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Physics

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Monday 7 September

Quantum Gases

Where Is the \(p\)-Wave Superfluid? Correlated Phase Diagram of Microwave-Shielded Polar Molecules

Tao Shi

Chiral $p_x\!\pm\! i p_y$ superfluidity in fermionic polar molecules offers a direct route to topological quantum matter with non-Abelian excitations, yet the parameter regime in which pairing survives strong correlations and competing instabilities has remained unresolved. Here we determine this regime for microwave-shielded polar molecules. Under tight confinement along the \(z\) direction, the microscopic molecular interaction collapses onto a universal quasi-two-dimensional form specified by an interaction length $\sigma$, defined as the position of its attractive minimum, and a single dimensionless coupling. We combine Fermi-hypernetted-chain Euler–Lagrange theory with correlated-basis pairing theory, thereby treating the correlation hole, density response, stability of the homogeneous fluid, and $p$-wave pairing within one framework. The largest pairing gap occurs immediately on the stable side of a long-wavelength spinodal instability at a two-dimensional density $4\times10^{-2}/\sigma^2$. Mapping this universal regime onto microscopic shielding schemes exposes an intrinsic limitation of single-microwave dressing: weakening the attraction to the optimal pairing range simultaneously weakens collisional shielding. Dual-microwave dressing removes this constraint by compensating the long-range attraction while retaining a large repulsive core. Imposing explicit requirements on collisional loss, confinement, and microwave-amplitude stability, we identify the regime of molecular mass and dipole moment favorable for \(p\)-wave superfluidity and determine experimentally realistic microwave and confinement conditions for its realization. These results turn the search for molecular $p$-wave superfluidity into a quantitative optimization problem and define a route toward the topological weak-pairing phase.
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High Energy Physics (Phenomenology)

Boosted dark particles and the LZ nuclear recoil event

Kristjan Kannike, Martti Raidal and Alessandro Strumia

The LZ experiment reported one anomalous event with nuclear recoil energy of 248 keV. Galactic halo dark matter (DM) cannot produce such a large energy unless heavier than 74 GeV, and heavy DM with spin-independent interactions would have produced unseen recoils at lower energy. Inelastic DM has been proposed as a way out. We consider, instead, an elastic collision of a dark sector particle with a momentum of at least 123~MeV and mass in the range 1-74 GeV as deuteron break-up in SNO disfavors sub-GeV masses. The absence of accompanying lower-energy recoils favours interactions whose rate grows with the momentum transfer, such as a pseudoscalar-pseudoscalar nucleon operator. This implies no leading-order signal in argon, an annual modulation below 1 %, and recoils in spinful light nuclei where inelastic halo DM gives nothing.
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Materials Science

Exciton Coherence in CsPbBr3 Nanocrystals is Bounded by Phonon-Mediated Bright-Triplet Relaxation

Tara Šverko, Annette J. Jones, Chantalle J. Krajewska et al. (+6 more)

Scalable sources of indistinguishable single photons or entangled photon pairs are fundamental to many quantum photonic technologies. Colloidal lead halide perovskite nanocrystals are promising such sources, but their exciton coherent properties are not fully understood. We show that in single CsPbBr3 nanocrystals at 4 K, acoustic phonon-mediated exciton fine structure relaxation (EFSR) drives leakage of population between the bright exciton triplet states, competing with the radiative lifetime. The leakage pathway reaches 0.64 $\pm$ 0.04 of the radiative rate, bounding state coherence to 0.81 times the transform limit at 4 K. This pathway is intrinsic to the nanocrystal, not its environment, making it a tractable target for materials and device design. We identify fine structure and acoustic phonon engineering as effective intrinsic routes to higher coherence in perovskite quantum light sources.
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All authors Tara Šverko, Annette J. Jones, Chantalle J. Krajewska, Peter C. Sercel, Alexander L. Efros, Alexander E. Kaplan, Niamh L. Brown, Stefano Toso, Moungi G. Bawendi

Plasma Physics

Thresholdless IBW Emission and Alpha-to-Thermal-Ion Energy Channeling via Pole Resonance of Fusion-Product Ions

Hong Qin and Nathaniel J. Fisch

Fusion reactions can release a substantial fraction, and in aneutronic reactions nearly all, of their energy as the kinetic energy of fusion-product ions. In magnetized plasmas, these energetic ions can form ring distributions in velocity space. Such distributions can drive Dory-Guest-Harris (DGH) electrostatic instabilities, but these self-instabilities require a finite energetic-ion density and can be stabilized by a thermal background. We show that the same background can instead enable a distinct instability mechanism: a cyclotron pole of the minority energetic-ion susceptibility destabilizes a stable ion Bernstein wave (IBW) eigenmode. When the energetic-ion harmonic is distinct from the thermal-ion harmonics, exact root-pole resonance is thresholdless in the ideal collisionless limit. A species-resolved power balance shows that the energetic ions supply the free energy while the thermal plasma receives it. In the LAPD proton–alpha example, $99.96\%$ of the alpha-particle power loss enters the coherent proton response. This self-excited, ion-directed transfer provides a possible linear building block for alpha-particle energy channeling in proton-Boron11 fusion.
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Quantum Physics

