Classical Physics
Lissajous-type orbits on a sphere and their non-Riemannian geometry
César Simón López-Monsalvo, Sergio Islas-Ramírez and Alberto Rubio Ponce
A charged test particle is confined to the round sphere in a uniform ambient
magnetic field. We reduce its motion to quadrature by elementary means and solve explicitly the family of trajectories which reaches the poles. On that family the azimuth advances at a constant rate and the latitude obeys a pendulum equation. The winding gained per oscillation is a complete
elliptic integral of the first kind. That integral is a strictly increasing bijection onto the positive numbers. Every positive rational winding is therefore carried by exactly one value of the half-cyclotron frequency. Then we ask which geometry has these trajectories. No affine connection has them among its geodesics. A Finsler metric of Randers type has all of them. The threshold which separates the two dynamical regimes is precisely the condition for that metric to exist. The closed trajectories are its closed geodesics. The example places a non-Riemannian geometry within reach of an upper-level undergraduate or beginning graduate course in classical mechanics. We supply the derivations, the numerical recipes and the exercises.
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High Energy Physics (Phenomenology)
A PQ-Symmetric High-Scale SUSY Interpretation of the LZ High-Energy Recoil
Wen Yin
The 248-keV
nuclear-
recoil-like event reported by LZ can be interpreted as near-threshold upscattering of 1.08-TeV thermal Higgsino dark matter. A neutral-Higgsino splitting of order $0.3$–$0.35$ MeV places the fixed weak-interaction cross section close to the observed LZ interval and implies electroweak gauginos at ${O}(10^7)$ GeV. This spectrum is compatible with
gravity-mediated high-scale supersymmetry and a Kim–Nilles Peccei–Quinn sector. Although the GUT scale is predicted to be lower than the conventional one,
proton decay is suppressed due to the high SUSY scale which also solves the conventional CP,
flavor, gravitino and
moduli problems. Indeed,
proton decay may be probed in the future. The PQ
symmetry lowers the Higgsino mass below the SUSY scale and also yields a QCD
axion that solves the strong-$CP$ problem. If the
axion and Higgsino constitute mixed dark matter, the
halo-profile-dependent H.E.S.S. limit can be relaxed.
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Plasma Physics
A novel objective function minimizes resonant trapped energetic particle losses in stellarators
John Anthony Labbate, Elizabeth J. Paul and Amelia Chambliss
Near-omnigenous stellarators are susceptible to energetic particle (EP) losses due to resonances between trapped EPs and non-omnigenous perturbations to the
magnetic field. Existing bounce-averaged objectives such as ${\Gamma}_c$, ${\Gamma}_{\delta}$ , and ${\Gamma}_{\alpha}$ target the non-resonant misalignment of drift and flux surfaces, but they do not capture resonant convective or diffusive motion. We develop a discrete map theory for the bounce points of trapped EPs in near-omnigenous fields, in which phase-space islands form due to resonance between the precession and bounce frequencies. We introduce ${\Delta}_{res}$, a differentiable, bounce-averaged objective function that penalizes the widths of these islands, promoting phase-space integrability. Optimizing a quasi-axisymmetric configuration using ${\Delta}_{res}$ combined with a two-term quasi-
symmetry objective yields a factor-of-four improvement in EP confinement by displacing low-order resonances and forming EP transport barriers. ${\Delta}_{res}$ is a powerful tool to combat both resonant convective and diffusive losses in power plant-relevant stellarators.
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Quantum Physics
Gouy Phase across PT-Symmetry Breaking in Non-Hermitian Dirac Systems
Dirlan J. C. de Morais Sousa, Lucas S. Marinho, Giandomenico Palumbo et al. (+1 more)
We study relativistic beam-like wave packets governed by a quasi-Hermitian massive Dirac
Hamiltonian and uncover anomalous Gouy-phase behavior in non-Hermitian dynamics. We show that the Gouy phase provides a sensitive probe of the global $\mathcal{PT}$-
symmetry-breaking threshold: it remains purely real in the globally unbroken, quasi-Hermitian regime, while, after crossing the exceptional point, the Gouy phase changes sign and acquires an imaginary component. At the exceptional point, the Gouy-phase variation vanishes in the small-mass limit but becomes maximal for large masses, revealing a counterintuitive crossover from effectively classical to increasingly wave-like
quantum behavior. We propose an experimental scheme to measure the components of the non-Hermitian Gouy phase in the broken regime by monitoring the attenuation of a light beam propagating through a lossy waveguide. These results highlight the potential of the non-Hermitian Gouy phase for photonic applications, including the determination of threshold conditions and the design and control of systems with gain and loss.
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All authors Dirlan J. C. de Morais Sousa, Lucas S. Marinho, Giandomenico Palumbo, Irismar G. da Paz
Mathematical Physics
Fractional oscillators with fractional damping in the presence of external forces
Fernando Olivar-Romero and Oscar Rosas-Ortiz
We investigate how a fractional oscillator reacts to external forces when the dynamic law includes a damping term that is explicitly fractional. We show that the corresponding three-parametric fractional differential equation (in the Caputo sense) admits formal solution. Two of the fractional parameters are associated with the intrinsic dissipation mechanism derived from the fractional nature of the oscillator. The third fractional parameter characterizes the damping term against which the oscillator is driven by the external force. In the absence of fractional damping, the two-parametric fractional dynamic law can be associated with the Newton-Scott-Blair model for viscoelastic materials, in which position and external force are linked to the material's strain and stress, respectively. In general, the Laplace transform of the external force defines the profile of the three-parametric solution; specific examples include the absence of external forces as well as constant, sinusoidal and stepped external forces. In the case where the three fractional parameters converge to the same value, it is observed that, under the action of a constant driving force, the system reaches a fixed position after a transient period. With a sinusoidal driving force, the system exhibits persistent oscillatory behavior. These results suggest that the external driving force strongly influences the long-term behavior of the fractionally damped oscillator.
