Fluid Dynamics · Cross-listed from math.NA
Accelerating droplet-laden Stokes flow simulations with hierarchical surrogate modeling
Davide Pradovera, Thomas Frachon and Sara Zahedi
We present a surrogate modeling strategy for Stokes flows with
liquid droplets suspended in a carrier fluid. Our approach is based on a multi-fidelity framework. At the lowest fidelity, droplets are treated as passive tracers, neglecting their influence on the ambient flow field. Building on this approximation, we derive a PDE that represents the current modeling error. This error equation is then solved approximately to correct the flow field and the procedure is iterated. Two fidelities are employed in an alternating fashion: Stokes flow in the absence of droplets and flow around a single droplet in free space. By systematically combining these models, the method captures droplet-flow, droplet-boundary, and droplet-droplet interactions. In this work, the framework is developed and validated for circular, non-deforming droplets in two spatial dimensions. The
geometric self-similarity of the droplets allows us to construct an efficient offline-online strategy based on the reuse of precomputed single-droplet solutions. Extensions to deformable droplets are also discussed. Numerical experiments demonstrate the accuracy and efficiency of the proposed surrogate in a variety of tests, including scenarios with up to $10^4$ droplets. Notably, we show that the proposed surrogate achieves substantially reduced computational cost compared to fully resolved multi-fluid simulations with state-of-the-art software.
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Physics and Society · Cross-listed from cond-mat.stat-mech
Variance of the $SIS$ Epidemic on Networks: A Diffusion Approximation
Lucija Nora Farkaš, Sebastian Morel Balbi, Hrvoje Štefančić et al. (+2 more)
Functional laws of large numbers (FLLNs) describe the mean-field trajectory of epidemics on networks, but say nothing about the fluctuations around it. These fluctuations are governed by moments of the degree distribution not relevant at the level of the mean. A rigorous functional central limit
theorem (FCLT) exists for the susceptible–infected ($SI$) process on configuration-model graphs, but no analogue exists for $SIS$, where recovery reintroduces vertices into the susceptible pool with partially known neighborhoods, breaking the clean neighborhood distribution the $SI$ derivation relies on. We develop a tractable variance approximation for Markovian $SIS$ on configuration-model graphs, combining Gleeson's approximate master equation (AME) framework with a van Kampen system-size expansion in the spirit of the $SI$ FCLT. We derive a closed drift and
diffusion matrix for a reduced susceptible/$SI$-edge/$SS$-edge count vector and obtain the time-dependent covariance via the associated Langevin/Lyapunov equation. Validation against Gillespie simulation across Poisson, regular, and power-law networks shows close agreement, with deviations near the epidemic threshold and in strongly heterogeneous networks.
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All authors Lucija Nora Farkaš, Sebastian Morel Balbi, Hrvoje Štefančić, István Zoltán Kiss, Vinko Zlatić
Atmospheric and Oceanic Physics · Cross-listed from cs.LG
A harmonised dataset for Earth system foundation models
Carlos Rodriguez-Pardo and Massimo Tavoni
Foundation models for Earth systems have so far been trained primarily on physical
climate and weather data, with limited representation of the human systems that both drive and respond to environmental change. The lack of a unified global training resource that combines
climate, land, ocean, cryosphere, infrastructure, hazards, and socioeconomic data on a common grid hinders progress toward truly
multimodal Earth system foundation models. We present WorldTensor, a harmonised global
dataset that aligns hundreds of environmental and socioeconomic variables to a standardised 0.25$^\circ$ spatial grid and annual temporal framework. WorldTensor integrates reanalysis products, remote sensing, emissions inventories, land use reconstructions, hydrological observations, infrastructure and hazard
datasets, and socioeconomic indicators within a single representation designed for machine learning workflows. To build the
dataset, we regridded inputs across heterogeneous native resolutions and projections, rasterised point and vector
datasets into spatially meaningful gridded fields, and reconciled temporal coverages ranging from daily observations to sparse multiyear socioeconomic snapshots. All outputs are distributed as NetCDF files with standardised coordinates, variable metadata, and a common CF metadata convention. WorldTensor provides a reproducible resource for training and evaluating foundation models that learn coupled dynamics across environmental and human systems at planetary scale.
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Physics and Society
Scaling laws in complex component systems as consequences of heterogeneous sampling
Luca Allegri, Johannes Nauta and Manlio De Domenico
Complex component systems are collections of discrete units such as species, words, genes, whose observed realizations are naturally summarized by component counts. Many empirical laws have been observed in those systems, such as Taylor's law, Zipf's law, and Heaps' law, and domain-specific mechanisms are often employed to explain their emergence but, despite their ubiquity, a unifying framework remains elusive. In this work, we propose a null model showing that, under heterogeneous latent rates and finite sampling, several commonly observed scaling relations can arise without invoking domain-specific mechanisms. Taylor's law, for instance, reflects a crossover between sampling noise and genuine system heterogeneity and it is largely insensitive to the detailed latent distribution, while Zipf's and Heaps' laws arise from the convergence of order statistics and distinct component counts under heavy-tailed but otherwise generic priors. Our work thus suggests that these ubiquitous patterns are better interpreted as a transient sign of statistical convergence instead of fundamental principles that require tailored generative explanations.
