Applied Physics · Cross-listed from cond-mat.supr-con
Direct laser micromachining of superconducting terahertz Josephson plasma emitters
Reo Yamaguchi, Takuma Sakurai, Kazuhiro Yamaki et al. (+6 more)
We demonstrate a rapid, maskless fabrication method for superconducting terahertz Josephson
plasma emitters (JPEs) based on direct ultraviolet
laser micromachining of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) single
crystals. Although machining debris is formed near the processed regions, uniform stacks of intrinsic Josephson junctions are preserved inside the
crystal, enabling stable terahertz emission. Devices fabricated with Ag, Cu, and Cr electrodes all exhibited terahertz radiation, with Cu electrodes showing performance comparable to Ag while offering a low-cost alternative. Spectroscopic and polarization analyses indicate that the emitted radiation is elliptically polarized and dominated by the geometrical cavity resonance mode. Structural and electrical characterizations reveal that the machining width and depth are not limited by the optical spot size but are governed by the anisotropic thermal conductivity of Bi-2212, consistent with a thermally dominated
laser ablation process. This direct
laser micromachining approach provides a fast and versatile fabrication technique for JPEs and is broadly applicable to superconducting electronics and terahertz devices.
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All authors Reo Yamaguchi, Takuma Sakurai, Kazuhiro Yamaki, Akinobu Irie, Junichiro Kato, Taichiro Nishio, Shigeyuki Ishida, Hiroshi Eisaki, Manabu Tsujimoto
Computational Physics · Cross-listed from cs.LG
Auxiliary Finite-Difference Residual-Gradient Regularization for PINNs
Stavros Kassinos
Physics-informed neural networks (PINNs) are often selected by a single scalar loss even when the quantity of interest is more specific. We study a hybrid design in which the governing PDE residual remains automatic-differentiation (AD) based, while finite differences (FD) appear only in a weak auxiliary term that penalizes gradients of the sampled residual field. The FD term regularizes the residual field without replacing the PDE residual itself. We examine this idea in two stages. Stage 1 is a controlled Poisson
benchmark comparing a baseline PINN, the FD residual-gradient regularizer, and a matched AD residual-gradient baseline. Stage 2 transfers the same logic to a three-dimensional annular heat-conduction
benchmark (PINN3D), where baseline errors concentrate near a wavy outer wall and the auxiliary grid is implemented as a body-fitted shell adjacent to the wall. In Stage 1, the FD regularizer reproduces the main effect of residual-gradient control while exposing a trade-off between field accuracy and residual cleanliness. In Stage 2, the shell regularizer improves the application-facing quantities, namely outer-wall flux and boundary-condition behavior. Across seeds 0-5 and 100k epochs, the most reliable tested configuration is a fixed shell weight of 5e-4 under the Kourkoutas-beta optimizer regime: relative to a matched run without the shell term, it reduces the mean outer-wall BC RMSE from 1.22e-2 to 9.29e-4 and the mean wall-flux RMSE from 9.21e-3 to 9.63e-4. Adam with beta2=0.999 becomes usable when the initial learning rate is reduced to 1e-3, although its shell benefit is less robust than under Kourkoutas-beta. Overall, the results support a targeted view of hybrid PINNs: an auxiliary-only FD regularizer is most valuable when it is aligned with the physical quantity of interest, here the outer-wall flux.
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Fluid Dynamics
Collective dynamics of active suspensions on curved viscous interfaces
Yuzhu Chen, Vishal P. Patil and David Saintillan
Self-propelled particles can navigate complex environments, including viscous fluid interfaces with curved geometries. In this work, we study the emergent dynamics of a suspension of self-propelled particles confined to a stationary curved viscous interface. The
evolution of the particle configurations is modeled using the Fokker-Planck equation on the curved surface, formulated using Cartan's moving frame method, and coupled to the bulk and surface Stokes equations with flows driven by an interfacial nematic active stress. Specifically, for a spherical vesicle, the flow field and the distribution of the particles are analyzed theoretically and numerically within the framework of
spin-weighted functions and
spin-weighted spherical harmonics, which provide a natural
geometric description of the probability distribution function on the sphere. A linear stability analysis about the uniform, isotropic state is performed and predicts a finite-wavelength instability, with mode selection arising from the competition between the vesicle radius and the Saffman-Delbrück length. This instability and the associated mode-selection mechanism are also confirmed in nonlinear numerical simulations using a pseudo-spectral method based on
spin-weighted spherical harmonics.
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Optics
Design and Verification of a Terahertz Bandpass Filter using a Spoof Surface Plasmon Polariton Waveguide with Gapped Unit Cells
Mohsen Haghighat, Ali Dehghanian and Levi Smith
This paper presents the experimental verification of a planar guided-wave terahertz (THz) spoof surface plasmon polariton (SSPP) bandpass filter (BPF) using a coplanar stripline (CPS) with internal grooves and periodic gaps. The proposed BPF operates by combining the low-pass behavior from the SSPP's band edge and the high-pass behavior from the gaps that act as series capacitors. The higher and lower cut-off frequencies can be tailored by the appropriate selection of the unit
cell geometry. For demonstration, a BPF with a center frequency of approximately 1 THz and a bandwidth of 0.25 THz was designed, fabricated, and experimentally validated. The passband around 1 THz is observed in the measurements, along with the lower and higher cut-off frequencies at approximately 0.91 THz and 1.16 THz, respectively, in agreement with simulation results.
