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Physics Physics

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Sunday 26 October

Medical Physics · Cross-listed from cs.CV

Projection Embedded Diffusion Bridge for CT Reconstruction from Incomplete Data

Yuang Wang, Pengfei Jin, Siyeop Yoon et al. (+6 more)

Reconstructing CT images from incomplete projection data remains challenging due to the ill-posed nature of the problem. Diffusion bridge models have recently shown promise in restoring clean images from their corresponding Filtered Back Projection (FBP) reconstructions, but incorporating data consistency into these models remains largely underexplored. Incorporating data consistency can improve reconstruction fidelity by aligning the reconstructed image with the observed projection data, and can enhance detail recovery by integrating structural information contained in the projections. In this work, we propose the Projection Embedded Diffusion Bridge (PEDB). PEDB introduces a novel reverse stochastic differential equation (SDE) to sample from the distribution of clean images conditioned on both the FBP reconstruction and the incomplete projection data. By explicitly conditioning on the projection data in sampling the clean images, PEDB naturally incorporates data consistency. We embed the projection data into the score function of the reverse SDE. Under certain assumptions, we derive a tractable expression for the posterior score. In addition, we introduce a free parameter to control the level of stochasticity in the reverse process. We also design a discretization scheme for the reverse SDE to mitigate discretization error. Extensive experiments demonstrate that PEDB achieves strong performance in CT reconstruction from three types of incomplete data, including sparse-view, limited-angle, and truncated projections. For each of these types, PEDB outperforms evaluated state-of-the-art diffusion bridge models across standard, noisy, and domain-shift evaluations.
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All authors Yuang Wang, Pengfei Jin, Siyeop Yoon, Matthew Tivnan, Shaoyang Zhang, Li Zhang, Quanzheng Li, Zhiqiang Chen, Dufan Wu

Atmospheric and Oceanic Physics

LO-SDA: Latent Optimization for Score-based Atmospheric Data Assimilation

Jing-An Sun, Hang Fan, Junchao Gong et al. (+8 more)

Data assimilation (DA) plays a pivotal role in numerical weather prediction by systematically integrating sparse observations with model forecasts to estimate optimal atmospheric initial condition for forthcoming forecasts. Traditional Bayesian DA methods adopt a Gaussian background prior as a practical compromise for the curse of dimensionality in atmospheric systems, that simplifies the nonlinear nature of atmospheric dynamics and can result in biased estimates. To address this limitation, we propose a novel generative DA method, LO-SDA. First, a variational autoencoder is trained to learn compact latent representations that disentangle complex atmospheric correlations. Within this latent space, a background-conditioned diffusion model is employed to directly learn the conditional distribution from data, thereby generalizing and removing assumptions in the Gaussian prior in traditional DA methods. Most importantly, we introduce latent optimization during the reverse process of the diffusion model to ensure strict consistency between the generated states and sparse observations. Idealized experiments demonstrate that LO-SDA not only outperforms score-based DA methods based on diffusion posterior sampling but also surpasses traditional DA approaches. To our knowledge, this is the first time that a diffusion-based DA method demonstrates the potential to outperform traditional approaches on high-dimensional global atmospheric systems. These findings suggest that long-standing reliance on Gaussian priors-a foundational assumption in operational atmospheric DA-may no longer be necessary in light of advances in generative modeling.
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All authors Jing-An Sun, Hang Fan, Junchao Gong, Ben Fei, Kun Chen, Fenghua Ling, Wenlong Zhang, Wanghan Xu, Li Yan, Pierre Gentine, Lei Bai

Optics

UC2-ESP: A General-Purpose Framework for Open-Source Microscopy Control

Benedict Diederich, Ingo Fuchs, Haoran Wang et al. (+3 more)

Building the optical setup for investigating biological questions comes with challenges. A major such challenge is setting up and synchronizing the control of multiple hardware components such as stages, cameras and lasers. With UC2-ESP we present a compact electronics system powered by the ESP32 microcontroller, designed to provide general-purpose control for various components in microscopy setups. Our system can interface with stepper motors, directed current (DC) motors, lasers (transistor-transistor logics, TTL or pulse width modulation, PWM), light emitting diodes (LEDs), and analog voltage outputs (galvo mirrors, led current control), allowing precise control over microscopy hardware. The platform is highly flexible, supporting custom pin configurations and multiple communication interfaces such as Bluetooth, universal serial bus (USB-serial), and HTTP via a built-in Webserver. A PlayStation controller can be used for haptic hardware manipulation, while commands are transmitted in a human-readable JSON format to ensure modularity and extensibility. The firmware is designed to receive parameters and execute actions dynamically, supporting complex control loops such as motor homing, stage scanning and temperature regulation via integrated controllers. Furthermore, the system integrates seamlessly with ImSwitch as well as MicroManager and offers a browser-based control tool using Web Serial. This open-source firmware enables microscopy research groups to develop custom setups and expand functionality efficiently, at low cost and high flexibility.
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All authors Benedict Diederich, Ingo Fuchs, Haoran Wang, Holger Bierhoff, Christian Kuttke, Rainer Heintzmann

