Physics Education
FlowMLLab: An open-source framework for reproducible computational-fluid-dynamics and scientific-machine-learning experiments
Ehsan Roohi
FlowMLLab is an open-source framework that connects validated fluid-mechanics solvers to scientific machine-learning experiments under a reproducible contract. Its computational fluid dynamics (CFD) pathway generates cavity data, whereas its direct simulation Monte Carlo (DSMC) pathway supplies rarefied-flow evidence with sampling diagnostics. Case-wise partitions prevent leakage, and matched non-neural baselines determine whether learning offers a measurable advantage. Examples include a coordinate network and a proper orthogonal decomposition (POD) deep operator network (DeepONet), together with learned kinetic closures. Python components regenerate every figure, while sixteen tutorials use the same interfaces as the command-line tools. By retaining numerical provenance, blind-case protocols and physical validation targets, FlowMLLab emphasizes traceable evidence rather than black-box curve fitting.
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Atmospheric and Oceanic Physics
Persistent memory and tail-risk amplification in Atlantic Meridional Overturning Circulation variability: a Volterra integral framework calibrated with CMIP6
Mauricio Herrera-Marín
The Atlantic Meridional Overturning Circulation (AMOC) carries multi-decadal
memory that ensemble-mean risk projections do not capture. We quantify this
memory and its consequences for tail risk with a Volterra integral framework applied to ensemble-mean-subtracted variability in 14 CMIP6 models (1850-2100, three SSP scenarios), so that results reflect intrinsic thermohaline
memory rather than the common anthropogenic forcing trend. Four results follow from leave-one-out cross-validation and an annealed-quenched tail decomposition. First, the ensemble-mean DFA1 Hurst exponent is H = 0.781 +/- 0.219, with 12 of 14 models showing long-range dependence (H > 0.5), consistent with thermohaline adjustment timescales near 33 yr. Second, a first-order Volterra model reduces out-of-sample RMSE by 16.8% over the best autoregressive baseline and by 12.3% over an unconstrained 20-lag distributed baseline, both robust to 200 circular-shift placebos (p < 0.05): the physically motivated kernel shape carries genuine predictive advantage. Third, the rolling 30-year lower-tail frequency rises 1.9-3.1x above the historical baseline depending on scenario, and the
memory amplification index exceeds 1 in 8 of 14 models under SSP5-8.5 (median 1.15): persistence-driven clustering of weak-AMOC states amplifies tail frequency beyond forcing-only projections. Fourth, model-specific optimal
memory horizons (15-52 yr) correlate with thermohaline regime (r = 0.74, p < 0.01), and the ensemble-mean Hurst exponent already exceeds a detection threshold H* = 0.70 in 9 of 14 models, with theoretical lead times to near-tipping conditions of 10-35 yr depending on scenario. These results support trajectory-specific,
memory-aware AMOC risk assessment under moderate-to-high forcing and a physically grounded, scenario-conditional early-warning framework.
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Geophysics · Cross-listed from astro-ph.EP
An Evolving Cosmic Shoreline and Sandbar Bounding the Rocky Airless Valley
Barron K. Nguyen, Laura K. Schaefer, Xuan Ji et al. (+7 more)
Recent JWST observations challenge the traditional '
cosmic shoreline' from both sides, revealing thick volatile atmospheres on the hottest close-in 'lava worlds,' where irradiation should drive the most extreme escape, and bare rocky surfaces on cooler terrestrial
planets around M
dwarfs, where atmospheres would be expected to survive. Using a coupled atmosphere-interior
evolution model, we show that atmosphere retention is governed not by a single escape boundary but by two: a hot, outgassing-regulated '
cosmic sandbar' and a cooler, escape-regulated '
cosmic shoreline,' separated by an 'airless valley' that may mark a graveyard of stripped sub-Neptune cores. The sandbar arises because long-lived magma oceans, sustained further by
tidal heating from secular eccentricity excitation in multi-
planet systems, keep most volatiles dissolved and expose only a small atmospheric reservoir to escape, whereas cooler
planets solidify, sequestering volatiles in the deep solid mantle while overexposing the rest to loss. This two-regime structure recasts the single
cosmic shoreline as two boundaries set by distinct physics: outgassing and escape. We provide time-evolving fits for both boundaries across G, K, and M
stellar types as a function of volatile inventory, planetary mass, age, and
tidal heating. Lava worlds with thick atmospheres are unlikely around
stars cooler than K-type unless sustained by extreme
tidal and/or other interior heating. This framework links atmosphere survival from USP lava worlds to habitable zone
planets, informing target selection and interpretation for TRAPPIST-1 and JWST DDT characterization.
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All authors Barron K. Nguyen, Laura K. Schaefer, Xuan Ji, Christopher A. Theissen, Fei Dai, Bo Peng, Yao Tang, Andrea Zorzi, Michelle Hill, Megan Weiner Mansfield
Fluid Dynamics
The Stokes resistance of an arbitrary particle: a classification of hydrodynamic symmetries
Clément Moreau
The linearity of the Stokes equations organises the hydrodynamic response of a rigid particle into a hierarchy of resistance operators, coupling successive truncations of the ambient-flow jet to moments of the surface traction. Since the work of Kelvin and Larmor, it has been known that this response does not resolve particle geometry faithfully: bodies with discrete rotational
symmetry may be indistinguishable from bodies of revolution (Brenner's helicoidal
symmetry) and a
chiral body may respond isotropically, as in Kelvin's isotropic helicoid. We regard the resistance operators as elements of finite-dimensional O(3)-representation spaces and use character formulae to determine, at every level of the hierarchy, which point-group
symmetries are hydrodynamically distinguishable and the dimension of each invariant space. This yields an explicit nested sequence of hydrodynamic
symmetry-group sets, from the translation-force level to the quadratic-flow level. The framework reveals hydrodynamic classes that no shape can realise geometrically, gives helicoidal
symmetry a level-dependent definition, and shows that polyhedral
symmetry becomes visible in a strict order: tetrahedral
symmetry in shear, octahedral
symmetry through the stresslet, and icosahedral
symmetry in quadratic flow. Projecting the resistance operators onto force- and torque-free motion provides
symmetry-based parameter counts and a constructive route to the corresponding dynamical normal forms. We thereby complete the Jeffery-Bretherton-Ishimoto classification, characterise all hydrodynamic classes producing Jeffery dynamics, and identify
chiral tetrahedral and octahedral normal forms that can generate irregular full-attitude dynamics.
