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Physics Physics

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Monday 17 August

Applied Physics · Cross-listed from quant-ph

zenDot: An LLM-integrated quantum TCAD platform for semiconductor quantum-device design and optimization automation

Zeheng Wang, Yan Liu, Yue Hao et al. (+1 more)

Semiconductor quantum-device design still lacks an integrated Technology Computer-Aided Design (TCAD)-like environment that connects material geometry, quantum many-body simulation, and automated design. Here we introduce zenDot, a large-language model (LLM)-integrated quantum TCAD platform that links a material-labelled device state to a unified condensed-matter physics toolbox. The device and calculation components are integrated into a desktop workbench, Python API, and an embedded LLM agent, allowing electrostatics, charge and transport characterization, correlated-state calculations, and qubit modelling to be executed within one reproducible environment. We demonstrate zenDot on a Si/SiO2 double quantum dot, where a single device state reproduces the characterization workflow and supports hybrid, tunnel-charge, and singlet-triplet qubit analyses. A platform-level universal-control scan revises the singlet-triplet operating point and reduces the predicted worst-gate infidelity by nearly 30-fold. Beyond analysis, the LLM agent directly operates the same physics environment as human users, proposing design changes, executing registered simulations, and iterating on solver-returned metrics under physics-aware validation. Across three demonstration tasks it completes 18 validated design iterations, including geometry modification followed by a full re-solve from the material stack. zenDot establishes a machine-operable quantum TCAD workflow that connects device physics with LLM-driven design exploration.
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All authors Zeheng Wang, Yan Liu, Yue Hao, Genquan Han

Optics

Transport-defined photodetection through electrically selectable nonequilibrium carrier transport

Jiaxuan Cai, Yan Xie, Ning Yang et al. (+9 more)

Broadband optical fields can change in both intensity and spectral distribution, but a fixed-response detector maps this evolving information onto a single electrical signal. Here we demonstrate transport-defined photodetection, in which electrical bias selects how photoexcited carriers are redistributed, escape and are collected, creating complementary response functions within one shared active region. In a GaAs/AlGaAs semiconductor ratchet, light-driven ratchet transport defines the response at 0 V, whereas the spectral evolution at -2 V is consistent with field-assisted hot-carrier transport. The overlapping states span a measured spectral range of 0.4-94.5 {\mu}m at 5 K, provide state-dependent calculated detection floors and support joint infrared operation at 30 K. Direct optical beat notes at 7.432 GHz in the mid-infrared and 17.103 GHz in the terahertz demonstrate optical-to-electrical conversion. Their common-path outputs recover an imposed spatial temperature gradient and the transient field-of-view-integrated effective radiation temperature of laser-excited graphite. These results establish post-photoexcitation transport as a function-defining design variable for semiconductor photodetectors, complementing structure-defined, field-tuned and optically encoded approaches to reconfigurable photodetection.
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All authors Jiaxuan Cai, Yan Xie, Ning Yang, Weidong Chu, Peng Bai, Lianhe Li, Edmund H. Linfield, Hanbing Wang, Meng Chen, Guanchen Li, Yingxin Wang, Ziran Zhao

Optics · Cross-listed from quant-ph

Sub-cycle metrology of bright quantum light

Shima Gholam-Mirzaei, Michael T. Weil, David N. Purschke et al. (+7 more)

In quantum optics, quantization of the electromagnetic field typically occurs in a finite volume - a cavity - which results in discrete frequency modes where photons are created, annihilated and exchanged between such modes. As a result, evolution of quantum optical states is periodic in the carrier wave of the field, measurement protocols return cycle-averaged information, and any sub-cycle evolution that is foundational to many light-matter interactions, especially at high field strengths, remains hidden. Adapting an attosecond technique, here we capture the electric-field evolution of a quantum optical state, femtosecond bright squeezed vacuum, with sub-cycle precision. We find that it consists of many stochastic, time-localized bursts within each pump pulse whose phase randomly switches between two values. We exploit the random phase flips to generate quantum random bit sequences with a generation rate that can reach petahertz frequencies. In addition, the sub-cycle resolution allows us to measure coherence functions of the waveforms between any two times, which we explain with a superposition of time-limited modes. These results bridge attosecond metrology and quantum optics and pave the way to measuring quantum light-matter interactions as they evolve on a few-femtosecond time scale, and integrate quantum randomness in petahertz electronics.
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All authors Shima Gholam-Mirzaei, Michael T. Weil, David N. Purschke, Katarzyna M. Kowalczyk, André Staudte, David M. Villeneuve, Paul B. Corkum, Jeff S. Lundeen, T.J. Hammond, Giulio Vampa

Optics · Cross-listed from quant-ph

Resolving and resetting the charge environment of single T-centers in silicon p-i-n waveguides

Chaoshen Zhang, Hanbin Song, Lukasz Komza et al. (+6 more)

The silicon T-center is a telecom-band spin-photon interface in a manufacturable photonics platform. In nanophotonic devices, however, its optical linewidth is broadened by a fluctuating charge environment, limiting photon indistinguishability for quantum networking. Here, we address this challenge through characterization and suppression of the local charge-noise of single T-centers in lateral p-i-n waveguides, demonstrating an unheralded method of T-center optical linewidth narrowing. Above-band illumination resets the charge environment, neutralizing the local field and suppressing spectral diffusion. Across 46 emitters this reset narrows the median linewidth 3.5-fold to 0.57(11) GHz, and an optimized emitter reaches 128(22) MHz, the narrowest unheralded linewidth reported for an integrated T-center. The narrowed transition supports coherent optical Rabi oscillations with a coherence time of 20(2) ns. Finally, we perform Stark-shift tuning using the p-i-n junction, and read out the local electric field and the charge-noise width at 15 mK. An analytical model of proximal surfaces, bulk, and junction field effects provides good agreement with our findings. Our multi-pronged characterization of the nanophotonic-integrated T-center charge environment enables future device optimization toward scalable quantum interconnects.
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All authors Chaoshen Zhang, Hanbin Song, Lukasz Komza, Aaron M. Day, Enrique Garcia, Donald Witt, Mihir K. Bhaskar, Alp Sipahigil, Evelyn L. Hu

