Optics
Probing the electromagnetic nonlinearity of vacuum with continuous-wave lasers
Alexey Arakcheev, Niv Barkai, Alexandr Vasilyev et al. (+1 more)
In classical electrodynamics, light waves propagating in
vacuum do not interact. In
quantum physics, however,
photon-
photon interactions are mediated by virtual particles, giving rise to the electromagnetic nonlinearity of
vacuum (EMNV). A direct measurement of EMNV would test a long-standing prediction of
quantum electrodynamics and constrain new physics models. Despite its fundamental significance and extensive efforts to detect it, free-space EMNV has not yet been directly measured in the laboratory. Here, we propose a tabletop all-optical measurement of EMNV based on resonantly enhanced four-wave mixing in focusing optical resonators with a circulating power of a few megawatts. As a key experimental step toward this measurement, we demonstrate a resonator reaching a circulating power of 2.5 MW, approaching the parameter range needed to detect EMNV at the level predicted by
quantum electrodynamics.
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All authors Alexey Arakcheev, Niv Barkai, Alexandr Vasilyev, Osip Schwartz
Instrumentation and Detectors
Characterisation of the Thermoflow due to the Dry Nitrogen Flushing Scheme in the ATLAS Inner Tracker using Computational Fluid Dynamics
Muaaz Bhamjee, Matthew Connell, Simon Connell et al. (+5 more)
The planned High Luminosity upgrade to the Large
Hadron Collider at CERN aims to increase the instantaneous luminosity peak to about 7.5 x 10^{34} cm^{-2}s^{-1}. The ATLAS detector will be extensively re-designed to meet the challenges of this upgrade. This paper focuses on the use of computational fluid dynamics to characterise the thermoflow in order to model the dry nitrogen flushing scheme in the Common Environmental Monitoring and Interlock System for the ATLAS Inner Tracker as part of the upgrade process. The Technical Design Report considers the possibility for the bi-phase CO2 coolant temperature to drop to as low as -55 degrees C in the case of a fault. The specification for the highest Relative Humidity within the ITk volume is therefore equivalent to a dew point temperature at or below -60 degrees C in order to prevent condensation which could damage the detector electronics. The design accommodates for humidity monitoring to detect the onset of such events and dry nitrogen flushing to remove moisture. Therefore, it is important to thoroughly understand all consequences of atmospheric air ingress due to air-leaks and/or air-ingress from the outlets due to the over-pressure. The computational fluid dynamics model presented in this study was used to provide quantitative and qualitative insight into the various operational and failure conditions, informing engineering design changes to optimise the flushing scheme and ensure that the ITk remains dry and within the design specification of the acceptable dew point range.
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All authors Muaaz Bhamjee, Matthew Connell, Simon Connell, Emmanuel Igumbor, Lerothodi Leeuw, Pedro Mafa, Marco Oriunno, Marcel Vreeswijk
Computational Physics · Cross-listed from cs.LG
When Attention Beats Fourier: Multi-Scale Transformers for PDE Solving on Irregular Domains
Brandon Yee, Pairie Koh, Jack Rodriguez et al. (+1 more)
We study the problem of architecture selection for deep learning models trained to solve partial differential equations (PDEs), asking when
transformer-based architectures with learned
attention outperform
Fourier-domain neural operators. We introduce the Multi-Scale
Attention Transformer (\msat{}), a deep learning architecture that encodes spatiotemporal solution histories as
token sequences and trains end-to-end via a composite supervised objective with optional physics-informed regularization terms. We conduct a comprehensive empirical evaluation against nine baselines – including physics-informed neural networks (PINNs), neural operators (FNO, DeepONet, GNOT), and state-space models (Mamba-NO) – across five
benchmark problems from the PINNacle suite, using identical train/test splits and reference data for all methods. \msat{} achieves state-of-the-art generalization on complex geometry problems ($L^2_\mathrm{rel} = 0.0101$ on Heat2D-CG, a $3.7\times$ improvement over FNO) at $34\,\mathrm{s}$ total inference vs.\ $120{,}812\,\mathrm{s}$ for Mamba-NO. Ablation studies over the physics regularization component reveal a precise inductive bias tradeoff: physics priors reduce test error on
diffusion-dominated problems but degrade generalization on chaotic and recirculating-flow regimes, directly characterizing the prior misspecification boundary. Approximation error bounds as a function of domain boundary complexity $\kappa$ provide a theoretical basis for these empirical findings and a principled rule for architecture selection.
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All authors Brandon Yee, Pairie Koh, Jack Rodriguez, Mihir Tekal
Biological Physics
Chiral-Induced Spin Selectivity Regulates Triplet formation in Heliobacterial Photosynthesis
Parul Raghuvanshi and Vishvendra Singh Poonia
Triplet formation and its regulation have always been of central interest in understanding the photophysical behavior of living systems. In organic systems, excessive triplet formation poses significant challenges, as it can promote photochemical damage and reduce the efficiency of charge separation processes, making its regulation critically important.Here, we present a theoretical investigation of the intrinsic
quantum spin dynamics governing triplet formation in the heliobacterial reaction center, a system that operates without any internal
magnetic field. Using an open
quantum systems approach based on the Lindblad formalism, we simulate the
spin-correlated radical pair dynamics occurring during charge separation in the heliobacterial reaction center. The study systematically examines how triplet formation is regulated by variations in two key parameters, hyperfine coupling strengths and recombination rates, and how this regulation is further influenced by the inclusion of chirality-induced
spin selectivity (CISS) in conjunction with the radical pair mechanism (RPM). Our results demonstrate that the CISS effect significantly suppresses triplet formation across the parameter space relevant to the heliobacterial molecular environment, revealing an intrinsic
quantum protective mechanism operating through
spin control in heliobacterial photosynthesis.
