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Physics Physics

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Saturday 8 August

Optics

Spectral Mixing, Skin Localization, and Linear Optical Response in Dissipative Photonic Lattices

Chen-Huan Wu

We study the linear optical response of a finite dissipative Hatano–Nelson photonic lattice. The response between selected input and output ports is resolved into a phase-coherent intensity and an incoherent modal-weight contribution using the biorthogonal Green function. Their comparison isolates interference among non-Hermitian modal residues, while a response-weight entropy and the associated participation number $\Neff$ quantify how broadly the measured signal is distributed over the complex modes. The numerical results show that loss broadens the modal distribution, periodic-boundary spectral winding increases modal participation, and onsite disorder reduces it. Time-domain quantum-walk dynamics independently display the drift and right-edge accumulation produced by non-reciprocal hopping under open boundaries. A parameter map in the $(g,W)$ plane, supplemented by disorder-ensemble averages, identifies a finite-size crossover in which $\Neff$ responds to disorder before the response-weighted center is displaced from the skin boundary. The analysis applies to coupled waveguides, microring arrays, driven cavity lattices, and other linear photonic platforms with loss, gain, or non-reciprocal coupling.
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Chemical Physics

Oxygen Reduction Reaction on Platinum Nanocatalysts Produces Long-Lived, Hysteretic Oxygenated Adsorbates

Jaehyeon Kim, Lalith Krishna Samanth Bonagiri, Fujia Zhao et al. (+1 more)

Aqueous electrocatalysis generates oxygenated intermediates at catalyst surfaces. While intermediate species on single-crystal catalysts have been observed, the nature and evolution of surface oxygenated species on industrially relevant nanoparticle (NP) catalysts remain largely unknown. Here, using in situ Raman spectroscopy, we tracked the formation and potential-dependent evolution of oxygenated adsorbates in alkaline media on NP catalysts with an active platinum (Pt) surface. By comparing spectroscopic features in Ar- vs O2-saturated electrolytes, we determined three key intermediates produced by the oxygen reduction reaction (ORR): adsorbed OOH, OH, and O2. In contrast to the conventional wisdom that intermediates exist only during catalytic reactions, we found these oxygenated adsorbates to be highly long-lived and hysteretic, and to persist even after the termination of ORR. This adsorbate-retention effect exhibits a modest dependence on the surface oxidation state and the electrolyte cations (K+ vs Li+), and is likely facilitated by the heterogeneous nature of the catalyst surface. The results highlight the complexity of surface adsorption structures on realistic catalysts, which often extends beyond that captured by measurements or simulations on model single-crystal surfaces.
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All authors Jaehyeon Kim, Lalith Krishna Samanth Bonagiri, Fujia Zhao, Yingjie Zhang

Plasma Physics

Beam experiments for reactive ion etching of silicon (Si)-based materials by silicon halide ions

Kazuhiro Karahashi, Tomoko Ito and Satoshi Hamaguchi

Etching yields of Si, SiO2, and Si3N4 have been determined for silicon ion (Si+), halogen ions (F+, Cl+, and Br+) and silicon halide ions (SiF+, SiF3+, SiCl+, SiCl3+, SiBr+, and SiBr3+) irradiation in 300 to 1000 eV using a mass-selected ion beam apparatus that can irradiate a single species ion to sample surfaces under an ultra-high vacuum condition. Si+ irradiation below 1000eV deposits silicon atoms on Si, SiO2, and Si3N4 surfaces. The etching yields of silicon tri-halide ions (SiF3+, SiCl3+, and SiBr3+) above 1000 eV are larger than those of halogen ions, respectively, and these etching yields depend on the incident ion energy and the etching material (especially Si3N4). At low incident energy, silicon mono-halide ions (SiF+, SiCl+, and SiBr+) deposit silicon on substrates, and the etching threshold energy depends on the halogen species. This information contributes to a database of experimental values needed to increase the precision of an etching process and a profile simulator.
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Applied Physics

Measured LWC-Specific Fog Attenuation and Frequency Scaling in Low-THz Channels

Jiabiao Zhao, Xiaoxiang Li, Kefeng Huang et al. (+6 more)

Fog can reduce the link margin of terahertz (THz) wireless systems. Earlier channel measurements mainly relied on visibility, and almost no liquid water content (LWC) referenced attenuation coefficients have been reported. This letter reports controlled fog measurements at low-THz frequencies (120, 140, and 160 GHz) over a 22 m channel. LWC is retrieved from a time-aligned droplet size distribution (DSD) and paired with the fog-induced attenuation to obtain the relationship between attenuation and LWC at each frequency. The comparison with ITU-R P.840 is posed as an errors-in-variables problem. This separates the absolute coefficient from its frequency dependence - how the coefficient grows with frequency. Expressed as a power law of frequency, the measured exponent is 1.347, matching the value of 1.343 implied by P.840 at 20 oC. The results provide reference data and a compact scaling law for fog link budgeting at low-THz frequencies.
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All authors Jiabiao Zhao, Xiaoxiang Li, Kefeng Huang, Yapeng Ge, Hanchen Liu, Jie Yang, Weidong Hu, Houjun Sun, Jianjun Ma

