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Physics Physics

physics Watch Physics

Wednesday 1 July

Geophysics

The effect of 20th century industrialization: Power station, acid rains, over-pumping, on an erstwhile uniform freshwater dune aquifer in Haifa Bay, Israel

Vasily Rogojin and Joel Kronfeld

A small phreatic sand dune aquifer lies along the shore of Haifa Bay. It has been exploited for its freshwater resources since the 1930s. During this time the salinity has increased continuously, partly by seawater intrusion due to overpumping. The chemistry of the young aquifer water is laterally variable and is characterized by excess SO$_4^{2-}$, high $Sr^{2+}$ concentrations above that of modern seawater, high alkalinity, and markedly enriched $\delta^{13}C_{DIC}$ values. Acidic winter rains, formed from $SO_x$ and $NO_x$ gaseous emissions from a nearby power station, leach the dry deposition that accumulated across the dune surface during the dry summers. The acidity also partially dissolves the aragonite sea shells in the dune sands, remnants of a previous marine transgression. As a consequence, this adds $Sr^{2+}$, $Ca^{2+}$ excess, and alkalinity, while leading to enriched $\delta^{13}C_{DIC}$ values, particularly during the winter, at which time the radiocarbon activity in the DIC is observed to decrease.
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Data Analysis and Statistics · Cross-listed from hep-ex

Modeling Falling Backgrounds with Exponential Mixtures

Austin Townsend, Marc Osherson, Mike Hildreth et al. (+1 more)

Searches for new physics at the LHC often look for localized excesses on smoothly falling background distributions. Several classes of background models have been considered, including polynomials and other parametric families; however, these approaches can require extensive analysis-specific development as datasets grow. In this work, we motivate the finite exponential mixture as a flexible semi-parametric class of functions for approximating falling distributions, drawing on results from extreme value theory. Using two published datasets ($n=28,619,185$ and $n=5,036$), we show that the exponential mixture performance is comparable to existing methods for both small and large datasets. Finally, in simulation studies ($n = 5,036$), we find that the finite exponential mixture exhibits small bias relative to the true statistical uncertainty while maintaining consistent nominal coverage in the bulk.
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All authors Austin Townsend, Marc Osherson, Mike Hildreth, Stefano Castruccio

Plasma Physics

Reexamination of collisional ionization cross sections including double photoionization processes

Lucas Ansia, Pedro Velarde, Marta Fajardo et al. (+1 more)

Collisional ionization (CI) cross sections in dense plasmas remain difficult to constrain due to uncertainties in plasma conditions and the overlapping spectral signatures of competing atomic processes. The use of x-ray free electron lasers (XFELs) to both heat and probe solid-density targets has significantly advanced the field by eliminating assumptions about ion density. However, questions remain regarding collisional cross sections, suprathermal electron evolution and competing atomic processes. In this work, we revisit experimental data from XFEL-heated aluminum, previously analyzed using collisional radiative models that did not treat the degenerate electron distribution and atomic processes self consistently. We present a new analysis using BibBarT which dynamically evolves non-thermal electron populations and explicitly includes degeneracy effects. Furthermore, we incorporate an important atomic process recently observed in plasma state that mimic signatures of CI, shake-off. Our results show that including shake-off processes improves agreement with observed emission features, and lowering recombination rates further improves the agreement with data – indicating a possible overestimate of three-body recombination in these conditions.
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All authors Lucas Ansia, Pedro Velarde, Marta Fajardo, Gareth Williams

Fluid Dynamics · Cross-listed from astro-ph.GA

Kolmogorov turbulence across multi-fractal gas in Polaris Flare

Xunchuan Liu, Pak-Shing Li and Yihuan Di

We reveal a pristine, scale-invariant 3D Kolmogorov velocity cascade ($\alpha_V^{\mathrm{3D}} \sim 2/3$) spanning $0.05$–$20$~pc in the Polaris Flare using PPCOS $^{12}\text{CO}$ data. A transition scale at $\sim 0.5$~pc marks a bifurcation in the structure functions' exponents, below which the degree of intermittency is also saturated. By deriving an analytical mapping relation ($\alpha_V^{\mathrm{3D}}=\alpha_V-\frac{1}{3}\alpha_I$), we obtain the scale-invariant value of $\alpha_V^{\mathrm{3D}}$, proving that the apparent transition stems from geometric projection and a changing density fractal dimension rather than a turbulent mode shift. Kolmogorov turbulence is smoothly inherited from the large-scale cold neutral medium, remaining uninterrupted by compression or gravity below 0.1 pc.
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Instrumentation and Detectors

Real-Time FPGA-Based SiPM Detector Emulation Using a Temporally Quantized Model

Stefano Carsi, Edoardo Proserpio, Andrea Abba et al. (+2 more)