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Computational Physics
Physics-informed Learning for Orbital Uncertainty Propagation with Error Bounds
Chun-Wei Kong, Morteza Lahijanian and Jay McMahon
The Fokker-Planck partial differential equation (FP-PDE) governs uncertainty
evolution in
stochastic dynamical systems. In orbital dynamics, solving the FP-PDE is challenging because of nonlinear motion, high-dimensional states, and large space-time domains. We develop a physics-informed neural network (PINN) approach that approximates the FP-PDE solution as a single space-time probability density, while also quantifying its worst-case approximation error. This approach is, in principle, independent of the choice of state coordinates and neural network architecture. Specifically, to enforce probability density function (PDF) properties into the neural network, we design a Physics-informed Gaussian mixture model (PINN-GMM). Then a companion error PINN learns the dynamics of the approximation error and yields time-dependent bounds that define an ambiguity set of PDFs. This ambiguity set enables rigorous computation of upper and lower bounds on event probabilities through tractable linear programs. Numerical studies on illustrative 1D examples and several 4D–6D orbital test cases demonstrate accurate uncertainty propagation, correct and informative error bounds, and improved reliability over common uncertainty-propagation baseline methods (Gaussian approximation, unscented transform, and Gaussian mixture model). Constructing the PINN-GMM requires offline training, making it costlier than the baseline approximations; once trained, however, a single forward pass returns the density at any time in sub-millisecond time $(0.16~\mathrm{ms}$ in our implementation).
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Astrophysics of Galaxies
EWOCS-IX: JWST/NIRCam observations of Westerlund 2 - Identification of candidate substellar members
V. Almendros-Abad, M.G. Guarcello, K. Muzic et al. (+26 more)
[Abridged] Investigating substellar populations in young massive clusters offers crucial insights into the formation of brown
dwarfs (BDs) and the role of environmental conditions in shaping their properties. Westerlund 2 (Wd2), as one of the nearest dense and massive clusters in the Milky Way, represents an ideal laboratory for studying the effects of high
stellar density and ionizing radiation from massive
stars on BD formation. This paper presents deep JWST/NIRCam observations of Wd2 in a large number of filters between 1.15 and 4.1 $\mu m$. Our analysis focuses on identifying and characterizing the BD population within the cluster. We carried out PSF photometry on deep JWST/NIRCam data obtained in 4 wide and 6 medium-band filters, using DOLPHOT. The resulting catalog was used to identify BD candidates in Wd2 through spectral energy distribution (SED) fitting with atmospheric models. The 50% detection limit of our NIRCam catalog is $\sim$0.015-0.02 $M_\odot$, at the distance, age, and extinction of Wd2, providing the deepest view of a supermassive
star cluster to date. We identify 353 substellar candidates. Most candidates (301) lie above the 10 Myr isochrone in the Hertzsprung–Russell diagram consistent with cluster membership, which are defined as strong candidates. Comparison with a control field indicates a contamination level of $\lesssim$5% for the strong candidate sample down to masses of $\sim$0.01–0.015~$M_\odot$. We identify 73 candidates exhibiting infrared excess indicative of circumstellar disks. These objects occupy the expected infrared-excess locus in de-reddened color diagrams and represent $27.7^{+3.4}_{-3.2}$% of the candidates detected in F410M. The resulting catalog provides a well-characterized sample for future spectroscopic confirmation and subsequent studies of the substellar population of Wd2.
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All authors V. Almendros-Abad, M.G. Guarcello, K. Muzic, A. Scholz, M. Andersen, A. Bayo, W. Best, D. Capela, M. Gennaro, A. Ginsburg, J.B. Lovell, K. Monsch, E. Moraux, L. Prisinzano, T. Rom, E. Sabbi, P. Zeidler, C. Argiroffi, R. Bonito, D. Calzetti, V. Cusimano, F. Damiani, J.J. Drake, T.J. Haworth, N.D. Richardson, M. Robberto, S. Sciortino, N.J. Wright, T. Ziliotto
Materials Science
Morphology and Dynamics of Self-interstitial Clusters in Irradiated Nickel
Ajay Annamareddy, Ibrahim Momohjimoh, Hangyu Li et al. (+3 more)
Self-interstitial atom (SIA) clustering is a key early step in radiation damage
evolution in face-centered cubic (FCC) metals, governing defect transport, recombination, and the long-term microstructural response of irradiated
alloys. We combine molecular dynamics (MD) simulations and high-speed (>1000 frames/s) in situ transmission electron microscopy (TEM) to investigate the structure, energetics, and migration dynamics of SIA clusters in FCC Ni. MD simulations show that interstitials initially form disordered dumbbell clusters that evolve into either sessile Frank loops or glissile perfect (prismatic) loops; the latter progressively reorganize into compact ordered configurations with increasing mobility. Direct construction of both loop types over a wide size range, validated against MD-relaxed structures, shows that perfect loops are thermodynamically favored over Frank loops for cluster sizes N greater than or equal to 14, where N is the number of SIAs, with the energetic advantage increasing with cluster size. Nevertheless, substantial kinetic barriers allow Frank loops to persist as metastable defects. For perfect loops,
diffusion coefficients computed over N = 16 to 400 reveal a nearly size-independent migration barrier of approximately 0.02 eV, while the
diffusion prefactor decreases approximately as N^(-0.54). Trajectory analysis reveals a non-rigid, row-wise relay mechanism in which the number of participating atoms increases systematically with loop size, accounting for much of the observed prefactor scaling. Sub-millisecond in situ TEM observations reveal intermittent loop motion at velocities higher than previously observed but still several orders of magnitude below the intrinsic mobilities predicted by MD, indicating migration through a heterogeneous energy landscape of mobile and pinned states.
