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Physics Physics

physics Watch Physics

Monday 1 December

Applied Physics

High-Speed NV Ensemble Magnetic Field Imaging via Laser Raster Scanning

Luca Troise, Nikolaj W. Hansen, Marvin Holten et al. (+4 more)

We present a technique that uses an ensemble of nitrogen-vacancy (NV) centers in diamond to image magnetic fields with high spatio-temporal resolution and sensitivity. A focused laser beam is raster-scanned using an acousto-optic deflector (AOD) and NV center fluorescence is read out with a single photodetector, enabling low-noise detection with high dynamic range. The method operates in a previously unexplored regime, quasi-continuous-wave optically detected magnetic resonance (qCW-ODMR). In this regime, NV centers experience short optical pump pulses for spin readout and repolarization – analogous to pulsed ODMR – while the microwave field continuously drives the spin transitions. We systematically characterize this regime and show that the spin response is governed by a tunable interplay between coherent evolution and relaxation, determined by the temporal spacing between pump laser pulses. Notably, the technique does not require precise microwave pulse control, thus simplifying experimental implementation. To demonstrate its capabilities, we image time-varying magnetic fields from a microwire with sub-millisecond temporal resolution. This approach enables flexible spatial sampling and, with our diamond, achieves $\text{nT}/\sqrt{\text{Hz}}$-level per-pixel sensitivity, making it well suited for detecting weak, dynamic magnetic fields in biological and other complex systems.
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All authors Luca Troise, Nikolaj W. Hansen, Marvin Holten, Dhiren M. Kara, Jean-Francois Perrier, Ulrik L. Andersen, Alexander Huck

Computational Physics · Cross-listed from cs.LG

Domain-Decomposed Graph Neural Network Surrogate Modeling for Ice Sheets

Adrienne M. Propp, Mauro Perego, Eric C. Cyr et al. (+5 more)

Accurate yet efficient surrogate models are essential for large-scale simulations of partial differential equations (PDEs), particularly for uncertainty quantification (UQ) tasks that demand hundreds or thousands of evaluations. We develop a physics-inspired graph neural network (GNN) surrogate that operates directly on unstructured meshes and leverages the flexibility of graph attention. To improve both training efficiency and generalization properties of the model, we introduce a domain decomposition (DD) strategy that partitions the mesh into subdomains, trains local GNN surrogates in parallel, and aggregates their predictions. We then employ transfer learning to fine-tune models across subdomains, accelerating training and improving accuracy in data-limited settings. Applied to ice sheet simulations, our approach accurately predicts full-field velocities on high-resolution meshes, substantially reduces training time relative to training a single global surrogate model, and provides a ripe foundation for UQ objectives. Our results demonstrate that graph-based DD, combined with transfer learning, provides a scalable and reliable pathway for training GNN surrogates on massive PDE-governed systems, with broad potential for application beyond ice sheet dynamics.
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All authors Adrienne M. Propp, Mauro Perego, Eric C. Cyr, Anthony Gruber, Amanda A. Howard, Alexander Heinlein, Panos Stinis, Daniel M. Tartakovsky

Fluid Dynamics · Cross-listed from cond-mat.soft

Renormalised hydrodynamics in polar chiral active matter: Spectral scaling and disorder-driven vortex clustering in phase-coupled, motile oscillators

Magnus F Ivarsen

Active turbulence in overdamped chiral systems presents a complex challenge, namely the frequent exhibition of non-universal spectral scaling, creating large-scale coherent structuring that seemingly defies standard inertial fluid descriptions. In this study, we investigate the hydrodynamic limit of a two-dimensional polar chiral active fluid modeled as an ensemble of locally coupled, motile Kuramoto-Sakaguchi oscillators. By introducing a Renormalised Fluid Element (RFE) operator, we coarse-grain microscopic phase singularities, and in so doing, we isolate the macroscopic transport dynamics. We demonstrate that while the raw particle distributions consistently exhibit steep, dissipative energy spectra, associated with enstrophy injection at the microscale, the RFE-filtered field reveals a dual behaviour characterized by an inverse energy cascade. When the intrinsic frequency dispersion, drawn from a scale-free power-law distribution, is broad enough to seed fluctuations at all resolved scales, this hidden cascade acts akin to a topological heat pump, driving the system toward a state of macroscopic vortex clustering, structurally analogous to supersonic shallow water dynamics. Conversely, a narrow frequency dispersion results in kinetic arrest, forming an active vortex glass. These results suggest that overdamped phase-slaved active matter can sustain effective inertial cascades, providing a mathematical framework for understanding scale-dependent energy transport in driven chiral systems.
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Instrumentation and Detectors

Beam-test evaluation of pre-production Low Gain Avalanche Detectors for the ATLAS High Granularity Timing Detector