We present a real-time hardware implementation of a versatile detector emulator capable of reproducing realistic silicon photomultiplier signals. Our approach builds upon the open-source SimSiPM framework, originally developed to simulate the microscopic response of silicon photomultipliers, including photon detection efficiency, optical crosstalk, afterpulsing, and dark counts. SimSiPM provides idealized photon-level data with arbitrary temporal and amplitude resolution. In contrast, our emulator, built on a field-programmable gate array, translates this fine-grained simulation into physically realizable analog signals, maintaining real-time operation and finite hardware resolution. The system receives simulated photon events either via a 10-gigabit Ethernet stream or directly from the processing system of a system-on-chip, and performs on-chip temporal quantization, dividing time into bins equal to one clock cycle. All photon hits within a bin are accumulated, and their contribution is combined through a weighted temporal averaging scheme that preserves sub-bin precision. Signal shaping is executed entirely in hardware, using parallel one-pole recursive filters that synthesize the rise and the two decay components of the response. The resulting waveform is converted to analog through dual 16-bit digital-to-analog converters operating at 2.5 gigasamples per second. This architecture generates physically accurate detector signals in real time, rather than replaying precomputed waveforms. It also generalizes beyond silicon photomultipliers, providing a flexible framework for hardware-in-the-loop testing of front-end electronics. The proposed implementation demonstrates high throughput, low latency, and minimal processor overhead.
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All authors Stefano Carsi, Edoardo Proserpio, Andrea Abba, Francesco Caponio, Valentina Arosio

Biological Physics

Dynamical noisy canalization in morphogenesis: lessons from Hydra regeneration

Oded Agam and Erez Braun

Developmental robustness is framed as progress through a fixed Waddington-type landscape. We argue that in morphogenesis this landscape evolves through coupled bio-signaling, mechanical, and physiological processes, while fluctuations aid exploration. In Hydra regeneration, stochastic Ca activity plays a major role in reshaping the landscape of accessible morphologies as regeneration unfolds, including the early progressive confinement of tissue fluctuations. We propose testing this framework of dynamical noisy canalization in developmental systems.
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Optics

Axion Polarimetric Experiment (APE)

Qazal Rokn, Ryan Netrval, Aldo Ejlli et al. (+1 more)

We present the Axion Polarimetric Experiment (APE), a cavity-enhanced polarimeter designed to search for ultralight axion and axion-like-particle dark matter through a time-dependent rotation of the linear polarization of laser light. In cavity-based schemes, intracavity quarter-wave plates can restore coherent buildup of the axion-induced orthogonal polarization, but their transmissive loss limits the achievable finesse. To avoid transmissive intracavity optics, we propose a folded Fabry-Perot cavity that employs dielectric phase-shifting mirrors. At an incidence angle near $45^\circ$, these mirrors provide a reflection-phase difference $\Delta\phi \equiv \phi_s-\phi_p \simeq \pi/2$ between $s$ and $p$ polarizations and therefore act as reflective quarter-wave plates. We present the coating design, thickness optimization, and measurements of the phase shift and optical loss of the phase-shifting mirrors. Using a heterodyne polarimetric readout and an explicitly stated noise model, we derive design-level sensitivity projections for the axion-photon coupling $g_{a\gamma\gamma}$. These projections should be interpreted as target sensitivities for the proposed cavity configuration, since the full-system birefringence noise and angular-jitter coupling remain to be measured.
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All authors Qazal Rokn, Ryan Netrval, Aldo Ejlli, Guido Mueller

Fluid Dynamics

Visualization of Inertial and Kelvin Waves on the Quantum Vortex Lattice in Superfluid Helium

Florian Lorin, Charles Peretti, Corentin Bourjaillat et al. (+3 more)

Superfluid $^4$He subjected to steady rotation develops a regular lattice of quantum vortices aligned with the rotation axis. We prepare this lattice in a rotating cryostat, perturb it with a constant heat flux, and visualize vortex deformation waves that propagate in the lattice and grow in energy with the forcing. Below twice the rotation rate, we show that these waves feature a continuous frequency spectrum whose structure corresponds to inertial waves. At larger frequencies, we report several observations suggesting the presence of Kelvin waves over a continuous range of frequency. These results, obtained through space- and time-resolved velocity measurements of quantum vortex lines, appear as quantitative constraints for modern two-way coupled vortex filament models. They further offer new insights into perturbed quantum vortex systems in three-dimensional quantum fluids.
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All authors Florian Lorin, Charles Peretti, Corentin Bourjaillat, Patrik Švančara, Pierre-Philippe Cortet, Mathieu Gibert

Chemical Physics

Inelastic electron scattering induced quantum coherence: isotope effect

Akshay Kumar and Vaibhav S. Prabhudesai

Recent discoveries of electron-induced coherence in both resonant and non-resonant interactions have introduced new perspectives in the field. In non-resonant processes, coherence has been observed in dipolar dissociation, where electron-induced excitation forms a coherent superposition of states of opposite parities, resulting in asymmetry in the angle-differential cross-section of the process relative to the incident electron beam. Notably, an isotope effect has been observed in $D_2$ at 50 eV, where heavier isotopes exhibit diminished asymmetry due to their longer dissociation times. Here, we report the isotope effect on quantum coherence in $D_2$ across different electron energies. Additionally, we investigate the role of coherence in the isotopologue HD. Our findings reveal that the asymmetric masses in HD do not influence electron-impact excitation, leading to similar asymmetry in the angular distributions of $H^-$ and $D^-$ ions. This observation is explained by the homonuclear-like behavior of HD within the Franck-Condon region.
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Space Physics · Cross-listed from astro-ph.IM

A First-Order Assessment of Permanent Magnet Deflection for Space Radiation Protection

Valerio Parisi, Roberto Capuzzo Dolcetta, Fabrizio Frezza et al. (+1 more)

