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Physics Physics

physics Watch Physics

Tuesday 4 August

Computational Physics

A Unified Graph Neural Network Framework for Non-Equilibrium Carrier and Lattice Dynamics Driven by Electric Fields

Jia-Wen Li, Sheng Meng, Xinghua Shi et al. (+2 more)

Finite-temperature simulations of electric-field-driven dynamics need a unified description of interatomic interactions, local electronic states, and configuration-dependent electric responses. First-principles simulations remain scale-limited, whereas conventional machine-learning potentials lack electric-field effects. Recent machine-learning frameworks have incorporated electric-field response or atom-resolved electronic-state information, but rarely both within a single framework. Here, we develop an electric-field-response graph neural network (EFR-GNN) that predicts energies, forces, Born effective charge tensors, atom-resolved charges and magnetic moments, and supports long-time field-driven molecular dynamics with atom-resolved tracking of localized electronic states. In hole-doped MgO, static fields rectify thermally activated hole-polaron hopping through a forward–backward asymmetry quantified by a nearest-neighbor model. In GaAs, resonant terahertz excitation generates a coherent $\Gamma$-point transverse-optical phonon with dephasing consistent with experiment, while opposite helicities reverse its rotation. In superionic $\alpha$-AgI, it reproduces temperature-dependent Ag$^+$ mobility and collective field-driven ionic drift. Together, EFR-GNN offers an approach to finite-temperature simulations of field-driven atomic and localized-carrier dynamics.
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All authors Jia-Wen Li, Sheng Meng, Xinghua Shi, Jin Zhang, Wei-Hai Fang

Computational Physics · Cross-listed from cond-mat.mtrl-sci

AccelNet: Exact backward-compatible acceleration of polynomial angular descriptors through Cartesian moment factorization

Yuki Nagai

We present AccelNet, an exact, backward-compatible method for accelerating existing trained aenet and n2p2 neural-network potentials without retraining. For angular terms with separable one-neighbor weights and a finite polynomial dependence on $\cos \theta$, the method exploits their hidden finite-rank structure to replace explicit neighbor-pair loops by one-neighbor Cartesian moments. AccelNet reads models trained with either package and reproduces their descriptors, energies, and analytic forces to floating-point roundoff. We verified this equivalence for H$_2$O and TiO$_2$ models and tested the resulting potentials in LAMMPS molecular-dynamics simulations. The implementation, model-conversion tools, and LAMMPS interfaces are released as open-source software. AccelNet also enables GPU-accelerated molecular dynamics with existing aenet and n2p2 potentials. Moment evaluation achieves speedups of up to 10.9 on a CPU and 15.8 on a GPU relative to direct evaluation within AccelNet. The implementation, model-conversion tools, and LAMMPS interfaces are released as open-source software.
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Optics

Valley polarization driven by two-color circular fields: a rotating frame and strong-field perspective

Rui E.F. Silva, Olga Smirnova, Misha Ivanov et al. (+1 more)

Valley polarization in hexagonal materials driven by the form of the lightwave and its orientation relative to the lattice, rather than solely by the helicity of the driver, has recently been demonstrated both theoretically and experimentally. This has extended valley control to the non-resonant, sub-cycle regime and to inversion-symmetric materials. One interpretation of this field-orientation-dependent valley polarization is that the laser-dressed, cycle-averaged band structure obtained from a Floquet-type approach is modified so as to lift the degeneracy between the valleys. Here, we derive a complementary explanation based on strong-field tunneling dynamics. We show that the effective valley gap at the dominant injection times depends on the orientation of the field relative to the lattice through the trigonal-warping term of the low-energy dispersion. We derive general expressions for co- and counter-rotating $\omega+N\omega$ fields and show that the leading orientation-dependent contribution survives the cycle average only for field configurations compatible with the threefold lattice symmetry, most notably counter-rotating $\omega+2\omega$ and co-rotating $\omega+4\omega$ fields. As a complementary weak-field result, we show that, for counter-rotating bicircular fields, the one-photon valley selection rules can be represented as valley-dependent energy detunings in a rotating frame where both colors acquire the same frequency.
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All authors Rui E.F. Silva, Olga Smirnova, Misha Ivanov, Álvaro Jiménez-Galán

Atmospheric and Oceanic Physics

Experimental validation of an open-source low-cost single-camera 6-DOF tracking of floating-body motion in wave tanks

Herman Martens Meyer, Paul Fromont, Øystein Lande et al. (+1 more)

Accurately measuring motion of floating structures in experimental settings is both important and non-trivial. In this paper, we present a single-camera, 6-degree-of-freedom motion-tracking system that is both low-cost and simple to set up for an experimental campaign. The system uses fiducial markers and open-source computer vision tools to estimate the positions and orientations of multi-marker geometries and track them. We validate the accuracy and limitations on a precisely controlled linear actuator with static, regular, and irregular motion. The performance is quantified depending on both the camera-to-marker distance and direction of motion relative to the camera plane. Additionally, we present a practical use case for our system in a wave tank. Although the motion direction perpendicular to the camera plane shows the highest errors, the system achieves sub-millimeter accuracy at short and moderate camera-to-marker distances. For the irregular motion validation, the best cases reproduced the displacements with an RMSE of approximately 0.5 mm. Overall, the results indicate that low-cost single-camera fiducial-marker tracking can provide sufficiently accurate, non-intrusive motion measurements for a range of hydrodynamic laboratory experiments.
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All authors Herman Martens Meyer, Paul Fromont, Øystein Lande, Atle Jensen