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Biological Physics
Indirect Detection of Lactate Through Voltammetry Using Glassy Carbon Microelectrodes
Amish Rohtagia, Elisa Barts, Neharika Ravichandran et al. (+5 more)
Glassy carbon (GC) microelectrodes are increasingly being used for voltametric detection of electroactive neurotransmitters such as dopamine and serotonin. However, non-electroactive molecules including lactate, glutamate, and gamma-aminobutyric acid (GABA) cannot be directly detected using conventional voltammetry without surface functionalization. In this study, lactate oxidase was immobilized within a chitosan
matrix on lithographically patterned GC microelectrodes to enable indirect detection of lactate via enzymatic generation of hydrogen peroxide, an electroactive byproduct. The resulting hydrogen peroxide was detected using fast-scan cyclic voltammetry (FSCV), enabling indirect in vitro detection of lactate at concentrations as low as 10 nM. The functionalized GC microelectrodes were integrated into a four channel array on a 1.6 cm flexible neural probe with potential for in vivo applications. Surface morphology and bonding interactions were characterized using scanning electron microscopy (SEM) and
Fourier transform infrared (FTIR) spectroscopy. FTIR analysis confirmed successful chitosan deposition through characteristic O-H, N-H, amide, and C-O stretching bands. Hydrogen peroxide detection was concentration-dependent, while lactate detection exhibited early saturation consistent with enzyme-limited kinetics. These results demonstrate a mechanically robust GC microelectrode platform for nanomolar-level indirect lactate sensing and provide insight into the reaction-
diffusion coupling governing enzyme-based electrochemical detection.
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All authors Amish Rohtagia, Elisa Barts, Neharika Ravichandran, Sandra Lara Galindoa, Surabhi Nimbalkara, Mantra Mittal, Samantha Omer, Sam Kassegnea
Plasma Physics · Cross-listed from astro-ph.HE
Magnetar field dynamics driven by chiral anomalies without magnetic helicity
Clara Dehman
The
chiral magnetic effect (CME), arising from the
chiral anomaly and enabling a mutual conversion between
magnetic topology and fermionic chirality, is a key mechanism in magnetar field
evolution. Previous work by Dehman & Pons (2025) demonstrated that the CME can efficiently generate dipolar fields $\left(B_{\rm dip} \gtrsim 10^{14}\,\mathrm{G}\right)$, consistent with magnetar timing measurements, provided that the initial
magnetic field carries net helicity. However, whether
neutron stars are born with
magnetic helicity remains uncertain. In this work, we investigate the CME across a range of initial helicity configurations, including non-helical initial conditions. We find that the CME efficiently generates magnetar-strength dipoles on timescales of decades, independently of the initial helicity content. The
chiral instability is driven by localized helical structures that induce a residual
chiral asymmetry and is primarily governed by the maximum
chiral chemical potential, requiring $\mu_5^{\rm max} \gtrsim \mathrm{few}\times10^{-11}\,\mathrm{MeV}$ for onset in the magnetar regime. Our results further show that these dipoles may either remain stable and subsequently evolve through standard Ohmic decay, or become unstable if they acquire sufficient helicity, in which case they decay through the
chiral anomaly, transferring energy to less helical modes. This outcome depends sensitively on the initial helicity distribution. These findings extend the applicability of the CME to more realistic
magnetic-field configurations and underscore the importance of the helicity distribution at birth, a quantity that remains poorly constrained in newborn
neutron stars, yet is crucial for determining their
magnetic evolution and the emergence of magnetars.
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Computational Physics
A Time-Domain Method of Auxiliary Sources for Analyzing Transient Electromagnetic Interactions with GSTC-Modeled Metasurfacess
Minas Kouroublakis, Nikolaos L. Tsitsas and Yehuda Leviatan
This paper presents a time domain (TD) formulation for modeling the transient electromagnetic response of two-dimensional (2D) metasurfaces using the Method of Auxiliary Sources (MAS) combined with the Generalized Sheet Transition Condition (GSTC). In the proposed approach, the frequency-domain impedance type GSTC is transformed into a causal, convolution-based TD representation and integrated within the MAS formulation. rfaces.