Data Analysis and Statistics · Cross-listed from cond-mat.stat-mech

Turning angle analysis reveals hidden anisotropies in the anomalous diffusion of molecules in live cells

Michał Balcerek, Adrian Pacheco-Pozo, Agnieszka Wyłomańska et al. (+1 more)

Molecular motion within living cells provides a window into the physical principles underlying intracellular organization and transport. Yet a fundamental limitation remains: measured trajectories are often short, noisy, and randomly oriented, rendering spatial anisotropies inaccessible to conventional analyses. We show that turning-angle statistics provide a robust approach for uncovering anisotropies in anomalous diffusion. Using a two-dimensional anisotropic fractional Brownian motion model with random orientations, we show theoretically and through simulations that turning-angle distributions preserve signatures of anisotropy. We apply this approach to single-particle tracking data, including quantum dots in the cytoplasm of HeLa cells and membrane proteins in hippocampal neurons. Turning angles reveal hidden anisotropies in the motion of quantum dots and Nav 1.6 channels, and in specific dynamical states of glycoprotein CD4. These results establish turning-angle analysis as a powerful strategy for detecting organization in complex environments and reveal that anisotropic anomalous diffusion is an overlooked feature of intracellular dynamics.
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All authors Michał Balcerek, Adrian Pacheco-Pozo, Agnieszka Wyłomańska, Diego Krapf

Instrumentation and Detectors

A High Gain Preamplifier Board for Low Charge Semiconductor Detectors

De Zhang, Kuo Ma, Juzheng Zhang et al. (+3 more)

We present a high-gain, low-noise preamplifier board designed for reading out low-charge semiconductor detectors–specifically Low-Gain Avalanche Detectors (LGADs) and three-dimensional (3D) silicon sensors–in high-energy physics applications. The circuit employs a three-stage architecture featuring a discrete SiGe:C bipolar junction transistor (BJT)-based transimpedance amplifier (TIA) front-end followed by two resistive feedback amplification stages using LTC6431 chips. This configuration achieves a charge gain of 115.27 mV ns/fC with excellent linearity over an input range of 0.5 fC to 25 fC and a wide bandwidth spanning from 34.0 MHz to 594.3 MHz. Experimental evaluations coupled with LGAD detectors demonstrate a time resolution of 36.41 ps and an equivalent noise charge (ENC) of 0.18 fC at 20 {\deg}C. Furthermore, tests with conventional PIN sensors without a gain layer yield a timing resolution of 76.10 ps with an ENC of 0.10 fC, and tests with the 3D silicon detector yield 39.40 ps with an ENC of 0.09 fC, all measured under the same thermal condition. All configurations confirm the board's capability in low-signal regimes, significantly outperforming previous reference designs. A six-channel variant of the board has also been developed to support position-sensitive measurements. These findings demonstrate the board's suitability for laboratory-based 4D tracking detector characterisation, while simultaneously providing the groundwork for dedicated ASIC development.
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All authors De Zhang, Kuo Ma, Juzheng Zhang, Jiajin Ge, Yanwen Liu, Hao Liang

Plasma Physics

Simulations of self-accelerating electron phase space holes in an applied electric field

Ran Guo

The self-acceleration of electron phase space holes in an applied electric field is investigated via one-dimensional electrostatic Vlasov simulations. The electron holes (EHs) are initialized in a self-consistent manner with immobile ions, and the ion response is enabled at the beginning of simulations. A benchmark simulation is conducted to confirm the EH self-acceleration in the absence of the external electric field. Then, we investigate the EH behaviors by applying the uniform and sinusoidal electric fields, respectively. The effects of different strengths and durations of these external electric fields are studied. It is found that the uniform electric field applied in the direction of the self-acceleration can delay the onset of this process and change the final speed of EHs. The applied sinusoidal electric field can fix the EHs at their initial positions and suppress the self-acceleration if the electric field amplitude and duration are appropriate. In addition, it is observed that these external electric fields can induce the splitting of EHs and the generation of secondary EHs. The physical mechanisms of these phenomena are discussed in detail.
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Fluid Dynamics

Splashing velocity of a viscous liquid squeezed between two parallel disks

Navin Kumar Chandra, Pierre Perrier and David Brutin

Squeezing of a liquid film between two approaching solid surfaces can generate a high-speed peripheral splash. Despite extensive studies on squeeze-film hydrodynamics, quantitative prediction of the splash velocity remains unresolved, with existing theory significantly overestimating experiments. Here, we present a theoretical framework to predict the ejection velocity of viscous liquid squeezed between two parallel circular disks. We show that discrepancy of theory from experiments arise due to incomplete treatment of liquid inertia and from using peak ejection velocity to represent splash velocity. By accounting for both local and convective inertia, and introducing a momentum-averaged ejection velocity, we obtain good agreement with experiments over a wide range of parameters.
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Physics and Society

Control of Harmful Information Spreading on Adaptive Higher-Order Networks via Group Dissolution

Longzhao Liu, Zhihao Han, Xingru Chen et al. (+4 more)

