Optics
Spatiotemporal Metasurface for Ultrafast All-Optical Wavefront Shaping
Mert Akturk, Giulia Crotti, Andrea Schirato et al. (+6 more)
Optical metasurfaces have established themselves as exceptional nanophotonic platforms to control the properties of light at subwavelength scales. By properly designing the geometry and spatial arrangement of their constituent meta-atoms, engineered phase gradients can be imparted to an incoming field, thereby tailoring its wavefront with a virtually unlimited number of control knobs. However, once fabricated, a metasurface has a permanently fixed optical response. Here, we introduce a strategy for dynamic control, by theoretically predicting and experimentally demonstrating all-optical, reversible, and ultrafast wavefront shaping in a periodic
semiconductor nanowire metasurface. A strongly astigmatic femtosecond optical pump pulse is used to photoexcite the resonant metasurface non-uniformly, inducing a transient, spatially inhomogeneous permittivity modulation that reshapes the wavefront of a delayed probe pulse. Ultrafast imaging measurements reveal transient defocusing of the transmitted field at selected probe wavelengths, with a switching time below one picosecond. Quantitative numerical modelling elucidates the defocusing mechanism as arising from the interplay between the unperturbed optical response of the resonant metasurface and the pump-induced spatial permittivity gradient. Our work establishes a fully all-optical and ultrafast route to the dynamic analogue of passive wavefront shaping in gradient metasurfaces, paving the way to all-optically reconfigurable metalenses.
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All authors Mert Akturk, Giulia Crotti, Andrea Schirato, Katsuya Tanaka, Isabelle Staude, Thomas Pertsch, Giulio Cerullo, Giuseppe Della Valle, Margherita Maiuri
Plasma Physics
On the ideal magnetohydrodynamic stability of the sheared-flow Z pinch
Daniel W. Crews and Jackson C. Turner
Sheared-flow Z-pinch stability has previously been studied within ideal MHD primarily through growth rate calculations, which find that even trans-Alfvénic sheared flows apparently fail to suppress the kink instability. Here, trans-Alfvénic sheared flow is shown to stabilize the MHD kink but also to excite shear-driven instabilities characteristic of high-Reynolds-number supersonic flow. This distinction is evident from the dispersion relations underlying the growth rates, computed as the analytic dispersion function in the complex-frequency plane. Regularization splits this function into adiabatic and resonant parts describing how discrete modes emerge from and interact with the continuous spectrum. The Doppler-shifted flow continuum is then seen to interact with the interchange and kink instabilities in distinct ways. For interchange, the continuum overlaps the instability branch at all wavenumbers, so even sub-Alfvénic sheared flow stabilizes profiles modestly beyond the interchange threshold. The kink, by contrast, is shielded from the continuum by a frequency gap, and trans-Alfvénic flow is required to Doppler-shift the continuum into resonance with it, giving a
geometric picture of the stabilization threshold. But shear-driven instabilities arise at this same threshold, including reflection modes and an acoustic kink. It is these shear-driven modes, not the original MHD instabilities, that dominate the ideal-MHD spectrum in trans-Alfvénic conditions. The ideal analysis thus describes the stabilization mechanism while showing that the stability of the sheared-flow Z pinch ultimately rests on non-ideal physics, such as finite orbit width and dissipation.
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Optics
Hybrid BaTiO3/TiO2 Metasurface for Efficient Gigahertz-Speed Free-Space Electro-Optic Modulation
Zhongpeng Sun, Kerolos M. A. Yousef, Michael Domm et al. (+13 more)
Free-space electro-optic modulators are key to emerging photonic systems, yet their performance remains limited by trade-offs between modulation efficiency, bandwidth, and device aperture. Here we report a hybrid BaTiO3 (BTO)/TiO2 metasurface for large-aperture, efficient, gigahertz-speed free-space electro-optic modulation. Combining scalable BTO film growth by
radio-frequency magnetron sputtering with mature TiO2 nanofabrication, we pattern the metasurface in TiO2 on an unetched BTO layer. The resulting devices support guided-mode resonances with quality factors exceeding 1300 and an optical confinement factor of ~0.8, while the continuous BTO layer makes efficient use of the applied voltage, together maximizing the overlap between the optical and driving fields within the BTO. A device with a 0.3 mm x 0.3 mm metasurface achieves a transmittance modulation efficiency of ~0.020 per volt and a -3 dB electro-optic bandwidth of ~0.8 GHz, with an effective Pockels coefficient of ~151 pm/V for the BTO. This establishes a scalable route to high-performance free-space electro-optic modulators for
LiDAR, free-space optical communication, and reconfigurable optical computing.