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Chemical Physics
Learning the Kohn-Sham map with neural operators for quasi-linear scaling density functional theory
Danish Khan, Maurice D. Hanisch, Nikolai Argatoff et al. (+3 more)
Kohn–Sham density functional theory (DFT) underpins electronic-structure simulations, but repeated orbital diagonalizations lead to cubic scaling, restricting
quantum calculations to modest scales only. Eliminating these auxiliary orbitals while retaining Kohn–Sham accuracy is the central goal of orbital-free DFT, but both analytical and machine-learning methods have so far fallen short. Prior learning approaches either try to learn the variational kinetic-energy functionals, which are ill-conditioned, or directly predict the ground state, which extrapolate poorly to larger systems. Instead, we identify the Kohn–Sham map as the right learning target for orbital-free DFT. It maps a Kohn–Sham potential directly to the corresponding density and noninteracting kinetic energy, quantities otherwise obtained through an orbital diagonalization. Focusing on the density component in this work, a domain-invariant $\mathrm{SE}(3)$-equivariant
Fourier neural operator learns to predict it from the potential as input on real-space grids, enabling stable quasi-linear scaling SCFs. Trained jointly on 8,504 molecules and solids, a single model generalizes to out-of-distribution organic molecules,
insulators, and metals. For the first time, the same method converges SCFs across these systems without explicitly constructing Kohn–Sham orbitals, while reproducing densities, electronic spectra, and structural observables at Kohn–Sham DFT accuracy. Linear-scaling SCFs additionally allow converging magnesium dislocation densities containing up to 82,500 valence electrons on a single GPU.
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All authors Danish Khan, Maurice D. Hanisch, Nikolai Argatoff, Evan Xie, Sandeep Sharma, Anima Anandkumar
Computational Physics
Macroparticles with different weights relax to different temperatures in Particle-In-Cell simulations
Remi Lehe, Arianna Formenti, Justin R. Angus et al. (+1 more)
A distinctive feature of Particle-In-
Cell (PIC) simulations is the use of macroparticles, each representing many physical particles. The associated macroparticle weight can vary from one species to another, or even from one macroparticle to another. Here we show that, when macroparticles have different weights, the
plasma evolves toward an unphysical thermal
equilibrium in which the temperatures are unequal: lower-weight macroparticles reach a higher temperature than physically expected, and higher-weight macroparticles a lower one. We show that this unphysical
equilibrium is difficult to avoid, but that reaching it takes time, and that the associated timescale depends on the effective collisionality of the PIC
algorithm. We derive an equation that predicts the full time
evolution of the temperatures, in good agreement with PIC simulations, and use it to identify strategies to delay the establishment of this unphysical thermal
equilibrium.
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All authors Remi Lehe, Arianna Formenti, Justin R. Angus, Jean-Luc Vay
Chemical Physics
Differential Learning for Robust Prediction of Thermal Stability with Application to Energetic Materials
Megan C. Davis, R. Seaton Ullberg, Jeremy N. Schroeder et al. (+5 more)
Predicting thermal stability during handling and storage is essential for the design of safe and reliable energetic materials. However, experimental measurements vary significantly across laboratories due to differences in protocols and analysis methods, making it difficult to train reliable predictive models. We address this challenge through differential learning. Rather than predicting absolute decomposition temperatures, we instead train message passing neural networks to predict relative differences between pairs of molecules. This approach reduces sensitivity to systematic experimental errors and achieves >85% accuracy in ranking compounds by thermal stability, outperforming conventional regression methods on the same heterogeneous
dataset. To understand what drives these predictions, we compare neural network models with interpretable alternatives built from descriptors derived from ab initio calculations and cheminformatics software. This analysis identifies bond dissociation enthalpy as a key determinant of thermal stability rankings, providing further insight into the complex chemistry of thermal decomposition. The differential learning framework generalizes across model architectures, from graph neural networks to classical descriptor-based approaches. Our results demonstrate that learning relative properties rather than absolute values offers a practical solution for modeling noisy experimental data, with direct applications in materials design where thermal stability predictions inform safety protocols.