We present a preliminary feasibility assessment of a magnetic shield designed to protect a space probe from cosmic radiation via magnetic deflection using neodymium permanent magnets. This work is grounded in theoretical considerations whose preliminary indications are intended to serve as the basis for future Monte Carlo simulations and laboratory validation. The novelty of our approach lies in the use of a magnetic shield; its competitiveness with conventional passive absorbing shielding is not investigated here but warrants dedicated future work. The primary objective is to protect a spacecraft from the flux of charged particles emitted by the Sun. To this end, we combine theoretical modeling and numerical simulations, followed by the construction of a prototype for laboratory testing and, potentially, for future experimental validation at the CubeSat scale.
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All authors Valerio Parisi, Roberto Capuzzo Dolcetta, Fabrizio Frezza, Luca Lunati

Atomic Physics · Cross-listed from cond-mat.mtrl-sci

The BiP-PRISM algorithm for fast and scalable core-loss STEM-EELS simulations

Philipp Pelz

Quantitative interpretation of atomic-resolution STEM-EELS requires dynamical simulation of the electron probe before and after core-loss transitions, which is computationally expensive. While the PRISM algorithm accelerates this by reusing scattering matrices, we introduce beam partitioning for both the probe-forming ($\mathcal{S}_1$) and detector-propagating ($\mathcal{S}_2$) PRISM matrices to further reduce computational and memory costs. Each matrix is calculated on a sparse set of parent beams and reconstructed via natural-neighbor interpolation locally at the ionized atom. A locality result demonstrates that the total error is governed entirely by this on-atom reconstruction error. The resulting BiP-PRISM algorithm removes per-scan exit wave propagation and significantly reduces memory requirements, enabling full-resolution elemental mapping, 4D cubes, and momentum-resolved qEELS on consumer-grade GPUs. We characterize the approximation's validity regime and demonstrate the simulation of a multimodal five-edge oxide-interface map and an FePt nanoparticle Fe-L map at 5x memory reduction, showing that the algorithm achieves high accuracy with significantly lower computational demands.
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Computational Physics

LSR-Net: Long-Short-Range Operator Learning for Pattern Dynamics on Manifolds

Qian Serena Hou and Zecheng Gan

We propose the Long-Short-Range Neural Network (LSR-Net), an extensible operator-learning framework for predicting pattern dynamics on planar domains, spherical surfaces, and general manifolds. The method decomposes the forward evolution operator into a long-range component, represented by a compact Fourier multiplier constructed via the Sum-of-Exponentials (SOE) approximation, and a short-range component adapted to the underlying geometry and its intrinsic symmetries. For general manifolds represented by irregularly sampled point clouds, the long-range component is implemented by Gaussian gridding onto an auxiliary regular grid, where the Fourier multiplier is efficiently applied in k-space using FFT and the result is interpolated back to the original sample points. We evaluate LSR-Net on several benchmark systems, including the Allen-Cahn, Cahn-Hilliard, Schnakenberg, and Turing systems, over planar domains, spherical surfaces, and a blob-shaped manifold. Numerical results demonstrate that LSR-Net consistently achieves higher accuracy and improved stability compared with baseline operator-learning models. In particular, for Allen-Cahn dynamics on the sphere, the RMSE is reduced by approximately three orders of magnitude compared with the Spherical Fourier Neural Operator (SFNO). Rotation and reflection equivariance tests further confirm that the learned operator is consistent with these geometric transformations. These results indicate that LSR-Net provides an effective and robust approach for learning pattern dynamics on complex geometries.
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Instrumentation and Detectors

Development for the Belle II vertex detector upgrade with depleted monolithic active pixel sensors

Y. Onuki, M. Babeluk, T. Bergauer et al. (+85 more)

The vertex detector upgrade project for the Belle II experiment, based on CMOS depleted monolithic active pixel sensor technology, is planned to be carried out in conjunction with the major modification of the interaction region of the SuperKEKB collider during Long Shutdown 2 from 2032 to 2034. The MAPS sensor, named OBELIX currently under development, is derived from the successor to TJ-Monopix2, with modifications implemented to ensure compatibility with the Belle II trigger system. The new vertex detector consists of two layers of four self-supported consecutive OBELIX sensors, and three layers of discrete OBELIX sensors mounted on mechanical support structures with readout flex circuits attached to the sensors. The detector is arranged cylindrically around the beam pipe at radii ranging from 14 mm to 140 mm. The minimization of the material budget is required in order to enhance physics performance. We present an overview of the project and its latest developments, with particular emphasis on the development of low-material-budget flex circuits employing aluminum conductors.
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All authors Y. Onuki, M. Babeluk, T. Bergauer, M. Friedl, C. Irmler, B. Pilsl, R. Russo, C. Schwanda, L. Gaioni, V. Re, E. Riceputi, G. Traversi, S. Giroletti, L. Ratti, G. F. Benfratello, S. Bettarini, F. Bosi, G. Casarosa, L. Corona, F. Forti, A. Gabrielli, M. Massa, L. Massaccesi, M. Minuti, A. Moggi, S. Mondal, G. Rizzo, M. Rovini, A. Taffara, M. Barbero, P. Barrillon, R. Boudagga, P. Breugnon, D. Fougeron, P. Pangaud, J. Serrano, V. Vobbilisetti, D. Xu, D. Auguste, J. Bonis, Y. Peinaud, M. Winter, J. Baudot, G. Bertolone, A. Dorokhov, G. Dujany, L. Federici, C. Finck, A. Himmi, C. Hu-Guo, A. Kumar, M. Maushart, F. Morel, H. Pham, I. Ripp-Baudot, R. Sefri, P. Stavroulakis, I. Valin, F. Bernlochner, C. Bespin, J. Dingfelder, T. Kishishita, H. Krüger, L. Schall, M. Vogt, M. Karagounis, Y. Buch, A. Frey, B. Schwenker, M. Schwickardi, K. Hara, D. Jeans, K. R. Nakamura, Y. Okazaki, T. Higuchi, S. Wang, C. Lacasta, C. Marinas, J. Mazorra de Cos, L. Molina-Bueno, A. Bevan, M. Bona, D. Howgill, W. Song, J. Gong, X. Gao, A. Fernandez Prieto, A. Gallas Torreira

