea Lapi
Quantum Physics
Entanglement distribution and quantum storage of more than 8000 modes over a metropolitan network
Angelo Gelmini Rodriguez, Louis Nicolas, Théo Sanchez Mejia et al. (+6 more)
Entanglement generation between telecommunication
photons and matter is central to fibre-based
quantum repeaters. Achieving practical communication rates requires multiplexing, which multimode
quantum memories can provide. Rare-earth-ion ensembles offer large temporal multimode storage by exploiting the numerous spectral channels within their absorption spectrum. Here, we report on a
quantum repeater node comprised of a $^{171}$Yb$^{3+}$:Y$_2$SiO$_5$ multimode
quantum memory, featuring a 250 MHz bandwidth and a $76.6~\mu\mathrm{s}$ lifetime, and a bandwidth-matched entangled
photon-pair source. We introduce and validate a quantitative measure of the effective temporal mode capacity using a Schmidt decomposition. With this platform, we demonstrate
entanglement between a telecom
photon propagating through a 25.3 km fiber spool and a 979 nm
photon stored for $125~\mu\mathrm{s}$ across 16340 temporal modes. Finally, we report a field deployment distributing
entanglement over 5.66 km through the Geneva metropolitan fibre network while storing 8235 modes for $63~\mu\mathrm{s}$.
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All authors Angelo Gelmini Rodriguez, Louis Nicolas, Théo Sanchez Mejia, Pavel Sekatski, Nicolas Brunner, Towsif Taher, Rob Thew, Philippe Goldner, Mikael Afzelius
High Energy Physics (Theory)
Lee-Yang paradigm of phase transition in eigenstate thermalized systems
Yongjiang Xu, Weixin Sun, Chushun Tian et al. (+1 more)
As phase transitions in isolated
quantum systems remain elusive, here we show how a thermodynamic-like phase transition, falling into the Lee-Yang paradigm, can arise in systems displaying eigenstate thermalization. Specifically, we show that in
holographic conformal field theories, the eigenstate expectation of the auto-correlation function can be mapped to the partition function ${\cal Z}_{{gauge}}(z)$ of a virtual interacting instanton gas, with the conformal mapping of the imaginary time: $z=1-e^{-\tau}$ and the central charge $c$ mimicking the instanton fugacity and volume, respectively. We find that akin to the Lee-Yang paradigm, for $c\to\infty$ a pair of complex conjugate zeros of ${\cal Z}_{{gauge}}(z)$ move to the real axis located at the famous forbidden singularity. Passing through the singularity the system transits from the low- to high-fugacity phase, accompanied by dramatic changes in scaling behaviors of the free energy and dominant microscopic configurations. Our findings indicate that physics of phase transitions from eigenstate thermalization is very rich.
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All authors Yongjiang Xu, Weixin Sun, Chushun Tian, Huajia Wang
Quantum Physics
Witnessing the architecture of quantum circuits
Raphaël Mothe and Otfried Gühne
Determining whether a target
unitary can be implemented within a prescribed
quantum circuit architecture is a fundamental problem in
quantum information, with direct implications for optimisation and compilation of
quantum circuits, and hardware-efficient
quantum computation. While existing synthesis and compilation methods are primarily constructive, they generally do not provide rigorous certificates that a
unitary cannot be realised using given implementation resources. Here we introduce a general framework to define
quantum circuit architecture witnesses, which certify the incompatibility of a
unitary transformation with a specified
quantum circuit architecture. We formulate the witness construction as a semidefinite program by maximising the fidelity between the Choi state of the target
unitary and those of tested
circuits. The resulting witnesses provide practical and quantitative certificates of incompatibility, implying lower bounds on implementation resources such as the gate count or
circuit depth, and can also be used experimentally to
benchmark quantum devices by certifying that an implemented
unitary channel goes beyond the capabilities of a given
circuit architecture. For Clifford
unitaries, we exploit the stabiliser formalism to reduce the construction to linear programming, enabling both more efficient numerical certification for
circuits containing on the order of seven two-
qubit gates, and analytical witnesses for some families of architectures made of an arbitrary number of gates.