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Optics
Hot biexcitons driven by extreme optical confinement
Xinyi Wang, Kaushik Kudtarkar, Wenjing Wu et al. (+6 more)
A powerful means to understanding condensed matter that possesses a multi-constituent, non-isolated, and complex nature, with a preeminent example being two-dimensional (2D) materials, is studying many-body interactions. However, experimentally observing high-order many-body interactions is a daunting task due to its heavy reliance on the abundance of low-order complexes. Here, we report the observation of four-body hot biexcitons in an energetically unfavorable
bilayer of tungsten disulfide (WS2) through creating extreme optical confinement. Specifically, we integrate a non-radiative bound state in the continuum (BIC) into a photonic
crystal (PhC) defect cavity, forming a quasi-three-dimensional (q-3D) but open confinement for
photons at the driving frequency. The extremely confined
photons in both reciprocal and physical spaces then excite inherently unproductive two-body hot
excitons situated slightly above the indirect bandgap so efficiently that they form overwhelmed higher-order four-body hot biexcitons. Distinctively, these hot biexcitons exhibit substantial valley polarization and coherence at room temperature, which we attribute to the topological nature of BICs and the associated q-3D confinement with an orbital angular momentum. Besides achieving room-temperature biexcitons, the q-3D confinement could be valuable for higher-order interactions, such as triexcitons, and many other many-body phenomena, including Bose-Einstein condensation.
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All authors Xinyi Wang, Kaushik Kudtarkar, Wenjing Wu, Yunjo Jeong, Yuxuan Cosmi Lin, Xiaofeng Qian, Junichiro Kono, Shengxi Huang, Shoufeng Lan
Atomic Physics · Cross-listed from astro-ph.GA
Space as a spectroscopic laboratory: High-resolution spectroscopy of the [$^{13}$C II] hyperfine structure with SOFIA/upGREAT
S. Kabanovic, V. Ossenkopf-Okada, S. Schlemmer et al. (+13 more)
The [$^{12}$C II] emission at 158 $\mu$m is a key cooling line of the interstellar medium and traces gas kinematics in spectrally resolved observations. Its spectral profile is often modified by optical depth effects. The intrinsic line shape can be reconstructed by comparison with emission from the less abundant $^{13}$C isotope. Due to the additional
neutron spin, [$^{13}$C II] emission splits into three hyperfine structure (hfs) transitions. Laboratory measurements have provided the centroid frequency and the strongest component ($F=2-1$); the two weaker components ($F=1-0$ and $F=1-1$) have been inferred only from
quantum-mechanical calculations. The
magnetic-dipole hfs constants, from which the transition frequencies follow, have not been measured experimentally. The high spectral resolution of observations with the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) on board SOFIA enabled simultaneous detection of all three hfs transitions. From these astronomical data we determine, for the first time, the
magnetic-dipole hfs constants $A_{1/2}^{\rm hf} = 810.71(11)$ MHz and $A_{3/2}^{\rm hf} = 162.18(5)$ MHz of the [$^{13}$C II] $2s^2\,2p\,{}^2P^\circ$ ground term. Combined with the laboratory centroid frequency, this yields the rest frequencies of all three hfs lines. Using [$^{12}$C II] as a reference, we also improve the precision of the [$^{13}$C II] centroid frequency. This work shows that spectrally resolved astronomical observations can constrain fundamental atomic properties, with hfs precision rivaling laboratory measurements. The approach extends to other atomic and molecular transitions where laboratory data are difficult to obtain.
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All authors S. Kabanovic, V. Ossenkopf-Okada, S. Schlemmer, J. Stutzki, N. Schneider, U. U. Graf, O. Asvany, D. A. Riechers, C. Guevara, R. Higgins, R. Simon, Y. Okada, M. Mertens, L. Schneider, R. Güsten, A. G. G. M. Tielens
Optics
Learning from Translation: Seasonal Errors and Feature Importance of the ERA5 Turbulence Predictions
Arial Tolentino, Markus Petters and Luat T. Vuong
Turbulence is a phenomena that is locally and statistically characterized by measurements, but it is caused by nonlocal energy cascades associated with the environment. The presence of
turbulence coincides with fluctuations in the refractive index, which impact optical sensing, imaging, and signaling applications. Here, we study the machine learning models that predict near-surface optical
turbulence strength $C_n^2$, derived from anemometer-based surface flux measurements through Monin-Obukhov similarity theory, using ERA5 reanalysis data as model inputs. We evaluate the model's ability to perform temporal extrapolation by training on one year of co-located $C_n^2$ observations and ERA5 data, and applying the model to ERA5 data from other years at the same site to reconstruct a multi-year time series. We compare the predictions across Southern California and New York. In spite of varying weather and terrain, the ML models show consistent performance and seasonal behavior across training years. All models show greater correlation, faster convergence, and lower prediction errors in the summer. However, some ERA5 features drive predictions in New York but not California and vice versa, and such feature dependence depends on the season. Seasonal error and feature trends suggest that
turbulence is affected by atmospheric composition or other seasonal environmental considerations that are not currently monitored by ERA5. We find, regardless of terrain, the primary feature of importance to
turbulence prediction is
solar radiation, which underlines the central role of radiative energy transfer in driving atmospheric
turbulence. We point toward physics-informed ML translation and feature selection as tools for improving the generalizability of data-driven models.