Classical Physics · Cross-listed from astro-ph.IM

Exact spherical-wave forward model for radio reflection from stratified media and implications for the anomalous-polarity events observed by ANITA

Paramita Dasgupta

Radio detection of ultra-high energy particles relies on the propagation and reflection of broadband radio pulses at boundaries between natural media. In the Sommerfeld–Weyl treatment, a spherical wave is decomposed into plane-wave components and their reflection from a single homogeneous interface is calculated exactly. We extend that treatment to an arbitrary number of laterally uniform spherical layers. Both the spherical-wave decomposition of the source and the spherical geometry of the boundary are retained, while the reflection and transmission coefficients of the plane-wave components are replaced by the exact characteristic-matrix coefficients of the layered medium, evaluated at the local incidence angle on the spherical boundary. When the layer contrast is removed, the formalism recovers the single-boundary result to machine precision, and it reproduces the published spherical-surface reflectivity calculation to better than $1.1\%$ at ten HiCal-2 elevation angles, with a mean deviation of $0.6\%$. We reproduce the measured HiCal-1 reflected pulses from their measured direct partners, with a best signed correlation of $0.83$ and a median of $0.70$ across $106$ pairs, of which $101$ show the expected polarity inversion. Applied to the six reported ANITA anomalous-polarity event geometries, the buried-layer refractive index required for a sign change of the reflection coefficient ranges from $1.68$ at the steepest event to $3.8$–$5.4$ at the four near-horizon events. The full waveform calculation gives no non-inverted reflected pulse at any of these angles, showing that shallow, laterally uniform firn layering does not account for the polarity of the anomalous ANITA events. Because the formalism depends only on the complex refractive index of the medium, it applies more generally to isotropic, nonmagnetic stratified media, including ice, lunar regolith, and conducting layers.
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Sunday 16 August

Atmospheric and Oceanic Physics · Cross-listed from stat.AP

Where should the null live? Surrogate tests for clustering of threshold-derived air-quality indices, with application to PM2.5 exceedances in Chile

Mauricio Herrera-Marín

Air-quality and climate monitoring routinely convert native-resolution measurements into exceedance counts before testing whether high values cluster in time. A surrogate null can be imposed on the derived index or on the native series and then propagated through the same thresholding and aggregation. We show that the two placements can encode different scientific hypotheses and lead to opposite conclusions. In 31 Chilean PM2.5 monitoring stations (2018–2025), weekly clustering of days above the 50 ug m^-3 national 24-hour standard was significant at all stations under an index-level IAAFT null but at only two under a daily native-resolution null; a native generative null with seasonal marginals and short-memory Gaussian-copula dependence agreed with the native surrogate at 30 of 31 stations. Across thresholds spanning the WHO guideline (15 ug m^-3) to the Chilean episode-alert level (80 ug m^-3), index-only rejections increased from 8 of 31 to all eligible stations as monthly event probabilities became more seasonally concentrated, and equalizing monthly event probabilities at the 50 ug m^-3 level reduced index-only decisions from 29 to five. We formalize the issue as null transport through a lossy observation map: an exact aggregate-level equivalent of a native null exists if and only if the randomization kernel is lumpable with respect to that map. A within-fiber diagnostic, which perturbs native amplitudes while keeping the observed index exactly fixed, shows that this condition fails in the monitoring data: the native null distribution moved by a median of 18 times its Monte Carlo variability. Weekly clustering of PM2.5 exceedances in Chile is therefore fully compatible with seasonality plus short-memory daily persistence, and index-level surrogate rejections should not be read as evidence about daily concentration dynamics.
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General Physics

Tsallis Holographic Dark Energy model with varying gravitational constant vs $\Lambda$CDM model: statistical analysis of observational data and tensions problem

Artyom V. Astashenok and Alexander S. Tepliakov

We investigate the cosmological evolution of a flat Friedmann–Robertson–Walker Universe filled with Tsallis holographic dark energy (THDE) under the assumption that the gravitational constant $G$ varies with time according to the power-law parametrisation $d\ln G / d\ln a = \alpha_G = \mathrm{const}$. In this framework, the holographic dark energy density is given by $\rho_{\mathrm{DE}} \propto L^{2\gamma - 4}$, where $L$ is the future event horizon and $\gamma$ is the Tsallis non-additivity parameter. We study both the past and future evolution of the Universe for various values of the model parameters $C$, $\gamma$, and $\alpha_G$. The viability of the model is tested against a combination of observational data, including the Pantheon+ Type Ia supernova sample, direct Hubble parameter measurements $H(z)$, and baryon acoustic oscillation (BAO) data. Using Markov Chain Monte Carlo (MCMC) methods and Bayesian analysis tools such as the Deviance Information Criterion (DIC), the Bayes factor, and the suspiciousness metric, we perform a rigorous statistical comparison with the standard $\Lambda$CDM model. Our results show that models with a varying gravitational constant are preferred over $\Lambda$CDM. The best fit to the combined data is obtained for the THDE model with $C < 1$. Furthermore, we analyse the internal consistency of the data sets using the Index of Inconsistency, the $Q_{\mathrm{DMAP}}$ statistic, and Bayesian suspiciousness. We find that the THDE model with varying $G$ and $C < 1$ partially alleviates the tensions between different probes, reducing the significance from $\sim 7.4\sigma$ to $\sim 5.3\sigma$.
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General Physics

