General Relativity and Quantum Cosmology
Radmehr Fathi and Nima Khosravi
The existence of
quantum gravity is the most important question in theoretical physics. Besides the theoretical development in this direction, looking for its low-energy consequences can provide clues. However, besides availability, it is crucial to ensure that what is observed uniquely comes from
quantum gravity and not from other forces in the environment. What is the unique feature of
gravity? The
spin-$2$ nature of its propagator. In this Letter, we calculate what the unique feature of the
spin-$2$ graviton is in the interaction of two
spin-$\frac{1}{2}$ particles. This unique feature shows itself in intertwining the
spin and momentum of two particles simultaneously as a dipole-dipole interaction. This cannot happen for any
spin-$0$ or
spin-$1$ propagator, at least at leading order, which scales as $\frac{1}{r^3}$ in real space. We re-calculate the results using an independent approach, i.e., the Foldy-Wouthuysen transformation, and reach the same results. Due to simultaneous coupling of both particles'
spins and momenta, a four-partite
entanglement framework is suggested to observe this effect.
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Strongly Correlated Electrons
Phase stability, charge ordering, and charge-liquid formation in the Falicov-Kimball model on triangular and kagome lattices
Ammar Nejati and Marvin Lenk
We present a systematic investigation of the stability of the phase diagram of the spinless Falicov-Kimball model on two-dimensional non-bipartite
lattices, the triangular and kagome
lattices, using Markov-chain Monte Carlo simulations. Three filling or chemical potential conditions are examined: fixed chemical potentials ($\mu_f = \mu_c = U/2$), "generalized" half-filling ($\bar{n}_f = 1/3$, $\bar{n}_c = 2/3$), and conventional half-filling ($\bar{n}_f = \bar{n}_c = 1/2$). For each condition, the effects of a perturbatively small next-nearest-neighbor hopping are studied. On the triangular
lattice, Anderson
insulator, Mott
insulator, and charge-density wave (CDW) phases are found in all cases, with the CDW driven by Coulomb-interaction-mediated nesting. Evidence for a charge-
liquid regime is found in the region between the weakly correlated regime and the CDW, characterized by competing charge-ordering wavevectors and the absence of universal scaling behavior, whose extent shrinks progressively from the grand-canonical to the conventional half-filling condition. On the kagome
lattice, the CDW phase is completely absent; instead, an insulating ground state, plausibly of the Mott type, is found, with signatures of a possible
quantum phase transition at zero temperature. Our results establish the crucial role of
lattice geometry and particle-hole
symmetry breaking in shaping the phase diagram of correlated electron systems.
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Quantum Physics
Rényi Entanglement of Purification Is Non-additive
Amir-Reza Negari and Zahra Baghali Khanian
Entanglement of purification is a fundamental measure of total correlations whose additivity remains unresolved. We study its additivity for classical states on two
qubits at different Rényi orders. For every $\alpha\in[0,1)$, we prove nonadditivity within this family, witnessed by two copies of a single state. We first solve the one-copy optimization exactly for the entire family at every Rényi order. We then restrict the two-copy optimization to a natural finite set of purifications and exhibit one whose
entropy is strictly below the product value. In contrast, for $\alpha\in[2,\infty]$ we prove additivity under tensor products within this family. The interval $\alpha\in[1,2)$, including the von Neumann case $\alpha=1$, remains open, and we
conjecture additivity there throughout the same family.
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High Energy Astrophysical Phenomena
A Terrestrial Gamma-ray Flash with an Asymmetric Footprint Observed at the Pierre Auger Observatory
The Pierre Auger Collaboration, John Ortberg, David M. Smith et al. (+1 more)
The Pierre Auger Observatory, a $3000km^2$ detector array that sits 1400m above sea level in Argentina, has the ability to map the entire footprint of Terrestrial Gamma-ray Flashes (TGFs), which are short, intense bursts of gamma rays associated with lightning. This is in contrast to the vast majority of TGF detections that only occur in a single detector in space. In this paper we leverage this capability to perform two important analyses on an event from 2007, chosen for its large footprint and high signal quality. First, we triangulate the source of the TGF to $2.3\pm0.5$km height above ground level using the arrival time of the gamma rays themselves at the detector array, independently of any information regarding the lightning channel. With the source position established, we can analyze the spatial distribution of the TGF on the ground with respect to that source. Not only do we find that one side of the TGF footprint shows an order of magnitude higher flux than the other, but we also find an asymmetric azimuthal structure consisting of two clear peaks in intensity. These peaks are offset by about $120^o$ from each other. This azimuthal structure is not possible under the traditional uniform electric-field model of a TGF. Using Geant4 simulations of collimated beams of the relativistic runaway electron-avalanche spectrum, we attempt to reconstruct the source geometry of the TGF and find that it likely had significant components in the $\theta > 75^o$ range, where $\theta$ is the off-nadir angle.