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All authors Zhongpeng Sun, Kerolos M. A. Yousef, Michael Domm, Agham Posadas, Xudong Li, Marcus Ossiander, Maryna L. Meretska, Yiwei Ju, Isabel Barth, Jason Tischler, Theodore P. Letsou, Moaz Waqar, Amirhassan Shams-Ansari, Xiaoqing Pan, Alexander A. Demkov, Federico Capasso
Fluid Dynamics
Elasto-hydrodynamics of droplet-pool-interactions
Md Sultan and Purbarun Dhar
In Newtonian fluids, impact of a droplet on a
liquid pool births a cavity, crown, capillary waves, and Worthington jet. The corresponding hydrodynamic events for elastic or Boger fluids, however, remain an uncharted domain of comprehension and exploration. We thoroughly investigate, via experiments, theory, and simulations, how elastic energy storage, fluid relaxation, and competitive inertio elasto capillarity govern the spatio temporal
evolution of the cavity, the crown, and the ensuing Worthington jet in polymeric elastic fluids. The events are systematically explored over a wide range of impact Weber and Deborah numbers, considering varied Newtonian and elastic fluid droplet pool combinations, and revealing new, and distinct morphological regimes compared to Newtonian counterparts. We illustrate that these new findings are purely driven by fluid elasticity, and not by viscosity or interfacial tension. We derive a theory for cavity radius
evolution, using energy conservation within potential-flow framework. We show that 30-40 % of the droplets kinetic impact energy may be stored as elastic energy by the stretching
polymer chains during cavity expansion. Appealing to the FENE P model, we derive a theory for the temporal
evolution of the radius of the elongated Worthington jet. We show that in elasto capillary regime, competitive elastic and capillary stresses lead to exponential decay of the jet radius. The role of elastic stresses and the local velocity field in governing cavity
evolution, morphology, and jet formation are further elucidated through computer simulations. Our findings significantly advance the uncharted paradigm of interplay between inertia, capillarity, and elasticity in droplet-pool interaction elastohydrodynamics.
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Space Physics
An Adaptive Approach for Modeling Collisionless Plasma Shocks and Ion Heating in the Shock Frame
Yuri A. Omelchenko, Igor V. Sokolov, Lulu Zhao et al. (+2 more)
We present a novel computational method for hybrid (kinetic ions, quasi-neutral fluid electrons) simulations of non-relativistic magnetized collisionless
plasma shocks, observed near the Sun, in the
solar system, and beyond. This Adaptive Frame-Of-Reference Approach (AFORA) enables simulations of shocks in their co-moving frames of reference, where shock
evolution remains quasi-steady for quasi-stationary upstream conditions, in contrast to moving shocks. We demonstrate our method in two spatial dimensions for a range of angles between the background
magnetic field and the shock normal (obliquities). Shock-frame simulations, conducted with a time-adaptive hybrid code, HYPERS, are shown to self-consistently capture upstream and downstream
magnetic fluctuations commonly observed by spacecraft at interplanetary shocks and Earth's bow shock. These fluctuations, which may be crucial for estimating the efficiency of ion acceleration at heliospheric and astrophysical shocks, are notably missing from many hybrid simulations of shocks, unless upstream external
turbulence is imposed. The quasi-stationary behavior of numerical shocks in the shock frame is confirmed in a series of animations and by demonstrating converged ion energy spectra in the downstream region. Our approach underscores computationally efficient and physically more accurate modeling of shock-driven
turbulence, downstream
plasma relaxation, and concomitant ion heating in the shock frame. The new method can be used for exploring ion relaxation at interplanetary (IP) shocks, more efficient studies of
cosmic rays (CRs) and
plasma turbulence, and more accurate predictions of seed populations of
Solar Energetic Particles (SEPs) at heliospheric shocks driven by coronal mass ejections (CMEs).
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All authors Yuri A. Omelchenko, Igor V. Sokolov, Lulu Zhao, Keheng Zhu, Michal Golan
Space Physics
Shrinking the Haystack: One-Class Machine Learning Detection of Magnetosheath Current Sheets in MMS Burst Data
Deep Ghuge, Daniel J. Gershman, Vadim Uritsky et al. (+1 more)
We present a morphology-first framework for narrowing the search for
magnetic-reconnection candidates in Magnetospheric Multiscale (MMS) burst-mode data. The target is the small, short, and frequently electron-only reconnecting current sheets that occur in turbulent magnetosheath
plasma. The pipeline operates in two stages. A local frame-quality gate based on minimum-variance analysis first retains only windows whose current-sheet coordinates are well defined. A one-class Deep Support Vector Data Description neural network then scores those windows against a library of 3,000 physically calibrated synthetic current sheets generated by Monte Carlo from a single published reference event. Acceptance into the surrogate library is governed by the second-order structure function $S_2(\tau)$: a candidate is admitted only if its multi-scale fingerprint tracks that of the seed event inside a tolerance band, together with a small number of shape-based checks. This $S_2(\tau)$-anchored construction defines the in-class distribution directly from a well-understood reference event and sidesteps the absence of a curated negative class in turbulent magnetosheath data. Applied to 15 magnetosheath
turbulence intervals from the literature (1.58 h of burst-mode coverage), the framework compresses 22,775 sliding windows to 270 candidate detections (a 98.8% reduction). Manual visual screening identifies 93 of these as candidate reconnection events and a further 118 as sheet-like, retaining 78% of the queue for follow-up; the candidate-reconnection pool extends well beyond the 22 detections that overlap the published reconnection-event catalog used here as a sanity check. The framework is intended as the data-reduction stage of a broader reconnection-search workflow, offered here as an initial proof of concept before extending the one-class design to additional feature channels.