Dark matter deformations of photon-ring echoes in horizon-scale interferometry

Mohsen Fathi

Strong lensing around a rotating black hole produces delayed and rotated higher-order images even in Kerr. We ask how a dark matter (DM) environment changes these photon-ring echoes after the leading ring scale is matched to Kerr. We follow the signal from rotating DM geometry to finite-order photon transfer, slow-light emission, interferometric visibilities, and source-population tests. For a strong central-spike benchmark with $a/M=0.8$ and $i=70^\circ$, a $1.49\%$ critical-parameter fingerprint remains after ring matching. The order-1 and order-2 delay medians are $13.33M$ and $33.06M$, and the 230-GHz static and dynamic visibility contrasts are $0.070F_0$ and $0.112F_0$. The differential signal also remains distinct in a shared-source oracle test. The harder step is attribution when the source is unknown. Raw EHT-like closures give AUC $0.658$, while fresh validation with total-flux and compact spatial source drivers gives $0.507$ and $0.500$. We therefore use the loss of separation on new sources to derive observing requirements rather than a detection claim. At the pre-defined Kerr threshold, 75% power requires $d=2.319$, compared with $d=0.553$ for the raw independent-source test. Under a fixed-mean diagnostic, the residual source scatter would need to be about $0.238$ of its present value, although the bootstrap range $0.022$–$0.444$ is broad. Daily gaps can also miss the smaller spike–Kerr delay difference. Finding a photon echo and attributing a small deformation to DM are therefore different tasks. Robust attribution needs source control and suitable delay coverage, not sensitivity alone.
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Fluid Dynamics

An improved phase-field framework for simulating impacts of solidifying metal drops

Ali Mostafavi, Vitaliy Yurkiv, Alexander L. Yarin et al. (+1 more)

Here, an improved phase-field method for simulating the impact dynamics of solidifying molten metal droplets is developed using targeted free-energy modifications. Conventional Cahn-Hilliard-Navier-Stokes (CHNS) formulations generally do not capture melt retraction over a solidified portion of the droplet, because the newly formed solid region is not treated as an actual internal boundary in a single-order-parameter diffuse-interface model. As a result, the formulation lacks an internal wetting condition or localized wall-energy mechanism capable of driving melt retraction over a solidified splat. To address this limitation, a diffuse-domain wall-energy term is added to the free energy, with a chemical-potential contribution that is active near the diffuse liquid-solidified-material-gas triple-line region, enabling the remaining melt to retract over a solidified splat. In addition, a solidification penalty term is introduced to immobilize the solidified splat formed during impact and suppress unphysical interface motion caused by residual Cahn-Hilliard diffusion inside the frozen region. The proposed formulation is validated against benchmark experiments on impacts of solidifying tin droplets. The results reveal that the localized wall-energy term captures post-maximum-spread melt retraction, while the penalty term effectively arrests motion of the solidified splat. Qualitative and quantitative comparisons with experiments, volume-of-fluid simulations, and standard phase-field predictions demonstrate that the proposed formulation captures post-maximum-spread melt retraction and provides an accurate estimate of the stabilized final splat diameter.
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All authors Ali Mostafavi, Vitaliy Yurkiv, Alexander L. Yarin, Farzad Mashayek

Optics

Monolithic high density integrated photonics on bulk lithium niobate

Zizheng Li, Harmen Smedes, Bruno Lopez-Rodriguez et al. (+3 more)

Functional electro-optic (EO) tunable photonic integrated circuits are crucial to next-generation information processing and advanced computing, where ferroelectric materials such as lithium niobate (LiNbO3) provide outstanding optical properties and versatile tuning mechanisms. However, beyond achieving high-performance devices, practical deployment of LiNbO3 photonic integrated circuits requires rapid and cost-effective scale-up, which remains challenging because of the fabrication complexity and high costs of ion-sliced thin-film lithium niobate and wafer bonding processes. To address this gap, we demonstrate a fully monolithic photonic platform, amorphous silicon carbide (a-SiC) on bulk LiNbO3 crystal substrate, enabling scalable, CMOS-compatible, low-cost, and high-density photonic integrated circuits without relying on thin-film LiNbO3. This integration approach breaks the long-standing cost-performance-scalability tradeoff, and intrinsically eliminates the need for sophisticated fabrication processes, including ion slicing, wafer bonding, and LiNbO3 etching. It realizes high-density, low-loss, and record high EO tuning efficiency of VpiL = 2.87 Vcm on bulk LiNbO3 crystal substrate. Furthermore, leveraging slow-light effect near photonic crystal bandgap, an 8.5-fold EO tuning efficiency enhancement is achieved, highlighting the platform's capability in confinement control and dispersion engineering.
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All authors Zizheng Li, Harmen Smedes, Bruno Lopez-Rodriguez, Thomas Scholte, Simon Groeblacher, Iman Esmaeil Zadeh

Instrumentation and Detectors · Cross-listed from cond-mat.supr-con

Identification and electrothermal modeling of persistent current switch operating regimes in a Siemens MRI magnet using external electrical measurements

