Physics and Society
Statistical physics of language change inferred from time evolving maps
James Burridge and Bert Vaux
Language change may be studied by tracking linguistic variant frequencies through space and time. Observed frequencies may be viewed as realisations of a statistical field. We first set out an efficient cross validated method for inferring the empirical field — the variant frequency distribution estimated directly from data — in our case, high resolution surveys from 20th century USA. We then derive a model of the statistical field, assuming that individuals diffuse locally, periodically migrate, and copy one another based on a form of replicator dynamics involving both bias and linguistic accommodation. We infer model parameters by comparing changes in model and empirical fields. Our inferences demonstrate that spatial linguistic patterns can be rapidly destroyed by migration but that accommodation can create them, protect them, and in combination with
diffusion, produce partially predictable pattern dynamics. The results provide the strongest evidence yet for surface tension driven phase ordering in human dialects. We quantify the model's forecasting ability up to a time horizon of twenty five years using the Kullback-Leibler divergence between forecasts and observations.
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Chemical Physics
Reply to Comment on "Efficient implementation of the superposition of atomic potentials initial guess for electronic structure calculations in Gaussian basis sets"
Susi Lehtola, Lucas Visscher and Eberhard Engel
We reply to the Comment by Surjuse, Deng, Asadchev, and Valeev [arXiv:2603.16989] on our article "Efficient implementation of the superposition of atomic potentials initial guess for electronic structure calculations in Gaussian basis sets" [J. Chem. Phys. 152, 144105 (2020)]. We do not disagree with their work, but point out that they appear to have misinterpreted a statement in our original abstract: our suggestion to evaluate the
matrix elements of the superposition of atomic potentials (SAP) using two-electron integral code was made on grounds of portability rather than as a recommendation against a dedicated one-electron implementation. Such an implementation is in fact already available in existing codes - in Dirac, for example, where a Gaussian SAP potential is formally indistinguishable from a Gaussian finite-
nucleus model at the level of the nuclear attraction integral routine. We further note that both routes reduce to the same three-Gaussian overlap kernel through the Obara-Saika Laplace transform, and that SAP itself enjoys a rigorous theoretical justification through Theophilou's
theorem on spherical densities and its extensions by Nagy.
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Instrumentation and Detectors
Pulse-shape discrimination with machine learning for CZT detectors at the DA$\Phi$NE beam test facility
Simone Manti, Francesco Artibani, Leonardo Abbene et al. (+36 more)
Cadmium zinc telluride (CZT) detectors offer versatility, operational simplicity, and room-temperature X- and gamma-ray spectroscopy, making them attractive for
collider applications, yet their use under high-flux conditions remains limited. Here, we present a preliminary feature-based pulse-shape analysis employing machine learning, on data acquired with a quasi-hemispherical CZT detector at the DA$\\Phi$NE beam test facility of the National Laboratory of Frascati of INFN. A 300-MeV electron beam impinging on a lead target produced characteristic Pb X-rays together with a broad background extending up to the electron-positron annihilation region. Physically motivated temporal and morphological features were extracted from the recorded waveforms and used to distinguish nominal
photon-like pulses from anomalous events. An XGBoost classifier trained and validated on 10,000 labeled waveforms achieved an accuracy of approximately 97%, with most of its classification performance reached using only a few hundred labeled examples. The trained model was applied to more than 700,000 events, substantially reducing the spectral continuum and coincidence peaks, while preserving the characteristic Pb X-ray lines up to the 511-keV annihilation peak. These preliminary results demonstrate the potential of machine-learning-assisted pulse-shape discrimination for improving CZT spectroscopy in
collider environments.
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All authors Simone Manti, Francesco Artibani, Leonardo Abbene, Massimiliano Bazzi, Manuele Bettelli, Giacomo Borghi, Damir Bosnar, Mario Bragadireanu, Antonino Buttacavoli, Mario Carminati, Alberto Clozza, Francesco Clozza, Luca De Paolis, Raffaele Del Grande, Kamil Dulski, Carlo Fiorini, Ivica Friščić, Gaetano Gerardi, Carlo Guaraldo, Mihai Iliescu, Masa Iwasaki, Alexander Khreptak, Johan Marton, Pawel Moskal, Hiroaki Ohnishi, Kristian Piscicchia, Fabio Principato, Alessandro Scordo, Francesco Sgaramella, Michał Silarski, Diana Sirghi, Florin Sirghi, Magdalena Skurzok, Antonio Spallone, Kairo Toho, Oton Vazquez Doce, Andrea Zappettini, Johann Zmeskal, Catalina Curceanu
Medical Physics
Towards Sustainable Magnetic Resonance Imaging: Insights from long-term, high-resolution energy recordings across an entire scanner fleet
Florian Leonhard Raab, Fiona Mankertz, Nour Maalouf et al. (+17 more)
Magnetic resonance imaging (MRI) is among the most energy-intensive diagnostic modalities in healthcare, yet its energy consumption and the factors influencing it remain insufficiently understood. This study aims to establish a comprehensive baseline of MRI energy consumption by characterizing energy demand across a scanner fleet, examining scanner utilization and operating patterns in clinical practice. Concurrently, it investigates the relationships between energy consumption and relevant operational and acquisition features. On average, a single MRI measurement consumed 0.43 kWh, while a complete examination consumed 13.50 kWh. In general, substantial differences in energy consumption were observed between MRI scanners and their corresponding operating modes (scan, idle, and eco-power mode). These variations may be related to differences in scanner operating patterns, employed examination protocols, and their resulting acquisition parameters. Idle and eco-power modes accounted for more cumulative energy consumption than active scanning. However, these energy shares should always be interpreted in relation to scanner occupancy, as utilization patterns strongly influence the distribution of energy across those operating modes. Lastly, linear regression analysis showed that energy consumption was more strongly associated with scan duration than with average power, suggesting that scan duration may be an important factor influencing MRI energy consumption. ...