Propaq: A Python package for Heisenberg Propagation

Hrishikesh Belagali and Ryan LaRose

We introduce Propaq, a performant and flexible Python package implementing Heisenberg propagation techniques for classically simulating quantum circuits. Propaq is compatible with major quantum software packages like Qiskit and Cirq, and matches or outperforms similar state-of-the-art packages for Heisenberg propagation. Beyond this, Propaq has multiple distinguishing features for simulation and research. These include Heisenberg propagation in any basis, hybrid Schrödinger-Heisenberg simulation, custom truncation and noisy simulation methods, and detailed logging information for analyzing simulation accuracy, runtime, and memory usage. We describe these features, how to use Propaq for research, and its backend implementation.
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Instrumentation and Detectors

Real-time blind indexing by cross-frame consensus

Stefano Marchesini and Yuan Ni

Classical crystallography determines orientation and unit-cell geometry from a rotation series collected from a single specimen, whereas serial crystallography acquires one still exposure from each of many randomly oriented microcrystals and must reconstruct a complete dataset by pooling partial measurements across the ensemble. In serial experiments, each frame typically contains only a subset of reflections, and frames with few reliable peaks (the small-N regime) are especially difficult to index blindly, because multiple incorrect lattices or orientations can explain sparse observations. The approach implemented in GLINT addresses this small-N regime by treating the dataset, rather than the individual frame, as the unit of inference. Candidate solutions are generated for many frames, weak but recurrent lattice hypotheses are pooled across the ensemble to identify a shared unit cell, and each frame is then registered against that consensus cell through a known-cell orientation search with lower dimensionality than blind indexing. In benchmark tests, GLINT matched the strongest blind indexer in the comparison on indexing yield at roughly 40x lower per-frame blind-indexing latency against XGANDALF's fastest configuration, and batched known-cell registration ran entirely on one GPU, allowing cell discovery on the fly during serial data collection. On experimental serial data, frames indexed blind by GLINT merged to crystallographic quality (CC* = 0.90), while the method rejected non-crystal images rather than forcing unsupported indexing assignments. These results demonstrate that indexing performance can be evaluated not only by indexing yield and throughput, but also by the quality of the resulting merged crystallographic data.
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Quantum Physics

Trapped Ion Qubit Gates and Entanglement Driven by an Integrated Photonic Laser

Chris Caron, Zhenyu Wei, Andrei Isichenko et al. (+8 more)

Trapped ions are a leading technology for quantum computing, but their reliance on bespoke tabletop laser and optical systems remains a major obstacle to scaling and robustness. Integrated silicon nitride lasers, compatible with future monolithic integration with surface electrode ion traps, have recently demonstrated frequency-selective qubit state preparation and measurement as well as interrogation of an optical clock transition. However, coherent qubit gates impose even more stringent requirements on laser phase noise, and their implementation with integrated laser sources has remained an outstanding challenge. Here, we use a visible-wavelength integrated Brillouin laser stabilized to an integrated coil resonator to drive coherent single- and two-qubit gates with \Sr optical qubits. We measure an average single-qubit fidelity of $99.61\%\pm 0.03\%$ per Clifford gate with randomized benchmarking and use a two-qubit Mølmer-Sørensen interaction to generate an entangled Bell state with a fidelity of $92.35\% \pm 1.50\%$. The qubit exhibits a bare Ramsey coherence time of $659 \pm 9~\mu$s, more than a tenfold improvement over our previous implementation, which extends to $1.750 \pm 0.033$~ms with an echo. These results demonstrate, for the first time, that integrated visible-wavelength narrow-linewidth photonic lasers can meet the phase-noise requirements for coherent quantum logic with trapped ion optical qubits, providing a path for scalable optical systems integrated within trapped ion quantum processors.
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All authors Chris Caron, Zhenyu Wei, Andrei Isichenko, David Heim, Meiting Song, Nitesh Chauhan, Nick Montifiore, Kaikai Liu, Josiah Dill, Daniel J. Blumenthal, Robert J. Niffenegger

Mesoscale and Nanoscale Physics

Metal-Insulator Coexistence and Gap-Crossing Domain-Wall Modes in an Aubry-André Model with Nonlocal Hopping

Xiarui Zhan, Mingsheng Tian, Qiongyi He et al. (+2 more)

Nonequilibrium transport remains a central theme in modern physics, spanning from condensed matter to synthetic systems. Here, we investigate particle transport in an extended Aubry-André model with system-scale hopping, namely nonlocal hopping with a range proportional to the system size, and uncover a metal-insulator coexistence regime in real space, where metallic and insulating spatial domains coexist within the same system and are separated by sharp spatial boundaries. In the insulating region, particles exhibit flat-band-like localization in the absence of quasiperiodic potentials, while a quasiperiodic potential induces distinct multi-point localization, different from conventional exponential localization. Meanwhile, particles can freely propagate and tunnel across spatially disconnected metallic domains separated by the insulating region. Beyond this coexistence phase, we identify unconventional gap-crossing domain-wall modes with comb-like spatial profiles that mediate nonlocal, multi-point transport across separated metallic domains. Our findings reveal a rich interplay between localization, nonlocality, and transport in systems with nonlocal hopping.
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All authors Xiarui Zhan, Mingsheng Tian, Qiongyi He, Kaiye Shi, Wei Zhang

High Energy Astrophysical Phenomena

Bridging the Population Synthesis of Supermassive Binary Black Holes and the Gravitational Wave Background

Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito et al. (+1 more)

