Classical Physics · Cross-listed from cond-mat.mes-hall
The principle of stationary action and Lagrangian for dissipative dynamics with velocity-proportional frictional force
Georgii Koniukov and Dmitry Nerukh
It has been known for a long time that the equation of motion for dissipative linear dynamical systems with constant coefficients cannot be derived from the classical principle of stationary action because the term proportional to velocity in the equation of motion leads to the time derivative of order one half in the Lagrangian. Thus, approaches utilising fractional calculus have been used; however, they suffer from deficiencies both from mathematical and physical points of view. We here present our version of such fractional calculus based approach that provides correct Euler-Lagrange and, ultimately, the Hamilton equations, energy change of the moving body, and an attempt for a
geometric interpretation of how energy dissipates.
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Optics · Cross-listed from quant-ph
Field-Widened Multimode Interferometer with Long Time-Bin Delay Using a Multi-Pass Herriott Cell
Ramy Tannous, Stéphane Vinet, Kaylee Sherk et al. (+2 more)
Interference of optical signals in free-space channels requires optical receivers to support many spatial modes due to atmospheric
turbulence, typically necessitating adaptive optics systems. Field-widened interferometers offer a passive alternative, making them particularly attractive for time-bin encoded signals with delays on the order of one nanosecond. Here, we demonstrate a field-widened, multimode interferometer design that achieves a high interference visibility for spatially multimode beams with large time bin separations. The interference of the multimode beams is enabled using a multi-pass Herriott
cell that enables a very long path separation with a small form-factor. The design is tested using both numerical ray-tracing simulations and proof-of-principle demonstrations. We create a prototype interferometer with a path length difference of 12ns and determine that it maintains a high interference visibility with a large field-of-view of $0.4^{\circ}$.
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All authors Ramy Tannous, Stéphane Vinet, Kaylee Sherk, Kimia Mohammadi, Thomas Jennewein
Fluid Dynamics
Intermittent Vortex Merging and Extreme Drag in Transitional Airfoil Flow
Shishir Gautam and Chitrarth Prasad
Intermittent departures from nominal Kelvin–Helmholtz shedding can produce rare and pronounced drag excursions in transitional airfoil flow. We examine these events using two-dimensional direct numerical simulations of flow over a NACA0012 airfoil at an angle of attack of $5^\circ$, a freestream Mach number of $0.4$, and chord-based Reynolds numbers of $5\times10^4$ and $5\times10^5$. At the lower Reynolds number, event-resolved analysis shows that individual primary
vortices are released from the separated shear layer through the eruption of wall-generated, opposite-signed secondary vorticity. Each eruption interrupts the connection between a developing primary
vortex and its feeding shear layer, releasing the
vortex downstream. During nominal shedding, the
vortex reaching the trailing-edge region is associated with a single such release and remains sufficiently isolated to pass the trailing edge without strong collective interaction. Extreme events instead arise through clustered
vortex release, in which several secondary-vorticity eruptions occur within a short interval and produce a compact group of primary
vortices with small initial streamwise spacing. Differential convection further reduces their spacing and promotes strong near-trailing-edge interactions, where the combined pressure footprint of these
vortices produces a localized suction peak and a sharp increase in drag. These interactions range from prolonged deformation and filamentation to rapid core coalescence. Similar compact
vortex organization and near-trailing-edge interactions are recovered at $Re=5\times10^5$, indicating that the downstream event pathway persists despite the smaller vortical scales.These findings suggest that controlling
vortex-release timing through secondary-vorticity dynamics may provide a route to disrupt clustered release and mitigate extreme aerodynamic loading.
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Fluid Dynamics · Cross-listed from math.DS
Data-driven linear analysis of dynamical systems via nonlinearity-subtracted dynamic mode decomposition
Benjamin Herrmann, Katherine Cao, Steven L. Brunton et al. (+1 more)
The Dynamic Mode Decomposition (DMD) has been consolidated as a basic tool for data-driven analysis of dynamical systems, allowing simultaneous identification of coherent structures and their dynamics from time-resolved measurements. However, with a linear regression at its core, DMD is unable to produce accurate models from recordings of dynamics that are inherently nonlinear, such as the response to large perturbations and the
evolution on chaotic attractors. Recent approaches attempt to simultaneously fit the linear and nonlinear contributions to the dynamics by performing a regression onto a physically motivated model structure. However, although the resulting nonlinear models can produce accurate short-term predictions, their linearization does not necessarily agree with that of the original system. In this work, we introduce a novel data-driven method — nonlinearity-subtracted DMD (NSDMD) — that focuses on producing an accurate linearization of a system when the nonlinear contribution to its dynamics are available while the linear part is not. This scenario is encountered, for example, when the nonlinear terms in the governing equations are known, while the linear operator contains uncertain material properties or it accounts for the closure of unresolved dynamics. This also arises when the data is generated by a black-box simulation code that is able to output the nonlinearity, but not the action of the linear operator on the snapshots. NSDMD leverages data snapshots of the nonlinearity to explicitly account for the purely nonlinear contributions to the dynamics and formulate a regression problem that finds a low-rank approximation of the underlying linear operator. We demonstrate the approach on several numerical examples, showcasing its improved capabilities for data-driven linear analysis of chaotic, partially observed, advection-dominated, and high-dimensional dynamics.