Plasma Physics

Generation of dense relativistic electron beams via vortex laser-driven self-generated magnetic pinching

Mingxuan Wei, Fengyu Sun, Zhongpeng Li et al. (+21 more)

In multi-petawatt laser plasma accelerators, achieving high-density relativistic electron beams is typically accompanied by large transverse divergence, limiting the attainable effective electron density needed for high-flux interaction regimes relevant to laboratory astrophysics. Here we report experimental demonstration of self-generated magnetic pinching (SMP), a collective mechanism that actively regulates transverse beam dynamics using a Laguerre-Gaussian laser at strong relativistic intensity (~8 x 10^19 W/cm^2) interacting with an underdense plasma. The electron beam evolves from a two-lobe high-charge injection structure into a compressed, high-density profile, yielding a threefold reduction in divergence and nearly an order-of-magnitude enhancement in effective beam density compared with a Gaussian driver. Particle-in-cell simulations agree with the experimental observations and reveal that a self-generated azimuthal magnetic field governs the electron dynamics within the SMP regime, which is defined by the forming condition S = 0.717 l a0 [ne(10^18 cm^-3)]^-3/4 = 1, where l, a0, and ne are topological charge, laser amplitude, and plasma density, respectively. A transient kick from a dense inner sheath electron population drives collective magnetic pinching, transforming an initially separated electron distribution into a compressed and well-collimated beam. For higher-power laser systems, the forming condition can be extended to higher plasma densities and larger orbital angular momentum modes, potentially enabling electron beams with charges exceeding several nC and effective densities above 10^19 cm^-3. This mechanism provides a route to overcoming transverse expansion and enhancing rare interaction processes relevant to high-flux particle sources.
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All authors Mingxuan Wei, Fengyu Sun, Zhongpeng Li, Xichen Hu, Huiting Ma, Guangwei Lu, Zhuofan Zhang, Lijie Cui, Qijin Zhang, Mengjiao Wang, Weijun Zhou, Qian Zhao, Wenqing Wei, Yi Xu, Zongxin Zhang, Jiayi Qian, Jiacheng Zhu, Xiaoyan Liang, Min Chen, Wenpeng Wang, Jian-Xing Li, Wenchao Yan, Yuxin Leng, Jie Zhang

Fluid Dynamics · Cross-listed from math.NA

An asymptotic-preserving adjoint unified gas kinetic scheme for sensitivity analysis

Yue Zhang, Junzhe Cao, Wenpei Long et al. (+1 more)

High-dimensional sensitivity analysis and uncertainty quantification for multiscale gas dynamics, spanning the continuum to rarefied regimes, require computationally efficient and mathematically consistent gradient evaluation. This paper develops a discrete adjoint method for the unified gas-kinetic scheme (UGKS) based on a dual-consistent formulation. The adjoint system is derived directly from the discrete microscopic velocity-distribution equation coupled with the macroscopic-moment compatibility conditions. To resolve the stiff cross-scale coupling, we propose an asymptotic-preserving (AP) adjoint formulation constructed via macroscopic-moment projection and microscopic lifting. Under this framework, the AP adjoint formulation eliminates the stiff collision coupling and removes the collision-time step restriction in the continuum regime. Numerically, a memory-efficient residual-evaluation algorithm that mirrors the forward UGKS cell-vertex data structure is implemented to bypass the memory bottleneck in velocity space. Furthermore, a macroscopic–microscopic predictor–corrector implicit marching scheme is designed to accelerate convergence without solving a globally coupled system. The accuracy, consistency, and robustness of the proposed AP-adjoint scheme are rigorously verified against an independent linearized UGKS solver across a wide range of Knudsen numbers, including lid-driven cavity heat conduction, microchannel thermal creep flow, and hypersonic flow past a circular cylinder.
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All authors Yue Zhang, Junzhe Cao, Wenpei Long, Kun Xu

Instrumentation and Detectors

Spectacular - A Modular DAQ System for Microdosimetry

Matthias Knopf, Simon Waid, Daniel Radmanovac et al. (+8 more)

Particle therapy using light ions like protons, helium ions or carbon ions enables precise tumor targeting with enhanced biological effectiveness while minimizing damage to healthy tissue. Successful treatment planning depends not only on the absorbed dose but also on quality of the radiation, as quantified by the linear energy transfer (LET). Microdosimetry provides a direct experimental determination of such quantities by measuring the energy deposited per incoming particle in micrometer-sized solid-state detectors representing the relevant biological scales. However, the small signal amplitudes and high particle rates in therapeutic ion beams challenge existing readout systems, which are not sufficiently optimized for reliable operation with respect to pileup and signal-to-noise ratio (SNR). To address this, a modular data acquisition (DAQ) system was developed to accelerate the design of custom readout electronics and sensor characterization in microdosimetry and related spectroscopic applications. Centered around a Xilinx Zynq system-on-chip, it combines real-time processing, high-bandwidth streaming, and high-resolution digitization (16 bit at 100 MSas$^{-1}$) to enable advanced digital signal processing. The platform integrates programmable power supplies, a bias-voltage filter, test-pulse generators, and flexible I/O. Detector and preamplifier front-ends are hosted on interchangeable daugtherboards connected via a standardized interface, allowing different hardware configurations and readout algorithms to be evaluated on the same platform. The Spectacular DAQ system was successfully tested at the MedAustron ion therapy facility with custom charge-sensitive amplifiers and a diamond microdosimeter. First results demonstrate the feasibility and provide a proof-of-concept for potential future applications in clinical practice.
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All authors Matthias Knopf, Simon Waid, Daniel Radmanovac, Sebastian Onder, Richard Thalmeier, Peter Fischer, Stefan Gundacker, Claudio Verona, Edoardo Domenicone, Thomas Bergauer, Albert Hirtl