A. Aboulhorma, M. Ait Tamlihat, H.M. Alfanda et al. (+229 more)

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS experiment as part of the Phase-II upgrade for the High Luminosity-Large Hadron Collider (HL-LHC). It will mitigate pile-up effects in the forward region, and measure per bunch luminosity. The design of HGTD is based on Low Gain Avalanche Detector (LGAD) sensors. This paper presents the results of beam-test campaigns conducted at CERN and DESY in 2023 and 2024 on single LGADs from HGTD pre-production test structures, before and after neutron irradiation up to fluences of $2.5 \times 10^{15}~\mathrm{n_{eq}/cm^2}$. The tested LGADs can meet HGTD requirements in terms of charge collection, time resolution, and hit efficiency, even under HL-LHC end-of-life conditions, supporting their deployment in the final detector.
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All authors A. Aboulhorma, M. Ait Tamlihat, H.M. Alfanda, O. Atanova, N. Atanov, I. Azzouzi, J. Barreiro Guimarães da Costa, T. Beau, D. Benchekroun, F. Bendebba, G. Bergamin, Y. Bimgdi, A. Blot, A. Boikov, J. Bonis, D. Boumediene, C. Brito, A.S. Brogna, A.M. Burger, L. Cadamuro, Y. Cai, N. Cartalade, R. Casanova Mohr, R. Cherkaoui El Moursli, Y. Che, X. Chen, E.Y.S. Chow, L.D. Corpe, C.G. Crozatier, L. D'Eramo, S. Dahbi, D. Dannheim, G. Daubard, Y. Davydov, J. Debevc, Y. Degerli, E. Delagnes, F. Deliot, M. Dhellot, P. Dinaucourt, G. Di Gregorio, P.J. Dos Santos De Assis, C. Duan, O. Duarte, F. Dulucq, J. Ehrecke, Y. El Ghazali, A. El Moussaouy, A. Falou, L. Fan, Y. Fan, Z. Fan, K. Farman, F. Fassi, Y. Feng, M. Ferreira, F. Filthaut, F. Fischer, P. Fusté, J. Fu, J. García Rodriquez, G. Gaspar De Andrade, V. Gautam, Z. Ge, R. Gonçalo, M. Gouighri, S. Grinstein, K. Gritsay, F. Guilloux, S. Guindon, A. Haddad, S.E.D. Hammoud, L. Han, A.M. Henriques Correia, M. Hidaoui, B. Hiti, J. Hofner, S. Hou, P.J. Hsu, X. Huang, Y. Huang, K. Hu, C. Insa, J. Jeglot, X. Jia, G. Kramberger, M. Kuriyama, B.Y. Ky, D. Lacour, A. Lafarge, B. Lakssir, A. Lantheaume, D. Laporte, C. de La Taille, M.A.L. Leite, A. Leopold, H. Li, L. Li, M. Li, S. Li, S. Li, Y. Li, Z. Li, S. Liang, Z. Liang, B. Liu, K. Liu, K. Liu, Y.L. Liu, Y.W. Liu, F.L. Lucio Alves, M. Lu, Y.J. Lu, F. Lyu, D. Macina, R. Madar, N. Makovec, S. Malyukov, I. Mandić, T. Manoussos, S. Manzoni, G. Martin-Chassard, F. Martins, L. Masetti, R. Mazini, E. Mazzeo, K. Ma, X. Ma, R. Menegasso, J-P. Meyer, Y. Miao, A. Migayron, M. Mihovilovic, M. Milovanovic, M. Missio, V. Moskalenko, N. Mouadili, A. Moussa, I. Nikolic-Audit, C.C. Ohm, H. Okawa, S. Okkerman, M. Ouchrif, C. Pénélaud, A. Parreira, B. Pascual Dias, R.E. de Paula, J. Pinol Bel, P.-O. Puhl, C. Puigdengoles Olive, M. Puklavec, J. Qin, M. Qi, H. Ren, H. Riani, S. Ridouani, V. Rogozin, L. Royer, F. Rudnyckyj, E.F. Saad, G.T. Saito, A. Salem, H. Santos, S. Scarfi, Ph. Schwemling, N. Seguin-Moreau, L. Serin, R.P. Serrano Fernandez, A. Shaikovskii, Q. Sha, L. Shan, R. Shen, X. Shi, P. Skomina, H. Smitmanns, H.L. Snoek, A.P. Soulier, A. Stein, H. Stenzel, J. Strandberg, W. Sun, X. Sun, Y. Sun, Y. Tan, K. Tariq, Y. Tayalati, S. Terzo, A. Torrento Coello, S. Trincaz-Duvoid, U.M. Vande Voorde, I. Velkovska, R.P. Vieira, L.A. Vieira Lopes, A. Visibile, A. Wang, C. Wang, S.M. Wang, T. Wang, T. Wang, W. Wang, Y. Wang, Y. Wang, J. Wan, Q. Weitzel, J. Wu, M. Wu, W. Wu, Y. Wu, L. Xia, D. Xu, H. Xu, L. Xu, Z. Yan, H. Yang, H. Yang, X. Yang, X. Yang, J. Ye, I. Youbi, J. Yuan, I. Zahir, H. Zeng, D. Zhang, J. Zhang, L. Zhang, Z. Zhang, M. Zhao, Z. Zhao, X. Zheng, Z. Zhou, Y. Zhu, X. Zhuang

Popular Physics

Classical Reconstruction of the PMNS Matrix Using a Mechanical Neutrino Oscillator

Nishil Savla

Neutrino oscillations arise from quantum interference between neutrino mass eigenstates and are governed by the PMNS matrix. Although this is an intrinsically quantum phenomenon, its mathematical structure is analogous to systems of coupled classical oscillators. In this work, a three–pendulum system connected by springs is constructed as a classical analog of three–flavor neutrino oscillations. Measurements of amplitude transfer, normal–mode structure, and beat frequencies are used to extract a mechanical mixing matrix, which is compared with the structure of the PMNS matrix under the assumption of zero CP violation. A scaling relation linking mechanical time evolution to the neutrino \(L/E\) behavior is derived, clarifying the scope and limitations of the analogy. The experiment demonstrates how abstract concepts of neutrino mixing can be visualized using simple and accessible classical systems, offering both pedagogical value and a qualitative understanding of flavor oscillation dynamics.
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Optics