Optics

All-photonic W-band terahertz receiver based on THz-to-optical carrier conversion with soliton microcomb dual carriers for high-speed OOK wireless transmission

Yudai Matsumura, Hiroki Kishikawa, Naoya Kuse et al. (+11 more)

We demonstrate an all-photonic terahertz receiver for a data-modulated signal, targeting a 106-GHz, 2.97-Gb/s OOK link. The scheme employs dual-wavelength optical carriers referenced to a soliton microcomb and performs THz-to-optical carrier conversion via nonpolarimetric electro-optic downconversion using an electro-optic polymer modulator. RF spectra and eye diagrams confirmed error-free transmission with a Q-factor of 5.78 and a bit-error rate of 3.73 x 10^-9, well below the hard-decision forward-error-correction (HD-FEC) threshold (Q = 2.67, BER = 3.8 x 10^-3). Comparative measurements using a single-wavelength optical-carrier configuration clearly revealed the superior signal-to-noise performance of the dual-wavelength scheme. System-level modeling further indicated scalability of the transmission distance beyond 100 m. These results establish soliton microcomb-referenced dual carriers as a promising platform for compact, integrated receivers enabling seamless wireless-optical convergence in future 6G networks.
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All authors Yudai Matsumura, Hiroki Kishikawa, Naoya Kuse, Yasuhiro Okamura Eiji Hase, Jun-ichi Fujikata, Masanobu Haraguchi, Takahiro Kaji, Akira Otomo, Isao Morohashi, Tomohiro Tetsumoto, Shintaro Hisatake, Atsushi Kanno, Yu Tokizane, Takeshi Yasui

Geophysics

Biotic Control of Earth's Climate: An Ecohydrological Perspective on the Phanerozoic Temperature Record

Allen Hunt and Didier Sornette

We propose a unified framework linking silicate weathering feedbacks, ecohydrological optimality and vegetation-climate interactions to explain Earth's Global Average Temperature evolution over the Phanerozoic. The framework integrates two complementary processes: (i) solute-transport-limited weathering, which governs long-term carbon sequestration, and (ii) ecohydrological optimality, which constrains vegetation productivity through the balance between water availability and carbon uptake. Together, these processes establish two emergent climatic thresholds, around 15 {\deg}C and 33 {\deg}C, that define a stable corridor for the Earth system. Below 15 {\deg}C, declining evapotranspiration and rising albedo accelerate cooling; above 33 {\deg}C, heat and water stress suppress vegetation and limit further warming. Analysis of ten independent studies (2019-2024) confirms the recurrent appearance of these thresholds in both modern ecosystems and Phanerozoic temperature reconstructions. Major biological innovations, such as the colonization of land by plants, the rise of forests, and the emergence of $C_4$ photosynthesis, have reorganized these feedbacks, repeatedly shifting the planet between quasi-stable climate states. The resulting picture is one in which the biosphere acts as an active regulator of climate, modulating and at times overriding geochemical feedbacks. This framework unifies climate, tectonics, and life into a single ecohydrological system, offering a coherent explanation for the bounded variability of Earth's temperature across 500 million years and insight into its future resilience. This perspective challenges the view of life as a passive climate responder, positioning the biosphere as an active regulator. Understanding these self-stabilizing mechanisms offers critical insight into how Earth might respond, or fail to respond, to ongoing human-driven climate perturbations.
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Optics

Rapidly Tunable Synthetic Wavelength Ranging with an RFSoC

Shawn M. P. McSorley, Benjamin P. Dix-Matthews, Andrew M. Lance et al. (+2 more)

Measurements of optical range and time-of-flight are crucial for a variety of high-precision technologies. Competitive optical measurement techniques have been developed that balance precision with accuracy and system complexity. Here, we present a continuous-wave synthetic wavelength interferometry technique that employs digitally tunable electro-optic frequency combs. With a software-defined radio, our approach can dynamically sweep the synthetic wavelength and measure absolute optical range. We demonstrate this digital approach over a free-space optical delay line of 1 m and over an 40 km fiber link. The best obtained precision over the delay line is better than 60 nm (0.2 fs). Through a 40 km fiber spool, this precision degrades to 15 um (50 fs), which is a fractional error on the order of 2e-10 m/m. Our design is simple to implement, and only relies on continuous-wave interference, decreasing system complexity.
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All authors Shawn M. P. McSorley, Benjamin P. Dix-Matthews, Andrew M. Lance, David R. Gozzard, Sascha W. Schediwy