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Optics
Hanbury Brown-Twiss effect and classical entanglement with OAM-carrying light
Jyrki Laatikainen, Sushil Pokharel and Olga Korotkova
Intensity-intensity correlation of a scalar optical beam carrying orbital angular momentum (OAM) across multiple modes is decomposed into intermodal contributions, thereby linking it, within the framework of the Hanbury Brown-Twiss effect, to the underlying modal coherence structure. Upon filtering the spiral phase dependence, the intensity-intensity correlations are governed by OAM-mode coherence and anisotropy reflecting classical
entanglement between OAM and statistical properties of light. These results extend intensity interferometry to structured light fields and provide direct access to modal coherence properties without phase-sensitive measurements.
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Data Analysis and Statistics · Cross-listed from astro-ph.CO
FAIR Universe Weak Lensing ML Uncertainty Challenge: Handling Uncertainties and Distribution Shifts for Precision Cosmology
Biwei Dai, Po-Wen Chang, Wahid Bhimji et al. (+15 more)
Weak gravitational
lensing, the correlated distortion of background
galaxy shapes by foreground structures, is a powerful probe of the matter distribution in our universe and allows accurate constraints on the cosmological model. In recent years, high-order statistics and machine learning (ML) techniques have been applied to weak
lensing data to extract the nonlinear information beyond traditional two-point analysis. However, these methods typically rely on cosmological simulations, which poses several challenges: simulations are computationally expensive, limiting most realistic setups to a low training data regime; inaccurate modeling of systematics in the simulations create distribution shifts that can bias cosmological parameter constraints; and varying simulation setups across studies make method comparison difficult. To address these difficulties, we present the first weak
lensing benchmark dataset with several realistic systematics and launch the FAIR Universe Weak
Lensing Machine Learning Uncertainty Challenge. The challenge focuses on measuring the fundamental properties of the universe from weak
lensing data with limited training set and potential distribution shifts, while providing a standardized
benchmark for rigorous comparison across methods. Organized in two phases, the challenge will bring together the physics and ML communities to advance the methodologies for handling systematic uncertainties, data efficiency, and distribution shifts in weak
lensing analysis with ML, ultimately facilitating the deployment of ML approaches into upcoming weak
lensing survey analysis.
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All authors Biwei Dai, Po-Wen Chang, Wahid Bhimji, Paolo Calafiura, Ragansu Chakkappai, Yuan-Tang Chou, Sascha Diefenbacher, Jordan Dudley, Ibrahim Elsharkawy, Steven Farrell, Isabelle Guyon, Chris Harris, Elham E Khoda, Benjamin Nachman, David Rousseau, Uroš Seljak, Ihsan Ullah, Yulei Zhang
Applied Physics
A Wide-Regulation-Range Hybrid Switched-Capacitor Converter for 48V Automotive Power Systems
Georgios Spanodimos, Guanyu Qian and Xiaodan Cui
This paper presents a hybrid switched-capacitor converter (HSCC) with a novel multi-mode modulation (3M) scheme for wide-range voltage regulation in 48-V automotive power systems. By introducing a three-state operating sequence beyond the conventional 2:1 resonant operation, the proposed converter achieves variable step-down conversion ratios while preserving soft-switching operation in most transitions. The proposed modulation supports both zero-current switching (ZCS) and zero-voltage switching (ZVS) modes, enabling efficient operation over a broad range of load and conversion conditions. To enable voltage regulation, a closed-loop control configuration is proposed with a linear proportional-integral (PI) controller, with gain tuning assisted by reinforcement learning (RL) to address the converter's nonlinear and variable-frequency nature while maintaining good transient performance. A hardware prototype was built to validate the proposed modulation scheme. The measured results verify ZCS operation over voltage conversion ratios of 0.2–0.4, with a peak efficiency exceeding 92% at 100~W, and efficiency above 88% over a wide operating range for 3:1 conversion. The feasibility of both ZCS and ZVS operation is also experimentally demonstrated. These results show that the proposed HSCC significantly extends the practical regulation range of resonant switched-capacitor converters while maintaining high efficiency.
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Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci
Ultra-high-vacuum cluster tool for epitaxial synthesis and optical spectroscopy of reactive 2D materials
M. Dembecki, J. Schabesberger, M. Bissolo et al. (+8 more)
The large-area synthesis of high-crystalline-quality two-dimensional (2D) materials is at the core of novel material integration for
semiconductor technology. This effort relies on developing fabrication and characterization techniques that can uncover the material's intrinsic properties by preserving its pristine conditions. In this article, we present an all ultra-high-
vacuum cluster for the growth using molecular beam epitaxy of 2D
semiconductors that are unstable under ambient conditions and optical spectroscopy using low temperature (20 K) photoluminescence and Raman scattering. The optical chamber of the setup provides micrometer scale spatial resolution and the ability to scan the entire wafer. The performance of its setup regarding spatial resolution, temperature control over a temperature range of 20-300 K using a closed-cycle cryostat and long-term preservation are demonstrated using as-grown post-transition metal monochalcogenides. Furthermore, we introduce a deconvolution-based
algorithm to recover spatial information under vibration using a system-specific point-spread function. This enables in situ analysis of the structural and optoelectronic properties of as-grown materials in their pristine form, providing rich and reproducible feedback for both fundamental studies and the optimization of scalable 2D material growth toward integration in advanced devices.