Dispersion-Mediated Space-Time States

Klaas De Kinder and Christophe Caloz

Space-time varying media enable unprecedented control over electromagnetic waves, yet most existing studies assume idealized, nondispersive materials and thus fail to capture the intrinsic frequency dispersion of realistic platforms. Here, we develop a general framework for dispersive space-time varying systems that rigorously identifies the physically allowed frequency transitions of waves scattered at moving interfaces. Unlike previous approaches, our method is valid for arbitrary dispersion profiles, including resonances, and does not rely on the commonly used frame hopping approach, allowing treatment of multiple-velocity and accelerated systems. Applying this framework to canonical Drude and Lorentz media, we uncover a family of dispersion-mediated space-time states that arise from the multiple frequency transitions permitted by material dispersion. These states extend beyond conventional nondispersive scattering, revealing qualitatively new regimes of space-time scattering behavior. Beyond the frequency transitions, we derive the scattering coefficients for dispersive moving interfaces and provide a Fourier-domain formulation that yields a complete electromagnetic scattering solution for both monochromatic waves and broadband pulses. Our results establish a rigorous foundation for the design of realistic space-time metamaterials, with immediate relevance to emerging experiments in epsilon-near-zero optical platforms and open pathways for dispersion-engineered wave manipulation.
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Applied Physics · Cross-listed from cond-mat.supr-con

Fabrication and Properties of NbN/NbNx/NbN and Nb/NbNx/Nb Josephson Junctions

Sergey K. Tolpygo, Ravi Rastogi, David Kim et al. (+3 more)

Increasing integration scale of superconductor electronics (SCE) requires employing kinetic inductors and self-shunted Josephson junctions (JJs) for miniaturizing inductors and JJs. We have been developing a ten-superconductor-layer planarized fabrication process with NbN kinetic inductors and searching for suitable self-shunted JJs to potentially replace high Josephson critical current density, Jc, Nb/Al-AlOx/Nb junctions. We report on the fabrication and electrical properties of NbN/NbNx/NbN junctions produced by reactive sputtering in Ar+N2 mixture on 200-mm wafers at 200 oC and incorporated into a planarized process with two Nb ground planes and Nb wiring layer. Here NbN is a stoichiometric nitride with superconducting critical temperature Tc =15 K and NbNx is a high resistivity, nonsuperconducting nitride deposited using a higher nitrogen partial pressure than for the NbN electrodes. For comparison, we co-fabricated Nb/NbNx/Nb JJs using the same NbNx barriers deposited at 20 oC. We varied the NbNx barrier thickness from 5 nm to 20 nm, resulting in the range of Jc from about 1 mA/um^2 down to ~10 uA/um^2, and extracted coherence length of 3 nm and 4 nm in NbNx deposited, respectively at 20 oC and 200 oC. Both types of JJs are well described by resistively and capacitively shunted junction model without any excess current. We found the Jc of NbN/NbNx/NbN JJs to be somewhat lower than of Nb/NbNx/Nb JJs with the same barrier thickness, despite a much higher Tc and energy gap of NbN than of Nb electrodes. IcRn products up to ~ 0.5 mV were obtained for JJs with Jc~ 0.6 mA/um^2. Jc(T) dependences have been measured.
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All authors Sergey K. Tolpygo, Ravi Rastogi, David Kim, Terence J. Weir, Neel Parmar, Evan B. Golden

Atomic Physics

Simultaneous optical and multi-band terahertz imaging using an atomic quantum sensor

Andrew Rae MacKellar, C. Stuart Adams and Kevin J. Weatherill

We demonstrate simultaneous imaging at 0.549 THz and 1.012 THz with an optical overlay using a two-species atomic-vapour-based technique. The atomic vapour, comprising laser-pumped rubidium and caesium atoms contained within the same cell, is used to convert two narrowband terahertz signals to optical frequencies which can then be detected using standard CMOS sensors. We use the system to image and perform spectral analysis of material samples. As atomic vapour is optically transparent, by using optically-transparent terahertz lenses, we can achieve simultaneous optical imaging, allowing for potential integration of terahertz sensitivity into a range of optical imaging devices.
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Physics and Society

The Hidden Cost of Straight Lines: Quantifying Misallocation Risk in Voronoi-based Service Area Models

JA Torrecilla Pinero, JM Ceballos Martínez, A Cuartero Sáez et al. (+2 more)

Voronoi tessellations are standard in spatial planning for assigning service areas based on Euclidean proximity, underpinning regulatory frameworks like the proximity principle in waste management. However, in regions with complex topography, Euclidean distance poorly approximates functional accessibility, causing misallocations that undermine efficiency and equity. This paper develops a probabilistic framework to quantify misallocation risk by modeling travel distances as random scaling of Euclidean distances and deriving incorrect assignment probability as a function of local Voronoi geometry. Using plant-municipality observations (n=383) in Extremadura, Spain (41,635 km2), we demonstrate that the Log-Normal distribution provides best relative fit among alternatives (K-S statistic=0.110). Validation reveals 15.4% of municipalities are misallocated, consistent with the theoretical prediction interval (52-65 municipalities at 95% confidence). Our framework achieves 95% agreement with complex spatial models at O(n) complexity. Poor absolute fit of global distributions (p-values<0.01) reflects diverse topography (elevation 200-2,400m), motivating spatial stratification. Sensitivity analysis validates the fitted dispersion parameter (s=0.093) for predicting observed misallocation. We provide a calibration protocol requiring only 30-100 pilot samples per zone, enabling rapid risk assessment without full network analysis. This establishes the first probabilistic framework for Voronoi misallocation risk with practical guidelines emphasizing spatial heterogeneity and context-dependent calibration.
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All authors JA Torrecilla Pinero, JM Ceballos Martínez, A Cuartero Sáez, P Plaza Caballero, A Cruces López