Applied Physics · Cross-listed from cond-mat.mes-hall

Electric Field-Induced Kerr Rotation on Metallic Surfaces

Farzad Mahfouzi, Mark D. Stiles and Paul M. Haney

We use a combination of density functional theory calculations and optical modeling to establish that the electric field-induced Kerr rotation in metallic thin films has contributions from both non-equilibrium orbital moment accumulation (arising from the orbital Edelstein effect) and a heretofore overlooked surface Pockels effect. The Kerr rotation associated with orbital accumulation has been studied in previous works and is largely due to the dc electric field-induced change of the electron distribution function. In contrast, the surface Pockels effect is largely due to the dc field-induced change to the wave functions. Both of these contributions arise from the dual mirror symmetry breaking from the surface and from the dc applied field. Our calculations show that the resulting Kerr rotation is due to the dc electric field modification of the optical conductivity within a couple of nanometers from the surface, consistent with the dependence on the local mirror symmetry breaking at the surface. For thin films of Pt, our calculations show that the relative contributions of the orbital Edelstein and surface Pockels effects are comparable, and that they have different effects on Kerr rotation of $s$ and $p$ polarized light, $\theta_K^s$ and $\theta_K^p$. The orbital Edelstein effect yields similar values of $\theta_K^s$ and $\theta_K^p$, while the surface Pockels effect leads to opposing values of $\theta_K^s$ and $\theta_K^p$.
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Fluid Dynamics

Numerical Investigation of Discontinuous Ice Effects on Swept Wings

Jiawei Chen, Maochao Xiao, Ziyu Zhou et al. (+1 more)

This study investigates the aerodynamic performance and flow structures of infinite swept wings with artificially simulated discontinuous ice using an enhanced delayed detached-eddy simulation. Comparisons are made among clean, continuous-ice, and discontinuous-ice configurations. Results show that discontinuous ice causes a more severe reduction in lift than continuous ice. While continuous ice forms a large separation bubble that helps maintain lift, discontinuous ice disrupts leading-edge vortex formation through gap jets, resulting in greater lift loss but a smaller drag penalty. Unlike the continuous-ice wing, the discontinuous-ice case does not exhibit a sudden stall-induced lift drop. The flow over the discontinuous-ice wing can be characterized by two canonical patterns: a separating shear layer and Kármán vortex shedding. However, the separating shear layer becomes irregular due to the interference of gap jets. Three characteristic chord-based Strouhal numbers (St)-11.3, 22.6, and 33.9-are identified. The lowest (St=11.3) corresponds to the shedding of vortex pairs; when nondimensionalized by the ice width, it yields St = 0.58, which is higher than that of a canonical cylinder wake. Furthermore, lift and drag fluctuations occur predominantly at St = 22.6, twice the shedding frequency, primarily induced by the gap jets-a phenomenon absent in the continuous-ice case.
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All authors Jiawei Chen, Maochao Xiao, Ziyu Zhou, Yufei Zhang

Fluid Dynamics

Data-driven Augmentation of a Turbulence Model in Three dimensional Separated Flows

Chenyu Wu, Shaoguang Zhang and Yufei Zhang

Classic turbulence models often struggle to accurately predict complex flows. Although data-driven techniques have addressed these shortcomings, most existing research has concentrated on two-dimensional (2D) cases. This study bridges this gap by enhancing a data-driven turbulence model, the SST-CND (shear stress transport-conditioned) model, which was originally trained on 2D separated flows, in 3D scenarios. An additional correction term, e̱ta}_3D, is introduced to account for 3D effects. The distribution of this term is determined through a 3D field inversion process using high-fidelity data obtained from the flow around a cube. An algebraic expression for e̱ta}_3D is then derived through symbolic regression and formulated to degrade to zero in 2D cases. The performance of the resulting SST-CND3D model is evaluated across a range of flows. In 2D flows, the SST-CND3D model performs identically to its 2D-trained predecessor. However, the model exhibits superior performance in 3D flows, such as the flow around the complex JAXA standard model high-lift configuration. These findings indicate that a sequential approach, constructing a 3D correction term that vanishes in 2D on top of a 2D-trained model, constitutes a promising method for developing data-driven turbulence models that perform accurately in 3D while preserving their effectiveness in 2D.
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Saturday 25 October

Classical Physics

Coulomb force between two Dirac monopoles

Alberto G. Rojo

The model of magnetic monopoles that was proposed by Paul Dirac in 1931 has long been a subject of theoretical interest in physics because of its potential to explain the quantization of electric charge. While much attention has been given to non-Dirac monopoles, Dirac's model, which involves an infinitely thin solenoid known as a Dirac string, presents subtleties in the interaction between monopoles. In this paper, we show that the force between two Dirac monopoles obeys a Coulomb-like interaction law. This derivation offers an instructive exercise in fundamental electromagnetism concepts and is appropriate for undergraduate and early graduate-level students.
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Instrumentation and Detectors

Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS) for gravitational wave detection

Yuki Inoue, Daiki Tanabe, M.Afif Ismail et al. (+3 more)

