Optics · Cross-listed from nlin.CD
Disentangling Memory and Nonlinearity in Time-Multiplexed Optical Reservoir Computing
Elias R. Koch, Julien Javaloyes, Svetlana V. Gurevich et al. (+1 more)
We analyze and disentangle the individual and combined roles of nonlinearity, transient dynamics, and delayed feedback, and investigate how these mechanisms contribute to different task requirements in photonic reservoir computing. This is achieved using a passive linear photonic reservoir in which a photodiode at the optical-to-electrical interface provides the sole source of nonlinearity. We demonstrate how the requirements of different tasks can be quantified and compared to the dynamics provided by the reservoir by explicitly calculating and comparing the contributing monomials. Our findings include that a reservoir with uncoupled virtual nodes and a quadratic nonlinearity can already achieve good performance for tasks derived from dynamical systems with quadratic nonlinearities, such as the Lorenz63 system. Furthermore, transient coupling and delayed feedback significantly enhance the computational capabilities by compensating for missing higher-order monomials through an effective multi-step integration scheme, given the minimum nonlinearity required for the task is present in the reservoir.
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All authors Elias R. Koch, Julien Javaloyes, Svetlana V. Gurevich, Lina Jaurigue
Optics
Anisotropy in Fourier space optical memory effect correlations
Niall Byrnes and Matthew R. Foreman
We investigate anisotropy in
Fourier-domain speckle correlations associated with the optical
memory effect in disordered scattering media. Within a single scattering framework, we show that while the conventional
memory effect constrains transverse wavevector shifts, the correlation strength also depends non-trivially on differences in the axial wavevector components. Our theory is supported by numerical simulations of a three-dimensional, single scattering medium, which show excellent agreement with theory. We extend the analysis to pseudo-correlations, demonstrating that analogous anisotropic behavior arises in the conjugate
memory effect. Our results highlight the often neglected role of axial disorder in scattered field correlations.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
Energy dissipation at the atomic scale explains how fracture energy depends on crack velocity in silica glass
Marthe Grønlie Guren, Sigbjørn Løland Bore, François Renard et al. (+1 more)
The fracture energy of brittle materials rises with crack velocity, and this effect is typically attributed to surface roughening from path instabilities. Here we show, using molecular dynamics simulations of silica glass with a first-principles machine learned interatomic potential, that the structural fracture energy rises by up to 33 % already below the branching threshold, showing that fracture energy is not a constant material property. This rise in fracture energy is roughly equally partitioned between an increase in the intrinsic surface energy density and nanoscale roughening that increases the real fracture surface area. Results demonstrate that dynamic fracture in silica glass increases the fracture energy not merely by creating more apparent surface, but also by creating a fundamentally different surface at the nanoscale.
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All authors Marthe Grønlie Guren, Sigbjørn Løland Bore, François Renard, Henrik Andersen Sveinsson
Geophysics
Estimating noise for airborne electromagnetic data from repeat flight lines or inversion residuals
Tim Scarr, Anandaroop Ray and Ross C. Brodie
Characterising the noise of an airborne electromagnetic (AEM) system is critical in correctly imaging the earth's subsurface conductivity. Deterministic and probabilistic geophysical inversion
algorithms require foreknowledge of the system noise to specify stopping criteria or a valid model likelihood. Repeat flight lines provide a way for geophysicists to calculate the statistical variability in AEM data acquired over the same ground, and therefore estimate the levels of noise to propagate into the inversion. The total noise can be separated into multiplicative and additive components. The multiplicative noise is derived by repeat lines at survey altitude. The method to calculate the multiplicative noise is scarcely documented and usual methods for height correcting acquired data require a linear trend removal. This study will outline the
algorithm used to estimate multiplicative noise of an AEM system, and non-linearly correct for varying altitudes during repeat flights. Additionally, this paper details a methodology to Gaussianise the data noise and provide a statistically valid Gaussian data misfit or likelihood function. Significantly, we provide methods for estimating the off-diagonal elements in the data covariance
matrix used within the misfit function, taking into account the time-channel data correlation that is usually neglected. While our methodology is general, our study of a rotary-wing system leads us to conclude that for regularised time-domain AEM imaging, a diagonal data covariance suffices – an important implication for rigorous yet practical AEM inversion.