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All authors Benjamin Herrmann, Katherine Cao, Steven L. Brunton, Beverley J. McKeon
Optics
Spectrally smooth broadband response via autocorrelation-constrained inverse design
Johannes Gedeon, Rasmus Ellebæk Christiansen and Ole Sigmund
Time-domain inverse design in photonics is known to be suitable for maximizing the efficiency of optical devices over broad frequency ranges. Objectives commonly used in this context include time-integrated field quantities derived from Poynting's
theorem, such as energy, flux, or dissipated power, which can be directly linked to integrated frequency-domain responses via Parseval's
theorem. While computationally efficient, these objectives measure only the total response over the targeted bandwidth and, as we demonstrate, are insufficient to capture undesired in-band ripple, narrow spectral features, or sidelobes. We overcome this limitation by introducing a time-domain metric quantifying such spectral variations based on the weighted long-lag autocorrelation energy of the optical response. We incorporate this metric into an FDTD-based
topology-optimization framework and demonstrate its beneficial effect on the example of inverse designing one-dimensional dielectric Bragg mirrors via the time-domain adjoint method.
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Chemical Physics
Evaluating Electrostatic Embedding MLIP/MM for Relative Binding Free Energy Calculations
Stephen E. Farr and Gianni De Fabritiis
Alchemical relative binding free energy (RBFE) calculations are limited by the fixed-charge approximation of classical force fields. Hybrid machine learning interatomic potential/molecular mechanics (MLIP/MM) schemes correct ligand strain, but under mechanical
embedding still describe ligand–environment electrostatics with static point charges. Electrostatic
embedding schemes coupling machine-learned charges to the MM environment have been proposed and validated against QM/MM for simple systems, but not tested in a production alchemical workflow. We take the electrostatic
embedding scheme of Semelak et al.\ and evaluate it on
protein–ligand RBFE. We trained a TensorNet2 model, AceFF-2-RESP-1, on $10^{6}$ conformations from the AceFF
dataset, jointly predicting energies, forces and Restrained Electrostatic Potential (RESP) charges. We chose RESP over MBIS for commensurability with the AMBER-family force field it couples to. The predicted charges enter the short-range direct-space part of the particle mesh Ewald sum, with Thole damping to prevent polarization catastrophes during alchemical transformations. We tested the scheme across five targets from the Wang et al.\
benchmark set, fixed in advance by a prior study, with three replicates per edge and matched protocols. Electrostatic
embedding improved every accuracy and correlation metric for TYK2 ($\Delta\Delta G$ RMSE $0.86 \rightarrow 0.45$~kcal/mol against GAFF2), but performed comparably to the classical and mechanical-
embedding baselines for CDK2, thrombin, p38 and JNK1. Standard single-molecule energy and charge
benchmarks were not good predictors of this target-dependent outcome. TYK2 combined good $\Delta\Delta G$ accuracy with the lowest force error on the Schrödinger
benchmark, but this pattern did not hold for the other targets.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Thermal transport in crystals: from the quantum Dyson equation to mesoscopic phonon hydrodynamics
Enrico Di Lucente, Michele Simoncelli and Nicola Marzari
Thermal transport in dielectric, non-
magnetic crystals is mediated by quantized
lattice vibrations, which drift and interact when driven out of
equilibrium by a temperature gradient. This phenomenon can be described at multiple theoretical levels, ranging from fully
quantum descriptions to semiclassical and mesoscopic continuum approaches. This review rigorously discusses the theoretical steps and approximations connecting these levels, bridging
quantum phonon Dyson and Kadanoff-Baym equations and semiclassical Boltzmann transport formalism, and discussing the coarse-graining procedures that yield mesoscopic viscous heat equations for non-diffusive, hydrodynamic heat transport in devices. We show how the Guyer-Krumhansl and dual-phase-lag equations emerge as special linear-isotropic-band and inviscid limits of the viscous heat equations, respectively; most importantly, we demonstrate that these equations predict not only Poiseuille flow and second sound, but also more exotic effects such as negative thermal resistance, steady-state thermal backflow and
vortices. We highlight how combining these frameworks with first-principles simulations connects microscopic
phonon physics to observable non-diffusive heat-transport phenomena and guides their detection, amplification, and control. We recast the viscous heat equations in terms of Helmholtz and biharmonic equations solved analytically, and use this to discuss similarities and differences between the macroscopic behavior of the
phonon fluid and other hydrodynamic systems, such as classical and electron fluids, focusing on compressibility, vorticity, and their influence on
phonon hydrodynamics. We conclude with a roadmap to generalize the tools used to describe
phonon hydrodynamics to other quasiparticles, motivating future advances in collective
quantum transport phenomena in solids.
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Applied Physics
Origin of effective non-Fourier heat conduction phenomena in heterogeneous materials
Róbert Kovács
Phenomenological models of non-
Fourier heat conduction often lack a strict microstructural foundation, leading to ambiguities when modeling complex heterogeneous materials. In this study, we derive a continuum heat equation beyond
Fourier's law using spatial volume averaging for a two-component system. We analytically prove that the experimentally observed static and dynamic thermal diffusivity arise directly from the distinct material properties, concluding that heterogeneous media are inherently over-diffusive. The resulting heat equation is thermodynamically compatible, and the microstructural origin allows the calculation of non-
Fourier transport coefficients. Furthermore, we demonstrate that finite-sample boundaries introduce higher-order spatial non-localities, thereby explaining the size dependence of over-
diffusion. We validate the model against experimental data across metal and carbon foams, rocks, and metal-organic frameworks.