Curbing harmful information contagion remains a critical challenge, motivating platform-level interventions such as group dissolution to sever transmission chains. However, in practice, users affected by dissolution often exhibit adaptive behavior, rewiring to form new groups. Yet, it remains unclear how these two mechanisms jointly shape information contagion and whether group dissolution remains effective in suppressing it. Here, we develop an adaptive higher-order contagion model that integrates platform-induced group dissolution with user adaptive rewiring, and derive a theoretical framework. Notably, we reveal an effective window for group dissolution, bounded by a critical infection rate. Above this threshold, dissolution backfires and amplifies information prevalence. Within this window, dissolution acts non-monotonically, initially exacerbating prevalence before eradicating contagion via a discontinuous transition beyond a critical dissolution rate. We further show that higher-order reinforcement expands this infection-rate window over which dissolution remains effective, whereas rewiring homophily substantially narrows it. Simulations on empirical hypergraph also validate these findings. Our work highlights the interplay between top-down platform interventions and bottom-up user adaptation, underscoring the need to account for adaptive responses when designing strategies to curb harmful information without unintended amplification.
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All authors Longzhao Liu, Zhihao Han, Xingru Chen, Chunyu Luo, Hongwei Zheng, Xin Wang, Shaoting Tang

Optics

Sub-Rayleigh Imaging of Unequal-Intensity Sources: Near-Quantum-Limit Multiparameter Estimation

Y. Batuhan Yilmaz, Kent A. G. Bonsma-Fisher, Muhammad Mohid et al. (+3 more)

In optical imaging, diffraction strongly degrades the performance of conventional intensity-based estimation once the separation between two sources is below the Rayleigh-Abbe limit. Recent developments showed that this limitation can be surpassed using spatial-mode demultiplexing (SPADE), and this was demonstrated in several experiments for two equal-intensity spots of unknown separation. When there are multiple unknown parameters, as in the case of several unequal sources with unknown intensities and unknown separation, cross-talk among the parameters makes the multi-parameter estimation problem significantly more challenging. In this paper, we adapt super-resolved position localization by inversion of coherence along an edge (SPLICE) to estimate both the separation and relative intensity of two incoherent sources simultaneously. We demonstrate a clear advantage over direct imaging (DI), achieving a root mean squared error (RMSE) approximately $50 \%$ larger than the quantum limit and a sixfold improvement over DI within the range of parameters we tested. This improvement can be even greater for smaller separations and larger intensity imbalances when crosstalk is suppressed.
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All authors Y. Batuhan Yilmaz, Kent A. G. Bonsma-Fisher, Muhammad Mohid, Noah Lupu-Gladstein, Arthur O. T. Pang, Aephraim M. Steinberg

Instrumentation and Detectors

Performance of an HRPPD in Tesla-scale magnetic fields

B. Azmoun, Y. Ilieva, Y. Jin et al. (+9 more)

High-Rate Picosecond Photodetectors (HRPPDs) are state-of-the-art microchannel-plate (MCP) photodetectors that offer excellent timing and spatial resolution, together with high single-photon detection efficiency. They are currently being considered for the ePIC experiment at the future Electron Ion Collider (EIC) at Brookhaven National Laboratory. A key requirement for the application of this technology is reliable operation in a strong magnetic field up to 1.5 T, with magnetic flux lines at an inclination of $\le15^\circ$ to the normal of the MCP surface. Magnetic field-induced distortions of the collected charge in MCP-based detectors can be compensated by tuning the operating parameters; however, the objective of this study is to quantify this performance in the case of the EIC-HRPPD, a particular MCP stack-up specialized for operation within ePIC. This photosensor employs a high quantum efficiency photocathode, 10$~\mu$m capillary pores, narrow transfer gaps, and a custom ceramic pixelated DC-coupled readout. This article explores the optimal operating parameters (mainly the voltages applied across the gaps and the MCPs) for single photon detection at various inclination angles in a uniform field up to 1.8 T. Ultimately, it was found that the gain and single photon detection efficiency of the HRRPD could be recovered over a range of polar inclination angles up to $\pm35^\circ$.
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All authors B. Azmoun, Y. Ilieva, Y. Jin, J. Kim, A. Kiselev, B.S. Page, M. Popecki, M.L. Purschke, A. Tamis, V. Teotia, C.P. Wong, C. Woody

Atomic Physics · Cross-listed from cond-mat.quant-gas

Coherent Control of Domain-Wall Transport in an Ultracold Bose Gas

O. Farion, M. Pourzand and J. M. McGuirk

Domain walls are carriers of spin transport whose controlled manipulation underlies a wide range of spintronic and information-processing technologies. Here we demonstrate tunable domain-wall transport in a weakly interacting nondegenerate ultracold Bose gas. We initialize a three-domain pseudo-spin-1/2 texture and observe spontaneous propagation of long-lived domain walls driven by exchange-mediated spin currents. By varying the orientation of the spin domains, we control the balance of spin currents across the walls and thereby tune their trajectories, including reversals of the initial direction of motion. Measurements reveal a crossover from an exchange-stabilized regime, in which coherent spin-exchange collisions suppress wall motion, to a diffusion-dominated regime characterized by rapid transport at thermal velocities. Numerical solutions of a quantum Boltzmann equation reproduce the observed dynamics and identify transverse phase gradients as an important control parameter governing domain-wall propagation. These results establish coherence and phase engineering as tools for programming spin transport in ultracold gases and provide a route toward controllable domain-wall dynamics in atomtronic systems.
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Friday 7 August