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Medical Physics
Contextual Cellular Growth (ConCeG) of neural cells for realistic grey matter tissue generation for diffusion MRI simulations
Charlie Aird-Rossiter, Kadir Şimşek, Maëliss Jallais et al. (+3 more)
Accurate interpretation of
diffusion magnetic resonance imaging (dMRI) signals in grey matter (GM) remains challenging due to the complex, heterogeneous, and densely packed cellular environment. Numerical phantoms provide a controlled framework for investigating the relationship between microstructure and
diffusion signals, yet existing approaches often lack the morphological realism and multi-cellular organisation required to faithfully represent GM tissue. In this work, we introduce Contextual Cellular Growth (ConCeG), a generative framework for creating individual
cells or constructing dense, three-dimensional, multi-cellular GM substrates informed by real neuronal and glial morphologies. The method combines topological
neuron synthesis with a spatially constrained growth network, allowing for the controlled generation of heterogeneous cellular environments with realistic intra- and extracellular compartments. Synthetic
cells are generated using morphological and topological characteristics derived from biological reconstructions. We validate the framework through comparisons of structural features with real cellular data, demonstrating strong agreement in branch order, length, angle, and tortuosity distributions. Power spectrum analysis further shows that both intracellular compartments reproduce the spatial correlations observed in biological tissue. Together, these results show ConCeG provides a biologically grounded framework for generating grey matter substrates suitable for large scale
diffusion MRI simulation.
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All authors Charlie Aird-Rossiter, Kadir Şimşek, Maëliss Jallais, Derek K. Jones, Lida Kanari, Marco Palombo
Optics
Overcoming the low signal-to-noise problem for hybrid mode-selective photonic lantern-based wavefront correction using machine learning
Nathan K Long, Barnaby Norris, Daniel S Dahl et al. (+10 more)
Hybrid mode-selective photonic lanterns transform an input complex point-spread function into several single-mode outputs, where a selected core feeds the fundamental mode to a photonic science instrument, while the remaining cores are used for wavefront sensing in a closed-loop adaptive optics system. A neural network maps the intensities of the wavefront sensing cores to an estimated wavefront correction, which is applied to an upstream deformable mirror. However, there exists a trade between maximizing the amount of light reserved for the photonic instrument and the reduced signal-to-noise ratios for the wavefront sensing cores. We explore wavefront correction for the Seidr instrument, a part of the Asgard Suite for the Very Large
Telescope Interferometer. We evaluate different neural network architectures, comparing wavefront estimation performance for different wavefront error types, as a first step toward addressing the signal-to-noise trade-off. Results show
transformer neural networks as a promising solution for temporal photonic lantern-based wavefront estimation.
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All authors Nathan K Long, Barnaby Norris, Daniel S Dahl, Christopher H Betters, Julia J Bryant, Nick Cvetojevic, Sergio Leon-Saval, Frantz Martinache, Marc-Antoine Martinod, Akira Rodziewicz-Ryan, Adam K Taras, Jin Wei, Peter G Tuthill
Optics
Seidr update: photonic 'black magic' for high-contrast interferometry using kernel-nulling and photonic lanterns
Nathan K Long, Daniel S Dahl, Christopher H Betters et al. (+13 more)
Seidr is a new interferometric beam combiner within the Asgard Suite, utilizing infrastructure common to the BIFROST instrument at the Very Large
Telescope Interferometer. Seidr combines hybrid mode-selective photonic lantern injection modules with a kernel-nulling photonic chip backend to enable deep H-band nulling for high-contrast studies of
exoplanets, exomoons, and circumstellar
dust. This instrument update summarizes Seidr's current design maturity and recent simulations of the point source - to - lantern outputs. We also outline progress on our neural network-based wavefront estimation scheme, which uses the photonic lantern outputs to sense phase fluctuations, designed to feed back to Baldr's deformable mirror, and improve nuller light injection.
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All authors Nathan K Long, Daniel S Dahl, Christopher H Betters, Julia J Bryant, Nick Cvetojevic, Michael J Ireland, Stefan Kraus, Sergio Leon-Saval, Frantz Martinache, Marc-Antoine Martinod, Barnaby Norris, Jyotirmay Paul, Akira Rodziewicz-Ryan, Adam K Taras, Jin Wei, Peter G Tuthill
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Enhanced hydrogen response of copper-doped TiO$_2$ synthesised by helium-assisted magnetron sputtering
Akash Kumar, Nirmal Kumar, David Kolenatý et al. (+4 more)
Cu-doped TiO$_2$ thin films for hydrogen sensing were synthesised by reactive DC magnetron sputtering in Ar/O$_2$/He mixtures, with the He fraction used as a control parameter for film growth. By combining normal-angle deposition (NAD) and glancing-angle deposition (GLAD) with post-deposition annealing, the effects of He on microstructure formation and sensor performance were examined. X-ray diffraction and electron microscopy revealed that He promotes nanostructuring,
lattice expansion in as-deposited NAD films, increased porosity after annealing, and a stronger anatase character in the final
oxide layers. These structural changes, which enhance the reactive surface area, lead to improved hydrogen sensing at 300\,$^\circ$C in 1~vol.\,% H$_2$. The response of NAD films increased from 1.4 to 6.0 simply by replacing part of the argon with helium, whereas GLAD films showed only a modest increase. The observed nanostructuring is discussed in terms of a simulation-supported growth scenario involving energetic backscattered He, a reduced hammering effect, and cooling-related suppression of adatom mobility, which together favour the formation of a more open sensing layer. Helium-assisted sputtering represents a useful physical route for tailoring
oxide thin films for gas-sensing applications.