Chemical Physics

Brownian dynamics simulations of electric double-layer capacitors with tunable metallicity

Paul Desmarchelier, Alexandre P. dos Santos, Yan Levin et al. (+1 more)

We introduce an efficient description of electrodes, characterized by their Thomas-Fermi screening length lTF inside the metal, for Brownian dynamics (BD) simulations of capacitors. Within a Born-Oppenheimer approximation for the electron charge density inside the electrodes, we derive the effective many-body potential for ions in an implicit solvent between Thomas-Fermi electrodes, taking into account the constraints of applied voltage and of global electro-neutrality of the system, as well as the 2D periodic boundary conditions along the electrode surfaces. We derive the average charge and the fluctuation-dissipation relation for the differential capacitance, highlighting the contribution of the fluctuations of the net ionic dipole moment, as well as those from the solvent polarization and of the electron density, whose fluctuations are suppressed within the Born-Oppenheimer description. We demonstrate the relevance of this model by validating its predictions against known results for the force on ions as a function of the ion-surface distance in simple geometries. The equilibrium ionic density profiles from BD simulations are in excellent agreement with those from an explicit electrode model for perfect metals, and are obtained at a significantly lower computational cost. Finally, we discuss with the present model the effect of the Thomas-Fermi screening length on the equilibrium ionic density profiles and the capacitance. While limited to parallel plate capacitors, the present simulation method allows to consider larger systems, lower concentrations, and longer time scales concentrations than molecular simulations in order to predict the electrochemical properties of Thomas-Fermi capacitors and correlate them with the ion dynamics.
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All authors Paul Desmarchelier, Alexandre P. dos Santos, Yan Levin, Benjamin Rotenberg

Optics

On the origin and properties of dipolar recoil force and torque

Sebastian Golat, Nathaniel Levy and Francisco J. Rodríguez-Fortuño

The recoil optical force and torque acting on an electromagnetic dipole are typically derived by computing the imbalance in radiated linear and angular electromagnetic momentum coming from the source, using Maxwell stress tensor integration. This quantifies the recoil's outcome without revealing its physical origin or the underlying forces that produce it. The recoil force and torque exist even in the absence of external illumination, such that an isolated dipole emitter can experience them. In contrast to the other terms, the recoil terms are odd under time reversal. To clarify their nature and properties, we re-derive the recoil force from first principles using the total Lorentz force on a system of charges that form a simultaneous electric and magnetic dipole. The results agree with the standard momentum-based derivation and reveal their ultimate origin from retardation effects – arising from the finite speed of light – in the mutual interactions between charges. This result provides fundamental insight into the recoil mechanism, offering a clearer conceptual foundation for future theoretical and experimental studies of light-induced forces.
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Plasma Physics

High-beta equilibrium in mirror machine with population of fast sloshing ions

Ivan Chernoshtanov

A method of constructing the high-beta (diamagnetic-bubble-like) equilibrium with a population of fast sloshing ions is discussed. Fast ions move along betatron orbits; such ions can arise because of off-axis neutral beam injection. Conservation of the adiabatic invariant of these ions is proposed; a simplified expression for the invariant is presented. Numerical examples of equilibrium with sloshing ions are shown and conservation of the invariant is justified by a direct numerical simulation of motion of fast ions even in the case with beta equal to 1.
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Instrumentation and Detectors · Cross-listed from quant-ph

Macroscopic Quantum Resonators Path Finder (MAQRO-PF) White Paper

Jack Homans, Laura da Palma Barbara, Jakub Wardak et al. (+3 more)

Optically levitated particles are used in a wide range of experiments to explore both fundamental physics and to act as sensors to a variety of external forces. One field of particular interest that these particles can be used to investigate is quantum mechanics. Previous research has yet to set an absolute upper bound on the size of objects that can be prepared in a quantum superposition. Exploring this limit involves allowing ever-larger objects to freely and coherently evolve to assess if their behaviour matches quantum or classical theoretical predictions. However, the long free evolution times required for these behaviours to be visible result in the experiments being gravitationally limited. Space based platforms therefore become the next key step in these investigations. In this white paper, we shall discuss our proposal for an optical levitation experiment in space that will explore the fundamental upper size limits of quantum mechanics. We shall cover the scientific motivation behind these investigations, then summarize the current status of our designs for the satellite. We will then review the aspects of the payload that require further development, then summarize the current estimates of the payload's requirements.
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All authors Jack Homans, Laura da Palma Barbara, Jakub Wardak, Elliot Simcox, Tim M. Fuchs, Hendrik Ulbricht

Geophysics

Granite sliding on granite: friction, wear rates, surface topography, and the scale-dependence of rate-state effects