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All authors M. Dembecki, J. Schabesberger, M. Bissolo, A. Thurn, A. Ulhe, P. Avdienko, J. Ulrichs, H. Riedl, G. Koblmüller, E. Zallo, J.J. Finley
Applied Physics
Additively manufactured Shape Memory Alloy Hybrid Composites with a polymer matrix featuring a re-entrant honeycomb structure
Manuel Kunzler, Sascha Bruk, Max Kaiser et al. (+1 more)
Stereolithography (SLA) and Tailored Fiber Placement (TFP) were combined to fabricate shape
memory alloy hybrid composites (SMAHC) featuring a three-layer structure and exhibiting out of plane bending deformation when activated, in a fully integrated, additive manufacturing process. SMA wires as active elements were attached to a textile reinforcement layer, which then was embedded within a UV-curable
polymer matrix and combined with a geometrically tailored toplayer, featuring the re-entrant honeycomb architecture. Exploiting the design freedom of SLA, the overall mechanical response of the SMAHC can be systematically adjusted, enabling controlled out-of-plane bending during thermal activation. Two different SMA integration strategies - manual
embedding and automated TFP were investigated to assess their influence on actuation behavior, reproducibility, and deformation behaviour. A total of eight
geometric configurations were manufactured and experimentally characterized using synchronized optical measurements. The results demonstrate that the combination of SLA-based fabrication and textile-mediated SMA integration enables precise control over the actuation response, while the use of re-entrant honeycomb structures provides an effective approach to tailor stiffness and deformation characteristics. In particular, the automated TFP integration yields improved reproducibility and more symmetric deformation behavior compared to manual fabrication. The presented approach establishes a fully additive manufacturing route for SMAHCs, enabling the realization of structurally integrated, morphing composite systems with programmable mechanical properties.
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All authors Manuel Kunzler, Sascha Bruk, Max Kaiser, Martin Gurka
Plasma Physics
A tensor invariant approach to energy flux in magnetohydrodynamic turbulence
Conan M. Liptrott, Sandra C. Chapman, Bogdan Hnat et al. (+1 more)
A scale-by-scale analysis of energy flux in the turbulent cascade can be performed using the spatially filtered magnetohydrodynamic (MHD) equations, while the gradient tensor invariants are widely used to characterize the structure of velocity and
magnetic fields. Physical mechanisms responsible for energy flux require specific field configurations whose strength is quantified by these tensor invariants. We explore this requirement, showing that the tensor invariants act as proxies for mechanistic energy fluxes under quantifiable conditions. As a special case, the purely hydrodynamic contributions to energy flux can be expressed exactly in terms of the invariants of the velocity gradient tensor. We also show that the invariants bound the available energy flux for distinct physical mechanisms, formalizing the idea that each transfer mechanism requires field configurations with gradients of sufficient strength to support a given energy flux. Results are illustrated using three-dimensional simulations of freely decaying MHD
turbulence. These findings advance our understanding of MHD
turbulence by revealing key relationships between field
topology and energy transfer across scales due to distinct physical mechanisms. They further provide a tool for probing the turbulent cascade using multispacecraft data where local tensor invariants are directly accessible.
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All authors Conan M. Liptrott, Sandra C. Chapman, Bogdan Hnat, Nicholas W. Watkins
Fluid Dynamics · Cross-listed from cs.LG
Non-intrusive Learning of Physics-Informed Spatio-temporal Surrogate for Accelerating Design
Sudeepta Mondal and Soumalya Sarkar
Most practical engineering design problems involve nonlinear spatio-temporal dynamical systems. Multi-physics simulations are often performed to capture the fine spatio-temporal scales which govern the
evolution of these systems. However, these simulations are often high-fidelity in nature, and can be computationally very expensive. Hence, generating data from these expensive simulations becomes a bottleneck in an end-to-end engineering design process. Spatio-temporal surrogate modeling of these dynamical systems has been a popular data-driven solution to tackle this computational bottleneck. This is because accurate machine learning models emulating the dynamical systems can be orders of magnitude faster than the actual simulations. However, one key limitation of purely data-driven approaches is their lack of generalizability to inputs outside the training distribution. In this paper, we propose a physics-informed spatio-temporal surrogate modeling (PISTM) framework constrained by the physics of the underlying dynamical system. The framework leverages state-of-the-art advancements in the field of Koopman autoencoders to learn the underlying spatio-temporal dynamics in a non-intrusive manner, coupled with a spatio-temporal surrogate model which predicts the behavior of the Koopman operator in a specified time window for unknown operating conditions. We evaluate our framework on a prototypical fluid flow problem of interest: two-dimensional incompressible flow around a cylinder.
