Plasma Physics
Hugoniot Relation for Multi-Temperature Euler Equations of Compressible Plasma Flows
Zhifang Du and Aleksey Sikstel
Shock solutions for multi-temperature Euler equations are inherently ambiguous due to the loss of microscopic physical detail during model reduction and occurrence of non-conservative terms. This paper presents a detailed analytical study of shock structures in such models. We derive two distinct Hugoniot relations, each corresponding to a physically admissible shock solution: one for the general multi-temperature case and one for two-temperature
plasma flows. Through classical analysis à la Courant–Friedrichs, we demonstrate that both satisfy admissibility conditions, revealing a fundamental non-uniqueness in shock structures. By relating these solutions to existing numerical schemes, the structure preserving and vanishing viscosity approaches, we provide physically justified references for constructing and evaluating discontinuous numerical approximations. In particular, we emphasize that the Hugoniot relation is not uniquely determined by the macroscopic PDEs alone, but must be supplied from external sources such as experiments or first-principles simulations. This insight demonstrates the essential role of microscopic physics in resolving shock ambiguity and contributes to the theoretical foundation for modeling discontinuous
plasma flows.
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Chemical Physics · Cross-listed from quant-ph
Variationally Compressing Quantum Circuits to Approximate Nonadiabatic Molecular Quantum Dynamics
Joshua M. Courtney and P.C. Stancil
Quantum simulation has begun to penetrate the field of
quantum chemistry in hopes of efficiently calculating ground state energies and approximating real-time
evolution. With modern research highlighting nonadiabatic dynamics, tunably approximating deep
circuits representing potential landscapes becomes crucial for simulating real
quantum systems. Variationally approximating
unitaries allows for shallower
circuits and accuracy tunable to hardware fidelity, so long as the observable quantities are preserved. We show the variational compression of Trotter terms preserve reaction rate coefficients via classical emulation of a hybrid
quantum-classical optimization method, as well as fast-forwarded adiabatic dynamics on
quantum hardware. Compressed
circuits can be incorporated with product-formula-based time
evolution to approximate dynamics of a particle in two coupled harmonic potentials, allowing tunability when removing high-cost
qubit interactions. Approximate rate coefficients are recovered after substituting terms in a nonadiabatic dynamic process, giving proof-of-principle for observable preservation under variational optimization.
Attention is paid to minimizing
qubit and gate-count resources.
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Plasma Physics · Cross-listed from astro-ph.HE
Tearing of charged current layers
Maxim Lyutikov
Astrophysical current layers, e.g., in
pulsar winds, can be electrically charged, while the
plasma is charge-symmetric, $e^\pm$. Using PIC simulations, we investigate dynamics and plasmoid formation (tearing instability) in charged Harris-type and rotational current layers. Electrically charged current layers, initially in global force-balance, are electrostatically unstable: the resulting dynamics is an intricate interplay between electrostatic Bernstein waves (BWs) and the current tearing mode. Besides overall density and
magnetic field,
plasma temperature is an important factor. In the charged Harris sheet set-up, the quickly generated BW are trapped within the layers (internally reflected at the upper hybrid resonance). BWs quickly redistribute the charge modifying the initial stage of tearing, but without strongly affecting overall plasmoid growth; resulting plasmoids are mildly charged. In rotational current layers: (i) even initially overall uncharged configurations develop large fluctuations of charge density; (ii) overall dynamics depends on the initial overall temperature; (iii) for certain combination of parameters tearing rate is greatly increased in the charged case.
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Fluid Dynamics
Topology optimization of two-fluid turbulent heat exchangers: A Darcy flow-based multifidelity approach
Hiroki Kawabe, Kaito Ohtani, Kentaro Yaji et al. (+2 more)
This paper presents a
topology optimization method for designing two-fluid heat exchangers under turbulent conditions using a Darcy flow-based low-fidelity (LF) model. The LF model is calibrated against a high-fidelity (HF) model based on the Reynolds-averaged Navier-Stokes (RANS) equations to increase the accuracy of predictions for fluid flow and heat transfer characteristics. Since the discrepancies between the LF and HF models can be significant, particularly for pressure drops, a multifidelity
topology optimization framework is adopted to leverage the strengths of both models. Using the calibrated LF model, we perform
topology optimization for various inlet velocities in the boundary conditions and trade-off parameters in the objective function to obtain diverse optimized designs. The optimized designs are then evaluated using the HF model to assess their performance with higher accuracy. The results demonstrate that the optimized designs significantly improve overall heat transfer coefficients while maintaining manageable pressure drops, achieving up to a 22% higher performance evaluation criterion (PEC) compared to a reference design enhanced by conventional twisted tape insertion. The improvements are attributed to the optimized configurations that promote enhanced fluid mixing and increased surface area for heat exchange, yet maintain streamlined flow paths to minimize pressure losses. Overall, the proposed
topology optimization method using the Darcy flow-based LF model proves effective in designing high-performance double pipe heat exchangers, showcasing the potential of the multifidelity approach in overcoming the challenges of optimizing heat exchangers under turbulent flow conditions.