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All authors The Pierre Auger Collaboration, John Ortberg, David M. Smith, Joseph Dwyer
Nuclear Theory
Strongly coupled quark matter in neutron stars and their mergers
Konstantin Maslov, Ralf Rapp, Joaquin Grefa et al. (+2 more)
The discovery of the strongly-coupled
quark-
gluon plasma (sQGP) in high-energy heavy-ion collisions has revealed remarkable properties of matter at high temperature, with transport coefficients close to conjectured bounds from
quantum field theory at strong coupling. The high sQGP collision rates imply very large energy uncertainties and the melting of quasiparticle structures. Deploying
quantum many-body theory based on the self-consistent $T$-
matrix approach for the sQGP at high temperature, we investigate its manifestation at high
baryon density and low temperature, as present in
neutron stars and their mergers. We constrain the chemical-potential dependence of the
quark interaction kernel using first-principles information from
Quantum Chromodynamics on
baryon-number susceptibilities. Very large collisional widths persist at large density and are found to relegate superconducting phases to rather small temperatures. Instead, a strongly coupled diquark
liquid prevails in the thermodynamics under the conditions relevant to
neutron-
star mergers. At lower densities, the diquarks take over from the single-
quark contributions, suggesting a pathway toward hadronization. Our results are consistent with observational constraints on the equation of state of
neutron stars, corroborating the presence of strongly coupled
quark matter in the interior of these objects.
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All authors Konstantin Maslov, Ralf Rapp, Joaquin Grefa, Veronica Dexheimer, Claudia Ratti
Optics
HALO: A Physics-Aware LLM Agent Framework for Nanophotonic Design
Yubo Zhang, Jinlin Xiang, Zijun Zhao et al. (+3 more)
Language models have recently been applied to nanophotonic design, but it remains unclear whether they can reliably translate optical objectives into simulation-ready designs, execute electromagnetic analysis, and revise decisions from numerical feedback. We introduce
HALO, a physics-aware framework that couples
language-model planners with typed design specifications, electromagnetic simulation, diagnostic evaluation, and optional reuse of prior failure trajectories in an iterative design loop. We further introduce
HALO-Bench, a 52-task
benchmark spanning lab-derived, paper-derived, and open-ended nanophotonic design tasks under a shared evaluation protocol. We compare three planner configurations: a Fixed Structured Workflow, an Autonomous Structured
Agent using the same simulation interface, and an Autonomous Coding
Agent that directly writes and executes simulation code. The Fixed Structured Workflow is the most
token-efficient and exhibits no observed code- or path-level failures, while autonomous coding can achieve higher task success with stronger models at the cost of additional operational failures. We also study reuse of prior failed trajectories. On targeted multi-round tasks, retrieved failure feedback reduces both iterations to first success and total
token use. These results clarify the tradeoffs between explicit interfaces, autonomous execution, and reusable design experience in scientific
agents.
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All authors Yubo Zhang, Jinlin Xiang, Zijun Zhao, Yang Zhao, Eli Shlizerman, Arka Majumdar
Computational Physics · Cross-listed from math.NA
High-Order-Accurate Continuity Enforcing Nyström Discretization of 3D Maxwell Combined Field Integral Equations
Bernd Hofmann, Reza Molavi and Constantine Sideris
In Nyström-collocation discretizations of the electric field integral equation (EFIE), the surface divergence acts on surface densities that may be discontinuous across patch boundaries, which degrades accuracy and convergence. We show that this not only affects the EFIE but every formulation in which the operator occurs, either in the equation itself or in the scattered field computation, and propose a high-order-accurate continuity-enforcing scheme for smooth surfaces as a remedy for the direct and indirect EFIEs,
magnetic field integral equations (MFIEs), and regularized combined field integral equations (CFIEs) alike. The scheme comprises two ingredients: i) We show how to discretize the equations via a Chebyshev-based Nyström scheme, which admits closed quadrature rules. ii) Since unknowns and test vectors are in terms of patch-local curvilinear bases, continuity is enforced by a change of basis: we construct sparse mapping
matrices assembled solely from the curvilinear geometry description. In doing so, we restore the accuracy of the EFIE such that it can be combined with the MFIEs with equal weights to form CFIEs. Numerical studies for the scattering from canonical and realistic geometries show that all considered formulations individually and combined benefit from the continuity enforcement in terms of better conditioning, reduced iterations of an iterative solver, and several more digits of accuracy in the scattered fields, despite reducing the total number of unknowns.
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Solar and Stellar Astrophysics
Statistical Energy Budget of the Solar Wind with Parker Solar Probe and Solar Orbiter : 1 - Unbalanced Total Energy Radial Evolution
Jean-Baptiste Dakeyo, Pascal Démoulin, Victor Réville et al. (+9 more)
The magneto-hydrodynamic (MHD) description of the
solar wind has long been regarded as one of the most successful frameworks for investigating
solar wind heating and acceleration. Under a set of simplifying assumptions, it provides a reduced large-scale description that is widely used to study the energetic role of electromagnetic fluctuations in the
solar wind energy budget. In practice, applying simplification to MHD can result in the loss of some physics compared to an exact set of equations. However, an observational energy budget can help us to verify whether any energetic information has been lost in the process of simplification. To do so, we directly test the validity of the large-scale non-linear ideal MHD energy budget with
solar wind observations from Parker
Solar Probe (PSP) and
Solar Orbiter (SO). After verifying the reliability of the measurements through comparison with previous studies of similar
solar wind properties, we test the conservation of the total energy predicted by the MHD theory. We find that the average total energy increases with radial distance by $56\%$ ($\pm9\%$) between 14 and 203
solar radii. The increase in kinetic energy is not sufficiently compensated by the decrease of the thermal and electromagnetic contributions. We investigate the major sources of observational uncertainty and find that they cannot account for the observed energy increase. These results suggest that the large-scale theoretical description may neglect an energetically significant contribution to
solar wind acceleration. Assuming that such a contribution exists, we predict that this extra energy would scale with radial distance as $r^{-0.54\pm0.38}$.