Instrumentation and Detectors

Super-Lindhard Ionization from 254 eVnr Nuclear Recoils in Germanium

A.R.L. Kavner, E. Todd, M. Babicz et al. (+11 more)

We report ionization produced by the stopping of monoenergetic 254 eVnr 73Ge ions within a germanium lattice which exceeds the Lindhard prediction. The observed deviation is based upon prior measurements of the ionization produced by monoenergetic 254 eVnr Ge nuclear recoils and newly performed systematic studies of relevant nuclear physics processes. Combined with our prior work, the incompatibility with the Lindhard prediction increases to the 4.5 sigma level. We employ an empirical excess ionization model that exhibits super-Lindhard ionization from sub-keV nuclear recoils and converges back to the Lindhard model for higher energy recoils, above 1 keVnr. The excess ionization model is preferred over a pure Lindhard model when fit to the literature of germanium quenching factor data.
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All authors A.R.L. Kavner, E. Todd, M. Babicz, H. Birch, K. Dwinger, A. Fazan, V. Fondement, M. Janoschek, I. Jovanovic, L. Juigne, K. Moraa, B. Penning, F. Piastra, F. Uwe

Applied Physics

Slow dynamics in concrete: Effects of temperature, strength variation, and microcracking damage

Clayton Malone and Jinying Zhu

In this study, we investigated the slow dynamic behavior of concrete with varying compressive strengths ($f'_c = 32\sim56$ MPa) and alkali-silica reaction (ASR) damage. Concrete prisms were conditioned by compressive loading and recovery was monitored by coda wave interferometry (CWI). A self-referencing temperature correction technique was used to minimize the effect of ambient temperature changes, demonstrating the importance of careful temperature control and correction. For intact specimens, both the recovery rate, $m_v$, and velocity drop magnitude, $|c|$, generally increased with compressive strength. Recovery times were calculated from the fit parameters, and higher strength specimens were found to recover faster (9.9 h for $f'_c = 32$ MPa, 6.6 h for $f'_c = 56$ MPa). When the same stress was applied, ASR-damaged specimens had increased softening and faster recovery rates, but longer recovery times (up to 458 h). These findings demonstrate the potential of slow dynamics in concrete characterization, through its ability to evaluate the strength of intact samples and its sensitivity to microcracking in damaged samples.
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General Physics

Optical-Fiber Activation of Observer-Split Source Terms in a Rotating Aluminum Disc

Antonio Iadicicco and Luigi Verolino

We propose an optical-fiber implementation of the Observer-Split source framework for finite rotating systems in extended Aharonov-Bohm electrodynamics. A covariantly conserved current, rewritten in a rotating 3+1 split, produces the observer-adapted source term $I_{\rm split}=N^{-1}D_i(\rho\beta^i)$, which in the weak-field rigid-rotation limit becomes $I_G=\Omega\partial_\phi\rho$. We use an optically gated rotating aluminum disc to create a localized, calibratable induced density, with the optical evanescent/tunneling coefficient acting only as a control gate rather than as a charge density. The resulting source scales as $I_{\rm opt}\simeq\Omega\partial_\phi\rho_{\rm ind,Al}$ and reverses sign under CW/CCW reversal. The proposed demonstrator combines ON/OFF gating, a localized 10–20 degree active sector, uniform-source suppression, material and dummy controls, quantitative null bounds, and independent density calibration. The residual response is parameterized by the experimentally identifiable product $\Lambda_{\rm opt}=\kappa_{\rm opt}\chi_{\rm Al}$, so both positive and null measurements constrain the phenomenology without assuming an uncalibrated force amplitude. Historical rotating magnetic systems, including the Roshchin-Godin report, are used only as benchmarks and not as evidence. The work is a falsifiable protocol for testing anomalous gravitational-response signatures; it reports no anomalous-weight measurement and makes no claim of evidence for a gravitational anomaly or for extended Aharonov-Bohm electrodynamics.
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Computational Physics · Cross-listed from cs.LO

Exploiting Structure in the Boolean Weighted Constraint Satisfaction Problem: A Constraint Composite Graph-Based Approach

Hong Xu

What is "structure," and how can we exploit it in combinatorial optimization? Reasoning tasks such as system design, state estimation, and prediction can be cast as combinatorial optimization problems (COPs), traditionally attacked by dedicated algorithms that fail outside their narrow subclass, while communities working on equivalent problems reinvent each other's techniques. The weighted constraint satisfaction problem (WCSP) is a general framework that subsumes COPs from many communities and represents complex physical and non-physical systems, from spin glasses to social networks. Is such generality a curse? Our answer is to exploit "structure": a general-purpose WCSP algorithm should automatically imitate the specialized algorithm for whatever subclass its input belongs to. A WCSP has macro (graphical) structure, which variables interact, and micro (numerical) structure, how they interact. Separate schools of thought exploit one or the other, never both. The constraint composite graph (CCG), introduced in 2008, unifies them: it is an undirected graph over a WCSP instance's variables plus auxiliary ones, on which minimum weighted vertex cover (MWVC) solves the original instance. It is efficiently constructible, but largely unexploited. This dissertation answers three questions affirmatively. The CCG has theoretical advantages beyond identifying tractable classes (new properties proved here); it is practically useful (efficient implementation and experiments); and it extends promisingly to non-Boolean variables (new encodings). We use the CCG to (a) kernelize a WCSP instance, fixing optimal values of some variables by maxflow before search begins, (b) improve min-sum message passing, (c) exploit integer linear programming solvers, and (d) solve COPs on quantum annealers. Solving general COPs faster classically also yields better baselines for the debated quantum advantage.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Sn-Doping in LPCVD-Grown (010) $\beta$-Ga$_2$O$_3$ Films