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Applied Physics
Analysis and Design of Double-Transmitting Coil Systems based on Parity-Time Symmetry
Xiaokui Kang, Hongbin Ma, Zihui Liu et al. (+4 more)
The wireless power transfer (WPT) system based on parity-time (PT)
symmetry has the advantages of robustness, stability, and efficient power transmission. However, traditional PT
symmetry structures have limited voltage power output and are susceptible to horizontal misalignment effects. Multiple transmission coils have been proven to improve the power and misalignment tolerance of WPT systems, but variations in inter-coil coupling significantly affect transmission power. Towards this end, this article proposes a double-transmitting coil WPT system based on PT
symmetry, which is innovative in that a novel negative resistance structure based on operational amplifier (OA) is proposed, and the parallel structure of double-transmitting coil is applied to this negative resistance structure. Compared with the traditional WPT system based on a single-transmitting coil PT, this system improves the power and misalignment tolerance in the PT
symmetry region. The large-sized and small-sized receiving coils increase the load power to 313% and 185% respectively. Moreover, in the
symmetry region, the displacement of the receiving coil in the horizontal and vertical directions results in variations of the equivalent coupling coefficient, which can achieve stable power transmission in three dimensions. The voltage fluctuation rate of both receiving coils does not exceed 3.4%, greatly improving the degree of freedom of the receiving system.
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All authors Xiaokui Kang, Hongbin Ma, Zihui Liu, Yuanyuan Wang, Jiangtao Huangfu, Rui Xi, Ying Li
Instrumentation and Detectors
Demonstration of a compact optical resonator-based displacement sensing technique with sub-femtometer precision
Shreevathsa Chalathadka Subrahmanya, Jonathan Joseph Carter and Oliver Gerberding
We demonstrate sub-femtometer displacement-sensing results achieved with a compact optical resonator-based
laser interferometry technique called heterodyne cavity-tracking, intended for local displacement or inertial sensing with ultra-high sensitivity. Displacement sensing at this sensitivity is required for ambitious improvements to current gravitational-wave detectors and to enable future ground- and space-based observatories. The optical
topology employs a centimeter-scale dynamic cavity incorporating a proof mass, and the relative length fluctuations of this cavity are measured using a heterodyne readout. The fundamental limits of the technique lie significantly below the femtometer level and are ultimately defined by the coating thermal noise of the cavity mirrors. In our experimental demonstration, we achieve a sub-femtometer per Hz$^{1/2}$ displacement sensitivity for
Fourier frequencies above 8 Hz and a sub-picometer per Hz$^{1/2}$ sensitivity above 3 mHz, with the sensitivity at lower frequencies limited by mechanical and temperature-induced noise sources. When the length of the dynamic cavity was intentionally actuated, the technique could track a maximum motion of about 0.6 $\mu$m, thereby achieving a dynamic range of roughly ten orders of magnitude in displacement sensing. We thus demonstrate the key features of this scheme - sub-femtometer performance and a dynamic range spanning ten orders of magnitude - in a laboratory setting, paving the way for development of an integrated system. Such a system is a currently unrealized technology that is necessary for precision physics experiments in the coming decades.
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Plasma Physics
Hybrid simulation of the energy cost of O($^1$D) and O($^3$P) generation in a capacitive Ar/O$_2$ discharge driven by sawtooth-type voltage waveforms
Jun-Xi Guo, Wan Dong and Yuan-Hong Song
Low-pressure
radio-frequency capacitively coupled
plasmas operated in Ar/O$_2$ gas mixtures are widely adopted in critical
semiconductor manufacturing processes. O($^3$P) and O($^1$D) are key highly reactive species for oxidation or as oxygen sources for deposited thin films. Optimizing external parameters to realize efficient generation of these species under limited energy deposition is essential for improving process yield.Based on a one-dimensional (1D) fluid/electron Monte Carlo (EMC) hybrid model, this study investigates the energy cost of O($^1$D) and O($^3$P) generation driven by sawtooth up-type voltage waveforms at a fixed peak-to-peak voltage, focusing on the effects of the harmonic number ($N$) and the O$_2$ ratio. The results show that O($^3$P) generation is consistently more efficient than that of O($^1$D). The generation energy cost decreases with increasing O$_2$ ratio, yet increases as $N$ increases. However, in the specific scenario of 10% O$_2$, an inflection point can be observed at $N = 2$. As $N$ increases from 1 to 2, the discharge mode shifts from the DA mode to the $\alpha$-DA hybrid mode, expanding the effective spatio-temporal range of the ionization rate and enhancing its peak, which increases electron density. Consequently, the generation rates are significantly enhanced, leading to a reduction in the generation energy cost.Moreover, as discussed above, monotonically increasing the harmonic number $N$ does not reduce the generation energy cost of O($^1$D) and O($^3$P) associated with medium-energy (8-20 eV) electrons. Only by selecting the appropriate $N$ to sustain the discharge in the hybrid $\alpha$-DA mode, thereby increasing the electron density and promoting the generation of these species, can the generation energy cost be reduced.