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All authors Hiroki Kawabe, Kaito Ohtani, Kentaro Yaji, Ryota Fukunishi, Akira Ogawara
Chemical Physics
Assessing excited-state geometry optimization strategies for adiabatic photophysical energies
Amrita Bera, Atreyee Majumdar and Raghunathan Ramakrishnan
Accurate prediction of adiabatic $0$-$0$ excited-state energies is crucial for modeling molecular photophysical processes. Here, we
benchmark computational strategies for evaluating excited-state energies and singlet-triplet gaps obtained using different geometry-optimization strategies, including time-dependent density functional theory (TDDFT),
spin-unrestricted Kohn-Sham (UKS) DFT for triplet states (${\rm T}_1$), and state-specific orbital-optimized UKS (ssUKS) DFT for singlet excited states (${\rm S}_1$). Zero-point vibrational energy corrections are evaluated consistently at the optimized geometries and combined with ADC(2) excitation energies for comparison with experimental anion photoelectron spectroscopy data for a representative set of molecules. Among the protocols considered, adiabatic $0$-$0$ energies evaluated at TDDFT-optimized ${\rm S}_1$ and ${\rm T}_1$ geometries show the best agreement with experiment, with a mean absolute error below 0.1 eV. Replacing these geometries with UKS-optimized ${\rm T}_1$ and ssUKS-optimized ${\rm S}_1$ structures yields comparable accuracy. Vertical excitation energies are substantially more sensitive to the choice of geometry than the corresponding ${\rm S}_1$-${\rm T}_1$ gaps, which are comparatively more robust because of partial error cancellation. As a larger case study, we examine rubrene and find that UKS/ssUKS-based geometries remain useful for evaluating singlet-fission energetics. Overall, UKS/ssUKS-based workflows provide an efficient and accurate route to excited-state geometry optimization and to the evaluation of adiabatic $0$-$0$ energies for states with dominant single-determinant character.
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Chemical Physics
Toward Reliable Spectroscopic Analysis of Reaction Kinetics in Polaritonic Chemistry
Robrecht M. A. Vergauwe, J. Jussi Toppari and Gerrit Groenhof
Recent reports suggest that chemical reaction rates can change when reactants are placed inside an optical cavity. These effects have been attributed to the hybridization of molecular vibrational modes with cavity modes into polaritons, but the underlying mechanism remains debated. Recently, attempts to reproduce the key experiments have sometimes failed, which poses also ambiguity and impedes the determination of the possible mechanism. Without a reliable theoretical framework, polaritonic chemistry – which seeks to use optical resonators as catalysts to control reactions – has reached a pivotal stage. Standardized protocols for reproducible cavity experiments are therefore urgently needed. Here, we identify pitfalls in approaches that monitor reaction progress with UV/Vis spectroscopy. Using the Transfer
Matrix Method, we analyze a model pseudo-first-order reaction and assess how transient cavity thickness variations, cavity inhomogeneity, and fitting protocols influence the extracted rate constant. We find that changes in cavity thickness upon reactant introduction can strongly distort apparent kinetics when monitoring at a single wavelength, an artifact that can be mitigated by spectral smoothing. Additionally, we demonstrate that, unlike in many previous studies, the asymptotic extinction should be treated as a fitting parameter rather than fixed to the final experimental value. By identifying these pitfalls, our work lays the foundation for more robust analyses and reliable measurements in polaritonic chemistry.
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Optics
Near-unity efficiency optical vortex generation in van der Waals materials
Sujeong Byun, Munseong Bae, Hangsung Cho et al. (+4 more)
Optical
spin-orbit coupling provides a promising, fabrication-free route for developing ultra-compact optical
vortex generators. However, the conversion efficiency has been theoretically limited to 0.5. Here, we demonstrate enhanced
vortex generation efficiency by employing a Bessel beam as the input and propagating it through van der Waals (vdW)
crystals. The large birefringence of vdW
crystals and the single transverse wave vector of a Bessel beam allow a near unity
spin-orbit conversion efficiency and a topological charge transition of $\ell \rightarrow \ell + 2$. Through combined analytical and experimental investigations, we demonstrate a conversion efficiency of up to 0.82 in hexagonal boron nitride (hBN)
crystals with a thickness of $27.4\,\mu\mathrm{m}$. The higher efficiency of Bessel input beams over Gaussian beams is attributed to their distinct transverse wave vector distribution of constituent plane wave components. Furthermore, we demonstrate the dependence of conversion efficiency on the numerical aperture (NA) of the objective lens, which is in good
alignment with theoretical predictions. These demonstrations provide a fabrication-free route to highly efficient optical
vortex generation via microscale vdW materials platforms.
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All authors Sujeong Byun, Munseong Bae, Hangsung Cho, Haejun Chung, Kostya S. Novoselov, James Bullock, Sejeong Kim
Physics and Society
Food-Embedded Cold Energy Flows in Decentralised Solar Cold Chains
Hange Lao, Binjian Nie and Wei He
Reliable cold storage is needed to reduce meat loss in informal food systems, but conventional cold-chain expansion is difficult where electricity supply is weak and battery-based
solar refrigeration is costly. This study develops an hourly techno-economic optimisation framework for decentralised
solar-powered cold storage in interconnected open-air meat
markets. Using five meat
markets in Abuja, Nigeria, the model combines field-derived cooling demand,
solar photovoltaic generation, refrigeration, battery storage, phase change material thermal storage, and directed inter-
market meat flows. A key feature is that pre-chilled meat is represented as a carrier of product-
embodied cooling credit, while phase change material storage remains a stationary cold-side storage component at each
market. This allows cooling supplied at one
market to reduce the sensible cooling load required at another
market. Results show that shifting part of the storage function from battery storage to phase change material thermal storage reduces battery capacity by approximately 67% and lowers total system cost by up to 15% compared with battery-only systems. Allowing inter-
market cooling-credit exchange further reduces total system cost by 8% and aggregate phase change material storage capacity by 35%, mainly by reallocating refrigeration and storage requirements across connected
markets. The findings show that product flows can change where cooling services are required, allowing refrigeration and storage capacity to be coordinated across connected sites. Accounting for the product-mediated redistribution of cooling demand extends decentralised energy-system planning beyond isolated demand nodes and may inform cluster-level cooling infrastructure design in other infrastructure-constrained food networks.