Saleh Ahmed Khan, Ahmed Ibreljic, Sourav Sarker et al. (+1 more)

In this work, Sn-doped (010) $\beta$-Ga$_2$O$_3$ homoepitaxial films were grown by low-pressure chemical vapor deposition (LPCVD), and the influence of Sn incorporation on their structural, morphological, and electrical properties was systematically investigated. Controlled room-temperature carrier concentrations ranging from $1.17 \times 10^{17}$ to $3.06 \times 10^{18}$ cm$^{-3}$ were achieved, with corresponding Hall mobilities decreasing from 113 to 63 cm$^2$ V$^{-1}$ s$^{-1}$. The films exhibited the monoclinic $\beta$-Ga$_2$O$_3$ phase, near-stoichiometric composition, and well-defined step-flow morphology, with a minimum rocking-curve FWHM of 68.4 arcsec and an RMS roughness of 2.63 nm. Film thicknesses ranging from 1.66 to 11.3 $\mu$m were obtained at growth rates of 6.4 to 16.6 $\mu$m h$^{-1}$, demonstrating the ability of LPCVD to produce thick epitaxial layers. The sample with a room-temperature carrier concentration of $1.17 \times 10^{17}$ cm$^{-3}$ exhibited room-temperature and low-temperature Hall mobilities of 113 cm$^2$ V$^{-1}$ s$^{-1}$ and 380 cm$^2$ V$^{-1}$ s$^{-1}$ at 84 K, respectively. Both represent the highest reported values for LPCVD-grown Sn-doped $\beta$-Ga$_2$O$_3$. Transport modeling of the same sample yielded a shallow donor activation energy of 32.7 meV, a deeper donor level at 95 meV, and a low compensating acceptor concentration of $2.0 \times 10^{16}$ cm$^{-3}$, indicating efficient donor activation and a low degree of compensation. These results demonstrate that LPCVD enables controlled Sn doping while maintaining excellent structural and electrical quality, providing a viable route for realizing thick $\beta$-Ga$_2$O$_3$ epitaxial drift layers.
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All authors Saleh Ahmed Khan, Ahmed Ibreljic, Sourav Sarker, Anhar Bhuiyan

Physics and Society · Cross-listed from econ.GN

The friendship paradox: Causal evidence of its behavioral consequences

Gary Charness, Francesco Feri, Matthew O. Jackson et al. (+2 more)

We provide a first causal analysis of the behavioral consequences of the friendship paradox-the fact that people's friends in a network have more connections than average. We find that people's behavior is biased by their network position: they do not best respond to what they should infer the average behavior of the population to be (which determines their payoff), but instead best respond to the average behavior of their friends. In these games of complements, the friendship paradox generates a systematic upward distortion in actions and increases behavioral dispersion. These behavioral distortions persist despite learning opportunities: subjects fail to overcome the bias even when relocated within the network which should help them to understand how average population behavior can differ from local friend behavior.
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All authors Gary Charness, Francesco Feri, Matthew O. Jackson, Miguel A. Melendez-Jimenez, Matthias Sutter

Atomic Physics

Probing $P,T$-Symmetry Violation with Optically Trapped Asymmetric Top Molecules

Yuxi Yang, Arian Jadbabaie, Lukáš Félix Pašteka et al. (+3 more)

Searches for $P,T$-violating electromagnetic moments are among the most sensitive probes of physics beyond the Standard Model. Extending beyond current limits will benefit from molecules with fully controllable orientation at low electric fields, long coherence times, and laser coolability—all offered by asymmetric top molecules (ATMs). Exploiting the intrinsic rotational $K$-doubling in ATMs and the associated long-lived ($T_1 \gtrsim 10$ s) parity doublets afforded by $C_{2v}$ symmetry and nuclear-spin statistics, these species combine large electric polarizability with long coherence times in modest laboratory fields. We study alkaline-earth(-like) monoamides, $\mathcal{M}$–NH$_2$ ($\mathcal{M}$ = Ca, Sr, Ba, Yb, Ra), which possess favorable electronic structure for laser cooling. We perform ab initio calculations of fine and hyperfine constants, identifying the importance of relativistic effects in the spin-rotation tensor. An effective Hamiltonian then models the rotational and hyperfine structure of the vibronic ground state, quantifying electron electric dipole moment (EDM) sensitivities and identifying feasible measurement schemes. We compute the effect of external fields and identify engineered clock transitions that suppress sensitivity to external perturbations while retaining strong EDM sensitivity, and characterize the magic trapping conditions that null differential light shifts in an optical trap. Under these conditions we project a statistical electron-EDM sensitivity over an order of magnitude beyond current best experimental limits, with further gains available from increased molecule number and coherence time. Our results establish asymmetric top molecules as a tunable platform for sensitive symmetry-violation measurements with long coherence times.
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All authors Yuxi Yang, Arian Jadbabaie, Lukáš Félix Pašteka, I. Agustín Aucar, Rob G. E. Timmermans, Nicholas R. Hutzler