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Plasma Physics · Cross-listed from astro-ph.HE
Synchrotron-cooled plasma distribution in the outer magnetosphere of a neutron star
Mikhail V. Medvedev, Anatoly Spitkovsky and Alexander Philippov
The guiding center formalism is employed to analyze the motion of a charged relativistic particle in an inhomogeneous
magnetic field, subject to
magnetic mirroring and energy loss due to cooling. The governing equation for the
evolution of the
magnetic moment is derived. An example representing a
neutron star (
pulsar or magnetar) magnetosphere is presented to illustrate typical particle orbits. Notably, radiative losses are most pronounced near a trapped particle's turning point. Depending on the initial particle's pitch angle, energy loss can become catastrophic, resulting in the rapid migration of the particle into the loss cone and subsequent precipitation onto a
neutron star. Conversely, particles with a larger pitch angle remain temporarily trapped and form a gradually decaying "cooled-loss-cone" or "funnel” distribution, characterized by the maximum momentum space particle density being located at the edge of the loss cone. The size of the loss cone is energy-dependent and scales as $\alpha_{c} \propto \gamma^{3/10}$. Synchrotron losses are strongest in a well-localized region of the magnetosphere, about a few hundred to a thousand
star radii under typical
pulsar and magnetar conditions. This region is a plausible site for synchrotron radiation originating in the outer magnetosphere, and could also be responsible for non-polar coherent
pulsar emission, as well as weak fast
radio bursts.
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Fluid Dynamics
Timescale Separation Enables Deep Reinforcement Learning Control of Rotating Detonation Engine Mode Transitions
Kristian Holme, Jean Rabault, Ricardo Vinuesa et al. (+1 more)
Rotating detonation engines (RDEs) are a promising propulsion concept that may offer higher thermodynamic efficiency and specific impulse than conventional systems, but nonlinear phenomena, including transitions to oscillatory or chaotic propagation modes, can hinder practical operation. Deep Reinforcement Learning (DRL) has emerged as a promising method for controlling complex nonlinear dynamics such as those observed in RDEs. However, the multi-timescale nature of the RDE system makes direct application of DRL challenging. We address this challenge by reformulating the DRL problem in a moving reference frame that follows the detonation-wave pattern, making the wave structure appear quasi-steady to the
agent. This reformulation enables scale separation between fast detonation propagation and slower operating-mode dynamics. We train DRL controllers to modulate spatially segmented injection pressure in a one-dimensional reduced-order RDE model and induce rapid transitions between different mode-locked states. Across a range of actuation periods, initial states, and target modes, controllers trained in the moving frame learn more reliably than those trained in a stationary frame and remain effective over a broader range of actuation periods. These results suggest that
symmetry-aware moving reference frame formulations may be useful for related multiscale flow-control problems and that scale separation should be exploited whenever possible to enable DRL control of multi-timescale systems.
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All authors Kristian Holme, Jean Rabault, Ricardo Vinuesa, Mikael Mortensen
Fluid Dynamics
Evaporative thermo-fluidics and deposition patterns in surface-active droplets
Randeep Ravesh, A R Harikrishnan and Purbarun Dhar
We investigate the thermo solutal transport phenomena and deposition patterns during the evaporation of surfactant laden droplets experimentally and through theoretical scaling based analysis. Experiments were conducted using the sessile droplet configuration in the acrylic chamber for both hydrophilic and hydrophobic substrates. Infrared thermography and particle image velocimetry measurements were conducted during evaporation to illustrate the temperature and velocity distributions, respectively. Sodium dodecyl sulphate SDS surfactant molecules enhanced the evaporation rate with an increase in concentration for the hydrophobic surface. In contrast, the evaporation rate increased up to 0.5 CMC and then decreased for droplets on a hydrophilic substrate. The evaporation rates computed from the shadowgraphy imaging were explained using the average velocities obtained from the PIV analysis. It was found that advection within the droplet is strongly dependent on surfactant concentration and wettability. Further, the theoretically obtained Marangoni velocities were in close agreement with the experimental values. It was found that Marangoni solutal advection dominates other advection mechanisms, such as Marangoni thermal advection and buoyancy driven flow. However, surfactant crowding and viscous resistance with increasing surfactant concentration can dampen the increase in solutal advection. The surface tension and viscosity measurements were also conducted with variation in surfactant concentration to understand the suppression of advection by viscous forces. The computation of contact line velocities showed sudden fluctuations, illustrating stick slip behaviour during droplet drying, complementing microscopic visual observations.
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Applied Physics
Magnet-Free Nonreciprocal frequency conversion using Sequential Temporal modulation: Theory and Simulations
Arya G. Pour, Jun Ji and Linbo Shao
Nonreciprocal conversion is essential for protecting sources and enabling unidirectional signal routing in photonic, phononic, electronics, and
quantum systems, yet conventional implementations rely on
magnetic bias that could be challenging to integrate on chip. We propose a magnet-free scheme for frequency-domain nonreciprocity based on sequential, time-gated couplings in a three-mode system. By activating interactions in a fixed temporal order, the forward and reverse frequency conversion pathways acquire unequal dwell times in a lossy intermediate mode, producing strong nonreciprocity without requiring nonlinearities or
magnetic materials. Using a harmonic-balance formulation and a Dyson-Born expansion, we derive a compact analytical expression for the isolation ratio that reveals the roles of Floquet sidebands, duty-cycle control, modulation frequency, and dissipation. The results are confirmed by direct time-domain simulations over a wide parameter range. From these results, we extract practical design rules for optimizing isolation through temporal sequencing, loss engineering, and modulation timing. The framework is general and directly applicable to integrated platforms in photonics, phononics, microwave electronics, and superconducting
circuits.