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Optics
Geometric Parametric Instability in Nonlinear Multipass Cells
Chao Mei, Junhong Yang, Tao Sun et al. (+5 more)
Geometric parametric instability (GPI) is the resonant growth of discrete spectral sidebands enabled by longitudinally periodic multimode
evolution and has been studied primarily in graded-index fibers. Here we show theoretically and numerically that GPI can occur in gas-filled nonlinear multipass
cells (MPCs). By mapping a mode-matched MPC onto an equivalent waveguide, we derive a Floquet quasi-phase-matching condition governed by the single-pass Gouy-phase imbalance of the signal–idler pair relative to the pump pair. The theory predicts the small-signal gain and bandwidth. A pump-depleted coupled-mode model (CMM) further relates the maximum converted fraction to the residual phase mismatch. The CMM predicts multiple geometrically tunable sideband pairs associated with different radial indices and Floquet orders. For argon at $5$~bar, varying the cavity geometry shifts the sideband detuning from approximately $96$ to $46$~THz when the $p_{\mathrm{s}}=1$, $h=0$ branch is considered. A truncated multimode generalized nonlinear Schrödinger equation (MMGNLSE) model is used for numerical simulations with a semiclassical
stochastic seed corresponding to one
photon per spectral mode. The MMGNLSE simulations reproduce the predicted sideband frequencies and reveal pump depletion and competition among the retained radial channels. GPI in MPCs may therefore limit spatial beam quality in nonlinear pulse compression while providing a tunable mechanism for broadband multicolor generation.
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All authors Chao Mei, Junhong Yang, Tao Sun, Qian Gao, Jinhui Yuan, Jintao Fan, Peilong Yang, Günter Steinmeyer
Optics
Inverse-Designed High-Q/V Silicon Nitride Photonic Crystal Cavities for Second- and Third-Harmonic Generation
M. Takiguchi, P. Heidt, X. Z. Lim et al. (+7 more)
SiN photonic
crystal (PhC) cavities are promising platforms for nonlinear and
quantum photonics because of their wide transparency window, CMOS compatibility, and negligible two-
photon absorption. However, realizing high-Q/V cavities remains challenging because of the relatively low refractive index of SiN. Here, we employ inverse design to optimize a two-dimensional SiN PhC cavity and experimentally demonstrate a quality factor of approximately 80,000, the highest reported for a near-stoichiometric SiN 2D PhC cavity. Furthermore, both second- and third-harmonic generation are observed from the same cavity, providing experimental evidence of strong optical confinement and large Q/V. Our results establish inverse-designed SiN PhC cavities as a promising platform for nonlinear photonics and future heterogeneous integrated photonic devices.
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All authors M. Takiguchi, P. Heidt, X. Z. Lim, J. Zöllner, S. Yanagimoto, K. Nakayama, T. Aihara, M. Ono, H. Sumikura, M. Notomi
Atomic Physics
Critical Microwave Mach-Zehnder-Type Interferometry with Dual-LO Rydberg Atoms
Jun-Rong Chen, Guo-Qing Qin, Peng-Fu Liang et al. (+7 more)
High-precision phase measurement of microwave fields underpins a wide range of applications, including wireless communications, distributed radar,
plasma diagnostics, and
antenna metrology. Existing Rydberg-atom-based approaches, however, often face trade-offs among phase resolution, measurement range, and system complexity. Here we demonstrate a Rydberg-atom-based microwave Mach-Zehnder-type interferometer using a dual-local-oscillator configuration. The two local oscillators establish two coherent interferometric pathways in the Rydberg medium. Their coherent mixing with the signal field produces an interferometric intermediate-frequency output governed by a phase-to-intensity transfer characteristic that enables critical-point enhancement. This scheme supports direct phase
retrieval with a resolution exceeding $0.1^\circ$ and unambiguous full $360^\circ$ phase coverage with the reconfigurable dual-LO architecture. Moreover, near the critical interference point, the system exhibits a sharply enhanced phase-to-amplitude transduction, where weak amplitude variations are converted into pronounced phase responses, yielding a sensitivity enhancement exceeding 25 dB. Besides, the same interferometric transfer mechanism enables microwave propagation-distance and polarization metrology, achieving a propagation-distance precision below 20 $\mu$m at 5.7 GHz together with a polarization-angle resolution exceeding $0.1^\circ$. This approach eliminates the need for complex optical configurations and lock-in detection, providing a simple, scalable, and reconfigurable Mach-Zehnder-type
quantum microwave interferometry framework for multifunctional high-precision microwave metrology.