Chemical Physics

Negative Differential Capacitance from Composition-Dependent Stern Capacitance in a Binary Mixture

Yuki Uematsu

We develop a thermodynamic theory of electric double layers in binary liquid mixtures by allowing the Stern-layer capacitance to depend on the local solvent composition. This coupling produces an additional negative contribution to the inverse differential capacitance. As a result, the surface potential can become a nonmonotonic function of the surface charge density, leading to negative differential capacitance and a voltage-induced first-order transition between two electric-double-layer states. We determine the coexistence condition using a common-tangent construction for the surface-charge-controlled grand potential and obtain phase diagrams in terms of the Stern-capacitance contrast, surface charge density, bulk composition, and surface potential. We also compare the theory with capacitance data for tetrabutylammonium chloride in water/1-propanol mixtures, finding semi-quantitative agreement in the continuous-response regime. These results suggest that solvent exchange inside the Stern layer can strongly control the capacitance and interfacial phase behavior of binary mixtures.
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Classical Physics · Cross-listed from cond-mat.stat-mech

Exact Resonances Are Not Sufficient for Phonon Energy Diffusion

Wei Lin, Yong Zhang and Hong Zhao

Multi-phonon resonance conditions underpin kinetic theories of phonon transport and lattice thermalization. We show that exact resonance matching, nonzero interaction coefficients, and network connectivity do not guarantee persistent energy diffusion. Symmetry-enforced balance relations drive exact-resonant collision currents to nonthermal zero-flux states, producing kinetic arrest from individual resonant sets to connected networks. Complete energy spreading is sustained by quasi-resonances. The thermodynamic and weak-nonlinearity limits do not commute: the leading kinetic behavior is recovered in the former, whereas at fixed finite size the thermalization time diverges through higher-order crossovers as the nonlinearity vanishes. Exact-resonance existence and connectivity are therefore kinematic, not sufficient dynamical, criteria for phonon energy diffusion.
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Optics

Zero-change foundry compatible silicon photonics MEMS optical switch

Arkadev Roy, Daniel Klawson, Jianheng Luo et al. (+3 more)

Large-scale photonic switches are emerging as essential devices for energy-efficient optical interconnect in data centers and AI/ML clusters as a key enabler for high-bandwidth and low-latency connectivity. Combining micro-electro-mechanical (MEMS) based mechanical reconfigurability with silicon photonic integrated circuits can enable a large-scale, low-loss, programmable platform required for large-scale optical circuit switches. We demonstrate a broadband silicon photonics MEMS switch with more than 30 dB extinction ratio operating in C-band using a zero-change foundry-compatible process and Back-end-of-Line (BEOL) post-processing. The optical switch element exhibits an insertion loss of less than 1.5 dB with a low static power consumption of approx 20 nW at maximum actuation voltage. Our results illustrate that MEMS-based silicon photonics modulators and phase shifters can be used alongside standard silicon photonics components seamlessly in scenarios where performance in terms of footprint, extinction ratio, broad bandwidth, and low-loss operation is of paramount importance.
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All authors Arkadev Roy, Daniel Klawson, Jianheng Luo, Yiyang Zhi, Sirui Tang, Ming Wu

Physics and Society

Performance appraisal promotes cooperation in spatial public goods games

Tianjiao Li, Qin Li, Kangxi Zhu et al. (+2 more)

In real organizations, performance appraisal serves as an important means of evaluating employees' work outcomes and behaviors, while performance pay directly links compensation to the evaluation results. However, in traditional spatial public goods games, the total payoff of a group is equally distributed among all participants without considering individual differences in contributions, an approach that ignores the heterogeneity of individual efforts. To overcome this limitation, we propose a spatial public goods game model based on performance appraisal, in which individual payoffs are divided into two parts: an equally distributed component and a performance-weighted component. Specifically, each individual receives scores from its neighboring groups, and the individual's reputation is dynamically updated by accumulating these scores, which further modulates the fitness function during strategy imitation. Extensive numerical simulation results demonstrate that the performance appraisal mechanism significantly promotes the emergence of cooperative behavior. The reputation reinforcement mechanism amplifies this positive effect by creating fitness advantages for high-reputation individuals. These findings suggest that incorporating performance appraisal into payoff allocation helps mitigate social dilemmas and promote collective cooperation.
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All authors Tianjiao Li, Qin Li, Kangxi Zhu, Minyu Feng, Manuel Chica

Plasma Physics

Quasi-single-stage optimization for advanced stellarators

Guodong Yu, Yidong Xie, Hengqian Liu et al. (+1 more)