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Fluid Dynamics
Bubble jetting in acoustic microdroplet vaporization
Anunay Prasanna, Samuele Fiorini, Gazendra Shakya et al. (+1 more)
Acoustic droplet vaporization denotes the phase-change of micron- and sub-micron-sized droplets upon the application of high-amplitude ultrasound. The asymmetric collapse of the incepted vapor bubbles within the droplets can give rise to high-speed
liquid microjets. Here, we describe acoustically-driven and bubble-pair jetting arising within the vaporizing droplet, observed experimentally with ultra-high-speed imaging at the microscale. The existence of complex pressure fields due to the continued acoustic wave-droplet interaction and the nucleation of multiple bubbles within the droplet leads to rich dynamics, with the jets presenting behavioral self-similarity to millimetric bubbles under comparable conditions. Evaporative instabilities that develop during bubble growth impede jet formation during bubble collapse. Furthermore, the ability of the jets to pierce the droplet interface and penetrate into the surrounding fluid is discussed. These powerful microjets could be harnessed to induce
cell permeabilization for targeted drug delivery and treatment of cancerous tissue.
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All authors Anunay Prasanna, Samuele Fiorini, Gazendra Shakya, Outi Supponen
Accelerator Physics
Multilayer model for coatings with arbitrary layers for superconducting radio-frequency applications
Aaron Gobeyn, Wolfgang Ackermann and Herbert De Gersem
We extend the multilayer model of \etal{Kubo} for
superconductor-
insulator-
superconductor (SIS) structures in two ways: first, by generalizing it to arbitrary sequences of layers of arbitrary type, i.e. superconducting, normal conducting, and insulating; and second, by accounting for all contributions, including ohmic losses and dielectric effects. We examine the maximum applicable field for $(\text{SI})^n\text{S}$ structures. We find that the optimum configuration corresponds to the $n=1$ case. However, the thickness of the superconducting coating layers can be reduced to below their penetration depth with minor performance penalty. We discuss the ability to model transitions in SS
bilayers by introducing a set of virtual layers that represent the transition region through interpolated parameters. We find degradation of the maximum applicable field with thicker transition layers, and a larger effective penetration depth of the electromagnetic fields. Furthermore, the surface impedance of the multilayer structure is calculated using the Leontovich boundary condition, yielding a formulation suitable for integration into finite element simulations. Additionally, the Poynting
theorem is used to determine the loss contributions of individual layers.
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Atomic Physics · Cross-listed from quant-ph
Reducibility of native weighted graphs on Rydberg Arrays
J. Kombe and J. D. Pritchard
We investigate the classical reducibility of random unit-disk graph (UDG) instances of the maximum independent set (MIS) and maximum weighted independent set (MWIS) problems, which can be natively realised in Rydberg atom
quantum processors. Using state-of-the-art kernelisation techniques, we systematically probe how far classical preprocessing can simplify such native optimisation problems of varying size and connectivity. While many small or sparse instances can be fully reduced, dense graphs often retain finite irreducible kernels even after extensive reductions. Introducing vertex weights tends to increase reducibility, whereas extending the interaction range in the underlying UDG connectivity suppresses the reduction efficiency. By exploring where classical reductions cease to be effective, we aim to delineate the regime of problem instances that remain computationally demanding - those most relevant for testing and benchmarking near-term
quantum optimisation hardware. We find that for the remaining finite kernels,
quantum execution would require non-native
embeddings with substantial resource overheads, suggesting that directly running native instances may be more practical than
embedding a reduced kernel.
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Optics · Cross-listed from cond-mat.mes-hall
Energy-Resolved Quantum Geometry from Středa Response: Driven-Dissipative Bosonic Lattices and Disordered Systems
Anaïs Defossez, Baptiste Bermond, Lucila Peralta Gavensky et al. (+1 more)
The Středa formula links the
Hall conductivity of an
insulator to the
magnetic-field response of its particle density, providing a local and universal probe of the topological Chern number. Beyond this quantized response, an energy-resolved Středa marker can be defined from the
magnetic response of the density of states, revealing detailed features of the
quantum geometry of Bloch bands. We show that driven-dissipative bosonic
lattices provide direct access to both the integrated and energy-resolved Středa responses. Our scheme uses controlled pumping with uniform strength and random phases across the
lattice, together with uniform loss, to yield a Lorentzian filter of eigenmode occupations. For generic dispersive bands, this enables reconstruction of a coarse-grained energy-resolved Středa response, establishing these platforms as versatile probes of anomalous spectral flow and energy-resolved
quantum geometry. As a striking application, we show that this marker elucidates the fate of topological bands under strong disorder, capturing the
quantum-
geometric structure underlying topological Anderson
insulators.
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All authors Anaïs Defossez, Baptiste Bermond, Lucila Peralta Gavensky, Nathan Goldman
Atomic Physics
Carrier Revival in Long Trapped-Ion Chains
Florian Egli, Chris Shanks, James Bounds et al. (+6 more)
For a single trapped ion, the excitation spectrum of a narrow optical transition consists of a Doppler- and
recoil-free carrier accompanied by motional sidebands, which are equally spaced by the trap secular frequency and lie under a Doppler-broadened envelope that is shifted by the
photon recoil. Outside the Lamb-Dicke regime, the large
photon recoil distributes the line strength across many sidebands and suppresses excitation of the carrier. With multiple ions, the motional spectrum becomes dense, and the carrier is further weakened. Here, we predict a counterintuitive revival effect: increasing the number of ions in a linear chain can restore strong carrier excitation even under trapping conditions far from the single-ion Lamb-Dicke regime. Using a
quantum-mechanical model of the excitation dynamics in linear ion chains, we find that sufficiently long chains concentrate the spectrum into the carrier. This effect enables efficient excitation of light ions at short wavelengths. It may also benefit multi-ion optical clocks and mixed-species
quantum-logic spectroscopy.