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All authors Akash Kumar, Nirmal Kumar, David Kolenatý, Mina Farahani, Jiří Rezek, Tomáš Kozák, Stanislav Haviar
Atmospheric and Oceanic Physics
A Wigner-based volumetric transport framework for paraxial waves in random media
Arnaud Coatanhay, Thomas Bonnafont and Angélique Dremeau
We develop a Wigner-based phase-space framework for mean paraxial wave propagation in random media. Starting from the random
parabolic wave equation, we derive the exact
evolution of the realization-dependent Wigner distribution and identify the ensemble-averaged Wigner function as the natural second-order state variable. The averaged equation contains a closure defect, given by a mixed field–medium correlation, which prevents a closed transport equation from being obtained without additional assumptions. We therefore organize the modelling as a hierarchy from the random wave equation to an exact Wigner formulation, then to a nonlocal kinetic closure, and finally to a local Fokker–Planck reduction in the small-angle regime. For the minimal homogeneous isotropic Fokker–Planck model, we derive closed
evolution laws for the quadratic moments, exhibit the cubic-in-distance contribution to beam spreading, and obtain explicit Gaussian and Gauss–Schell propagation formulas. These analytical results are used to validate a phase-space splitting solver in one-dimensional transverse
benchmarks. Comparisons with nonlocal kinetic models show that the diffusive approximation is accurate for narrow momentum-transfer kernels and loses validity in a controlled way as finite-jump effects become significant. Finally, we introduce a first atmospheric specialization based on a regularized
turbulence spectrum, yielding an effective
diffusion coefficient expressed in terms of standard atmospheric parameters.
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Atomic Physics
Development of a High-Performance Permanent Magnet System for Ion Trapping Experiments
Jifei Wu, Jiawei Wang, Tianhang Zhang et al. (+4 more)
This work presents the design and fabrication of a compact permanent magnet based on an optimized stacked structure of fifteen NdFeB rings. The tunable NS-SN-NS configuration generates a central
magnetic field of 0.8T with a reconstructed uniformity of 99.988% within a 1mm radius spherical volume. The remaining field inhomogeneity is dominated by radial dipole components. Requiring neither cryogenics nor external power, this design provides a high-performance and cost-effective alternative to superconducting magnets for applications in ion-trap development and
Fourier-transform ion cyclotron resonance mass spectrometry.
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All authors Jifei Wu, Jiawei Wang, Tianhang Zhang, Zichen Su, Liangyu Huang, Wei Wu, Bingsheng Tu
Instrumentation and Detectors
Secondary electron yield from aluminium-coated foils for muon tagging and beam monitoring up to 60 MeV/c
Gianluca Janka, Michael W. Heiss, Maxime Lamotte et al. (+2 more)
The feasibility of foil-based
muon tagging is investigated in the momentum range below 60 MeV/c, with particular focus on its applicability to the low-momentum range spanning approximately 2.5 MeV/c to 20 MeV/c, where no efficient and minimally invasive detection scheme is currently established for continuous beams. Secondary electron emission from a 7 um Mylar foil coated with 50 nm aluminium is investigated using a continuous negative
muon beam with nominal momenta between 12 MeV/c and 60 MeV/c at the piE1 beamline at PSI. The emitted electrons are detected with position-sensitive microchannel plate detectors, enabling particle tagging and spatial characterization of the beam. The detection efficiency and corresponding secondary electron yield are extracted and benchmarked against literature data for
protons, showing good agreement and confirming reliable
muon tagging. The observed trend for negative
muons is consistent with the well-established increase in ion-induced secondary electron emission toward lower particle velocities, suggesting improved performance in the low-momentum regime. A proof-of-principle reconstruction of the
muon beam profile is demonstrated by correlating detected electron positions with their emission point at the foil. These results establish foil-based tagging as a viable approach for combined timing and minimally invasive beam monitoring, bridging the gap between high- and low-energy
muon instrumentation.