Optics

On-Demand Coherent Nanolaser Metalens and Beam Steering Enabled by Physics-Informed Neural Networks

Omar A. M. Abdelraouf

The integration of artificial intelligence with physical modeling offers a transformative route for accelerating the design of active nanophotonic devices. Here, we present NanoPhotoNet-Lase, a physics-informed neural network (PINN) framework that embeds the electromagnetic and rate equations of lasing directly into its learning process to expedite the design of metasurface nanolasers. By coupling Maxwell's vector Helmholtz equation with the four-level population dynamics of dye gain media, the model achieves physics-guided prediction of optical responses, enabling rapid estimation of lasing thresholds across arbitrary nanostructure geometries and material configurations. Using high-index metasurfaces cavity, the NanoPhotoNet-Lase model identifies optimized geometries supporting quasi-bound states in the continuum (BICs) with strong confinement and high-quality factors. The predicted lasing was experimentally realized using Rhodamine B dye as gain medium. The measured lasing threshold (Pth = 565 uJ/cm2) and emission wavelength of 620 nm exhibited below 1% deviation from model predictions. Importantly, the framework enables design phase-gradient nanolaser metalens and beam steering that demonstrated coherent, directional, focused or steered emission. This work bridges physics-informed machine learning with experimental nanophotonics, establishing a scalable paradigm for real-time, physically interpretable design of coherent light-emitting metasurfaces.
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Optics

Universal Design Path for Optomechanical Crystals and One-dimensional Photonic Crystals

Berke Demiralp, Nien-Hsuan Lee and Eva M. Weig

We have shown a pattern that connects the refractive index, area and the cavity modes of the optomechanical crystals (OMCs) by the same order function. By keeping the fundamental and second cavity modes within a range of -+16 nm and -+23 nm we have shown the link between the design area of the OMC and the refractive index of the material, by keeping the design area same we have shown the link between the refractive index and the cavity mode wavelength and by keeping the refractive index the same, we have shown the link between the cavity mode wavelength and the design area. We have performed simulations for 2 different OMC designs and 10 different refractive indices (9 different materials) to prove the first two claims and we have performed both simulations and experiments on a 3C-SiC OMC, which resulted as 100 nm shift of the second cavity mode, to prove the last claim. Our findings prove that a universal design for optomechanical crystals is possible, making the transition to different material bases easier to exploit their specific properties, suggesting a path to commercialize such devices for hybrid quantum technologies and having flexibility of tuning such devices for their own relative applications.
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Optics

Near-Field Characterisation of Guided Modes in WS2 Nanobeams and Quasi-Bulk Crystals

Zara S. Taylor, Luke M. Hallacy, Xuerong Hu et al. (+7 more)

The exceptionally high in-plane refractive index, low sub-bandgap absorption, and strong optical anisotropy of WS2 make it a promising material platform for next-generation integrated circuits for nanophotonics. Its layered van der Waals structure further enables heterogeneous integration with silicon photonics and emerging two-dimensional optoelectronic materials. However, despite increasing interest in the waveguiding properties of WS2, experimental studies of wavelength-dependent modal confinement and attenuation remain limited. Additionally, though the extinction coefficient of WS2 is expected to be near-negligible beneath the bandgap, reported values span orders of magnitude, leading to large uncertainty in predicted modal decay lengths and wafer-scale integration feasibility. To resolve these ambiguities we perform hyperspectral cavity-enhanced imaging, determining high-resolution upper and lower bounds on the extinction coefficient of WS2 within the visible-NIR edge. We further employ scattering-type scanning near-field optical microscopy (s-SNOM) to probe TE0, TM0, and higher-order modes in both quasi-bulk and nanobeam WS2 waveguides across the 800-1400 nm spectral range, enabling identification of mode-specific trends in wavevector dispersion and loss. This work simultaneously assesses s-SNOM as a probe of waveguide performance, and we find that while absolute loss values depend on measurement geometry, s-SNOM reliably captures relative modal trends and provides upper bounds on propagation loss, supporting its use as a diagnostic tool for anisotropic waveguides. We further identify significant artefacts in nanobeam measurements arising from transverse interference and spatial sampling effects when the structure size approaches the excitation wavelength, which can shift extracted effective indices by up to 0.25.
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All authors Zara S. Taylor, Luke M. Hallacy, Xuerong Hu, Oliver T. Williams, Simone Strohmair, Fabian Felixberger, Alexander J. Knight, Timothy Chester-Parsons, Luke R. Wilson, Alexander I. Tartakovskii