Biological Physics · Cross-listed from q-bio.MN

Permutation theory governs long-term dynamics of critical Boolean networks

Venkata Sai Narayana Bavisetty, Matthew Wheeler, Julian Vignes et al. (+4 more)

Boolean networks are widely used to model gene regulatory Attractors of Boolean networks model stable gene-expression patterns, yet deriving their properties from network structure remains an open problem. We solve this problem for critical $K=1$ networks by showing that their feedback loops induce a permutation whose order bounds the average attractor length both above and below by universal constant factors. This correspondence allows classical results from combinatorics and number theory to be applied directly to Boolean network dynamics. We find three distinct asymptotic scales for both average and maximum attractor lengths: typical networks scale as $\exp[(1/8+o(1))(\ln N)^2]$, the ensemble means grow as $\exp[N^{1/3+o(1)}]$, and extremal networks attain $\exp[(1+o(1))\sqrt{N\ln N}]$. Thus, ensemble averages are governed by rare network realizations and are unrepresentative of typical dynamics.
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All authors Venkata Sai Narayana Bavisetty, Matthew Wheeler, Julian Vignes, Matthew Stephen Jones Jr., Ruodan Liu, Sean Campbell, Claus Kadelka

Optics

Design of a Compact Monolithic Catadioptric Lens for CubeSat Hyperspectral Imaging Payloads

Iliya Shofman and Kenya He

Monolithic catadioptric lenses have emerged as a novel class of compact long-focal-length lenses. Fabricated from a single fused silica substrate with distinct optical prescriptions across annular zones, these systems fold the optical path within the substrate, achieving long effective focal lengths at a fraction of the track length of refractive equivalents. The monolithic architecture and low coefficient of thermal expansion provide inherent athermal performance and preserve optical alignment under the thermal and vibrational loads of nanosatellite launch and orbital operation. Despite these advantages, commercial offerings of monolithic catadioptric lenses are limited and no comprehensive optical design literature review has been published for this lens class. We survey of monolithic catadioptric design variants, including Schmidt-Cassegrain-derived, annular folded, and gradient-index configurations. Building on this design space, we also present a novel monolithic catadioptric objective lens optimized for a CubeSat pushbroom hyperspectral Earth imaging payload. Pushbroom hyperspectral imagers require a precision entrance slit at the focal plane of the objective lens, and maintaining slit-to-focal-plane alignment under launch shock and thermal cycling is a significant optomechanical challenge. The proposed design places the focal plane coincident with the back surface of the substrate, enabling the slit to be lithographically etched directly onto that surface. This approach eliminates the slit-to-objective alignment degree of freedom, yielding an integrated, mechanically robust, and thermally stable objective-slit module for pushbroom imaging. We present the completed optical design of a near-diffraction-limited F/3 f=100mm VSWIR monolithic catadioptric lens, assess imaging performance, and discuss preliminary fabrication and tolerancing considerations.
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Biological Physics

Nuclear mechanics controls the temporal dynamics of cell unjamming

Leon Hillmann, Quirine J. S. Braat, Pablo Gottheil et al. (+9 more)

Cell unjamming in dense tissues is a complex but essential process in embryogenesis and cancer metastasis. Increasing evidence suggests that nuclear mechanics and density effects play a vital role in collective cell unjamming. However, state-of-the-art cell-shape-based theories fail to include nuclear and density effects, while computer models featuring rigid nuclei disagree with experimental observations of elongated nuclei promoting unjamming. Here, we introduce a computational model of confluent cells with explicitly deformable nuclei to study the dynamics of cell unjamming. Our simulations show an unjamming transition controlled by nuclear size and shape, reconciling conflicting theories of density-driven versus shape-driven mechanisms. We predict general relations connecting cellular and nuclear shape to collective cell motion, verified experimentally in distinct monolayers of MCF-10A and MDA-MB-436 breast cells, with striking accuracy. Our work establishes a rational connection between nuclear mechanics and tissue-scale rigidity transitions, highlighting the nucleus's key role in collective cell unjamming.
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All authors Leon Hillmann, Quirine J. S. Braat, Pablo Gottheil, Eliane Blauth, Anne Marie Scholz, Kolya M. Lettl, Jürgen Lippoldt, Pieta C. M. Wielstra, Sibylle Hess, Mitko Veta, Josef A. Käs, Liesbeth M. C. Janssen

Fluid Dynamics

Set-up and Characterisation of Atmospheric Boundary Layers in the 10'x5' Wind Tunnel