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Fluid Dynamics
Flow instability in Stokes layer of Carreau fluids
Mengqi Zhang, Dongdong Wan and Huanshu Tan
This study investigates the influence of shear-thinning on the instability of a prototype time-periodic flow, the Stokes layer, in Carreau fluids. The time-dependent base flow was solved using a numerical method and a binomial expansion method. The expansion is conducted in terms of the nondimensional characteristic time ($\Lambda$), which quantifies the fluid's response time in viscosity to changes in shear rate. The expansion method shows good agreement with the numerical solution, provided that $\Lambda$ remains small. To understand the effect of shear-thinning on time-periodic flow instability, a Floquet analysis was conducted to examine two key parameters of the Carreau model, i.e., $\Lambda$ and the power-law exponent $n$. Our results show that decreasing $n$, which signifies stronger shear-thinning behavior, has a monotonic stabilizing effect on the flow within the range of investigated $n$. In contrast, increasing $\Lambda$ has a non-monotonic effect on the flow instability, which can be observed in both the weakly and strongly shear-thinning regimes. To clarify the instability mechanism, we perform an energy analysis showing that instability arises when the perturbation field is in phase with the oscillatory base flow, enabling efficient energy extraction from the time-dependent shear. A phase mismatch suppresses this transfer and stabilises the flow. This mechanism parallels the classical energy-production process in steady shear flows, where streamwise and wall-normal velocity perturbations exhibit a characteristic phase difference. Crucially, it is identified here for the first time in a time-periodic shear flow.
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Applied Physics
Critical study of A. Eswari and S. Sarvana kumar, "Chronoamperometric response of electrochemical reaction diffusion system: a new theoretical and numerical investigation for EC2 scheme", in J. Iran. Chem. Soc. 21(8), (2024), 2183-2199
Dieter Britz and Jörg Strutwolf
The title paper is discussed critically. There are major problems with incorrect statements, irrelevant citations, incorrect mathematics leading to incorrect results, which are compared with our own simulations.
Atomic and Molecular Clusters
Reflections on future problems in cluster science
K.Hansen, V.V.Kresin, R.Alhyder et al. (+22 more)
This article is a collection of contributions from speakers at the 2025 DEAMN [Dynamics of Electrons in Atomic and Molecular Nanoclusters] workshop at the Majorana Centre in Erice. Not ordinary contributions to a conference proceeding, this gives a new and different perspective on the work done by the workshop participants.
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All authors K.Hansen, V.V.Kresin, R.Alhyder, M.Lemeshko, M.Fárník, J.Fedor, P.Ferrari, L.X.Worutowicz, R.J.Louwerse, D.Kiawi, L.B.F.M.Waters, S.M.Lang, J.M.Bakker, B. v.Issendorff, W.Kong, J.Mehmel, R.Schäfer, S.Pedalino, B.E.Ramírez-Galindo, R.Ferstl, S.Sindelar, S.Gerlich, M.Arndt, S.G.Sayres, L.-S.Wang
Atmospheric and Oceanic Physics · Cross-listed from cs.LG
PODiff: Latent Diffusion in Proper Orthogonal Decomposition Space for Scientific Super-Resolution
Onkar Jadhav, Tim French, Matthew Rayson et al. (+1 more)
Probabilistic super-resolution of high-dimensional spatial fields using
diffusion models is often computationally prohibitive due to the cost of operating directly in pixel space. We propose PODiff, a structured conditional generative framework that performs
diffusion in a fixed, variance-ordered Proper Orthogonal Decomposition (POD) coefficient space, exploiting the orthogonality of POD modes to impose an interpretable, variance-ordered latent geometry. This design enables efficient ensemble generation, preserves dominant spatial structure, and yields spatially interpretable, well-calibrated uncertainty at substantially lower computational cost. We evaluate PODiff on sea surface temperature downscaling over the West Australian coast and on a controlled advection-
diffusion benchmark. PODiff achieves reconstruction accuracy comparable to pixel-space
diffusion while requiring significantly less
memory and producing more reliable uncertainty estimates than deterministic and Monte Carlo Dropout baselines.