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Mathematical Physics
Exact analytical solution for the non-selfadjoint problem of Maxwell–Cattaneo–Vernotte heat conduction with heat-transfer boundary condition
Mátyás Szücs and Tamás Fülöp
The most well-known beyond-
Fourier heat conduction model, the Maxwell–Cattaneo–Vernotte equation is solved analytically in the presence of heat transfer boundary condition. In contrast to the corresponding
Fourier problem, this boundary condition renders the underlying differential operator non-selfadjoint. With a suitable scalar product, the adjoint
eigenvalue problem is established. The resulting left and right eigenfunctions constitute a biorthogonal system, allowing the expansion coefficients to be determined from arbitrary square-integrable initial conditions. This enables a convenient infinite-sum analytical solution, which is presented and thoroughly investigated for various values of the model parameters (including near-
Fourier and highly
hyperbolic regimes) and for two practically important initial conditions (
equilibrium and flash pulse initiated). The spectral structure is analyzed in detail, including the occurrence of real, imaginary, and complex-conjugate
eigenvalue roots, their asymptotic distribution, and their dependence on the dimensionless relaxation time and Biot number. We find good agreement with corresponding finite-difference numerical solutions. The comparison also illustrates the effects of spectral truncation (i.e., the Gibbs phenomenon) and numerical dissipation near propagating thermal-wave fronts. Completeness of the eigenfunction set is numerically demonstrated. The initial condition induced by the flash pulse is derived analytically. The results provide an analytical
benchmark for non-selfadjoint
hyperbolic heat conduction, unveil how boundary heat transfer and relaxation time influence the transition between
Fourier-like
diffusion and thermal-wave propagation, and open the possibility to find and investigate beyond-
Fourier heat conduction via heat transfer in experiments and practical applications.
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Earth and Planetary Astrophysics
A Radon Transform Perspective on Exoplanet Transits
Shotaro Tada
Transit light curves are usually analyzed under the assumption that the transiting
planet has a circular sky-projected silhouette. However, planetary rotation, tides, rings, or atmospheric inhomogeneities can produce non-circular silhouettes. This raises the question of what information transit light curves can provide about the underlying two-dimensional attenuation map. In this paper, we show that, in a simple and transparent limit, the time derivative of the transit light curve during ingress or egress can be interpreted as a Radon-transform measurement of the planetary attenuation map, with the projection direction set by the local normal to the
stellar limb. This viewpoint makes the information content of a single transit clear. Ingress and egress provide at most two projection angles, so the data constrain the
Fourier transform of the attenuation map only along at most two radial slices, leaving a large null space. Physical constraints on the attenuation values and shape priors can reduce the range of viable solutions, but non-uniqueness generally remains. We further examine how realistic effects modify this picture. In particular, small
stellar-limb
curvature introduces weak sensitivity to transverse
Fourier-space structure around the ideal slices, a sensitivity that is absent in the strict Radon-transform limit. These results provide a framework for understanding what transit light curves can and cannot reveal about non-circular planetary silhouettes.
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Quantum Physics
Controlled dynamics of a multi-component discrete-time quantum walker
Vikash Mittal and Tomasz Sowiński
We investigate a discrete-time
quantum walk of a three-component
quantum particle on a one-dimensional
lattice. As coin operators, we employ parameterized rotations generated by the Gell-Mann
matrices, which enable systematic tuning of the couplings between the internal components. We analyze how these couplings influence and control the dynamics by systematically exploring the position-space probability distribution across a broad region of the parameter space. To quantify the impact of different inter-component couplings, we further examine the ratio of the mean position to the variance in each half of the
lattice. Our results indicates that the system supports a rich variety of transport regimes, ranging from nearly symmetric, rapidly spreading walks to strongly anisotropic dynamics with partial localization. This framework thus provides a new avenue for engineering targeted spreading and trapping behavior in multicomponent discrete-time
quantum walks.