Sergey V. Sukhomlinov, Martin H. Müser and B.N.J. Persson

We study tribological granite-granite contacts as a model for tectonic faulting, combining experiments, theory, and molecular dynamics simulations. The high friction in this system is not dominated by particulate wear or plowing, as frequently assumed, but by cold welding within plastically deformed asperity junctions. We base this conclusion on the observation that wear is repeatedly high after cleaning contacts but decreases as gouge accumulates, while friction shows the opposite trend. Moreover, adding water reduces wear by a factor of ten but barely decreases friction. Thermal and rate-dependent effects-central to most earthquake models-are negligible: friction remains unchanged between -40{\deg}C and 20{\deg}C, across abrupt velocity steps, and after hours of stationary contact. The absence of rate-state effects in our macroscopic samples is rationalized by the scale-dependence of pre-slip. The evolution of surface topography shows that quartz grains become locally smooth, with height spectra isotropic for wavelength below 10 microns but anisotropic at longer wavelengths, similar to natural faults. The resulting gouge particles have the usual characteristic sizes near 100 nm. Molecular dynamics simulations of a rigid, amorphous silica tip sliding on {\alpha}-quartz reproduce not only similar friction coefficients near unity but also other experimentally observed features, including stress-introduced transitions to phases observed in post-mortem faults, as well as theoretical estimates of local flash temperatures. Additionally, they reveal a marked decrease of interfacial shear strength above 600{\deg}C.
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Instrumentation and Detectors

Characterization of cutting-edge CMOS Active Pixel sensors within the CYGNO Experiment

B.D. Almeida, F.D. Amaro, R. Antonietti et al. (+43 more)

Time Projection Chambers equipped with Gas Electron Multipliers and optical readout by scientific CMOS cameras are a promising technology for low-energy particle detection, as demonstrated by the CYGNO experiment. To help identify the optimal CYGNO detector configuration, we performed a detailed characterization of two state-of-the-art scientific CMOS sensors, focusing on dark-signal behavior across different exposure times and on detection sensitivity, assessed using the well-defined X-ray emissions from a 55Fe source, which reproduce the low-light conditions expected in CYGNO. CYGNO currently employs a very low-noise Hamamatsu sensor, the ORCA-Fusion, for testing and validation of its detection system. Hamamatsu has recently introduced two new sensors that may be of interest for future upgrades. The first is an improved version of the current model, the ORCA-Fusion-BT, featuring a back-illuminated design that reaches a quantum efficiency of up to 95% at 550 nm. The second is a next-generation sensor, the ORCA-Quest. Although its peak quantum efficiency is not as high as that of the Fusion-BT, it offers high sensitivity over a broader spectral range, extending into the ultraviolet region, and provides ultra-low readout noise of 0.27 electrons, about 2.6 times lower than that of the Fusion family. These two sensors therefore represent a significant opportunity to enhance the performance of scientific experiments, including those conducted by the CYGNO collaboration. This document presents a comprehensive characterization of these sensors to evaluate their relevance for experiments operating in photon-limited environments and their suitability for integration into the CYGNO detector system.
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All authors B.D. Almeida, F.D. Amaro, R. Antonietti, E. Baracchini, L. Benussi, S. Bianco, C. Capoccia, M. Caponero, L.G.M. de Carvalho, G. Cavoto, I.A. Costa, A. Croce, M. D'Astolfo, G. D'Imperio, E. Dane, G. Dho, E. Di Marco, J.M.F. Dos Santos, D. Fiorina, F. Iacoangeli, Z. Islam, E. Kemp, H.P. Lima Jr., G. Maccarrone, R.D.P. Mano, D.J.G. Marques, G. Mazzitelli, P. Meloni, A. Messina, C.M.B. Monteiro, R.A. Nobrega, I.F. Pains, E. Paoletti, F. Petrucci, S. Piacentini, D. Pierluigi, D. Pinci, F. Renga, R.J.C. Roque, A. Russo, G. Saviano, P.A.O.C. Silva, N.J. Spooner, R. Tesauro, S. Tomassini, D. Tozzi

Plasma Physics

Evolution of ion distribution functions in ionospheric plasmas perturbed by Alfvén waves

Dario Recchiuti, Luca Franci, Lorenzo Matteini et al. (+3 more)

This study investigates ion kinetic effects during the parametric decay instability (PDI) of parallel-propagating Alfvén waves under plasma conditions characteristic of the Earth's ionosphere. By using a series of hybrid particle-in-cell simulations, we examine the evolution of ion velocity distribution functions (VDFs) in ultra-low-beta plasmas. Our numerical campaign systematically explores the dependence on key parameters (plasma beta, pump-wave amplitude and polarization, and ion composition). To emphasize the role of kinetic effects, we choose to trigger the PDI with a dispersive mother wave with wavelength comparable to the ion characteristic inertial length. Our results reveal pronounced nonthermal VDF modifications, including parallel heating and the formation of secondary ion beams, linked to the nonlinear evolution of parametric decay instability. By varying the plasma beta and the pump-wave amplitude, we identify a critical regime where rapid and complete broadening of the velocity distribution function is observed, triggering bidirectional ion acceleration. Notably, simulations modeling realistic ionospheric conditions demonstrate that even low-amplitude Alfvénic perturbations can induce significant VDF spreading and ion beam generation, with hydrogen ions exhibiting stronger effects than oxygen. These nonthermal microscopic processes offer a plausible mechanism for particle precipitation in space weather events. This work represents the first comprehensive study with hybrid simulations of PDI-driven ion kinetics in ultra-low-beta plasmas, providing quantitative estimates for the time delay between electromagnetic wave impact and ion VDF modification and new insights into wave-particle interactions that may contribute to ion acceleration, precipitation processes and space plasma dynamics.
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All authors Dario Recchiuti, Luca Franci, Lorenzo Matteini, Emanuele Papini, Roberto Battiston, Mirko Piersanti