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All authors Gianluca Janka, Michael W. Heiss, Maxime Lamotte, Xiao Zhao, Thomas Prokscha
Classical Physics · Cross-listed from math.AP
Isotropy and Galilean invariance of Lattice Boltzmann Method: Theoretical and numerical analysis using oblique dipole benchmark *
François Dubois, Souleymane Kadri Harouna, Pierre Lallemand et al. (+1 more)
This work focuses on the two-dimensional, nine-velocity (D2Q9)
lattice Boltzmann model. First, we show that the D2Q9 scheme cannot achieve secondorder accuracy unless the cubic velocity terms are neglected, and we explain how some of these parasitic terms can be eliminated. Second, we demonstrate that the standard choice of the
equilibrium distribution has no effect on the equivalent PDE at second order. Finally, we numerically investigate the effect of these cubic terms and study different choices of
equilibrium distributions using a new
benchmark called the Oblique Dipole
Benchmark, which describes obliquely propagating 2D
vortex dipoles with periodic boundary conditions.
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All authors François Dubois, Souleymane Kadri Harouna, Pierre Lallemand, Mohamed Mahdi Tekitek
Data Analysis and Statistics · Cross-listed from cs.CE
Uncertainty Quantification Study of a Re-entry Breakup
Tommy Williamson, Beatriz Jilete, Emma Stevenson et al. (+3 more)
The uncertainty associated with breakup events that occur during atmospheric re-entry is severe. Limited attempts to gain a better knowledge of this environment have included the use of breakup recorder-type sensor capsules that are designed to escape the demising debris cloud and survive in order to transmit data. This work models a breakup recorder undergoing this process as a rigid body experiencing hypersonic aerothermodynamic loads alongside collision dynamics with components of the demising container vehicle. The re-entry of the Edoardo Amaldi Automated Transfer Vehicle (ATV3) and the recorder placed on board, the Re-Entry Breakup Recorder 4 (REBR4) is studied in the present work. After a deterministic exploration of the nature of the dynamics of the problem, uncertainty quantification is performed to investigate the effects of initial spacecraft state, REBR detachment conditions and spacecraft fragmentation states. From this data, inferences about the nature of the real re-entry event indicate that detachment of the recorder from the cargo bay prior to main breakup events is more likely than the alternate hypothesis of the container vehicle experiencing high rotation rates.
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All authors Tommy Williamson, Beatriz Jilete, Emma Stevenson, Stijn Lemmens, Massimiliano Vasile, Marco Fossati
Optics
Griffiths Anomalous Absorption in Sparse-Loss Photonic Lattices
Stefano Longhi
Light absorption in photonic
lattices with sparsely distributed loss sites exhibits behavior analogous to Griffiths physics. Under uniform excitation, the transmitted power shows a stretched-exponential decay and a non-monotonic dependence on the loss strength, with an optimal loss rate that maximizes absorption. This behavior arises from rare, long loss-free segments that act as weakly coupled, long-lived photonic channels, rather than from exceptional point physics or interference effects. Using a minimal tight-binding model with binary quenched dissipation, we show that rare regions produce a universal Griffiths-type subexponential decay. Sparse-loss photonic
lattices thus provide an accessible platform to observe disorder-induced anomalous absorption and rare-region Griffiths physics.
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Optics · Cross-listed from quant-ph
Broadband characterization of polarization mode dispersion for quantum communication channels
Vadim Rodimin, Konstantin Kravtsov, Rui Ming Chua et al. (+5 more)
We present a method for characterizing depolarization in fiber channels carrying broadband polarization-encoded optical signals. Wavelength-dependent polarization mode dispersion maps each input polarization to a trajectory on the Poincaré sphere; we show that the singular value decomposition of the band-averaged rotation
matrix yields, in closed form, the optimal input states, the associated mutually unbiased measurement bases, and the resulting projection error probabilities. The three singular values provide a compact, bandwidth-dependent channel signature that distinguishes first- from higher-order dispersion, and yield the bandwidth at which the worst-case error probability reaches 3% as a practical filtering budget. We perform a second-order analysis of the band average that treats the two higher-order mechanisms: variation of the differential group delay at a fixed principal-state axis and wander of that axis with wavelength. We characterize 12 deployed fiber links in Masdar City and demonstrate mitigation by concatenating two channels through a single polarization controller, a step towards nonlocal compensation. The analysis is implemented in an openly available Python library for fiber-channel characterization.
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All authors Vadim Rodimin, Konstantin Kravtsov, Rui Ming Chua, Xingjian Zhang, Aleksei Ponasenko, Yury Kurochkin, Alexander Ling, James A. Grieve
Optics
Efficient broadband second-harmonic generation in a multi-pass cell
Arthur Schönberg, Nikolas Rupp, Ana Oliveira e Silva et al. (+6 more)
Second-harmonic generation (SHG) is a widely used nonlinear optical process that has been optimized for high frequency conversion efficiency, broad bandwidths, and optimum spatial and temporal quality of the generated light. However, limitations of the generation efficiency arise due to temporal dispersion and pulse walk-off effects introduced by the nonlinear
crystal. To circumvent these limitations, quasi-waveguide schemes, in particular multi-pass
cells (MPCs), can be employed, providing flexible phase-tuning capabilities. In this work, we demonstrate for the first time broadband and efficient SHG in an MPC. SHG efficiencies of 72% (for 63 fs, 50 uJ pulses) and 47% (for 15 fs, 20 uJ pulses) are obtained by simultaneously matching the relative phase and group delay between the fundamental and second-harmonic fields over multiple passes through the MPC. Our work sets a new record for efficient Gaussian-beam, ultrashort-pulse SHG and provides a general route to address efficiency-bandwidth limitations of nonlinear optical processes.