Pulsar Timing Arrays (PTAs) constrain population properties of supermassive binary black holes (SMBHBs) through the observation of the gravitational wave background (GWB). Unlike other approaches that interpolate population-synthesis libraries or only consider the mean of the strain spectrum, here we capture its full strain probability density directly from semi-analytic population models. We apply our new method to the semi-analytic SMBHB population model, independently reproducing the parameter estimation for this model performed by the NANOGrav Collaboration with their 15-yr data. We also show the extent to which discrete SMBHB contributions to the GWB resolve degeneracies in the population parameter space. Finally, using the source-count intensity as the intermediate product in our calculation, we map PTA observations, as a proof of principle, to the SMBHB model based on the galaxy merger prescriptions from numerical hydrodynamical simulations "Illustris". We find the effect of delay times $\tau$ between kiloparsec and subparsec SMBHB separations following galaxy mergers, finding $h_{\rm c}$ spanning $(1$-$6)\times10^{-16}$ and $N_{\rm c}$ spanning $(0.3$-$7.1)\times10^{-3}$ for $\tau$ up to 8 Gyr.
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All authors Kanyuni Iemoto, Boris Goncharov, Gabriela Sato-Polito, Xiaoming Bi

Quantum Physics

Subsystem self-correction of the GKP qubit

Brian Chung Hang Cheung, Lasse Bjørn Kristensen, Frederik Nathan et al. (+1 more)

Passive quantum error correction, also known as self-correction, is a holy grail in quantum information science. Recent theoretical advances suggest that the Gottesman-Kitaev-Preskill (GKP) code can exhibit self-correction properties, positioning it as a candidate for the realization of self-correcting quantum memories. In this article, we provide a self-contained derivation of the self-correcting behavior of the ideal GKP Hamiltonian, manifested in the Arrhenius type scaling of the logical lifetime, from a quantum-information perspective based on the subsystem code decomposition. When coupling through the physical quadrature $q$ and $p$, the detailed-balance jump operators decompose into a dominant part acting only on the gauge subsystem and a boundary term that acts non-trivially on the logical qubit. The boundary term is then exponentially suppressed by the Gibbs weights near the edge of the modular cells. In contrast to spin-based quantum memories such as the two-dimensional surface code, the GKP Hamiltonian realizes an effective string tension in modular phase space, whereby the energy cost increases as an error approaches the boundary of a logical sector.
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All authors Brian Chung Hang Cheung, Lasse Bjørn Kristensen, Frederik Nathan, Michael Kastoryano

Astrophysics of Galaxies

Improving constraints on the Yukawa correction at the Galactic Center with multiple stellar orbits

GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar et al. (+76 more)

We investigate the presence of a Yukawa-like correction ($\propto \, \alpha e^{- r/\lambda}$) to Newtonian gravity at the Galactic Center, using a multi-star fitting code, including the newly discovered star S$301$, to improve the constraints obtained using S$2$ orbit alone. We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of stars S$2$, S$55$, S$29$, S$38$ and S$301$ collected by GRAVITY, GRAVITY$^+$, NACO and SINFONI instruments, covering the period from $1992$ to $2025$. Compared to GRAVITY Collaboration 2025 (Paper I), in which only S$2$ was fitted, the tightest bound on the Yukawa coupling is again reached at $\lambda = 3\cdot10^{13}\,\rm m\ (\sim 200\,AU)$, where we find $|\alpha| < 6 \cdot10^{-4}$, an improvement of roughly a factor five. The addition of S$301$ extends the constraint to short ranges that were inaccessible to S$2$, yielding $|\alpha| < 0.004$ at $\lambda =10^{12}\,\rm m$ and $|\alpha| < 0.006$ at $\lambda =5\cdot 10^{11}\,\rm m$, while S$29$, with its larger apoapsis, gives $|\alpha| < 0.1$ at $\lambda \sim 2\cdot10^{15}\,\rm m$. The latter two represent the tightest limits at these scale lengths on a Yukawa correction obtained to date around a supermassive black hole.
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All authors GRAVITY+ Collaboration: A. Foschi, K. Abd El Dayem, N. Aimar, A. Berdeu, J.-P. Berger, G. Bourdarot, W. Brandner, Y. Cao, C. Correia, S. Cueves Cardona, R. Davies, D. Defrère, F. Delplancke-Ströbele, A. Drescher, F. Eisenhauer, L. Esteras Otal, M. Fabricius, H. Feuchtgruber, S. Flesch, N.M. Förster Schreiber, Q. Fournier, P. Garcia, R. Garcia Lopez, R. Genzel, S. Gillessen, F. Gonté, X. Haubois, S.F. Hönig, M. Houllé, S. Joharle, J. Kammerer, A. Kaufer, P. Kervella, L. Kreidberg, L. Labadie, S. Lacour, O. Lai, R. Laugier, J.-B. Le Bouquin, J. Leftley, R. Li, B. Lopez, D. Lutz, F. Mang, A. Mérand, F. Millour, M. Montargès, N. Morujão, H. Nowacki, M. Nowak, J. Osorno, T. Ott, S. Pappert, C. Paladini, T. Paumard, K. Perraut, G. Perrin, R. Petrov, N. Pourré, S. Rabien, D.C. Ribeiro, S. Robbe-Dubois, M. Sadun Bordoni, J. Sanchez-Bermudez, J. Sauter, J. Scigliuto, J. Shangguan, T.T. Shimizu, F. Soulez, C. Straubmeier, E. Sturm, M. Subroweit, C. Sykes, L.J. Tacconi, P. Thévenet, I. Urso, F.H. Vincent, J. Woillez, G. Zins