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Applied Physics · Cross-listed from cond-mat.supr-con
Massive Mitigation of Transport AC Losses in Superconducting Hybrid CORC-TSTC Cables
Hasan N. Al-Ssalih, Antonio Badía-Majós and Harold S. Ruiz
High-current superconducting cables are emerging as key enablers for next-generation power transmission systems; however, their deployment is often limited by transport AC losses. Hybrid superconducting cables combining Conductor-on-Round-Core (CORC) and Twisted Stacked-Tape Conductor (TSTC) architectures have recently been proposed as a promising route toward cables with high current capacity and compact form factors. However, their electrodynamic response under transport current operation remains poorly understood, particularly regarding how current injection conditions govern internal current redistribution. Here, we employ a fully-3D electromagnetic model, previously validated against magnetisation experiments in equivalent cables, to investigate the influence of current injection strategy on the electrodynamics of hybrid CORC-TSTC cables under self-field conditions. By comparing configurations in which the total current is either injected through a common connection between the CORC and TSTC conductors (non-insulated feeding) or supplied independently to each conductor (insulated feeding), we show that electrical coupling in non-insulated designs leads to strong current redistribution, pronounced waveform distortion and elevated AC losses once the CORC layers approach
magnetic saturation. In contrast, independent current feeding suppresses inter-conductor current exchange, stabilises the current waveforms, and exhibits an outstanding reduction in transport AC losses of up to 90% at practical operating currents, compared with conventional feeding schemes. These findings reveal the central role of the current injection strategy in governing the internal electrodynamics and energy dissipation of hybrid superconducting cables, and identify the electrical decoupling of the constituent conductors at the feeding point as a simple and scalable route toward ultra-efficient power cables.
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Fluid Dynamics · Cross-listed from cs.LG
Physical Fidelity Reconstruction via Improved Consistency-Distilled Flow Matching for Dynamical Systems
Sicheng Ma, Tianyue Yang, Xiuzhe Wu et al. (+1 more)
Reconstructing high-fidelity flow fields from low-fidelity observations is a central problem in scientific machine learning, yet recent
diffusion and flow-matching models typically rely on iterative sampling, making them costly for latency-sensitive workflows such as ensemble
forecasting, real-time visualization, and simulation-in-the-loop inference. We study whether a high-fidelity flow-matching generative model can be compressed into a compact one-step model for fast scientific flow reconstruction. Our approach distills an optimal-transport flow-matching teacher into a one-step consistency model. Low-fidelity observations are incorporated at inference by initializing the generative trajectory from a noised observation along the transport path, allowing an unconditional high-fidelity flow model to perform conditional reconstruction without retraining the teacher. We evaluate this
distillation strategy on three fluid
benchmarks, Smoke Buoyancy, Turbulent Channel Flow, and Kolmogorov Flow, using coarse-to-fine reconstruction as a controlled testbed at field sizes up to $256 \times 256$. Across these settings, the distilled student retains similar performance of the teacher's model on spectrum metrics, while using roughly half as many parameters and achieving a $12\times$ inference speedup over the flow-matching teacher. Under the same training budget, the distilled student also outperforms a one-step consistency model trained directly from scratch by $23.1\%$ in SSIM, showing that teacher
distillation improves training efficiency rather than merely accelerating sampling. These results suggest a promising route for turning future high-capacity scientific generative models into compact reconstruction models that are faster to train, cheaper to run, and easier to deploy.
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All authors Sicheng Ma, Tianyue Yang, Xiuzhe Wu, Xiao Xue
Optics · Cross-listed from quant-ph
Passive Imaging with Quantum Advantage
Li Gong, Aonan Zhang, Madhura Ghosh Dastidar et al. (+2 more)
Far-field optical imaging inevitably involves low-pass spatial filtering, limiting the resolution. Moreover, conventional imaging suppresses high spatial frequency components close to the cutoff, making them invisible under noise, particularly the shot noise arising from discrete and random nature of
quantum light. Here we propose and implement a method for reducing the effect of this noise by optically pre-processing the incoming light prior to detection, thereby optimizing the
quantum measurement performed on it. Our scheme, termed
Fourier Domain Division (FDD), partitions the
Fourier plane into multiple regions for independent detection and subsequent post-processing for image reconstruction. By analyzing the
quantum and classical Fisher information, we show that our method is advantageous with respect to direct imaging for high spatial-frequency components. As a result, the number of
photons required to achieve a certain signal-to-noise-ratio in the
Fourier domain is reduced, thus enhancing the overall resolution in the
photon-starved regime. We demonstrate our method in microscopy, achieving 5-fold improvement of Fisher information on high spatial-frequency components. Unlike active super-resolution methods, FDD is passive, making it broadly applicable in microscopy and other imaging scenarios where active illumination is impractical, including astronomy and remote sensing. Our work establishes a general strategy for designing
quantum optimized superresolution imaging systems, bridging fundamental
quantum limits, practical image analysis and computer
vision applications.