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All authors Florian Leonhard Raab, Fiona Mankertz, Nour Maalouf, Josephine Berger, Andreas Lingg, Reza Dehdab, Sebastian Werner, Judith Herrmann, Andreas Brendlin, Sebastian Gassenmaier, Suhas Siddaramu, Fabian Wagner, Julian Wohlers, Shreeja Varadarajan, Gurlal Singh, Jens Gühring, Rainer Schneider, Konstantin Nikolaou, Saif Afat, Thomas Küstner
Optics
Spin-multiplexed terahertz image edge detection based on extrinsic chirality in all-dielectric metasurface
Yuxin Tang, Shichao Zhao, Li Luo et al. (+3 more)
Extrinsically chiral metasurfaces can exhibit pronounced chiral responses in planar structures without intrinsic chirality, making them attractive for
spin-selective light manipulation. Here, we propose a transmissive all-dielectric terahertz metasurface for image edge detection. Owing to the extrinsic chiral response, the metasurface enables edge-enhanced imaging under right-handed circularly polarized incidence near 0.69 THz, while preserving bright-field imaging under left-handed circularly polarized incidence. Spatial-frequency analysis shows that the effective numerical aperture of the device is approximately 0.4, indicating the terahertz image edge detection can be achieved over a broad spatial-frequency range. This work provides a new design route toward transmissive terahertz all-optical image processing with
spin selectivity and a large numerical aperture.
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All authors Yuxin Tang, Shichao Zhao, Li Luo, Tingting Tang, Hang Xu, Jie Li
Medical Physics
Clinical Commissioning of the First Ultra-Compact Gantry-less Upright Proton Therapy System
Serdar Charyyev, Adam Johansson, Zhuoran Jiang et al. (+17 more)
This study reports the comprehensive clinical commissioning and benchmarking of a novel ultra-compact, gantry-free, upright PT system.
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All authors Serdar Charyyev, Adam Johansson, Zhuoran Jiang, Veng Jean Heng, Cynthia Fu-Yu Chuang, Melanie R Piantino, Samuel Graham, Lawrie B Skinner, Nataliya Kovalchuk, Vivek Maradia, Xianjin Dai, Xuejun Gu, Bin Han, Lloyd Emmanuel Kamole Ghomsi, Susan M Hiniker, Yuan James Rao, Billy W Loo Jr, Lei Xing, Murat Surucu, Yong Yang
Biological Physics · Cross-listed from q-bio.PE
Stochastic Field Theory of HIV Latency: Instanton Dynamics and the Path to Viral Rebound
Jose de Jesus Bernal-Alvarado, David Delepine and Georges Delepine
The transition from clinical latency to active HIV infection is a
stochastic process. Traditional deterministic models based on ordinary differential equations (ODEs) fail to capture the extinction boundary and the subsequent rebound of the virus because they neglect demographic noise in the small-population limit. We map the resulting Master Equation onto a coherent-state path integral using the Doi-Peliti second-quantization formalism and verify that the
stochastic Hamiltonian reproduces the correct mean-field ODEs on the classical
manifold $\bar{\phi}_i = 1$. In the semiclassical (large system-size) limit we derive eight coupled Hamilton-Jacobi equations, identify the virus-free and endemic fixed points, and obtain the basic reproduction number $R_0$ for the four-species network. For the analytically tractable case of single-virion bursting ($n=1$) we show that the
stochastic Hamiltonian factorizes into two bilinear terms, exposing a non-trivial zero-energy surface that constitutes the instanton trajectory. A quasi-steady-state reduction then yields a first-order linear ODE whose closed-form solution gives the instanton action $S_{\rm inst}$ in terms of biological parameters. Calibrating to clinical data—infected-
cell half-life $\delta_I^{-1}\approx 2\,\rm d$, viral burst size $N\approx 10^3$, clearance rate $\delta_V\approx 23\,\rm d^{-1}$, reactivation rate $\eta\approx 10^{-3}\,\rm d^{-1}$, and latent reservoir size $L_0\approx 10^6$
cells—we obtain a mean first-passage time (MFPT) to viral rebound of $\approx 6$ months for a typical patient, with a range of days to years depending on reservoir size. These predictions are qualitatively consistent with observed post-interruption rebound timescales.