We present the optical design and sensitivity modeling of the Cryogenic sub-Hz cROss torsion-bar detector with quantum NOn-demolition Speed meter (CHRONOS), a triangular Sagnac speed-meter interferometer incorporating power and signal recycling. Using ABCD-matrix analysis and Finesse3 simulations, we obtain stable optical eigenmodes with mode-matching efficiencies above 99.5%. The optimized configuration achieves a quantum-noise-limited strain sensitivity of $h \simeq 3\times10^{-18},\mathrm{Hz^{-1/2}}$ at 1 Hz, with a ring-cavity finesse of $\mathcal{F}\simeq3.1\times10^{4}$ and a round-trip Gouy phase of $\psi\approx153^{\circ}$. The low-frequency quantum noise is primarily governed by the power-recycling cavity detuning, while the signal-recycling cavity produces an approximately uniform quadrature rotation. An optimal homodyne angle of $\zeta\simeq46^{\circ}$ provides the best sensitivity near 1 Hz. Assuming an end-mirror reflectivity of $R_{\mathrm{ETM}}=99.9999%$ at 10 K, CHRONOS can achieve quantum-noise-limited performance on a laboratory scale. Its projected science reach includes intermediate-mass black-hole binaries out to approximately $271,\mathrm{Mpc}$, a 10-year stochastic-background sensitivity of $\Omega_{\mathrm{GW}}\simeq4.7\times10^{-4}$ at $2.15,\mathrm{Hz}$, constraints on Yukawa-type deviations from Newtonian gravity, and prompt gravity-gradient signals from nearby earthquakes.
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All authors Yuki Inoue, Daiki Tanabe, M.Afif Ismail, Vivek Kumar, Mario Juvenal S Onglao III, Ta-Chun Yu

Instrumentation and Detectors

Torque cancellation effect of Intensity noise for Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS)

Daiki Tanabe, Yuki Inoue, Vivek Kumar et al. (+2 more)

Detection of sub-Hz gravitational waves is of significant importance for astrophysics. It enables the observation of intermediate-mass black hole mergers, the issuance of early alerts for gravitational-wave events, and the exploration of the stochastic gravitational-wave background. The Cryogenic sub-Hz cROss torsion-bar detector with quantum NOn-demolition Speed meter (CHRONOS) is a proposed gravitational-wave detector based on a Sagnac speed-meter topology that uses torsion bars as test masses. Its prototype design aims to achieve a strain sensitivity of $3 \times 10^{-18}~\mathrm{Hz}^{-1/2}$ at 1~Hz and thus enable the detection of $\mathcal{O}(10^4),M_\odot$ intermediate-mass black hole mergers at 100~Mpc with a signal-to-noise ratio of 3. We show that the torsion-bar-based speed meter can suppress noise originating from laser intensity fluctuations by canceling the net torque on the bar and by using a balanced homodyne readout. We further present, for the first time, an analytic intensity-noise model for a gravitational-wave detector employing a torsion-bar Sagnac speed-meter configuration. Using this model, we evaluate the expected performance of a 2.5~m arm-length CHRONOS prototype. The projected laser-intensity noise is $2.9 \times 10^{-20}~\mathrm{Hz}^{-1/2}$ at 1~Hz, which is sufficiently low to allow the detection of binary intermediate-mass black hole mergers.
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All authors Daiki Tanabe, Yuki Inoue, Vivek Kumar, Miftahul Ma'arif, Ta-Chun Yu

Atomic and Molecular Clusters

Non-equilibrium Molecular Dynamics Study of Surface Wettability Effects on Pool Boiling of Water over Nanoscale Aluminum Substrate

Farhad Sotoudeh and Jafar Ghazanfarian

Non-equilibrium molecular dynamics (NEMD) simulations were used to study pool boiling of water films on an ultra-thin planar aluminum substrate as well as the effect of surface wettability. The simulation geometry is a 10 nm-thick water film on an FCC aluminum substrate heated from 300 K to 900 K. The first peak acceleration onset time of the film, as the measure of the nucleation start, has been observed. The average heating rates of the near-wall water were 0.064, 0.048, and 0.035 K/ps for hydrophilic, neutral, and hydrophobic surfaces, respectively. Boiling curves shows that the critical heat flux (CHF) equals 5216, 3979, and 2525 MW/m^2 at wall temperatures of 466, 502, and 561 K, respectively. The minimum heat flux (MHF, Leidenfrost point) is equal to 2157, 2463, and 2366 MW/m^2 at wall temperatures of 767, 784, and 746 K, respectively. Interfacial HTC remains higher for longer times under the hydrophilic condition, whereas Kapitza resistance is low initially but then increases sharply after transition to film boiling with the highest values for the hydrophobic surface. In general, the results demonstrate that engineering aluminum wettability towards intense hydrophilicity diminishes the explosive boiling point, increases CHF, and enhances nanoscale thermal management performance.
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Chemical Physics

Computing Solvation Shell Dynamics and Energetics in Electron Transfer Reactions via Molecular Dynamics Simulations

Zhenyu Wang, Mira Todorova, Christoph Freysoldt et al. (+1 more)

Marcus theory is fundamental to describing electron transfer reactions and quantifying their rates, effectively representing the energy surface associated with an electron transfer from the reactant to the product ionic state via parabolas within a reaction coordinate diagram. Here, we present an intuitive and computationally efficient generalised reaction coordinate amenable to molecular dynamics simulations. By utilising the nuclear charge of the ion, we are able to quantify in a targeted approach changes in the ion's solvation shell, thereby efficiently obtaining the free energy profile associated with the electron transfer, the transition state geometry and the evolution of the water network.
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All authors Zhenyu Wang, Mira Todorova, Christoph Freysoldt, Jörg Neugebauer