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All authors Li Gong, Aonan Zhang, Madhura Ghosh Dastidar, Alexander Duplinskii, A. I. Lvovsky
Optics
Local droplet etching-assisted quantum dot epitaxy for telecom C-band quantum light emitters
Karolina E. Połczyńska, Paweł Wyborski, Michał Gawełczyk et al. (+4 more)
Significant progress in
quantum light sources for
quantum communication applications requires reproducible and symmetric
quantum emitters acting as single-
photon sources capable of generating entangled
photons on demand at specific telecom wavelengths. Here, we propose telecom-emitting epitaxial
quantum dots (QDs) fabricated using the local droplet etching (LDE) approach. The resulting well-defined, low-density ($10^9$/cm$^2$) QDs based on In$_{x}$Ga$_{1-x}$As are formed in symmetric LDE nanoholes (in-plane aspect ratio of 1.14) in In$_{0.52}$Al$_{0.48}$As. Detailed transmission electron microscopy provides comprehensive insight into the structural integrity, interface quality, and compositional profiles of the QDs, which underpin their promising optical properties. Photoluminescence spectroscopy reveals narrow emission lines (0.2 meV) and high optical quality, while second-order autocorrelation measurements confirm clear single-
photon emission, with $g^{(2)}(0)=0.07\pm0.02$ under above-band continuous-wave excitation and $g^{(2)}(0)=0.16 \pm 0.18$ under pulsed excitation. Precise numerical modeling, combining multiband $\boldsymbol{k} \cdot \boldsymbol{p}$ and configuration-interaction methods, supports the optical characterization and identifies thermal excitation pathways that explain the persistence of emission up to
liquid-nitrogen temperatures. These results highlight the versatility of the LDE approach for integrating new material systems and pave the way toward scalable fabrication of
quantum light sources with tailored emission properties.
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All authors Karolina E. Połczyńska, Paweł Wyborski, Michał Gawełczyk, Shima Kadkhodazadeh, Battulga Munkhbat, Stefano Sanguinetti, Elizaveta Semenova
Instrumentation and Detectors
Analysis of mixed radiation fields at the MoEDAL experiment based on real-time data from a Timepix detector network
Benedikt Bergmann, Petr Burian, Josef Janeček et al. (+6 more)
The primary objective of this work is the determination of fluences and characteristics of fast
neutrons, other
hadrons, and highly ionizing particles (HIPs) in the environment of the MoEDAL experiment at the Large
Hadron Collider. These particles may constitute an experimental background for the passive
Nuclear Track Detectors (NTDs) used by MoEDAL to search for tracks potentially produced by
magnetic monopoles, in particular by particles indistinguishable in NTD from monopoles. The study is based on data acquired by the Timepix hybrid silicon pixel detector network, which represents the first and only active detector system installed and operated as part of the MoEDAL experiment from 2013 to 2018. The Timepix detector network enables real-time measurements of mixed radiation fields, including the composition, spectral properties, and directional characteristics of individual radiation components across different regions of the MoEDAL experimental area. The paper presents detailed results of the radiation field analysis with emphasis on
neutrons and HIPs, including their directional distributions. The first results demonstrating the spatial tracking capabilities of the Timepix detectors are also reported, illustrating the reconstruction of particle direction and energy-loss profiles from individual detector frames.
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All authors Benedikt Bergmann, Petr Burian, Josef Janeček, Claude Leroy, Petr Mánek, James Pinfold, Stanislav Pospíšil, Richard Soluk, Michal Suk
Chemical Physics · Cross-listed from cond-mat.stat-mech
Emergent conserved quantities via irreversibility
Alex Blokhuis, Martijn van Kuppeveld, Daan van de Weem et al. (+1 more)
Conserved quantities increasingly underpin the inference of physical models. Recently new conserved quantities have been found in this context, that currently lack an interpretation. Here, we show that irreversible reactions in CRNs and Markov Chains lead to emergent conservation laws and broken cycles. Linearly dependent currents - characterized by the "co-production index" - arise due to irreversible reactions. We derive a law relating conserved quantities, broken cycles, and co-production. This resolves a recent conundrum posed by a machine-discovered candidate for a non-integer conservation law. Our findings introduce heretofore overlooked extensions to a widely used index law for CRNs and Markov Chains that undercounts conservation laws. This furnishes new tools and immediate applications for the inference and analysis of models based on conservation laws.
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All authors Alex Blokhuis, Martijn van Kuppeveld, Daan van de Weem, Robert Pollice
Optics
Narrowband-to-broadband switchable and polarization-insensitive terahertz metasurface absorber enabled by phase-change material
S. Hadi Badri, M. M. Gilarlue, Sanam SaeidNahaei et al. (+1 more)
A terahertz absorber with controllable and switchable bandwidth and insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO2) and verify its performance by the finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a resonator separated from a gold ground-plane by a polyimide spacer. Switching from narrowband to broadband absorber is achieved via connecting VO2 patches to the gold first-order cross fractal converting the resonator to a third-order cross fractal. In the
insulator phase of VO2, the main narrowband absorption occurs at the frequency of 6.05 THz with a 0.99 absorption and a full-width half-maximum (FWHM) of 0.35 THz. Upon
insulator-to-metal transition of VO2, the metasurface achieves a broadband absorption with the FWHM of 6.17 THz. The simulations indicate that by controlling the partial phase-transition of VO2, we can tune the bandwidth and absorption level of the absorber. Moreover, the designed absorber is insensitive to polarization due to
symmetry and works well for a very wide range of incident angles. In the metallic state of VO2, the absorber has an absorption exceeding 0.5 in the 3.57-8.45 THz frequency range with incident angles up to 65{\deg}.