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Instrumentation and Detectors · Cross-listed from gr-qc
Analytical estimates of core optics stray light noise and design requirements for ground based gravitational wave detectors
M. Andrés-Carcasona and M. Evans
We present an analytical framework to translate detector sensitivity into stray light requirements for the core optics region of ground based gravitational wave interferometers. We derive analytical estimates for several relevant scattering regimes, extend the treatment to collections of planar baffles, and obtain an analogous requirement for deterministic ghost beams intercepted by beam dumps. The framework is intended to provide conservative design requirements before a complete optical layout is available. We apply it to
Cosmic Explorer to show how these estimates can be used to derive requirements for next generation detectors. The resulting expressions provide a compact set of tools for stray light budgeting and early design studies in current and future gravitational wave detectors.
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Accelerator Physics
Bayesian Optimization of The Relativistic Heavy Ion Collider Luminosity via $s^*$ Control
Xiaofeng Gu, Benjamin Coe, Guillaume Robert-Demolaize et al. (+7 more)
Maximizing luminosity at the interaction point (IP) requires the collision location $s_{IP}$ to coincide with the longitudinal position of the minimum beta function, $s^$. Accurate optics measurements and control of $s^$ are therefore essential for luminosity optimization. At the Relativistic Heavy Ion
Collider (RHIC), average horizontal beta-beat measurements between operating IPs are approximately $20%$, with significant variation in measured $s^*$. Precise control of the beam waist position $s^$ is particularly challenging for modern high-energy
colliders with short bunch lengths and large crossing angles. We present an online
Bayesian optimization (BO) application using the GPTune framework to optimize sPHENIX luminosity through $s^$ control at RHIC. GPTune was first validated at the RHIC Electron Beam Ion Source (EBIS), where it achieved up to a $70%$ increase in beam intensity over the baseline, although experienced operators could reach similar performance with longer manual tuning. The framework was subsequently deployed during sPHENIX operations. Using an intensity-normalized Zero-Degree Calorimeter (ZDC) signal as the optimization objective, due to the unavailability of the live sPHENIX MVTX signal, GPTune identified local luminosity maxima, recovered from intentionally degraded $s^$ configurations, and revealed residual horizontal and vertical waist offsets in the interaction region. These results demonstrate the robustness and efficiency of
Bayesian optimization for real-time
collider tuning under noisy, time-varying conditions. The $s^$ control methodology provides a promising tool for precision luminosity optimization and is particularly relevant to next-generation short-bunch
colliders such as the Electron-Ion
Collider (EIC).
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All authors Xiaofeng Gu, Benjamin Coe, Guillaume Robert-Demolaize, Takeshi Kanesue, Masahiro Okamura, William Fung, Yue Hao, Ji Qiang, Xiaoye S. Li, Yang Liu
Optics
Fisher-information training of optical sensing front ends from natural fluctuations
Abhinav Sinha and Kai Wang
Fisher-information-based optimization of programmable optical front ends in situ generally requires a response model or parameter-labeled measurements. We show that natural parameter fluctuations can instead provide the training signal. We construct proxies for the Fisher information (FI) of one parameter and the prior-weighted FI spectrum of multiple parameters from measured covariances after subtracting conditional detection noise, assuming locally affine responses. We use simulated
photon counts from two incoherent point sources to train a mode sorter that approaches the
quantum limit for separation and the Nagaoka–Hayashi single-copy bound for joint centroid–separation estimation. We demonstrate count-only updates that require no instrument response model and achieve performance comparable to model-based gradients. Our results provide a route to adaptive optical measurements without controlled parameter scans.
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Atmospheric and Oceanic Physics · Cross-listed from cs.LG
Learning Prognostic Variables for AI Convective Parameterizations via Symbolic Distillation
Jurij Schönfeld, Tom Beucler, Julien Savre et al. (+2 more)
Hybrid AI-physics
climate modeling aims to improve coarse (~100km-resolution) Earth system models by learning to parameterize subgrid processes from high-fidelity data. However, this so far mostly involves local-in-time, diagnostic parameterizations, in which the subgrid state depends only on the current coarse state with no
memory of previous states, which is unrealistic for processes such as convection that have intrinsic persistence. To address this, we enhance local-in-time parameterizations by learning prognostic variables that compactly carry important, additional past information where no explicit sub-grid information is available. First we compress past information into a low-dimensional latent space using an autoencoder, which then informs a neural network trained to parameterize targeted subgrid-scale processes. We then replace the autoencoder with symbolic equations that govern the time
evolution of the latent variables, yielding additional prognostic
memory variables that can be integrated alongside the resolved atmospheric state. We evaluate this approach on two systems: the Lorenz-96 model (online) and surface precipitation from high-resolution atmospheric simulations (offline). A forced multivariate linear ordinary differential equation recovers most of the added value achieved by the autoencoder-based approach in both experiments. Benchmarked against diagnostic parameterizations without
memory, our
memory-informed approach improves
climate statistics and temporal structure, including a realistic diurnal cycle of tropical land precipitation.