Instrumentation and Methods for Astrophysics

Approximating the statistics of a gravitational wave background

Mikel Falxa

The astrophysical origin of the gravitational wave background (GWB) reported by pulsar timing array (PTA) collaborations has yet to be confirmed. A GWB signal made of the sum of individual gravitational wave (GW) from the population of supermassive black hole binaries (SMBHB) would show the imprint of a discrete Poissonian statistics in its spectral properties. In this work, we propose a tool based on the saddlepoint approximation method to estimate the distribution of characteristic strain for any given population model. This tool can be used for Bayesian inference or for a quick visualization of the statistics of the GWB from the output of more realistic semi-analytical models. We introduce the general family of variance mixture Gaussian distributions that models heavy-tailed behavior distributions that is expected for a non-Gaussian GWB signal. We show that setting the correct hierarchical priors to a Gaussian free spectrum PTA likelihood is effectively equivalent to a non-Gaussian likelihood. Using ideal simulations, we compare the performance of the saddlepoint approximation with a log-Normal distribution to infer the parameters of the astrophysical model from the statistics of the GWB and show that correctly modeling higher order moments is essential. Future PTA analyses should include the statistics of the GWB in their pipelines.
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Applied Physics

Quantum Sensing for Spatial Spin Noise Mapping via Nitrogen-Vacancy Magnetic Quenching in Diamond

Ashley J. Tyler, Thomas D. Bateman-Price, Bradley T. Flinn et al. (+4 more)

Detecting and mapping spin noise can reveal spatial variations in surface defect states, catalytic residues, free radicals, and spintronic materials. However, bulk measurements average over spatial heterogeneity, while scanning-probe maps require sequential rastering. Here, we demonstrate a microwave-free magnetic quenching (MQ) method for wide-field spin-noise mapping using nitrogen-vacancy (NV) centres in diamond. The protocol combines continuous LED illumination with a low-frequency, amplitude-modulated magnetic field, avoiding resonant microwave delivery or pulsed optical hardware. Field-induced spin-state mixing reduces NV photoluminescence, providing the primary contrast mechanism. We examine the response as a function of optical power and magnetic modulation amplitude, interpreting the results using a spin-state mixing model. The method is validated with aqueous gadobutrol concentration series, showing trends consistent with optically detected magnetic resonance (ODMR) measurements. We map spin-noise variations across boron nitride and single-walled carbon nanotube samples with differing defect and metallic catalyst contributions, supported by electron microscopy and spectroscopy. Notably, MQ detects a spin-noise response in boron nitride nanotubes that is silent in bulk EPR spectroscopy. This approach provides a practical framework for spatially resolved spin-noise sensing across quantum technologies and advanced functional materials.
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All authors Ashley J. Tyler, Thomas D. Bateman-Price, Bradley T. Flinn, William J. Cull, Tom J. P. Irons, Andrei N. Khlobystov, Melissa L. Mather

Quantum Physics

Dynamical Crossover of the Quantum Fisher Information in the Spin-Boson Model

D. Parlato, G. Di Bello, F. Pavan et al. (+2 more)

We investigate the dynamical quantum Fisher information of a two-level system coupled to a bosonic environment, focusing on the estimation of the qubit gap. We combine analytical calculations with numerically controlled matrix-product-state simulations. In the exactly solvable pure-dephasing Ohmic regime at zero temperature, the long-time quantum Fisher information displays a coupling-dependent algebraic behavior, leading to a dynamical crossover: it grows without bound at weak coupling, approaches a finite asymptotic value at the crossover coupling, and vanishes at strong coupling. At finite temperature, thermal fluctuations suppress the long-time growth and generate a finite-time maximum, whose dependence on the dephasing coupling retains a clear signa- ture of the zero-temperature crossover. We show that this crossover is absent at zero temperature in non-Ohmic baths: the long-time quantum Fisher information vanishes in the sub-Ohmic and diverges in the super-Ohmic regimes. At non-zero temperature instead, the crossover appears for a super-Ohmic quadratic bath and the crossover coupling becomes temperature-dependent. Moreover, in the zero-temperature Ohmic regime, we introduce an additional amplitude-damping system-bath coupling that induces energy relaxation. This relaxation channel replaces the unbounded long-time growth with a finite asymptotic quantum Fisher information associated with the reduced interacting ground state, while a signature of the pure-dephasing crossover persists in the early-time dynamics. These results establish a direct connection between the low-frequency structure of the bath and the asymptotic metrological behavior of dynamical gap sensing, and show how thermal fluctuations and energy relaxation regularize the ideal pure-dephasing dynamical crossover of the quantum Fisher information.
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All authors D. Parlato, G. Di Bello, F. Pavan, G. De Filippis, C. A. Perroni

Fluid Dynamics

Propeller-wing interactions of a lift + cruise eVTOL configuration during transition

Oliver Westcott, Robert Entwistle and Swathi Krishna

The wakes of a lift + cruise aircraft's vertical lift propellers interact with the wing during the transition from hover to forward flight. This study investigates how variations in axial and longitudinal separations between the vertical lift propellers and the wing affect aerodynamic performance during this critical phase. Axial variations were introduced by orienting the motors either upright or inverted at two longitudinal positions relative to the wing. Wind tunnel tests were conducted on the resulting lift + cruise wing configurations over a Reynolds number range of 52,000 to 377,000, using tufts, pressure taps, and load cells to capture aerodynamic behaviour. Results show that the early transition phase (front propeller advance ratios between 0 and 0.25) is particularly sensitive to configuration changes. Rear motor orientation had a pronounced effect: when oriented upright at the shortest longitudinal separation, the active lift propellers increased the lift-drag ratio of the design by approximately 4 units, whereas in the rear motor inverted case the design suffered a 4-point reduction in the lift-drag ratio. Decreasing the longitudinal separation amplified both the beneficial lift contribution of the rear propeller and the generally adverse effects of the front propeller. However, placing the front propeller closer to the wing in the upright orientation enhanced performance at advance ratios between 0.11 and 0.25, due to favourable interactions between the wing and the front propeller's trailing vortices.
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High Energy Physics (Phenomenology)