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All authors Megan C. Davis, R. Seaton Ullberg, Jeremy N. Schroeder, Andrew H. Salij, Marc J. Cawkwell, Christopher J. Snyder, Ivana Matanovic, Wilton J. M. Kort-Kamp
Chemical Physics
Wide-Field Opto-Iontronic iSCAT Mapping of Interfacial Charging and Electrical Connectivity
Zhu Zhang and Sanli Faez
Spatial variations in electrical connectivity and interfacial ion accumulation can strongly influence electrochemical performance, yet these properties are difficult to visualize directly with conventional ensemble measurements. Here, we introduce potential-modulated opto-iontronic microscopy, an interferometric scattering microscopy (iSCAT) approach for wide-field imaging of electric-double-layer (EDL) dynamics at nanostructured electrodes. Sinusoidal potentials were applied to focused-ion-beam-fabricated indium tin
oxide (ITO) nanoholes, and the optical response was extracted at the modulation frequency by
Fourier demodulation. The optical modulation amplitude increased approximately linearly with modulation voltage above a low-voltage roll-off and decreased with increasing frequency, consistent with kinetically limited interfacial charging. We then mapped the potential-synchronized optical amplitude across patterned ITO electrodes. Electrically isolated blocks exhibited strongly suppressed modulation signals, whereas electrically connected and partially milled nanogrid structures showed pronounced responses. These results demonstrate label-free optical mapping of local charging dynamics and electrical connectivity at heterogeneous electrochemical interfaces using a commercially available iSCAT platform.
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Optics · Cross-listed from cond-mat.mes-hall
Quantum encoding of structured light into in-plane topological spin textures
Pavel A. Vorobyev, Daichi Kurebayashi and Oleg A. Tretiakov
Structured light offers a powerful means of controlling light-matter interactions through multiple tunable optical degrees of freedom. Using micromagnetic simulations, we investigate the nucleation of asymmetric bimerons and antibimerons by pulsed Laguerre-Gaussian optical
vortices in
chiral ferromagnetic thin films with $C_{nv}$ and $D_{2d}$
symmetries, respectively. For optical
vortices with orbital angular momentum (OAM) $|m|=1$, circularly polarized beams deterministically nucleate a single bimeron or antibimeron via the interplay of
spin angular momentum, OAM, and
magnetic chirality, whereas linearly polarized beams produce textures whose topological charge directly follows the OAM ($Q=m$). Optical
vortices with OAM $|m|>1$ nucleate clusters and other configurations composed of multiple
spin textures, whose morphology and topological charge depend sensitively on the optical
quantum numbers and pulse parameters. These findings reveal a route to
topology-selective writing through the encoding of optical
quantum numbers into distinct in-plane topological
magnetic states.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Can Strain or Anion Interchange Make an Unstable Structure Stable? Energetics, Lattice Dynamics and Strain-Tunable Band Gaps of Lithium Chalcohalide Antiperovskites (Li$_{3}$$BA$) and their Anion Interchange Variants (Li$_{3}$$AB$)
Ismail A. Buliyaminu, Ehsan Gowdini, Phillip Duxbury et al. (+1 more)
Lithium chalcohalide antiperovskites are a promising, non-toxic alternative to lead halide perovskites, with potential as solid electrolytes for Li-ion batteries. we computationally investigate a relatively unexplored anion-interchange mechanism by which cubic Li$_{3}$$AB$ derivatives are obtained from the parent cubic antiperovskite Li$_{3}$$BA$ ($A$ = O, S, Se, Te, Po; $B$ = F, Cl, Br, I). The calculated relative energy landscape provides a useful guide for anion-site selectivity and its role in structural stability. The energetic stability results reveal that the smaller anion inside the octahedron stabilizes the structures. The
lattice-dynamic calculations confirm that Li$_{3}$F$A$ ($A$ = Te, Po) and Li$_{3}$O$B$ ($B$ = Cl, Br, I), which are the most energetically stable compounds, are dynamically stable cubic phases without imaginary
phonon modes. However, Li$_{3}$FS and Li$_{3}$FSe, while energetically stable, are dynamically unstable at
equilibrium and become dynamically stable under triaxial compressive strain. In addition, we report the electronic structure and density of states (DOS) of all compounds, which show a substantial change in band gap upon anion interchange. The strain engineering of the lithium chalcohalide family illustrates how a few percent of the strain can tune the electronic band gap within the electrochemical stability window for solid battery applications. This study unveils essential characteristics of the anion site-interchange mechanism and provides a foundation for the understanding and design of lithium chalcohalide antiperovskites.
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All authors Ismail A. Buliyaminu, Ehsan Gowdini, Phillip Duxbury, Jose L. Mendoza-Cortes
Computational Physics · Cross-listed from math.NA
Computing statistical Euler limits of the Navier–Stokes equations in three dimensions
Johannes L. Grafen, Tobias Rohner and Stephan Simonis
We develop a Monte Carlo
lattice Boltzmann method to compute statistical solutions to the three-dimensional incompressible Navier–Stokes and Euler equations. Entropic space-time adaptive relaxation of the higher order kinetic moments yields stable numerical solutions with decreasing viscosity. We provide a convergence analysis that is conditional on four explicitly stated assumptions regarding the discrete dynamics. Under diffusive scaling, the laws of the discrete ensemble converge along a subsequence to a limit satisfying the Foias–Temam Liouville formulation of the Navier–Stokes equations. Consequently, provided the structure function scaling holds uniformly, the vanishing viscosity limit of these measures satisfies the multi-point statistical Euler hierarchy of Fjordholm, Mishra, and Weber. The limit measures inherit the known weak-strong uniqueness principle on the interval of existence of a strong Euler solution. Under explicit scaling assumptions, a Kuznetsov-type argument yields a fractional 1-Wasserstein convergence rate. We present three-dimensional computations of time-dependent statistical solutions along the inviscid limit of the incompressible Navier–Stokes equations together with convergence measurements in the Wasserstein metric. Numerical experiments on a randomized Taylor–Green
vortex with 24-dimensional initial uncertainty recover Kolmogorov's K41 scaling for energy spectra and structure functions, exhibit the failure of pathwise strong convergence, and yield Wasserstein convergence rates of about $0.5$ at the onset of
turbulence. Finally, error measurements with respect to spectral hyperviscosity computations indicate that the computed limit measure is independent of the numerical regularization.