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All authors Ajay Annamareddy, Ibrahim Momohjimoh, Hangyu Li, Kevin G. Field, Paul M. Voyles, Dane Morgan
Materials Science · Cross-listed from cs.CV
RAFT-DVC: Resolution-Aware Machine Learning-Based Digital Volume Correlation
Zixiang Tong, Lehu Bu and Jin Yang
Digital volume correlation (DVC) provides three-dimensional full-field displacement measurements from volumetric images, but how the internal resolution of a machine-learning-based DVC model affects accuracy and operating range remains poorly understood. Here, we present RAFT-DVC, a resolution-aware family of recurrent all-pairs field transforms (RAFT)-based DVC solvers with encoder downsampling factors s = 2, 4, and 8. Using a matched design, we find that the three solvers localize displacement to approximately 0.017 feature-grid voxel, giving an empirical raw-volume error scaling of approximately 0.017s voxel. The solvers exhibit complementary operating regimes governed jointly by displacement reach and volumetric-texture compatibility. Synthetic
benchmarks show that RAFT-DVC achieves errors of the same order as tuned classical DVC under fine-texture, small-to-moderate-displacement conditions and becomes competitive or advantageous under coarse-texture, large-displacement conditions. Frequency-swept tests quantify deformation spatial resolution, while tiled inference enables dense estimation on large volumes. Evaluation on confocal volumetric images acquired during indentation illustrates the importance of matching solver operating regime to deformation magnitude and image texture. Tests on micro-CT images of elastomeric foam, despite training only on particle-labeled synthetic data, provide evidence of cross-texture transfer. We also identify coordinate-order inconsistencies in three-dimensional RAFT correlation sampling and introduce a non-cubic impulse test to verify sampler geometry independently of network training. Correcting the sampler improves native-input accuracy and generalization to unseen volume dimensions. Together, these results establish RAFT-DVC as a fast, resolution-aware framework for dense DVC with characterized accuracy and operating regimes.
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Materials Science
Molecular spin qubits in a van der Waals bottle
Anna Champ, Eleanor Mackintosh, André Koch Liston et al. (+22 more)
Advancing
quantum information technologies requires
qubits whose coherence can be precisely engineered. Among the
qubit platforms in development, molecular
spin qubits (MSQs) stand out for their atomic scale tunability and chemical specificity, making them powerful candidates for sensing, simulation, and information processing. However, integrating MSQs into solid-state architectures without degrading their coherence remains a central challenge. Here, we introduce van der Waals (vdW) confinement within two-dimensional materials as a strategy for stabilizing
quantum states in MSQs by engineering their local electronic, vibrational, and
symmetry environments. Using cobaltocene as a model system, we show that confinement within vdW SnS2 and CdPS3 single
crystals reorganizes the single-ion energy landscape and slows
spin-
lattice relaxation by over two orders of magnitude relative to unconfined cobaltocene. The confined MSQs adopt deterministic orientations and self-assemble into ordered, atomically precise superlattices, establishing vdW confinement as a pathway for integrating MSQs into functional
quantum devices.
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All authors Anna Champ, Eleanor Mackintosh, André Koch Liston, Sanghyo Lee, Eric D. Walter, Raphaël P. Hermann, George Yumnam, Eric Seewald, Xuehao Wu, Willa Mihalyi-Koch, Augustin Braun, Johan van Tol, Tomas Orlando, Mykhaylo Ozerov, Byeongjun Gil, Myung-Geun Han, Yimei Zhu, Miyoung Kim, Abhay N. Pasupathy, Milan Delor, Michael L. Steigerwald, Timothy C. Berkelbach, Colin Nuckolls, Xavier Roy, Arun Ramanathan
Chemical Physics
Latent unified smooth Hamiltonians for excited state chemistry
David Juergens, Martin Stöhr, Andreas E. Hillers-Bendtsen et al. (+2 more)
We describe a neural network architecture and training procedure designed to model electronic ground and excited states of arbitrary molecular systems. By indirectly learning a latent, implicit basis representation of the electronic-state
Hamiltonian, the model offers a unified treatment of multiple electronic states, conical intersections, and non-adiabatic couplings. The formalism can be further extended to learn consistent latent representations of additional operators such as transition dipole moments, for example. To demonstrate the general capabilities of our architecture, we train and evaluate networks on two realistic photochemical systems, thymine and azobenzene. The resulting models accurately reproduce energies and oscillator strengths for the ground- and low-lying excited states relevant to the photochemistry of these systems. We highlight the performance of the trained networks by studying critical molecular geometries, including conical intersections and excited state minima. By construction, the proposed framework also recovers the emergence of Berry phase accumulation around conical intersections. By pairing key mathematical structure from
quantum chemistry with the representation learning power of
transformers, the presented architecture offers a qualitatively new path toward fast and accurate ground- and excited-state simulations.