Gravitational Wave in an $A_4 \otimes Z_4$ Neutrino Model with Generalised CP

Pulakesh Borah and Mrinal Kumar Das

We extend the Standard Model with an $A_4 \times Z_4$ flavor symmetry and generalized CP (GCP) symmetry, realized through two flavon triplets that spontaneously break $A_4$ and generate the observed lepton mixing pattern. A new $A_4$-singlet flavon couples to one of these triplets through a complex quartic interaction that breaks GCP and fixes the reactor mixing angle; this same coupling biases the domain walls formed when that triplet breaks $A_4$. A global fit to oscillation data reproduces all mixing angles and mass splittings, predicting a maximal Dirac CP phase of $270^\circ$ and an effective Majorana mass near $15\text{ meV}$, testable by upcoming neutrinoless double-beta-decay ($0\nu\beta\beta$) experiments. The same coupling generates a stochastic gravitational-wave background peaking in the pulsar-timing-array and LISA bands, with peak frequency and amplitude predicted to scale as $\sin\theta_{13}$ and $\sin^{-4}\theta_{13}$, a falsifiable link between neutrino oscillation and gravitational-wave (GW) observations.
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Statistical Mechanics · Cross-listed from stat.CO

Thermodynamic Cyclic Processes with Markov Samplers in Bayesian Inference

Heinrich von Campe and Bjoern Malte Schaefer

The concept of Markov chain Monte Carlo (MCMC) cycles, an analogy to cyclic processes in heat engines, is presented in order to examine Bayesian inference problems. In this effort, we develop adaptive ensemble schedulers that allow the tuning of external parameters of a Bayesian canonical ensemble during an MCMC run, realising the MCMC cycles in practice. We run these cycles on different statistical models. As a fundamental insight, we find (both theoretically and in practice) that such systems can produce a non-zero net work output if and only if the considered model is non-Gaussian. As such, they may serve as a measure of non-Gaussianity in Bayesian inference, which we test on an example from supernova cosmology.
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General Relativity and Quantum Cosmology

The generalized second law for Kerr-Taub-NUT black holes perturbed by test field

Koray Düztaş and Ahmet Cem Erdoğan

We evaluate the variations in the area and the entropy of Kerr-Taub-NUT black holes perturbed by bosonic and fermionic test fields. We demonstrate that the critical frequency for a test field at which the variation of the area vanishes is strictly larger than the superradiance limit for Kerr-Taub-NUT black holes. Therefore both bosonic fields in the relevant range and fermionic fields which do not exhibit superradiant scattering can induce a decrease in the area of a Kerr-Taub-NUT black hole. However, the entropy is not directly proportional to the area for Kerr-Taub-NUT black holes. Only fermionic fields with frequencies below the superradiance limit can induce an entropy decrease. The simultaneous loss of entropy by the black hole and the environment identifies a generic violation of the Generalized Second Law (GSL) for fermionic perturbations that fail to satisfy the Null Energy Condition (NEC). For bosonic perturbations that satisfy the NEC, we evaluate the limiting case, where a nearly extremal black hole is perturbed by a scalar field with frequency slightly above the superradiance limit. Our analysis reveals that the minimum increase in the black hole entropy compensates for the entropy loss of the environment, when one assigns Von Neumann entropy to the test field. The GSL remains valid for perturbations satisfying the NEC.
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Optics

Non-Hermitian reconstruction of hybridized hyperbolic shear polaritons

Zijia Dang, Zhe Cui, Gang Zhong et al. (+2 more)

Hyperbolic shear polaritons (HShPs) represent a distinctive class of anisotropic polaritonic states that enable directional subwavelength light manipulation through asymmetric momentum-space dispersion, while their control in twisted systems has so far relied mainly on geometric and spectral parameters. Here, we introduce non-Hermitian dissipation as an additional degree of freedom for tuning HShPs in twisted van der Waals heterostructures. In twisted {\alpha}-MoO3/{\alpha}-V2O5 heterostructures with closely matched isofrequency contours but distinct dielectric losses, dissipation modifies the complex hybrid polaritonic states and thereby tunes the resulting momentum-space and real-space asymmetry. Near-field infrared imaging combined with analytical modeling and full-wave simulations reveals the evolution of the shear response with twist angle, excitation frequency, layer thickness, and substrate dielectric environment. The interplay between material dissipation and dielectric screening enables continuous regulation of the shear degree and reversible switching between shear-off and shear-on states. Furthermore, we demonstrate a proof-of-concept binary-state encoding scheme based on dissipation-controlled shear-state switching. Our work identifies non-Hermitian dissipation as an additional control parameter in twisted polaritonic systems, expanding the available design space for reconfigurable mid-infrared nanophotonics.
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All authors Zijia Dang, Zhe Cui, Gang Zhong, Jingying Liu, Qingdong Ou

Materials Science · Cross-listed from cs.LG

Online Surrogate Repair: Decoupling High-Fidelity Feedback from Search Length in Closed-Loop Discovery