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All authors Jun-Rong Chen, Guo-Qing Qin, Peng-Fu Liang, He Hao, Ming-Min Zhao, Ling-Qiang Meng, Gui-Lan Li, Min-Jian Zhao, Bin-Bin Wei, Hao Tian
Atmospheric and Oceanic Physics
Statistical Noise and Missing Forcing Limit Estimates of Earth's Feedback from Prescribed Sea-Surface Temperature Simulations
Gergana Gyuleva, Reto Knutti, Robin Noyelle et al. (+3 more)
Earth's feedback parameter measures how the Earth system responds to forcing and is inversely proportional to
climate sensitivity. Sea-surface temperature (SST) patterns can modulate the value of the feedback parameter. Differences between observed and simulated SSTs have raised the question how the observed SSTs
evolution impacts the global feedback. The standard method for estimating this effect uses observed SSTs prescribed to an atmospheric model with fixed pre-industrial atmospheric forcing. This method makes two assumptions: first, that the observed SSTs capture all relevant effects from the forcing, so that prescribing a time-varying forcing is unnecessary; second, that the temporal variations in the feedback parameter are driven by the evolving SST pattern and can be estimated via moving-window regressions. We test these assumptions by running controlled experiments in which SSTs from fully-coupled historical simulations are prescribed to an atmospheric model. We find that the prescribed-SST experiments fail to capture the coupled feedback
evolution. This is explained by two effects: First, the absence of prescribed atmospheric forcing, and second, statistical noise arising from the computation of moving-window regressions. We find no evidence of any significant relationship between evolving SST patterns and changes in the feedback time series in a 4000-year pre-industrial control simulation. Any trends in the feedback parameter detected on timescales shorter than ~100 years are indistinguishable from statistical noise, making their attribution to the evolving SST pattern extremely difficult. Our results imply that prescribed SST simulations offer limited potential for inferring temporal changes in Earth's parameter over the observational period.
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All authors Gergana Gyuleva, Reto Knutti, Robin Noyelle, Urs Beyerle, Erich Fischer, Sebastian Sippel
Optics · Cross-listed from quant-ph
Heterogeneously Integrated Squeezed-Light Generation and Detection on a Single Photonic Chip
Haoran Chen, Benjamin Westcott, Fatemehsadat Tabatabaei et al. (+10 more)
Squeezed light underpins
quantum-enhanced sensing and continuous-variable
quantum information processing, and integrated photonics offers a route to producing it at scale. Universal to these applications are squeezed-light generation and measurement. Importantly,
quantum measurements serve not only as readout but also as active operations in
quantum-state
evolution. However, integrating squeezed-light generation and photodetection on the same photonic chip has remained challenging because they impose fundamentally conflicting material requirements: low optical loss to preserve
quantum correlations, but efficient
photon absorption for photodetection. Here, we demonstrate squeezed-light generation, routing, and balanced homodyne detection integrated on a single photonic chip through heterogeneous integration. A two-mode squeezed
quantum microcomb comprising 34
quantum modes is measured with approximately 3 dB squeezing. Our work establishes a scalable architecture for fully integrated squeezed-light
quantum photonic systems, unifying
quantum-state generation, processing, and detection on a single chip.
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All authors Haoran Chen, Benjamin Westcott, Fatemehsadat Tabatabaei, Xiangwen Guo, Shuman Sun, Zijiao Yang, Gedalia Y. Koehler, Beichen Wang, Shadrach Sarpong, Steven Bowers, Olivier Pfister, Andreas Beling, Xu Yi
Plasma Physics
Flow-thermochemistry coupling governs pressure-dependent CO$_2$ conversion in vortex-stabilized microwave plasma reactors: Insights from three-dimensional CFD modeling
Qinghao Shen, Cas van Deursen, Pieter Willem Groen et al. (+2 more)
In this work, a three-dimensional computational fluid dynamics model is developed for a
vortex-stabilized microwave CO$_2$
plasma reactor operating over the pressure range of 100-400 mbar. The model combines experimentally constrained, emission-based
plasma sizes and volumetric heat-source distributions with thermally dominated finite-rate heavy-particle chemistry for a multi-component mixture. Turbulent flow and transport are described using the SST k-omega model. The model reproduces the measured radial gas-temperature profiles in the
plasma core and the non-monotonic pressure dependence of CO$_2$ conversion, including a maximum at 150 mbar and a pronounced decrease at 400 mbar. A
vortex-driven recirculation region redistributes gas upstream. Turbulent mixing and cooling are strongest near the upper reactor boundary, but their contribution decreases as pressure increases. The pressure dependence of conversion is determined by the competition between CO$_2$ dissociation and CO recombination. CO$_2$ direct dissociation reaction dominates in the high-temperature
plasma core, whereas O-assisted conversion reaction contributes near the
plasma edges and in the surrounding hot region. At 150 mbar, enhanced CO$_2$ dissociation is accompanied by limited CO loss, resulting in the highest conversion. With pressure increasing to 400 mbar, slower cooling and more frequent three-body collisions promote CO recombination in the afterglow, causing more than 60% of the CO formed near the
plasma to be lost downstream. Moreover, additional CO loss occurs in the upper region of the reactor at higher pressures because of the reduced cooling rate.