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All authors Deep Ghuge, Daniel J. Gershman, Vadim Uritsky, Julia E. Stawarz
Atmospheric and Oceanic Physics
From Flight Logs to Atmospheric Science: Paragliders as Convection Sensors for Identifying Thermal Predictors
César Hernández-Aguayo, Matthieu Cristelli and Michael Benzaquen
Atmospheric thermal convection drives boundary-layer dynamics and vertical exchange of heat, moisture, and momentum, yet fundamental questions about thermal structure remain open due to limited in situ observational coverage. We introduce a novel high-resolution observational
dataset for atmospheric convection based on paragliding flight logs collected over metropolitan France during 2017-2024. Paragliders probe thermal updrafts by circling within them while carrying GPS variometers that record position and altitude; each climbing segment samples the vertical velocity field within a thermal column. Aggregated across 1.47 million climbing segments from 110,730 flights, this
dataset provides unprecedented spatial coverage and temporal resolution. To demonstrate the value of this observational resource, we extract three physically distinct observables from climbing segments and characterize their dependence on terrain, season, time of day, cloud state, and soil moisture. Coupling the paragliding observations with global atmospheric reanalysis data (ERA5, 0.25 degrees hourly) through a regression framework against 118 physically interpretable predictors, we identify leading atmospheric predictors of these observables. The empirical relationship between ceiling height and temperature-dew point depression matches the theoretical lifting condensation level scaling with striking precision supporting our methodology. Boundary-layer height emerges as the leading independent predictor of both ceiling height and thermal strength across all terrains and seasons, while vertical-velocity variability is controlled by surface heat-flux and wind variables. Taken together, our results highlight the utility of crowdsourced flight-log data for investigating atmospheric convection.
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Fluid Dynamics · Cross-listed from math.AP
Delayed Dissipation for Two-Dimensional Vortex Sheets
Victor Armegioiu
We quantify viscous energy loss for two-dimensional Delort
vortex sheets. Let $u^\nu$ be Leray-
Hopf solutions on $\mathbb{T}^2$ with uniformly bounded kinetic energy and total vorticity variation, and write $\omega_0^\nu=\mu_0^\nu+f_0^\nu$, where $\mu_0^\nu\geq0$ and $f_0^\nu$ is bounded in $L^p$, $p>1$. For every fixed $0<\delta<T$, $\nu\int_\delta^T\|\omega^\nu(t)\|_2^2\,\mathrm{d}t\lesssim_{\delta,T}\frac{1}{|\log\nu|}$. This improves the $O(|\log\nu|^{-1/2})$ bound of De Rosa and Marcotullio under the same assumptions and thereby disproves their
Conjecture 1.6 (arXiv:2602.15670, v1). The proof uses a sharp $L^2$-$H^1$-$H^{-1}$ interpolation inequality for nonnegative densities, retaining the total interaction energy of the positive vorticity rather than only its largest local mass. The bound also remains effective when the observation time grows with the Reynolds number. If the initial velocities are relatively compact in $L^2$, the loss still vanishes whenever $\log T_\nu=o(|\log\nu|)$; in particular, any prescribed energy loss must wait at least until $\nu^{-a}$ for some $a>0$. Previous estimates covered only $T_\nu=o(\exp(|\log\nu|^\kappa))$, $\kappa<1/2$, so this gives a
polynomial lower bound on the energetic lifetime of the inviscid
vortex-sheet model. If instead $f_0^\nu$ is bounded in $L(\log L)^\alpha$, the rate is $O(|\log\nu|^{-q_\alpha})$, $q_\alpha=\min\{2\alpha,1\}$, and the loss vanishes when $\log T_\nu=o(|\log\nu|^{q_\alpha})$. On $\mathbb{R}^2$, exact radial solutions attain these exponents for $0<\alpha\leq1/2$. At the endpoint, a bounded-energy $L^p$ family attains the rate $1/|\log\nu|$, while every fixed radial datum dissipates $o(1/|\log\nu|)$ and can lose a fixed amount of energy only on the diffusive scale $1/\nu$.
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Optics
Controlled generation of high-harmonic spatiotemporal optical vortices
Titouan Gadeyne, Vartika Vishnoi and Thierry Ruchon
Spatiotemporal optical
vortex (STOV) pulses are puzzling states of light, which see their transverse orbital angular momentum being debated in spite of possessing a topological charge. Thus far studied at conventional optical wavelengths, we herein demonstrate their upconversion to extreme ultraviolet (XUV) frequencies via high-harmonic generation (HHG). Circularly-symmetric infrared STOV pulses of topological charges $\ell=\pm1$ and $\pm2$ from a bespoke pulse shaper are focused in argon to drive harmonics, each order $q$ forming a spatiospectral ring in the far-field. Dependence of their radii on $q$ and $\ell$ indicates XUV
vortices of charge ${\ell}_{q} = q \times \ell$, and sensitivity of these modes to the focus position further establishes control over their production. The availability of XUV STOVs unlocks investigations and applications of their elusive angular momentum in the context of photoionization and other ultrafast spectroscopies.