Sita M. Nair and Kevin Gouder

The Atmospheric Boundary Layer (ABL) plays a critical role in influencing objects exposed to atmospheric conditions, making its study crucial. Due to the high cost of real-world testing, this thesis focuses on replicating marine ABLs in a wind tunnel environment. Two profiles were developed: one that served as a framework for establishing commonality among the various international wind engineering standards ('Profile 1'), and a second profile, which is more suitable for modelling the inflow to wind farms in the English Channel and the North Sea ('Profile 2'). The ABLs were generated using Irwin spires without floor roughness elements, and the flow characteristics were measured using Laser Doppler Anemometry (LDA) and a multi-hole probe (MHP). MHP showed a reasonably high accuracy when compared to LDA, with less than 1% deviation in the streamwise velocity and under 5% standard deviation in the streamwise, spanwise, and wall-normal velocity components. The profiles achieved good agreement with target metrics such as normalised velocity and turbulence intensity. Spanwise uniformity and spectral analysis confirmed the robustness of the simulation across varying inflow velocities. Overall, Irwin spires proved to be a cost-effective and reliable method for simulating marine ABLs, offering valuable insights for optimising offshore wind energy systems.
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Atmospheric and Oceanic Physics

Models of Wildland Fire and Ember Spread

Kevin Speer, Bryan Quaife and Jie Sun

In this Chapter we explore the nature and theory of ember transport using observations from controlled laboratory settings, prescribed fire, and wildland fire. Specific examples and statistics from fires are used to gain insight and motivate a hierarchy of modeling approaches from simple idealized models to full-physics atmospheric boundary layer models. The emphasis is on the fundamental processes involved in moving embers away from their sources in vegetation and structures on and near the ground or in the atmospheric boundary layer winds and turbulent flows. We describe the problem first in terms of basic theory about the rate of spread of wildland fire, examine the physical principles at work in ember transport for two principle modes of transport near the ground and in the atmosphere well above the surface, and connect these to statistical models for transport.
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Optics · Cross-listed from quant-ph

A Quantum-Enhanced Feedback Oscillator

Hudson A. Loughlin, Daniel M. DeSantis, Nergis Mavalvala et al. (+1 more)

Feedback oscillators, such as lasers and masers, serve as time references in modern computing, communication, and measurement. Quantum fluctuations ultimately limit their phase stability and ability to keep time precisely; in the absence of quantum engineering, their phase stability is bounded by a standard quantum limit (SQL). Techniques to improve the frequency stability of feedback oscillators beyond the SQL have been theorized, but have not yet been demonstrated. We demonstrate an opto-electronic oscillator (OEO), a type of feedback oscillator, with phase stability approaching the SQL. We then engineer the OEO's quantum state to improve its phase stability, thereby demonstrating the essential principle quantum-enhancement of feedback oscillators. Similar techniques may be employed to evade the SQL in other feedback oscillators such as masers and lasers.
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All authors Hudson A. Loughlin, Daniel M. DeSantis, Nergis Mavalvala, Vivishek Sudhir

Fluid Dynamics · Cross-listed from cs.LG

Neural Operators for Immersed-Boundary Soft Swimmers Locomotion

Mohammad Sadegh Eshaghi, Yizheng Wang, Navid Valizadeh et al. (+2 more)

High-fidelity immersed-boundary simulation resolves the coupled motion of a deforming swimmer and its surrounding flow, but the resulting cost limits repeated evaluations for engineering design, parameter studies, and control. We develop neural-operator surrogates for temporal prediction of the hydrodynamic fields generated by planar and volumetric eel swimmers. The surrogates are trained on regular-grid fields exported from adaptive fluid–structure simulations and are conditioned on swimmer geometry and Reynolds number. The planar model jointly predicts two velocity components, scalar vorticity, and pressure. On five held-out high-Reynolds-number trajectories, its full-domain global relative L^2 error is 3.51 %. The volumetric formulation uses three target-specific models with a common multichannel input: one model predicts three-dimensional velocity, one predicts vorticity, and one predicts pressure. Their full-domain global relative L^2 errors on five held-out within-range trajectories are 3.44 %, 5.58 %, and 19.2 %. Together, the results demonstrate the feasibility of field-resolved neural surrogates for moving-boundary swimmer flows while identifying pressure accuracy and physical consistency as priorities for further development.
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All authors Mohammad Sadegh Eshaghi, Yizheng Wang, Navid Valizadeh, Xiaoying Zhuang, Timon Rabczuk

Plasma Physics

PASCHEN-1D: A one-dimensional fluid plasma solver with multi-mechanism surface emission and flexible external circuit coupling

Asif Iqbal, Yves Heri, Bingqing Wang et al. (+3 more)

We present PASCHEN-1D (Plasma Advanced Solver with Coupled High-fidelity Emission and external Network), a one-dimensional time-dependent fluid plasma solver developed for self-consistent simulation of gas discharges and plasma breakdown with coupled electrode surface emission and flexible external circuit networks. The code solves drift-diffusion continuity equations for electrons and ions together with Poisson's equation. It is dynamically coupled to lumped RLC circuits, which self-consistently treat plasma transport, plasma-surface interaction, dielectric effects, and circuit response within a single framework. The electrode emission module includes ion-induced secondary electron emission, Fowler-Nordheim and Murphy-Good field emission, Richardson-Dushman thermionic emission, and photoemission based on a general, exact quantum mechanical emission theory. A finite-volume formulation with Kurganov-Tadmor fluxes, explicit diffusion, and fourth-order Runge-Kutta time integration is employed to ensure stable transient (sometimes ultrafast) evolution across breakdown and glow regimes. The solver is validated against multiple benchmark cases, including nanosecond pulsed dielectric-barrier discharges, DC breakdown and glow transitions, and Paschen curve construction for argon and nitrogen, with results consistent with published studies. With high-fidelity emission physics and a flexible circuit-coupling framework, PASCHEN-1D provides a versatile and efficient tool for modeling breakdown and transient discharge phenomena.
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All authors Asif Iqbal, Yves Heri, Bingqing Wang, Lan Jin, Md Arifuzzaman Faisal, Peng Zhang