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All authors Onkar Jadhav, Tim French, Matthew Rayson, Nicole L. Jones
Biological Physics
Predicting and controlling nonlinear neuro-mechanical locomotion dynamics
Alexander E. Cohen and Jörn Dunkel
Neuromechanics aims to understand the link between an animal's neural activity and its physical behaviors. Recent advances in experimental and machine learning techniques enable simultaneous recordings of neural and locomotion dynamics over long time periods and across multiple behavioral transitions in worms, flies, and other organisms. These high-dimensional
datasets present the challenge of inferring interpretable low-dimensional dynamical models that quantitatively connect neural activity and behavioral dynamics. However, despite major experimental and theoretical progress, there is currently no end-to-end model for predicting locomotion and other behaviors from neural activity. Here, we present a theoretical and computational framework for inferring multiscale neuromechanical models from state-of-the-art experimental data. Our data-efficient approach combines interpretable spectral mode representations with Helmholtz-Nambu decompositions and
Bayesian inference to identify a predictive
stochastic model that converts neural activity time series into behavioral locomotion patterns. We first apply this framework to recently published recordings of neural activity and locomotion in the roundworm Caenorhabditis elegans, showing that it accurately describes experimentally observed dynamics. We further demonstrate how the inferred model can be used to predict neural activation patterns for controlling C. elegans locomotion in real time, providing a basis for future optogenetic experiments. Due to its generic formulation, the framework introduced here is broadly applicable to neuromechanical recordings for a wide range of animal species.
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Applied Physics
WGAN based Inverse Design of Active Dual Band FSS with Switchable Transmission
Rui Xi, Xinke Kuang, Huanran Qiu et al. (+5 more)
This letter presents a novel design method for switchable dual band transmissive frequency selective surface (FSS). The proposed FSS possesses characteristics of maintaining passband characteristics at high frequencies, while switching from transmission to reflection at low frequencies with pin diodes states altering. Specifically, we propose a
crystal growth-based
topology generation strategy, and utilize a simplified U-Net Wasserstein GAN (WGAN) neural network model to establish an inverse mapping model from electromagnetic response to structure
topology parameters. The trained WGAN achieves training and validation accuracies of 95.59% and 90.84%, while the simplified U-Net attains training and validation accuracies of 98.5% and 94.1%. Using the trained WGAN. The generated structural
topologies were validated through full-wave simulations and experimental measurements. The proposed method enhances the design flexibility and overcomes the time- consuming drawbacks of conventional FSS design.
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All authors Rui Xi, Xinke Kuang, Huanran Qiu, Shiyun Ma, Xiaokui Kang, Yuanyuan Wang, Ying Li, Long Li
Plasma Physics · Cross-listed from astro-ph.SR
COCONUT: Toward practical time-evolving Sun-to-Earth magnetohydrodynamic modeling
Haopeng Wang, Stefaan Poedts, Andrea Lani et al. (+16 more)
Due to computational efficiency and numerical stability limitations, coronal simulations constrained by static magnetograms are typically performed first and then used to drive inner-heliosphere (IH) models. In this paper, we calculate the Sun-to-Earth coronal and wind evolutions using a single time-evolving MHD model, showing that implicit MHD models have the potential to meaningfully simplify and improve the overall Sun-to-Earth modelling pipeline. We extend the implicit time-evolving coronal MHD model COCONUT out to 1 AU, and utilise it to investigate
solar coronal and wind evolutions around a
solar maximum Carrington rotation (CR). We compare quasi-steady-state and time-evolving Sun-to-Earth simulations to evaluate the impact of the inner-boundary
magnetic field
evolution, which is neglected in steady-state simulations, on background
plasma parameters. Comparisons with commonly used coupled Sun-to-Earth simulations are also conducted to further validate and assess the Sun-to-Earth model COCONUT. The results show that the time-evolving implicit MHD modelling approach yields noticeable differences compared to oversimplified steady-state simulations, and is efficient enough for practical applications. Modelling the
solar corona and wind using a single MHD model simplifies the modelling pipeline and avoids uncertainties associated with coupling different coronal and IH models. The noticeable differences in the temporal
evolution of
plasma parameters at the L1 and L5 points highlight the need to use continuously evolving, synchronised
magnetic field observations to improve global coronal and
solar wind simulations, whereas the overall consistent evolutionary trend reveals the reliability of using L5 observations to forecast
solar wind conditions near Earth about four days in advance.