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Computational Physics · Cross-listed from cs.LG
A Physics-Chemistry-Informed Neural Network (PCINN) for Real-Time Spatial-ALD Coverage Prediction and Reliable Kinetics Inversion
Ning Hu, Chang Liu, Yunlei Jiang et al. (+1 more)
Spatial atomic layer deposition (SALD) is a leading atmospheric-pressure, high-throughput route to industrial ALD, but design and control are limited by the cost of predicting surface coverage: high-fidelity CFD is far too slow for operating-window scans, while analytic models miss transport modulation such as the gas curtain. We present a physics-chemistry-informed neural network (PCINN), a hybrid surrogate with CFD-level accuracy at real-time speed: a query returns coverage in about 7 ms, roughly 5x10^4 times faster than a CFD solve, reaching a test R^2_log = 0.998 (leave-one-out R^2_raw = 0.974) from only 30 training cases spanning four orders of magnitude in coverage. The architecture is not a black box: a small network learns only the operating-condition to near-wall concentration closure, while the known surface kinetics is a hard-coded, trainable chemistry layer integrated along the substrate trajectory. This single-scalar bottleneck keeps it accurate under sparse data, interpretable and invertible. We add a full identifiability analysis (Fisher information, profile likelihood). The adsorption energy E_ads and desorption rate k_des are robustly identifiable; k_ads is not separately identifiable at a single temperature (only k_ads*c_wall is). Across four temperatures the prefactor nu and E_ads bind along a weakly identifiable degeneracy valley of slope 0.065 eV/decade, derived analytically as k_B T_eff ln(10) and turned into a reliability diagnostic: a seven-chemistry mismatch
matrix shows it is invariant under any single-Arrhenius mismatch and shifts only when a second thermally activated process appears, so a slope departure flags unmodelled site heterogeneity. Data come from simulation with known ground truth inverted by the same kinetic form, so the study verifies pipeline self-consistency and the identifiability boundary, not real parameters.
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All authors Ning Hu, Chang Liu, Yunlei Jiang, Yuan Dong
Fluid Dynamics
Multiscale passive scalar turbulence in a compressed subspace via tensor trains
Stefano Pisoni, Egor Tiunov and Chiara Calascibetta
Capturing the multiscale statistics of
turbulence in compressed form remains a central challenge for reduced-order modeling. We introduce a hybrid Tensor Train (TT) approach for a highly intermittent passive scalar. The hybrid TT matches Galerkin, wavelet, and standard TT decompositions for the structure functions while improving the representation of intermittent, non-Gaussian fluctuations. These results open a route toward evolving the linear dynamics of passive scalars directly in compressed tensor form, with potential applications to
quantum algorithms for fluid transport.
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Physics and Society
Discovery is not the opposite of application
Hiranya V. Peiris
Restructuring research funding as a choice between discovery and application gets the economics wrong, the evidence wrong and the people wrong.
Data Analysis and Statistics
Lossless Compression Performance for PETRA III Datasets
Malte Buschmann, Yannis Schumann, Christian Voss et al. (+2 more)
Large-scale research facilities increasingly face the challenge of managing rapidly growing data volumes while maintaining sustainable archival infrastructures. We present the first comprehensive study of data heterogeneity and lossless general-purpose compression performance for representative
datasets from the PETRA III synchrotron radiation source. Our corpus comprises more than 212 TiB of raw and processed data from ten experiments spanning multiple beamlines, detector systems, and scientific workflows. We observe substantial heterogeneity both between and within experiments, resulting in compression ratios that vary by more than two orders of magnitude across
datasets. Evaluating nine widely used lossless compression tools, we find that Zstandard and LZ4 consistently occupy the high-throughput region of the Pareto front, whereas ZPAQ achieves the highest compression ratios. Furthermore, heterogeneous compression strategies that adapt compressor choice to the underlying file category outperform uniform compression policies. Extrapolating from the benchmarked
datasets to the full PETRA III non-tape storage system, we estimate achievable compression ratios ranging from approximately 1.6 at $\sim$900 MiB/s throughput to 2.1 at $\sim$2 MiB/s. These results provide a quantitative basis for future archival and storage decisions at PETRA III, its future successor, PETRA IV, and other large-scale scientific facilities.
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All authors Malte Buschmann, Yannis Schumann, Christian Voss, Tigran Mkrtchyan, Philipp Neumann
Optics
A 2D Holographic Approach for All-Optical Single-Shot Temporal Characterization of SASE FEL Pulses
A. Azzolin, O. Cannelli, K.-F. Wong et al. (+31 more)
X-ray Free-electron
lasers (XFELs) deliver ultrashort and ultrabright radiation in a
photon-energy range spanning from extreme ultraviolet to hard X-rays. Supporting pulse durations down to hundreds of attoseconds, these sources are unique in enabling imaging of matter with unprecedented temporal and spatial resolution. However, schemes that produce such ultrashort pulses typically rely on Self-Amplified Spontaneous Emission (SASE), a
stochastic process that introduces significant temporal and spectral jitter, therefore requiring single-shot characterization methods for post sorting the acquired data. Although various methods have been developed for pulse characterization and delay tagging, they often come with experimental and computational complexity. Moreover, no existing method currently combines both single-shot pulse reconstruction and delay tagging at the attosecond time scale. To close this gap, we present two-dimensional time-domain Double-Blind Holography (2D-TDDBH), an entirely novel approach combining double-blind holography with concepts from diffractive imaging and ptychography. By recording the 2D spatial profile of the spectral interference between an extreme ultraviolet (XUV) FEL source and a high-harmonic generation (HHG)-based source, we achieve simultaneous waveform reconstruction and delay tagging of sub-10 fs FEL pulses with attosecond precision.