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All authors Arthur Schönberg, Nikolas Rupp, Ana Oliveira e Silva, Lorenzo Pratolli, Yujiao Jiang, Vincent Wanie, Terence Mullins, Francesca Calegari, Christoph M. Heyl
Atomic Physics
Calculation of the energy levels and hyperfine structure for Xe~II, Rn~II, and Og~II ions
T. H. Dinh, V. A. Dzuba and V. V. Flambaum
Energy levels, Landé $g$-factors, and hyperfine-structure constants are calculated for the singly ionized noble-gas atoms Xe II, Rn II, and Og II. The calculations are performed using the configuration-interaction method with perturbative treatment of high-lying configurations. Core polarization effects in the hyperfine interaction are included within the time-dependent Hartree-Fock method. Calculations for Xe II are used to test the accuracy of the approach by comparison with available experimental data. The agreement is at the level of about one percent for the energies and typically about ten percent for the hyperfine constants, with better accuracy for states with large hyperfine constants. Predictions are then presented for Rn II and Og II, for which experimental spectroscopic data are limited or absent. Special
attention is paid to Breit and
quantum-electrodynamic corrections to the hyperfine structure in heavy many-electron ions. We show that these corrections may be strongly enhanced by configuration mixing when interacting states with very different hyperfine
matrix elements are separated by small energy intervals. This effect is demonstrated explicitly for odd-parity $J=1/2$ states of Og II. The calculated hyperfine-structure constants for Rn II and Og II provide electronic factors needed for extracting
nuclear magnetic dipole and electric quadrupole moments from future spectroscopic measurements. These results may be useful for experimental studies of radon and oganesson ions and for testing
nuclear models in the superheavy region.
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Optics
Bidirectional phase sensitivity in holographic phototransient microscopy
Emmanuel Kotu Robertson, Dennis van de Lockand and Matz Liebel
Mid-infrared photothermal microscopy combines the chemical specificity of infrared absorption with the spatial resolution of visible-light detection, but practical implementations face a persistent trade-off between forward-scattering (FWS) and backward-scattering (BWS) detection geometries. FWS provides quantitative, shape-independent phase contrast but requires two-sided optical access that is difficult to achieve in aqueous or thick samples. BWS offers convenient single-sided access, but its signals are strongly distorted by depth-dependent interference for micron-scale objects. Here we present a bidirectional femtosecond mid-infrared pump-probe
holographic microscope capable of switching between FWS and BWS geometries within a single instrument, and use it to introduce and validate a new imaging modality, internal forward scattering (IFS). IFS exploits the back-reflection generated at the top surface of the mid-infrared-transparent sample substrate as an internally generated forward-scattering illumination wave, isolated from the directly backscattered field via temporal coherence gating. Using polystyrene beads on CaF2 substrates in air, water, and a refractive-index-matched glycerol-water mixture, we show that IFS reproduces the signal magnitudes and temporal dynamics of true FWS measurements while retaining the mechanical simplicity and single-sided accessibility of BWS. These results establish IFS as a practical, quantitative alternative to conventional FWS and BWS geometries for photothermal, and more broadly quantitative phase, imaging, with direct relevance to single-sided imaging of biological or solvent-contained specimens.
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Optics · Cross-listed from quant-ph
Geometric modulation of transition and survival intensities in non-Hermitian systems
Ryu Frieson, Takashi Oka and Hideaki Obuse
The time
evolution of non-Hermitian systems is generally nonunitary. Dynamics governed by time-dependent non-Hermitian
Hamiltonians lead to a variety of novel phenomena, one of which is state amplification or suppression induced by the complex Berry phase. Here, we extend the framework of
geometric modulation to multi-level systems and show that both transition and survival intensities can be modulated. We apply our theory to the non-Hermitian Landau-Zener (LZ) problem. First, we show that, in the half-LZ problem, both the transition and survival probabilities exhibit nonreciprocity due to the complex Berry phase. In the non-Hermitian standard LZ problem, only the survival intensity is known to exhibit nonreciprocity, whereas the transition intensity does not. However, the physical origin of this nonreciprocal behavior remains unclear. In this work, we show that the nonreciprocity originates from the complex Berry phase.