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Earth and Planetary Astrophysics
The atmospheric vertical structure of Uranus and Neptune from thermochemical models: the impact of model assumptions
Thomas Douçot, Ravit Helled, Daniel Kitzmann et al. (+2 more)
The composition and temperature-pressure profile of the atmospheres of Uranus and Neptune are not well-determined. As observational data are limited, we often rely on chemical
equilibrium computations to infer atmospheric abundances and cloud formation. The inferred atmospheric structures, however, strongly depend on several fundamental assumptions such as the elemental abundances and ratios, the condensation properties of the assumed species, or a reference temperature for the adiabatic structure. In this study we investigate the effects of different
metallicities (1 to 80
solar), element ratios (C/O and S/N, from 0.1 to 2 and 0.19 to 1.6) and 1 bar temperatures (66 to 86 K) on the vertical structure of ice
giant atmospheres. In particular, we use the chemical
equilibrium code FastChem to derive mixing ratios and cloud structures for CH$_4$, NH$_3$, H$_2$S, H$_2$O and NH$_4$SH. We find that the models are very sensitive to the assumed parameters, yielding drastically different possible atmospheric structures. For the cases considered here, we find that mixing ratios and cloud deck altitudes can vary by more than an order of magnitude. Additionally, thermal profiles can differ by several tens of kelvins due to composition and 1-bar temperature. We advise that future ground-based observations and a dedicated mission to Uranus and/or Neptune are required to better characterize the atmospheric structure and composition of ice
giants.
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All authors Thomas Douçot, Ravit Helled, Daniel Kitzmann, Ricardo Hueso, Audrey Vorburger
High Energy Physics (Theory)
Single-Variable Solutions in Supergravity
W. A. Sabra and R. Slim
We construct four families of spacetime metrics depending on a single variable for a broad class of $D$-dimensional gravitational theories coupled to scalar and Abelian gauge fields. As applications of the general formalism, we derive one-variable solutions of ungauged $\mathcal{N}=2$, $D=4$ supergravity coupled to vector multiplets. We also obtain explicit solutions for a consistent truncation of $\mathcal{N}=8$, $D=4$ supergravity, as well as for theories whose scalar fields parametrize the symmetric coset
manifolds $SL(N,\mathbb{R})/SO(N,\mathbb{R})$. In all cases, the geometry of the scalar
manifold plays a central role in determining the structure of the resulting solutions with nontrivial scalar and gauge field configurations.
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Cosmology and Nongalactic Astrophysics
Forecast for the detectability of patchy hydrogen reionization in WEAVE-QSO measurements of the Lyman-$\alpha$ forest power spectrum at redshift $z \geq 4$
Ke Ma, James S. Bolton, Vid Iršič et al. (+9 more)
We present the first detailed forecasts for the detectability of patchy hydrogen reionization in the one-dimensional Ly$\alpha$ forest power spectrum to be measured by the WEAVE-QSO survey. Using the Sherwood-relics reionization simulations and a WEAVE-QSO survey configuration, we generate mock spectra in four
redshift bins, $z=4.0,4.2,4.4,$ and $4.6$, in which relic ionization and temperature fluctuations from patchy hydrogen reionization enhance the Ly$\alpha$ forest power spectrum on large scales (i.e., at wavenumber $k\sim 10^{-3},\mathrm{s\,km^{-1}}$). Our Ly$\alpha$ forest pipeline forecasts the power spectrum covariance by considering sample size, spectral resolution, noise subtraction, continuum placement, metal contamination, and damping wings from high-column density absorbers. Applying our covariance forecast within a
Bayesian parameter inference framework, we find that the signature of patchy hydrogen reionization should be detectable at a significance of $\simeq 4.5\sigma$. The forthcoming WEAVE-QSO 1D power spectrum measurements should therefore be able to directly detect and characterize the large-scale relic imprint of patchy hydrogen reionization in the Ly$\alpha$ forest power spectrum at $z\geq 4$.