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All authors David Juergens, Martin Stöhr, Andreas E. Hillers-Bendtsen, O. Jonathan Fajen, Todd J. Martínez
Chemical Physics
Dodecahydrogen uranium: an icosahedral f-electron superatom with 26-electron shell structure
Andrii Shyichuk and Eugeniusz Zych
A new icosahedral superatom UH$_{12}$ is reported and analyzed using post-Hartree-Fock multiconfigurational methods. A RASSCF/CASPT2/RASSI/SINGLE_ANISO workflow is employed to determine the electronic energy levels and
magnetic properties. Superatomic characteristics, such as orbital
topologies and shell filling order, are discussed. The high hydrogen-to-uranium ratio and potential for optically stimulated decomposition make UH$_{12}$ worth investigation in the context of hydrogen storage. The electric-dipole transition oscillator strengths of the molecule vanish, while its lowest electronic transitions fall in the THz and infrared ranges. The lowest septet
manifold exhibits
crystal-field splitting into a 1+3+3 pattern, as expected from icosahedral
symmetry. In turn, the interlevel gaps within these
crystal-field triplets are 30-150 GHz (1-5 cm$^{-1}$). The molecule is magnetically isotropic at low fields, while its levels exhibit higher-order Zeeman anisotropy that becomes significant around 2 Tesla. These properties suggest potential relevance for
quantum computing,
quantum communication, and
quantum memory, including
qubit- and qudit-based architectures.
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Mathematical Physics
Applying the convolution theorem to the two-dimensional magnetic inverse problem
Michael T. M. Woodley
A collection and clarification is given of the key mathematical details of the method of applying the convolution
theorem as part of the solution to the two-dimensional
magnetic inverse problem: reconstructing current density from
magnetic field data. Particular emphasis is given to obtaining a closed-form solution for the
Fourier transform of the convolution kernel that features in the Biot-Savart law. Having done this, the
Fourier-transformed current density is obtained, via the convolution
theorem, as a function of
Fourier-transformed
magnetic field data and other variables.
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Quantum Physics · Cross-listed from cs.IT
Comments on the recent improvements of the MRRW bounds
Alexander Barg
The asymptotic McEliece–Rodemich–Rumsey–Welch bound (1977) limits the largest attainable rate of binary codes as a function of the relative distance. After a nearly half-century hiatus, this result was recently improved in two concurrent works, by OpenAI and by O. Alrabiah and V. Guruswami. The two arguments look entirely different, a Delsarte certificate on the one hand, a classical-
quantum channel and the pretty good measurement on the other, and they yield the same bound. The purpose of this note is to explain why: in both proofs, a subspace is attached to every codeword and moved with it, and the bound counts how many such subspaces fit in the ambient space, exactly in the first case and in the probabilistic sense of typicality in the second. We also present the OpenAI proof in the
language and context of coding theory, as an extension of the spectral method in which the single vector attached to a codeword is replaced by a subspace.
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Nuclear Theory
Unveiling QCD Criticality with Cross-Rapidity Net-Baryon Cumulants
Jianing Li, Shuzhe Shi and Lipei Du
Fluctuations of conserved charges are a primary tool in the search for the QCD critical endpoint, but their beam-energy dependence is complicated by global
baryon-number conservation, whose influence changes as the experimental acceptance covers different fractions of the collision system. We propose using correlations of net-
baryon fluctuations between two separated rapidity windows to exploit the distinct signatures of conservation and critical dynamics. Global conservation produces a negative cross-window correlation, whereas a common long-wavelength critical fluctuation produces a positive one. We show that, within a canonical independent-source framework, the conservation-induced background and the critical signal enter additively at leading order, allowing the leading conservation term to be estimated and subtracted. The resulting yield-scaled correlator follows the nonmonotonic enhancement of an Ising-mapped
equilibrium correlation length along a freeze-out trajectory passing near a hypothetical critical endpoint, while wider rapidity windows reduce the response through thermal smearing. Cross-rapidity cumulants therefore provide a rapidity-differential strategy for reducing the leading conservation background and sharpening fluctuation-based searches for QCD criticality in beam-energy-scan experiments.