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All authors A. Azzolin, O. Cannelli, K.-F. Wong, V. J. Yallapragada, E. P. Månsson, C. Papadopoulou, E. Appi, U. Frühling, A. Magunia, M. Seitz, J. Hahne, A. bin Wahid, P. Biesterfeld, P. Mosel, S. Fröhlich, G. Cirmi, N. Kschuev, J. Roensch-Schulenburg, S. Schulz, S. Düsterer, M. Kovacev, U. Morgner, R. Moshammer, T. Lang, C. M. Heyl, V. Wanie, O. Raz, C. Ott, T. Pfeifer, E. Schneidmiller, N. Dudovich, D. Oron, A. Trabattoni, F. Calegari
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Vibrational spectroscopy identifies the bond asymmetry of hexagonal diamond
Li Zhu
Bulk hexagonal diamond has been synthesized by independent routes, but its structure remains contested: the two recent refinements disagree even on the sign of the difference between its two inequivalent bond lengths, 238~mÅ apart, and both depart from an earlier 2003 refinement. Here we test the competing structures with first-principles
lattice dynamics. Relaxed hexagonal diamond has an interlayer bond longer than the intralayer bonds by 24~mÅ in both functionals, an effect of its eclipsed conformation that scales with polytype hexagonality. The bright zone-center $A_{1g}$ mode gauges the interlayer bond at $\approx\!-2{,}100$~\icm~Å$^{-1}$, and neither refined coordinate reproduces the full pattern of measured modes. The only structure matching the twinned sample's three bands requires tens-of-gigapascals confining stress and
lattice constants excluded by its own diffraction. Raman spectroscopy and diffraction jointly select a small positive bond asymmetry: inverting the spectrum of the phase-pure sample gives $\OB-\OA=24\pm3$~mÅ (95% interval), and two determinations on separate samples give $+33\pm8$ and $+60\pm45$~mÅ. The 1{,}529~\icm{} feature cannot be assigned to homogeneous ideal 2H diamond, and the local HRTEM observation remains an open puzzle.
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Fluid Dynamics · Cross-listed from cond-mat.mtrl-sci
Centimeter-scale fully suspended metal and metal oxide thin films by one-step transfer-free liquid metal capillary forming
Chunlei Song, Zhenqi Guo, Yuanting Su et al. (+4 more)
Fully suspended thin films can decouple substrate effects and provide additional tuning degrees of freedom compared with their substrate-supported counterparts, making them unique platforms for next-generation thin film devices. Here we report one-step, transfer-free and substrate-free fabrication of centimeter-scale ultrathin fully suspended metal and metal
oxide film structures via
liquid metal capillary forming. We show that, analogous to soap film formation, the instantaneously developed few-nanometer-thick native surface
oxide can laminate various
liquid metals into micrometer-thick metallic films. Surprisingly, the surfactant-like metal
oxide bilayer can survive dewetting-induced
liquid metal drainage, forming suspended two-dimensional films featuring an enormous lateral size-to-thickness ratio on the order of 10^7. We further demonstrate rapid prototyping of metallic minimal-surface thin-walled structures and ultra-sensitive acoustic wave detection with these suspended thin film platforms.
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All authors Chunlei Song, Zhenqi Guo, Yuanting Su, Changren Tian, Yeqi Zhu, Liang Lei, Jianbo Tang
Applied Physics · Cross-listed from quant-ph
Release-free phononic crystal with strong microwave coupling
Joey Frey, Paul Burger, Trond Hjerpekjøn Haug et al. (+2 more)
Phonons hold promise for storing and transferring
quantum information, including in mechanically-mediated
quantum interconnects between superconducting
qubits and light. Phononic
crystal cavities confine gigahertz sound to micron-scale volumes well matched to near-infrared light. So far, these devices have typically been suspended to suppress phononic radiation loss into the substrate, but suspension limits thermal anchoring leading to excess noise. Release-free phononic
crystals have emerged as a way to address this challenge – but had yet to be shown compatible with strong electromechanical interactions. Here, we demonstrate a release-free phononic
crystal cavity strongly coupled to a high-impedance microwave resonator, with an electromechanical coupling rate $g_\mathrm{em}/(2\pi) \approx 30\,\text{MHz}$ that exceeds both the mechanical and microwave loss rates, leading to a cooperativity up to $\mathcal{C} \approx 180$ on resonance. In addition, our lithium niobate phononic
crystals reach quality factors above $10^4$ at millikelvin temperature on both silicon and sapphire substrates. Our results establish release-free phononic
crystals as compact, scalable interfaces between microwaves and gigahertz sound for emerging sensing, communication, and computing systems.
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All authors Joey Frey, Paul Burger, Trond Hjerpekjøn Haug, Johan Kolvik, Raphaël Van Laer
Atmospheric and Oceanic Physics
Distribution and Transport of Fragmenting Microplastics in a 3D Global Eulerian Model
Zih-En Tseng, Yue Wu, Chris Ruf et al. (+2 more)
Fragmentation, the breakage of matter into smaller pieces, is an important mechanism responsible for generating microplastics (MPs). We present the first global three-dimensional Eulerian model that resolves fragmentation alongside MP transport. The
evolution of particle size is modeled as a transfer from larger- to smaller-size bins, governed by a fragmentation kinetics framework. Relative to a reference simulation without fragmentation, two distinct effects are identified: (1) the surface concentration field of MPs becomes horizontally dispersed, and (2) MPs sink to depths of 500 m where the reference simulation shows negligible concentration. The vertical shift can be explained by the loss of buoyancy when particle size decreases, which facilitates horizontal sub-mixed layer transport once the particles sink below 100 m depth. Neutrally buoyant particles (with diameter d < 1 um) are continuously produced in the ocean by the fragmentation of larger particles and accumulate in the major oceanic gyres. Ultimately, the concentration of these neutrally buoyant MPs peaks at the gyre centers, a behavior that is not captured by prior models. Furthermore, the globally integrated size spectrum exhibits a steepening power-law slope over time that continues to evolve throughout our 25-year simulation. Comparisons with the AOMI Level-3wm observational
dataset demonstrate a meaningful improvement in predictive skill relative to previous models: including fragmentation elevates the spatial correlation between modeled and observed surface concentrations from 45% to 58%.