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All authors Jurij Schönfeld, Tom Beucler, Julien Savre, Steven Sherwood, Veronika Eyring
Atomic Physics
Anomalously enhanced lifetimes of low angular momentum Rydberg states in singly charged alkaline-earth metal ions
Simon Euchner, Weibin Li and Igor Lesanovsky
Trapped ions excited to high-lying electronic states, so-called Rydberg states, open new opportunities for
quantum simulation and
quantum computing. Generally, the fidelity of
quantum coherent operations critically depends on the longevity of Rydberg states. However, scaling laws predict that the lifetimes of Rydberg states in singly charged alkaline-earth metal ions are 16 times shorter, compared to their neutral atom counterparts. Here, we show that this is not generally the case. We report an anomalous lifetime enhancement of certain low angular momentum ionic Rydberg series by factors larger than eight. The anomaly is present at both zero and finite temperature, although it is caused by different mechanisms. At zero temperature, the anomalously enhanced lifetimes are caused by accidental cancellations of the relevant dipole transition
matrix elements, while at room temperature the anomaly originates from the enlarged energetic separation of ionic Rydberg levels with respect to neutral-atom levels.
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Fluid Dynamics
Resolved multiple-droplet evaporation
Alexander W Wray
A simple, accurate asymptotic formula is derived for the spatially resolved evaporative flux from multiple spherical-cap droplets of arbitrary contact angle. Kelvin transforms are used to determine the exact response of a spherical-cap droplet to a point source, with extensions to higher multipoles. This yields explicit formulae for evaporative shielding and reveals a universal spatial structure in the point-source problem. Resolving the spatial variation enables the determination of the associated
liquid flow and particle transport. The resulting flux is used to derive an explicit measure of shielding-induced
liquid transport.
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Optics · Cross-listed from quant-ph
Overcoming the Hong-Ou-Mandel interference limitation for the second photon from a two-photon cascade
Raphael Joos, Michal Vyvlecka, Tim Strobel et al. (+8 more)
Quantum emitters such as
semiconductor quantum dots can provide entangled
photon pairs emitting from a system of cascaded states. However, the resulting temporal correlation between the two
photons from the three-level ladder system has been shown to set a limit on the achievable two-
photon interference. In this work, we show that such limitation, for
photons emitted by the second transition, is only due to reduced temporal overlap at the interference beam splitter. We investigate this theoretically and experimentally by determining time-resolved four-
photon coincidences between two successively emitted
photon pairs. Post-emission synchronization shows the recovery of maximum interference visibility; in prospective
quantum networks this could be achieved via deterministic
quantum memories.
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All authors Raphael Joos, Michal Vyvlecka, Tim Strobel, Benjamin Breiholz, Furkan Aglarci, Ponraj Vijayan, Hans-Georg Babin, Arne Ludwig, Michael Jetter, Simone L. Portalupi, Peter Michler
Biological Physics
Towards Accurate Prediction of Mutation-Induced Changes in Protein Structure
Zhuoyi Liu, Alex Calabrese and Corey S. O'Hern
Proteins can possess numerous mutations relative to their wild-type amino acid sequences with minimal impact to their structure and function. However, in other cases, even a single amino acid mutation relative to the wild-type sequence can lead to a large change in structure or even a disease phenotype. While the accuracy of wild-type
protein structure prediction has improved significantly in recent years, it remains difficult to accurately predict the structure of mutant
proteins. Here, we characterize the local mutation-induced structural changes in
proteins for a
dataset of wildtype and the corresponding single-amino acid mutant x-ray
crystal structures from the
Protein Data Bank (PDB). We find that mutation-induced structural changes in these
proteins are localized at the site of the mutation, decaying rapidly with increasing spatial distance from the mutation site. In addition, we evaluate how well AlphaFold3 can recapitulate the observed mutation-induced structural deformations in the x-ray
crystal structures. We find that the accuracy of the AlphaFold3 predictions decreases strongly with increasing mutation-induced deformation. In contrast to the results for AlphaFold3, the Pearson correlation between a single physical feature, i.e. the change in solvent accessibility, and the mutation-induced deformation does not depend on the magnitude of the deformation. Our results and analyses provide a framework for further studies aimed at predicting the structural changes in
proteins caused by single amino acid mutations.