Instrumentation and Detectors

In-Situ Polarimetry in Collimated Magneto-Infrared Spectroscopy System

Zeping Shi, Wenbin Wu, Zhiwei Zhang et al. (+14 more)

Magneto-infrared spectroscopy under strong magnetic fields provides a powerful probe of Landau quantization and field-induced collective excitations, yet its full potential has long been constrained by the lack of in-situ polarization control, because the highly divergent infrared beam propagating through narrow light tubes undergoes multiple wall reflections, leading to severe polarization degradation. Here we report a collimated magneto-infrared spectroscopy system that integrates continuous in-situ polarimetry. The system employs incident and exit collimation chambers forming a Kepler type optical architecture, which converts the large-aperture FTIR output into a low-divergence beam and strongly suppresses multi-reflection trajectories inside long gold-plated light tubes, thereby enhancing both optical throughput and polarization fidelity. A remotely controlled polarization module, consisting of an automated linear polarizer and a switchable Fresnel rhomb positioned entirely outside the high-field region, enables continuous in-situ tuning between linear, circular, and arbitrary elliptical polarization states without thermal cycling, manual realignment, or breaking vacuum. Interchangeable compact focusing modules further support Faraday and Voigt geometries in both transmission and reflection experiments within a 50 mm magnet bore, providing efficient beam focusing and signal collection while maintaining polarization fidelity. The setup achieves a minimum root-mean-square noise of 0.0033%, an average noise of 0.0082%, and a linear polarization extinction ratio up to 40:1. We demonstrate the capability through continuous in-situ linear polarimetry and broadband circular polarimetry in the magneto-infrared spectroscopy of various single crystals. This platform establishes a robust experimental framework for in-situ polarization-resolved magneto-infrared spectroscopy.
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All authors Zeping Shi, Wenbin Wu, Zhiwei Zhang, Yuhan Du, Chenyao Xu, Congming Hao, Xiangyu Jiang, Xin Chen, Guangyi Wang, Mingsen Zhou, Chunhui Pan, Wei Lu, Hao Shen, Haifeng Pan, Zhenrong Sun, Junhao Chu, Xiang Yuan

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

Spinterface-like mechanism of the chirality-induced spin selectivity in donor chiral-bridge acceptor complexes

Subhajit Sarkar, Oliver L. A. Monti and Yonatan Dubi

The chirality-induced spin selectivity (CISS) effect has been invoked to explain recent reports of differences in the time-resolved EPR signals between chiral and achiral molecules. However, the microscopic origin of these differences and their connection to CISS remains contested, particularly since these systems lack a metal interface. Here we introduce an intramolecular spinterface-like mechanism that naturally arises within donor-chiral bridge-acceptor (D–$\chi$B–A) complexes and quantitatively reproduces experimentally reported observed spin polarization in time-resolved EPR studies. In our two-electron Lindblad model, the photoexcited charge-transfer electron traversing the chiral bridge exchanges with the residual donor electron, which acts as a localized magnetic moment analogous to an induced magnetic moment on an electrode surface. The resulting through-bridge charge current produces an effective solenoidal field at the donor–bridge interface, breaking spin degeneracy and directional symmetry, thus enabling spin-selective transport without invoking intrinsic spin-orbit coupling on the bridge. We show that the interplay between this current-induced field, donor thermalization (which breaks time-reversal symmetry), and bridge spin mixing yields tens-of-percent polarization over realistic experimental conditions and charge-transfer time scales, matching reported CISS signatures in triads and DNA hairpins. By explicitly resolving the dependence on solenoidal coupling strength, temperature, and spin-mixing rates, the model identifies the regime in which internal spinterfaces can generate robust CISS-like spin filtering. These findings demonstrate that CISS-like signals in isolated D–$\chi$B–A complexes are fully compatible with a spinterface mechanism, providing a unified conceptual framework for interpreting both device-based and molecule-internal CISS platforms.
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Atmospheric and Oceanic Physics · Cross-listed from astro-ph.EP

Unveiling the Mysteries of Lightning: Exploring its fundamental Physical Processes with SKA-LOW

Brian M Hare, Sjoerd Bouma, Stijn Buitink et al. (+15 more)

Lightning is a surprisingly poorly understood phenomena. It consists of a wide variety of complex processes such as initiation, propagation, connection to ground, even emission of high-energy radiation. However, due to the extreme challenges in observing lightning at fast time scales, small spatial scales, and behind obscuring clouds, these processes are not well understood. In the past, interferometers such as the LOFAR radio telescope have provided unique insight and discoveries into the physics of lightning. The new SKA-LOW being built in western Australia will provide unrivaled spectral bandwidth and sensitivity, which will be combined with high resolution resulting from large antenna baselines. We will use SKA-LOW to observe lightning in order to explore its fundamental plasma physics, such as how it initiates and propagates. SKA's high bandwidth will allow us to test how lightning emits VHF radiation, giving tremendous insight into precisely how the plasma behaves. SKA's sensitivity will allow us to explore extremely faint lightning processes, such as the very first radio emission from a lightning flash. Here, we detail the lightning physics that can be explored with SKA, as well as the observation strategy needed explore such physics.
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All authors Brian M Hare, Sjoerd Bouma, Stijn Buitink, Arthur Corstanje, Steve Cummer, Joseph Dwyer, Vital De Henau, Tim Huege, Philipp Laub, Ningyu Liu, Marten A.A. Lourens, Katie Mulrey, Anna Nelles, Olaf Scholten, Chris Sterpka, Karen Terveer, Paulina Ťureková, Keito Watanabe