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All authors Zih-En Tseng, Yue Wu, Chris Ruf, Dimitris Menemenlis, Yulin Pan
Biological Physics · Cross-listed from cond-mat.soft
Superselectivity as a Receptor-Fluctuation Response
Xiuyang Xia
Superselective multivalent binding enables sharp receptor-density discrimination in targeting and sensing, but what its logarithmic response measures microscopically remains unclear. Here, we derive an exact response decomposition of the selectivity into receptor-state reweighting and a direct occupation response. In the dilute quenched Poisson limit, the direct term vanishes and selectivity is exactly the mean receptor excess beneath bound particles, which can be measured at a single density from a sufficiently large co-registered receptor-particle image. Beyond Poisson statistics, the excess is normalized by the Fano factor for a linear count response, while changes in distribution shape require the full count-resolved response.
Lattice simulations verify these relations across distinct receptor statistics, while off-
lattice simulations show that particle crowding enters through the direct term. These results establish a fluctuation-response framework linking multivalent selectivity to the local receptor fluctuations preferentially sampled by adsorption.
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Fluid Dynamics
Oscillatory shear flows and a new 2D self-sustaining process
Theo A. Lewy and Rich R. Kerswell
A new self-sustaining process (SSP) is identified in an oscillating spatially-homogeneous shear flow using a nonlinear Kelvin mode model. This SSP consists of energetic spanwise-invariant 1D `sheets' and weaker spanwise-dependent 2D fluctuations. It is instantaneously 2D, with a time-dependent invariant direction in the flow-cross-shear plane, and has a varicose
symmetry. The sheets oscillate in time and are linearly unstable generating fluctuations which then nonlinearly self-interact to reinforce the sheets. The linear instability of the sheet is shown to be due to a lift-up mechanism acting in tandem with `push-forward', which arises due to the `streamwise' shear of the sheets. As the Reynolds number $Re\rightarrow\infty$, both asymptotics and numerics show SSP lower branches with fluctuation velocity $|\boldsymbol{u}'|\sim Re^{-1/2}$. Implications are discussed for oscillatory wall-bounded flows.
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Optics
PROPEL: A Memory-Driven, Adaptive Vector-Flow-Field Router with Process-Aware Waveguide Generation for Large-Scale Photonic Integrated Circuits
A Abdur Rahman Akib, Eunso Shin, Jonathan Rogers et al. (+2 more)
Photonic integrated
circuits (PICs) are increasing in scale and routing complexity, driven by photonic computing, optical switching, programmable interferometer meshes, wavelength-routed optical networks-on-chip, and chip-to-chip optical interconnects. Manual waveguide planning becomes impractical as designs approach thousands of photonic components because routing must satisfy
geometric, optical, electrical, and manufacturing constraints. This paper presents the Photonic Routing Optimization and Placement Engine (PROPEL), a
memory-driven, native-accelerated adaptive vector-flow-field routing framework with process-aware waveguide generation for large-scale PIC design. PROPEL builds a routing kernel based on a bounded vector-flow-field
algorithm and DRC validation. The same kernel supports passive optical routing, active optical-electrical routing, and
topology-driven net assignment. C++ accelerates field and routing calculations, while Python performs detailed DRC replay, legality checking, route commitment, and GDSFactory-based geometry generation. Compared with state-of-the-art routing solutions, PROPEL is faster on 17 of 18 shared passive-routing cases, with a median speedup of 2.6x and a
geometric-mean speedup of 2.5x, while maintaining zero design-rule violations. PROPEL also supports length, delay, and optical-path-length matching, process-map-aware waveguide generation, route-
memory reuse, selective rip-up/reroute, and GDS-level legality replay. These capabilities address heterogeneous PIC layouts where optical, electrical, process,
topology, matching, and manufacturability constraints must be handled together.
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All authors A Abdur Rahman Akib, Eunso Shin, Jonathan Rogers, Jonathan Wierer, Stanley Cheung
Biological Physics · Cross-listed from q-bio.NC
Quantifying the cost of network computations to unpack structure-function relationships in the brain
Suman S. Kulkarni, Jason Z. Kim, Panagiotis Fotiadis et al. (+2 more)
The
brain supports computations through coordinated patterns of activity on an underlying network. These networks—from microscale navigational
circuits in insects to macroscale
brain areas in humans—are organized in structured ways that are thought to support their function. We seek a unifying quantitative framework to understand how network structure shapes the computations a network can readily support. To do so, we frame computation as a goal-directed transition of activity and quantify its cost on a given network using control theory. We then define the distribution of costs across all possible transitions as a $\textit{computational affordance landscape}$ that encodes which computations a network structure readily supports. We apply this framework to a
circuit model for how insects maintain a sense of direction and show that updating orientation is the least costly computation, with predicted inputs consistent with known circuitry. In the human
brain, we find that the affordance landscape varies systematically with the functional role of each network. Sensory networks display more heterogeneous landscapes (reflecting their role in specialized information processing), whereas association networks display more homogeneous landscapes (reflecting their role in generalized information processing). In recurrent neural networks trained on cognitive tasks, we show that learning progressively increases landscape heterogeneity, reshaping the distribution of affordable computations. Generally, we establish a quantitative framework for studying relationships between structure and computation in neural
circuits, with future applications extending to other biological and physical networks.