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All authors Jean-Baptiste Dakeyo, Pascal Démoulin, Victor Réville, Stuart Bale, Tamar Ervin, Milan Maksimovic, Olga Alexandrova, Mingzhe Liu, Roberto Livi, Nikos Sioulas, Orlando Romeo, Alexis Rouillard
Fluid Dynamics
A priori Assessment of Tensor-Network Encoding for Isotropic Turbulent Flows
Massen Esmaeili, Hirad Alipanah, Robert Pinkston et al. (+5 more)
Tensor networks (TNs), originally developed for simulating many-body
quantum systems, provide a systematic framework for approximating high-dimensional fields. This is achieved by factorizing the field into interconnected tensors with small bond dimensions, thereby restricting the correlations captured across field bipartitions. Belonging to the family of TNs, the
matrix product state (MPS) ansatz is utilized here as a reduced-order modeling framework to construct truncated representations of isotropic turbulent flow data. Two direct numerical simulation (DNS)
datasets are considered: the hydrodynamic field of an incompressible three-dimensional flow, and a conserved Fickian scalar in a similar flow. Each field is encoded as an MPS through a sequence of singular value decompositions (SVDs) in which small singular values are discarded. The truncated representation is contracted back to the full grid, and the resulting reconstructed field is compared against DNS. An interleaved ordering of the spatial tensor indices of the transport variables is applied prior to decomposition in order to localize the dominant inter-tensor correlations. Velocity reconstructions achieve $99.8\%$ fidelity using only $5\%$ of the original DNS
memory, while the scalar field reaches the same fidelity at $15\%$
memory usage. A wide range of lower- and higher-order statistics, including velocity gradients, dissipation, and structure functions, are systematically examined. At these compression levels, the total kinetic energy and the scalar energy are both recovered within $0.2\%$ relative error, while the mean dissipation and mean scalar dissipation remain within approximately $10\%$ of the DNS generated values. These findings support the suitability of MPS for scalable reduced-order analysis of complex turbulent
datasets and motivate further exploration of TN-based methods in computational
turbulence.
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All authors Massen Esmaeili, Hirad Alipanah, Robert Pinkston, Peyman Givi, Daniel Livescu, Andrew J. Daley, Dieter Jaksch, Juan José Mendoza-Arenas
Quantum Gases
Regularization of Vortex Core Size in Photon BECs due to Harmonic Trap: An Analytical Approach
Joshua Krauß, Tabitha Bates, Francisco Ednilson Alves dos Santos et al. (+1 more)
Quantized
vortices are a hallmark of superfluidity. However, in a
photon Bose–Einstein condensate, the
photon-
photon interaction is so weak that in a homogeneous system the healing length exceeds the experimentally achievable size of the condensate itself. Here we show that a harmonic confinement regularizes the
vortex size to experimentally achievable scales. Moreover, such an external confinement closely resembles the standard experimental setup of a pumped dye-filled microcavity. We model the condensate via a complex Gross–Pitaevskii equation and obtain an approximate dynamical single-
vortex solution by applying the recently proposed projection optimization method. The latter generalizes the variational approach of closed systems to open-dissipative systems without assuming a specific form for the condensate phase. The radial
photon flow, which is characteristic for driven-dissipative systems, yields a definition of the
vortex core size based on the competition of gain and loss. However, this condition reproduces the heuristic closed system definition now based on physical grounds. A subsequent linear stability analysis shows that interaction, as well as pumping and loss can drive the system to an unstable regime. In this way one can fundamentally distinguish between closed and open-dissipative systems.
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All authors Joshua Krauß, Tabitha Bates, Francisco Ednilson Alves dos Santos, Axel Pelster
Materials Science
Engineering Excitons through Polymorphism and Dimensional Confinement in Low-Dimensional Tellurium
Gabriel Elyas Gama Araujo, Alexandre Cavalheiro Dias and Andreia Luisa da Rosa
The interplay between dimensionality, band-edge electronic structure, and electron-hole interactions governs the optical response of low-dimensional tellurium, yet the microscopic origin of its excitonic behavior remains largely unexplored. Here, we investigate the quasiparticle, excitonic, and optical properties of two-dimensional tellurium polymorphs and one-dimensional helical nanowires using many-body GW and the Bethe–Salpeter equation. Our results reveal a strong dependence of the excitonic response on band-edge dispersion,
crystal symmetry, and dimensional confinement. $\alpha$-tellurene exhibits comparatively weak and spatially extended electron-hole correlations, whereas the SOC-induced quasi-flat band-edge states of $\beta$-tellurene give rise to a strongly bound and anisotropic near-infrared
exciton. Momentum-resolved BSE eigenvectors and real-space
exciton wave functions directly reveal the contrasting localization and anisotropy of these excitonic states. Remarkably, hydrogen-passivated hexagonal tellurene, previously identified as a
quantum spin Hall phase with $Z_2=1$, supports an even larger direct
exciton binding energy of 0.51 eV together with a compact and nearly isotropic in-plane excitonic distribution. This demonstrates that strong electron-hole correlations are fully compatible with nontrivial band
topology, while the binding strength and spatial character of the
exciton remain strongly dependent on the underlying band-edge electronic structure and
crystal symmetry. The one-dimensional helical nanowire represents the strong-confinement limit, exhibiting a direct high
exciton binding energy and a pronounced shift of the optical response toward the ultraviolet.