Physics and Society · Cross-listed from cs.MA

Group size effects and collective misalignment in LLM multi-agent systems

Ariel Flint, Luca Maria Aiello, Romualdo Pastor-Satorras et al. (+1 more)

Multi-agent systems of large language models (LLMs) are rapidly expanding across domains, introducing dynamics not captured by single-agent evaluations. Yet, existing work has mostly contrasted the behavior of a single agent with that of a collective of fixed size, leaving open a central question: how does group size shape dynamics? Here, we move beyond this dichotomy and systematically explore outcomes across the full range of group sizes. We focus on multi-agent misalignment, building on recent evidence that interacting LLMs playing a simple coordination game can generate collective biases absent in individual models. First, we show that collective bias is a deeper phenomenon than previously assessed: interaction can amplify individual biases, introduce new ones, or override model-level preferences. Second, we demonstrate that group size affects the dynamics in a non-linear way, revealing model-dependent dynamical regimes. Finally, we develop a mean-field analytical approach and show that, above a critical population size, simulations converge to deterministic predictions that expose the basins of attraction of competing equilibria. These findings establish group size as a key driver of multi-agent dynamics and highlight the need to consider population-level effects when deploying LLM-based systems at scale.
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All authors Ariel Flint, Luca Maria Aiello, Romualdo Pastor-Satorras, Andrea Baronchelli

Chemical Physics

Unraveling vibronic interactions in molecules functionalized with optical cycling centers

Pawel Wojcik, Haowen Zhou, Taras Khvorost et al. (+7 more)

We report detailed characterization of the vibronic interactions between the first two electronically excited states, A and B, in SrOPh (Ph = phenyl, -C6H5) and its deuterated counterpart, SrOPh-d5 (-C6D5). The vibronic interactions, which arise due to non-adiabatic coupling between the two electronic states, mix the B,v0 state with the energetically close vibronic level A,v21v33, resulting in extra transition probability into the latter state. This state mixing is more prominent in the deuterated molecule because of the smaller energy gap between the interacting states. We model the mixing of the A and B states using the Koppel-Domcke-Cederbaum (KDC) Hamiltonian parametrized in the diabatic framework of Ichino, Gauss, and Stanton on the basis of equation-of-motion coupled-cluster calculations. The simulation attributes the observed mixing to a second-order effect mediated by linear quasi-diabatic couplings between the A-C and B-C states. Based on the measured spectra, we deduce an effective coupling strength of 0.5 cm-1. Non-adiabatic couplings between different electronic states is an important factor that should be considered in the design of laser-cooling protocols for complex molecules.
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All authors Pawel Wojcik, Haowen Zhou, Taras Khvorost, Guo-Zhu Zhu, Guanming Lao, Justin R. Caram, Anastassia N. Alexandrova, Eric R. Hudson, Wesley C. Campbell, Anna I. Krylov

Atomic Physics

Vibronic coupling limits the use of high-lying electronic states in complex molecules for laser cooling

Haowen Zhou, Pawel Wojcik, Guo-Zhu Zhu et al. (+7 more)

Laser cooling of large, complex molecules is a long-standing goal, instrumental for enabling new quantum technology and precision measurements. A primary consideration for the feasibility of laser cooling, which determines the efficiency and technical requirements of the process, is the number of excited-state decay pathways leading to vibrational excitations. Therefore, the assessment of the laser-cooling potential of a molecule begins with estimate of the vibrational branching ratios of the first few electronic excited states theoretically to find the optimum cooling scheme. Such calculations, typically done within the BO and harmonic approximations, have suggested that one leading candidate for large, polyatomic molecule laser cooling, alkaline earth phenoxides, can most efficiently be laser-cooled via the third electronically excited C state. Here, we report the first detailed spectroscopic characterization of the C state in CaOPh and SrOPh. We find that nonadiabatic couplings between the A, B, and C states lead to substantial mixing, giving rise to vibronic states that enable additional decay pathways. Based on the intensity ratio of these extra decay channels, we estimate a non-adiabatic coupling strength of 0.1 cm-1. While this coupling strength is small, the large density of vibrational states available at photonic energy scales in a polyatomic molecule leads to significant mixing. Thus, this result is expected to be general for large molecules and implies that only the lowest electronic excited state should be considered when judging the suitability of a molecule for laser cooling.
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All authors Haowen Zhou, Pawel Wojcik, Guo-Zhu Zhu, Guanming Lao, Taras Khvorost, Justin R. Caram, Wesley C. Campbell, Anastassia N. Alexandrova, Anna I. Krylov, Eric R. Hudson

Optics

Coherent Perfect Absorption: Zero Reflection Without Linewidth Suppression

M. Ebrahimi, Y. Huang, A. Rashedi et al. (+1 more)

Motivated by recent claims, we revisit how coherent perfect absorption (CPA) influences cavity and polaritonic linewidths. Using standard input output theory and measurements on single port bare microwave cavities and cavity magnon hybrids, we find that CPA drives the on resonance reflection to zero while the spectral width remains set by the total decay rate. Apparent narrowing observed near CPA is found to be a visual artifact that does not remain upon quantitative analysis. Extending the analysis to cavity magnomechanics, we show that logarithmic plots can exhibit apparent polaromechanical normal mode splitting, whereas linear scale spectra display no true splitting. These results clarify when CPA modifies amplitudes versus spectral poles, offer practical guidance for data presentation, and indicate that CPA alone is not a route to linewidth suppression or polaromechanical mode splitting in the linear, weak-probe regime.
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All authors M. Ebrahimi, Y. Huang, A. Rashedi, J. P. Davis