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Optics
Classification of Non-Hermitian Flat Bands
Chang-geun Oh and Jun-Won Rhim
Exact flat bands provide a versatile setting for correlated and topological phenomena, yet their properties are controlled not only by their dispersion but also by the structure of their Bloch projectors. Here, we establish a projector-based classification of non-Hermitian flat bands. In contrast to Hermitian flat bands, non-Hermiticity introduces a biorthogonal projector whose left-right pairing permits a distinct norm-pole singularity. We identify four classes: analytic NH-A, continuous but nonanalytic NH-C, bounded but discontinuous NH-D, and pole-singular NH-E. We show that continuity of the biorthogonal projector preserves the locking of the right, left, and biorthogonal Chern numbers, $C_R=C_L=C_{\rm bi}$, thereby realizing non-Hermitian critical topological flat bands. Once continuity is lost, this locking can break down; in particular, a mismatch $C_R\neq C_L$ can occur in the NH-E class. Finally, we show that this Chern number mismatch ensures to produce an anomalous enhancement of resonant cross-orbital transfer. Our results establish biorthogonal projector regularity as the organizing principle linking compact localized states,
topology, and driven response in non-Hermitian flat bands.
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Atomic Physics
Multi-hour stable trapping and threshold steady state of non-laser-coolable ions with ultracold atoms in a hybrid trap
Satyabrata Baidya and Sourav Dutta
We report multi-hour stable trapping and steady state of non-
laser-coolable Cs$^{+}$ ions in a linear Paul trap, achieved via resonant charge-exchange (RCE) cooling with a precisely centered ultracold Cs cloud. Without cold atoms, all ions are lost within 3 minutes. With centered cold atoms, RCE cooling establishes a stable population of ions for 6 hours with no measurable decay – more than two orders of magnitude longer hold times compared to prior hybrid atom-ion systems. We observe a threshold behavior in the steady-state number of ions ($N_{s}$): initial ion loadings above $N_{s}$ ions converge downward to $N_{s}$ ions and remain constant thereafter; initial loadings below $N_{s}$ ions show no measurable decay. The dynamics is governed by a competition between ion-ion rf heating and ion-atom collisional cooling. The prolonged, simultaneous ion-atom trapping suggests an upper bound on the three-body recombination-induced Cs$_{2}^{+}$ formation rate constant: $k_{3} << 1.4 \times 10^{-25} cm^{6} s^{-1}$. This remarkable realization of long-lived steady state overcomes a critical limitation of prior hybrid atom-ion systems and enables extended studies of ultracold ion-neutral chemistry, rare inelastic collisions, and sympathetic cooling routes for complex molecular ions.
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Biological Physics · Cross-listed from cond-mat.stat-mech
Entropy Production Bounds the Accuracy of Computation in Markov Networks
Songela W. Chen and David T. Limmer
Biological and artificial networks compute by transforming time-dependent inputs into functional outputs. Because the internal state of a
stochastic network relaxes on finite timescales, its output generally lags behind a changing environment, producing computational errors. We show that for reversible continuous-time Markov networks the error admits a universal thermodynamic bound. Decomposing the total error into representation and lag contributions, we derive an inequality relating the lag error to the
entropy production rate and a
memory time equal to the integrated
equilibrium autocorrelation of the output observable. The bound implies that accurate dynamical computation requires either substantial dissipation or long-lived
memory encoded in slowly relaxing modes. We demonstrate these principles in artificial Markov networks and in models of biochemical information processing. Our results establish a thermodynamic limit on information processing in
stochastic networks and provide a quantitative framework for understanding the energetic costs of biological computation.
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Applied Physics · Cross-listed from quant-ph
Sustained macroscopic quantum coherence in a superradiant solid under ambient conditions
Wei-Jiang Wu, Da-Wu Xiao, Wen-Tao Wang et al. (+5 more)
Macroscopic
quantum coherence, such as in
laser, Bose-Einstein condensates, superfluids, and
superconductors, is important to fundamental physics and useful for
quantum technologies. Superradiance provides a mechanism to produce coherence among a large number of particles and
photons. Its implementation, however, has been limited to gaseous systems, solids at very low temperature, or short pulses. Here we demonstrate a solid-state superradiant maser under ambient conditions, which establishes long-lived coherence among about $10^{14}$ nitrogen-vacancy center
spins in diamond and about $10^9$
photons in a microwave cavity. By varying the system parameters to access the above-threshold, well-above-threshold, and deep-above-threshold regimes, we observed continuous-wave masing, periodic amplitude modulation, and sequences of superradiant bursts, which are attributed, correspondingly, to macroscopic
spin coherence synchronized at a fixed frequency, a coherent time
crystal of large
spins, and unsynchronized superradiant transients. This work demonstrates that macroscopic
quantum coherence can be spontaneously generated and maintained in solids under ambient conditions and provides a solid-state platform for exploring bright
quantum lights with many-body correlations.