Xiaotang Feng, Philip Torr and Bruno Andreis

Closed-loop AI scientists can generate candidate designs at low marginal computational cost, whereas reliable feedback may require wet-lab synthesis, characterization, or high-fidelity computation. Addressing this imbalance through custom laboratory automation remains infrastructure-intensive and costly, while replacing new experiments with a fixed surrogate leaves persistent model errors that can be amplified by optimization. We propose online surrogate repair (OSR), a closed-loop algorithm that uses sparse high-fidelity evaluations to update the surrogate throughout a longer agent search conducted primarily with inexpensive surrogate feedback. An acquisition rule selects which designs from the agent's accumulated proposals receive high-fidelity evaluation, and the resulting labels update the surrogate used in subsequent episodes. Across controlled synthetic environments, we demonstrate that improving global surrogate fit does not necessarily reduce maximum regret, whereas Q90-UCB and expected improvement (EI) substantially reduce regret by directing evaluations toward regions that determine the optimizer's decisions. \osradded{Across LLM and Chemeleon workflows, Online EI reduces the amount of oracle queries required by 84.3–90.3% for matching discovery counts and by 77.9–81.6% for matching the quality of the best material found.} Online surrogate repair introduces a third feedback regime between fixed-surrogate operation and high-fidelity feedback after every episode, separating the frequency of high-fidelity evaluation from the duration of the agent's search.
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Quantum Physics

Microwave-Free $^{13}$C Hyperpolarization of Diamond Particles Enabled by Magic Angle Spinning and NV Centers

Rémi Blinder, Guzel Musabirova, Daehee Kim et al. (+6 more)

Nuclear hyperpolarization from optically pumped color centers in solids offers an alternative to conventional microwave-driven dynamic nuclear polarization (DNP). Diamond can host the nitrogen vacancy (NV) center, whose ground spin state can be readily polarized by light at room temperature, making diamond a candidate platform for nuclear hyperpolarization. We report $^{13}{\rm C}$ nuclear hyperpolarization in randomly oriented diamond particles with sizes ranging from 0.2 to 2 $\mu$m, both at natural $^{13}{\rm C}$ abundance (1.1 %) and at 20 % isotopic enrichment, at magnetic fields of 7.1 T and 9.4 T. The protocol combines optical illumination with magic angle spinning (MAS) and does not require microwave irradiation. By investigating the nuclear polarization as a function of the MAS frequency between 0 and 6 kHz at the magnetic field of 7.1 T, we find maximum light-induced polarization enhancements of $280$-fold for the isotopically enriched sample and $411$-fold for the natural abundance sample. Under continuous illumination, steady-state absolute $^{13}{\rm C}$ polarization levels above 0.1 % are reached. A model involving optical pumping of NV centers and spin dynamics near level anticrossings (LACs) in three-spin clusters formed by NV, a substitutional nitrogen (P1) and $^{13}{\rm C}$ is used to describe these findings. The protocol strongly mitigates the effect of the anisotropy of the NV spin Hamiltonian, allowing more than $99.9\%$ of NV orientations to participate in the polarization transfer process. These results represent a first step toward transferring nuclear polarization from diamond particles to external nuclei, with potential applications in sensitive and high-resolution NMR at room temperature.
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All authors Rémi Blinder, Guzel Musabirova, Daehee Kim, Anshuman Nayak, Jason Twamley, Viateschlav N. Agafonov, Raiker Witter, Jörg Matysik, Fedor Jelezko

Solar and Stellar Astrophysics

R-matrix calculations for opacities: V. Temperature-density dependence of photoabsorption cross sections and opacity spectra of oxygen ions O VI and O VII

Divya Chari, Sultana N Nahar and Anil K Pradhan

We present R-matrix photoabsorption cross sections for Li-like oxygen O VI and He-like oxygen O VII and examine how plasma broadening modifies them as a function of temperature and density in astrophysical and laboratory high-energy-density (HED) plasma sources. All atomic systems are subject to plasma environment effects, and the propagation of radiation depends on photoabsorption via bound-bound transitions as spectral lines and autoionizing resonances in bound-free photoionization cross sections. We identify and illustrate low and high temperature-density limits for the onset of plasma broadening in O VI and O VII, demonstrating general features and methodology applicable across a broad range of plasma conditions. Calculations are presented along two representative isotherms corresponding to the solar base of convection zone (BCZ) at $T = 1 \times 10^6$ and $2 \times 10^6$ K, and electron densities $N_e = 10^{18}$-$10^{23}$ cm$^{-3}$. Autoionizing resonances progressively dissolve into the continuum with increasing electron density at each isotherm, flattening and merging into the background cross sections at BCZ conditions, at much lower densities than bound-bound line features require. Illustrative examples are given for energy regions containing Rydberg resonance series, including large photoexcitation-of-core (PEC) resonances. Comparisons with previous Opacity Project results reveal that (i) the R-matrix photoionization cross sections cover a much higher energy range where a significantly richer spectrum of autoionizing resonances are present that are not included in OP, and (ii) the corresponding monochromatic opacities show significant quantitative differences. This work is generally applicable to modeling HED plasmas in astrophysics, and to the analysis of transmission spectra in laboratory experiments on inertial confinement fusion (ICF) devices.
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Optics

A 0.35 mm Silicon Carbide Diffractive Waveguide with Dual Parameter Apodization for Full Color Augmented Reality

Xiaoxuan Li, Ce Li, Yinggang Chen et al. (+5 more)