Instrumentation and Detectors · Cross-listed from hep-ph

The effect of Coulomb interactions on relic neutrino detection via beta decaying impurities in (semi)metals

Karel van der Marck and Vadim Cheianov

Measuring the electron neutrino mass is a long-standing objective and requires a high energy resolution of certain $\beta$-decay experiments, as well as a visible cosmic neutrino background (C$\nu$B) spectrum. Many quantum mechanical and chemical effects could potentially impair the required resolution/visibility, e.g., the Coulomb interactions between the electrons in the $\beta$-decaying impurity and in the solid-state environment. We analyze the effect when hybridization is suppressed completely using a dielectric spacer, and also when hybridization is present up to the lowest nontrivial order in perturbation theory.
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Atmospheric and Oceanic Physics

Buoy observation of high frequency ocean wave energy: accuracy, consistency, and concerns for predictive applications

W. Erick Rogers and Jim Thomson

Observational data from buoys are of primary importance during the development, calibration, and evaluation of ocean wave models, and these data are also used to make real-time corrections to operational models via data assimilation. By association, systematic inaccuracies in any buoy data are equally important, and thus when two buoy types provide systematically inconsistent information, this is a concern for anyone using an ocean wave model. This report is concerned with the accuracy of the high frequency portion of the ocean wave spectrum commonly observable by buoys, roughly 0.2 to 0.6 Hz. We evaluate four buoy types (two moored, two drifting) using two quantitative measures. The first involves comparing each type with a co-located ocean wave model. The second method involves evaluation of high frequency energy level as a function of wind speed. Both evaluation methods suggest that the Datawell Waverider (DWR) buoys have a strong tendency to report higher energy levels than the other three buoy types. We evaluate high frequency energy level using three different metrics (mean square slope, energy in a band of high frequencies, and spectral density at a single, specific band, 0.4 Hz), and the conclusions are found to be insensitive to the parameter used.
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Plasma Physics

Injection and Acceleration of Electrons by Radially Polarized Laser Pulses in a Plasma Channel

P. Hadjisolomou, P. Valenta, R. Shaisultanov et al. (+4 more)

We consider injection and subsequent acceleration of electrons in narrow plasma channels irradiated by linearly and radially polarized ultraintense laser pulses. Using three-dimensional particle-in-cell simulations, we show that radially polarized beams significantly promote electron release from the channel walls and lead to enhanced injection. We compare an f/10 linearly polarized laser beam with two radially polarized cases: one focused more tightly (f/5) to match peak intensity, and one at equal f/10 to capture polarization effects. The radially polarized f/10 case injects approximately one-third more charge than the linearly polarized case, while the f/5 radially polarized case outperforms the linearly polarized one by about a factor of two in terms of maximum electron energy. These results highlight polarization and focusing geometry as key parameters for optimizing laser-driven electron acceleration setups.
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All authors P. Hadjisolomou, P. Valenta, R. Shaisultanov, T. M. Jeong, D. Gorlova, C. P. Ridgers, S. V. Bulanov

Plasma Physics

Light drag in nonuniformly moving anisotropic media through the lens of gradient-index optics

Julien Langlois and Renaud Gueroult

The trajectory of light rays propagating through a nonuniformly moving anisotropic medium is determined by considering the Fresnel drag experienced by the wave at each point along the ray. By showing that symmetries in the velocity field manifest as symmetries in the effective wave index representing the moving medium, methods classically employed to model gradient index media are then used to obtain analytical forms for the ray trajectory. When applied to isotropic media, the results are verified to be consistent with those obtained using an optical (Gordon) metric. The potential of this method to model light rays in anisotropic media is finally demonstrated by considering waves in a nonuniformly moving magnetized plasma, exposing how nonuniform motion and anisotropy can compete with one another.
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Chemical Physics

Multidimensional tunnelling of molecules aligned by strong electric fields

J. Amira Geuther, Marit R. Fiechter and Jeremy O. Richardson

Strong electric fields can be used to align molecules. However, a non-polar molecule such as H$_2$ has no preference for its orientation. There are thus two equivalent configurations with equal energy separated by a potential-energy barrier. Quantum mechanically, the molecule can tunnel between these configurations resulting in a tunnelling splitting, which in the case of H$_2$, is the same as the ortho–para splitting. In this work, we generalize semiclassical instanton theory to calculate the energy splitting of molecules in electric fields in full dimensionality. This goes beyond a perturbative treatment of the field and takes into account changes in molecular geometry during the tunnelling process which influence its electrical properties and can have a significant impact on the result. We first study the case of H$_2$ in a static electric field and then show how it can be applied to larger polar molecules subjected to oscillating electric fields, where we find that even large-amplitude heavy-atom tunnelling can lead to observable splittings.
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Optics

Effects of Zero-Point Motion in the High Harmonic Generation Spectrum of Solids

Aday Cárdenas, David N. Purschke, Graham G. Brown et al. (+3 more)