Fluid Dynamics

Dynamical hysteresis in the dissipation in turbulent flows

M. Ahmad, P.D. Mininni, M. Obligado et al. (+1 more)

We present evidence of the dynamical hysteretic nature of dissipation in unsteady turbulent flows. Wind tunnel experiments and direct numerical simulations in oscillating flows show that, at stationary mean Reynolds number, the dissipation constant is larger for decelerating flows. Consequently, a periodic behavior of the flow produces a hysteresis cycle, whose area scales with a parameter combining the Strouhal number and the relative amplitude of the forcing. This phenomenon can be explained and quantified through the influence of the unsteady term in the Karman-Howarth equation, with implications for a wide range of out-of-equilibrium systems.
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All authors M. Ahmad, P.D. Mininni, M. Obligado, J.A. Farnsworth

Atomic Physics

Tensor gravity gradiometry with a single-axis atom gradiometer

Ryan J. Thomas, Samuel Legge and John D. Close

We propose a method for using a single-axis atom interferometric gravity gradiometer to measure off-diagonal elements of the gravity gradient tensor. By tilting the gradiometer, the measured gradient becomes a linear combination of different components of the gravity gradient tensor, and through multiple measurements at different tilts the separate tensor components can be inferred. We present a theoretical and numerical investigation of this technique, both for terrestrial surveys where the tilt is statically set by the user and for surveys where a strapdown sensor is dynamically tilted by the motion of the platform. We show that the gradiometer's sensitivity to the vertical gravity gradient is only slightly reduced by this method while allowing for more gradiometer information to be obtained. Major sources of error and loss of sensitivity on dynamic platforms are shown to be mitigated using an optical-gimbal technique employing commercially-available fibre-optic gyroscopes and tip-tilt mirrors.
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Optics

Nonlinear optical behavior of confined electrons under torsion and magnetic fields

Carlos Magno O. Pereira and Edilberto O. Silva

In this work, we investigate the influence of torsion, Aharonov-Bohm flux, and external magnetic fields on the linear and nonlinear optical properties of a confined quantum system. The confinement potential is not assumed a priori, but emerges as a radial effective potential, analogous to a quantum dot, geometrically induced by the torsion of the material. Starting from an effective radial equation derived in a nontrivial geometric background, we analytically solve for the energy spectrum and wave functions. These solutions are then employed to evaluate the optical absorption coefficients and refractive index changes, including both linear and third-order nonlinear contributions. The formalism incorporates the electric dipole approximation and accounts for intensity-dependent effects such as saturation and spectral shifts. Our results reveal that torsion and topological parameters significantly modify the optical response, leading to tunable resonances and nontrivial dispersive behavior. This work highlights the potential of geometric and topological engineering in low-dimensional systems to control and enhance nonlinear optical phenomena.
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Fluid Dynamics

Boundary layer transition induced by surface roughness distributed over a low-pressure turbine blade

Xianwen Zhu, Yuchen Ge, Yaomin Zhao et al. (+2 more)

Direct numerical simulations of a low-pressure turbine with roughness elements distributed over the blade surface have been performed. A series of fifteen cases with varying roughness heights and streamwise wavenumbers are introduced to present a systematic study of the effect of roughness on the various transition phenomena in the suction-side boundary layer. For cases with large roughness heights, the boundary layer is violently disturbed by the wake of rough elements in the leading edge (LE) region, and maintains the turbulent state over the whole blade suction-side. For cases with small roughness heights, however, the disturbances induced by the LE roughness are suppressed by the favourable pressure gradient in the downstream boundary layer, and the relaminarized flow does not undergo transition until the separation near the blade trailing edge (TE). Furthermore, the streamwise wavenumber of the distributed roughness plays an important role in cases with intermediate roughness height. Specifically, cases with larger streamwise slope show earlier transition induced by strong shear layer instability, which manages to suppress the mean flow separation near the TE region. Overall, the combined effect of several factors, including the geometric effect at the blade LE and TE, the complex pressure gradient distribution across the turbine vane, and the various roughness configurations, is responsible for the intriguing boundary layer behaviours in the present study.
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All authors Xianwen Zhu, Yuchen Ge, Yaomin Zhao, Zuoli Xiao, Richard D. Sandberg

Optics

Tunable narrowband THz generation in the organic crystal BNA

D. Pavicevic, M. Nishida, J. Song et al. (+2 more)

The generation of tunable narrowband pulses is increasingly being pursued in terahertz science, for example to study the nonlinear response of individual modes of solids and molecules. Here, we extend the chirp-and-delay method to achieve collinear phase-matched difference-frequency generation in the organic crystal N-benzyl-2-methyl-4-nitroaniline (BNA-S), which results in tunable narrowband terahertz pulses. In this configuration, the fundamental frequency of a Ti:sapphire amplifier is used - eliminating the need for optical parametric amplifiers typically required for THz generation in other organic crystals. Chirped-pulse excitation suppresses multiphoton absorption in BNA, improving stability and extending crystal lifetime. The source delivers THz transients tunable from 0.25 THz to 2.1 THz with adjustable spectral width.
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All authors D. Pavicevic, M. Nishida, J. Song, M. Buzzi, A. Cavalleri