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All authors Ke Ma, James S. Bolton, Vid Iršič, Prakash Gaikwad, Matthew M. Pieri, Trystyn A. M. Berg, Rajeshwari Dutta, Matteo Fossati, Michele Fumagalli, Emanuel Gafton, Ignasi Pérez Ràfols, Francesco Pistis
Strongly Correlated Electrons
Accelerating a Strong-Coupling Non-Equilibrium Steady-State Impurity Solver using (Quantics) Tensor Trains
Bastian Schindler and Martin Eckstein
Including higher order diagrammatic corrections to the strong-coupling expansion is mainly limited by the evaluation of high-dimensional, time-ordered integrals. In this work we present and compare four different parametrizations of the integrands in order to obtain a low-rank (quantics) tensor-train representation using tensor cross interpolation. Particular emphasis is placed on a quantics time-difference formulation in which the required retarded convolutions are performed directly in quantics tensor-train form. Using controlled Gaussian
benchmarks, we analyze the accuracy, bond dimensions, and computational scaling of the different approaches. We then validate the most promising formulations in self-consistent
equilibrium and nonequilibrium DMFT calculations and demonstrate calculations up to the third order in the strong-coupling expansion. Finally, we extend the solver to
impurity models with retarded density-density interactions and apply it within nonequilibrium extended DMFT. Our results show that tensor cross interpolation substantially reduces the cost of evaluating higher-order diagrams and provides a controlled, systematically improvable framework for nonequilibrium
quantum impurity calculations.
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High Energy Physics (Phenomenology)
Decay widths of radially excited vector mesons of the $U(3)$ nonet with production of three pseudoscalar mesons in the extended NJL model
M. K. Volkov, A. A. Pivovarov and K. Nurlan
In the extended NJL model, the decays of the first radially excited vector
mesons $\rho'$,$\omega'$, $\phi'$ and ${K^*}'$ with production of $3P$, where $P=K,\pi,\eta$ are calculated. The box channels and the channels with intermediate vector
mesons in the ground and first radially excited states are considered. The obtained results can be considered as predictions for future experiments.
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Fluid Dynamics · Cross-listed from math.AP
Uniformly Rotating Vortex Patches with 90-Degree Corners
De Huang, Jiajun Tong and Xiaopeng Zheng
For the 2-D incompressible Euler equation, we prove the existence of $m$-fold symmetric uniformly rotating
vortex patches with 90-degree corners for all $m\geq 12$. Properties of these patches and the induced stationary flows in the co-rotating frame are characterized. Our construction is based on a novel fixed-point method.
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Optics
Micro- and nanoscale focusing across the XUV range of the ASTRID2 light source with a capillary optic
Alfred J. H. Jones, Zhihao Jiang, Asger Petersen et al. (+5 more)
Focusing of synchrotron light across extreme ultraviolet (XUV) and soft X-ray regimes is increasingly desired for photoemission-based techniques where reduced beam width gives access to smaller samples such as microscopic single
crystals and functioning two-dimensional (2D)
heterostructures and devices. Many existing focusing methods, however, are not able to take full advantage of the synchrotron beam due to limited
photon energy range or low transmission. Modern capillary optics have enabled achromatic, high transmission focusing of XUV and X-ray light. Here, we present a detailed characterisation of such an achromatic capillary optic installed at the AU-SGM4 beamline for spatial- and angle-resolved photoemission spectroscopy (ARPES) experiments at the ASTRID2 light source. The transmission of the capillary as a function of
photon energy is given, and the dependence of the beam width, position, and transmission are measured against the source size. Analysis of the far-field image of the beam allows for slope errors on the inner surface of the capillary to be overcome by selectively aperturing the beam, resulting in a minimum beam width of 900 nm measured in a photoemission geometry.