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Applied Physics
A State-Space Framework for trivial and Topological Metamaterial Stochastic Analysis
Luiz Henrique Marra da Silva Ribeiro, Abhilash Sreekumar, Vinícius Fonseca Dal Poggetto et al. (+4 more)
Topological phononic
crystals and elastic metamaterials support edge states defined by global topological invariants, offering a route toward vibration-control and wave-guiding devices that remain functional in the presence of defects. However, manufacturing-induced spatial variability can perturb these invariants and compromise their robustness, making its quantification essential during design. In this work, we first demonstrate that a previously proposed linear time-varying (LTV) formulation is mathematically equivalent to the spectral element method based on transfer
matrices for elementary rod, Saint-Venant shaft, and Euler-Bernoulli beam theories. The deterministic formulation is then extended to
stochastic analyses through a
stochastic linear time-varying (SLTV) framework. The proposed methodology combines Monte Carlo simulations with
stochastic Fourier series and an analytical Karhunen–Loève expansion, providing closed-form
stochastic fields and their derivatives required by the LTV formulation. The SLTV approach enables the computation of
stochastic dispersion diagrams and forced responses of one-dimensional waveguides with arbitrarily varying geometry and mechanical properties. Because the LTV-based transition
matrix isolates individual wavemodes without requiring the mode tracking needed by conventional eigenproblem-based formulations, the framework is particularly suited for evaluating topological invariants, specifically the Zak phase, and assessing the robustness of topological bands under spatial variability. Numerical results for rods, shafts, and Euler-Bernoulli beams demonstrate the applicability of the proposed framework as a unified methodology for deterministic and
stochastic analyses of trivial and topological periodic waveguides under continuous spatial uncertainty.
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All authors Luiz Henrique Marra da Silva Ribeiro, Abhilash Sreekumar, Vinícius Fonseca Dal Poggetto, Vicent Romero-García, Dimitrios Chronopoulos, Carlos De Marqui Jr., José Roberto de França Arruda
Optics
Collective cavity quantum electrodynamics in solid-state optical clocks
Karen Mamian, Georgy A. Kazakov, Thorsten Schumm et al. (+1 more)
Solid-state frequency standards are generally limited by strong decoherence, rendering conventional interrogation schemes inefficient. The $^{229}$Th nuclear clock provides a unique and timely platform for solid-state optical metrology and nuclear cavity
quantum electrodynamics (QED), featuring a coherence time many orders of magnitude shorter than the radiative lifetime in current experiments. Here, we propose and analyze three cavity QED-enhanced clock interrogation schemes that turn this timescale mismatch into an advantage, leveraging collective coupling of thorium
nuclei to nanophotonic modes to enable fast interrogation and detection despite the long population lifetime. We reveal the central role of collective cooperativity in determining the clock frequency instability, and derive the optimal conditions (power, working-point detuning, thorium density) for clock operation.
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All authors Karen Mamian, Georgy A. Kazakov, Thorsten Schumm, Charles Roques-Carmes
Optics
Non-Hermitian mode locking in an L-band monolithic InP dual-ring laser
Xiao Sun, Mohanad Al Rubaiee, Jue Wang et al. (+4 more)
Coupling between
laser cavities provides a means of controlling optical modes through their gain, loss, and hybridization. Here we demonstrate electrically controlled mode locking in a monolithic InP dual ring
laser operating in the L band without a dedicated saturable absorber. Independent biasing of the two rings accesses single mode emission, mode locking, and hybridized supermode operation, with a measured intermode beat frequency of 542 MHz in the latter regime. The
laser generates 7.9 ps pulses at 18.11 GHz. A coupled cavity model describes how differential nonlinear detuning modifies the modal gain loss contrast, and time domain simulations yield pulse durations and spectral widths close to those measured experimentally. In a device incorporating saturable absorbers, reverse bias enables 3.1 ps pulses and reduces the integrated timing jitter from 9.06 to 2.46 ps relative to the unbiased condition. These results connect electrical control of coupled-cavity states with picosecond pulse generation in a monolithic InP
semiconductor platform for high repetition rate optical communications and microwave photonics.
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All authors Xiao Sun, Mohanad Al Rubaiee, Jue Wang, John H. Marsh, Stephen J. Sweeney, Anthony E. Kelly, Lianping Hou
Data Analysis and Statistics · Cross-listed from hep-ex
Goodness-of-fit for multi-distribution neutrino cross-section measurements with shared events
Francisco Martinez Lopez, London Cooper-Troendle, Steven Gardiner et al. (+2 more)
When multiple differential cross-section measurements are extracted from a common event sample, the same events contribute simultaneously to multiple distributions. This event-sharing structure imposes exact linear constraints among the bin counts, reducing the effective dimensionality of the measurement below the total number of bins. Since the covariance
matrix obeys these inter-distribution constraints, it contains a rank deficiency. While limited numerical precision may inadvertently restore invertibility, the $\chi^{2}$ contributions along constrained dimensions will be arbitrary, yielding unphysically inflated $\chi^{2}$ values in global goodness-of-fit tests. We present the range-projected $\chi^{2}$, a test statistic that restricts the goodness-of-fit test to the subspace carrying independent statistical information, yielding a $\chi^{2}$ with $N_\text{bins} - N_\text{null}$ degrees of freedom, where $N_\text{null}$ is the number of independent constraints. We show that this rank deficiency is a predictable consequence of the event-sharing structure, and that $N_\text{null}$ decomposes into a structural contribution determined a priori from the binning geometry and a kinematic contribution that depends on the phase-space occupancy. The method is validated with an analytical toy model and a simulated
neutrino–argon cross-section measurement including unfolding and multi-source systematic uncertainties.