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All authors Haopeng Wang, Stefaan Poedts, Andrea Lani, Rayan Dhib, Luis Linan, Tinatin Baratashvili, Fan Zhang, Quentin Noraz, Hyun-Jin Jeong, Nicolas Wijsen, Martina Condoluci, Lingyu Dong, Junyan Liu, Rui Zhuo, Mahdi Najafi-Ziyazi, Ketevan Arabuli, Myrthe Flossie, Jasmina M. Magdalenić Zhukov, Brigitte Schmieder
Optics
Quantitative cavity-enhanced photothermal dynamics in TMDC-integrated ultrahigh-Q microcavities
Hidetoshi Kanzawa, Ryo Sugano, Hajime Kumazaki et al. (+4 more)
We investigate photothermal effects in monolayer transition metal dichalcogenides (TMDCs) integrated with an ultrahigh-Q silica microcavity. Launching a continuous-wave
laser into a cavity resonance enables controlled intracavity heating, allowing direct observation of excitonic photoluminescence (PL) modulation. A distinct
redshift of the PL peak energy is observed as the pump wavelength is tuned across resonance. This behavior is quantitatively reproduced by a temperature-dependent bandgap model that combines the Varshni relation with the thermo-optic response of the microcavity, from which the local temperature rise can be estimated. We further find that PL collected through a fiber waveguide exhibits spectral and temporal characteristics markedly different from free-space emission, indicating selective coupling of the microcavity to specific excitonic channels. These results provide a quantitative framework for understanding photothermal effects in TMDC-microcavity hybrid systems and offer a versatile approach for all-optical control and probing of thermal states in integrated nanophotonic devices.
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All authors Hidetoshi Kanzawa, Ryo Sugano, Hajime Kumazaki, Yuta Takahashi, Mayori Terada, Shinichi Watanabe, Shun Fujii
Optics
Microscopic theory of a radiation-balanced solar laser
Ahmed Jaber, Michael Küblböck, Jean-Michel Ménard et al. (+2 more)
We develop a microscopic open-
quantum-system theory for a radiation-balanced
solar laser (RBSL) based on ytterbium-doped yttrium aluminum garnet (Yb:YAG), in which optical gain, thermal redistribution among sublevels of the electronic ground and excited
manifolds, and
lattice-temperature dynamics are treated within a unified framework. Starting from a Lindblad master equation for a multilevel gain medium coupled to a cavity mode, we include incoherent
solar pumping, spontaneous emission, cavity loss, and
phonon-assisted intra-
manifold relaxation obeying detailed balance. In the regime of fast thermalization within each electronic
manifold, a compact temperature-dependent two-level model is derived, in which the gain, inversion, and lasing threshold are controlled by Boltzmann occupation factors and partition functions of the electronic sublevels. This microscopic reduction is then coupled self-consistently to a thermal balance equation accounting for anti-Stokes fluorescence cooling,
quantum-defect heating, parasitic absorption, and heat exchange with the environment. The theory predicts several operating regimes, including pure cooling, lasing with net cooling, and lasing with net heating, as well as dynamical effects such as delayed lasing onset induced by self-cooling into threshold. In contrast to earlier radiation-balanced
laser (RBL) models based mainly on macroscopic rate equations and thermodynamic balance arguments, the present approach provides a microscopic description of the feedback between
quantum optical dynamics and temperature redistribution. It therefore offers a physically transparent framework for analyzing RBSLs and for identifying design strategies that exploit level structure, thermalization, and photonic-environment engineering to stabilize
laser operation while minimizing internal heat load.
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All authors Ahmed Jaber, Michael Küblböck, Jean-Michel Ménard, Hanieh Fattahi, Claudiu Genes
Physics Education
A smartphone-based simple method for determination of the free space permeability
Sanjoy Kumar Pal, Soumen Sarkar and Pradipta Panchadhyayee
A simple and novel method is designed to determine the free space permeability. This value is computed from the expression of the terminal velocity of a magnet falling through a conducting pipe using the
magnetic sensor of a smartphone and a
video player. This method deserves its importance because of the accuracy and precision of the results.