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All authors Florian Egli, Chris Shanks, James Bounds, Jorge Moreno, Muhammad Thariq, Erdem Yilmaz, Theodor W. Hänsch, Thomas Udem, Akira Ozawa
Accelerator Physics
An electron injector for the Electron-Ion Collider based on proton-driven plasma wakefield acceleration
J. P. Farmer, H. Jaworska, A. Caldwell et al. (+5 more)
We describe an electron bunch injector scheme based on
proton-driven
plasma wakefield acceleration for the Electron-Ion
Collider. The
proton bunches are assumed to have the same energy as those used in the EIC, and the polarized electron source is that used in the current EIC design. We describe the different elements making up the injection scheme and give an estimate for the performance. Using a novel top-up injection scheme for electrons, the charge in the ring is accumulated over many injection events, avoiding deleterious beamloading in the
proton-driven wakefield stage and allowing the polarization in the ring to be maintained. Our initial study indicates that for electron bunches at 10 GeV, 1160 bunches can be stored in the ring over a 10-hour period with an average bunch charge of 19.3 nC and an average polarization of 75.8 %, representing 69 % of the EIC design specification for charge and exceeding the specification for polarization. Operation at 18 GeV is achieved by shortening the electron beam lifetime to increase the average polarization. Paths to improve upon these results are identified.
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All authors J. P. Farmer, H. Jaworska, A. Caldwell, N. Lopes, A. Pukhov, L. Reichwein, F. Willeke, M. Wing
Computational Physics · Cross-listed from astro-ph.IM
Systematic Comparison between Constrained Transport and Mixed Divergence Cleaning Methods for Astrophysical Magnetohydrodynamic Simulations
Kengo Tomida, Kenji Eric Sadanari, Shinsuke Takasao et al. (+1 more)
Magnetohydrodynamic (MHD) simulations are indispensable research infrastructure in astrophysics today. In order to satisfy the solenoidal constraint of the MHD equations on discretized grids, modern simulation codes often employ either constrained transport (CT) with a staggered grid or divergence cleaning using an additional variable. We compare CT and Dedner's mixed divergence cleaning schemes systematically, and find that the divergence cleaning scheme can produce substantial artifacts in certain situations. Through numerical experiments including both idealized tests and practical applications, we show that the original implementation of Dedner's scheme becomes inaccurate when
magnetic fields are strongly localized or when the timestep suddenly changes. We find that some previous results, such as the extremely rapid growth of
magnetic fields during
star formation in the early Universe, may be affected by the spurious behavior of the divergence cleaning scheme. We propose a few modifications to improve the robustness of the divergence cleaning method. Nevertheless, we find that the CT scheme is more accurate and reliable in many situations.
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All authors Kengo Tomida, Kenji Eric Sadanari, Shinsuke Takasao, Kazunari Iwasaki
Fluid Dynamics
Vortex ring formation from the interaction of a cavitation bubble with a confined air bubble: experiments and a timing criterion
Charul Gupta, Yashwant Singh, Lakshmana D Chandrala et al. (+2 more)
We study
vortex ring formation arising from the interaction between a cavitation bubble and a confined air bubble in a cylindrical blind hole, using high-speed shadowgraphy imaging. As the cavitation bubble grows above the hole, it drives a downward flow that compresses the air bubble at the base. The air bubble subsequently expands, expelling the overlying
liquid column upward as a coherent slug; impact of this slug on the far boundary of the collapsing cavitation bubble produces a
vortex ring. Parametric experiments across the dimensionless stand-off distance $\mathcal{H} = h/R_{\max}$ and the air bubble fill fraction $\mathcal{B} = (d_\text{hole} - d_\text{top})/d_\text{hole}$ identify three regimes: (i)
liquid column impact during collapse, producing a
vortex ring ($\mathcal{H} \lesssim 0.5$, $\mathcal{B} \lesssim 0.5$); (ii) late impact near the end of collapse (large $\mathcal{H}$); and (iii) direct air bubble impact after bypassing the
liquid column (large $\mathcal{B}$), with neither (ii) nor (iii) producing a ring. Two one-dimensional models, based on the Rayleigh-Plesset equation and isentropic air bubble expansion, predict the
liquid column impact location and its speed $U_\text{lc}$, respectively. A dimensionless timing parameter $\Pi = (h + R_{\max}) / (U_\text{lc} \cdot t_\text{cav}/2)$, comparing the
liquid column travel time to the cavitation collapse half-period, distinguishes the three regimes: ring formation occurs for $1 \lesssim \Pi \lesssim 1.5$. The ring propagates from the hole at an initial speed of $5$ m/s, decelerating quadratically, and breaks apart via azimuthal instabilities at $Re \approx 4500$.