Volodymyr Pupkov

The persistent current switch (PCS) closes the superconducting loop of an MRI magnet. During ramping it is commonly treated as a binary element: with the heater on, the PCS branch is assumed effectively open; after heater turn-off, it is assumed superconducting. Field measurements with an MPS2 service power supply (Digit Systems) on a Siemens MAGNETOM Avanto show that the PCS remains electrically active and that its resistive state can persist after heater turn-off through Joule self-heating. Dedicated maneuvers identified two resistive regimes. With the heater on, the low-voltage resistance is nearly constant; after heater turn-off, self-heating produces a power-law voltage dependence. Both are described by a single effective electrothermal relation, $R_{sw}=C\,(P_h h+V_{node}^2/R_{sw})^a$, where $h$ is the recorded heater state, spanning a 690-fold resistance range. Final-hold data from 17 Siemens magnet sessions confirmed the voltage dependence of effective PCS resistance. Since branch-current relaxation follows $\tau=L/R_{sw}$, the required hold time depends on switch state rather than a fixed delay; the median margin after source settling was $3.6\,\tau$. The intersection of the PCS characteristic with the external-circuit load line defines the boundary of self-sustained resistive operation. For Avanto, the predicted 0.062 V threshold lay between superconducting recovery at 0.06 V and resistive-state persistence at 0.07 V, and retrospectively classified all 24 archived segments correctly. Including both PCS resistive regimes in the dynamic model reproduced the observed current redistribution: RMSE decreased from 1.449 to 0.154 A, a factor of 9.4. This improvement required explicit representation of heater state.
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Fluid Dynamics

Similarity of start-up flow in porous media for large pressure gradients

Yoshiyuki Sakai, Lukas Unglehrt and Michael Manhart

We investigate the start-up flows through ordered porous media (hexagonal close-packed, face-centred cubic and body-centred sphere packs) by means of direct numerical simulations. The flows are initiated from rest and driven by a constant pressure gradient, allowing us to examine the transient development across a wide range of Hagen numbers. Dimensional analysis identifies two relevant time scales: the viscous diffusion time $\tau_\mathrm{visc}$ and the inviscid time $\tau_\mathrm{inv}$. While the small-time behaviour follows the viscous asymptotics of Johnson et al. [J. Fluid. Mech. 176, 379 (1987)], the subsequent emergence of nonlinear effects is universally governed by the inviscid time $\tau_\mathrm{inv}$, rather than by any critical Reynolds number. At the pore scale, the transient evolution is characterised by the growth of thin vorticity layers on the sphere surfaces, their detachment into the pore space around $t \sim \tau_\mathrm{inv}$, and the formation of inertial cores. Despite geometric differences, these processes occur in a remarkably similar sequence across all three packings. Vorticity magnitude exhibits laminar boundary-layer scaling with Hagen number, while in the body-centred cubic sphere pack case a transition towards turbulent-type scaling is observed. These results establish $\tau_\mathrm{inv}$ as a unifying measure for the onset of nonlinearity in strongly accelerated porous media flows, with direct implications for the modelling of unsteady transport in natural and engineered systems.
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Optics

Information-optimized color metalenses for camera imaging

Hyoseok Park and Yeonsang Park

A metalens is conventionally built by prescribing a target phase and matching each meta-atom to it, and making that phase achromatic across the visible band is the main difficulty in color imaging. We remove the prescribed phase entirely. The meta-atom width map is optimized directly against the information the raw, noisy, mosaic-sampled camera measurement carries about the target image, differentiated through Maxwell propagation, the color-filter mosaic, pixel integration and sensor noise, with material, thickness and library held fixed. On a single-layer silicon-nitride platform, starting from a hyperbolic design, this raises delivered target information by 15.8% despite lower collected charge, produces the most balanced set of channel responses at the sensor plane relative to their respective axial maxima, and reduces blue-channel blur. A high-signal-to-noise held-out reconstruction improves in spatial fidelity and color accuracy. The same width-only optimization improves color across silicon-nitride, silicon-dioxide and titanium-dioxide libraries.
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Fluid Dynamics

Compressibility Driven Wake Transition and Hysteresis over Cargo Aircraft Aftbodies

Chitrarth Prasad, Rajesh Ranjan, Daniel J. Garmann et al. (+1 more)

Aft sections of military cargo aircraft employ flat surfaces at high upsweep angles to accommodate ramp doors, producing flow features that affect cargo-drop accuracy, paratrooper safety, and aerodynamic performance. Fundamental studies have primarily examined near incompressible flow over a canonical surrogate consisting of a freestream aligned cylinder with a planar, sharp edged upswept base. The flow exhibits peripheral separation, a horseshoe vortex, and a counter-rotating streamwise vortex pair that persists downstream. The present investigation delineates the effects of compressibility on the wake and examines how these effects depend on basal upsweep angle. Wall-resolved large-eddy simulations are performed at Mach numbers of $0.1$, $0.3$, and $0.5$ for upsweep angles of $32^\circ$ and $45^\circ$ at a nominal Reynolds number of $25{,}000$. For the $32^\circ$ afterbody, increasing Mach number enlarges the upstream recirculation region and delays vortex-pair formation, while these effects diminish downstream. For the $45^\circ$ afterbody, similar recirculation-region growth triggers a bifurcation at Mach~0.5 from the vortex-pair state to a broad separated turbulent wake. A descending-Mach sequence to 0.3 and 0.1 reveals hysteresis, with the separated-wake state persisting at lower Mach numbers and remaining robust to Reynolds-number variation. Thus, both states can occur at identical Mach and Reynolds numbers, with topology and pressure loading governed by Mach number history.
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All authors Chitrarth Prasad, Rajesh Ranjan, Daniel J. Garmann, Datta V. Gaitonde

Applied Physics

On-chip nanoplasma for adaptive electromagnetic protection

Ruiqi Huang, Hanqing Liu, Kui Dang et al. (+12 more)