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All authors S. Hadi Badri, M. M. Gilarlue, Sanam SaeidNahaei, Jong Su Kim
Medical Physics
Injectable Thermochemical Micro-Explosion for Prompt Thrombolysis via Liquid Alkali Metal
Xin Liao, Yi Hou, Jie Zhang et al. (+5 more)
Thrombotic vascular diseases contribute to significant global mortality, yet current therapeutic strategies face persistent challenges including bleeding risks, suboptimal efficiency, and procedural complexity. Here, we report a micro-explosive thermochemical thrombolysis (METCT) therapy via injectable
liquid alkali metal (LAM) encapsulated in dimethyl silicone (LAM@oil), which enables
prompt, efficient and safe vascular recanalization within an ultrafast timeframe (< 90 seconds). This LAM@oil system effectively disrupts thrombus tissue through a synergistic triple-action mechanism: Mechanical micro-explosions forces, alkaline ablation due to highly localized exothermic chemical reactions, and thermal thrombolysis mediated by elevated temperature. Upon thrombolysis completion, the non-toxic reaction byproducts (sodium and potassium ions) exhibit physiologically biocompatible and metabolizable effects. Critically, the LAM@oil demonstrates significantly higher thrombolytic efficacy compared to clinically available thrombolytic drugs (residual thrombus area percent 10.87%+-7.16% for LAM@oil vs. 80.86%+-13.32% for urokinase), with no associated bleeding risks. This strategy opens a byproduct-free, cost-effective, and high-efficiency alternative to conventional thrombolytics, holding big potential for clinical translation in acute thrombosis management.
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All authors Xin Liao, Yi Hou, Jie Zhang, Bo Wang, Minghui Guo, Hua Qu, Wei Rao, Jing Liu
Physics and Society
Compound effects of traffic and climate on electric vehicle HVAC energy consumption: a spatiotemporal framework with city-level attribution
Liang Zhang and Wei He
Real-world electric vehicle (EV) energy consumption can deviate by 20-40% from rated values, driven by ambient temperature, traffic congestion, and route characteristics. Existing studies treat these factors in isolation or as static loads, leaving the compound effect of co-varying
climate and traffic on HVAC energy unquantified and per-route attribution unavailable. We develop a spatiotemporal simulation framework that couples traffic-aware driving speed, time- and location-specific ambient temperature, and physics-based submodels (cabin HVAC, traction, battery thermal management) at the segment level, paired with a regression-based decomposition that attributes HVAC variability to temperature and trip-duration components on a per-route basis. Applied through a factorial design across seven UK cities and eight radial routes from Manchester, the framework shows total energy varying by 14% across cities while HVAC energy varies by up to 89%, making cabin thermal management the primary differentiator under winter conditions. Trip duration, set by traffic and road type, is frequently the dominant driver of HVAC variability: in London, 83% of above-average HVAC energy is attributable to congestion-extended trip time rather than to temperature. The decomposition yields a closed-form HVAC model from three inputs (ambient temperature, average speed, trip distance), with physically interpretable coefficients and straightforward transfer to other vehicles or regions through three coefficient re-fits. EV range variability is substantially shaped by traffic and road-network characteristics, with implications for route planning, infrastructure design, and energy equity.
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Optics
Thermally reconfigurable extraordinary terahertz transmission using vanadium dioxide
S. Hadi Badri, Hadi Soofi and Sanam Saeidnahaei S
We numerically demonstrate a reconfigurable extraordinary terahertz transmission based on a phase-change material of vanadium dioxide (VO2). The proposed hybrid metasurface is composed of an array of subwavelength apertures perforated on a gold film. The holes are partially filled with annular VO2 and gold disks to control the effective aperture area and the modes inside the aperture. Switching between the
insulator and the metallic phase of VO2 provides a convenient way to shift the transmission window. We present two designs offering
redshift or blueshift of the extraordinary terahertz transmission. Upon phase transition from the
insulator to the metallic phase, in the first design, the transmission peak
redshifts from 1.02 to 0.82 THz while in the second design the transmission peak blueshifts from 0.71 to 0.77 THz. Furthermore, the transmission level and resonance frequency can be modulated by controlling the partial phase transition of the VO2. The potential applications for the proposed structures are terahertz modulators and reconfigurable filters.
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Fluid Dynamics · Cross-listed from cs.RO
Cycle-resolved Cephalopod-Inspired Pulsed-Jet Robot With High-Volume Expulsion and Drag-Reduced Gliding
Yiyuan Zhang, Anye Zhong, Junkai Chen et al. (+1 more)
Cephalopod pulsed-jet locomotion is not a single isolated expulsion event, but a coordinated cycle involving jet expulsion, passive gliding, and mantle refilling. Inspired by this cycle-resolved biological strategy, this paper presents a cephalopod-inspired pulsed-jet
robot with a rigid-soft hybrid origami mantle that enables large, actively driven, and geometry-guided body deformation. The proposed mantle integrates rigid folding panels with a compliant silicone framework, allowing a 75% effective cavity-volume reduction during expulsion and reducing the projected cross-sectional drag area by approximately 75.7% in the contracted gliding configuration. Using this platform, we formulate a cycle-resolved framework to separately investigate how expelled volume, glide duration, and refill pathway influence whole-cycle locomotion performance. Experiments show that the
robot reaches a peak speed of approximately 0.5 m/s (3.8 BL/s) and an average speed exceeding 0.2 m/s (1.5 BL/s) within the first jetting cycle. The results further demonstrate the roles of high expelled-volume-ratio contraction in speed generation, reduced-drag-area gliding under different glide durations, and mantle-aperture-inspired passive inlet valves in assisting refill. This work provides both a robotic implementation of actively deformable cephalopod-like jet propulsion and a unified experimental platform for studying expulsion-gliding-refilling dynamics in pulsed-jet locomotion.