Advanced stellarator design requires a balance between plasma performance and the manufacturability of three-dimensional modular coils. In conventional two-stage optimization, the coils required to realize an optimized equilibrium can be limited by engineering feasibility. Here, we develop a quasi-single-stage (QSS) framework that incorporates coil feasibility directly into plasma-boundary optimization. QSS uses the maximum normalized normal-field error, evaluated rapidly from surface currents on a uniformly offset winding surface, as a coil-feasibility surrogate. We apply this method to optimize configurations targeting quasi-axisymmetry, quasi-helical symmetry, quasi-isodynamicity, and a combination of omnigenity with piecewise omnigenity. The QSS-optimized configurations exhibit smoother plasma boundaries and winding surfaces, lower normal-field reconstruction errors, and reduced coil complexity, while preserving favourable magnetic-symmetry and transport properties. QSS provides a practical proof-of-principle strategy for co-optimizing plasma physics and coil engineering in stellarator design.
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All authors Guodong Yu, Yidong Xie, Hengqian Liu, Caoxiang Zhu

Fluid Dynamics

Construction of flexible wing models by combined manufacturing of additive and subtractive processes for transonic wind tunnel testing

Natsuki Tsushima, Kensuke Soneda, Kenichi Saitoh et al. (+1 more)

This study presents a systematic manufacturing approach that combines metal additive manufacturing and subtractive machining to construct flexible wing models for transonic wind tunnel testing. Two wing designs were fabricated and evaluated in terms of geometric accuracy, structural characteristics, and aeroelastic behavior. Three-dimensional scanning, static load tests, ground vibration tests, finite element analyses, and transonic wind tunnel tests were conducted. The fabricated models reproduced the designed geometries and structural properties with good accuracy. The average surface roughness was below 1.0 micrometer, and the average surface deviation was below 0.3 mm, improving geometric precision over previous skill-dependent polishing methods. Independently manufactured models also exhibited highly consistent flutter behavior, with measured flutter frequencies of 157.0 and 158.0 Hz. The results demonstrate that the combined additive and subtractive manufacturing approach enables efficient and reproducible production of flexible wing models for reliable aeroelastic wind tunnel experiments.
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All authors Natsuki Tsushima, Kensuke Soneda, Kenichi Saitoh, Kazuyuki Nakakita

Optics · Cross-listed from quant-ph

Heralded Free-Electron Writing of the Most Subradiant State in an Atomic Array

Tong Shen, Zhexin Zhao and Meng Xiao

The most subradiant eigenstate of a finite subwavelength atomic chain in free space, protected by strongly suppressed radiative decay, offers a powerful resource for photon storage, quantum sensing, and many-body quantum optics. Yet its optical preparation is hindered by the simultaneous need to match a wave vector outside the light cone and a nonuniform envelope. Here, we show that a free electron can overcome these constraints: its velocity sets the imprinted wave vector, while the trajectory of the diffracting wave packet shapes the excitation envelope. This simultaneous momentum and envelope matching enables heralded preparation with near-unity conditional fidelity ($F>99.5\%$) even in a deeply subwavelength regime that is difficult to access with propagating free-space photons. We further show that a path-superposed free electron can excite an antisymmetric state in two closely spaced parallel chains, whose interchain destructive interference yields stronger subradiance than a single chain with the same total number of atoms. These results establish free electrons as quantum writers for collective excitations that are difficult to access with propagating optical fields.
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Optics

Breaking the trade-off between invisibility and sensitivity in electromagnetic sensing

Yichao Liu, Jiaxue Zhou, Weifeng Han et al. (+6 more)

Weak electromagnetic signals demand highly sensitive sensors, yet increasing a sensor's sensitivity inevitably strengthens its interaction with the surrounding field, producing scattering that perturbs the very signals being measured. Conversely, existing cloaking strategies suppress scattering only by isolating the sensor from incident waves, thereby compromising signal reception. Resolving this long-standing trade-off between invisibility and sensitivity has remained an outstanding challenge. Here we overcome this dilemma through an integrated transformation-optical architecture that co-designs the entire sensing system, including the electrically large sensor body, the subwavelength sensing probe, and their electrical interconnection. The proposed multifunctional core-shell structure guides incident waves around the sensor body while simultaneously concentrating them into the sensing region without disturbing the external electromagnetic field. A deep-subwavelength aperture preserves electrical connectivity without degrading either cloaking or field concentration, enabling invisible sensing within a single platform. A microwave prototype based on practical optic-null-medium metamaterials experimentally demonstrates broadband scattering suppression exceeding 3 dB together with an average sixfold enhancement of the detected signal over 4.9-5.1 GHz. By simultaneously eliminating measurement-induced field perturbation and amplifying the local sensing field, our approach establishes a general framework for invisible yet highly responsive electromagnetic sensors, opening new opportunities for weak-signal detection in biomedical diagnostics, secure communications, quantum technologies, and deep-space exploration.
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All authors Yichao Liu, Jiaxue Zhou, Weifeng Han, Hanchuan Chen, Fei Sun, Qin Liao, Hengxiang Zhang, Xiaofan Ji, Yawen Qi

Atmospheric and Oceanic Physics

Recent Sharp Rise in Inhomogeneous Hydrological Extremes Stress Vegetation Growth in China