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All authors Francisco Martinez Lopez, London Cooper-Troendle, Steven Gardiner, Patrick Green, Tanaz Mohayai
History and Philosophy of Physics
The wavelength of light as Thomas Young invented it
Olivier Morizot
This paper documents Thomas Young's invention of a concept which he alternately refers to as the ”magnitude”, ”breadth”, ”interval” or ”length of an undulation” of light. First, the paper highlights that Young was first to link some concept of a wavelength to a theory of optics and to assign a precise value to this length for each component of the colour spectrum. Then, it sets out an explanation of how Young made up these values. Finally, it examines the reasons why Young introduced an optical wavelength into his theory of light, insofar as these reasons might in turn shed light on why he was first to do so.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
III-V antiphase boundaries are not generated by Si or Ge substrate step edges
Charles Cornet, Sreejith Pallikkara Chandrasekharan, Audrey Gilbert et al. (+7 more)
We critically review recent experimental and theoretical advances on the valence- and structure-mismatched heteroepitaxy of III-V
semiconductors on group-IV substrates. We examine key aspects including wetting behavior, atomic configurations at the hetero-interface, substrate passivation, and the stability of antiphase boundaries (APBs). By synthesizing these findings with pioneering studies, we propose a refined description of antiphase boundaries formation. Our analysis shows that hetero-interface formation is dictated by substrate terrace reconstruction, demonstrating that APBs are not generated at monoatomic step edges. This generalized III-V/IV growth framework provides new insights for the integration of III-V
semiconductors on group-IV platforms and, more broadly, for valence-mismatched heteroepitaxy.
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All authors Charles Cornet, Sreejith Pallikkara Chandrasekharan, Audrey Gilbert, Milan Silvestre, Rozenn Bernard, Pascal Turban, Gilles Patriarche, Eric Tournie, Laurent Pedesseau, Jean-Baptiste Rodriguez
Fluid Dynamics
A high-order ghost-point immersed boundary method coupled with auxiliary differential equations for time-domain impedance walls
Abdoulaye Ouattara
A ghost-point immersed boundary method is coupled with auxiliary differential equations to impose a locally-reacting impedance condition on a wall that does not conform to a Cartesian grid, in the framework of the linearized Euler equations. The ghost-point reconstruction follows the normal-stencil approach: an elliptical least squares cloud of fluid nodes is used to build a high-order
polynomial along the local wall normal, which is then extrapolated onto the ghost points by one-dimensional La grange interpolation. The impedance, modeled as a massspringdamper oscillator, is advanced in time through two auxiliary state variables per ghost point, coupled to the reconstruction at every RungeKutta stage. The method is validated against exact and semi-analytical references on a flat immersed wall, a cylindrical wall reflecting an acoustic pulse, and a cylinder scattering a harmonic monopole. Convergence orders ranging from about three on the curved wall to about four and a half on the flat wall are measured, and a cross-check against an exact harmonic reference shows that a persistent offset observed against a semi-analytical reference is a property of that ref erence rather than of the coupled solver. A spectral stability analysis of the linearized semi-discrete operator further shows that the normal-stencil reconstruction reduces, without eliminating, a known instability that occurs when the immersed wall becomes tangent to the grid.
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Optics
Broadband Single-Particle Absorption Circular Dichroism Reveals Chiroptical Heterogeneity in Gold Helicoids
Rohit B. Raj, Susanna Bertuletti, Jeong Hyun Han et al. (+7 more)
Quantitative measurements of absorption circular dichroism (CD) at the single-particle level are essential for understanding how individual chiral nanostructures dissipate optical energy, yet broadband absorptance measurements remain experimentally challenging. Here, we introduce a wavelength-tunable integrating-sphere microscope that determines the absorptance of individual nanoparticles under right- and left-circularly polarized illumination through direct optical energy balance, enabling broadband measurement of the absorption dissymmetry factor, gabs. Measurements of achiral gold nanospheres and strongly anisotropic gold nanorods establish the apparent absorption CD baseline and demonstrate minimal detectable linear-dichroism-to-circular-dichroism (LD-to-CD) leakage under the experimental conditions. Applying this approach to 87 chiral gold helicoids synthesized using L-glutathione (L-helicoids) and 96 synthesized using D-glutathione (D-helicoids) reveals mean particle-level gabs values of opposite sign, with a statistically significant difference between the two populations. Individual particles nevertheless exhibit pronounced heterogeneity in response sign, magnitude, spectral position, and line shape. More than one-third of the particles in each population display opposite-sign absorption CD responses relative to their population-average tendency. Correlative SEM analysis of the L-helicoid population further shows that opposite-sign responses persist among isolated particles exhibiting the characteristic projected helicoid morphology, indicating that aggregation and gross differences in projected morphology are insufficient to explain the observed heterogeneity. These results establish broadband single-particle absorption CD spectroscopy as a direct probe of absorptive chiroptical heterogeneity and reveal particle-specific responses obscured by ensemble averaging.