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All authors Suman S. Kulkarni, Jason Z. Kim, Panagiotis Fotiadis, Fabio Pasqualetti, Dani S. Bassett
Plasma Physics
Runaway Electrons in Stellarators: Unlikely or Unavoidable?
Ida Ekmark and Matt Landreman
Generation of relativistic runaway electrons has historically not been considered a possible problem in stellarators, but this may not hold in reactor-scale stellarators despite the lack of an externally driven
plasma current. The magnitude of the
plasma current governs the exponential generation of runaways, and even if there is no externally driven
plasma current, the bootstrap current could be considerable in reactor-relevant stellarators. In this paper, we present a pilot study on the generation of runaway electrons in stellarator temperature collapse scenarios. To reliably study runaway electrons in stellarators, we implemented a stellarator
plasma model in the runaway electron simulation tool DREAM. The model is used to explore when runaway electrons can be generated with regard to combinations of initial
plasma current, temperature decay time scale, and post-decay temperature. Special consideration is given to runaway generation through avalanche multiplication in stellarators, and how it compares to tokamaks. We find that significant runaway electron generation is possible also in stellarators, and demonstrate under which conditions it could be a concern. However, our findings support the conception that runaway electrons will be less of a concern in reactor-scale stellarators compared to tokamaks.
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Biological Physics · Cross-listed from cond-mat.soft
Elastodynamics from Eulerian Poisson-bracket formalism: application to chiral odd solids
Cheng-Tai Lee and Tomer Markovich
The Poisson-bracket (PB) formalism is widely used to derive dynamics of coarse-grained (CG) fields to capture large-scale physics, extending the role of PBs in classical particle mechanics to macroscopic fields. It has been applied to fluctuations in critical phenomena, hydrodynamics of
liquid crystals,
liquid crystal elastomers, tissues, and the emergence of odd viscosity from spinning particles. The PB formalism can be formulated in either the Lagrangian framework, using reference space, or the Eulerian framework, using real space. Conventionally, the Lagrangian formulation is used for elastic solids, and the Eulerian one for fluids. However, growing interest in Eulerian descriptions of solids has emerged for phenomena naturally defined in real space, such as viscoelastic responses, moving interfaces, and field-induced structural changes in particles. Here we develop a systematic formulation for applying the Eulerian PB formalism to elastic systems with potentials typically written in Lagrangian space, and clarify its consistency with the Lagrangian counterpart. We show that the Eulerian formulation generates additional nonlinearities absent in the Lagrangian framework. Such nonlinearities originate from CG volume changes under coordinate transformation and from particle flow across neighboring CG volumes. They must be retained when nonlinear effects are important. To illustrate, we study
chiral active solids of finite-sized particles, where active torques drive internal particle rotations and generate
geometric nonlinearities. These nonlinearities give rise to the odd elastic modulus, which non-reciprocally couples two different shear modes in stress-strain response. By recovering this modulus directly from the Eulerian PB formalism, we demonstrate its ability to capture emergent nonlinear elastic behavior in driven active solids, whose stresses are naturally measured in real space.
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Atomic Physics
A single atom emitting resonance fluorescence into a coherent beam, and its use for non-destructive atom thermometry
Tomáš Lamich, Laura Zarraoa, Sondos Elsehimy et al. (+2 more)
Using a far-off-resonance optical dipole trap, we place a single neutral $^{87}$Rb atom in a weak, atom-resonant coherent beam, while also strongly illuminating it from an orthogonal direction to produce resonance fluorescence. The atom-modified coherent beam is then collected and its
photon statistics analyzed. We observe first-order interference that can increase or decrease the beam flux, depending on the relative phase of the coherent beam and resonance fluorescence. This confirms predictions of Goncalves et al. [Phys. Rev. A 104, 013724]. The interference visibility is also shown to be a sensitive, time-resolved, non-destructive thermometer: by fitting the resulting
photon count distributions, we infer the center-of-mass localization of the atom within the trap. With $1200$ atoms and integration time of $80\mathrm{ms}$ per atom, we demonstrate temperature uncertainties of $4 %$ for $\sim 30 \mu\mathrm{K}$ temperatures at $\sim 200\mu\mathrm{s}$ time resolution.