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All authors Wei-Jiang Wu, Da-Wu Xiao, Wen-Tao Wang, Xin-Yu Chen, Xian-Feng Wang, Ming-Zhong Ai, Quan Li, Ren-Bao Liu
Space Physics · Cross-listed from astro-ph.EP
GravDyn: A Python Framework for Gravitational Modeling of Irregular Celestial Bodies Using Polyhedral, mascon, and Series Expansion Methods
Safwan Aljbaae, valerio Carruba, Allan K. de Almeida Jr et al. (+4 more)
GravDyn is an open-source Python package for computing gravitational potentials and accelerations around irregular celestial bodies. It implements three approaches within the same workflow: the constant-density polyhedral method, a layered mascon approximation based on tetrahedral decomposition, and the Potential Series Expansion Method (PSEM). The package handles shape-model preprocessing, builds the selected
gravity representation, and evaluates potentials and accelerations efficiently. The three implemented methods serve different regimes: the polyhedral model provides a reference solution near the surface, the mascon model supports layered internal density structures, and PSEM offers fast evaluation outside the Brillouin sphere once the
polynomial coefficients have been generated. Validation tests against the polyhedral solution show that the mascon and PSEM models reproduce the reference potential with small relative errors while reducing evaluation costs. GravDyn is intended for mission design and studies of spacecraft motion, orbital stability, and gravitational modeling around asteroids and other small bodies.
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All authors Safwan Aljbaae, valerio Carruba, Allan K. de Almeida Jr, Gabriel Antonio Caritá, Antonio F. B. A. Prado, Marcelo L. Mota, Carlos E. Ferreira Lopes
Atomic Physics · Cross-listed from cond-mat.quant-gas
Observation of electron spin interactions between Rydberg atoms
Le Ruan, Ziqi Zhou, Yuchen Guo et al. (+2 more)
We report the observation of electron
spin interactions between Rydberg atoms, which are driven by
spin-orbit coupling through second-order dipole perturbation and exhibit a spatial anisotropy governed by the atomic configuration. Specifically, we observe coherent electron
spin exchange dynamics, with the measured coupling strength agreeing well with both numerical calculations and theoretical models. Furthermore, we show that global microwave dressing enables active engineering and dynamical freezing of the
spin exchange by introducing a differential AC Stark shift between the participating states. Additionally, we achieve tunability of the interaction by applying a stronger
magnetic field, which effectively modifies the energy contributions of the underlying
spin-orbit coupling channels. Finally, measuring
spin dynamics in one-dimensional multi-atom chains aligned parallel or perpendicular to the
magnetic field provides a self-consistent validation of the anisotropic XXZ framework. This electron
spin interaction natively features
spin-position coupling and enables a natural mapping onto the Heisenberg-Kitaev model. Our findings reveal a new class of electron
spin-
spin interactions among Rydberg atoms, expanding the scope of
quantum simulation with Rydberg atom arrays.
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All authors Le Ruan, Ziqi Zhou, Yuchen Guo, Chengshu Li, Cheng Chen
Optics
Collective Topological Dark Solitons, Platicons, and Bright-Like Solitons in Normal Dispersion Optical Frequency Combs
Seyed Danial Hashemi, Ankitkumar Maisuriya and Sunil Mittal
Bright dissipative Kerr
solitons generated in anomalous-dispersion microresonators underpin integrated optical frequency combs that have enabled applications including precision metrology, spectroscopy, coherent communications, and optical frequency synthesis. In contrast, Kerr resonators operating in the normal-dispersion regime can support dark
solitons and platicons, but even the initiation of frequency comb generation typically requires auxiliary mechanisms, such as avoided mode crossings or pulsed pumping, to satisfy the phase-matching condition for four-wave mixing. Here we show that topological edge states in two-dimensional Kerr resonator
lattices intrinsically satisfy this phase-matching condition, enabling the generation of optical frequency combs and novel coherent dissipative structures in the normal-dispersion regime without any auxiliary mechanisms. The resulting frequency combs self-organize into collective dark
solitons that exhibit large-scale spatiotemporal synchronization across multiple resonators at the entire
lattice edge. By tuning the pump detuning, we demonstrate the continuous
evolution of topological dark
solitons into topological platicons while preserving collective synchronization. Remarkably, we show that the topological
lattice also supports collective bright-like
soliton states despite all constituent resonators operating in the normal-dispersion regime. Our results establish topological Kerr resonator arrays as a versatile route for engineering a broad family of coherent dissipative structures, ranging from dark
solitons to bright-like
soliton states, within a single platform. They also provide a route toward integrated frequency-comb generation in material platforms and wavelength ranges where normal material dispersion has traditionally constrained comb generation in conventional single-resonator systems.
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Atomic Physics · Cross-listed from cond-mat.quant-gas
Universal Spin-Position Coupled Rydberg Interactions
Chengshu Li and Hui Zhai
Strong interactions between $s$-orbital Rydberg atoms underpin atom-array-based
quantum computation and
quantum simulation. Typically, the
spin dependence of these interactions is negligible and plays no practical role. In this Letter, we uncover that a strong electron-
spin-dependent Rydberg interaction can emerge when the principal
quantum numbers of the two $s$-orbital atoms differ by a sweet-spot value. This interaction originates from the fine-structure splitting of nearby $p$ orbitals, which endows it with distinct
symmetry properties such that the electron
spins are coupled to the relative position of the two atoms, featuring a spatially defined anisotropy. We further demonstrate that this interaction admits a universal form, independent of the principal
quantum numbers, and highlight its fundamental distinction from conventional
magnetic dipolar interactions, establishing it as a new type of native
magnetic interaction in nature. Our findings introduce a new element to the Rydberg
quantum simulation toolbox. As a concrete application, we propose a native realization of the Kitaev-Heisenberg model, which hosts an unusual stripe phase as a
quantum many-body manifestation of
spin-space locking.