Optics

Self-selected phase-matched second harmonic generation in nonlinear optical materials: from phenomenon to applications

Niklas Dömer, Tobias Hehemann, Felix Sauerwein et al. (+3 more)

Self-selected phase-matched second harmonic generation is introduced as an all-optical probe of refractive-index dispersion in birefringent nonlinear optical materials. Rather than requiring wavelength or angular tuning, the exposure with a spectrally broad, intense ultrashort pulse allows the material to self-select the fundamental spectral component that satisfies the type-I noncritical phase-matching condition. This produces a narrow peak in the second harmonic spectrum whose position is governed by the refractive indices and is therefore highly sensitive to material parameters that affect the optical dispersion. We demonstrate the application of this phenomenon for the optical inspection of stoichiometry and temperature gradients in technologically relevant lithium niobate, as well as composition inhomogeneities in newly grown lithium niobate-tantalate solid solutions. These results establish self-selected phase-matched second harmonic generation as a rapid, non-contact method for inspecting nonlinear optical materials, with potential relevance for bulk crystals, wafers, and thin-film platforms.
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All authors Niklas Dömer, Tobias Hehemann, Felix Sauerwein, Sebastian Inckemann, Steffen Ganschow, Mirco Imlau

Optics

Generation of strongly localized skin solitons in non-Hermitian waveguide arrays with the Kerr effect

Chong Hou, Boris A. Malomed and Qin Zhou

We address two distinct nonlinear propagation problems in nonlinear optical waveguide arrays (WGAs) with non-reciprocal (non-Hermitian) couplings. First, we investigate the light propagation launched by initial excitations of two different types. The single-channel excitation creates stable solitons supported by the interplay of the Kerr nonlinearity and non-Hermitian skin effect (NHSE). In this case, we derive, by means of the symbolic-regression method, an analytical formula defining the soliton existence boundary. For the broad-pulse excitation, we produce perturbed soliton solutions analytically in the continuum approximation, which is accurately corroborated by numerical results. We thus conclude that NHSE accelerates the propagation of the broad soliton towards the boundary, ultimately causing tight localization at the edge, which is a hallmark of the NHSE in the continuum limit. Second, we identify stationary solitons in the system – specifically, nonlinear bulk modes in the Hermitian regime and near-edge skin solitons in the non-Hermitian one. The nonlinear bulk modes are compressed toward the edge of the WGA under the action of the non-reciprocality, which is the nonlinear extension of NHSE.
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Optics

Evanescent absorption spectroscopy of transition metal dichalcogenide materials using guided photoluminescence in Si$_3$N$_4$ photonic waveguides

Victor Gonzalez-Morote, Marianna Sledzinska, Arkadiusz P. Gertych et al. (+3 more)

On-chip integration of two-dimensional transition metal dichalcogenides (TMDs) with photonic waveguides underpins a growing class of compact optoelectronic and sensing devices, whose performance depends on the optical absorption of the 2D material in this integrated environment. We demonstrate source-free, on-chip evanescent absorption spectroscopy of MoS$_2$ and WS$_2$ flakes integrated on Si$_3$N$_4$ waveguides, in which the broadband defect-related photoluminescence of the Si$_3$N$_4$ core itself acts as the internal probe. Light generated inside the core propagates under the TMD flake and is spectrally attenuated by evanescent interaction with the 2D material, and normalizing the transmitted spectrum to a reference waveguide without TMD yields the energy-dependent absorption response without any external illumination. The extracted guided absorption agrees with Raman and local micro-photoluminescence characterization and resolves differences between spatially uniform and non-uniform flakes. A complementary top-pumping scheme recovers guided WS$_2$ photoluminescence, whose spectral reshaping during propagation is quantitatively reproduced by the measured absorption. This source-free platform qualifies 2D materials in their integrated photonic environment and provides a direct route toward waveguide-integrated TMD photodetectors and sensors.
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All authors Victor Gonzalez-Morote, Marianna Sledzinska, Arkadiusz P. Gertych, Syed Hassan Abbas Jaffery, Mariusz Zdrojek, Daniel Navarro-Urrios

Chemical Physics

Ai2-Kit: Streamlining AI-Accelerated Ab Initio Workflows for Complex Chemical Systems

Sheng Bi, Wei-Hong Xu, Yong-Bin Zhuang et al. (+47 more)