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Optics
Sub-Nyquist time-domain surface-enhanced Raman mapping
Ting Wang, I. Brian Becerril-Castro, Ana Sousa-Castillo et al. (+3 more)
Surface-enhanced Raman scattering (SERS) combines analyte-specificity and single-molecule sensitivity, but its potential is limited by slow readout where sophisticated nanosensors are analysed in a serial fashion, one particle at a time. We introduce SERS lock-in sampling to resolve the decades-old trade-off between spectral resolution and widefield imaging. By leveraging the inherent sparsity of Raman spectra, we demonstrate that a simple digital lock-in scheme allows high-quality chemical imaging far beyond the Nyquist-Shannon limit. Our approach integrates an in-situ temporal reference to transform mechanical jitter into an exploitable feature, enabling near-random sampling. We validate SERS lock-in sampling through the multiplexed and simultaneous imaging of thousands of individual SERS-encoded sensors, achieving an orders-of-magnitude throughput-increase over the state-of-the-art. Furthermore, we demonstrate volumetric 3D chemical imaging in biomedically relevant
matrices. This robust, computationally simple strategy transforms SERS from a point-observation tool to an imaging modality for clinical diagnostics and real-time chemical observations.
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All authors Ting Wang, I. Brian Becerril-Castro, Ana Sousa-Castillo, Miguel A. Correa-Duarte, Ramón A. Alvarez-Puebla, Matz Liebel
Physics and Society
Where diverse populations gather: Transit accessibility and the spatial structure of social mixing
Yuan Liao
Urban venues serve as arenas for social mixing. While residential and activity-space segregation have been extensively studied, less is known about how the spatial structure of cities, particularly public transit infrastructure, shapes the geography of social mixing at specific locations. This study examines how transit accessibility associates with visitor diversity – the compositional heterogeneity of visitors sharing a venue, used here as an indicator of social mixing potential – at points of interest (POIs) in nine cities in Sweden and three cities in the United States (New York, Washington DC, Atlanta). Using mobile phone GPS data in 2024, we compute visitor diversity indices based on the birth background composition of visitors' home neighborhoods. Transit catchment diversity positively predicts visitor diversity, but this association is robust only in the largest metropolitan areas; in smaller Swedish cities, the coefficient attenuates to insignificance once geographic catchment composition, centrality, and venue density are controlled. Transit-diversity hotspots concentrate not in already diverse venues, but in lower-diversity POIs with lower commercial density, greater distance from transit in US cities, and greater centrality in Sweden. These patterns are consistent with transit infrastructure playing a bridging role, linking diverse populations to venues where alternative pathways are limited.
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Atmospheric and Oceanic Physics · Cross-listed from astro-ph.EP
A Fast and Physically Grounded Ocean Model for GCMs: The Dynamical Slab Ocean Model of the Generic-PCM (rev. 3423)
Siddharth Bhatnagar, Francis Codron, Ehouarn Millour et al. (+5 more)
Ocean dynamics are often sidelined in
exoplanet climate studies due to the high computational cost of fully coupled atmosphere-ocean general circulation models (GCMs). However, ocean heat transport (OHT) can play a critical role in shaping the
climate and observables of terrestrial
planets. As a compromise, most
exoplanet GCMs rely on slab ocean models without OHT. Here, we present an improved compromise - a fast and physically grounded dynamical slab ocean model, implemented in the Generic Planetary
Climate Model (Generic-PCM). The model extends previous frameworks by incorporating a Sverdrup balance formulation for wind-driven Ekman transport, the first application of the Gent-McWilliams parameterisation of mesoscale eddies in a slab ocean model, and a spectrally and thickness-dependent treatment of sea ice and snow albedo. In aquaplanet simulations, enabling OHT produces substantial changes in both surface
climate and atmospheric circulation, including cooler tropical sea surface temperatures, reduced sea ice, and the emergence of a double-banded equatorial precipitation pattern driven by Ekman-induced upwelling. The resulting OHT profiles show first-order agreement with fully coupled atmosphere-ocean GCMs. Applied to modern Earth, the model reproduces key large-scale
climate properties, including a global mean surface temperature of 13{\deg}C (within 1{\deg}C of observations), planetary albedo of 0.32 (within 0.01), and sea ice extent with significantly reduced seasonal biases relative to simulations without OHT. Due to model parallelisation, these improvements are achieved at almost no additional computation cost compared to OHT-disabled simulations run over the same number of model years. This enables long integrations, making the model particularly well suited for
exoplanet and paleoclimate studies where broad parameter exploration is essential.