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Biological Physics · Cross-listed from eess.SP
Physics-Constrained Deep Learning Model for Contactless Blood Pressure Monitoring from Triaxial Bodyseismography
Yuanyuan Zhang, Yida Zhang, Jiahui Li et al. (+6 more)
Ballistocardiography (BCG) is promising for unobtrusive long-term blood pressure (BP) monitoring in laboratory settings, but traditional BCG signals are vulnerable to the variations in body-bed interaction with shifted fiducial points in temporal or amplitude axis, and BP varies with personal hemodynamic changes, causing misaligned representations that affect model generalizability and robustness. In this work, we propose Phy-BP, a physics-constrained BP estimation framework based on triaxial bodyseismography (BSG) acquired using bed-mounted sensors as an extension of single-axis BCG. Firstly, we design an adaptive quality-control
algorithm combining neighboring beat patterns and universal cardiogenic templates to retain reliable cardiac components. Secondly, we propose a physical model of wave propagation through the body-bed system to constrain latent feature
evolution, aligning triaxial representations generated by a shared cardiogenic excitation. These mechanical constraints connect multi-axis feature learning to body-bed dynamics and complement data-driven regression from vibration signals. Evaluation on a 162-hour hospital
dataset from 21 subjects against invasive arterial BP yields a mean absolute error of 5.07 mmHg, a prediction-error standard deviation of 7.24 mmHg, and a Pearson correlation coefficient of 0.86 for mean arterial pressure. This framework is intended for unobtrusive monitoring during rest and sleep, with potential applications in overnight hospital and home monitoring.
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All authors Yuanyuan Zhang, Yida Zhang, Jiahui Li, Yuyan Wu, Fei Dou, Xiao Yin, Zhenlin An, Hae Young Noh, Wenzhan Song
Optics
Diffractive optical element for super-Gaussian beam shaping on intersatellite optical communications
Mario Badás Aldecocea, Ziheng Wang, Mohammad Dabiri et al. (+1 more)
Pointing jitter can significantly degrade the performance of intersatellite optical communication links. This work investigates diffractive optical beam shaping as a means of generating super-Gaussian profiles with reduced sensitivity to transmitter misalignment. Phase screens are designed using a Gerchberg–Saxton phase-
retrieval algorithm and evaluated for different super-Gaussian orders. Lower-order profiles are reproduced accurately, whereas higher orders are increasingly limited by numerical discretization and finite-aperture effects. The practical implementation of the phase screens using fused-silica diffractive optical elements is assessed through sensitivity analyses of radial manufacturing resolution, phase quantization, phase-depth errors, and incident-beam wavefront aberrations. The results provide manufacturing tolerances and wavefront-quality requirements for preserving the desired beam shape.
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All authors Mario Badás Aldecocea, Ziheng Wang, Mohammad Dabiri, Iman Tavakkolnia
Atomic Physics
Extreme-ultraviolet spectroscopy using quantum logic: a feasibility study for the 1S-2S transition in singly-ionized helium
A. Martínez de Velasco, V.P.J. Barbé, E.L. Gründeman et al. (+10 more)
Extreme-ultraviolet (XUV) spectroscopy represents an important new direction in precision physics, with potential applications ranging from the metrology of fundamental constants to tests of physics beyond the Standard Model. However, the application of
quantum control methods for precision spectroscopy remains an open challenge in the XUV range. Here we present a novel
quantum logic (QL) spectroscopy method for precision spectroscopy of weak XUV transitions, and numerically validate its feasibility for the $1S-2S$ transition at 40.81\,eV in singly-ionized helium (He$^{+}$). We propose a scheme based on a single He$^{+}$ ion co-trapped with a Be$^{+}$ ion in a Paul trap, and He$^{+}$ excitation with pairs of frequency-comb (FC)
laser pulses upconverted to the XUV via High-Harmonic Generation (HHG). We investigate a nondestructive QL scheme to detect $1S-2S$ excitation, and compare its performance with a destructive readout based on state-selective ionization. Phase coherence of the XUV light is modelled and an optical cavity is used to filter the FC pulses prior to HHG. We model the motional excitation dynamics of trapped ions outside the Lamb-Dicke regime, and numerically validate a scheme we proposed in \cite{Grundeman} to cancel the first-order Doppler broadening and the
recoil shift by synchronizing the ion's secular period with the time delay between the two excitation pulses. We show that precision spectroscopy of the $1S-2S$ transition in He$^{+}$ at the 10 kHz level is feasible, for improved tests of
quantum electrodynamics (QED), a measurement of the Rydberg constant $R_{\infty}$ independent of hydrogen measurements, or an improved determination of the alpha particle and helion charge radii. The proposed method may also be applied to XUV spectroscopy of other ions outside the Lamb-Dicke regime.