The interpretation of high-harmonic generation (HHG) in solids typically relies on phenomenological dephasing times far shorter than what is expected from microscopic scattering processes. Here we show that zero-point fluctuations associated with optical phonons naturally suppress long-range electronic coherences and generate clean harmonic spectra without introducing ad-hoc decoherence parameters. Using a 1D semiconductor composed of two distinct sites per unit cell and realistic phonon amplitudes, we demonstrate that random per-site optical-phonon jitter reproduces the spectral sharpening typically attributed to ultrafast $T_2$ dephasing. In contrast, acoustic phonons and local strain, whose distortions are correlated over nanometer scales, produce negligible spectral cleaning. We further show that such long-range site coherence leads to carrier-envelope-phase-dependent effects in the HHG spectrum driven by long pulses, but these effects collapse once optical-phonon-induced decoherence is included. Our results (i) identify optical zero-point motion as a key mechanism governing coherence in solid-state HHG, (ii) demonstrate that it can be qualitatively modeled in periodic solids through site-distance-dependent dephasing, and (iii) suggest that CEP-resolved measurements can probe electronic coherence lengths and atomic fluctuations in crystalline materials.
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All authors Aday Cárdenas, David N. Purschke, Graham G. Brown, Pablo San-Jose, Rui E.F. Silva, Álvaro Jiménez-Galán

Geophysics

Slip, Differentiate, Observe: State and Parameter Estimation for Rate and State Friction from Noisy Data

David Michael Riley, Diego Gutiérrez-Oribio and Ioannis Stefanou

Quantifying frictional properties of interfaces remains a major challenge in both terrestrial and extraterrestrial geomechanics, where available samples, laboratory apparatuses, and geophysical observations are inherently limited. We introduce an analytic and numerical framework, grounded in nonlinear control theory, to infer the emergent frictional behavior of seismic faults. From noisy slip measurements, we first reconstruct the slip rate and frictional response in finite time using a Robust Exact Filtering Differentiator (REFD) that attenuates measurement noise. Building on these reconstructions, we design an exponentially convergent adaptive-gain observer that estimates the internal state variable and the key parameters (a - b) and dc of the rate-and-state friction (RSF) law, widely used in fault mechanics. Numerical experiments show that, in fast slip regimes where data are sufficiently rich, the method recovers RSF parameters with errors on the order of 20% and accurately tracks the RSF state variable despite noise contamination, whereas slowly varying sliding periods lack the observability required for reliable estimation. We also establish observability and identifiability conditions for the extended system, enabling the determination of additional parameters and outlining pathways for more advanced control-theoretic approaches to friction and state identification in fault systems. Although we apply the approach to a reduced spring-slider analogue, it improves on classical RSF calibration methods that depend on laboratory access to shear and normal stress. It also offers convergence guarantees and explicit error bounds, and it can further support model-based inversions that embed RSF in forward simulations.
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Applied Physics

Optical modulation of Gate-Induced Electron Trapping via Persistent Photoconductivity in STO/AlOx Heterostructures

Peiwen Luo, Huizhong Zeng, Bin Peng et al. (+2 more)

The dynamic interplay between light and electric field control of charge states lies at the heart of developing multifunctional optoelectronic devices. While persistent photoconductivity (PPC) and gate-voltage (VG)-induced electron trapping are well-known phenomena in oxide heterostructures, their mutual coupling remains poorly explored. Here, we report that the non-equilibrium state established by PPC can effectively modulate the efficacy of VG-induced electron trapping in a STO/Al heterostructure. The PPC, characterized by a slow relaxation (8.5 hours at 4 K) after sub-illumination, originates from the re-trapping of photoexcited carriers into deep-level states. In contrast, VG-induced trapping, governed by shallow states, exhibits much faster dynamics ({100 - 400 s). Crucially, we discover that the strength of VG-induced trapping is not constant but is dynamically modulated by the PPC relaxation process. The trapping amplitude is strongly amplified after illumination and recovers only after the deep-level states are substantially refilled, precisely following the PPC relaxation time constant. Furthermore, the electron trapping effect diminishes with increasing temperature and vanishes near the ferroelastic phase transition of STO (110 K), confirming that ferroelastic twin walls and associated oxygen vacancy clusters are the physical origin of the traps. Our findings reveal a novel optical gating mechanism for electron trapping, paving the way for designing non-volatile, optically programmable electronic devices.
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All authors Peiwen Luo, Huizhong Zeng, Bin Peng, Wanli Zhang, Wenxu Zhang

Optics

Approaching the Low Optical Loss Limit of Plasmonics using Potassium Metals

Yuhan Yang, Yi Zhang, Yuhong Shi et al. (+7 more)

Plasmonics enables the miniaturization of photonic devices beyond the optical diffraction limit,yet its potential is hindered by inherently large ohmic losses. Hence, it is prudent to explore low loss alternatives to the current mainstay of plasmonics-the noble metals. In this work, we demonstrate the potential of potassium as a plasmonic material with intrinsically low losses in the optical region. The ultraflat, high quality potassium film, fabricated via a rapid slipping-assisted oxide-free crystallization process, achieves an experimentally observed optical damping rate of 3.7 meV,with a measured imaginary permittivity of approximately 0.1 across the entire visible to near-infrared range (400-2000 nm). Near field optical spectroscopic measurements further confirmed the reduced losses by revealing deeply subwavelength confinement of optical modes. This result enhances our understanding of the factors governing plasmonic materials and devices and establishes a new platform for exploring extreme light-matter interactions in a variety of plasmonic systems.
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All authors Yuhan Yang, Yi Zhang, Yuhong Shi, PengCheng Yao, Hanyu Fu, Jacob B. Khurgin, Fengrui Hu, Jia Zhu, Shining Zhu, Lin Zhou