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All authors Alfred J. H. Jones, Zhihao Jiang, Asger Petersen, Søren V. Hoffmann, Nykola C. Jones, Philip Hofmann, Jill A. Miwa, Søren Ulstrup
Computational Physics
Using Diffusion Models to Estimate Uncertainties in Analytic Continuation
Sagi Meir, Daniel Freedman and Barak Hirshberg
Inverse problems are ubiquitous in physics, chemistry, and engineering, arising when reconstructing hidden quantities from indirect measurements. A key example is the analytic continuation of imaginary-time correlation functions (iTCFs) to the real-frequency domain. This process requires an inverse Laplace transform, which is inherently ill-posed and highly sensitive to small input variations. Recent neural network (NN)-based methods have shown promising results by learning mappings from imaginary-time to real-frequency spectra, often outperforming traditional techniques such as maximum
entropy. However, because the problem is ill-posed, many spectra fit the same iTCF. Regression-based approaches output a single solution, which approximates an average over the true solution space, and therefore fail to capture the full distribution of plausible power spectra. To address this issue, we introduce a
diffusion-based framework for analytic continuation that learns the distribution of spectra consistent with a given iTCF. It offers two key advantages. First, it quantifies uncertainty directly from the learned distribution. Second, by analyzing the spread and structure of this distribution, we can quantitatively assess the intrinsic hardness of each inversion problem. We measure this hardness with a new metric, the uncertainty pseudo-volume. Applying the framework to an iTCF from a path-integral molecular dynamics simulation of
liquid parahydrogen, we obtain the self-
diffusion coefficient with an error bar and flag a secondary high-frequency peak as a possible spurious artifact. In contrast to previous attempts at uncertainty quantification, our generative approach rests on a concrete probabilistic basis, providing a more theoretically grounded measure of confidence in the reconstructed power spectra.
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High Energy Physics (Theory)
Exact Evaluation of Lattice-Regularized Scalar Field Vacuum Amplitude via Site Permutations
Vadim Asnin
A novel approach to a computation of
vacuum amplitude for a single scalar field in any number of dimensions with arbitrary potential on a
lattice is proposed. The computation involves symmetrization of kinetic exponential factor in the path integral over all permutations of
lattice sites and Waring decomposition of the symmetrized expression.
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Mathematical Physics · Cross-listed from math.AP
Semiglobal uniqueness for the Lorentzian Calderón problem
Lauri Oksanen, Rakesh and Mikko Salo
We prove uniqueness in the Lorentzian Calderón problem in a semiglobal setting, comparing a potentially large perturbation of the Minkowski metric against a small one. Our proof uses a reduced amount of data, solving a formally determined version of the problem. In contrast to traditional approaches, it employs neither control-theoretic arguments nor a reduction to a
geometric inverse problem via microlocal methods or high-frequency solutions. Instead, it relies on distorted plane waves and weighted $L^2$-estimates.