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All authors A. Martínez de Velasco, V.P.J. Barbé, E.L. Gründeman, A. Díaz Calderón, M. Collombon, J.J. Krauth, C.F. Roth, M. Favier, R. Taieb, T.E. Mehlstäubler, P.O. Schmidt, L.S. Dreissen, K.S.E. Eikema
Instrumentation and Detectors
Post-diffusion cooling effects on Hall-derived active lithium donor profiles in high-purity germanium
Kunming Dong, Dongming Mei, Anupama Karki et al. (+2 more)
Lithium (Li)
diffusion is commonly used to form $n^{+}$ contacts in high-purity germanium (HPGe) detectors, but the final electrically active donor profile can be sensitive to the post-
diffusion thermal history. Li was introduced into HPGe coupons using a lithium-in-oil suspension and diffused for $30~\mathrm{min}$ at nominal temperatures of $240$–$310~^{\circ}\mathrm{C}$. Short- and long-cooling protocols were documented by measured witness-Ge cooling histories. Sequential material removal combined with
Hall-effect measurements at $77~\mathrm{K}$ was used to reconstruct difference-derived apparent
Hall donor profiles. Because
Hall response in a nonuniform conducting layer is mobility weighted, these profiles are operational electrically active-donor metrics rather than direct local or total-Li concentration profiles. Complementary-error-function fits were used to obtain the extrapolated apparent intercept $N_{s,\mathrm{app}}$ and the apparent profile-width parameter $D_{\mathrm{app}}$. For the coupons studied, short cooling was associated with larger $N_{s,\mathrm{app}}$ and sharper profiles, whereas long cooling was associated with lower $N_{s,\mathrm{app}}$ and broader low-concentration tails. Fit-derived concentration-threshold depths likewise extended farther into the Ge bulk for the long-cooling coupons. These results show that the complete post-
diffusion thermal history should be considered when parameterizing
Hall-active Li-diffused $n^{+}$ contacts for HPGe detector fabrication.
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All authors Kunming Dong, Dongming Mei, Anupama Karki, Partrick Burns, Sanjay Bhattarai
Computational Physics · Cross-listed from cs.CG
Riesz Energy Subset Selection in the Euclidean Plane is NP-Hard: A Reduction from the Ising Model on Planar Cubic Graphs
Michael Emmerich
We prove that minimum Riesz $s$-energy subset selection in the Euclidean plane is NP-complete already for the fixed exponent $s=2$. To our knowledge, this is the first Euclidean hardness result for exact Riesz-energy subset selection in which both the ambient dimension and the exponent are fixed. The reduction uses Barahona's planar cubic Ising model with uniform field. A
spin is encoded by one diagonal of a four-point square. Axis-aligned selector chains implement
ferromagnetic consistency, while a $45^\circ$ terminal geometry yields an
antiferromagnetic source interaction. Rational diagonal perturbations realize the
magnetic field, and all remaining interactions are dominated by
polynomial separation. Because $s=2$ and all coordinates are rational, every constructed energy and the decision threshold are rational exactly.
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Space Physics · Cross-listed from math.PR
Stochastic Dynamics of Low Earth Orbit Near Full Capacity
Priyank Behera, Aditya S. Gopalan and Harsha Honnappa
The capacity of Low Earth Orbit (LEO) to sustain space operations is under mounting pressure from megaconstellations, legacy fragmentation debris, and new payload classes. Existing assessments of orbital capacity and debris
evolution are largely deterministic, tracking mean populations of intact satellites and fragments with ordinary differential equations; they cannot capture the inherent randomness of collisions, breakup sizes, and launch schedules. We develop a
stochastic extension of the two-species Lotka–Volterra model of Bradley and Wein, formulated as a density-dependent Markov chain, and study its deterministic and
stochastic scaling limits. Because intacts and fragments differ by many orders of magnitude, these limits emerge on distinct time-scales, and different pathways to a collisional Kessler cascade become visible only on the appropriate time horizon. On a fast intact time-scale we obtain an ODE approximation and a Gaussian SDE approximation; on an intermediate fragment time-scale we obtain an ODE approximation, a Gaussian SDE approximation, and the critical Kessler threshold, above which the ODE approximation runs away in Kessler syndrome. Crucially, on a third, slow time-scale at the critical threshold, the fragment count converges to a Feller
diffusion, in which runaway is triggered purely by fluctuations rather than by the drift—an effect the ODE approximations and their Gaussian SDE approximations cannot see. Debris runaway may occur sooner, and with higher probability, than deterministic models predict: the intact population can appear well-behaved while fragments quietly accumulate risk. Constellation deployment, debris-removal investment, and slot allocation should account for these
stochastic effects, and planning for runaway must depend on the variance of the collision dynamics, not on the mean alone.
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Fluid Dynamics · Cross-listed from cond-mat.soft
Approaching the theoretical limit of wicking on textured surfaces
Zhaoyang Lv, Chen Ma, Li-Chen Huang et al. (+1 more)
Wicking in a capillary tube could happen as long as the
liquid contact angle is smaller than 90 degrees, making it possible for weak hydrophilic
liquids to spontaneously invade the tube. For textured surfaces, energy minimization argument predicts the same. However, wicking of weak hydrophilic
liquids on textured surfaces has not been possible due to energy barriers induced by the textures. We demonstrate how these barriers could be avoided by adjusting the shape and arrangement of the pillars, thus the wettability required for wicking reaches the theoretical limit. An unprecedented wicking contact angle of 82 degrees is reported. More surprisingly, wicking coefficients of such surfaces can be larger than that of rectangular grooves at the same porosity. These findings may significantly advance biomedical and thermal management technologies.
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All authors Zhaoyang Lv, Chen Ma, Li-Chen Huang, Yanshen Li
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Emergent Noncollinearity and Near-Degenerate Magnetic Superlattices in AT6X6 Kagome Metals
Weiyi Xia, Wei-Shen Tee, Peter Minch et al. (+3 more)
Ferromagnetic AT6X6 Kagome compounds are a popular class of systems in which
quantum magnetism with topological features has been observed. These systems allow easy chemical substitution, creating an opportunity to fine-tune their properties. In this paper, we present electronic-structure and
magnetic ground-state studies of several AT6X6 compounds with relatively low
magnetic-ground-state stability. We find unusual
magnetic orderings, including complex
spin-spiral states and the formation of
magnetic long-range superstructures. While LiFe6Ga6 and TiMn6Ge6 retain collinear AFM ground states with low-energy FM/AFM layer sequences, competing
spin-spiral and long-period
antiferromagnetic structures in MgFe6Ga6 and a double-
spin-spiral ground state in TiFe6Ga6 were determined. Magnetism in all these systems appears local, with adiabatic energy profiles suggesting non-Heisenberg long-range interactions, including a strong biquadratic term. In TiMn6Ge6, we found the conditions for
magnetic tunneling. Our results show that, in addition to traditional
magnetic topological features in such FM Kagome systems, near-degenerate
magnetic superstructures suitable for spintronic switching applications can form naturally. Overall, these systems represent a potentially rich playground for
neutron diffraction and spintronics experimental studies.