Shengyuan Liu, Jeremy Cheuk-Hin Leung, Jianjun Xu et al. (+6 more)

The intensifying spatial inhomogeneity of rainfall under greenhouse warming implies that more inhomogeneous hydrological extremes (IHEs), i.e., coexistence of extreme rainfall or drought, may be triggered. While vegetation growth in China is sensitive to hydrological hazards, the variability of IHEs and their ecological impacts remain underexplored. Here, we find a significant increase in IHEs during China's growing season since 2000 (+2.1 events or +14.52 days per decade), with a rapid sharp rise to an annual average of 6.4 events or 42.0 days in the past five years. The primary driver is the enhanced inhomogeneity of moisture-dynamic coupled weather conditions, overlapping with a northward shift of climatological precipitation distribution. This results in a "Wet-North and Dry-South" pattern of IHE impacts, which poses severe and asymmetric threats to vegetation growth in China, with the expansion of drought areas exerts stronger stress on vegetation than the compensatory effects of rainfall. Our findings suggest that the sharp rises of IHEs tend to yield net negative impacts on vegetation growth, highlighting the need for stronger hydrological management to reduce future risks.
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All authors Shengyuan Liu, Jeremy Cheuk-Hin Leung, Jianjun Xu, Kunlun Xiang, Shifei Tu, Meiying Zheng, Daosheng Xu, Yi Li, Banglin Zhang

Fluid Dynamics

Statistical Analysis of Droplet Size Distributions in Liquid-Jet-in-Crossflow Atomization

Tom Johny, Bharat Bhatia, Zafar Alam et al. (+1 more)

This study investigates the droplet size distribution (DSD) and atomization characteristics of a liquid jet injected into a crossflow (LJICF) under varied momentum flux ratios, Weber numbers, and flow conditions. Numerical simulations are performed using the validated compressible Volume of Fluid-Lagrangian Particle Tracking (VOF-LPT) coupled framework to capture both the primary and secondary atomization processes. Key parameters, including momentum flux ratio, Weber number, crossflow pressure, and velocity, were analyzed to assess their impact on droplet size characteristics, including Sauter mean diameter (SMD) and standard deviation (STD) in the downstream region. The discrete size distribution of droplets comprising probability density and cumulative distribution reveals a shift toward finer, more uniform droplets under enhanced breakup conditions. The findings emphasize the critical role of aerodynamic forces and instabilities in driving efficient atomization, with higher momentum flux ratios and Weber numbers leading to finer and more uniform droplets. Increased crossflow pressure promotes finer droplet formation but is found to reduce droplet density in the downstream domain due to a confined spray plume, delayed particle conversion, and reduced droplet residence time. The log-normal and Rosin-Rammler distributions effectively capture droplet size trends, with the former closely representing the skewness and tail behavior and the latter accurately representing intermediate and larger droplets. However, both have limitations in replicating sharp peaks and the smallest droplet sizes, respectively.
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All authors Tom Johny, Bharat Bhatia, Zafar Alam, Ashoke De

Fluid Dynamics

Flame Dynamics of Air-Diluted Methanol spray Combustion in Confined Swirling Vitiated Hot Coflow

Zafar Alam, Bharat Bhatia and Ashoke De

This study employs swirling hot coflow to ensure improved fuel-air mixture and stable flame, which are essential for designing low-emission, swirl-stabilized combustors. The present study introduces a swirling confined hot coflow around an air-diluted methanol spray. We have used the Eulerian-Lagrangian approach for multiphase simulation, resolving the dispersed liquid phase via the Lagrangian framework while addressing the continuous gas phase through the Eulerian framework. The Modified Flamelet Generated Manifold (FGM) model facilitates accurate and computationally efficient simulation of gas-phase reactions. The swirl numbers (SN), which are 0.2, 0.6, 1.0, 1.4, 2.0, and 3.0, are employed in this study to evaluate their impact on flame stability and auto-ignition. A higher lift-off height is observed as the swirl number rises from lower to moderate (SN = 0.2, 0.6, and 1.0). It decreases after the lift-off height reaches the critical swirl number (SN=1.0). These large swirl numbers also cause the time-averaged flame structure to change from a sharp columnar flame to an evenly spread combustion region. It also produces a more compact and widely dispersed flame for higher swirl numbers. Particle statistics, Flame Index, proper orthogonal decomposition (POD), and the mean gas-phase flow field distribution are used to study these impacts on flame dynamics in detail.
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Biological Physics

A Landau-Ginzburg Phenomenology of Sleep-Stage Transitions

Alexander Poltorak

Sleep staging provides a reproducible clinical description, but it does not by itself explain why some boundaries are abrupt while others are graded, or why transition windows contain instability, synchrony, and apparent state coexistence. We develop a local Landau-Ginzburg phenomenology in which each boundary is represented by motion in an effective potential of a spatially extended, noisy, dissipative neural field. A latent cortical-ordering coordinate phi is inferred from prespecified EEG/PSG observables through a measurement model designed to avoid circularity. The canonical boundaries are treated separately. Existing data support a fold-like loss of wake stability at sleep onset; whether that fold lies on a globally bistable cusp with hysteresis remains open. N1-to-N2 and N2-to-N3 are posed as continuous-like ordering crossovers, NREM-to-REM as a candidate first-order-like desynchronizing switch, and a possible within-N3 mixed or tricritical-like regime as a speculative hypothesis. The Ginzburg term adds spatial predictions - growth of correlation length and local-to-global recruitment - that are absent from scalar sleep-onset models. We specify the evidence needed to distinguish bifurcation, coexistence, noise-driven escape, smooth crossover, and scoring-induced discontinuity. Illustrative time-dependent Ginzburg-Landau simulations reproduce the proposed signature classes. A synthetic classification experiment partially distinguished six archetypes (cross-validated accuracy 0.49 +/- 0.005; balanced baseline 0.17), with little change under a noise-regime shift. These analyses establish the internal consistency and testability of the framework, not the proposed taxonomy in human sleep. Transition-centered EEG validation is required before clinical or neuromodulation applications are pursued.
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Optics