Augmented reality eyewear offers a transformative interface poised to reshape human information interaction. In this context, silicon carbide (SiC) offers unique advantages for diffractive waveguides with its high refractive index and excellent thermal conductivity. However, in single-layer full-color displays, existing SiC waveguides generally remain thicker than 0.5 mm to reduce the bounce count of total internal reflection, thereby avoiding severe spatial variations in luminance and color. Here, we demonstrate a 0.35 mm SiC diffractive waveguide with an ultra-lightweight of only 1.98 g. The challenge of spatial non-uniformity is addressed by dual-parameter apodized gratings with continuously varying depth and duty cycle, enabling fine spatial control over local diffraction efficiency. To realize high-throughput production, a parallel gradient transfer method compatible with nanoimprint lithography is introduced, enabling wafer-scale patterning of four lens pairs per 8-inch SiC wafer. Furthermore, magnesium fluoride planarization suppresses grating visibility and achieves a high see-through transmittance of 92%. Optical simulations confirm that this architecture achieves balanced full-color transmission across a 30-degree field of view. This strategy provides a scalable route toward ultra-light and visually unobtrusive glasses, opening new opportunities for practical consumer-grade wearable displays.
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All authors Xiaoxuan Li, Ce Li, Yinggang Chen, Chenting Fang, Boqu Chen, Lu Cai, Kaikai Du, Min Qiu

High Energy Astrophysical Phenomena

Interior Magnetic Fields in Magnetars and Radio Pulsars

Raj Kishor Joshi, Brynmor Haskell, William Cook et al. (+1 more)

Magnetic fields are fundamental for neutron star physics and play a central role in powering the extreme phenomenology of magnetars, including Soft Gamma Repeaters and Anomalous X-ray Pulsars. However, the structure and stability of their internal magnetic fields remain largely unconstrained, as they cannot be directly probed by electromagnetic observations. Using 3D general-relativistic magnetohydrodynamics simulations across a range of rotation rates and magnetic field strengths, we identify two distinct evolutionary regimes leading towards dynamically stable magnetic configurations. In rapidly rotating stars, the Alfvén crossing timescale exceeds the rotation period, allowing differential winding to amplify a strong toroidal magnetic component before the onset of instabilities, leading to long-lived, stable configurations. In contrast, in magnetically dominated stars, instabilities in the poloidal field drive rapid field decay, leaving only a comparatively weak toroidal component. These results imply that the internal magnetic structure of neutron stars depends sensitively on their rotational state: rotation-dominated stars like radio pulsars develop strong toroidal fields, while magnetars are characterized by predominantly poloidal configurations. Our findings therefore show that a neutron star's rotational history shapes its internal magnetic structure, providing a unifying physical picture that connects the observed diversity of neutron star classes to their hidden field configurations.
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All authors Raj Kishor Joshi, Brynmor Haskell, William Cook, Sebastiano Bernuzzi

Quantum Physics

Geometric inflation of deviations challenges neural quantum states in dynamics of quantum Ising models

Wladislaw Krinitsin, Jonas B. Rigo, Mohammad Abedi et al. (+1 more)

Neural quantum states (NQS) have emerged as a powerful framework for simulating non-equilibrium dynamics in strongly correlated quantum systems, offering scalable variational representations of highly entangled states. Yet, accurate NQS simulations have been found to be surprisingly challenging in some physical regimes of limited complexity. Here, we address paradigmatic quench dynamics of a one-dimensional quantum Ising model as a controlled benchmark. Through supervised state reconstruction we establish substantially tighter empirical upper bounds on the required parameter count than previous estimates, ruling out representational limitations as the key obstruction. Instead, we uncover a geometric inflation of small deviations as a hitherto overlooked challenge for accurate solutions of the infinitesimal time-dependent variational principle (TDVP): the dynamical rotation of the kernel of the quantum geometric tensor (QGT) can suddenly lend physical significance to previously irrelevant parameter deviations. The stability of matrix product state solutions of the same TDVP suggests that the non-linearity of the neural network ansatz is the origin of the sensitivity. These results identify QGT-null-space rotation as a geometric diagnostic of sensitive NQS dynamics and as a concrete target for improving TDVP algorithms.
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All authors Wladislaw Krinitsin, Jonas B. Rigo, Mohammad Abedi, Markus Schmitt

Quantum Physics

Analog-to-digital conversion in the quantum regime

Thomas Pousset, Matteo Schiavon, Guillaume Ricard et al. (+3 more)

Digital signal processing has become essential in quantum optics, particularly for continuous-variable (CV) information encoding, enabling coherent detection schemes and mitigation of linear impairments. While linear signal processing in double homodyne detection has been studied under the assumption that all post-measurement processing can be backpropagated in the optical domain, a rigorous treatment of the digitization chain, spanning optical, electronic, and sampling stages, is still lacking. In this work, we consider the continuous mode description of double homodyne detection to fully capture the maximum mode-matching coefficient achievable as a function of electronic noise, signal bandwidth, receiver electronics bandwidth, and sampling rate, that is the entry point of digital signal processing. We establish a dimensioning rule that generalizes the Nyquist-Shannon criterion to account for quantum fluctuations of the measured signal, not merely its bandwidth. Analyzing the case of additive white electronic noise, we find numerically that optimal signal-to-noise ratio is achieved when the electronic bandwidth is large enough to pass the signal yet narrower than the sampling rate in order to mitigate noise amplification, yielding a concrete design criterion for coherent detection.
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All authors Thomas Pousset, Matteo Schiavon, Guillaume Ricard, Elie Awwad, Romain Alléaume, Nicolas Fabre