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All authors Charul Gupta, Yashwant Singh, Lakshmana D Chandrala, Harish N Dixit, Badarinath Karri
Plasma Physics · Cross-listed from astro-ph.SR
Investigating Pre-flare Signatures in Spectroscopic Observations of an X9-class Solar Flare
Louis Seyfritz, Maria Kazachenko and Ryan French
On October 3rd, 2024, the Sun emitted an X9.0-class
flare from active region NOAA 13842. The event was recorded by multiple space-based instruments, beginning hours before the eruption, granting a unique opportunity to provide insight into the
flare's pre-
flare phase. In this study, we employ analysis of Interface Region Imaging Spectrograph (IRIS) spectroscopic data to investigate pre-flaring phenomena associated with this
flare. We present time-series and wavelet analysis of non-thermal velocity, Doppler velocity, and line intensity quantities of the IRIS Si IV 1403 angstrom line. We find two ranges of periodic oscillations during the pre-
flare phase: ~7-10 min and ~18-21 min oscillations, with local enhancements occurring near the polarity inversion line. We also find a steady rise in Si IV line parameters beginning 3 hours before the
flare in the same region, transitioning into strong non-thermal velocities and blueshifts ~15 minutes before onset. These findings are consistent with a slow destabilization of the coronal
magnetic field, possibly driven by the gradual activation of a flux rope, followed by a rapid shift to intense reconnection activity leading to
flare onset.
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Applied Physics · Cross-listed from cond-mat.other
Bulk-mediated reflection of chirality-protected surface spin waves
Vitaliy I. Vasyuchka, Florin Ciubotaru, Andrii V. Chumak et al. (+2 more)
Surface
spin waves of the Damon-Eshbach type exhibit intrinsically nonreciprocal transport properties with a
chiral dynamical field structure that localizes counterpropagating waves at opposite film surfaces. Such chirality has been predicted to suppress direct backscattering in thin films within frequency ranges free of bulk modes. However, how chirality influences reflection in thicker three-dimensional
magnetic media, where a dense spectrum of bulk excitations overlaps with surface waves, remains unclear. Here we demonstrate that, in micrometer-thick yttrium iron garnet films, reflection of the
chiral Damon-Eshbach wave from the boundary of the
magnetic medium is accompanied by excitation of spatially localized thickness-quantized bulk modes, whereas reciprocal backward-volume waves reflect nearly elastically. Brillouin light scattering spectroscopy, infrared thermography, and micromagnetic simulations reveal standing bulk excitations at the reflecting boundary and quantify the associated
magnon energy accumulation and dissipation. These results identify bulk-mode excitations as the physical pathway enabling reversal of chirally localized surface waves in thick films, thereby defining the limits of chirality-based backscattering immunity and providing a general framework for wave transport in nonreciprocal
magnetic media.
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All authors Vitaliy I. Vasyuchka, Florin Ciubotaru, Andrii V. Chumak, Burkard Hillebrands, Alexander A. Serga
Fluid Dynamics
Species Transport Driven by Droplet Impact in Wavy Thin Films
Hatim Ennayar, Frederik Roy Patria and Jeanette Hussong
Droplet impact on thin
liquid films is commonly studied on quiescent surfaces, although practical systems often involve residual capillary waves generated by preceding droplets. This study examines how such traveling waves modify impact dynamics and mixing. Controlled surface disturbances were produced using an acoustic excitation system that replicated droplet-induced waves, and a two-color
laser-induced fluorescence method was implemented to obtain simultaneous measurements of film thickness and dye concentration. Impacts on wavy films deviated markedly from quiescent conditions. Rim
evolution, cavity collapse, and jet formation became asymmetric, governed by the phase of the wave relative to the impact. These behaviors were linked to local variations in film depth, which redirected cavity retraction and the associated mixing flow. Reconstructed concentration fields confirmed that droplet
liquid is displaced according to these depth gradients, producing asymmetric mixing at moderate Weber numbers. A dimensionless asymmetry index quantified the dependence on wave amplitude, phase, and distance from the acoustic wave generator. At higher Weber numbers, inertial mixing attenuated these effects, and the dynamics approached those of static films.
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Accelerator Physics
Coherent {\gamma}-ray Generation By Partially Stripped Ion Beams
Nicola Piovella and Gordon R.M Robb
We describe a scheme for generation of coherent $\gamma$-rays by backscattering intense visible
laser light from a beam of partially stripped ions. The scheme is similar in principle to the proposed Gamma Factory at CERN, with the important difference that the scattering becomes coherent as a result of a collective instability which microbunches the ions. This instability is analogous to that which occurs in high-gain free electron
lasers (FELs). The scheme potentially offers a route to a source of tuneable, coherent $\gamma$-rays, opening up a wide range of possible new applications and opportunities. We find that the parameter requirements for realization of coherent $\gamma$-ray generation regime are considerably more stringent than those proposed for the Gamma Factory, requiring significant increases in the pump
laser intensity and possibly the ion beam current.