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Instrumentation and Methods for Astrophysics
96 kHz on-sky imaging on an adaptive optics system with a single-photon avalanche diode
Theodore A. Grosson, Maaike A. M. van Kooten, Kathryn Jackson et al. (+2 more)
Astronomical observations requiring extremely high angular resolution necessitate advanced adaptive optics (AO) systems to overcome blurring caused by the atmosphere. In addition to obtaining much sharper point-spread functions (PSFs) with these systems, it is beneficial to be able to characterize the behaviour of the resulting PSF across time and wavelength. We have installed a commercially-available Single-
photon avalanche diode (SPAD) array on the focal plane of the REVOLT AO testbench at the Dominion Astrophysical Observatory, allowing us to observe the visible PSF of the system at rates up to 96 kHz. This provides a time-resolved view of the PSF at $\sim$100 times the frequency of the AO system itself. We use this detector to analyze the high-frequency behaviour of the PSF of the AO system, including residual tip/tilt and deformable mirror response. We also explore the performance of AO-assisted lucky imaging, in which we average together only the frames which result in the best image quality. We find that high-framerate imaging can significantly improve the PSF beyond the native capabilities of the AO system.
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All authors Theodore A. Grosson, Maaike A. M. van Kooten, Kathryn Jackson, Jean-Pierre Veran, Simon Carrier
Instrumentation and Methods for Astrophysics
Exploring the trade-space of distributed aperture telescopes for faint-object spectroscopy
Theodore A. Grosson, Deborah M. Lokhorst and Alan W. McConnachie
Scientific programs targeting the faintest objects push modern
telescopes to increasingly large sizes, high costs and complex designs. Obtaining spectra of low surface brightness
galaxies, for example, requires hours of observations on state-of-the art instruments. Increasing
telescope diameters beyond 40 m raises potentially insurmountable challenges for design and funding. An innovative strategy for combating these costs is to use many small
telescopes in place of a single large aperture. For observations in which high angular resolution is not necessary, this can be equivalent to a large diameter
telescope in terms of sensitivity, while diffraction limited by the individual aperture. Improvements in commercial off-the-shelf (COTS) components have made this concept a possibility, as demonstrated by instruments such as the Dragonfly Telephoto Array, the Huntsman
Telescope, and the Argus Array. In this work, we discuss the merits of "distributed aperture
telescopes" as applied to the use case of spectroscopic observations of ultra-diffuse
galaxies (UDGs). We compare the cost and simulated scientific performance of different configurations of apertures, detectors, and other components for this purpose, finding that an array of half-metre
telescopes can obtain comparable observations to large
telescopes for a fraction of the cost. Finally, we discuss the path to prototyping an array which will enable a spectroscopic survey of UDGs.
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Superconductivity
Superconductivity and Magnetism in Bi-Ni System: From Bulk to Heterostructures
Gabriel Sant'Ana, Yutao Xing and Milton A. Tumelero
Unconventional superconductivity with ingredients of magnetism such as time reversal breaking, triplet pairing and proximity effects has been a long time pursued topic in physics and material science as a new source of innovative phenomena and effects to drive further scientific advances and technologies. The Bi-Ni system has emerged as a convenient candidate for the investigation of such phenomenology. Strictly speaking, the term Bi-Ni system refers to two different schemes, first to the NiBi$_{3}$ intermetallic compound, a 4 K
superconductor in which a complex magnetism seems to govern electrical properties in the normal phase, but without implication in the superconducting properties. The second Bi-Ni system is not quite a material but a
heterostructure formed by a
bilayer of Bi and Ni. Here the superconducting phase has to steal the spotlight by showing strong evidence of time-reversal breaking and triplet pairing featuring a complex unconventional state. The ease of preparing the samples, compared to other candidates for such unconventionality, usually Uranium-based compounds, has accelerated the research in this system. Here, we went through a detailed review of the main results about the electronic properties of these two systems as well as a discussion of the main open questions to be solved in order to reach the complete understanding in this topic.