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Statistical Mechanics · Cross-listed from q-bio.PE
A greedy nearest-neighbor approach to quantify site revisitation: comparing two sympatric raven species
Bar Ashkenazi, Miguel de Guinea, Michael Assaf et al. (+1 more)
A central challenge in movement ecology is to describe ecologically meaningful residence sites from raw tracking data due to heterogeneous sampling frequency and uncertain site boundaries. Here, we develop a greedy nearest-neighbor clustering approach with local reassignment and polygon-based site construction that generates timestamped sequences of site visits for each tracked individual, and apply it to nine years of GPS data from two sympatric raven species in the Dead Sea region—the Fan-tailed Raven (Corvus rhipidurus) and the Brown-necked Raven (C. ruficollis). Using the resulting visitation sequences, we quantify recursion patterns using the non-Markovian individual mobility model (IMM), which captures the balance between novel-site discovery $\beta$ and preferential return $\alpha$. The inferred dynamics are consistent with IMM predictions and reveal clear interspecific differences: Brown-necked Ravens continue to discover new sites at a higher rate (lower $\beta$), whereas Fan-tailed Ravens show a steeper concentration of visits among top-ranked sites.
Entropy analyses further separate the species, with Brown-necked Ravens exhibiting higher site
entropy and higher conditional
entropy of site-to-site transitions. Together, these results provide a robust framework for describing interspecific differences in movement strategies that can be used to infer
memory from GPS data and suggest distinct space-use strategies in two closely related sympatric species.
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All authors Bar Ashkenazi, Miguel de Guinea, Michael Assaf, Ran Nathan
Mathematical Physics · Cross-listed from math.DS
The Hessian of Planar Central Configurations in Pair Space: Decomposition, Morse Index and Symmetry Reduction
Manuele Santoprete
We give a variational derivation of the central configuration equations in pair space, where the relative position vectors between pairs of bodies serve as the primary variables. Vector Lagrange multipliers enforce the linear triangle relations required for these pair vectors to be realizable in the plane. For arbitrary $N$, we show that the constrained Hessian decomposes as $H_{\mathcal C}=L^\Delta+\widetilde L$, where the gap
Laplacian $L^\Delta$ is positive semidefinite and the transverse
Laplacian $\widetilde L$ is signed and contains all possible negative directions. For non-collinear planar four-body central configurations, the signed part has rank two. This yields a new proof of the known bound that the Morse index is at most two. We then characterize positive definiteness and degeneracy of the Hessian by the
eigenvalues of an explicit $2\times2$
matrix or, equivalently, by two generalized
eigenvalues of a pencil of symmetric
matrices. We illustrate the general criterion using the equal-mass square central configuration. For reflection-symmetric configurations, the generalized
eigenvalue problem decomposes into two independent smaller problems. This reduction applies to kite and isosceles trapezoidal configurations. For the trapezoid, however, the reflection acts non-orthogonally on the pair coordinates, giving a different, non-orthogonal reduction. Applying the reflection-
symmetry reduction to the rhombus family, we prove that the Hessian is positive definite modulo the rotational zero mode; equivalently, every rhombus central configuration is nondegenerate modulo rotations and has Morse index zero.
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Cosmology and Nongalactic Astrophysics
Blast.jl: Differentiable Non-Limber Power Spectra for Joint Clustering, Shear, and CMB lensing Analyses
Sofia Chiarenza, Marco Bonici, Stefano Camera et al. (+4 more)
Upcoming large-scale structure surveys require accurate theoretical predictions for angular power spectra on the largest angular scales, where the commonly used Limber approximation breaks down and multiple relativistic and observational effects become relevant. At the same time, modern cosmological analyses increasingly rely on gradient-based inference techniques, motivating the development of fast, fully differentiable
algorithms. In this work, we present a major extension of Blast.jl, a numerical toolkit for the efficient computation of non-Limber angular power spectra. Building on the Chebyshev-
polynomial decomposition of the original framework, the updated
algorithm incorporates
redshift-space distortions, magnification bias,
primordial non-Gaussianity, intrinsic
alignments, CMB
lensing, and the integrated Sachs-Wolfe effect, while remaining fully differentiable through custom automatic differentiation rules. Despite the increased physical complexity, the
algorithm retains favorable scaling by precomputing all cosmology-independent quantities. We validate the expanded framework against brute-force integration and established cosmological codes, and provide a detailed analysis of the trade-off between computational speed and precision as a function of the
algorithm hyperparameters. We demonstrate the readiness of Blast.jl for gradient-based inference through a simulated likelihood analysis with LSST Y10-like mock data, recovering unbiased cosmological and nuisance parameter constraints from a 35-parameter model using gradient-based samplers.
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All authors Sofia Chiarenza, Marco Bonici, Stefano Camera, Giulio Fabbian, Carlos García-García, Alex Krolewski, Will J. Percival
Mesoscale and Nanoscale Physics
Magnons in Metallic Altermagnetic $\text{KV}_2\text{Se}_2\text{O}$
Daniel Lourenço R. Santos and António T. Costa
We investigate the
spin excitation in altermagnetic vanadium oxyselenides, focusing on the metallic quasi-two-dimensional compound $\text{KV}_2\text{Se}_2\text{O}$. Using a fermionic
Hamiltonian derived from ab initio calculations, we compute the transverse
spin susceptibilities within the random phase approximation and extract the
magnon dispersion relation. We show that the altermagnetic
symmetry leads to characteristic degeneracies and directional splittings in both the electronic bands and the
magnon spectra along high-
symmetry paths of the Brillouin zone. The metallic $\text{KV}_2\text{Se}_2\text{O}$ exhibits finite
magnon linewidths arising from the coupling to the particle-hole continuum. Furthermore, by fixing the magnitude of the wave vector and varying its in-plane direction, we uncover a pronounced angular dependence of the
magnon energies and lifetimes, with complementary damping behavior between the two
magnon branches. Upon including
spin-orbit coupling, the system exhibits an out-of-plane easy c-axis anisotropy, which opens a
magnon gap of approximately 6 meV at the $\Gamma$-point, possibly rendering the
magnetic order stable at room temperature. Our results demonstrate that altermagnetism controls not only the dispersion but also the anisotropic decay of
spin excitations, highlighting altermagnetic metals as promising platforms for directionally selective
magnon transport.