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Physics Education
Determination of the acceleration due to gravity by studying magnet s motion through a conducting pipe
Sanjoy Kumar Pal, Soumen Sarkar and Pradipta Panchadhyayee
We determine the acceleration due to
gravity (g) in a novel way using a
magnetic sensor and
video analysis technique of a smartphone. The same applications are used to measure the terminal velocity of a magnet falling through a conducting pipe and the
magnetic moment of the magnet from its torsional oscillations. This experiment would appear to be intriguing, as it combines elements of magnetism, terminal velocity, and electromagnetic damping to determine g.
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Physics Education
Study of the effect of electromagnetic damping force on a magnet oscillating near a non-ferromagnetic conducting plate
Sanjoy Kumar Pal, Soumen Sarkar, Pradipta Panchadhyayee et al. (+1 more)
We have designed an experiment that involves studying the effects of a conducting plate on the motion of an oscillating disc magnet. We have employed the
video analysis method by Tracker software to investigate the variation of electromagnetic damping coefficient with distance between the plate and the magnet. This experiment can indeed serve as a valuable educational tool for undergraduate students, covering topics such as damped oscillation, electromagnetic damping, Lenz's law, and eddy currents.
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All authors Sanjoy Kumar Pal, Soumen Sarkar, Pradipta Panchadhyayee, Debapriyo Syam
Applied Physics
Ultrafast acoustic modulation of second-harmonic generation in monolayer transition metal dichalcogenides
Takumi Yamamoto, Hidetoshi Kanzawa, Yuta Takahashi et al. (+4 more)
High-speed modulation and deterministic control of optical nonlinear processes in nanomaterials are essential for realizing future nanoscale optoelectronic devices. Applying strain is a ubiquitous and versatile approach to deform atomically thin materials, allowing direct modification of their electronic and optical properties. Yet, strain engineering of nonlinear processes has so far relied predominantly on static approaches, which inherently limit modulation speed, reproducibility, and device scalability. Here, we demonstrate ultrafast acoustic modulation of second-harmonic (SH) generation in monolayer transition metal dichalcogenides using surface acoustic waves (SAWs). By employing a fully phase-synchronized SH measurement combined with stroboscopic surface displacement detection, we directly visualize dynamic SH modulation at a frequency of 226 MHz. Moreover, theoretical modeling and determination of photoelastic coefficients enable quantitative extraction of the SAW-induced dynamic strain. Our results establish a direct link between acoustic fields and optical nonlinearities, providing a robust platform for dynamic strain engineering in two-dimensional nanophotonic devices.
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All authors Takumi Yamamoto, Hidetoshi Kanzawa, Yuta Takahashi, Hajime Kumazaki, Jiang Pu, Shinichi Watanabe, Shun Fujii
Plasma Physics
Inertial-Range Energy Transfer Free from Isotropic Assumption in Turbulent Space Plasma
Zhuoran Gao, Yan Yang, Francesco Pecora et al. (+5 more)
The idea of an energy cascade in the inertial range is often invoked in turbulent space
plasmas to estimate the energy dissipation rate. Laws governing the behavior of third-order structure functions in the inertial range, so-called third-order laws, are among the few rigorous theoretical results quantifying cross-scale energy transfer. The widely used third-order-law derived rate assumes isotropy, which fundamentally conflicts with the anisotropic nature of space
plasmas. Elementary questions persist regarding how such anisotropic energy cascades can be quantified using multi-spacecraft constellations. As the heliospheric community increasingly progresses towards multi-spacecraft, multi-scale constellations, such as
Plasma Observatory and HelioSwarm, we revisit these crucial issues pertinent to accurately measuring the inertial-range energy transfer. Here we make a systematic comparison between two methods: direction-averaging (DA) and lag polyhedral derivative ensemble (LPDE) to determine the full three-dimensional (3D) dependence of cross-scale energy transfer. We find that DA exhibits both polar and azimuthal dependence, but is insensitive to spacecraft configuration. By contrast, LPDE is strongly affected by spacecraft separation and tetrahedral shape, while being comparatively insensitive to the sampling trajectory. Our findings have direct implications for current and future multi-spacecraft missions. Both DA and LPDE will provide crucial information on the nature of
turbulence in space and astrophysics.