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Classical Physics · Cross-listed from cond-mat.stat-mech
Finite-Time Thermodynamics of Battery Discharging: Power-Efficiency Trade-Off and Optimization
Rui-Han Liu, Yun-Qian Lin and Yu-Han Ma
Battery discharging is governed by a fundamental trade-off between output power and energy conversion efficiency due to internal dissipation. In this paper, we demonstrate that such a trade-off universally yields a
parabolic envelope $P\propto\eta(1-\eta)$. The efficiency at maximum power is exactly one half, mirroring the well-known half-Carnot limit in finite-time thermodynamics. To extend this bound into practical operational rules, we formulate a multistage constant-current discharging (MSCD) schedule subject to simultaneous real-time load demands and a global discharging deadline. Analytical resolution via the Karush–Kuhn–Tucker conditions reveals a remarkably compact optimal policy: $I_{i}^{\star}=\max(I_{i}^{-},I_{0})$. Under this rule, stages limited by external demand run exactly at their minimum required currents, while all remaining stages are elevated to a uniform baseline $I_{0}$ fixed by the deadline constraint. By tracing the dissipation–time Pareto front, we quantify how internal resistance shifts the operational boundaries and sharpens the trade-off corner. This analysis establishes a rigorous thermodynamic baseline for the scheduling layer of battery management systems, offering natural extensions to nonlinear models incorporating temperature and state-of-charge dependencies.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Self-Driven Atomic Dispersion in Graphitic Layers
Zhaoxi Chen, Yulu He, Zhuoran Yao et al. (+9 more)
Carbon-supported single-atom catalysts maximize metal utilization, but how metal nanoparticles transform into isolated atoms within carbon remains unclear. We show that metal nanoparticles can undergo a self-driven dispersion process under hydrocarbon oxidation conditions, transforming into single atoms that are confined in carbon
matrix. Using Pt-catalysed hydrocarbon oxidation as a model, we combine operando electron microscopy, near-ambient-pressure X-ray photoelectron spectroscopy and mass spectrometry to track coupled structural and chemical
evolution. Graphitic carbon grows at step edges of Pt nanoparticle, continuously reconstructing Pt surface and generating undercoordinated sites for atom release. In-situ generated CO accumulates at the metal-carbon interface, weakening bonding and facilitating self-amplified atom release and migration. Defective carbon overlayers then trap, stabilize and transport liberated atoms, while oxidative etching preserves interfacial access of reaction-gas. Similar behaviour across other metals suggests a general atomization pathway for single-atom catalyst synthesis, yielding products with electrocatalytic hydrogen production activity beyond standard commercial
benchmarks.
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All authors Zhaoxi Chen, Yulu He, Zhuoran Yao, Jian Liu, Jun Cai, Ziyi Fan, Wenjun Zhang, Lei Lei, Zupeng Chen, Bo Yang, Zhi Liu, Zhu-Jun Wang
Optics
Exceptional light propagation via generalized bulk-edge correspondence
Heitor da Silva, Sergey K. Ivanov, Isaac Suárez et al. (+2 more)
In topological photonics, the bulk-edge correspondence is conventionally imported by direct analogy with electronic systems, overlooking the fundamentally distinct spacetime
symmetries of Maxwell's and Schrödinger's equations. In this work, we challenge this prevailing paradigm by demonstrating that non-trivial bulk
topology alone is insufficient to guarantee localized edge states in photonic platforms. Using a Su-Schrieffer-Heeger-inspired photonic
crystal, we unveil a generalized bulk-edge correspondence intrinsically shaped by the relativistic nature of electromagnetic waves. This constraint imposes a strict frequency cutoff, a feature fundamentally absent in electronic topological
insulators, which enables a new regime of frequency-controlled spatial localization near the cutoff. Furthermore, we demonstrate that this generalized correspondence is polarization-dependent: transverse electric (TE) and transverse
magnetic (TM) edge modes exist in different parameter regimes and exhibit distinct dispersion relations, including distinct zero-dispersion points. Our framework redefines the theoretical boundaries of topological photonics, unlocking new opportunities for polarization-selective dispersion engineering and robust pulse propagation in topological photonic platforms.
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All authors Heitor da Silva, Sergey K. Ivanov, Isaac Suárez, José R. Salgueiro, Albert Ferrando
Applied Physics · Cross-listed from cond-mat.mes-hall
Substrate-Mediated Persistent Photodoping in WSe2/hBN Field-Effect Transistors Enabled by Defect States in SiO2
Sung-Ha Kim, Seong-Yeon Lee, Tae-Jeong Kim et al. (+6 more)
Photodoping plays an important role in determining the optoelectronic response of two-dimensional
semiconductor devices; however, the origin of the responsible trap states remains unclear. In this work, we investigate UV-induced photodoping in multilayer WSe2 field-effect transistors (FETs) based on WSe2/hBN
heterostructures on SiO2/p-Si substrates. Wavelength-dependent measurements reveal pronounced n-type photodoping under 405 nm illumination, whereas the effect is orders of magnitude weaker under 640 nm excitation and for p-type photodoping. Furthermore, when the SiO2 layer is removed, both n-type and p-type photodoping are strongly suppressed, demonstrating that the
oxide layer is essential for persistent photodoping. Analysis of defect-state distributions in amorphous SiO2, together with first-principles calculations for hBN defects, shows that the experimental observations cannot be explained by defects in hBN. Instead, the results indicate that defect states in the SiO2 substrate act as charge reservoirs that facilitate charge transfer and long-term carrier trapping. These findings highlight the dominant role of substrate-related trap states in UV-induced photodoping and photogating behavior in WSe2 FET devices.