Solar and Stellar Astrophysics

Amplification of active region equatorial dipole

Ismo Tähtinen

The effect of active region parameters on the evolution of solar axial dipole is well understood. However, their effect on the solar equatorial dipole has not been studied in detail. Understanding the development of the equatorial dipole is important as it drives the interplanetary magnetic field on intracyclic timescales (~ 1yr). We study how the latitude, tilt angle, and the polarity separation affect the evolution of solar equatorial dipole. We use dipole flux transport (DFT), a matrix implementation of surface flux transport (SFT) model, to simulate the dipole evolution of synthetic bipolar magnetic regions (BMRs) with a wide range of tilt angles and latitudes. We also study the evolution of active regions in HMI SHARP database and their associated BMRs. We quantify the dipole evolution by means of the maximum and mean amplification and the growth and decay times of the equatorial dipole. Tilt angle controls the amplification of the equatorial dipole, with larger tilt angles leading to stronger equatorial dipole. Latitude controls the timescale at which the equatorial dipole grows and decays. Low-latitude regions produce the longest living equatorial dipole. We find that only 31% of anti-Joy regions experience amplification of equatorial dipole, compared with 96 of regularly tilted active regions. Latitudes and tilt angles of active regions can have considerable effect on the solar equatorial dipole. Systematic changes in their properties could increase/decrease the strength of the equatorial dipole relative to the solar activity, which could lead to similar relative change in geomagnetic activity. We suggest that large low-latitude coronal holes and relatively high geomagnetic activity in the declining phase of solar cycle 20, could be related to emergence of unusually low-latitude active regions that produced strong and persistent equatorial dipole.
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Astrophysics of Galaxies

A new clump-based star formation model for galaxy simulations: implications for high-redshift compact star clusters

Shu Horie and Hidenobu Yajima

We develop a new star formation model for galaxy simulations in which star-forming gas clumps are identified on-the-fly and converted into stars with an efficiency $\epsilon_{\rm SF}$ set by the clump surface density $\Sigma_{\rm c}$, calibrated against radiation hydrodynamics simulations of star cluster formation. Applying this model to isolated disc galaxies embedded in haloes of $M_{\rm h}=10^{9}$, $10^{10}$ and $10^{11}\,\mathrm{M_\odot}$, with disc compactness corresponding to redshift $z=0$–$10$, we find that more compact discs form more massive and denser clumps. The maximum clump mass increases from $\sim 10^{5}$ to $\sim 10^{7}\,\mathrm{M_\odot}$, and the fraction of clumps exceeding the surface density of $300\,\mathrm{M_\odot\,pc^{-2}}$ rises from $0.25$ to $0.38$ between $z=0$ and $10$ in $10^{10}\,\mathrm{M_\odot}$ haloes. Star formation becomes correspondingly bursty, and the global star formation efficiency after three disc rotations increases from $5 \times 10^{-3}$ to $2 \times 10^{-1}$ in $10^{10}\,\mathrm{M_\odot}$ haloes and from $2 \times 10^{-2}$ to $4 \times 10^{-1}$ in $10^{11}\,\mathrm{M_\odot}$ haloes as the redshift increases from $z=0$ to $10$. The accompanying feedback disrupts the gas discs of the most compact systems, while prominent stellar spiral arms emerge. Self-gravitationally bound star clusters form only in compact discs. We find no bound star clusters at $z \leq 2$ in $10^{10}\,\mathrm{M_\odot}$ haloes, whereas the bound cluster mass fraction reaches $\approx 40$ per cent at $z \geq 8$ and $\approx 70$ per cent in the most compact $10^{11}\,\mathrm{M_\odot}$ halo. These fractions are broadly consistent with those inferred for high-$z$ clumpy galaxies observed by the James Webb Space Telescope.
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Quantum Physics

Benchmarking dynamical-structure-factor protocols in programmable neutral-atom geometries

Matteo Grotti, Sergi Julià-Farré, Elisa Ercolessi et al. (+1 more)

The dynamical structure factor is a central observable in condensed-matter physics, providing direct insight into the excitation spectrum and dynamical response of quantum materials. While it is traditionally accessed in real materials through inelastic neutron scattering, recent works have shown that analogous information can be extracted in quantum simulators using suitable dynamical protocols. So far, these approaches have been demonstrated mainly in paradigmatic integrable one-dimensional models. In this work, we use numerical emulations of a neutral-atom quantum processing unit to assess the feasibility of measuring the dynamical structure factor in a broader class of Ising-like spin systems. Beyond the standard one-dimensional transverse-field Ising chain, we benchmark the protocol in chains with dimerized interactions and in the two-dimensional transverse-field Ising model, where spectral properties are difficult to access with classical numerical methods at large scales. We further analyze the robustness of the protocol under realistic experimental conditions, including finite simulation times, pulse modulation, positional disorder, and laser noise. Our results show that neutral-atom quantum simulators can provide a practical route to probing dynamical response functions in regimes where classical simulations become increasingly demanding, paving the way toward experimental implementation.
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All authors Matteo Grotti, Sergi Julià-Farré, Elisa Ercolessi, Alexandre Dauphin

Other Condensed Matter

General solution of the Dirac equation for electrons bound by a charged atomic chain

Alexander Eremko, Larissa Brizhik and Vadim Loktev

The system of electrons bound by a charged atom chain is studied within the Dirac theory. The general analytical solution of the Dirac equation is obtained. Analytical expression for electron energy is derived from which it follows that the principal quantum number can be introduced for electron states in such a system, similar to the case of a hydrogen atom. We prove that electrons bound by the atomic chain, are fully collectivized and the energy can be calculated as a function of the occupation number. The spectral band with the principal quantum number $n$ is shown to be split into $n$ subbands forming the fine structure. The scale of the fine structure splitting is calculated.
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