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All authors Qinghao Shen, Cas van Deursen, Pieter Willem Groen, Lex Kuijpers, Mauritius C.M. van de Sanden
Optics
Ultrafast Tracking of the Spallation Layer in Bulk Gold, Aluminum, and Steel
Nicolas Thomae, Julian Vollmann, Julian Freundel et al. (+3 more)
Extreme manufacturing with ultrashort-pulse (USP)
lasers at the physical limit of precision and efficiency requires understanding ablation dynamics on the picosecond-to-nanosecond timescale. Pump-probe reflectometry (PPR) provides direct access to photomechanical spallation through Newton ring (NR) interference, but this signature vanishes when the spallation layer becomes optically opaque or the ablated material strongly attenuates the probe. Here, we combine PPR with phase-sensitive interferometric pump-probe (PPI) measurements to track the spallation layer in bulk steel, aluminum, and gold. PPI resolves the propagating layer even when the reflected probe signal is suppressed by >95%. Joint PPR/PPI analysis with transfer-
matrix modelling (TMM) yields spallation layer thickness, vapor layer absorption, and the layer disintegration times. These quantities are key determinants of the energy coupling of subsequent pulses in GHz burst processing.
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All authors Nicolas Thomae, Julian Vollmann, Julian Freundel, Maximilian Spellauge, David Redka, Heinz P. Huber
Physics and Society
Beyond persuasion: Mobile electoral interfaces in polarized societies
Nuno Crokidakis and Celia Anteneodo
Many traditional models of electoral dynamics emphasize opinion change, social influence and persuasion mechanisms. In contrast, contemporary polarized societies often exhibit relatively stable partisan blocs coexisting with an electorally relevant mobile population. We propose a minimal dynamical model in which electoral competition is governed not by direct persuasion between opposing blocs, but by the dynamics and allocation of a mobile electoral interface. The electorate is partitioned into two stable partisan blocs and a mobile fraction, while direct transitions between the polarized blocs are strongly suppressed. Mobile voters are allocated between the competing blocs through a
Fermi-like probabilistic rule governed by rejection asymmetries. Analytical calculations show that the electoral susceptibility to political shocks is proportional to the stationary size of the mobile electoral interface, identifying electoral mobility as the key quantity controlling the macroscopic response of polarized systems to external perturbations. The model naturally predicts a continuum of mobility regimes, ranging from frozen polarization to highly responsive electoral states characterized by a broad mobile interface. These results suggest that, in strongly polarized elections, aggregate electoral changes may be governed primarily by fluctuations at the mobile electoral interface rather than by large-scale ideological conversion.
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Classical Physics · Cross-listed from math-ph
Exact analytical solution for the non-selfadjoint problem of Maxwell–Cattaneo–Vernotte heat conduction with heat-transfer boundary condition
Mátyás Szücs and Tamás Fülöp
The most well-known beyond-
Fourier heat conduction model, the Maxwell–Cattaneo–Vernotte equation is solved analytically in the presence of heat transfer boundary condition. In contrast to the corresponding
Fourier problem, this boundary condition renders the underlying differential operator non-selfadjoint. With a suitable scalar product, the adjoint
eigenvalue problem is established. The resulting left and right eigenfunctions constitute a biorthogonal system, allowing the expansion coefficients to be determined from arbitrary square-integrable initial conditions. This enables a convenient infinite-sum analytical solution, which is presented and thoroughly investigated for various values of the model parameters (including near-
Fourier and highly
hyperbolic regimes) and for two practically important initial conditions (
equilibrium and flash pulse initiated). The spectral structure is analyzed in detail, including the occurrence of real, imaginary, and complex-conjugate
eigenvalue roots, their asymptotic distribution, and their dependence on the dimensionless relaxation time and Biot number. We find good agreement with corresponding finite-difference numerical solutions. The comparison also illustrates the effects of spectral truncation (i.e., the Gibbs phenomenon) and numerical dissipation near propagating thermal-wave fronts. Completeness of the eigenfunction set is numerically demonstrated. The initial condition induced by the flash pulse is derived analytically. The results provide an analytical
benchmark for non-selfadjoint
hyperbolic heat conduction, unveil how boundary heat transfer and relaxation time influence the transition between
Fourier-like
diffusion and thermal-wave propagation, and open the possibility to find and investigate beyond-
Fourier heat conduction via heat transfer in experiments and practical applications.
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Computational Physics · Cross-listed from cond-mat.str-el
Accelerating a Strong-Coupling Non-Equilibrium Steady-State Impurity Solver using (Quantics) Tensor Trains
Bastian Schindler and Martin Eckstein
Including higher order diagrammatic corrections to the strong-coupling expansion is mainly limited by the evaluation of high-dimensional, time-ordered integrals. In this work we present and compare four different parametrizations of the integrands in order to obtain a low-rank (quantics) tensor-train representation using tensor cross interpolation. Particular emphasis is placed on a quantics time-difference formulation in which the required retarded convolutions are performed directly in quantics tensor-train form. Using controlled Gaussian
benchmarks, we analyze the accuracy, bond dimensions, and computational scaling of the different approaches. We then validate the most promising formulations in self-consistent
equilibrium and nonequilibrium DMFT calculations and demonstrate calculations up to the third order in the strong-coupling expansion. Finally, we extend the solver to
impurity models with retarded density-density interactions and apply it within nonequilibrium extended DMFT. Our results show that tensor cross interpolation substantially reduces the cost of evaluating higher-order diagrams and provides a controlled, systematically improvable framework for nonequilibrium
quantum impurity calculations.
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Fluid Dynamics · Cross-listed from math.AP
Uniformly Rotating Vortex Patches with 90-Degree Corners
De Huang, Jiajun Tong and Xiaopeng Zheng
For the 2-D incompressible Euler equation, we prove the existence of $m$-fold symmetric uniformly rotating
vortex patches with 90-degree corners for all $m\geq 12$. Properties of these patches and the induced stationary flows in the co-rotating frame are characterized. Our construction is based on a novel fixed-point method.