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General Relativity and Quantum Cosmology
Stationary Rotating Geometries Associated with Nonsingular Pulsating Collapse
A. D. Souza, F. A. Brito and J. Spinelly
Since the first exact solutions of General Relativity (GR) were obtained, it became clear that the theory predicts a new class of compact objects: black holes. The Hawking–Penrose singularity
theorems show that, under appropriate assumptions, gravitational collapse in GR leads to singular behavior. Motivated by the expectation that such regimes require physics beyond classical GR, effective approaches inspired by Loop
Quantum Cosmology (LQC) and braneworld scenarios introduce high-density corrections. In this work we consider the static exterior geometry introduced by Gao, Lu, Shen, and Faraoni, associated with a comoving interior model in which the singularity is avoided through a sequence of collapse and bounce phases. Using the Newman–Janis
algorithm in the Azreg-Aïnou formulation, we construct a stationary rotating exterior extension of this geometry. The resulting line element describes a stationary axisymmetric rotating spacetime whose horizon geometry, angular velocity, surface
gravity, and Hawking temperature recover the Kerr and Schwarzschild limits when the
quantum/braneworld correction becomes negligible ($l\to 0$). We further analyze the thermal response at fixed rotational state-space parameter, identify Davies-type singular points, and formulate an extended thermodynamic state-space relation.
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Superconductivity
Direct Evidence of Unconventional Superconductivity in Doped Kagome system RV$_3$Sb$_5$
Avior Almoalem, Yuqing Xing, Iksu Jang et al. (+7 more)
The superconducting pairing
symmetry of kagome metals remains a central unresolved question largely because phase-sensitive experiments capable of distinguishing between different possible order parameters have been difficult to implement. The spatial and energetic characteristics of
impurity bound states measured by spectroscopic-imaging scanning tunneling microscopy encode information on the superconducting order parameter. Here, we use
impurity-bound state spectroscopy to investigate optimally doped RbV$_3$Sb$_{5}$ where the charge-density wave instability is fully suppressed. We find that the superconducting state is fully gapped and exhibits two distinct energy scales, consistent with a multiband order parameter. Atomic-scale spectroscopy around nonmagnetic defects reveals pronounced particle-hole asymmetric bound states. Comparison with theoretical calculations demonstrates that these bound states are incompatible with conventional $s$-wave and sign-changing $s^{\pm}$ pairing. Our calculations also show that the data are fully consistent with a
chiral order parameter. Our results establish
impurity-bound-state spectroscopy as a powerful phase-sensitive probe of superconductivity in kagome materials and provide strong evidence that optimally doped RbV$_3$Sb$_{5}$ realizes a fully gapped
chiral superconducting state.
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All authors Avior Almoalem, Yuqing Xing, Iksu Jang, Daniel J. Schultz, Grgur Palle, Andrea N. Capa Salinas, Stephen D. Wilson, Rafael M. Fernandes, Jörg Schmalian, Vidya Madhavan
Medical Physics
A Reconfigurable Pipelined-SAR ADC with Embedded Compression for Temporal Compressed-Sensing Ultrasound Imaging
Reza Pakdaman Zangabad, Xitie Zhang, Levent Degertekin et al. (+1 more)
Compact ultrasound imaging systems are increasingly constrained by receiver-side sampling, conversion,
memory, and data-transfer requirements. This work presents a compressed-sensing pipelined successive-approximation-register analog-to-digital converter (CS-SAR ADC) for acquisition-side temporal compression of pre-beamformed medical ultrasound
radio-frequency (RF) data. Pseudo-random polarity modulation and charge-domain accumulation are embedded in the SAR sampling network so that multiple consecutive RF samples are encoded into one measurement before quantization, supporting temporal compression ratios of $N_{cT}=1$, 2, and 4. The compressed outputs are recovered off chip using a probe-specific pulse-dictionary RF model and then processed with conventional ultrasound beamforming. A 65-nm CMOS prototype was measured with a 1.2-V supply and 50-MHz master clock. In the non-compressed mode, it operates at 10 MS/s, consumes 964.49~$\mu$W, and achieves 44.12-dB SNDR and 56.40-dB SFDR for a 7.7-kHz input. The ADC output rates decrease to 5 MS/s and 2.5 MS/s for $N_{cT}=2$ and 4. Across all evaluated RF traces, median NCC values were 0.981 and 0.932, with median NRMSE values of 0.36 and 0.56, respectively. Wire-phantom localization error remained below 0.04 mm with no appreciable FWHM degradation. In the speckle-rich cyst phantom, SSIM remained 0.94 and 0.87, while CNR decreased from 3.534 in the reference to 2.047 and 1.379. These results demonstrate a hardware-realistic tradeoff in which temporal compression substantially reduces ADC conversion count and output data rate while preserving point-target geometry, whereas low-contrast cyst conspicuity is more compression-sensitive.
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All authors Reza Pakdaman Zangabad, Xitie Zhang, Levent Degertekin, Shaolan Li
Quantum Physics
Quantum Preconditioning For Constrained Optimization Problems
Anurag Ramesh, Bhuvanesh Sundar, Maxime Dupont et al. (+1 more)
We study the effect of
quantum preconditioning on constrained combinatorial optimization problems, focusing on balanced graph bi-partitioning. The proposed approach uses two-point correlations between decision variables derived from the
Quantum Approximate Optimization
Algorithm (QAOA) to construct a modified objective function that is subsequently provided to mixed-integer programming (MIP) solvers. The preconditioned MIP formulation retains the original hard constraint, and all incumbent solutions are evaluated under the original objective. Computational experiments on dense, weighted complete-graph instances show that the preconditioned problem instances reach near-optimal solutions faster, with most of the benefit already realized at the shallowest QAOA depth tested. Solver callback trajectories show this arises from earlier discovery of high-quality incumbents during the solution search. These results support a hybrid optimization framework in which
quantum algorithms provide problem-specific information to guide classical exact MIP solvers.