Chiral optics without chiral matter

Jingxuan Wei

Strong chiral light-matter interactions are conventionally believed to require structurally chiral materials. However, emerging evidence challenges this assumption, prompting a fundamental question: do chiral matters really matter in circularly polarized light (CPL) responses? While chiral structures favor circular dichroism generation in isotropic media, non-chiral systems with anisotropy can generate circular dichroism, and CPL can drive directional charge transport and spin-selective processes without structural chirality. By unifying these phenomena through fundamental light-matter interaction principles, recognizing that light carries both chiral and achiral components while matter exhibits diverse degrees of freedom such as charge, moment and angular momentum, we reveal a broader landscape of chiral optics. This perspective reconciles seemingly disparate findings and opens pathways to advanced technologies including high-performance CPL devices, ultrasensitive chiral sensors, and spin-selective photocatalysts, fundamentally expanding chiral optics beyond traditional structural constraints.
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Atomic Physics · Cross-listed from quant-ph

Rydberg-Mediated Nonlinear Quantum Optics

Yun-Hui He, Chang-Cheng Li, Xu Shen et al. (+5 more)

Rydberg atoms have emerged as a versatile platform for quantum optics due to their exaggerated properties, particularly their strong long-range interactions, which enable a new regime of light-matter interaction. By mapping the interactions between Rydberg atoms onto photons, effective photon-photon interactions can be realized at the single-photon level, thereby overcoming the intrinsic weakness of conventional optical nonlinearities. In this review, we first introduce the fundamental physical principles of Rydberg-mediated quantum optics, and then discuss some key developments, including single-photon engineering, photonic quantum gates, contactless nonlinear optics, and quantum entanglement, providing a comprehensive overview of the current state and prospects of this rapidly developing field.
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All authors Yun-Hui He, Chang-Cheng Li, Xu Shen, Jing-Xu Bai, Xiao-Feng Shi, Lin Li, Yue-Chun Jiao, Jian-Ming Zhao

Monday 3 August

Instrumentation and Detectors

Imaging performance of a Single-Plane Readout Compton Camera

Om Prakash Dash, Tomislav Bokulić, Damir Bosnar et al. (+1 more)

This work presents the design, development, and characterization of a compact Compton camera employing a novel single-plane readout architecture. The proposed concept simplifies conventional multilayer Compton cameras by optically coupling the scatterer and absorber into a single compact detector element using a light guide, enabling readout exclusively from one side with silicon photomultipliers. The system was validated through Monte Carlo simulations, prototype construction, and experimental characterization using standard gamma-ray sources. Detector performance for 511~keV and 662~keV photons was optimized using simulations based on the Geant4 framework, by guiding event selection strategy. Event reconstruction relied on coincidence detection consistent with Compton scattering kinematics, while image reconstruction was performed using maximum likelihood expectation maximization algorithm. The prototype comprises 64 detector elements arranged in an $8\times8$ matrix, read out by an $8\times8$ silicon photomultiplier array. Each element consists of two GAGG:Ce scintillators coupled by a 20 mm long light guide. Measured energy resolutions were $8.9\%\pm1.9\%$ and $10.8\%\pm1.6\%$ for the front and back layers, respectively. Successful gamma-ray imaging was demonstrated for Na-22 and Cs-137 sources, achieving angular resolutions of $12.4^\circ$–$14.3^\circ$ at 511~keV and $14.3^\circ$–$16.8^\circ$ at 662~keV, confirming the feasibility of the proposed single-plane architecture for compact and cost-effective gamma-ray imaging applications.
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All authors Om Prakash Dash, Tomislav Bokulić, Damir Bosnar, Mihael Makek

Physics and Society · Cross-listed from cs.SI

Higher-order rich clubs and configuration models on general directed hypergraphs

Jason P. Smith, Celia Hacker, Jānis Lazovskis et al. (+3 more)