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Strongly Correlated Electrons
Magnetism in antiperovskite (Li$_2$M)ChO (M = Fe, Mn, Co; Ch = S, Se) diluted magnets with fixed 1/3 filling: the key role of magnetic anisotropy
Jieyuan Zheng, Frederik L. Carstens, Lennart Singer et al. (+7 more)
We report the
magnetic properties of a series of lithium-rich antiperovskites (Li$_2M$)$Ch$O ($M$ = Fe, Co, Mn and $Ch$ = Se, S) where transition metal and lithium ions are randomly distributed on the X-sites of the X$_3$BA structure, thereby forming a strongly diluted
magnetic sublattice. Our study hence enables us to investigate the
evolution of
magnetic order at fixed 1/3-filling – which is in the vicinity but slightly above the percolation threshold – upon variation of the
spin size, the
magnetic anisotropy, and the orbital configuration. The data imply the absence of a distinct Curie-Weiss behavior up to 350~K but show rather large and weakly temperature-dependent
magnetic susceptibility. We observe clear signatures of long-range
antiferromagnetic order evolving in the 1/3-filled and strongly diluted
magnetic X-site
lattice with increasing Néel temperatures from $T_{\rm{N}}\simeq 30$~K in (Li$_2$Mn)$Ch$O to $\simeq 50$~K in (Li$_2$Fe)$Ch$O and $70-90$~K in (Li$_2$Co)$Ch$O. Except for $M$ = Co, the chalcogenide has no sizable effect on $T_{\rm N}$. We conclude significant
magnetic coupling and short-range
magnetic correlations at well above $T_{\rm N}$ which is in line with the observation of a broad electron
spin resonance signal at room temperature. The actual ordering temperatures are strongly diminished by
magnetic dilution. While structural parameters such as the tolerance factor and bonding angles do not strongly affect $T_{\rm N}$, a key parameter is the
magnetic anisotropy of the transition metals.
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All authors Jieyuan Zheng, Frederik L. Carstens, Lennart Singer, Mohammed A.A. Mohamed, Luca Bischof, Alexey Alfonsov, Jan Arneth, Silke Hampel, Nico Gräßler, Rüdiger Klingeler
Quantum Physics
Classical Simulation and Design Frontiers for IBM's Doped Clifford Sampling Experiment
Hidetaka Manabe, Hanfeng Gu and Feng Pan
We classically simulate the IBM doped Clifford random
circuit sampling experiment, comprising $70$
qubits, $70$ entangling layers, and $468$ inserted $T$ gates, as reported in the first version of arXiv:2607.25941. A deterministic temporal-boundary tensor network contraction approach is specifically designed to tackle such open-boundary one-dimensional brickwork
circuits with operator-Schmidt-rank-$2$ entangling gates. For an $n$-
qubit circuit of depth $d$, the resulting unsliced path evaluates an exact amplitude with contraction width $\lceil d/2\rceil$; Ratcatcher calculations certify that no smaller width is possible for the tested instances. Because one-
qubit gates are absorbed without changing the network
topology, the width and dense scheduled contraction cost are independent of their values and of the number and placement of $T$ gates. For this initial instance, its largest intermediate tensor contains $2^{35}$ complex64 entries (256 times smaller than IBM's estimation), corresponding to a tensor payload of $256$ GiB, and is distributed across eight GPUs within a node. Using 32 nodes, with eight NVIDIA H100 GPUs per node, we completed all 2051 amplitude batches corresponding to IBM's published output bitstrings in 37.3 minutes. The resulting probabilities yield a log-XEB estimate of $0.35034$ with a 95% interval of $[0.29763,0.40305]$. Under the Porter–Thomas and scrambled-noise assumptions, this is numerically compatible with IBM's fidelity lower bound; separately, fidelity-weighted resource accounting projects a 583-contraction workload with a 10.6-minute makespan on the same 32 nodes. More broadly, the approach provides a practical diagnostic for experimental outputs and a quantitative tool for designing future doped Clifford sampling experiments.
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Quantum Physics
Controlling quantum transport by measurement-rate modulation
Jesús Casado-Pascual and Luis Octavio Castaños-Cervantes
Temporal modulation of the measurement rate provides a powerful mechanism for controlling open-system dynamics through measurement backaction. We demonstrate this mechanism in a minimal exactly solvable model of a continuously monitored
quantum particle on a switching
lattice. We derive exact analytical expressions for the long-time current under both periodic and
stochastic switching, revealing a common slow-switching limit and identifying a measurement-induced crossover between Zeno- and anti-Zeno-dominated transport regimes that controls the direction of the current.