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All authors Anurag Ramesh, Bhuvanesh Sundar, Maxime Dupont, David E. Bernal Neira
Atomic Physics
Estimating the ground-state hyperfine shifts of group-1 atoms due to long-range collisions, static electric fields, and nearby surfaces
B. H. McGuyer, K. Choksi, N. VonHeeder et al. (+1 more)
Many interactions perturb (or shift) the hyperfine coupling in group-1 atoms between their
nuclear spin and single valence electron. Previous work provided an approach to estimate this shift for non-reactive collisions with other atoms or molecules at long range, and extended it to estimate the shift from static electric fields. We further extend this approach to estimate the shift due to a nearby conductive surface, and improve all these estimates by numerically computing updated values for the characteristic energies they use. We investigate how to estimate these energies by scaling arguments, and suggest how to adapt the approach to other applications. The results are relevant to pressure shifts in vapor
cells, Stark shifts, and wall shifts in nanoscale devices.
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All authors B. H. McGuyer, K. Choksi, N. VonHeeder, B. A. Olsen
Mesoscale and Nanoscale Physics
Electrochemical impedance spectroscopy of graphene nanogaps
Patrick A. McKee, Chris S. DeMellier, Robin N. Schipper et al. (+1 more)
Graphene nanogaps represent an emerging platform for nanoscale electrochemical and sensing devices, with potential applications in next-generation biomolecular sequencing. However, their interfacial behavior in aqueous environments remains poorly characterized, particularly with respect to frequency-dependent impedance and charge transport mechanisms at the
graphene edge. We fabricate
graphene nanogaps by controlled electrical breakdown in an inert atmosphere and study their electrochemical response. Upon exposure to ambient conditions, a surface contamination layer supports electrochemical activity within an adsorbed ultrathin conductive film between the
graphene edges. Electrochemical impedance spectroscopy reveals distinct frequency-dependent responses consistent with a Warburg element associated with
diffusion in this confined interfacial film. The impedance evolves systematically with
liquid $\mathrm{p}H$, reflecting changes in electrochemical reaction-
diffusion processes at the
graphene edges. A quantitative equivalent-
circuit model captures these effects and enables extraction of an effective nanogap length scale from impedance spectra, providing information complementary to that obtained from tunneling measurements.
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All authors Patrick A. McKee, Chris S. DeMellier, Robin N. Schipper, Henk W.Ch. Postma
General Relativity and Quantum Cosmology
Torsion and Nonmetricity Constraints From Neutron Spin Rotation in Polarized Matter
Sepehr Samiei, Ralf Lehnert and W. Michael Snow
Many modified-
gravity frameworks employ non-Riemannian connection degrees of freedom, including torsion and nonmetricity. In Einstein-Cartan-type theories, torsion is associated with
spin density, while more general metric-affine frameworks can be investigated through phenomenological searches for in-matter torsion and nonmetricity backgrounds. This work applies an effective field theory approach to characterize general couplings of electron and
neutron operators to spacetime torsion and nonmetricity up to mass dimension six, predicting novel
neutron-polarization signatures in the presence of an electron background.
Neutron spin-rotation data from a polarized-electron ensemble inside a compensated ferrimagnet are used to constrain for the first time axially symmetric, direction-dependent in-matter torsion and nonmetricity combinations.
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Mesoscale and Nanoscale Physics
Domain walls with alternating magnetic order in a model with dipolar coupling
G. M. Wysin
A model for a one-dimensional chain of elongated nano-scale
magnetic islands with dipole interactions is analyzed here for the properties of its static domain walls with site-by-site alternating order. The anisotropic
magnetic islands on a nonmagnetic substrate have their longer axes oriented transverse ($y$-direction) to the chain direction ($x$-direction), in a transverse applied
magnetic field. The islands'
magnetic dipoles $\vec{\mu}_n$ are represented as macrospins of fixed length $\mu$. The nearest-neighbor (NN) dipole interactions drive transverse alternating order, allowing for doubly-degenerate, uniform, static, $y$-alternating states, where the dipoles alternately point transverse to the chain direction, as in $\vec{\mu}_n = \pm(-1)^n \mu \hat{y}$. Assuming only NN interactions, the domain walls connecting these two alternating states are found with numerical relaxation simulations and analyzed in a two-sublattice continuum theory. As the uniaxial anisotropy constant $K_1$ descends from larger values until it closely approaches the NN dipolar coupling constant $D$, the domain wall width grows indefinitely, and the large-$x$ continuum solutions closely approach the
lattice numerical solutions. The applied field produces a very slight canting of the dipoles towards the field, maximum in the center of the domain wall. The dipoles on the two sublattices are found to rotate in opposite senses as one scans along the
lattice, resulting in a large longitudinal
magnetic moment of the domain wall. A much smaller transverse
magnetic moment has a topological contribution that depends on whether the chain length is odd or even.