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All authors Weiyi Xia, Wei-Shen Tee, Peter Minch, Feng Zhang, Cai-Zhuang Wang, Vladimir Antropov
Fluid Dynamics
Increased throughput in antisymmetrically actuated acoustofluidic flow-through devices
Klara Andersson, Sazid Z. Hoque, Wei Qiu et al. (+4 more)
Separation of low-abundance biological objects requires high throughput for practical use of an acoustofluidic system. Increasing the flow rate helps in achieving high-throughput if the acoustic energy density can be increased proportionally, and this may be possible with an efficient coupling of the transducer to the device. In particular, antisymmetric actuation using two electrodes with opposite phases is theoretically proven to enhance the acoustic energy density of the device. In this work, we study the symmetric and antisymmetric actuation mechanisms of an acoustofluidic system using both experiments and three-dimensional numerical simulations. The acoustic focusability experiments show that under the same electrical input power, the antisymmetric actuation mode performs better than the symmetric actuation, quantified in terms of the normalized width of the band formed by the focused particles. Numerical simulations of this particle bandwidth are performed for both actuation modes, and the results suggest that the antisymmetric actuation mode is more robust than the symmetric one, being weakly dependent of the
geometric symmetry properties of the system. The simulation results corroborate the experimental findings, which indicate that the antisymmetric actuation increases the acoustophoretic efficiency and robustness for high-throughput applications.
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All authors Klara Andersson, Sazid Z. Hoque, Wei Qiu, Andreas Lenshof, Pelle Ohlsson, Henrik Bruus, Thomas Laurell
Plasma Physics
Helical jets driven by a ring of laser irradiation
Kian Orr, Brandon K. Russell, Kirill Lezhnin et al. (+5 more)
Plasma jets are formed in various astrophysical systems as
plasma is rapidly ejected from a source, with a subset of these jets being magnetized and having a helical structure. Here, we demonstrate that helical jets may be formed using a ring of
laser pulses that arrive on planar foils sequentially with increasing energy. The formation of the jets and their properties, including kinetic helicity, are studied through a set of three-dimensional magneto-hydrodynamics simulations with conditions informed by the parameters of the OMEGA
laser facility. We find that jets with a higher degree of helicity may be generated under realistic experimental conditions when compared to a uniform jet. Synthetic x-ray and Thomson scattering diagnostics computed from simulated data demonstrate that the helical jet provides a unique fingerprint in both its morphology and
plasma parameters. This laboratory helical jet platform may allow for controlled experimental study of the dynamics of helical
plasma structures and, through interaction with other jets or targets, can allow for studies of shear-driven
turbulence and mixing relevant to interactions between astrophysical jets and ambient clouds or crosswind.
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All authors Kian Orr, Brandon K. Russell, Kirill Lezhnin, Yang Zhang, Geoffrey Pomraning, Petros Tzeferacos, Hantao Ji, Lan Gao
Chemical Physics
Environmental Control Extends Beyond Quantum Dephasing in Exciton Energy Transfer
Junhua Zhou, Tianrui Chen, Dehao Yuan et al. (+8 more)
Excitation-energy transfer underpins the conversion of light into usable energy in photosynthetic organisms and serves as a paradigm for evolutionary optimized transport in open
quantum systems. Although this process is often described as incoherent thermally assisted hopping, such descriptions become inadequate when electronic coupling, vibronic interactions and environmental fluctuations occur on comparable energy scales. Determining how the environment controls transport therefore remains a fundamental challenge. Here, we use temperature-dependent 2DES to investigate energy transfer in the photosynthetic
antenna protein allophycocyanin over the range 10 - 296 K. The dominant $\beta \rightarrow \alpha$ transfer step exhibits a pronounced non-monotonic temperature dependence: the transfer time decreases from 400 fs at 10 K to 200 fs near 30- 40 K before increasing again to 400 fs at 296 K. In contrast, the homogeneous optical dephasing time decreases monotonically across the same temperature range. To interpret these observations, we model APC as a vibronically coupled excitonic dimer interacting with a structured environment and solve the dynamics using hierarchical equations of motion. Conventional fixed-bath models, including Drude-Lorentz and explicit intermolecular-mode spectral densities, fail to reproduce the observed turnover. Quantitative agreement is obtained only when the low-frequency sector of the environmental spectral density is allowed to anharmonically evolve strongly with temperature, while the high-frequency bath remains essentially unchanged. More broadly, these findings demonstrate that transport efficiency is controlled not simply by the magnitude of environmental fluctuations, but by the distribution of environmental spectral weight across frequency space, providing new experimental constraints on theories of molecular transport in complex
quantum environments.
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All authors Junhua Zhou, Tianrui Chen, Dehao Yuan, Enhu He, Vandana Tiwari, Maxim Gelin, Francoise Remacle, R. J. Dwayne Miller, Fulu Zheng, Ajay Jha, Hong-Guang Duan