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All authors Zhuoran Gao, Yan Yang, Francesco Pecora, Bin Jiang, Kristopher G. Klein, Alexandros Chasapis, Julia E. Stawarz, William H. Matthaeus
Chemical Physics
Can phaseless auxiliary-field quantum Monte Carlo with broken symmetry trials describe iron-sulfur clusters?
Eirik F. Kjønstad, Huanchen Zhai, James Shee et al. (+2 more)
Phaseless auxiliary-field
quantum Monte Carlo (AFQMC) has in several cases been found to perform well on strongly correlated systems. Here, we
benchmark the method for three iron-sulfur clusters ([2Fe-2S], [4Fe-4S], and the FeMo cofactor) using a hierarchy of trial states derived from coupled cluster (CC) theory, including up to quadruple excitations, as well as multi-Slater trial states derived from the density
matrix renormalization group. Our results reveal for these systems that, as the
symmetry-broken trial is improved, the phaseless AFQMC energy can become less accurate, and in some cases even less accurate than the underlying trial projected energy, displaying an inverted energy pattern that is only corrected once the trial fidelity is sufficiently high. For [2Fe-2S], we show that this can coincide with a simultaneous improvement in the trial state and the walker ensemble. We further find that this is not solely due to the use of
spin-unrestricted trial states, as the inversion persists in [2Fe-2S] when we explicitly break the
symmetry of the
Hamiltonian by applying a fictitious
spin-Zeeman field. Instead, we find that the energy inversion is related to the choice of measurement trial, where using a high-order CC trial state for measurements may introduce errors that are suppressed when the measurement wave function is restricted to lower excitation subspaces. In particular, measuring the energy with the mean-field reference while guiding the walkers with a CC trial improves the overall accuracy across the iron-sulfur clusters, with a possible exception for [4Fe-4S]. Taken together, our findings suggest that the relatively accurate energies obtained with an HF trial state in these systems arise from favorable error cancellation, warranting significant caution about the reliability of phaseless AFQMC with such trials for strongly correlated transition-metal systems of this kind.
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All authors Eirik F. Kjønstad, Huanchen Zhai, James Shee, Sandeep Sharma, Garnet Kin-Lic Chan
Data Analysis and Statistics · Cross-listed from stat.ML
Partial Effective Information Decomposition for Synergistic Causality
Mingzhe Yang, Shuo Wang and Jiang Zhang
Causality is a central topic in scientific inquiry, yet for complex systems, the identification and analysis of synergistic causation remain a challenging and fundamental problem. In the context of causal relations among multivariate variables, a decomposition framework grounded in interventionist causation is still lacking. To address this gap, this paper proposes Partial Effective Information Decomposition (PEID), a framework that decomposes the influence of multiple source variables on a target variable under maximum-
entropy interventions into unique and synergistic information, thereby providing a unified and computable characterization of synergistic causal relations. Theoretically, in the three-variable case, the proposed framework is compatible with the major axioms of Partial Information Decomposition (PID). Empirically, under maximum-
entropy interventions, correlations among input variables are removed, causing redundancy to vanish and thereby enabling PEID to compute synergistic relations. Furthermore, based on this framework, it is possible to define causal graphs containing hyperedges as well as downward causation, thus offering a unified toolkit for analyzing cross-scale and multivariate causal mechanisms in complex systems. Finally, applying the framework to a machine-learning-based air quality
forecasting task on KnowAir-V2, we demonstrate that PEID can extract interpretable inter-station causal structures from a learned dynamical model. These results suggest that PEID provides a general interventionist information-theoretic tool for analyzing multivariate and synergistic causal mechanisms in complex systems.
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Classical Physics
Revisiting the Stress Field Inside an Elastic Sphere Subjected to a Concentrated Load
Yosuke Mori, Kiwamu Yoshii and Satoshi Takada
We present a complete analytical solution for the stress field inside a homogeneous, inside a homogeneous, linearly elastic solid sphere subjected to a concentrated normal load applied on its surface. Starting from the three-dimensional linearized elastodynamic equations, the displacement and stress fields are derived using scalar and vector potential representations combined with spherical harmonic expansions. All expansion coefficients are determined explicitly by enforcing the traction boundary conditions. The static elastic solution is obtained rigorously as the long-time limit of the dynamical formulation. Closed-form expressions for all components of the stress tensor are provided, enabling direct evaluation of the principal stresses and their differences throughout the interior of the sphere. The analytical solution is further generalized to arbitrary loading positions by means of rotational transformations, allowing systematic treatment of multiple concentrated loads through superposition.