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Plasma Physics
Warm Topological Langmuir Cyclotron Wave
Virginia Billings, Hong Qin, Chuang Ren et al. (+1 more)
Finite-temperature effects in magnetized electron
plasmas create a new Weyl-point degeneracy between the warm Langmuir and right-circularly polarized waves. The associated topological charge at this warm Weyl point is found to be 1, which, by the index
theorem, predicts a gap-traversing topological edge mode. Solving the full warm-fluid eigenmode problem In a 1D inhomogeneous
equilibrium, we numerically identify this anticipated mode as the warm topological Langmuir-cyclotron wave, which is absent in the cold limit and occurs in a parameter regime relevant to the LArge
Plasma Device (LAPD) at UCLA.
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All authors Virginia Billings, Hong Qin, Chuang Ren, J. B. Marston
Data Analysis and Statistics · Cross-listed from cond-mat.str-el
Probabilistic denoising for reliable signal extraction in spectroscopy
Younsik Kim and Changyoung Kim
While deep learning offers powerful capabilities for scientific research, its application is often hindered by a lack of quantitative reliability. To address this, we introduce a probabilistic denoising framework that simultaneously extracts denoised signals and element-wise predictive uncertainties from noisy data. We demonstrate this approach on three-dimensional angle-resolved photoemission spectroscopy data, showing that the model reliably recovers the spectral features of a cuprate
superconductor from Poisson-distributed noise with an average count of only 0.02 electrons per voxel. Crucially, we show that these predicted uncertainties can be propagated into subsequent superconducting gap analyses, enabling quantitative parameter extraction with scientifically meaningful error bars. Furthermore, we validate the broad applicability of our approach by successfully extending it to two-dimensional X-ray diffraction data. Ultimately, this approach establishes uncertainty-aware deep learning not merely as a visualization tool, but as a rigorous framework for scientific data analysis.
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Optics
Pre-training Enables Extraordinary All-optical Image Denoising
Xudong Lv, Yuxiang Sun, Shuo Wang et al. (+3 more)
Optical neural networks are emerging as powerful machine learning and information processing tools because of their potential advantages in speed and energy efficiency. The training methods of these physical models, however, remain underexplored compared to their digital counterparts and are leading to suboptimal performance. This paper reports a pre-training-driven approach that leads to snapshot image denoising with substantially improved quality. We demonstrated effective free-space optical denoising by a diffractive network optimized by a two-step process including (1) pre-training using a massive
dataset of 3.45 million diverse but simple images and (2) fine-tuning with the corresponding task-specific
datasets. Compared to conventional
Fourier-domain filtering and directly trained diffractive networks, such a transfer learning process exhibited prominent advantages for denoising images degraded by severe noise, peak signal-to-noise ratio (PSNR) below 8 dB, while preserving fine image features and improving the PSNR to above 18 dB. Importantly, the same pre-trained optical network could be consistently fine-tuned to process degraded images from highly diverse styles ranging from handwritten digits (MNIST) and chest X-rays (ChestMNIST) to CIFAR-10 images and human faces (CelebA). We further demonstrated the critical role of our optical denoisers in
vision-based applications, including face detection, plate recognition, and localization of
UAVs in noisy conditions.
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All authors Xudong Lv, Yuxiang Sun, Shuo Wang, Nanxing Chen, Jun Guan, Jingtian Hu
Atomic Physics
$J=0$ metastable state of $\mathrm{Th}^{2+}$ for a hyperfine-free nuclear clock
S. Sagar Maurya, V. Lal, J. Tiedau et al. (+2 more)
We present measurements on a metastable state in $\mathrm{Th}^{2+}$ with the electronic configuration $6d^2\,{}^3P_0\,(5090\ \mathrm{cm^{-1}})$. This is motivated by the prospect of using the state in
laser excitation of the low-energy $^{229}$Th
nuclear resonance independent from the leading hyperfine interactions. The $6d^2\,{}^3P_0$ state has no dipole-allowed radiative decay channel and is connected to the second ground state $6d^2\,{}^3F_2\,(63\ \mathrm{cm^{-1}})$ through an electric quadrupole transition only. We populate the state by
laser excitation at 484~nm via a higher excited level and detect its population in
laser-induced fluorescence. The isotope shift of the $J=0$ level between $^{232}\mathrm{Th}^{2+}$ and $^{229}\mathrm{Th}^{2+}$ is determined as a measure of the interaction of electronic and
nuclear charge distributions. The lifetime of the level in our ion trap with buffer gas is limited by collisional mixing with the nearby state $5f6d\,{}^3G_3\,(5060\ \mathrm{cm^{-1}})$. In ultrahigh
vacuum, it could serve as a hyperfine-free
nuclear clock that is largely immune to field-induced frequency shifts via the electron shell.