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Quantum Physics
Error accumulation in dissipative quantum circuits
Nadir Samos-Sáenz de Buruaga, Rodrigo M. C. Pereira, Karol Życzkowski et al. (+2 more)
Present-day
quantum processors are open systems in which dissipation and decoherence degrade the information carried by a
quantum state as it propagates through a
circuit. We study this degradation in dissipative random
quantum circuits, modeling each two-
qubit gate as a diluted
unitary that interpolates between the intended
unitary operation and a random dissipative
quantum channel. Using the fidelity between the ideal and noisy output states as a diagnostic, we show that sufficiently random
unitary gates or dissipative Kraus operators lead to a universal decay of the average fidelity. This decay is determined only by the dissipation strength, system size, and
circuit depth, while microscopic details of the gates and noise, including the Kraus rank, appear only in subleading corrections to higher moments. We derive a closed-form expression for the average fidelity in terms of three physically meaningful error parameters, dissipation strength, coherent two-
qubit gate-error strength, and connectivity-error probability. Finally, we identify the cases when dissipative effects can be reproduced by an
unitary-noise model and when dissipation-induced decoherence remains distinguishable from coherent noise at the level of the average fidelity.
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All authors Nadir Samos-Sáenz de Buruaga, Rodrigo M. C. Pereira, Karol Życzkowski, Sergey Denisov, Pedro Ribeiro
Computational Physics
Learning a general class of admissible multi-species collision operators from molecular dynamics
Yue Zhao, Andrew Christlieb and Huan Lei
We develop a structure-preserving, data-driven collision operator for spatially homogeneous multi-species kinetic systems from molecular dynamics (MD). The operator consists of diagonal self-collision blocks and ordered off-diagonal cross-species blocks to describe intra- and inter-species momentum and energy exchange. Within a local and point-wise identifiable kernel class, we develop the necessary and sufficient condition for the admissible kernel class satisfying the conservation laws, the H-
theorem, and the frame indifference. Unlike the classical Landau operator, the off-diagonal kernels are not restricted to be symmetric under permutation of the two velocity variables. This unique structural freedom captures the distinct responses of different species to unresolved correlations and many-body effects arising from micro-scale particle interactions. The equivalent parameterizable kernel formalization enables us to learn a generalized data-driven collision operator directly from MD, where the low-rank tensor representations and random sampling are used to achieve efficient kernel training and numerical simulation. Numerical experiments show that the learned operator accurately predicts transport coefficients and the non-
equilibrium relaxation, while retaining discrete conservation and
entropy production. In particular, it captures
plasma kinetics in the moderately coupled regime, where the predictions of both the Landau and the data-driven model restricted to velocity-permutation
symmetry show significant discrepancies.
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Materials Science
Symmetry-selective nonrelativistic spin splitting in antiferromagnets driven by coherent phonons
Sangeeta Rajpurohit, Mohsen Yarmohammadi, Sheikh Rubaiat Ul Haque et al. (+3 more)
Nonrelativistic
spin splitting (NRSS) in antiferromagnets (AFMs) enables magnetization-free
spin polarization for ultrafast spintronics. Here, we demonstrate that coherent
phonons can dynamically induce and control NRSS in collinear AFMs. Excitation of $\Gamma$-point infrared-active
phonons lifts the
spin degeneracy of the ground state, while the residual sublattice-connecting
symmetries determine the momentum-space form of the induced splitting. Because the relevant infrared modes couple to orthogonal in-plane light polarizations, distinct
spin-split phases can be selectively activated by the polarization of the driving field. Using first-principles calculations for MnPS$_3$, we show that a mode that breaks all sublattice-connecting
symmetries induces an $s$-wave
spin-split state with $\Delta(\Gamma)\neq0$, whereas a
symmetry-distinct mode that preserves a sublattice-connecting mirror
symmetry generates a $d$-wave altermagnetic state with $\Delta(\Gamma)=0$. In both cases, the
spin splitting grows linearly with the
phonon amplitude and reverses the induced
spin polarization when the displacement is reversed. Our results establish coherent
lattice driving as a direct, polarization- and mode-selective route to dynamically induce distinct NRSS phases in AFMs.