Over the past decade, semiconductor diodes have served as the primary switching elements in adaptive electromagnetic (EM) protection, yet their performance has been compromised by parasitic effects and thermal accumulation, rendering them inadequate against the rapidly evolving landscape of high-power microwave (HPM) threats. Here we show that on-chip nanoplasma switches (NPMS), composed of gallium nitride electrodes on silicon carbide substrates, exhibit superior radio frequency (RF) and thermal characteristics, positioning them as ideal field-driven switches in RF front-end protectors. By integrating NPMS into metasurfaces, antennas and circuit limiters, we achieve an adaptive response that ensures low-loss transmission for normal signals and high shielding against HPMs, while offering extended operating bandwidth and substantially higher tolerance than conventional solid-state devices. This robust, nanoscale structure has significant potential for protecting unmanned aerial vehicles, radars, satellites and other highly integrated platforms requiring strength and stability in EM environments. The findings of this study open up new routes to support EM safety of high-precision detection and imaging for next-generation RF front ends, with straightforward scalability to millimetre-wave and terahertz frequencies.
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All authors Ruiqi Huang, Hanqing Liu, Kui Dang, Yue Lang, Ruiyang Peng, Qihui Zhou, Qian Dong, Xiaocheng Ni, Yuan Xu, Jibin Liu, Yanlin Xu, Chenxi Liu, Song Zha, Jincheng Zhang, Peiguo Liu

Chemical Physics

Gas-generating reactive flows in bicontinuous catalyst support structures

J.M.P. Beunen and J. Harting

A major challenge in the field of heterogeneous catalysis is selecting an optimal catalyst support structure. Commercially available structures can be easily manufactured at scale, but their stochastic nature makes their chemical and transport properties suboptimal. This is particularly relevant for gas-generation reactions, where non-uniformity of a porous structure leads to bubble trapping. Such trapping impedes the flow of reactants to catalyst sites, leading to conversion inefficiencies. Previous experimental work demonstrated that spinodally-derived architectures, in particular bicontinuous interfacially jammed emulsion gels (bijels), can alleviate these issues and deliver superior performance. However, to the best of our knowledge, numerical studies to optimize the operating conditions for such a morphology have not been performed yet. In this work, we aim to close this gap using color-gradient lattice Boltzmann simulations of reactive flows with a novel central moments collision operator. We develop an analytical model to predict catalyst performance based on our simulation data. Our findings show that this type of morphology can achieve very high conversion efficiencies. Moreover, we demonstrate that its catalyst performance can be optimized using superhydrophilic surface coatings.
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Optics

Burst-Driven Collective Ultrafast Interactions for Confined Optical Absorption

Burak Aray{\i}t, Seydi Yavaş, Mehmet Burçin Ünlü et al. (+1 more)

Ultrafast bursts, groups of closely spaced femtosecond pulses, can drive light-matter interactions that are not possible with single-pulse excitations. This occurs when earlier pulses create a transient effect that nonlinearly alters the interaction of later pulses, provided that the inter-pulse spacing is shorter than the relaxation time of the transient. A long-standing trade-off in optical excitation is between multiphoton absorption, which provides strong spatial confinement but low energy-transfer efficiency, and linear absorption, which is efficient but offers limited spatial localization. Here, we show that a burst of ultrafast pulses can collectively build up a population of free carriers in semiconductor nanoparticles via multiphoton absorption. The free carriers absorb linearly and strongly, and dissipate rapidly once the burst ends. The result is a more efficient absorption process that is strongly gated spatially and temporally by multiphoton absorption and burst duration, respectively. We develop an analytical model that couples carrier generation with Auger and surface recombination, yielding a piecewise-exact description of the carrier dynamics and an intuitive scaling relation for the collective energy-deposition enhancement. A signature consequence of collective absorption is its dependence on one extra power of the light intensity, effectively raising the order of an m-photon process to m+1 without requiring higher intensities for the individual pulses. While we focus on nonlinear photoacoustic imaging as a potential application, we anticipate diverse applications, including nonlinear fluorescence microscopy.
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All authors Burak Aray{\i}t, Seydi Yavaş, Mehmet Burçin Ünlü, Fatih Ömer Ilday

Optics

Infrared light scattering and emission from epsilon near-zero hyperbolic phonon-polaritons in two-dimensional crystals

Flavio Henrique Feres, Martin Bearzatto, Adrien Debacq et al. (+24 more)

This work presents the near-field super-scattering and the near-field thermal emission from 2D hyperbolic crystals as general optical phenomena that link near-field nanophotonics to far-field photonics.
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All authors Flavio Henrique Feres, Martin Bearzatto, Adrien Debacq, Gergely Nemeth, Rafael A. Mayer, Yuri B. Marcal, Marcus V. de Paiva, Maximilian Obst, Felix Kaps, Jakob Wetzel, Osama Hatem, Wenjun Zhou, Ran Jing, Heng Whang, Adrian Cernescu, Stephan Winnerl, J. Michael Klopf, Mengkun Liu, Ferenc Borondics, Ingrid D. Barcelos, Raul O. Freitas, Ana I. F. Tresguerres-Mata, Yannick De Wilde, Lukas M. Eng, Michaël Lobet, Susanne C. Kehr, Francisco C. B. Maia

Plasma Physics

Hybrid kinetic-MHD simulation on the formation of runaway electron current plateau during a current quench process

Weimin Fu and Ping Zhu

Runaway electron (RE) generation is of great concern for high-current tokamak operations. A full-f particle-in-cell (PIC) model for RE dynamics has been developed and coupled with the 3D nonlinear extended magnetohydrodynamic (MHD) model implemented in the NIMROD code. Our model accounts for RE generation using analytical source terms and advances the RE motion along guiding-center (GC) orbits. The model was employed to simulate the formation of RE current plateau during a disruption, in which the plasma current becomes dominated by the RE current. The model agrees well with several RE codes based on fluid models when the RE GC drifts are ignored. For highly relativistic REs, the grad-$B$ and curvature drifts can play a significant role in the RE generation and motion due to the increase in the safety factor profile during the current quench process.
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Chemical Physics · Cross-listed from cond-mat.supr-con