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All authors S. Sagar Maurya, V. Lal, J. Tiedau, M. V. Okhapkin, E. Peik
Atomic Physics · Cross-listed from quant-ph
Limits of Stable Near-Field Probing in Nanophotonic Traps
Johannes Piotrowski, Constanze Bach, Nicolás Vera Paz et al. (+2 more)
Near-fields around nanophotonic structures and waveguides can be used to optically interface particles ranging from atoms and molecules to microscopic biological and synthetic particles. Due to the strong, non-linear dependence of the near-field coupling strength on the particles' position, a change of the spread of the particles' position will change their mean coupling strength. When the particles are trapped, this position spread depends on their temperature, generally leading to temperature-dependent coupling. Here, we experimentally demonstrate that this effect renders optical probing of trapped particles with near fields an inherently transient process. Specifically, we trap cold atoms in a two-color dipole trap surrounding an optical nanofiber and probe them with the evanescent field of guided, resonant light. The scattering of this probe light heats up the atoms, leading to a decrease of the coupling strength as well as loss of atoms. We observe both effects via a concurrent decrease of the absorption signal. In addition, we demonstrate that the coupling strength can be recovered by cooling the atoms back to their initial temperature. Our findings are relevant for numerous situations where stable coupling of trapped particles to a nanophotonic structure is required.
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All authors Johannes Piotrowski, Constanze Bach, Nicolás Vera Paz, Philipp Schneeweiss, Arno Rauschenbeutel
Fluid Dynamics
On the repeatability of turbulence
Noé Clavier, Eberhard Bodenschatz and Florencia Falkinhoff
Turbulence has strong and seemingly random fluctuations. Assessing its repeatability is key to predicting flows in technology and nature, much of which decay as viscosity dissipates energy. Much has been done to this end since the work of Lorenz, but mostly in theory and simulations. Here we present experimental results from the Max Planck Variable Density
Turbulence Tunnel where we generated decaying
turbulence using an active grid, repeating the process with nominally identical initial conditions up to 30,000 times. In contrast with the case of stationary
turbulence we found that the energy-carrying large scales show significant repeatability, irrespective of flow development time and
turbulence strength. Small scales, however, can effectively be modeled by independent random variables, supporting current numerical approaches in which they are parametrised.
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Physics and Society
Is a team only as strong as its weakest link? Quantifying the short-board effect with AI Agents
Xin Xu, Jiu Zhang, Xiao-Ling Lei et al. (+2 more)
The short-board effect, analogous to Liebig's Law of the Minimum, postulates that the collective performance of a team is constrained by its weakest component. This principle has profound implications for the optimization of collaboration in a variety of contexts, including management, education, and organizational structures. Despite its theoretical significance, empirical validation remains elusive due to challenges of assessing individual capabilities, controlling real-world variables, and data biases towards successful outcomes, as well as high employee turnover.To address this absence of knowledge, we employ multi-
agents driven by large
language models to simulate a teamwork with standard operating procedure, revealing the relationship between individual capability and collective team performance.In homogeneous team configurations, three capability regimes are observed, particularly the Sisyphus predicament state at the critical capability threshold characterized by extensive ineffective efforts and pseudo-high efficiency. Furthermore, with a single weak link quantifying the short-board effect, we highlight different impacts across core and non-core members on the team performance.More importantly, when the team exhibits multiple weak links, a cumulative product effect emerges, demonstrating that team performance is shaped by the aggregated impact of all weaknesses rather than the weakest link solely.This suggests that mitigation strategies should extend beyond the remediation of individual weak links.These findings rigorously elaborate the short-board theory and provide actionable insights to optimize team management, organizational operations, and supply chain resilience.
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All authors Xin Xu, Jiu Zhang, Xiao-Ling Lei, Xiong-Fei Jiang, Long Xiong
Fluid Dynamics · Cross-listed from cond-mat.soft
Elastocapillary morphing of self-encapsulated droplets floating at the oil-air interface
D. Andrini, D. Riccobelli, L. Gazzera et al. (+3 more)
Self-encapsulated droplets floating at an oil–air interface undergo striking shape changes during evaporation, including flattening and localized loss of membrane tension leading to crumpling and wrinkling. Here we combine experiments, modeling and simulations to obtain predictive morphological maps. We perform contact-angle and evaporation experiments on water droplets coated by a hydrophobin
protein film and floating in a fluorinated oil, providing reference profiles and volume-loss sequences for quantitative validation. We develop an axisymmetric mechanics framework in which
equilibria follow from minimization of a total free energy combining surface energies, membrane strain energy and gravitational potential, subject to volume and contact-line constraints. A quasi-convex tension-relaxation rule accounts for compression-free states and enables coexistence of taut, wrinkled (one principal tension vanishes) and crumpled (both vanish) membrane domains. A finite element
algorithm computes quasi-static morphing under volume reduction; key parameters are identified by fitting the reference contact-angle profile and then used without further tuning. The model reproduces the experimentally observed shape
evolution and resolves the associated stress redistribution. Systematic parameter scans yield morphological phase diagrams governed by the Bond number, the oil–droplet surface-tension ratio and the density ratio. For buoyant droplets, crumpling relocates between exposed and submerged caps as parameters vary; for heavy droplets, a crossover to circumferential wrinkling along the immersed sidewall emerges. Wall-meniscus variations shift phase boundaries and can suppress bottom crumpling, consistent with wall-affected experiments.
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All authors D. Andrini, D. Riccobelli, L. Gazzera, S. Molteni, P. Metrangolo, P. Ciarletta