Detecting structure in complex networks, especially those arising from physical systems, is a central problem across the sciences. One approach is via rich club analysis, which identifies important vertices using a centrality metric and measures whether those vertices are more tightly interconnected than expected by chance. While informative, this approach captures only pairwise interactions, missing out on higher-order ones known to shape the structure and function of many complex systems. We propose a hyper-rich club pipeline that asks whether central vertices are more tightly interconnected than expected by chance through hyperedges encoding higher-order interactions, which also enables the inclusion of important, often omitted, directional information. We work in a broad class of hypergraphs, which we call general directed hypergraphs, that includes as special cases undirected hypergraphs, head-and-tail directed hypergraphs, and totally ordered hypergraphs (a hypergraph related to directed simplicial complexes from topological data analysis). This unifies several non-equivalent notions of directed hypergraph under one definition. On these hypergraphs we define a hyper-rich club framework whose concrete construction depends on explicit choices the domain scientist fixes according to their research goals. Particular choices recover the existing rich club notions for graphs and undirected hypergraphs, and yield the first such notion for each version of directed hypergraphs. We demonstrate that the pipeline recovers meaningful structure in data by studying networks of very different origins: connectomes, temporal networks of infectious spread, networks of poems, and the XGI hypergraph database, in each case detecting structure the standard graph rich club misses.
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All authors Jason P. Smith, Celia Hacker, Jānis Lazovskis, Florian Unger, Keith M. Smith, Daniela Egas Santander

Instrumentation and Detectors

Mitigating warp divergence in GPU optical photon Monte Carlo: an order of magnitude speedup with Shader Execution Reordering

Gabor Galgoczi

In high energy, nuclear, and medical physics, optical photon transport Monte Carlo is a frequent bottleneck in detector simulation. GPU ray tracing accelerates photon propagation, but one thread per photon megakernels suffer from SIMT execution divergence when photon lifetimes vary widely. Short-lived photons leave inactive lanes while a few long-lived photons delay warp completion. We evaluate NVIDIA Shader Execution Reordering (SER) in an OptiX based optical photon transport kernel and use it to regroup surviving photons during propagation. In a 14.7 kton liquid argon time projection chamber benchmark with ~61 million photons from a 2.5 GeV electromagnetic shower, SER capable execution reduces propagation kernel cycles by 16.55(23)x and end-to-end optical simulation time, including transfers and initialization, by 14.72(30)x with bit-identical hit output. We decouple the speed-up into a 3.2x contribution from the launch configuration changes introduced when SER is enabled and a further 5.1x from executing the reorder. Profiling identifies active lane recovery as the dominant mechanism, while branch efficiency and memory bandwidth change little. A volume coherent SER hint enables an analytic navigation fast path in bulk argon, adding a further 1.13x wall-time speedup. Utilizing SER resulted in a ~90% reduction in GPU energy per simulated event.
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Instrumentation and Detectors

Cryogenic Mechanical Loss of GaAs/AlGaAs Crystalline Coatings

Nicholas A. Didio, Steven D. Penn, Satoshi Tanioka et al. (+3 more)

Optical coatings with minimal thermal noise are essential for high-precision, laser-based metrology experiments. Substrate-transferred crystalline GaAs/Al$_{0.92}$Ga$_{0.08}$As coatings have the lowest thermal noise for high-reflectivity mirror coatings with $\lambda =900$ nm – 12 $\mu$m. Time-frequency stabilization experiments have demonstrated that GaAs/AlGaAs mirror coatings have a lower noise floor than amorphous mirror coatings. These mirrors are now being developed at sizes $\ge 300$ mm for gravitational-wave detectors. In order to understand the coating's fundamental loss mechanisms, which cause thermal noise, we have performed the first measurement of the mechanical loss at cryogenic temperatures using a cryogenic, multimodal, gentle nodal suspension system, which operates from 12 K to room temperature. This initial measurement used a silicon substrate whose asymmetry produced excess friction with the nodal support. Accounting for this friction and Akhiezer loss in the substrate and coating, the mechanical loss agrees well with the thermal noise observed in experiments using cryogenic fixed-cavities with GaAs/AlGaAs mirrors.
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All authors Nicholas A. Didio, Steven D. Penn, Satoshi Tanioka, Elenna M. Capote, Garrett D. Cole, Stefan W. Ballmer

Atmospheric and Oceanic Physics

A black-box-model-enhanced interaction method for water-wave scattering by large group of arbitrary-shaped ice floes in Arctic route planning

Chongwei Zhang, Hongli Yang, Peng Wu et al. (+2 more)

This study develops an enhanced interaction (EI) method for efficient prediction of the water-wave field among a large group of ice floes in Arctic route planning. A novel black-box model, termed the wave component detection (WCD) method, is proposed for constructing the diffraction transfer matrix (DTM) within the framework of interaction theory. The DTM, which is conventionally mathematically intractable for three-dimensional ice floes with arbitrarily complex geometry, can now be determined using this readily implementable and universally applicable approach. Without loss of generality, four ice-floe shapes are taken as example models to demonstrate the capability of the EI method. Operation rules are recommended for the practical implementation of the EI method. The error range of the EI method is identified in scenarios with multiple ice floes of different sizes and distances.The super-high efficiency of the EI method is demonstrated in cases involving an ultra-large group of ice floes. It takes less than 1.5 hours to calculate wave amplitudes at 160,000 locations in the wave field of 1,800 ice floes (based on 1,440,000 boundary elements) on an ordinary personal computer with a 2017-released CPU. Based on the wave field predicted by the EI method, users can take advantage of the wave-sheltering effect of the ice floes to optimize routes. For demonstration, the dynamic programming strategy is used to recommend optimized navigation routes among 1561 ice floes of mixed shapes. The average wave amplitude the ship encounters can be reduced to about half of the incident wave amplitude.
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All authors Chongwei Zhang, Hongli Yang, Peng Wu, Peng Lu, Dezhi Ning