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All authors Sung-Ha Kim, Seong-Yeon Lee, Tae-Jeong Kim, Beomkyu Shin, Young-Jun Yu, Kenji Watanabe, Takashi Taniguchi, Soungmin Bae, Ki-Ju Yee
Optics
Free-space multipass optical parametric amplifier
Milan Fayat, Giovanni Cichelli, Michele Natile et al. (+5 more)
Scaling the efficiency of optical parametric amplifiers (OPAs) without degrading spatio-temporal pulse quality is fundamentally limited by spatio-temporal walk-off, intensity dependent gain, and back-conversion. Here, we numerically and experimentally demonstrate an OPA architecture based on a free-propagating quasi-periodic geometry that overcomes these bottlenecks. Operating within a single nonlinear
crystal, the system utilizes pass-by-pass dichroic idler rejection to suppress back-conversion, a birefringent
crystal for temporal resynchronization, and free-space diffraction to improve the spatial overlap along propagation. Starting from 1.9 {\mu}J 330 fs pulses at 515 nm and a continuous-wave seed at 783 nm, the generation of 0.8 {\mu}J 160 fs signal pulses at the same wave-length is obtained at a repetition rate of 500 kHz. This simple architecture achieves a 64%
quantum efficiency, a 42% pump-to-signal conversion efficiency, and 80 dB of gain while maintaining excellent spatial and temporal quality, providing a scalable platform for ultrafast sources with arbitrary emission wavelengths
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All authors Milan Fayat, Giovanni Cichelli, Michele Natile, Yoann Zaouter, Marie Ouillé, Patrick Georges, Marc Hanna, Xavier Délen
Applied Physics
Complex Refractive Index Determination via Microspectroscopy Through Magnifying Optics: Challenges and Opportunities
Julian Schwarz, Johannes Bauer, Mathias Rommel et al. (+1 more)
For the design and optimization of optoelectronic devices, accurate knowledge of the complex refractive indices of the constituent materials is essential. Herein, we present a fast and non-destructive approach for the extraction of the refractive indices from reflectance and transmittance spectra of samples with lateral dimensions down to the micrometer scale. Microspectroscopy, based on the combination of a standard optical microscope and a spectrometer, enables the assessment of the optical response of multilayer stacks using high-magnification optics with correspondingly large numerical apertures. Employing a numerical formalism explicitly accounting for the influence of the numerical aperture, allows for precise
retrieval of the refractive index without resorting to dispersion models. We demonstrate the applicability of the proposed method for large-area, homogeneous, optically incoherent samples such as transparent glasses and absorbing 4H-SiC, for a SixNy thin film on glass substrate, and for mechanically exfoliated flakes of highly oriented pyrolytic graphite and MoO3, as representatives of uniaxial and biaxial optical anisotropy. While the results prove excellent agreement with values reported in literature, the case of graphite highlights the limitation for probing the out-of-plane refractive indices due to reduced sensitivity. Finally, we discuss possible extensions towards retrieving the full anisotropic tensor of the refractive index, establishing the proposed approach as a methodologically sound alternative to spectroscopic ellipsometry.
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All authors Julian Schwarz, Johannes Bauer, Mathias Rommel, Andreas Hutzler
Optics
Robust optical design and closed-form tolerancing through autodiff-based Hessian spectral analysis
Bastien Laville and Benjamin Aymard
Robust optical design demands quantitative knowledge of how manufacturing and
alignment tolerances degrade system performance. We show that analysing the perturbation eigenmodes of the Hessian
matrix gives qualitative insight about the mechanisms of performance degradation (such as couplings) that is invisible to classical sensitivity-
matrix analysis based on the Jacobian alone. Via the envelope
theorem, we prove that the first-order sensitivity of the fully compensated system is identical to that of the uncompensated one; refocusing only acts at second order through the Schur complement of the Hessian. We propose the trace of the tolerance-scaled Hessian %,$\Tr(\mathbf{S}\mathbf{H}\mathbf{S})$, as a single scalar robustness metric. Demonstrated on an off-axis three-mirror anastigmat and scaled to a twenty-three-parameter surface-figure model, eigenmode decomposition reveals the dominant sensitivity directions and yields deterministic tolerance budgets that replace costly Monte Carlo sampling.
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Instrumentation and Detectors
Miniaturized Photoacoustic Spectroscopy Gas Probe for In-Situ Detection in Oil
Yi Zhong, Yuxiang Zhao and Ping Lu
This paper designs and develops a miniaturized photoacoustic spectroscopy gas probe with acoustic pressure enhancement for in-situ detection in oil-immersed power equipment. The probe adopts a single-cavity single-fiber structure, integrating the photoacoustic
cell and the Fabry-Pérot optical sensing cavity within a ceramic ferrule with an outer diameter of only 800 um. Through the electro-mechanical-acoustic equivalent model analysis of the semi-open photoacoustic
cell, the enhancement mechanism is revealed that reducing the radius of the photoacoustic
cell can form a flat region in the acoustic pressure response. The CrAgAu composite metal diaphragm is fabricated by electron-beam evaporation, and the gas vents are precisely machined by focused-ion-beam etching, successfully realizing the preparation of the sensor prototype. Experimental results demonstrate that the sensor exhibits a flat acoustic response in the frequency range of 2800-10000 Hz with a sensitivity of -15 dB re 1 mV/Pa. Using acetylene as the target gas, the detection limit reaches 71.4 ppb (with an integration time of 130 s) at the optimal operating frequency of 3275 Hz, and the linearity exceeds 0.998. In-oil tests verify its stable detection capability in oil-phase environments, providing a miniaturized, high-sensitivity all-optical technical solution for in-situ monitoring of dissolved gases in
transformer oil.