Applied Physics

Self-Organized Freeform Waveguiding

Fadhila Chehami, Cyril Decroze, David R. Smith et al. (+1 more)

Nature offers remarkable examples of complex photonic architectures such as those responsible for the iridescent colors of butterfly wings that emerge spontaneously during growth, well before any centralized control takes place. Arising from local rules, these structures exhibit advanced optical functionalities, such as photonic band gaps, without relying on in-situ optimization or top-down design. Inspired by biological morphogenesis, we introduce an optimization-free approach for the automated generation of self-organized freeform waveguides that adapt to complex propagation paths. Our method relies on local reaction-diffusion dynamics to produce robust, spatially distributed structures. In contrast to conventional waveguides based on periodic media, which impose strong geometric constraints and require extensive fine-tuning, the proposed structures support nontrivial geometries while maintaining photonic band gap behavior. We experimentally demonstrate that these self-organized waveguides achieve superior transmission efficiency along complex paths. This optimization-free strategy enables the automated design of advanced electromagnetic components with intrinsic adaptability and resilience.
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All authors Fadhila Chehami, Cyril Decroze, David R. Smith, Thomas Fromentèze

Optics

Transient laser-induced periodic surface structures revealed by time-resolved EUV diffuse scattering

D. Ksenzov, F. Capotondi, A. A. Maznev et al. (+12 more)

The formation of permanent laser-induced periodic surface structures (LIPSS) on solid surfaces under impulsive laser irradiation above the damage threshold has been subject of extensive research. We demonstrate the formation of transient surface displacement patterns under femtosecond laser irradiation at fluences well below this threshold. Time-resolved extreme ultraviolet scattering measurements reveal distinct reciprocal-space features similar to those observed for permanent LIPSS but dissipating on the hundreds-of-picoseconds time scale. We show that the transient surface displacement patterns responsible for these features are produced via thermal expansion by the spatial modulation of absorbed laser intensity caused by scattering of the laser radiation by surface roughness and present a model accounting for the experimental observations. We suggest that our experiment revealed a universal phenomenon that will be observed on any strongly absorbing material under ultrafast laser irradiation.
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All authors D. Ksenzov, F. Capotondi, A. A. Maznev, F. Bencivenga, D. Engel, D. Fausti, L. Foglia, R. Gruber, N. Jaouen, M. Kläui, I. Nikolov, M. Pancaldi, E. Pedersoli, B. Pfau, C. Gutt

Optics · Cross-listed from quant-ph

Formal equivalence between Maxwell equations and the de Broglie-Bohm theory for two-dimensional optical microcavities

Aurélien Drezet and Bernard Michael Nabet

We analyze the formal equivalence between the electromagnetic energy conservation law derived from Maxwell's equations in an optical microcavity and the conservation of a probability fluid associated with the de Broglie-Bohm theory for an effective massive particle describing a photon in this cavity. This work is part of a critical analysis of recent experiments [Nature 643, 67-72 (2025)] carried out with a view to refuting the de Broglie-Bohm theory. Furthermore, the consequences of our analysis for microphotonics go far beyond these experiments. In particular, extensions that take into account photon spin and stochastic aspects associated with radiative or absorption losses are considered.
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Accelerator Physics

Impact of local bunching factors in single-pass THz free electron lasers

Xiangkun Li and Mikhail Krasilnikov

In simulations for modern free-electron lasers (FEL), shot noise plays a crucial role. While it is inversely proportional to the number of electrons, shot noise is typically modeled using macroparticles, with their bunching factors corresponding to the bunching factors of the much larger number of electrons. For short-wavelength FELs, the macroparticles are assumed to be uniformly distributed on the scale of the resonant wavelength, since shot noise dominates the initial radiation - for instance, in the self-amplified spontaneous emission (SASE) regime. In this paper, we show that this assumption does not hold at longer wavelengths, particularly in the THz range, where the bunch current profile is not uniform even within the length of the resonant wavelength. Instead, the current profile dominates the initial bunching factors, which can be several orders of magnitude higher than shot noise. The slice-based bunching factors and bunching phases are derived for Gaussian distributions and compared with shot noise under the assumption that the current within each slice remains constant. Using the THz FEL at the photoinjector test facility at DESY in Zeuthen (PITZ) as a case study, the influence of the current profile has been benchmarked through simulations under very low bunch charge, where the full number of electrons can be modeled using the Genesis1.3 code. Additional simulations with the nominal working parameters of PITZ THz FEL have been compared with experimental data, indicating better agreement when the actual current profile is taken into account.
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Biological Physics

From Toggle to Tuning: Controlling Turing Patterns in Gene Circuits

Antonio Matas-Gil and Robert G. Endres

Controlling spatial patterns in synthetic biological systems remains challenging due to poor parameter robustness and limited experimental tunability. We introduce two complementary mechanisms-the pattern switch and the pattern dial-to systematically control Turing pattern formation in gene circuits. The switch toggles pattern onset via a single parameter, while the dial enables transitions between distinct pattern types using weakly nonlinear amplitude equations. Analyzing network size reveals a key trade-off: small networks are easier to control but less robust, while larger networks gain robustness at the cost of tunability-suggesting a sweet spot for both evolvability and designability. Our results offer practical design rules for engineering programmable patterns in living systems.
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