Molecular simulations of complex chemical systems, such as catalysis, electrochemistry, and energy storage, often need to capture the interplay of effects such as electronic structure, finite-temperature fluctuations, and electric-field response. Such complexity is difficult to address with traditional ab initio calculations, which are limited by the time and length scales they can reach. AI-accelerated ab initio (AI2) methods use machine learning potentials trained on first-principles data to replace expensive electronic-structure calculations, extending ab initio accuracy to these regimes, but their routine application requires reliable workflows that connect first-principles calculations, model training, molecular dynamics, enhanced sampling, trajectory analysis, and HPC orchestration. Here we present ai2-kit, a software toolkit for developing accessible, reproducible, and extensible AI2 workflows. ai2-kit provides high-semantic-density command-line interfaces and Python APIs for structure and dataset conversion, batch task generation, active-learning screening, job orchestration, and workflow recovery. We demonstrate ai2-kit in four representative applications: active-learning-based machine learning potential construction, free-energy perturbation for redox and acid-base processes, electrochemical machine learning potentials for electrified interfaces, and spectroscopies from machine learning molecular dynamics. ai2-kit also provides AI-agent skills that help users adapt these use cases into customized workflows for their own chemical systems and computational software stacks. Together, ai2-kit helps turn AI2 methods from bespoke computational protocols into reusable and extensible workflows for complex chemical systems, from model construction to property prediction.
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All authors Sheng Bi, Wei-Hong Xu, Yong-Bin Zhuang, Jia-Xin Zhu, Jiang-Peng Qiu, Yu-Hang Tang, Xiang-Long Du, Qi You, Yun-Pei Liu, Fu-Qiang Gong, Yu-Xin Guo, Yi-Ze Wang, Cheng-Xuan Wang, Zi-Heng Gong, Zi-Qiang Chen, Chang Liu, Siyuan Han, Jian Gu, Jia-Xin Li, Yi-Ming Chen, Lin Huang, Si-Jie Chen, Bo-Ying Huang, Jie-Zhen Xia, Fan-Jie Xu, Su-Yang Zhong, Peng-Wei Xu, Jun-Yi Wang, Xing-Yun Xie, Yu-Lei Gong, Yan-Yi Su, Yue Liu, Rui-Hao Bi, Lang Li, Fei-Teng Wang, Jing-Xiang Zou, Mei Jia, Jie-Qiong Li, Min Lin, Qi-Yuan Fan, Juan-Juan Sun, Jia-Bo Le, Zixuan Wei, Jin-Yuan Hu, Meng-Lei Jia, Yan Sun, Xiao-Hui Yang, Fujie Tang, Feng Wang, Jun Cheng

Atomic Physics

Nondipole Contributions to Attosecond Chiral Photoionization Asymmetries

Zheming Zhou, Yang Li, Yueming Zhou et al. (+1 more)

Photoelectron circular dichroism (PECD) reads molecular chirality from forward-backward asymmetries in photoelectron emission, but the same observable can also contain non-dipole contributions from photon momentum transfer. Here we show that such contributions can reshape attosecond PECD measurements in both one- and two-photon ionization of chiral molecules. Calculations beyond the dipole approximation, interpreted with perturbation theory, reveal that non-dipole effects modify not only the magnitude but also the phase of the emitted electron wave packet. In two-photon interferometry, pathway interference amplifies the non-dipole response and can reverse the apparent chiral asymmetry. We further identify a practical separation principle: the non-dipole component is insensitive to enantiomeric handedness and can therefore be obtained from a racemic mixture. Subtracting this background isolates the purely chirality-induced asymmetry, enabling more accurate measurements of chiral electron dynamics.
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All authors Zheming Zhou, Yang Li, Yueming Zhou, Peixiang Lu

Chemical Physics · Cross-listed from quant-ph

Reducing quantum resources for ADAPT-VQE via plateau-operator elimination and correlated mean-field downfolding

Phuoc Minh Vo, Thai Cong Ngoc Vu, Thien Ngoc Tran et al. (+2 more)

Adaptive Derivative-Assembled Problem-Tailored variational quantum eigensolvers (ADAPT-VQE) represent one of the most promising approaches for quantum chemistry on near-term quantum devices. However, their optimization is slow and may stall due to vanishing parameters and redundant operators in the ansatz. In this work, we propose a simple strategy of operator elimination that removes non-contributing operators from the pool once they are detected, enabling the optimization to continue progressing toward convergence. We examine two variants, with and without pool restoration after elimination, and find that the former converges more smoothly and faster than the latter and the standard ADAPT-VQE. To capture dynamical correlations between the active space and its environment, we combine ADAPT-VQE with our recently developed downfolding approach, the one-body downfolding framework (OBDF). In OBDF, the bare molecular Hamiltonian in the active space is replaced by a correlated effective Hamiltonian that incorporates dynamical correlation effects outside the active space. We benchmark our implementation on a linear \ce{H_6} chain, an \ce{H_6} lattice, an \ce{H_6} ring, and the \ce{N_2} molecule using the OpenFermion simulator. Our results show that operator elimination significantly reduces circuit depth and iteration count, and that OBDF-ADAPT-VQE yields energies closer to the full configuration interaction (FCI) reference than the standard approach within the same active space.
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All authors Phuoc Minh Vo, Thai Cong Ngoc Vu, Thien Ngoc Tran, Hoang Thanh Nguyen, Lan Nguyen Tran

Atomic Physics

Nuclear-size correction to the one-loop self-energy in hydrogenlike ions

Ping Yang, Aleksei V. Malyshev, Aleksandr N. Kochnev et al. (+4 more)