Applied Physics · Cross-listed from cs.CR

Adapting Noise-Driven PUF and AI for Secure WBG ICS: A Proof-of-Concept Study

Devon A. Kelly and Christiana Chamon

Wide-bandgap (WBG) technologies offer unprecedented improvements in power system efficiency, size, and performance, but also introduce unique sensor corruption and cybersecurity risks in industrial control systems (ICS), particularly due to high-frequency noise and sophisticated cyber-physical threats. This proof-of-concept (PoC) study demonstrates the adaptation of a noise-driven physically unclonable function (PUF) and machine learning (ML)-assisted anomaly detection framework to the demanding environment of WBG-based ICS sensor pathways. By extracting entropy from unavoidable WBG switching noise (up to 100 kHz) as a PUF source, and simultaneously using this noise as a real-time threat indicator, the proposed system unites hardware-level authentication and anomaly detection. Our approach integrates hybrid machine learning (ML) models with adaptive Bayesian filtering, providing robust and low-latency detection capabilities resilient to both natural electromagnetic interference (EMI) and active adversarial manipulation. Through detailed simulations of WBG modules under benign and attack scenarios–including EMI injection, signal tampering, and node impersonation–we achieve 95% detection accuracy and sub-millisecond processing latency. These results demonstrate the feasibility of physics-driven, dual-use noise exploitation as a scalable ICS defense primitive. Our findings lay the groundwork for next-generation security strategies that leverage inherent device characteristics, bridging hardware and artificial intelligence (AI) for enhanced protection of critical ICS infrastructure.
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Optics

Beam shaping techniques for pulsed laser ablation in liquids: Unlocking tunable control of nanoparticle synthesis in liquids

S. Molina-Prados, N. M. Bulgakova, A. V. Bulgakov et al. (+3 more)

Nanoparticle synthesis via pulsed laser ablation in liquids has gained prominence as a versatile and environmentally friendly approach for producing ligand-free colloids with controlled composition, size, and morphology. While pulsed laser ablation in liquids offers unparalleled advantages in terms of nanoparticle purity and material versatility, enhancing the size control and productivity require modifications of the standard pulsed laser ablation in liquid technique such as the incorporation of beam shaping techniques. Recent developments in spatial and temporal beam shaping have demonstrated their potential to revolutionize pulsed laser ablation in liquids by enabling more precise energy deposition and modified nanoparticle production dynamics. This review highlights the critical role of beam shaping, encompassing spatial shaping of the beam to influence laser-material interaction, and temporal modification to optimize pulse duration and energy delivery. The current advancements in beam shaping techniques, their impact on the nanoparticle characteristics, and their broader implications for scaling pulsed laser ablation in liquids to meet industrial demands are highlighted, offering a comprehensive perspective on the future of this dynamic field.
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All authors S. Molina-Prados, N. M. Bulgakova, A. V. Bulgakov, J. Lancis, G. Mínguez Vega, C. Doñate-Buendia

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

Glymphatic Clearance in the Optic Nerve: A Multidomain Electro-osmostic Model

Shanfeng Xiao, Huaxiong Huang, Robert Eisenberg et al. (+2 more)

Effective metabolic waste clearance and maintaining ionic homeostasis are essential for the health and normal function of the central nervous system. To understand its mechanism and the role of fluid flow, we develop a multidomain electro-osmotic model of optic-nerve microcirculation that couples hydrostatic and osmotic fluid transport with electro-diffusive solute movement across axons, glia, the extracellular space, and arterial/venous/capillary perivascular spaces. Cerebrospinal fluid enters the optic nerve via the arterial parivascular space, passes both the glial and ECS before exiting through the venous parivascular space. Exchanges across astrocytic endfeet are essential and they occur in two distinct and coupled paths: through AQP4 on glial membranes and gaps between glial endfeet, thus establishing a mechanistic substrate for two modes of glymphatic transport, at rest and during stimulus-evoked perturbations. Parameter sweeps show that lowering AQP4-mediated fluid permeability or PVS permeability elevates pressure, suppresses radial exchange and slows clearance, effects most pronounced for solutes reliant on PVS V export. The model reproduces baseline and stimulus-evoked flow and demonstrates that PVS-mediated export is the primary clearance route for both small and moderate solutes. Small molecules clear faster because rapid ECS diffusion broadens their distribution and enhances ECS PVS exchange, whereas moderate species have low ECS diffusivity, depend on transendfoot transfer, and clear more slowly via PVS V convection. Our framework can also be used to explain the sleep-wake effect mechanistically: enlarging ECS volume or permeability increases transinterface flux and accelerates waste removal.
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All authors Shanfeng Xiao, Huaxiong Huang, Robert Eisenberg, Zilong Song, Shixin Xu