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All authors Sangeeta Rajpurohit, Mohsen Yarmohammadi, Sheikh Rubaiat Ul Haque, Tony F. Heinz, Aaron M. Lindenberg, Tadashi Ogitsu
Instrumentation and Detectors
Characterization of a low-power 3D photon-to-digital converter readout improved for system integration in meter-scale applications
Olivier Lepage, Tommy Rossignol, Nicolas Roy et al. (+5 more)
Digital silicon photomultipliers (dSiPM) are arrays of single
photon avalanche diodes (SPADs) where each SPAD has its own electronic readout. To maximize the photodetection area, we developed a readout integrated
circuit (ROIC) 3D-integrated to a custom-designed SPAD layer fabricated at Teledyne Dalsa (Bromont, Canada) to form a
photon-to-digital converter (PDC). This paper presents an improved version of a previously demonstrated ROIC, fabricated in TSMC 180 nm technology to manage a 64 x 64 pixel architecture. This ROIC has different outputs, such as a flag output that produces a pulse whenever one of the pixels triggers and a digital sum that samples the amount of triggered SPADs. Improvements lead to a reduction of the timing jitter on the flag output from 72.0 ps RMS to 22.6 ps RMS through optimized H-tree design. A tunable hold-off
circuit provides adjustable dead time from 32 ns to 18 {\mu}s, addressing both afterpulsing mitigation and SPAD-to-SPAD variations due to process defects. Power consumption is lowered by 30% at trigger rates exceeding 10 kHz through digital logic optimization and clock gating. These measurements validated that the ROIC is ready for 3D integration into a PDC for systems in medical imaging, particle physics, and
quantum sciences.
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All authors Olivier Lepage, Tommy Rossignol, Nicolas Roy, Gabriel Lessard, Frédéric Vachon, Lorenzo Fabris, Serge A. Charlebois, Jean-François Pratte
Quantum Gases
Kelvin-Helmholtz instability in annular superfluids across the UFG-BCS crossover
Michał Śliwiński, Klejdja Xhani and Gabriel Wlazłowski
We investigate the Kelvin-Helmholtz instability of counter-rotating annular
Fermi superfluids using time-dependent superfluid density functional theory. When the two initially separated superflows merge, a necklace of quantized
vortices forms at their interface and subsequently becomes unstable. We extract mode-resolved instability growth rates and study their dependence on relative flow velocity, interaction strength, and temperature across the strongly interacting
unitary regime and the weakly attractive BCS regime. In the
unitary gas and moderate BCS regimes, the growth rates remain qualitatively consistent with the point-
vortex model, though systematically at or above its predictions, with no significant dependence on interaction strength or temperature up to approximately $0.3 T_c$. Deeper in the BCS regime, the dynamics change qualitatively: boundary-generated antivortices proliferate faster than the Kelvin-Helmholtz instability itself, destroying the initial
vortex necklace before the instability can fully develop. These results provide a microscopic
benchmark for Kelvin-Helmholtz dynamics in fermionic superfluids and help constrain possible explanations of the existing experiment-theory discrepancy.
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Mathematical Physics
Extended Body Propagators
Rory O'Dwyer
Three seemingly distinct extended-body propagators devised by Ansoldi et al., Erbin et al., and Stanford et al.\ respectively arise in completely different settings, though each can be considered a realization of the Polyakov path integral. This paper proves that the Ansoldi propagator corresponds to the characteristic function of the random variable with the probability density function $f(A)=C\,A\,(\alpha^{2}+A^{2})^{-D/2}\mathbf{1}_{A>0}$ in ambient dimension $D$, of scale $\alpha=\sqrt{b/2}$. The exponent is fixed by the dimension and by nothing else in the Ansoldi/
geometric comparison; the on-shell two-point amplitude of Erbin et al. and JT
gravity agree with its $D=4$ member in the senses made precise below. After an extensive literature review, the author believes that this observation and constructed area measure is novel. The area measure will, however, emerge as the natural candidate for the extension of the earlier non-extended body path space measures to two dimensional simplicial complexes. We further show that the area measure of this paper is exactly the law of the area of a triangle, two of whose sides are drawn from the measure obtained in the companion manuscripts for the one-dimensional Polyakov integral. We close with an argument, rigorous in part, which reduces the measure of tubular worldsheets between two arbitrary boundary curves to that of this triangle.
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Mathematical Physics · Cross-listed from math.AP
Fully fractional Schrödinger equations with memory: well-posedness via extension
Nicola Garofalo and Gigliola Staffilani
We study the nonlinear Schrödinger equation with
memory $\Le^s u=\mu|u|^{p-1}u$ for $t>0$, where $\Le^s=(\partial_t-i\Delta_x)^s$, $0<s<1$, and the solution is prescribed for all $t\le0$. We identify a
Hilbert space of histories and prove local well-posedness for $1<p\le p_*(s)=1+4s/(d+2-2s)$, with global solutions for sufficiently small histories at the critical exponent. We also establish the passage from this
memory problem to the classical nonlinear Schrödinger equation as $s\uparrow1$. For every fixed Schwartz history and $1<p\le1+4/d$, including the classical mass critical exponent, the
memory solutions converge in $C([0,T];L^2\cap L^{p+1})$ to the classical solution with initial value $u_0(\cdot,0)$, for every finite $T$ below its maximal existence time. Thus the limiting
evolution depends on the prescribed past only through its value at time zero. Our construction uses an oscillatory Poisson extension and an exact identity expressing the weighted $L^2$ norm of the lifted initial datum in terms of the history. This identity allows us to apply the boundary estimates of our earlier work to the
memory problem. We recover $\Le^s$ as a weighted Dirichlet-to-Neumann map and establish the corresponding extension bounds on $L^2$ for $0<s\le\frac12$, and from $\operatorname{Dom}(\Le^s)$ to $L^2$ for $\frac12<s<1$.