Superconducting Hydride Mg2RhH6 Experimentally Achieved at Lower Pressure

Linjing Wu, Zelong Wang, Guiqi Liu et al. (+18 more)

Although tremendous progress has been made in recent years in the field of polyhydride superconductors, the realization of high critical temperature superconductivity still relies on formidable high pressures. Searching for superconducting hydrides at lower pressures is of particular importance. Here we report the first experimental synthesis of the Mg2RhH6, which achieves superconductivity under a significantly reduced pressure of 30 GPa. The synthesis of Mg2RhH6 proceeds via a two step process (1) preparation of the Mg2RhH5 precursor containing hydrogen atoms stabilized by covalent bonds, followed by (2) hydrogen supplementation resulting in the filling of electrons into anti bonding orbitals above 30 GPa, which was accompanied by the structural transition from RhH5 square pyramid to RhH6 octahedron. Superconductivity is achieved at 30 GPa with a Tc of 24 K, which is further enhanced to 29 K at 53 GPa, evidenced by a sharp drop of resistivity to zero and characteristic suppression of Tc under applied magnetic fields. Our experiments prove the Mg2RhH6 superconductor to be thermodynamically stable above 30 GPa, making it the first case exhibiting a Tc of approximately 30 K at a readily accessible pressure. This study pioneers a highly promising pathway for the rational design and discovery of high temperature superconductors within phonon mediated BCS framework.
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All authors Linjing Wu, Zelong Wang, Guiqi Liu, Jun Zhang, Yanfeng Ge, Yuanhao Su, Runteng Chen, Hongyu Liu, Wenmin Li, Sijia Zhang, Jingcheng Zhu, Jianfa Zhao, Zheng Deng, Shaomin Feng, Jing Song, Qingqing Liu, Xiang Li, Haozhe Liu, Panpan Kong, Xiancheng Wang, Changqing Jin

Fluid Dynamics

Rheology-controlled hydraulic selection in fracture-matrix heat transport: Mechanisms and thermal signatures

Alessandro Lenci and Irene Daprà

Geological fractures exhibit heterogeneous aperture fields that localize flow along preferential pathways and produce nonuniform fluid-matrix contact times. Heat transport combines channelized advection with conductive matrix exchange. For non-Newtonian fluids, shear thinning biases the aperture-to-flux mapping toward larger apertures, while yield stress suppresses flow below the mobilization threshold. A stochastic semi-analytical model represents aperture classes as parallel pathways with constitutive fluxes and superposes their channel-scale advection-conduction solutions for a semi-infinite matrix. Matrix diffusion sets the late-time scalings of breakthrough curves and front moments, while aperture variability and rheology control their amplitudes and crossover. Rheology affects spreading through high-order flux-weighted aperture moments that determine persistent inter-channel variance. For monomial flux laws, the reduced late-time amplitudes collapse onto a single similarity variable, so shear thinning acts as amplified effective aperture variability. Global sensitivity analysis attributes flux reweighting to shear thinning and hydraulic accessibility to yield stress. Two-dimensional simulations verify the construction for Newtonian and power-law flow. A connected rough-field comparison at low aperture variability recovers mean advance and outlet survival but overestimates variance, so Ellis and Herschel-Bulkley results remain independent-channel predictions. The model provides an interpretable reference limit separating rheology-controlled hydraulic selection from matrix-controlled transport.
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Physics and Society

A memory-based three-state model of competing technology adoption: substitution regimes, multi-homing, and churn

Stefano Scialla, Marco Patriarca, Els Heinsalu et al. (+1 more)

Technologies, products, platforms, and behavioral routines often compete through gradual adoption, reinforcement-dependent use, and temporary multi-homing. We formulate a homogeneous, well-mixed, three-state agent-based model of competition between an incumbent option (X) and a challenger (Y). Agents are exclusive users of (X), exclusive users of (Y), or dual adopters (Z). Adoption is memory-based: an exclusive user adds the alternative only after enough adoption-relevant encounters within a finite learning window. Retention is also memory-based: a dual adopter continues to use both options only if each is sufficiently reinforced within a finite retention window. This microscopic mechanism reproduces aggregate usage signatures analogous to the four Adner–Kapoor technology-substitution regimes—creative destruction, robust coexistence, the illusion of resilience, and robust resilience—without explicitly representing ecosystems, complementors, prices, or strategic investment. Starting from the same small challenger seed, the benchmark simulations differ only in adoption burden, retention burden, post-adoption usage preference, and the teaching role of dual adopters. Rolling usage shares reproduce the four aggregate substitution patterns, while state-resolved trajectories and phase portraits reveal distinct microscopic pathways. Thus, similar market-level substitution curves need not have unique causal interpretations: although ecosystem mechanisms may be essential in many empirical cases, finite-memory learning and retention alone can generate qualitatively similar regimes. The model provides a compact baseline linking technology-substitution trajectories to observable individual-level adoption, multi-homing, and discontinuance.
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All authors Stefano Scialla, Marco Patriarca, Els Heinsalu, Julyan H. E. Cartwright

Fluid Dynamics

Finite-Strength Sensitivity and Euler–UTSD Correspondence for Guderley–Mach Reflection