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All authors Yiyuan Zhang, Anye Zhong, Junkai Chen, Wenci Xin
Fluid Dynamics
Comparative Numerical Study of Film Cooling Strategies for Thermal Protection of a Kerosene-Fueled Oblique Detonation Combustor
Jianghong Li, Songbai Yao and Wenwu Zhang
Thermal protection remains a major challenge for oblique detonation engines (ODEs), whose combustors combine intense heat release, anchored on oblique detonation waves (ODWs). This study numerically investigates the effects of coolant type and mass flow rate on the flow structure, thermal environment and propulsion performance of a film-cooled kerosene-air ODE combustor at Mach 10 and 15 km altitude. Three active cooling strategies are compared under identical conditions: air film cooling, gaseous-kerosene film cooling, and
liquid-kerosene mist cooling. Stable, wall-attached oblique-detonation propagation and the canonical wave structure are maintained, with the wave-coolant interaction depending systematically on the coolant medium. Air injection causes the greatest disturbance to the initiation region and downstream wave interactions, yielding the largest propulsion penalty. The cooling strategies substantially reduce the near-wall thermal load but produce distinct wall-temperature distributions. Gaseous-kerosene cooling yields a spatially periodic response from the discrete injection slots, whereas
liquid-kerosene mist cooling gives a smoother and lower near-wall temperature through two-phase mixing and phase-change heat absorption.
Liquid-kerosene mist cooling provides the most favorable balance between thermal protection and propulsion performance at low to moderate injection levels. With further increases in injection level, the thermal benefit approaches saturation while the propulsion penalty continues to grow: the mean near-wall fluid temperature reduction remains about 87% across both the inter-slot and cooling-slot wall segments, whereas the total specific impulse is reduced by about 3%-5%. These results quantify the thermal-propulsive trade-off across film-cooling media and demonstrate the potential of fuel-based cooling for thermal management in hypersonic ODE combustors.
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Atomic and Molecular Clusters
Locally-Induced Stark Shifts of Collective Excitonic Modes in Polyradical Aggregates
Amandeep Sagwal, Rodrigo Cezar de Campos Ferreira, Petr Kahan et al. (+4 more)
Active control of dark long-lived excitonic states in molecular aggregates using local electric fields is a pivotal challenge for advancing nanoscale optoelectronics and
quantum device engineering. This experimental study investigates the collective excitonic states in aggregates composed of radical chromophores. With the strong optical enhancement provided by tip-enhanced photoluminescence (TEPL) spectroscopy, bright and dark excitonic modes are observed emerging due to interexciton coupling and induce changes in their spectra with the electric field locally applied within the nanocavity gap. Proportionally scaling Stark shifts are revealed as well as the emission peak sharpening of the dark states and a divergent behavior of the bright states in asymmetric measurement positions of the nanocavity above the aggregates. The observed complex behavior is discussed in terms of influence of the field, molecule arrangement, nanocavity coupling, dark mode lifetimes and electrostatic charge inhomogeneities in the clusters. This sensitivity to the external parameters demonstrates an effective means of control over radical excitonic aggregates.
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All authors Amandeep Sagwal, Rodrigo Cezar de Campos Ferreira, Petr Kahan, Maximilian Rödel, Jindřich Nejedlý, Jiří Doležal, Martin Švec
Optics · Cross-listed from quant-ph
Pontus-Mpemba effect in cavity quantum electrodynamics
Stefano Longhi
The
quantum Pontus-Mpemba effect is a counterintuitive phenomenon in which a
quantum system relaxes faster through a two-step
evolution protocol than through a single, unquenched relaxation. This work proposes its realization in cavity
quantum electrodynamics using the Jaynes-Cummings model with
photon loss. The model captures the coherent interaction between a two-level atom and a single quantized mode of a lossy cavity, providing a minimal yet realistic setting to explore dissipative
quantum dynamics. Restricting the analysis to the single-excitation sector, the dynamics feature damped
vacuum Rabi oscillations for weak dissipation that transition to near-exponential atomic decay under strong dissipation. A sudden quench of the cavity decay rate generates distinct relaxation trajectories from the same initial atom-cavity state. The atomic excitation then displays a non-monotonic, accelerated decay, where a trajectory with a quenched dissipation relaxes faster than fixed-loss
evolution. The effect originates from the interplay between coherent atom-
photon exchange and cavity dissipation, establishing a clear and experimentally accessible realization of the
quantum Pontus-Mpemba effect in both optical and
circuit QED platforms.
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Optics
Room temperature Purcell enhanced single erbium ions in silicon-carbide-on-insulator microring resonators
Joshua Bader, Shin-ichiro Sato, Jeffrey C. McCallum et al. (+8 more)
Spin-carrying single-
photon emitters operating in the telecommunication C-band (1530-1565nm) are
prime candidates for integrated
spin-
photon interfaces, offering seamless compatibility with existing fiber-optic infrastructure, an essential component for future
quantum networks. In this context, erbium-dopants ($\text{Er}^{3+}$) are particularly compelling due to their exceptional emitter properties, including small spectral
diffusion and long
spin coherence times. However, their low C-band
photon-emission rate and operation at cryogenic temperatures has limited the realization of this technology. In this work, we demonstrate fully integrated single-
photon emission from an ion implanted $\text{Er}^{3+}$-embedded into a 4H-silicon-carbide-on-
insulator (4H-SiCOI) microring resonator operating at room temperature. By optimizing the mode overlap between the resonator and the $\text{Er}^{3+}$-defect, we achieved a $\sim$70$\times$ Purcell enhancement and recorded small spectral
diffusion of $\sim$54 MHz. We further characterize the $\text{Er}^{3+}$ single
photon emission via
photon correlation g$^{(2)}$-histograms and investigate its performance under varying
magnetic-field, demonstrating Zeeman splitting on single emitters.