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All authors Rohit B. Raj, Susanna Bertuletti, Jeong Hyun Han, Sepin Cho, Debapriya Pal, Nick Feldman, Ki Tae Nam, Willem L. Noorduin, A. Femius Koenderink, Erik C. Garnett
Atomic Physics · Cross-listed from cond-mat.quant-gas
From harmonic to sound-like oscillations in a quantum gas confined in a gravity compensated shell trap
Matthieu Cassus, Rishabh Sharma, Maxime Pesche et al. (+4 more)
We study the center of mass oscillations of a
quantum gas in a shell shaped trap in the presence of a vertical force opposed to
gravity. The measured harmonic frequency at the bottom of the shell is compared with an analytical formula for the trap potential including corrections beyond the rotating wave approximation. When
gravity is partially compensated, a quartic correction to the harmonic motion has to be included due to the shell
curvature. As
gravity is nearly canceled, the
quantum gas occupies a large fraction of the lower hemisphere. Driving the center of mass induces internal excitations in the
quantum gas, whose time
evolution is governed by the presence of sound waves. Relaxation processes induce a strong damping of the center of mass oscillation in this limit.
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All authors Matthieu Cassus, Rishabh Sharma, Maxime Pesche, Laurent Longchambon, Thomas Badr, Romain Dubessy, Hélène Perrin
Plasma Physics · Cross-listed from astro-ph.HE
Particle Acceleration in Stratified 2D MRI Turbulence: From Reconnection to First- and Second-Order Fermi and Shear Acceleration
Astor Sandoval, Mario Riquelme and Jorge Cuadra
Low-luminosity
accretion disks around black holes are weakly collisional, potentially enabling nonthermal particle acceleration. Local two-dimensional particle-in-
cell simulations of the stratified magnetorotational instability (MRI) in pair
plasmas by Sandoval et al. (2024; hereafter S24) revealed nonthermal populations with maximum energies proportional to the scale-separation ratio $\omega_{c,0}/\Omega_0$, where $\omega_{c,0}$ and $\Omega_0$ are the initial particle cyclotron and Keplerian frequencies, respectively. We identify the acceleration mechanisms involved and quantify their scale-separation dependence. Acceleration occurs primarily within large-scale current sheets associated with an MRI dynamo. Particles are initially injected by non-ideal electric fields during reconnection driven by plasmoid splitting, attaining energies independently of scale separation. They subsequently undergo rapid first-order Fermi-like acceleration occurring within converging flows between newly formed, separating plasmoids. During this stage, energies grow at a rate proportional to the instantaneous non-relativistic cyclotron frequency, independently of $\omega_{c,0}/\Omega_0$. This fast acceleration rate implies a maximum energy proportional to $\omega_{c,0}/\Omega_0$. Particles then continue interacting repeatedly with plasmoids, undergoing slower, predominantly second-order Fermi acceleration, with a subdominant contribution from shear acceleration. This stage increases particle energies by only a factor of a few over several orbits, regardless of $\omega_{c,0}/\Omega_0$. The combination of these three stages implies a maximum energy proportional to $\omega_{c,0}/\Omega_0$, explaining the scaling found by S24 and suggesting that the MRI may accelerate particles to ultrarelativistic energies in low-luminosity disks. Testing these results in three dimensions remains an important next step.
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Fluid Dynamics
High-order immersed boundary method for subsonic aeroacoustics and compressible Navier-Stokes equationsHigh-order immersed boundary method for subsonic aeroacoustics and compressible Navier-Stokes equations
Abdoulaye Ouattara, David Marx, Christian Prax et al. (+3 more)
In computational fluid dynamics, the immersed boundary method is a classical technique to account for complex geometries when Cartesian grids are used, as is the case in finite difference methods. The present paper presents a new discrete ghost point method, which is one of the different immersed boundary methods available, for solving problems in acoustics and aeroacoustics with the linearized Euler equations or the compressible Navier-Stokes equations. This method is based on high-order schemes and a ghost point method. The flow field values at the ghost points are determined in two steps. A least-squares interpolation is first used to reconstruct the flow on a stencil of points located on the normal to the immersed boundary. Then, a 4th order Lagrangian extrapolation based on the normal stencil points adjacent to the boundary point is used to impose the boundary conditions at the immersed boundary by reconstructing the field values at the ghost points. This approach is verified and validated for the acoustical problem of a pressure pulse impinging on a cylinder. The approach is also validated for compressible flow past a circular cylinder at several Reynolds numbers.
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All authors Abdoulaye Ouattara, David Marx, Christian Prax, Véronique Fortunée, Manuel Diaz, Peter Jordan
Optics
Phase fields in momentum space of photonic crystal slabs
Chuanlin Li, Aobo Ren and Jiang Wu
Optical phase modulation is of great significant importance in fields such as optical communication, information processing, and precision measurement. Compared with real-space modulation, momentum-space phase modulation has distinct advantages: it is free from structural center constraints, supports unlimited mode capacity, and possesses intrinsic topological protection. This inherent flexibility and scalability allow practical applications systems to operate without stringent optical
alignment while providing a large number of independent control channels, thereby advancing the development of high-performance, highly integrated optical systems. Photonic
crystal slabs, with their open boundary periodicity and capabilities for momentum-space optical field manipulation, have become a crucial platform for research on momentum-space phase fields. Based on polarization orthogonal decomposition and the scattering
matrix within temporal coupled-mode theory, this paper systematically elucidates the generation mechanisms of both two-dimensional momentum-space phase fields, including phase
vortices, phase gradients, and phase difference, and multidimensional synthetic momentum-space phase fields in photonic
crystal slabs, and reviews recent research and application progress in this area. Finally, the development status, advantages, and possible breakthroughs in the field of momentum-space phase fields are summarized and prospects for future work are discussed.