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Optics
Micro- and nanoscale focusing across the XUV range of the ASTRID2 light source with a capillary optic
Alfred J. H. Jones, Zhihao Jiang, Asger Petersen et al. (+5 more)
Focusing of synchrotron light across extreme ultraviolet (XUV) and soft X-ray regimes is increasingly desired for photoemission-based techniques where reduced beam width gives access to smaller samples such as microscopic single
crystals and functioning two-dimensional (2D)
heterostructures and devices. Many existing focusing methods, however, are not able to take full advantage of the synchrotron beam due to limited
photon energy range or low transmission. Modern capillary optics have enabled achromatic, high transmission focusing of XUV and X-ray light. Here, we present a detailed characterisation of such an achromatic capillary optic installed at the AU-SGM4 beamline for spatial- and angle-resolved photoemission spectroscopy (ARPES) experiments at the ASTRID2 light source. The transmission of the capillary as a function of
photon energy is given, and the dependence of the beam width, position, and transmission are measured against the source size. Analysis of the far-field image of the beam allows for slope errors on the inner surface of the capillary to be overcome by selectively aperturing the beam, resulting in a minimum beam width of 900 nm measured in a photoemission geometry.
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All authors Alfred J. H. Jones, Zhihao Jiang, Asger Petersen, Søren V. Hoffmann, Nykola C. Jones, Philip Hofmann, Jill A. Miwa, Søren Ulstrup
Computational Physics
Using Diffusion Models to Estimate Uncertainties in Analytic Continuation
Sagi Meir, Daniel Freedman and Barak Hirshberg
Inverse problems are ubiquitous in physics, chemistry, and engineering, arising when reconstructing hidden quantities from indirect measurements. A key example is the analytic continuation of imaginary-time correlation functions (iTCFs) to the real-frequency domain. This process requires an inverse Laplace transform, which is inherently ill-posed and highly sensitive to small input variations. Recent neural network (NN)-based methods have shown promising results by learning mappings from imaginary-time to real-frequency spectra, often outperforming traditional techniques such as maximum
entropy. However, because the problem is ill-posed, many spectra fit the same iTCF. Regression-based approaches output a single solution, which approximates an average over the true solution space, and therefore fail to capture the full distribution of plausible power spectra. To address this issue, we introduce a
diffusion-based framework for analytic continuation that learns the distribution of spectra consistent with a given iTCF. It offers two key advantages. First, it quantifies uncertainty directly from the learned distribution. Second, by analyzing the spread and structure of this distribution, we can quantitatively assess the intrinsic hardness of each inversion problem. We measure this hardness with a new metric, the uncertainty pseudo-volume. Applying the framework to an iTCF from a path-integral molecular dynamics simulation of
liquid parahydrogen, we obtain the self-
diffusion coefficient with an error bar and flag a secondary high-frequency peak as a possible spurious artifact. In contrast to previous attempts at uncertainty quantification, our generative approach rests on a concrete probabilistic basis, providing a more theoretically grounded measure of confidence in the reconstructed power spectra.
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Instrumentation and Detectors
Scan-Coil Delay Causes Anisotropic Signal Loss in Fast 4D-STEM
Vishal Kumar, Andreas Jehle, Tizian Lorenzen et al. (+4 more)
Fast pixelated detectors are driving 4D-STEM toward microsecond dwell times, a regime in which the finite response of the scan deflection coils becomes comparable to the dwell time itself. Using direct probe imaging and sub-frame diffraction analysis, we document a significant intra-dwell scan-coil delay that systematically smears the recorded signal anisotropically along the fast scan direction, with a settling timescale of several tens of microseconds. We present a phase-correlation-based sub-frame
alignment procedure that measures and corrects this smearing, and we assess its impact on focused and defocused 4D-STEM reconstructions over a range of scan step sizes. The correction restores signal across a broad range of spatial frequencies, with the largest gains at the large step sizes required for low-dose biological imaging. Because it operates on existing data with no modification to the microscope, the method offers a practical route to recovering signal that would otherwise be lost to scan-coil delay.
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All authors Vishal Kumar, Andreas Jehle, Tizian Lorenzen, Julika Radecke, Knut Müller-Caspary, Massimo Kube, Henning Stahlberg
Optics · Cross-listed from cond-mat.dis-nn
Graph-theoretic design of lasing networks for physical vision
Paul Obernolte, Jakub Dranczewski, Yixiu Yin et al. (+10 more)
Physical neural networks perform learning through the intrinsic nonlinear dynamics of matter. Optimising their design presents a considerable challenge: complex many-body physics can provide powerful computation, but are expensive to simulate and large experimental optimisation runs are impractical to fabricate. Hence, the high-dimensional space of possible network
topologies cannot be effectively directly searched. Here, we show that this search can be efficiently performed in an abstract graph space that is vastly cheaper to explore. Using random lasing networks – composed of interconnected nanoscale waveguides and hosting strongly coupled lasing modes – as an exemplar physical
vision system, we establish a quantitative three-layer link: simple graph-theoretic metrics predict the nonlinear lasing physics, which in turn predicts
vision performance. After validating this relationship using physical simulations, we exploit it to drive an evolutionary
algorithm using graph metrics, producing network
topologies that outperform random designs at a fraction of the computational cost (3000$\times$ speed-up compared to physical simulation). On simulated image-classification tasks, graph-optimised networks substantially improve classification accuracy. As our framework operates on network
topology rather than substrate-specific physics, we anticipate it can transfer to other network-based physical learning systems, providing an efficient route for the directed design and optimisation of complex, strongly-interacting physical neural networks.