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Optics
Anderson Localization with Single Photons from a Quantum Emitter
Simon J. U. White, Diego N. Bernal-García, Toan Trong Tran et al. (+2 more)
Anderson localization of light is a fundamental emergent phenomenon in disordered systems. In arrays of coupled waveguides, it suppresses transport and causes
photons to remain localized near the excitation site as coupling disorder increases. Here, we experimentally demonstrate Anderson localization using single
photons emitted by a single-
photon emitter in hexagonal boron nitride at room temperature. Despite the limited temporal coherence of the emitter, the
photons undergo pronounced Anderson localization, evidenced by exponentially localized output intensity profiles in disordered waveguide
lattices. Beyond the experimental demonstration, we develop a general theoretical framework for wave propagation in disordered tight-binding systems, showing that the configuration-averaged output intensity converges to a stationary spatial distribution at large propagation distances. In the case of off-diagonal disorder, this stationary profile is characterized by an effective localization length that exhibits a robust inverse-variance scaling with the disorder strength. These results establish defect-based room-temperature emitters as practical platforms for studying Anderson localization in integrated photonics and support their use in applications that exploit controlled disorder, including neuromorphic and
quantum photonic architectures.
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All authors Simon J. U. White, Diego N. Bernal-García, Toan Trong Tran, Igor Aharonovich, Alexander S. Solntsev
Optics
OptiLookUp: An Optical ROM-Based Lookup Table Engine for Photonic Accelerators
Ankur Singh and Akhilesh Jaiswal
Read-only
memory (ROM) provides deterministic access to predefined data mappings. Extending ROM concepts to the optical domain enables high-bandwidth, low-latency, and parallel
memory access, but realizing compact and reconfigurable optical ROM remains challenging due to loss, wavelength control, and integration constraints. This work presents a high-speed, reconfigurable photonic ROM architecture implemented using integrated microring resonators (MRRs). The ROM encodes predefined input-output mappings directly in the spectral response of the photonic devices, enabling deterministic lookup-based operation without dynamic computation during readout. To improve scalability and reduce cumulative insertion loss, the architecture employs compact banked sub-arrays that are selectively addressed through an optical decoding mechanism. Reconfigurability is achieved using transistor-based optical selectors, allowing different ROM banks to be activated without physical light rerouting or interferometric structures. The proposed photonic ROM is designed and evaluated using device-level simulations based on the GlobalFoundries 45SPCLO silicon photonics platform. Simulation results demonstrate reliable operation at data rates up to 12.5 GHz, with stable light-to-current transfer characteristics obtained through integrated photodiode readout. The optical ROM can be used to implement nonlinear activation functions utilised in photonic accelerator architectures, including sigmoid, tanh, ReLU, and exponential mappings.
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Fluid Dynamics
Squid funnels time their elastic recoil to amplify pulsed jets
Daehyun Choi, Paras Singh, Ian Bergerson et al. (+12 more)
Pulsed jets propel squid across nearly four orders of magnitude in body size. Each pulse leaves through the funnel, a soft nozzle, but whether its compliance acts within a pulse is not known. We tracked chromatophores on two squid species and found that the funnel dilates and
recoils, with a repeatable phase lag, while the mantle is still contracting, and that the lag persists after denervation. For inertia-dominated jets, silicone nozzles, 3D fluid-structure simulations and a reduced-order model agree that the impulse reaches about 4$\times$ the rigid value when the nozzle response time is 0.2 to 0.4 of the jet-acceleration time, a range that overlaps the in vivo timing. The wall stores strain energy during acceleration and returns it during expulsion (akin to an elastic capacitor), which we term "superpropulsion". Synthetic nozzles tuned for superpropulsion launch jets farther in air, disperse dye faster, and drive a boat faster at a lower cost of transport.
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All authors Daehyun Choi, Paras Singh, Ian Bergerson, Minho Kim, Jieun Park, Halley J. Wallace, Kenny Zhang, Sandy Y. Hsieh, Aqua T. Asberry, Theodore A. Uyeno, William F. Gilly, Hyungmin Park, Daeshik Kang, Chandan Bose, Saad Bhamla