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All authors Joshua Bader, Shin-ichiro Sato, Jeffrey C. McCallum, Ruixuan Wang, Shao Qi Lim, Alexey Lyasota, David Broadway, Brett C. Johnson, Sven Rogge, Qing Li, Stefania Castelletto
Physics and Society
The multi-fractal nature of pedestrian arrival times
Caspar A. S. Pouw, Alessandro Corbetta, Alessandro Gabbana et al. (+1 more)
Pedestrian arrival times exhibit complex temporal organization across multiple scales, shaped by working hours, transportation schedules, and collective behaviors - features often neglected in conventional pedestrian arrival models. Using a
dataset comprising over 23 million pedestrian movements at a Dutch railway station, we show that arrival processes cannot be fully characterized by inter-arrival time statistics alone. Instead, we demonstrate that pedestrian arrivals exhibit clear multifractal scaling, revealing scale-dependent correlations across a broad range of timescales. To quantify these properties, we apply a framework based on generalized fractal dimensions, which captures the heterogeneous structure of arrivals beyond standard point-process descriptions. This approach enables the identification of distinct temporal regimes associated with external forcing and provides a quantitative basis for constructing more realistic synthetic arrival processes. Beyond pedestrian dynamics, this approach offers methodological relevance for understanding non-trivial arrival processes in other physical or biological systems.
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All authors Caspar A. S. Pouw, Alessandro Corbetta, Alessandro Gabbana, Federico Toschi
Optics
Robustness of bound states in the continuum in metasurface based on Ge$_2$Sb$_2$Te$_5$ versus structural imperfections
Nikolai A. Vlasov, Alexander I. Solomonov, Zarina F. Kondratenko et al. (+3 more)
We study the impact of lithography imperfections on quasi-bound states in the continuum (quasi-BICs) supported by a one-dimensional metasurface of Ge$_2$Sb$_2$Te$_5$ (GST) bars with trapezoidal deviations from rectangular cross-sections. Several mechanisms of quality ($Q$) factor scaling, including the impact of material losses, dispersion, and
geometric imperfections are established. We demonstrate that transition to identical isosceles trapezoids, despite preserving the required $C_2$
symmetry, reduces the $Q$ factor in the amorphous phase due to absorption changes accompanying the resonance shift. Further, the $Q$ factor remains robust for both GST phases under random element-to-element variations of the trapezoid angle, while analytical and numerical estimations in the absence of material losses show inverse-quadratic scaling of the Q factor with the disorder amplitude. We reveal that in the GST-based metasurface, the $Q$ factor is tolerant to
geometric imperfections for insignificant dispersion near the BIC wavelength, but changes in case of substantial dispersion. The phase shifting and established robustness of BICs in GST can be useful for applications where stable moderate $Q$ factors are essential.
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All authors Nikolai A. Vlasov, Alexander I. Solomonov, Zarina F. Kondratenko, Kirill A. Bronnikov, Mikhail V. Rybin, Ekaterina E. Maslova
Optics
Hybrid integrated narrow linewidth semiconductor laser based on the distributed feedback from an external deformed microcavity
Da Wei, Leilei Shi, Yujia Li et al. (+8 more)
Optical microcavities with rotational
symmetry have been widely used for narrowing linewidth and reducing frequency noise, however, the narrow but wavelength dependent optical feedback restricts the narrow linewidth
laser works only at some discrete wavelength matching the resonance of the microcavity. Here, we demonstrate a narrow linewidth
semiconductor laser with continuous wavelength tunability by hybrid integrating a DFB
laser chip with a deformed microcavity fabricated on a 220 nm SOI wafer. The deformed microcavity with
vortex radius demonstrates the unique characteristics of unidirectional energy storage, wavelength self-adaptivity, and self-focusing of the Rayleigh scattering based distributed feedback. In addition, the strength of Rayleigh scattering is also significantly enhanced by the high numerical aperture silicon waveguide. The optical feedback signal measured by the optical frequency domain reflectometry (OFDR) shows that the deformed microcavity can effectively lengthen the equivalent propagation distance without wavelength dependence. With the wavelength self-adaptive optical feedback from the deformed microcavity, the intrinsic linewidth of a DFB
laser diode is narrowed to 525 Hz and the side mode suppression ratio (SMSR) is improved to 76 dB in a maximum allowable continuous wavelength tuning range of 2.25 nm. The frequency noise and relative intensity noise (RIN) are reduced to 2.98 Hz2 /Hz and -148.74 dB/Hz at the offset frequency of 1 MHz, respectively. The work demonstrated here paves a new way for integrated tunable narrow linewidth
lasers, which are of crucial importance in high-speed communication and high-precision spectroscopy
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All authors Da Wei, Leilei Shi, Yujia Li, Minzhi Xu, Chaoze Zhang, Xianming Huang, Jianxian Yu, Lei Zhai, Wenxuan Huang, Huan Tian, Tao Zhu
Optics
Programmable spatial coherence tomography: diffraction-limited three-dimensional reflection imaging under modulated monochromatic illumination
Herve Hugonnet, Jieun Choi, Gyoung Hwan Kim et al. (+9 more)
Depth sectioning in reflection microscopy has predominantly relied on temporal coherence gating. Here we show that volumetric reflection
tomography at diffraction-limited resolution can be achieved under monochromatic illumination by engineering spatial, rather than temporal, coherence. In programmable spatial coherence
tomography (PSCT), a sequence of pupil-coded illumination patterns with angular-spectrum diversity generates measurement redundancy enabling the system to calibrate itself, jointly retrieving aberrations, illumination profiles, and sample motion without guide
stars or modal priors. We demonstrate label-free volumetric imaging of thick human tissues, organoids, frequency-resolved dynamic contrast, and high-resolution in vivo
brain imaging through a cranial window. These results position PSCT as an alternative to temporal coherence based reflection imaging in complex biological systems.