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Instrumentation and Detectors
Scan-Coil Delay Causes Anisotropic Signal Loss in Fast 4D-STEM
Vishal Kumar, Andreas Jehle, Tizian Lorenzen et al. (+4 more)
Fast pixelated detectors are driving 4D-STEM toward microsecond dwell times, a regime in which the finite response of the scan deflection coils becomes comparable to the dwell time itself. Using direct probe imaging and sub-frame diffraction analysis, we document a significant intra-dwell scan-coil delay that systematically smears the recorded signal anisotropically along the fast scan direction, with a settling timescale of several tens of microseconds. We present a phase-correlation-based sub-frame
alignment procedure that measures and corrects this smearing, and we assess its impact on focused and defocused 4D-STEM reconstructions over a range of scan step sizes. The correction restores signal across a broad range of spatial frequencies, with the largest gains at the large step sizes required for low-dose biological imaging. Because it operates on existing data with no modification to the microscope, the method offers a practical route to recovering signal that would otherwise be lost to scan-coil delay.
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All authors Vishal Kumar, Andreas Jehle, Tizian Lorenzen, Julika Radecke, Knut Müller-Caspary, Massimo Kube, Henning Stahlberg
High Energy Physics (Theory)
Limits of the inverse scattering problem
Matvei Fedin, Kirill Gubarev and Andrey Morozov
The main goal of
tomography is the reconstruction of density function out of its line integrals (integral measurements of this density along x-ray lines). Such construction is possible and known as inverse x-ray/Radon transformations. We are interested in generalization of this problem to the case of particles. For this we need to limit the speed of these particles, otherwise the problem is reduced to the previous one. The question we discuss in this paper is how low can this speed be depending on the parameters of the studied potential. We study this problem using simple theoretical examples and Machine Learning pipeline to restore the potential.
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Quantum Physics
Formal Verification of Quantum Ancilla Safety
Jiqi Li, Jingyi Mei, Wang Fang et al. (+1 more)
Ensuring ancilla safety is a critical correctness requirement for
quantum compilation, since ancilla
qubits are routinely introduced to implement complex operations with fewer gates and reduced depth. However, formally verifying this property is computationally hard due to state-space explosion in the number of
qubits, particularly for dirty ancillae, which carry unknown initial states and must be restored after use. We propose an end-to-end verification-and-repair framework that rigorously addresses both clean and dirty ancilla safety. Our core contribution is a two-step reduction strategy: we first prove that verifying an $m$-
qubit dirty ancilla register decomposes into $2m$ independent clean ancilla safety checks; subsequently, we reduce each clean ancilla safety instance to an algebraic commutativity check against Pauli-$Z$ and Pauli-$X$ operators. This approach yields an efficient and naturally parallel verifier and enables actionable diagnosis by classifying violations into logic errors and phase errors. Leveraging this diagnosis, we further design lightweight repair routines that append local single-
qubit rotations to eliminate a broad class of local ancilla faults. We implement the full pipeline in a prototype tool using a dual-backend architecture combining decision diagrams and weighted model counting, and validate it on diverse
circuits ranging from arithmetic
benchmarks to Grover's
algorithm. Our experiments demonstrate scalability to thousands of
qubits and show that the proposed repairs effectively improve ancilla safety while preserving
circuit functionality.
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All authors Jiqi Li, Jingyi Mei, Wang Fang, Ji Guan
Disordered Systems and Neural Networks
Graph-theoretic design of lasing networks for physical vision
Paul Obernolte, Jakub Dranczewski, Yixiu Yin et al. (+10 more)
Physical neural networks perform learning through the intrinsic nonlinear dynamics of matter. Optimising their design presents a considerable challenge: complex many-body physics can provide powerful computation, but are expensive to simulate and large experimental optimisation runs are impractical to fabricate. Hence, the high-dimensional space of possible network
topologies cannot be effectively directly searched. Here, we show that this search can be efficiently performed in an abstract graph space that is vastly cheaper to explore. Using random lasing networks – composed of interconnected nanoscale waveguides and hosting strongly coupled lasing modes – as an exemplar physical
vision system, we establish a quantitative three-layer link: simple graph-theoretic metrics predict the nonlinear lasing physics, which in turn predicts
vision performance. After validating this relationship using physical simulations, we exploit it to drive an evolutionary
algorithm using graph metrics, producing network
topologies that outperform random designs at a fraction of the computational cost (3000$\times$ speed-up compared to physical simulation). On simulated image-classification tasks, graph-optimised networks substantially improve classification accuracy. As our framework operates on network
topology rather than substrate-specific physics, we anticipate it can transfer to other network-based physical learning systems, providing an efficient route for the directed design and optimisation of complex, strongly-interacting physical neural networks.