Justin Kin Jun Hew

Weak shock reflection at nearly glancing incidence is governed, after the transonic weak-shock scaling, by a self-similar unsteady transonic small-disturbance (UTSD) free-boundary problem. We derive and differentiate the first finite-strength perturbation of the corresponding isentropic potential-flow problem along paths of fixed canonical incidence $a=\alpha/\delta$, where $\mu=\delta^2=2(M^2-1)$. A second-order refluxed adaptive finite-volume method, exact discrete tangents and adjoints, and a Rankine–Hugoniot-constrained fitted principal front give the fixed-$a$ canonical sensitivity $H_{2,a}^{\PF}(0.5;1.4)=-0.217\pm0.012$; a fully differentiated physical back-map gives the diagnostic fixed-$a$ coefficient $K_{2,a}^{\PF}\simeq-0.266$. We derive the exact chain rule that converts these quantities to the distinguished fixed-$\lambda$ path $\lambda=(M-1)/\alpha^2$, showing explicitly that the conversion requires the independent incidence derivative of the leading UTSD branch and therefore cannot be inferred from the fixed-$a$ calculation alone. A matched-boundary self-similar Euler study with strength-dependent refinement contains 21 qualified nonlinear states and 252 evaluations of a common front-functional family. Coupled extrapolation gives $g_0^{\Eul}=0.510\pm0.006$ and the physical leading-angle coefficient $G_0^{\Eul}=0.256\pm0.004$, consistent with the shock-fitted UTSD limits. A separate same-strength phase-bracket audit using 18 Euler states shows that the captured-shock subcell phase is comparable to the desired cubic signal. The resulting finite-resolution Euler secants are compatible with the potential-flow correction, but their $\rho=h_\eta/\sqrt\mu\to0$ extrapolation is not model-stable. Thus leading-order Euler–UTSD correspondence is numerically verified, whereas cubic-order Euler correspondence remains unresolved.
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Medical Physics

Low-rank modal endpoints from beat-resolved retinal arterial Doppler holography velocity waveforms characterize the response to flicker provocation

Sienna O'Shea, Maxime Boy Arnould, Adrien Gordon et al. (+3 more)

Conventional retinal flicker endpoints quantify changes in diameter, mean velocity, or flow but do not capture the modal concentration of the cardiac velocity waveform during neurovascular stimulation. Here, beat-resolved retinal Doppler holography and low-rank modal decomposition are combined to derive compact arterial endpoints from unfiltered arterial segment-velocity waveforms sampled across beats and vessel locations. For each acquisition, locally centered waveforms are assembled into a common matrix and decomposed by singular-value decomposition (SVD). Robust summaries quantify total pulsatile scale, modal amplitude, residual amplitude, mean-to-pulsatile balance, and singular-spectrum dimensionality; the same construction can also be applied descriptively to individual beats. We demonstrate the framework using 33 temporally ordered Baseline~1/Flicker/Baseline~2 acquisitions from one eye. Relative to the pooled baselines, 13-Hz flicker was associated with lower centered-waveform RMS scale $R_0$ and leading-mode amplitude $A_1$, and with higher robust residual-amplitude ratios $\rho_1$ and $\rho_2$, mean-to-pulsatile ratio MPR, effective rank, and participation ratio; these contrasts showed exploratory within-session separation after Holm adjustment. No evidence of differences in the absolute residual amplitudes $R_1$ and $R_2$ was detected; together, these observations are consistent with reduced concentration in the leading acquisition-specific arterial pulse mode rather than an increase in absolute residual pulsatility.
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All authors Sienna O'Shea, Maxime Boy Arnould, Adrien Gordon, Yann Fischer, Zacharie Auray, Michael Atlan

Atomic Physics

A scalable chip-integrated single-photon source array based on 50 individually addressable neutral atoms

Ya-Dong Hu, Tian-Yang Zhang, Dong-Qi Ma et al. (+10 more)

Scalable arrays of identical single-photon sources are a central resource for photonic quantum information processing, quantum networks and quantum metrology. Neutral atoms provide intrinsically identical emitters that can be assembled and rearranged in optical tweezers, but a many-channel fiber interface to individually trapped atoms has remained a major technical challenge. Here we demonstrate a chip-interfaced single-photon source array based on 50 individually addressable $^{87}\mathrm{Rb}$ atoms. A glass waveguide fan-out converts the \SI{5}{\micro m} pitch of the optical-tweezer array to the \SI{127}{\micro m} pitch of a commercial fiber array, mapping each atom to its own waveguide, fiber and single-photon detector. We resolve all 50 channels with an average nearest-neighbor cross-talk of $0.4\%$ and a uniform insertion loss of \SI{2.9}{dB}, and verify single-photon emission with $g^{(2)}(0)=0.29$, presently limited by detector dark counts and residual cooling-light scattering. Combining per-channel atom discrimination, rearrangement and reservoir replenishment, we prepare source subarrays of up to 24 atoms with a $93\%$ fill fraction. For small target numbers, atom loss is repaired from the reservoir at the detection-limited rate of \SI{118}{Hz}. We further fabricate a 784-channel waveguide chip, showing that the photonic interface can be extended well beyond the present number. This architecture establishes a fiber-native neutral-atom platform for larger arrays of identical single-photon sources.
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All authors Ya-Dong Hu, Tian-Yang Zhang, Dong-Qi Ma, Yi-Chen Zhang, Liang Chen, Wen-Yi Zhu, Hong-Jie Fan, Yan-Lei Zhang, Zhu-Bo Wang, Gang Li, Xi-Feng Ren, Guang-Can Guo, Chang-Ling Zou

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

Complex nonlinear dynamics of area-preserving, active vesicles

Reiner Kree and Annette Zippelius

We investigate the nonlinear shape dynamics and autonomous propulsion of actively driven quasi-spherical vesicles with locally inextensible membranes at low Reynolds number. Starting from Stokes hydrodynamics, linearized membrane elasticity, and harmonic active forcing, we derive a reduced description in terms of spherical harmonic deformation modes. The global area constraint enforced by local inextensibility is the sole source of dynamic nonlinearity. It confines the dynamics to compact manifolds in the space of possible shapes. Autonomous propulsion arises through nonlinear mode coupling and is determined geometrically by the oriented area swept by the trajectories in shape space. For two active modes, the dynamics reduces to a periodically driven phase equation exhibiting synchronization, phase slips, and mode locking. Introducing a third active mode fundamentally changes the dynamics, giving rise to quasiperiodic invariant tori and resonant periodic cycles. A recurrence diagnostic reveals the resulting resonance structure, while fluctuations of the cycle-averaged propulsion provide an experimentally accessible signature of the underlying shape dynamics. Our results demonstrate that, for actively driven vesicles, a geometric constraint is sufficient to transform an otherwise linear dynamical system into one exhibiting rich nonlinear dynamics.
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Optics