Medical Physics

Vendor-Agnostic Joint Relaxometry and Myelin Water Fraction Mapping with B1 and Motion Correction

Unay Dorken Gallastegi, Shohei Fujita, Yohan Jun et al. (+19 more)

Obtaining consistent quantitative maps of myelin content and relaxation times across different sites and vendors is essential for advancing our understanding of brain development. Herein, we present a harmonized, vendor-agnostic magnetic resonance acquisition method designed for joint T1, T2, and myelin water fraction mapping, along with a method for rapid B1+ and B1- field estimation. We used our dictionary-based fitting and multi-compartment modeling for joint mapping of T1, T2 and myelin water fraction. Self-navigation-based retrospective motion correction was integrated with subspace reconstruction to track and correct rigid head motion during scanning, operating without the need for external hardware. Simulations, phantom and in vivo experiments confirmed the sensitivity and accuracy of the method, particularly for short T2 values corresponding to myelin, and demonstrated consistent performance across multiple scanner types. Coupled with the harmonized calibration scan, the proposed package offers a practical tool for multi-site, multi-vendor neuroimaging studies in both adult and pediatric populations.
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All authors Unay Dorken Gallastegi, Shohei Fujita, Yohan Jun, Antoine Delattre-Klauser, Gian Franco Piredda, Tom Hilbert, Cemre Ariyurek, Eugene Milshteyn, Shizhuo Li, Yuting Chen, Xingwang Yong, Kwok-Shing Chan, Qiang Liu, Seonghwan Yee, Yogesh Rathi, Maxim Zaitsev, Jon-Fredrik Nielsen, Onur Afacan, Camilo Jaimes, Patricia Ellen Grant, Borjan Gagoski, Berkin Bilgic

Applied Physics

Determination of acoustic nonlinearity parameters using thermal modulation of ultrasonic waves

Hongbin Sun and Jinying Zhu

This study presents a test method and its theoretical framework to determine the acoustic nonlinearity parameters ($\alpha,\beta,\delta$) of material using thermal modulation of ultrasonic waves. Temperature change induced thermal strain excites the nonlinear response of the material and modulates the ultrasonic wave propagating in it. Experimental results showed a strong correlation between the relative wave velocity change and the temperature change. With a quadratic polynomial model, the acoustic nonlinearity parameters were obtained from the polynomial coefficients by curve fitting the experimental curves. Their effects on thermal-induced velocity change were discussed. The parameters $\alpha,\beta,\delta$ govern the hysteretic gap, average slope, and curvature of the correlation curve, respectively. The proposed theory was validated on aluminum, steel, intact and damaged concrete samples. The obtained nonlinear parameters show reasonable agreements with values reported in the literature. Compared to other nonlinear acoustic methods using vibration or acoustic excitation, the thermal modulation method generates more uniform, slow changing, and larger strain field in the test sample. Employing thermal effect as the driving force for nonlinearity instead of an undesired influencing factor, this method can measure the absolute values of $\alpha,\beta,\delta$ with good accuracy using a simple ultrasonic test setup.
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Data Analysis and Statistics · Cross-listed from cs.LG

PhysAttNet: Enhancing Predictive Performance in Industrial and Astrophysical Time Series via Physics-Informed Attention

Amal Saadallah, Julia Tjus, Petra Wiederkeher et al. (+1 more)

Accurate and robust time series forecasting is essential in many applications involving physical processes, such as manufacturing monitoring and astrophysical event detection. In these settings, predictive models must remain reliable under noise, variability, and measurement uncertainty while capturing temporally localized structures corresponding to physically meaningful events. Convolutional neural networks (CNNs) are widely used for such tasks due to their computational efficiency and strong representational capacity. However, their learned temporal representations often exhibit unstable or physically inconsistent attention patterns, reducing robustness, generalization, and interpretability. This paper introduces PhysAttNet, a physics-informed attention framework for time series forecasting. PhysAttNet augments a lightweight CNN forecaster with an attention head guided by domain-informed regularization reflecting the structural properties of physical signals. Specifically, three complementary constraints are imposed during training: an alignment regularization that encourages attention to follow smooth, peak-centered temporal structures derived from the input signal, a smoothness regularization that enforces continuous temporal evolution, and a sparsity regularization that promotes selective focus on informative intervals. These differentiable regularization terms introduce physics-guided inductive bias without requiring annotated explanations or manual supervision. Experiments on two distinct applications, namely predicting cutting forces during milling and forecasting flares in blazar time series, demonstrate that PhysAttNet improves forecasting accuracy, generalization, and prediction performance on structurally important events.
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All authors Amal Saadallah, Julia Tjus, Petra Wiederkeher, Wolfgang Rhode