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All authors Paul Obernolte, Jakub Dranczewski, Yixiu Yin, Tobias Farchy, Wai Kit Ng, Tobias Simonsen, Elias Großhauser, Alexis Arnaudon, Robert L. Peach, Mauricio Barahona, Riccardo Sapienza, Jack C. Gartside, T. V. Raziman
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Yingjie Wei, Fan Zhang, Ying Zhao et al. (+4 more)
Room-temperature
spin-optoelectronic devices require a combination of robust ferromagnetism and
giant exciton binding, a pairing mutually exclusive in conventional
semiconductors due to
magnetic localization that screens
excitons. Cluster-assembled V4S9X4 (X = F, Cl, Br and I) monolayers overcome this bottleneck via a hierarchical design, that is, intra-cluster localized states host both local
magnetic moments and strong electron-hole interactions, while inter-cluster coupling mediates long-range ferromagnetism. Remarkably, these two-dimensional
semiconductors exhibit intrinsic ferromagnetism with Curie temperature up to 507.6 K. As a prototype, V4S9Br4 monolayer possesses a
giant exciton binding energy of 1.85 eV. Its lowest
exciton is a dark state (DI) with a radiative lifetime of 1.20 ns, whereas the first bright
exciton (BI) exhibits an ultrafast radiative decay of 86.87 ps. This stark lifetime contrast enables simultaneous ultrafast optical response and long-lived
spin information storage. Most notably, switching between
ferromagnetic and
antiferromagnetic order allows for wide-range tuning of
exciton lifetime, with the
giant binding energy remaining nearly intact. Our findings establish cluster assembly as a powerful paradigm for designing next-generation
spin-photonic and
quantum information devices operating at room temperature.
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All authors Yingjie Wei, Fan Zhang, Ying Zhao, Lixin Zhou, Yan Su, Yu Guo, Jijun Zhao
Optics · Cross-listed from quant-ph
Time-resolved correlation engineering in DLCZ Raman photon sources
Jiun-Shiuan Shiu, Chang-Wei Lin, Chi-Ming Yang et al. (+2 more)
Memory-assisted
quantum networks require
photon sources with controllable temporal and correlation properties. The Duan-Lukin-Cirac-Zoller (DLCZ) protocol provides a platform based on spontaneous Raman scattering in atomic ensembles, but a unified predictive theory connecting control parameters to correlations under realistic propagation and noise conditions remains lacking. Here we present a propagation-inclusive open-system
quantum theory that retains write-induced population redistribution while combining Heisenberg-Langevin dynamics with Maxwell-Schrödinger propagation. We experimentally validate its key predictions. The theory predicts time-dependent Stokes generation,
spin-wave
evolution, retrieved anti-Stokes wavepackets, and time-resolved cross-correlations. Experiments confirm robust correlations under
retrieval tuning and enhanced correlations for shorter write pulses, consistent with the different scaling of correlated coincidences and accidental backgrounds with the mean
spin-wave excitation number. Classically controlled
retrieval enables temporal gating and slicing of the anti-Stokes wavepacket, establishing a quantitative framework for correlation engineering in
memory-compatible DLCZ
photon sources.
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All authors Jiun-Shiuan Shiu, Chang-Wei Lin, Chi-Ming Yang, Ite A. Yu, Yong-Fan Chen
Chemical Physics · Cross-listed from cond-mat.other
Adiabatic perturbation theory of energy transfer and charge transport in condensed matter
Ryan Requist and Fran Dabo
Energy and charge transfer in condensed matter systems are often described in terms of quasiparticles. The order of accuracy of the results in terms of the electron-to-
nucleus mass ratio $\epsilon$, an adiabatic small parameter, is usually not known. To quantify energy transfer with controlled accuracy in $\epsilon$, we use adiabatic perturbation theory to derive a formula for the rate of change of the
nuclear kinetic energy. Applying a sequence of near-identity
unitary transformations decouples the electronic and
nuclear degrees of freedom to higher and higher order and produces an effective
Hamiltonian. In the special case that the
nuclei are treated classically, the energy transfer formula reduces to the usual formula for the rate of work done on a classical particle but the mass of the particle is enhanced by the factor $M_0^{-1}(M_0+\epsilon M_1)$, where $M_1$ is a nonadiabatic correction to the bare
nuclear mass tensor $M_0$. Additional
quantum geometric corrections appear at higher orders. Adiabatic perturbation theory is further used to incorporate, order-by-order in $\epsilon$, nonadiabatic transitions into linear response calculations. The nonadiabatic frequency-dependent conductivity and Drude weight of an electron-ion system are calculated.