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All authors Tomáš Lamich, Laura Zarraoa, Sondos Elsehimy, Morgan W. Mitchell, Romain Veyron
Optics
High-NA vectorial hologram optimization
Michael Wischert, Fiona Hellstern, Paul Uerlings et al. (+3 more)
We present a vectorial phase-only framework for the gradient-based optimization of computer-generated holograms. Our approach addresses a critical limitation in high numerical aperture (NA) optical systems, where standard scalar approximations often experience significant fidelity degradation. We highlight the limitations of scalar diffraction models (Fraunhofer and Debye) at high NA for representative classes of target intensities, namely tweezer arrays and extended flat-top profiles. Using a differentiable Richards-Wolf forward model, we numerically demonstrate stable algorithmic convergence and the generation of highly uniform intensity profiles in the deep non-paraxial regime. At NA=0.9, Richards-Wolf (RW) optimization reaches flat-top and tweezer uniformities of 99.97 % and 99.98 %, respectively, with a mean tweezer ellipticity of $\varepsilon=$1.007, while scalar forward models show target-dependent degradation in plateau fidelity or focal geometry. Furthermore, because the RW model returns the full vectorial field, the same framework can optimize objectives that depend on local polarization. We demonstrate this for a polarization-sensitive optical-dipole-potential target, where direct RW-potential optimization reduces the mean normalized residual by more than an order of magnitude when including vector and tensor light-shift terms.
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All authors Michael Wischert, Fiona Hellstern, Paul Uerlings, Tilman Pfau, Stephan Welte, Ralf Klemt
Optics
Causality-Aware Interaction Selection for Retarded Green-Function Assembly
Sushil Kumar, Wolf van der Hert, Giampiero Gerini et al. (+1 more)
In time-domain integral-equation (TDIE) solvers, the assembly of the retarded Green-function interactions remains a major computational bottleneck. We present a causality-aware assembly strategy that exploits the finite space–time support of the retarded Green function to identify admissible interactions prior to numerical evaluation. By using causality as an exact interaction-selection criterion, causally inadmissible interactions are excluded a priori, reducing assembly complexity without modifying the underlying TDIE formulation or introducing approximations. Numerical validation confirms that the proposed
pruning preserves the TDIE transient response. The remaining admissible interactions are organized into vectorized shared-
memory workloads for efficient assembly. The results demonstrate a 41 % reduction in evaluated interactions, a 2.6 times single-worker algorithmic speedup, and a total assembly-time speedup of up to 109 times using 64 CPU workers.
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All authors Sushil Kumar, Wolf van der Hert, Giampiero Gerini, M. C. van Beurden
History and Philosophy of Physics
Erwin Schroedinger: His Poetry and Fragment of a Galilean Dialogue
Helge Kragh
While Erwin Schroedinger's contributions to
quantum mechanics and other areas of theoretical physics are very well known, his works as a poet and literary writer are usually ignored. In this paper I reconsider his poetry and refer to a few poems written about him. A short fragment of a Galileo-inspired dialogue that Schroedinger published in 1955 is as interesting as it is puzzling and little known. The dialogue is essentially about atomic theory as known much earlier, namely in the early 1910s. Indeed, there is the slight possibility that Schroedinger may originally have conceived it at that time and even composed a version of it. Apart from considering the origin and reception of the manuscript, I analyze its content from the point of view of the history of physics.
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Optics
Universal Phase Contrast in Micro-CT Systems
Grammatiki Lioliou, Alberto Astolfo, Marco Endrizzi et al. (+3 more)
Conventional high-resolution micro-CT systems are regarded as attenuation-based unless visible Fresnel fringes reveal the presence of propagation-based phase contrast. Here we show that this interpretation is incomplete. When propagation-induced phase transfer is non-negligible relative to the system blur, micro-CT operates in a phase-transfer regime in which propagation improves spatial resolution relative to that expected from source and detector blur alone, irrespective of whether Fresnel fringes remain visible. Because micro-CT systems possess finite source and detector blur, this phase transfer is accompanied by a degree of hardware-induced phase
retrieval (HIPR), ranging from under-HIPR to matched-HIPR and over-HIPR. We further identify detector-induced phase
retrieval (DIPR) as the optimal case in which the detector provides all of the filtering required for phase
retrieval, thereby preserving the phase-induced resolution enhancement while introducing spatial correlations between detected
photons that reduce high-spatial-frequency noise. We derive analytical conditions for HIPR and DIPR, introduce frequency-domain metrics quantifying preserved phase transfer and detector compatibility, and validate the framework numerically with simulations and experimentally using custom and commercial micro-CT systems. Our results demonstrate that phase-induced resolution enhancement can occur in conventional micro-CT systems even in the absence of visible Fresnel fringes, changing how image formation, spatial resolution, and optimization should be interpreted.
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All authors Grammatiki Lioliou, Alberto Astolfo, Marco Endrizzi, David Bate, Charlotte K. Hagen, Alessandro Olivo
Optics
Tomographic Phase Imaging with Randomized Probe Imaging
Jordan T. O'Neal, Byeongdu Lee, Soenke Seifert et al. (+6 more)
We demonstrate tomographic phase imaging of cubic gold nanoparticles with sub-100 nm resolution requiring just a single far-field coherent diffraction pattern per projection. By using randomized probe imaging (RPI), a real-space amplitude and phase image can be reconstructed from a single diffraction pattern. These phase images are then fed into a standard tomographic workflow to retrieve the 3D volume. Nanoscale X-ray phase
tomography has often relied on ptychography, which requires slow 2D scanning for each projection. By using RPI, the data collection is greatly sped up at the cost of some resolution. We compare an RPI-
tomography volume to a ptychography-
tomography volume of the same sample, finding high consistency between the two methods. To the best of our knowledge, this is the first application of RPI to
tomography.
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All authors Jordan T. O'Neal, Byeongdu Lee, Soenke Seifert, Hanna Ruth, Michael Wojcik, Haidan Wen, Yanqi Luo, Yi Jiang, Junjing Deng