The nuclear-size effect on both diagonal and off-diagonal one-loop self-energy matrix elements is considered for hydrogenlike ions with $Z=60$, $82$, $90$, and $92$. Specifically, the $1s$, $2s$, $3s$, $2p_{1/2}$, and $2p_{3/2}$ states, as well as the off-diagonal $1s-2s$, $1s-3s$, and $2s-3s$ matrix elements are considered. The calculations are performed within the rigorous quantum-electrodynamics framework, nonperturbatively in the nuclear-strength parameter $\alpha Z$. Excellent agreement is found with results reported in the literature. Simple and useful approximate formulas to treat the nuclear-size correction are obtained, which, in particular, can be used to study the self-energy contributions to the field-shift factors.
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All authors Ping Yang, Aleksei V. Malyshev, Aleksandr N. Kochnev, Vladimir M. Shabaev, Aleksandr S. Shamanaev, Ting-Yun Shi, Dmitry V. Sychkov

Physics and Society · Cross-listed from astro-ph.IM

Open Science in Astrophysics: Citation Benefits of Open Code, Open Data, and Open Access

Parth Joshi and Rupert Croft

We analyze the relationship between open-accessibility in data, code, and paper text in astrophysics using a sample of 53,194 peer reviewed papers published between January 2021 and April 2025, drawn from NASA's Astrophysics Data System (ADS). We measure eleven quantities: open accessibility of text, open-code status, open-data status, number of grants received, code size, programming language, data repository size, citation count, number of authors, paper length, and publication date. We break down citation advantages based on six astrophysical sub-fields: Solar System, Planet, Stellar, ISM, High Energy, and Galaxies+Cosmology, determined by keywords. This is accomplished by tuning a multivariate least-squares regression model with alongside partial correlations and non-parametric tests to isolate the contribution of each facet of openness. After controlling for the aforementioned quantities, we find significant citation advantages associated with all three forms of openness: open data (+32%, p < 10^-24), open access (+26%, p < 10^-67), and open code (+16%, p = 0.003). The open-data citation advantage is present in all six sub-fields, and especially in Galaxies+Cosmology and ISM, which have the strongest cultures of sharing simulation outputs and observational data products. Open-code and open-data sharing rates are highest in Galaxies+Cosmology and HEA (~0.9% and ~2.9%), reflecting their more developed community data infrastructure, and lowest in Solar System and ISM, where data is distributed on platforms not taken into account by this study. Our findings support the long held notion that public access comes with concrete personal incentives for authors in terms of citations.
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Atomic Physics

Surface charges in a Rydberg atom-nanowaveguide hybrid quantum system

Aswathy Raj, Anna Kortel, Krishna Jadeja et al. (+4 more)

Hybrid quantum platforms based on highly excited Rydberg atoms coupled to nanophotonics devices offer a promising route toward scalable quantum networks and integrated quantum technologies. However, the close proximity of Rydberg atoms to dielectric nanostructures makes these systems particularly susceptible to uncontrolled surface electric fields that can lead to a degradation of the excitation process. Here, we experimentally investigate Rydberg excitation of laser-cooled $^{87}$Rb atoms via the evanescent field of an optical nanofiber in the presence of fiber-guided red- and blue-detuned light fields as used to trap ground state atoms in fiber-based dipole traps. We observe a time evolution of the Rydberg excitation spectrum when both the dipole trapping fields are on and the additional spectral features that appear can be suppressed by applying an external oscillating electric field to the system, strongly indicating that surface charge accumulation is responsible for the observed spectral feature. The experimental results are reproduced qualitatively by a model that incorporates DC energy level shifts arising from electric fields generated by charges deposited on the nanofiber surface. We identify Rydberg-ground state collisional ionization, which is enhanced by the dipole trapping fields, as the dominant mechanism for charge generation. These results provide new insight into charge dynamics at dielectric nanophotonic interfaces and establish practical guidelines for mitigating surface charge-induced electric fields in fiber-integrated Rydberg quantum systems.
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All authors Aswathy Raj, Anna Kortel, Krishna Jadeja, Dylan J. Brown, Alexey Vylegzhanin, Robert Löw, Síle Nic Chormaic

Medical Physics

Closed-loop coupling of personalised and foundation models for real-time treatment guidance with MRI

James Grover, Emily A. Hewson, Andrew Phair et al. (+5 more)

Image-guided therapies, including radiotherapy, biopsy and deep brain stimulation, rely on real-time targeting of anatomical structures. However, in the presence of motion, imaging latencies create a temporal misalignment between observed and true anatomy, compromising treatment accuracy. Artificial intelligence-based frameworks have increasingly been presented to close this latency gap, but leading personalised models can fail due to a lack of stable anatomical grounding. Foundation models can provide grounded behaviour, but they do not adapt to real-time, individual patient dynamics. Here we introduce a closed-loop coupling framework that synergises patient-specific temporal prediction with continuous segmentation-based anatomical interpretation from a foundation model. A personalised model predicts future anatomy to compensate for system latency, while a streaming foundation model provides anatomical supervision used to continuously update the temporal predictor in real time during treatment. We validate the framework using a digital phantom and intrafraction magnetic resonance imaging (MRI) from patients undergoing MRI-guided radiotherapy. For a prediction horizon of 400 ms, the proposed method improves anatomical prediction and reduces dosimetric error compared with existing approaches, within clinically relevant latency constraints. These results establish closed-loop coupling as a general strategy for real-time image-guided intervention.
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All authors James Grover, Emily A. Hewson, Andrew Phair, Michael Ferraro, Hilary L. Byrne, Paul Keall, Michael G. Jameson, David E.J. Waddington