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Solar and Stellar Astrophysics
The Hot, Continuum-compact State of the Yellow Hypergiant V509 Cassiopeiae: CHARA Diameters, CO-band Angular-extension Constraints, and Companion Limits
Narsireddy Anugu, Gail H. Schaefer, Douglas R. Gies et al. (+4 more)
Yellow hypergiants are rare, evolved massive
stars generally interpreted as post-red-supergiant objects evolving blueward through or near the dynamically unstable Yellow Evolutionary Void. V509~Cassiopeiae is a remarkable example: its spectroscopically inferred effective temperature increased from approximately 5000~K in the mid-1980s to about 7900~K by the late 1990s and has since remained near this value during its post-heating state. We use simultaneous six-
telescope CHARA observations obtained in 2023 with MIRC-X in the $H$ band and MYSTIC in the $K$ band to measure its photospheric diameter, search for a luminous companion, and constrain any spatially extended CO atmosphere. Interferometric data fitting with fixed atmosphere-model center-to-limb variation profiles yield limb-darkened angular diameters of $1.1840$–$1.1950$~mas. Although nominally about 5% smaller than the previous Palomar Testbed Interferometer measurement, the difference is only $1.8\sigma$, indicating no significant secular change over 17–21~yr. The closure phases are consistent with a centrosymmetric brightness distribution, and no near-infrared-bright companion is detected over the sampled separations. The median $3\sigma$ limits are $\Delta H=5.28$~mag and $\Delta K=6.48$~mag. The B1~V companion proposed from ultraviolet spectroscopy is expected to lie below these limits and is not excluded. The CO first-overtone channels give a weighted mean CO-to-continuum diameter ratio of $1.011\pm0.004$, below the adopted $3\sigma$ detection criterion. We find no significant CO-band angular extension. V509~Cas is thus hot and molecularly compact despite retaining spectroscopically visible atomic circumstellar gas.
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All authors Narsireddy Anugu, Gail H. Schaefer, Douglas R. Gies, Anni Kasikov, John D. Monnier, Stefan Kraus, Karolina Kubiak
Quantum Physics
Representation Learning with Quantum Signal Processing
Junqi Wang and Junyu Liu
Representation learning begins when training changes the features that define similarity between data. A frozen-kernel model only reweights a fixed geometry. We establish
quantum signal processing (QSP) as a solvable
quantum model of the representation-learning regime. At arbitrary depth, we compute the exact mean and variance of its
quantum neural tangent kernel, revealing an input-dependent angular geometry whose diagonal remains non-self-averaging even when the underlying
unitary approaches Haar randomness. We also prove a sparse-data guarantee for the full nonlinear gradient flow without freezing or ensemble-averaging the kernel: the realized dynamics converges to an integrable scalar flow with a time-dependent kernel closure and explicit convergence times. A finite-depth speed limit holds for every data set and trajectory. At higher data density, numerical results show coupled
evolution beyond both the scalar and frozen-kernel descriptions. These results give a controlled theory of learned
quantum data geometry with provable training dynamics beyond the frozen limit.
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Mathematical Physics · Cross-listed from math.SP
Non-Elliptic Quadratic $\mathcal{PT}$-Symmetric Operators and Similarity to Self-Adjoint Operators
Stepan Malkov
We prove a similarity result for non-self-adjoint non-
elliptic quadratic $\mathcal{PT}$-symmetric operators with real spectrum satisfying a dynamical averaging condition. In particular, we show that such an operator is weakly similar to a self-adjoint operator precisely when the fundamental
matrix of the associated quadratic form is diagonalizable.
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Quantum Physics
Dissipation across the ultrastrong-coupling regime of nanomechanical quantum Rabi systems
Janine C. Franz and Fabio Pistolesi
Mechanical resonators ultrastrongly coupled to
quantum two-level systems provide a promising route towards mechanical
qubits by introducing significant anharmonicity to the mechanical modes, particularly in the slow-oscillator regime. Although the resulting hybrid system is well described by the
quantum Rabi model, a consistent treatment of dissipation remains challenging across the broad parameter space routinely probed in current nanotube electromechanical devices. Here, we investigate dissipation in the open
quantum Rabi model using a Born-Markov framework based on the slowly varying bath spectrum approximation, yielding a Lindblad master equation applicable far beyond conventional descriptions while recovering them in their respective limits. Using this framework, we analyze experimentally accessible observables across this parameter space. As the secular approximation breaks down,
phonon blockade progressively washes out. Our approach remains valid in this regime, enabling a quantitative description of the continuous
evolution of
phonon blockade with coupling strength and dissipation. At finite temperature, we find a suppression of the temperature-induced increase of coherence decay rate for weak anharmonicity. Under driving, our approach remains applicable to substantially stronger perturbations than conventional dressed-state master equations and shows that an apparently classical observable can coexist with Wigner negativity. We further capture the weakly anharmonic regime arising from finite detuning in the double-
quantum dot. These results establish a unified description of dissipation from weakly anharmonic operating regimes to the strongly anharmonic mechanical-
qubit regime and provide experimentally relevant predictions for ultrastrong electromechanical systems.
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Quantum Physics
BAHAMAS: A Control Plane for Optimization and Execution of Variational Quantum Circuits
Amit Samanta, Mohammad Abrarul Hasanat, Jason Ludmir et al. (+3 more)
Variational
quantum algorithms (VQAs) suffer from unstable optimization due to temporal noise drift and static
qubit mappings that distort gradient signals across iterations. We present BAHAMAS, an online control framework that stabilizes noise exposure by adaptively selecting physical mappings via consensus-based fidelity estimation, without requiring simulators, offline training, or prior executions. Across real
quantum devices, BAHAMAS improves optimization reliability and supports inference-time retargeting under drift through robust, per-iteration control.