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All authors Siddharth Bhatnagar, Francis Codron, Ehouarn Millour, Emeline Bolmont, Maura Brunetti, Jérôme Kasparian, Martin Turbet, Guillaume Chaverot
Optics
Modal analysis of electromagnetic resonators: MAN software expansion to 2D materials and coupled systems
Thomas Christopoulos, Tong Wu and P. Lalanne
This work presents an updated version of the previously released freeware MAN (Modal Analysis of Nanoresonators) [Comput Phys Commun 284, 108627 (2023)], a software package designed to efficiently compute and normalize quasinormal modes (QNMs) and to use them for the analysis of the optical response of electromagnetic resonators. This release substantially extends the capabilities of the original software through three major developments. First, it introduces dedicated models and numerical tools for resonators incorporating two-dimensional materials, including
graphene, using a surface-conductivity formulation. Second, it implements a coupled-QNM formalism that computes the complex coupling coefficients between resonator modes directly from the QNMs of the individual resonators. Unlike conventional coupled-mode theory, where these coefficients are often introduced phenomenologically or determined by fitting, MAN evaluates them rigorously from first principles. Third, it provides post-processing tools that determine the Fano parameters governing extinction spectra directly from the computed QNM field distributions. Together, these advances broaden the range of nanophotonic systems accessible to MAN while providing new tools for the quantitative interpretation of complex resonant phenomena.
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History and Philosophy of Physics · Cross-listed from quant-ph
Warring Contextualities - Provably Classical vs Provably Nonclassical
Enrico Bozzetto and Jonte R. Hance
In the literature, there are two differing definitions of contextuality: Kochen and Specker's, and Spekkens' (or “generalised”). However, researchers using one of these definitions rarely consider the other, meaning comparative analysis of these two notions is rare. In this paper, we advance the idea that Kochen-Specker contextuality provides a generalisation of the idea of system being fundamentally nonclassical, while Spekkens' noncontextuality provides a generalisation of the idea of a system being classical. This allows us to reconcile the two approaches, as different stages in a hierarchy of classicality/nonclassicality.
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Plasma Physics · Cross-listed from astro-ph.SR
The Damping and Instability of Ion-acoustic Waves in the Solar Wind: Solar Orbiter Observations
Hao Ran, Daniel Verscharen, Jesse Coburn et al. (+6 more)
Observations of
solar wind velocity distribution functions (VDFs) commonly reveal fine-scale structures. These features strongly influence kinetic processes such as wave damping and instability, yet their role remains poorly understood. We use a Gaussian Mixture Model (GMM) to separate
proton and $\alpha$-particle (fully ionized helium) VDFs from
Solar Orbiter
Proton and Alpha-particle Sensor (PAS) measurements, and assess how measured VDFs affect the damping of compressive fluctuations with the Arbitrary Linear
Plasma Solver (ALPS). We analyze the dispersion relation and polarization properties of ion-acoustic (IA) waves in the
solar wind.
Protons and $\alpha$-particles are represented by the measured VDFs derived from PAS observations. For comparison, we also perform calculations using the bi-Maxwellian assumption for the VDFs. Fine-scale structures of the measured
proton VDFs reduce the damping rate of IA waves, even when $T_e \simeq T_i$. In some cases, we find that the measured VDFs drive the IA mode unstable, while the corresponding bi-Maxwellian representations predict strong damping. These results demonstrate that resolving the fine-scale structures of VDFs is essential for accurately capturing the kinetic physics of the
solar wind.
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All authors Hao Ran, Daniel Verscharen, Jesse Coburn, Georgios Nicolaou, Charalambos Ioannou, Xiangyu Wu, Jingting Liu, Kristopher Klein, Christopher Owen
Biological Physics
Seabird trajectories map onto a reduced optimal-control bound for dynamic soaring
Louis González, John P.Y. Arnould and Saad Bhamla
Dynamic soaring allows seabirds to harvest mechanical energy from vertical wind shear, yet there is no common
benchmark for comparing flight performance across species based on their trajectories. We derive a reduced lower bound on transport effort from a simplified Hamilton-Jacobi-Bellman optimal-control model in which slow flight incurs an induced-drag penalty, fast flight incurs a dissipative penalty, and wind shear supplies an effective energetic subsidy. \add{We rescale each of the four species to its own baseline speed and accelerometer-based effort, then map them onto a common reduced speed–effort plane and estimate each one's lower frontier. We calibrate the optimal-control bound to one species, the wandering albatross, and test the other three against it. Two further dynamic soarers, the Buller's albatross and short-tailed shearwater, lie progressively above the bound. The common crane, a thermal soarer of comparable body mass, lies about 33 times as far from it as the albatross. Proximity to the boundary, therefore, measures the extent to which a bird's transport is powered by wind shear. More generally, our work offers a framework for testing optimal-control limits in bird flight using field data.
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Fluid Dynamics
Investigation of Mist and Air Film Cooling in a Two-Phase Rotating Detonation Combustor with Liquid Kerosene
Yeqi Zhou, Songbai Yao and Wenwu Zhang
We present a numerical investigation of kerosene droplet mist film cooling for the thermal protection of the rotating detonation combustor (RDC) and compare its performance with conventional air film cooling and combined mist/air cooling scheme. In the study, the cooling behavior of kerosene droplets injected through wall film holes is numerically examined and compared with air film cooling and a combined mist/air cooling strategy, building on a
benchmark validation against flat-plate experimental data. The results show that air film cooling exhibits an optimal operating range, beyond which excessive injection degrades film stability due to strong interaction with the rotating detonation wave. In contrast, kerosene-based mist cooling forms a more persistent near-wall cooling layer, providing enhanced heat removal through phase change and exhibiting improved resistance to film separation. In mist cooling, the droplet size primarily affects the immediate downstream cooling performance, with intermediate-sized droplets offering the improved balance between evaporation rate and film continuity. A combined mist/air cooling scheme can further improve cooling efficiency and accelerate wall temperature recovery after detonation wave passage while maintaining moderate impacts on the mainstream flow. Additionally, although kerosene droplets partially participate in combustion under film hole injection, the associated thermal load does not offset the overall cooling benefit. These findings demonstrate the feasibility and advantages of kerosene-based cooling schemes for RDC thermal management.