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Optics · Cross-listed from quant-ph
Single-acquisition tomography of photonic qubits with structured media
Francesco Di Colandrea, Yingwen Zhang, John Grace et al. (+3 more)
Quantum state
tomography is an essential tool for characterizing
quantum systems and underpins nearly every experimental realization of
quantum technologies. Conventional
tomography relies on performing a sequence of projective measurements on many identical copies of a
quantum state, requiring the measurement apparatus to be reconfigured between successive acquisitions. As the
Hilbert-space dimension increases, the number of required measurements grows rapidly; in practice, additional overcomplete measurements are often performed to improve robustness to experimental imperfections. Here, we introduce a
tomography platform based on structured anisotropic media that performs informationally complete measurements of photonic polarization
qubits within a single acquisition. The approach employs three
liquid-
crystal metasurfaces with spatially varying optic-axis orientations that transform the input polarization into a far-field distribution of discrete transverse-momentum modes. Each diffraction pattern uniquely determines the polarization state, enabling its reconstruction without sequential changes to the measurement apparatus. Unlike previous implementations, our scheme is intrinsically
photon-number independent: the same optical device operates identically for arbitrary
photon numbers, while the desired
photon-number sector can be selected afterwards through post-selection of the corresponding $n$-fold coincidence events. We experimentally demonstrate single-frame
quantum state
tomography of both single- and two-
photon polarization states, providing a simple and scalable route toward efficient
quantum-state characterization.
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All authors Francesco Di Colandrea, Yingwen Zhang, John Grace, Dilip Paneru, Alessio D'Errico, Ebrahim Karimi
Optics
Programmable Hybrid Exceptional Points in Passive Scattering Networks
Kaiyuan Wang, Niall Byrnes and Matthew R. Foreman
Exceptional points (EPs) have long promised enhanced sensing of physical signals, but have practically been limited by simultaneous enhancement of noise. Aligning an EP's non-analytic response with target perturbations while suppressing noise has, however, remained challenging. Here we show that fully passive, phase-tuned multi-port scattering networks enable scattering EPs with tailored anisotropic response to perturbations. We leverage projection-induced non-unitarity to realize effective non-Hermitian behavior when measuring only a subset of system ports. By formulating EP design in terms of the discriminant of the projected scattering sub-block and its directional derivatives, we give control-counting rules relating the number of programmable link phases to achievable Riemann surface
topologies. We demonstrate our framework in a four-port photonic network by designing both an anisotropic EP and a Dirac-type EP with linear splitting along two parametric directions. We further suppress the global thermal drift response of a network-based sensor to a 3/2 power-law scaling while retaining square-root sensitivity to localized signals. Since the effective non-Hermiticity arises purely from port projection, our approach transfers to integrated photonic and microwave meshes, acoustic
circuits, and projected metasurfaces, offering a phase-only route to reconfigurable non-Hermitian response and noise-robust EP sensing.
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Fluid Dynamics
Contrary to Newtonian trends: Early flow transition and drag enhancement at low to intermediate Reynolds number flows of structured fluids
Kartik, Anant Chauhan and Chandi Sasmal
The flow of structured fluids, such as polymeric and micellar solutions, involves a strong two-way coupling between flow kinematics and internal microstructural dynamics, including
polymer stretching, micellar scission, and reformation. These interactions yield complex nonlinear rheological responses, including viscoelasticity, shear-thinning, and thixotropy. In this study, we perform high-fidelity numerical simulations of micellar solution flow past a circular cylinder using the Modified Bautista-Manero (MBM) model, which couples a viscoelastic constitutive equation with a kinetic equation for fluidity to capture reversible micellar breakage and reformation. Model parameters are derived from quantitative fitting of experimental data for the EHAC-NaSal system. Our results reveal substantially richer flow dynamics than in Newtonian fluids under the same conditions. Transitions to unsteady flow occur at significantly lower Reynolds numbers, indicating greater instability driven by microstructural effects. At intermediate Reynolds numbers, micellar flows exhibit quasi-periodic behaviour, contrasting with classical periodic
vortex shedding in Newtonian cases. Unlike the monotonic drag reduction in Newtonian fluids, micellar solutions show an anomalous drag increase. Wake characteristics reverse with regime: larger recirculation zones at low Reynolds numbers but more compact wakes in unsteady flows. Lift coefficients and Strouhal numbers are consistently increased. Vorticity fields display pronounced spatial localisation within thin near-wake shear layers. A dynamic mode decomposition analysis reveals coexisting unstable time-decaying and self-sustained modes in micellar flows, whereas only self-sustained modes appear in Newtonian cases.
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