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All authors Amit Samanta, Mohammad Abrarul Hasanat, Jason Ludmir, Ryan Stutsman, Tirthak Patel, Rohan Basu Roy
Quantum Physics
Quantum synchronization of spin-1 system: Enhanced synchronization due to additive Lindblad operators
Tran Duong Anh-Tai, S. Zhong, X. Molenda et al. (+2 more)
We experimentally investigate
quantum synchronization for one of the simplest possible
quantum systems, namely an externally driven few-level system with equally spaced energy levels effectively acting as a
spin-1 system. Coupling to excited auxiliary states, we realize additive effective Lindblad operators that are associated with non-conventional dissipative pathways, which are shown to enhance, in certain parameter regimes,
quantum synchronization. The experimental set-up, which utilizes cold $^{87}$Rb atoms in a MOT, and associated synchronization extraction protocol are benchmarked carefully through dedicated simulations. Convincing agreement is found between experiment and simulations. The dissipation engineering approach established in our work can be readily extended to systems with more energy levels, such as effective
spin-$3/2$ or
spin-$2$ systems, and has implications for
quantum synchronization studies in higher-
spin systems as well as for a wide range of
quantum science studies and technology applications.
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All authors Tran Duong Anh-Tai, S. Zhong, X. Molenda, A. M. Marino, D. Blume
Earth and Planetary Astrophysics · Cross-listed from q-bio.OT
Geochemical Hazard Assessment of Martian Regolith for Future Human Exploration
Mavia Anjum and Gwendolyn D. Bart
As human missions to Mars move from concept to planning to reality, a systematic quantitative health risk assessment of martian regolith exposure has become critically important. This study presents a comprehensive multi-element, multi-pathway health hazard analysis of martian regolith for a 70 kg adult astronaut on an 18-month surface mission, using bulk silicate Mars geochemical data and Earth Upper Continental Crust reference values as baseline comparators. We computed Average Daily Dose, Hazard Quotient, Hazard Index, Enrichment Factor, Ecological Risk Factor, and Incremental Lifetime Cancer Risk across all three exposure pathways (oral ingestion, inhalation, and dermal contact) for toxic and heavy metals, under four filtration scenarios (0%, 25%, 50%, 95%). Results demonstrate that Cr and Co represent the most critical non-carcinogenic hazards, exceeding the regulatory threshold (HI > 1) even at 50% filtration, while Cr also poses the most significant carcinogenic risk, near the $10^{-4}$ regulatory threshold level. At least 92% regolith filtration efficiency is required to reduce Cr to acceptable non-cancer hazard levels. Nickel exceeds the acceptable cancer risk threshold of $10^{-6}$ at all filtration levels below 95%. No element other than Cr and Co exceeds HI = 1 in the unfiltered scenario, although Fe, Ni and Mn approach concerning levels. These results establish that a minimum 95% High-Efficiency Particulate Air (HEPA)-grade filtration efficiency combined with active chemical sorption is required for acceptable Cr and Co short term exposure and Cr, Ni long term exposure management. This study provides a pathway-specific quantitative risk framework applicable to habitat air quality standards and EVA suit specifications for Mars surface operations
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Instrumentation and Methods for Astrophysics
X-ray grating spectroscopy as a mission enhancement
Hans Moritz Guenther, Ehud Behar, Joel N. Bregman et al. (+27 more)
We propose to add instruments to any potential future X-ray mission with focussing optics that is considered in NASA's ASTRA framework. Such an instrument is a necessity to study AGN wind
outflows and feedback, find the missing
baryons, study the intergalactic medium, and analyze abundances and chemical bonds in
dust grains throughout the Milky Way. We conclude that those science goals can be achieved with a spectral resolving power > 3000 in the soft X-ray band (about 10-40 Ang) and an effective area a few times larger than current instruments. We describe a possible mission implementation for a soft X-ray grating spectrometer that can be folded in and out or be mounted permanently in the beam. Such an instrument can reach the requirements for a wide variety of host mission properties. A small UV imager and a UV spectrograph can be mounted on the same platform with independent optics. These added instruments vastly enhance the science capabilities of the host mission for a modest cost (100-200 million $) and with weight and power needs that can be easily accommodated in any major mission.
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All authors Hans Moritz Guenther, Ehud Behar, Joel N. Bregman, Laura W. Brenneman, Alexander R. Bruccoleri, Lía Corrales, Elisa Costantini, Thomas Dauser, Casey T. DeRoo, Abraham D. Falcone, Adam R. Foster, Luigi Gallo, Catherine E. Grant, Sean J. Gunderson, Ralf K. Heilmann, David P. Huenemoerder, Maurice Leutenegger, Eric D. Miller, Michael Nowak, Frits Paerels, David A. Principe, Ioanna Psaradaki, Andrew Ptak, Agata Rozanska, Randall K. Smith, Pasquale Temi, Todd M. Tripp, Lynne Valencic, Joern Wilms, Scott J. Wolk