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Atmospheric and Oceanic Physics
Revisiting the Dynamical Properties of Pedlosky's Two-Layer Model for Finite Amplitude Baroclinic Waves
Nicolas De Ro, Jonathan Demaeyer and Stéphane Vannitsem
Baroclinic instability is a fundamental mechanism driving atmospheric dynamics. In this work, we revisit Pedlosky's two-layer model for finite amplitude baroclinic waves - a seminal framework for studying the unstable growth of finite perturbations - leveraging modern nonlinear techniques and computational resources. We show that the geophysical state of the baroclinic wave exhibits a rich diversity of dynamical regimes governed by the level of dissipation induced by Ekman boundary layers. In the inviscid limit, we demonstrate that the model is integrable. Upon increasing dissipation, the system undergoes a complex sequence of bifurcations. On one hand, deterministic chaos, identified by means of the Lyapunov exponents, provides a genuine mechanism for destabilization of the wave. On the other hand, in regimes where the wave equilibrates, dependence on the initial condition is crucial, eventually leading to the coexistence of multiple attractors. We study the governing equations of the model and their truncation to a finite-dimensional system of ordinary differential equations, together with the minimal low-order truncated system which is structurally equivalent to the Lorenz model. Its bifurcation diagram allows for elucidating the transition of the wave amplitude from stable equilibration to periodic oscillations - terminating in homoclinic orbits - and, ultimately, deterministic chaos through a period-doubling route. We finally comment on the robustness of these features for higher-dimensional models.
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Optics
Sub-micromolar imaging of intrinsic chromophores by two-photon photothermal microscopy captures mitochondrial response to chemotherapy
Nathaniel Hai, Chinmayee Vallabh Prabhu Dessai, Dingcheng Sun et al. (+4 more)
Intracellular chromophores (e.g., NADH and FAD) play a central role in regulation of cellular metabolism. Though autofluorescence has been extensively used for label-free mapping of chromophores inside a
cell, its sensitivity and molecular specificity are constrained by the low
quantum yield and the fluorescence spectral overlap. Here, we address these challenges by employing a photothermal approach to measure the optical absorption of chromophores rather than its autofluorescence. By combining near-infrared pump and visible probe beams, our two-
photon photothermal (2PPT) microscope exploits localized thermal transients generated through two-
photon absorption, enabling detection of chromophore-specific signatures beyond the reach of autofluorescence. We demonstrate sub-micromolar limit of detection for the metabolic coenzymes NADH and FAD of 0.87 uM and 0.99 uM, respectively. Such high sensitivity enables differentiating the influence of different mitochondria shapes on metabolism activity. Importantly, the fluorescence crosstalk-free 2PPT can identify the biomolecular source of contrast from cellular mitochondria in a label-free manner based on spectroscopy. 2PPT microscopy is utilized to study metabolic alterations of mitochondria in cancer under chemotherapy at the single organelle level.
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All authors Nathaniel Hai, Chinmayee Vallabh Prabhu Dessai, Dingcheng Sun, Jianpeng Ao, Pin-Tian Lyu, Yifan Zhu, Ji-Xin Cheng
Optics
Single Plane Spatial Mode Sorter
Khen Cohen, Yoav Yosif-Or, Yaron Oz et al. (+1 more)
A mode sorter separates a set of M orthogonal spatial modes in a shared input channel into M different output channels. Here we present an analytic derivation and experimental validation of a single plane device for sorting spatial modes from a diverse variety of mode families, including Hermite-Gaussian (HG), Laguerre-Gaussian (LG), Bessel-Gaussian (BG), with almost no cross-talk. This sorting capability is required for a wide range of applications that employ classical or
quantum light. We also show that applying this design in order to sort a set of Orbital Angular Momentum (OAM) modes with zero radial index reproduces the well-known Fork grating configuration. Furthermore, by taking the limit of M -> inf, we present an analytical expression for sorting all the modes of a given family. By operating this device in reverse, it can be used to generate arbitrary modes, by illuminating it with a Gaussian beam. The power transmission coefficient for this sorter goes as 1/M and we provide a mathematical proof that this is optimal for any typical arrangement of the detector positions. We further study the sorter sensitivity to wavelength and random phase noise.
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All authors Khen Cohen, Yoav Yosif-Or, Yaron Oz, Ady Arie
Chemical Physics
Configuration interaction extension of AGP for incorporating inter-geminal correlations
Airi Kawasaki, Fei Gao and Gustavo E. Scuseria
In this paper, we develop a class of antisymmetrized geminal power configuration interaction (AGP-CI) wave functions that extend the AGP framework by incorporating inter-geminal correlations through a CI expansion. To make these wavefunctions computationally tractable, we evaluate them by rewriting the AGP-CI ansatz as a linear combination of AGPs (LC-AGP), for which overlaps and
Hamiltonian matrix elements can be computed with standard AGP machinery. Motivated by border-rank decompositions, we further reorganize this ansatz into a compact linear combination of AGPs depending on a small deformation parameter $\tau$, which controls how closely the truncated expansion approximates the full AGP-CI state.