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Medical Physics
A digital-twin framework for forecasting treatment-day imaging with contour uncertainty in adaptive proton radiotherapy
Yizhou Wu, Jie Ding, Justin Roper et al. (+6 more)
Head-and-neck anatomy changes over a six-to-seven-week
proton course, and the anatomy of a later week cannot be imaged when the plan is made. We present a digital-twin framework that forecasts a patient's treatment-day anatomy as an ensemble of predicted CTs with propagated contours and quantifies the uncertainty of the forecast contours. The twin is a library of previously treated patients with planning and weekly quality-assurance CTs (QACTs), made patient-specific by a two-step foundation-model deformable registration: a cross-patient field carries each library patient onto the current patient, and a longitudinal field, estimated in the current patient's frame, carries that patient's planning-to-QACT change onto the current patient's own planning CT. A library of 302 observations from 88 patients yields about 300 replicates per patient, each a deformation that occurred in a treated patient. The dispersion of the propagated contours, resolved by outward normal, is six-direction contour uncertainty in millimeters. This is uncertainty in the input to the forecast, which library patient the current patient follows, rather than in model parameters, and it is unchanged when the registration engine is exchanged. On ten patients with clinician contours on two QACTs, the library alone fixes the anisotropic shape of the uncertainty (4.5 to 6.2 mm); the first QACT narrows it by a factor of 3.2 to 3.6 without a contour being drawn; an approved contour improves the center but not the width. The estimate orders directions correctly but is not Gaussian-calibrated. A clinical target volume expansion is worked out as one application.
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All authors Yizhou Wu, Jie Ding, Justin Roper, Minglei Kang, Yuheng Li, Sibo Tian, David S. Yu, Xiaofeng Yang, Chih-Wei Chang
Classical Physics · Cross-listed from cond-mat.stat-mech
Lowest-known Energy Configuration of $N=100\,000$ Coulomb Charges in a Disk: Breaking the $10^{5}$ Barrier
Georgiy K. Lavrov and Eduard G. Nikonov
We report the first calculation of the lowest-known energy configuration for $N=100\,000$ classical point charges confined to a disk and interacting via the $1/r$ Coulomb potential - a system size never before achieved for the Thomson problem in a disk, more than doubling the previous record of $N=40\,886$ reported by Amore and Zarate. An adaptive defect-targeting subdomain optimization strategy yields an approximately linear growth of the wall-clock time per cycle with $N$; for $N=100\,000$ a single $24$-core CPU workstation without GPU acceleration required $\approx31$ hours. The energy $E_{\min}=7.80466624157\times10^{9}$ deviates from the standard empirical asymptotic expansion by only $2.525\times10^{-7}$. We demonstrate that this remarkable agreement provides a stringent test of the rigorous next-order asymptotic theory for Riesz interactions, while the residual deviation is consistent with an $O(N^{4/3})$ boundary-layer correction whose absence from the standard fitting basis biases the empirical $N^{3/2}$ coefficient away from its exact crystalline value, thereby tying the deviation to the two-dimensional crystallization
conjecture. Bond-orientational order analysis reveals a polycrystalline bulk threaded by radial grain boundaries, establishing a new
benchmark for two-dimensional Coulomb systems.
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Physics Education
Design and Initial Evaluation of a Photovoltaics-focused Course-based Undergraduate Research Experience in Physics
Rachael L. Merritt and H.J. Lewandowski
Traditional physics laboratory courses often focus on experiments with well-known results, limiting students' engagement in authentic scientific practices. Course-based undergraduate research experiences (CUREs), where students engage in real research with unknown outcomes, have been shown to support positive student outcomes, such as increased self-efficacy, persistence, and engagement in scientific practices. However, discipline-specific studies of CUREs in physics remain limited. We describe the development, structure, and initial implementation of a photovoltaics-focused CURE in a second-year undergraduate physics laboratory course at the University of Colorado Boulder. To examine how students experienced the course, we analyzed end-of-semester reflection assignments using the five CURE components (i.e., scientific practices, discovery, relevance, collaboration, and iteration), as well as established dimensions of research authenticity, as analytic frameworks. Students described experiences associated with all five CURE components, with collaboration, relevance, and scientific practices appearing most prominently in their reflections. Students also associated authentic research with meaningful scientific contribution, engagement in authentic scientific practices, and navigating the uncertainty and setbacks inherent in research, although fewer explicitly identified themselves as researchers or scientists. A subset of students additionally connected the course to their immediate thinking about future academic and professional pathways. This work contributes both a discipline-specific model for implementing CUREs in experimental physics laboratory courses and provides insight into how students interpret and experience authentic research within this course context.
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