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Computational Physics · Cross-listed from cond-mat.mes-hall
Emergence of moiré magnetic chaos in twisted bilayer CrI3
Gyuyoung Park, OukJae Lee and Kyoung-Min Kim
The study of
magnetic chaos has traditionally focused on macroscopic variables under external driving. Here we demonstrate a new type of
magnetic chaos, termed moiré
magnetic chaos, associated with mesoscopic
magnetic domain variables in twisted
bilayer CrI3 without external driving. The domains are stabilized by a characteristic interlayer exchange frustration, which supplies the multiple dynamical degrees of freedom required for autonomous chaos. Through micromagnetic simulations, we show that relaxation toward moiré
magnetic textures is extremely sensitive to minute local perturbations of the initial state, characterized by substantial finite-time Lyapunov exponents and a final-state sensitivity that persists over five decades of perturbation amplitude. Statistical analysis further reveals that the resulting domain configurations are
stochastic and pairwise uncorrelated. Our results identify a form of microscopic, undriven chaos in twisted magnets that extends nonlinear magnetism beyond the conventional driven regime.
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Optics
Reconfigurable Terahertz Multi-Harmonic Dual-Combs
Ma Xuhong, Qin Zhiwei, Bi Xianglong et al. (+7 more)
Dual-comb spectroscopy, constructed from two frequency combs with slightly different repetition frequencies, enables real-time and high-precision measurements without mechanical scanning. In the terahertz spectral range, dual-comb techniques provide a powerful tool for high-resolution and rapid spectroscopy.
Quantum cascade
lasers (QCLs), owing to their compact footprint and favorable size, weight, and power, have emerged as promising sources for THz dual-comb systems. In QCL frequency combs, the repetition frequency generated through intrinsic four-wave mixing is typically equal to the cavity round-trip frequency, corresponding to the fundamental comb. Although this repetition frequency can be tuned via current and temperature control, the accessible tuning range remains limited. Recently, harmonic frequency combs, whose repetition frequencies are integer multiples of the cavity round-trip frequency, have attracted increasing
attention, offering enhanced single-line signal-to-noise ratios and providing direct insight into the strong nonlinearity of QCLs. Here, we demonstrate a reconfigurable multi-harmonic dual-comb system realized on a single self-detected THz QCL platform. By precisely controlling the driving current and thermal conditions, we achieve and switch between multiple dual-comb configurations, including fundamental-fundamental, fundamental-second-harmonic, second-harmonic-second-harmonic, and second-harmonic-third-harmonic dual-combs. These results establish harmonic order as an additional degree of freedom for dual-comb operation within a single
laser system. The demonstrated platform enables high-resolution and high-sensitivity measurements while significantly simplifying the system architecture. This reconfigurable multi-band dual-comb approach based on a single QCL opens new opportunities for compact THz spectroscopy and frequency metrology.
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All authors Ma Xuhong, Qin Zhiwei, Bi Xianglong, Li Ziping, Wan Wenjian, Liu Binbin, Liu Guibin, Pan Yue, Lu Yanming, Li Hua
Optics
Imaging-system-aware color routers optimized for imaging information
Hyoseok Park, Sehyeon Park, Myungjae Lee et al. (+1 more)
Conventional nanophotonic color routers are typically optimized under idealized, normal plane waves. However, this standard assumption fails in real-world imaging-system environments, where structures are illuminated by converging light cones and field-dependent chief-ray angles. Here, we present an imaging-system-aware, end-to-end inverse-design framework that directly maximizes the mutual imaging information $\Iimg$ preserved by a single-layer silicon nitride color router under realistic pupil illumination. By analytically
embedding the optimal reconstruction decoder directly inside the gradient loop, we co-design the optical nanostructures and the digital recovery pipeline. To scale this approach across a full sensor, we exploit the $D_4$
symmetry of the square pixel
lattice, tiling $48$ distinct sensor-field regions using only six unique lithographic masks. Our optimized router is predicted to collect $2.8\times$ more photoelectrons than a conventional color-filter array. Consequently, under low-light conditions, below a green-site signal-to-noise ratio of $13.7$~dB, the color router preserves superior image information compared to the color-filter array; evaluated from its measured routing fractions together with the modeled throughput, the fabricated device reproduces this crossover at $11.1^{+2.1}_{-2.3}$~dB. This marks the first experimental demonstration, from measured routing and a modeled throughput, of a single-layer nanophotonic color router achieving a performance crossover against the color-filter array. These results establish that next-generation flat optics must shift from isolated device efficiency toward system-level co-design optimized under physical imaging-system-pupil geometry.
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All authors Hyoseok Park, Sehyeon Park, Myungjae Lee, Yeonsang Park
Biological Physics · Cross-listed from cond-mat.soft
Blinking membrane patterns induced by protein binding/unbinding
Hiroshi Noguchi
Nonequilibrium membrane pattern formation is studied using meshless membrane simulation. Bound
proteins are considered to have two states that generate different membrane spontaneous
curvatures.
Protein binding and unbinding occur cyclically owing to chemical potential differences, as an off-
lattice active Potts model. It is found that this cyclic binding/unbinding can induce blinking domains, with oscillating size: convex domains of the
proteins with a higher spontaneous
curvature grow, and subsequently, the
proteins change to the other state with a lower spontaneous
curvature, resulting in domain shrinkage. These processes repeat. In thermal
equilibrium, hexagonal convex domains are formed by the competition between bending and surface tension energies, so that they are stably formed only under positive surface tension. However, blinking domains can form even in tensionless membranes.
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