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

Lateral Ventricular Brain-Computer Interface System with Lantern-Inspired Electrode for Stable Performance and Memory Decoding

Yike Sun, Yaxuan Gao, Kewei Wang et al. (+9 more)

We present a lateral ventricular brain-computer interface (LV-BCI) that deploys an expandable, flexible electrode into the lateral ventricle through a minimally invasive external ventricular drainage pathway. Inspired by the framework of traditional Chinese lanterns, the electrode expands uniformly within the ventricle and conforms to the ependymal wall. Compared with conventional subdural ECoG electrodes, the LV-BCI shows superior signal stability and immunocompatibility. Resting-state spectral analyses revealed a maximum effective bandwidth comparable to subdural ECoG. In evoked potential tests, the LV-BCI maintained a consistently higher signal-to-noise ratio over 112 days without the decline typically associated with scarring or other immune responses. Immunohistochemistry showed only a transient, early microglial activation after implantation, returning to control levels and remaining stable through 168 days. We further designed an "action-memory T-maze" task and developed a microstate sequence classifier (MSSC) to predict rats' turn decisions. The LV-BCI achieved prediction accuracy up to 98%, significantly outperforming subdural ECoG, indicating enhanced access to decision-related information from deep structures such as the hippocampus. These results establish the lateral ventricle as a viable route for neural signal acquisition. Using a lantern-inspired flexible electrode, we achieve long-term stable recordings and robust memory decision decoding from within the ventricular system, opening new directions for BCI technology and systems neuroscience.
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All authors Yike Sun, Yaxuan Gao, Kewei Wang, Jingnan Sun, Yuzhen Chen, Yanan Yang, Tianhua Zhao, Haochen Zhu, Ran Liu, Xiaogang Chen, Bai Lu, Xiaorong Gao

Optics

Giant Cotton-Mouton effect of suspensions of iron nanorods

Shu-guo Lei and Cheng-ping Huang

The Cotton-Mouton (CM) effect, referring to linear birefringence induced by a magnetic field, is usually very weak in natural materials. We propose theoretically that a giant CM effect may be achieved in the THz region with the suspension of iron nanorods. The unusual effect stems from the dual nature of the iron nanorods, which exhibit both ferromagnetic and plasmonic characteristics. Our results suggest that, with an ultralow magnetic field of 20 mT, a large linear birefringence up to 0.10 can be realized. The CM coefficient attains 2.2*10 7 T-2m-1, four orders of magnitude larger than that obtained currently in optical range. The results may advance the study and applications of the THz CM effect in artificial magneto-optic materials.
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Computational Physics

A DSMC-PIC coupling method for the Vlasov-Maxwell-Landau system

Andrea Medaglia, Lorenzo Pareschi and Mattia Zanella

We present a numerical framework for the simulation of collisional plasma dynamics, based on a coupling between Direct Simulation Monte Carlo (DSMC) and Particle-in-Cell (PIC) methods for the Vlasov-Maxwell-Landau system. The approach extends previously developed DSMC techniques for the homogeneous Landau equation to the fully inhomogeneous, electromagnetic regime. The Landau collision operator is treated through a stochastic particle formulation inspired by the grazing-collision limit of the Boltzmann equation, which enables an efficient and physically consistent representation of Coulomb interactions without relying on the full Boltzmann structure. The resulting collisional solver is combined, via operator splitting, with standard PIC schemes for the Vlasov-Maxwell dynamics, providing flexibility in the choice of field discretisation and time integration. The overall method preserves the main physical invariants of the system while maintaining computational efficiency and simplicity of implementation. Numerical experiments on benchmark problems demonstrate the accuracy, robustness, and effectiveness of the coupled DSMC-PIC approach across a wide range of collisional regimes.
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Computational Physics · Cross-listed from quant-ph

HPC-Driven Modeling with ML-Based Surrogates for Magnon-Photon Dynamics in Hybrid Quantum Systems

Jialin Song, Yingheng Tang, Pu Ren et al. (+8 more)

Simulating hybrid magnonic quantum systems remains a challenge due to the large disparity between the timescales of the two systems. We present a massively parallel GPU-based simulation framework that enables fully coupled, large-scale modeling of on-chip magnon-photon circuits. Our approach resolves the dynamic interaction between ferromagnetic and electromagnetic fields with high spatiotemporal fidelity. To accelerate design workflows, we develop a physics-informed machine learning surrogate trained on the simulation data, reducing computational cost while maintaining accuracy. This combined approach reveals real-time energy exchange dynamics and reproduces key phenomena such as anti-crossing behavior and the suppression of ferromagnetic resonance under strong electromagnetic fields. By addressing the multiscale and multiphysics challenges in magnon-photon modeling, our framework enables scalable simulation and rapid prototyping of next-generation quantum and spintronic devices.
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All authors Jialin Song, Yingheng Tang, Pu Ren, Shintaro Takayoshi, Saurabh Sawant, Yujie Zhu, Jia-Mian Hu, Andy Nonaka, Michael W. Mahoney, Benjamin Erichson, Zhi Yao