A complete photoluminescence polarization palette from a photonic-crystal slab

A.V. Peretokin, M.V. Stepikhova, N.A. Gippius et al. (+6 more)

Integrated light sources with tailored polarization are essential for integrated photonics, optical communication, sensing, and structured-light applications. However, generating a broad set of polarization states from spontaneous emission usually relies on structures with broken mirror, rotational, or inversion symmetries, or on emitters with predefined polarization properties. Here, we demonstrate a complete photoluminescence polarization palette in a single achiral photonic-crystal slab with a hexagonal lattice of holes and embedded self-assembled Ge(Si) nanoislands. We show that the polarization of the emitted light is governed by the interplay among modes with different symmetries rather than by the properties of unpolarized emitters. Along the high-symmetry directions of the Brillouin zone, symmetry enforces purely linear emission and enables direct polarization-based classification of the photonic-crystal modes. Away from these directions, all Stokes parameters become non-zero, providing full-Stokes control of photoluminescence and highly polarized emission. We further demonstrate polarization vortices associated with symmetry-protected and Friedrich-Wintgen bound states in the continuum, as well as radiating polarization singularities not associated with bound states in the continuum. Through appropriate geometric optimization, the same platform supports photoluminescence with a full polarization palette as well as polarization vortices. Our results establish achiral photonic-crystal slabs as monolithic sources of symmetry-programmable photoluminescence polarization.
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All authors A.V. Peretokin, M.V. Stepikhova, N.A. Gippius, A.A. Bogdanov, S.G. Tikhodeev, R.K. Nazarov, M.V. Shaleev, A.V. Novikov, S.A. Dyakov

Fluid Dynamics

Filtered turbulent flame model with wrinkling correction on chemical source for nonpremixed combustion simulation

Haoyu Lu, Junyi He and Lipo Wang

One of the most critical challenges in turbulent combustion modeling is the chemical source closure. In the recently developed filtered turbulent flame model (FTFM), a oneto-one correspondence between filtered scalar quantities and filtered chemical sources can be constructed by inversely solving the filtered flame equations, without the use of conventional presumed probability density functions (PDFs). However, the turbulence induced flame wrinkling, and thus the enhancement of the chemical source, has not been explicitly considered at the resolved scale. In the present study, the wrinkling effect is analytically quantified in a counterfow flame setup, from which FTFM is then further updated by incorporating such a physics grounded stretching correction on the chemical source. The satisfactory accuracy and robustness of the present model are justified from case tests of the non-premixed Sydney swirl flame and the Delft III flame.
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Applied Physics

A Passive Daytime Colored Radiative Cooler with DBR-Engineered Color Selectivity

Rajib Lochan Ghadei, Rohit Gupta and Rishi Maiti

Passive daytime colored radiative cooling (PDCRC) offers an attractive approach to thermal management while enabling structural coloration. However, achieving both strong daytime cooling and vivid, stable colors remains challenging. Here, we propose a lithography-free PDCRC comprising a polydimethylsiloxane (PDMS) emitter, SiC/SiO2 distributed Bragg reflector (DBR), MgF2 spacer, and Ag back reflector. The DBR and MgF2 spacer enable selective visible-spectrum reflection for cyan, magenta, and yellow (CMY) color generation, while the PDMS layer provides strong thermal emission within the atmospheric transparency window (8-14 micrometers). Finite-difference time-domain (FDTD) simulations, validated using the transfer matrix method (TMM), yield an average emissivity of 92% in the atmospheric window and an average reflectivity of 93.3% over 0.75-6 micrometers. CIE 1931 chromaticity analysis confirms high-contrast CMY colors with low color differences from standard subtractive primary colors. Under daytime conditions with a heat-transfer coefficient of 6 W m-2 K-1, the proposed cooler achieves cooling powers of approximately 140-145 W m-2 and a temperature reduction of about 12 degrees C below ambient. The color characteristics remain stable over a broad range of incidence angles, with only a gradual reduction in color intensity at larger angles, while the spectral response remains nearly insensitive to TE and TM polarizations. Simulations using meteorological conditions from different global cities further demonstrate robust cooling performance under diverse environmental conditions. The combination of high cooling performance, vivid coloration, simple multilayer architecture, and fabrication feasibility makes the proposed PDCRC promising for energy-efficient thermal management in buildings, vehicle coatings, wearable devices, and other outdoor applications.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Intrinsic Wannier Functions for Hamiltonian downfolding

Shuoxue Li and Garnet Kin-Lic Chan

Downfolding ab initio material band structure into a low-energy subspace spanned by orbitals of specified atomic character, a procedure known as Wannier downfolding, is a common task in the simulation of complex materials. We introduce the Intrinsic Wannier Function (IWF) method to Wannierize bands with given atomic character. The method is non-iterative and requires only a single dimensionless parameter to disentangle bands. In benchmarks on silicon, graphene, and the three-band model of a mercury cuprate, we show that Intrinsic Wannier Functions provide high quality downfolded band structures compared to those from standard approaches such as Maximally Localized Wannier Functions and the Selected Columns of the Density Matrix method. Further, their straightforward implementation and robustness positions Intrinsic Wannier Functions as a general and useful tool for Wannier downfolding in materials electronic structure and in high-throughput applications.
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