Benchmark applications to the Hubbard model and to the small molecules H$_2$O and N$_2$ demonstrate that the proposed wavefunctions achieve consistently high accuracy and outperform the LC-AGP, particularly for systems with more electrons and in strongly correlated regimes.
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Space Physics
Simultaneous TRACERS and THEMIS Observations of Reversed Cusp Ion Dispersions and Dual-Lobe Reconnection
M. Øieroset, S. A. Fuselier, J. B. Bonnell et al. (+20 more)
We present observations from two consecutive TRACERS-2 orbits through the northern low-altitude cusp. During the first crossing, TRACERS-2 observed reversed cusp ion dispersion and sunward convection, consistent with magnetopause reconnection tailward of the cusp during this northward IMF interval. Simultaneous THEMIS-D observations at the equatorial magnetopause show heated magnetosheath
plasma captured on closed field lines, with similar particle spectra as in in the low-altitude cusp, indicating that reconnection indeed occurred tailward of the cusp and in both hemispheres. When TRACERS-2 traversed the northern cusp again, 95 minutes later, the IMF was dominated by a negative BX component. Despite the different IMF conditions, TRACERS-2 recorded nearly the same cusp signatures as before, i.e., reversed ion dispersion and sunward convection. The observations indicate that tailward-of-cusp reconnection can occur for both northward and BX-dominated IMF and that these distinct IMF geometries can produce remarkably similar
plasma and field signatures in the low-altitude cusp.
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All authors M. Øieroset, S. A. Fuselier, J. B. Bonnell, R. A. Roglans, J. S. Halekas, R. J. Strangeway, T. D. Phan, R. G. Gomez, S. M. Petrinec, K. J. Trattner, S. R. Shaver, K. A. Goodrich, S. A. Henderson, S. L. Soni, V. Angelopoulos, B. L. Burkholder, H. Cao, L-J. Chen, H. K. Connor, D. M. Miles, A. Moore, J. Ng, Y. Shen
Computational Physics
Distributional Inverse Homogenization
Arnaud Vadeboncoeur, Mark Girolami, Kaushik Bhattacharya et al. (+1 more)
For many materials, macroscopic mechanical behavior is determined by an intricate microstructure. Understanding the relation between these two scales helps scientists and engineers design better materials. The relation which maps microstructure to bulk material properties can be understood via the well-established theory of homogenization. However inverting the homogenization process, to recover microstructural information from measured macroscopic properties, is fraught with difficulties because of the averaging processes that underlie homogenization. Therefore, scientists and engineers usually need recourse to more invasive, often highly localized, investigations to estimate the microstructure. In this work, we develop a noninvasive methodology by which one can leverage large collections of measured bulk material properties to infer information about the statistics of microstructure at a global level. We call this, distributional inverse homogenization. We study this problem in one and two dimensions, considering both periodic and
stochastic homogenization. We demonstrate the methodology in the context of 2D Voronoi constructions and underpin the observed empirical success with theory in 1D. We also show how the natural spatial variability of microstructure can be exploited to gather data that enables distributional inversion. And we concurrently learn a surrogate model, approximating the homogenization map, that accelerates the resulting computations in this setting. The work formulates a new class of inverse problems, bridging ideas from probability and homogenization to facilitate the inference of microstructural material variability from macroscopic measurements.
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All authors Arnaud Vadeboncoeur, Mark Girolami, Kaushik Bhattacharya, Andrew M. Stuart
Computational Physics · Cross-listed from gr-qc
Finding and characterising physical states of Euclidean Abelianized loop quantum gravity using neural quantum states
Hanno Sahlmann and Waleed Sherif
We study physical (near-kernel of constraints) states of 4-d Euclidean loop
quantum gravity in Smolin's weak coupling limit on the complete graph $K_5$ using variational Monte Carlo with neural network
quantum states. We investigate the Hamilton constraint $\hat{H}$ in the ordering proposed by Thiemann, as well as $\hat{H}^\dagger$ and $\hat{H}+\hat{H}^\dagger$. We find that the variational optimisation selects distinct solution families for $\hat{H}$ and $\hat{H}^\dagger$ across several considered cutoffs on the kinematical degrees of freedom. The solution family of $\hat{H}$ is flat on all minimal loops and has non-vanishing volume expectation values. Its edge-charge marginals delocalise with increasing cutoff, which indicates they are approximations to solutions that are non-normalisable in the kinematical inner product. The solution family for $\hat{H}^\dagger$ is normalisable, shows non-trivial charge correlations, lies in the kernel of volume and is not flat. $\hat{H}+\hat{H}^\dagger$ turns out to be much harder to solve and yields quasi-solutions combining features of both previous families. We characterise all solutions using chromaticity 1- and 2-point functions, minimal loop holonomies,
geometric area and volume observables and show that the two families can be interpreted as, on the one hand, a family of states close to the Ashtekar-Lewandowski
vacuum and the Dittrich-Geiller
vacuum with some numerical noise on the other hand. We also present some results that link solutions of the truncated theory to solutions of the continuum theory.
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