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All authors Herve Hugonnet, Jieun Choi, Gyoung Hwan Kim, Chulmin Oh, Jimin Cho, Chungha Lee, Su-Jin Shin, Sujin Park, Bon-Kyoung Koo, Wang-Yuhl Oh, Pilhan Kim, YongKeun Park
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Polarizable atomic multipoles for learning long-range electrostatics
Yoonjae Park, Dongjin Kim, Daniel S. King et al. (+5 more)
Long-range electrostatics and polarization remain central obstacles to extending machine learning interatomic potentials (MLIPs) to ionic, polar, and interfacial systems. Here we introduce a semi-local framework for learning electrostatics from energies and forces using polarizable atomic multipoles. Local equivariant descriptors predict environment-dependent latent monopoles, dipoles, and quadrupoles, while residual non-local charge transfer and polarization are captured by non-self-consistent linear response in induced charges and dipoles. Across four diverse
benchmarks and four short-range MLIP architectures, the multipole hierarchy and response terms systematically improve potential energy surface accuracy, with the largest gains in systems where long-range effects are essential. More importantly, physically meaningful electrical responses emerge without direct supervision. The learned latent multipoles yield accurate Born effective charge tensors and infrared spectra in close agreement with experiments. The induced-dipole extension introduces new capabilities: it predicts polarizabilities and thereby enables semi-quantitative Raman spectra for bulk water and hybrid MAPbI$_3$ perovskite, as well as the essential features of the surface-specific vibrational sum-frequency generation spectrum at the water-air interface. In ferroelectric HfO$_2$, the predicted electrical response also captures LO-TO splitting and polarization switching. This systematically improvable, physically transparent framework enables MLIPs trained on standard energy and force labels to predict polarization-sensitive observables.
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All authors Yoonjae Park, Dongjin Kim, Daniel S. King, Nam H. {\DJ}ào, Roya Savoj, Sebastien Hamel, Xiaoyu Wang, Bingqing Cheng
Accelerator Physics
A Temporal Retrieval Method for Modulated Electron Bunches via Adaptive Kernel Reconstruction
Zixiao Guo, Ke Feng, Zhiheng Lou et al. (+3 more)
Femtosecond electron beams with complex modulation play a crucial role in applications such as X-ray Free Electron
Lasers (XFELs) and
plasma wakefield accelerators. However, diagnostics for the electron beam current profile still face challenges with complex structure. In this letter, we propose a novel temporal
retrieval algorithm for the coherent transition radiation (CTR) diagnostics of complex modulated electron beams. Starting from the time-frequency analysis of the electron bunch train, the
algorithm separates and reconstructs the high- and low-frequency components. A temporal kernel was derived from the inverse sampling of the measured spectrum to construct the high-frequency component, while the low-frequency envelope was composed of several basis functions. Tested on the electron bunch trains from the complex multi-gaussian model and bunching-enhanced coherent harmonic generation, the
algorithm successfully reconstructed the temporal signals and achieves better performance than the Kramers-Kronig method. This method is expected to crucial provide temporal evidence for potential electron beam modulation schemes, and will enable broad prospects for future applications.
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All authors Zixiao Guo, Ke Feng, Zhiheng Lou, Guiyao Wang, Wentao Wang, Ruxin Li
Chemical Physics
Density diversity in training data governs thermodynamic transferability of machine learning interatomic potentials
Minwoo Kim, Seungtae Kim, Je-Yeon Jung et al. (+2 more)
Machine learning interatomic potentials (MLIPs) offer first-principles accuracy with reduced computational cost, but their transferability across different thermodynamic states remains questionable, particularly for fluid systems where molecules experience local environments far from crystalline
equilibrium. Here, we demonstrate that diversifying the density of training configurations, rather than temperature, is the most effective strategy for building thermodynamically transferable MLIPs within a fixed computational budget. We first show that foundation MLIPs trained on solid-state databases accurately describe
liquid-like densities but fail at gas-like conditions, while molecular-database-trained models exhibit the opposite behavior. Controlled from-scratch training and
distillation experiments confirm that density-diverse
datasets resolve both failure modes, whereas temperature-diverse
datasets cannot compensate for missing density regimes. Coordination number analysis reveals the physical origin of this behavior: local coordination
topology is more susceptible to density than temperature, leading to further structural diversity. These results establish density diversity as a design principle for thermodynamically transferable MLIPs and provide a validation framework for assessing the thermodynamic coverage of both foundation and from-scratch models, enabling reliable atomistic simulation of fluid-phase processes across diverse operating conditions.
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All authors Minwoo Kim, Seungtae Kim, Je-Yeon Jung, Min Young Ha, Won Bo Lee