Computational Physics · Cross-listed from eess.IV

ScoreField: Neural Inverse Scattering with Score-Based Generative Priors

Wenhan Guo, Yuan Gao and Yu Sun

Designing an effective electromagnetic inverse-scattering solver requires faithful enforcement of nonlinear full-wave physics together with an expressive prior on the unknown permittivity contrast. We propose ScoreField, a neural inverse scattering framework that integrates coupled implicit neural representations (INRs) with a pretrained score-based generative prior. ScoreField employs two INRs to parameterize the permittivity contrast and the induced current fields, and jointly optimize them under the Lippmann-Schwinger equations. In addition to the implicit regularization by the INR architecture, the score model provides a learned prior gradient on the contrast, which is propagated to the contrast INR through the chain rule. This formulation enables ScoreField to effectively handle strong multiple scattering, where nonlinear wave interactions require accurate modeling of the coupled full-wave physics. We evaluate ScoreField on simulated weak- and strong-scattering benchmarks, the canonical Austria phantom, and experimental Fresnel measurements. We note that ScoreField significantly improves reconstruction fidelity and suppresses artifacts relative to classical full-wave methods and deep learning baselines, achieving an average PSNR improvement of $1.8 \, \mathrm{dB}$ over the best competing method on real Fresnel data.
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Chemical Physics

Cooling down trees for finite-temperature quantum dynamics: Purification within ML-MCTDH

Niclas Krupp and Oriol Vendrell

Simulating multidimensional quantum systems at finite temperature is inherently challenging as the system is no longer described by a single, pure-state wavefunction but by a density operator, squaring an already exponential scaling of the Hilbert space. Building upon the compact wavefunction ansatz of the multi-layer multiconfiguration time-dependent Hartree (ML-MCTDH) method, we present a new scheme for simulating finite-temperature quantum dynamics based on purification. Here, a density operator is mapped to a single ML-MCTDH wavefunction in an enlarged Hilbert space, comprising physical and auxiliary degrees of freedom. In the key step, one obtains a pure-state representation of the canonical density operator via imaginary time-propagation of the infinite-temperature state. The most important observation is that this state can be exactly decomposed as a Hartree product of maximally entangled combined modes, each combined mode consisting of a physical degree of freedom and its auxiliary counterpart. Through dynamically pruning the node ranks of the ML-tree during the "cool down" stage yields a compact finite-temperature wavefunction, thus accelerating the real-time propagation and enabling finite-temperature simulations of multidimensional, correlated molecular systems. Our method circumvents both intensive statistical sampling and costly tensor-decomposition of the full density-operator, while being broadly applicable to model Hamiltonians and general ab initio potential energy surfaces alike. Two applications of the method are presented, benchmark results on the thermal ground-state of H2O as well as temperature-dependent infrared absorption spectra of the more challenging, floppy H3O2- anion.
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Chemical Physics

Resolving Peak Shifting Effects in Real-Time Time-Dependent Orbital Propagation Methods Through Nonorthogonal Expansions

Matheus M. F. de Moraes and Lee M. Thompson

Self-consistent field real-time electronic structure methods are a powerful approach for modeling ultrafast processes but suffer from systematic errors in predicted transition energies, commonly known as peak shifting, that obscure direct comparison with experiment. Although this effect has been explored in single reference methods, a general understanding that extends to multiconfigurational methods remains unresolved. Here, we develop a real-time nonorthogonal multiconfigurational self-consistent field (RT-TD NOMCSCF) formalism in which independently propagated orbital sets generate a compact, nonorthogonal wavefunction. The approach establishes a unified framework for nonlinear real-time electronic structure theories, which we use to reveal the common origin of peak shifting across single and multireference limits. Using this framework, we demonstrate that peak shifting does not arise exclusively from the effect of state averaging over the internal space basis, but also from the accessible external configurational space. By systematically expanding the internal space with independently propagated orbital sets, RT-TD NOMCSCF suppresses this aver- aging, recovers correct transition energies, and distinguishes intrinsic peak shifting from numerical peak drifting caused by propagation errors. Thus, these developments establish nonlinear real-time electronic structure methods that enables more accurate simulations of ultrafast processes.
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Optics

Compound symmetries and double antisymmetry groups in linear time-invariant photonic systems

Yunrui Wang, Shiyu Li and Cheng Guo

Symmetry is fundamental to photonic systems. External (spatial) symmetries and internal symmetries—Lorentz reciprocity, energy conservation, and time-reversal symmetry—constrain the electromagnetic response. Photonic systems can also possess compound symmetries that combine external and internal transformations, exemplified by parity-time (PT) symmetry. However, a unified framework for general compound symmetries involving reciprocity, energy conservation, and time reversal remains lacking, leaving their classification and physical implications unexplored. In this paper, we present such a framework for linear photonic systems. We define compound transformations and symmetries, and derive their constraints on electromagnetic fields and scattering matrices. We show that internal, external, and compound symmetries are naturally described by the theory of double antisymmetry groups. This theory classifies linear time-invariant photonic systems into twelve symmetry categories, each imposing characteristic constraints on the electromagnetic response. We illustrate two representative categories with numerical examples of photonic crystal slabs and apply the theory to examine Kirchhoff's law of thermal radiation for a gyrotropic sphere. Our work provides a systematic foundation for analyzing and engineering symmetry in photonic systems.
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