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Optics
Optical air waveguides in strong turbulence
A. Goffin, G.I. Babić and H.M. Milchberg
Filament-generated air waveguides offer a route to low loss long-distance optical transport, but their viability in atmospheric
turbulence has remained uncertain. Here, we demonstrate with experiments and simulations that guided beams in air waveguides can overcome prior estimated
turbulence limits by orders of magnitude in the refractive index structure parameter C_n^2; turbulent index fluctuations much larger than the waveguide index contrast average out along the propagation path. Instead,
turbulence imposes two distinct limits: scattering of the guided field beyond the waveguide acceptance aperture and, more importantly at atmospheric strengths, scintillation of the waveguide-forming beam. Scaling of experimentally validated models indicates that filament-generated air waveguides remain viable over kilometer-scale paths under strong near-ground
turbulence. Our results establish
turbulence limits for long-range optical guiding in the atmosphere.
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Solar and Stellar Astrophysics
Mass-dependent multiplicity fraction in low mass stars revealed by Gaia astrometry
Ben Pennell, Hans-Walter Rix, Kareem El-Badry et al. (+3 more)
Stellar multiplicity at different orbital periods is probed by different techniques: radial velocities at the shortest periods, direct imaging at the longest, and astrometry in between.
Gaia DR3 provides unprecedented astrometric information to constrain binary populations with periods of tens to thousands of days. Beyond the small fraction of direct orbit solutions,
Gaia publishes coarser astrometric diagnostics for all objects, such as on-sky accelerations, jerks, or the single-
star goodness-of-fit measure, RUWE. We show that these diagnostics together are sensitive to a far wider range of orbital periods than orbit solutions alone. Built on the Gaiamock emulator, we develop a forward-modelling framework to constrain rates of multiplicity from
Gaia data, using all astrometric solution types. We apply this framework to $366~027$ primaries of $0.2$–$0.75\,M_\odot$ between $50$ and $200$ pc, including vastly more M-
dwarfs than previous multiplicity studies. For fiducial models of the period and mass-ratio distributions, the inferred multiplicity fraction is approximately constant at ${\sim}45\%$ from the
solar-type regime down to $0.4\,M_\odot$, only then dropping to ${\sim}15\%$ by $0.2\,M_\odot$. This mass-multiplicity relationship revises the conventional picture of a monotonically rising mass–multiplicity relation, and aligns the upper M-
dwarf regime with
solar-type
stars rather than placing it on a continuous decline.
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All authors Ben Pennell, Hans-Walter Rix, Kareem El-Badry, Sahar Shahaf, Johanna Müller-Horn, Jiadong Li
Quantum Physics
Bosonic quantum control with a weakly coupled fluxonium qubit
Anaida Ali, Shantanu R. Jha, Shoumik D. Chowdhury et al. (+4 more)
Echoed Conditional Displacement (ECD) gates constitute a fundamental building block for
quantum control of harmonic oscillator modes. However, bit-flips of the auxiliary
qubit remain a dominant error mechanism for this kind of bosonic control. In this work, we present a numerical case study of a bit-flip protected fluxonium operating as the control
qubit and numerically implement ECD gates in a single-mode resonator-fluxonium device, demonstrating that fidelities exceeding 99.9% are possible. We systematically investigate the resonator dynamics using a combination of semiclassical trajectories and master equation simulations, numerically revealing asymptotic saturation of the dispersive shift in the strongly driven regime of the resonator. We develop an efficient technique to numerically simulate the strongly driven regime of the resonator using a semiclassical formulation that maps the full perturbation series in the dispersive expansion as order-by-order frequency shifts. This provides a compact
polynomial description of the resonator which is intuitive and remains valid throughout the dispersive regime. Furthermore, we propose an improved ECD sequence that accounts for the effects of
photon loss and spurious nonlinear terms on resonator trajectories.
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All authors Anaida Ali, Shantanu R. Jha, Shoumik D. Chowdhury, Lev-Arcady Sellem, Max Hays, William D. Oliver, Baptiste Royer
Mesoscale and Nanoscale Physics
Tuning Boron-Vacancy Qubit Coherence through Layer Number in hBN
Juan M. Florez and Eric Suárez Morell
The negatively charged boron vacancy ($\VB$) in hexagonal boron nitride (\hBN{}) was the first optically addressable
spin qubit identified inside a van der Waals
crystal, allowing atomically defined placement relative to a target. Its coherence in bulk \hBN{} is limited by the boron
nuclei of the layers flanking the defect plane, which a thin flake removes. Here, we use a generalized cluster-correlation expansion with an extended central-
spin block to calculate the Hahn-echo coherence time of $\VB$ in h$^{11}$B$^{15}$N as a function of layer number. Our results show that $T_2$ rises from $199\ns$ in the bulk limit to $653\ns$ in a monolayer, a factor of $3.3$ that is already saturated at three layers and that a sublattice decomposition attributes entirely to boron. The enhancement is confined to low field, is insensitive to stacking registry and twist angle, and requires
alignment to within about two degrees, an onset we reproduce with no free parameters. Under dynamical decoupling, a $1/e$ threshold returns $206\ns$ for every thickness, but this is a zero of the first-shell modulation rather than a decay: measured without a threshold, the layer contrast survives and reaches a factor of $170$. Layer number thus emerges as a design parameter for $\VB$-based sensing.
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