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All authors Paul Obernolte, Jakub Dranczewski, Yixiu Yin, Tobias Farchy, Wai Kit Ng, Tobias Simonsen, Elias Großhauser, Alexis Arnaudon, Robert L. Peach, Mauricio Barahona, Riccardo Sapienza, Jack C. Gartside, T. V. Raziman
Materials Science
Yingjie Wei, Fan Zhang, Ying Zhao et al. (+4 more)
Room-temperature
spin-optoelectronic devices require a combination of robust ferromagnetism and
giant exciton binding, a pairing mutually exclusive in conventional
semiconductors due to
magnetic localization that screens
excitons. Cluster-assembled V4S9X4 (X = F, Cl, Br and I) monolayers overcome this bottleneck via a hierarchical design, that is, intra-cluster localized states host both local
magnetic moments and strong electron-hole interactions, while inter-cluster coupling mediates long-range ferromagnetism. Remarkably, these two-dimensional
semiconductors exhibit intrinsic ferromagnetism with Curie temperature up to 507.6 K. As a prototype, V4S9Br4 monolayer possesses a
giant exciton binding energy of 1.85 eV. Its lowest
exciton is a dark state (DI) with a radiative lifetime of 1.20 ns, whereas the first bright
exciton (BI) exhibits an ultrafast radiative decay of 86.87 ps. This stark lifetime contrast enables simultaneous ultrafast optical response and long-lived
spin information storage. Most notably, switching between
ferromagnetic and
antiferromagnetic order allows for wide-range tuning of
exciton lifetime, with the
giant binding energy remaining nearly intact. Our findings establish cluster assembly as a powerful paradigm for designing next-generation
spin-photonic and
quantum information devices operating at room temperature.
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All authors Yingjie Wei, Fan Zhang, Ying Zhao, Lixin Zhou, Yan Su, Yu Guo, Jijun Zhao
Quantum Physics
Time-resolved correlation engineering in DLCZ Raman photon sources
Jiun-Shiuan Shiu, Chang-Wei Lin, Chi-Ming Yang et al. (+2 more)
Memory-assisted
quantum networks require
photon sources with controllable temporal and correlation properties. The Duan-Lukin-Cirac-Zoller (DLCZ) protocol provides a platform based on spontaneous Raman scattering in atomic ensembles, but a unified predictive theory connecting control parameters to correlations under realistic propagation and noise conditions remains lacking. Here we present a propagation-inclusive open-system
quantum theory that retains write-induced population redistribution while combining Heisenberg-Langevin dynamics with Maxwell-Schrödinger propagation. We experimentally validate its key predictions. The theory predicts time-dependent Stokes generation,
spin-wave
evolution, retrieved anti-Stokes wavepackets, and time-resolved cross-correlations. Experiments confirm robust correlations under
retrieval tuning and enhanced correlations for shorter write pulses, consistent with the different scaling of correlated coincidences and accidental backgrounds with the mean
spin-wave excitation number. Classically controlled
retrieval enables temporal gating and slicing of the anti-Stokes wavepacket, establishing a quantitative framework for correlation engineering in
memory-compatible DLCZ
photon sources.
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All authors Jiun-Shiuan Shiu, Chang-Wei Lin, Chi-Ming Yang, Ite A. Yu, Yong-Fan Chen