Optics
Resolution and Robustness Bounds for Reconstructive Spectrometers
Changyan Zhu, Hsuan Lo, Jianbo Yu et al. (+2 more)
Reconstructive spectrometers are a promising emerging class of devices that combine complex light scattering with inference to enable compact, high-resolution spectrometry. Thus far, the physical determinants of these devices' performance remain under-explored. We show that under a broad range of conditions, the noise-induced error for spectral reconstruction is governed by the Fisher information. We then use random
matrix theory to derive a closed-form relation linking the variance bound to a set of key physical parameters: the spectral correlation length, the mean transmittance, and the number of frequency and measurement channels. The analysis reveals certain fundamental trade-offs between these physical parameters, and establishes the conditions for a spectrometer to achieve “super-resolution” below the limit set by the spectral correlation length. Our theory is confirmed using numerical validations with a random
matrix model as well as full-wave simulations. These results establish a physically-grounded framework for designing and analyzing performant and noise-robust reconstructive spectrometers.
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All authors Changyan Zhu, Hsuan Lo, Jianbo Yu, Qijie Wang, Y. D. Chong
Chemical Physics
Topological resolution of conical intersection seams and the coupled cluster bifurcation via mixed Hodge modules
Prasoon Saurabh
The rigorous description of Conical Intersections (CIs) remains the central challenge of non-adiabatic
quantum chemistry. While the “Yarkony Seam” – the $(3N-8)$-dimensional
manifold of degeneracy – is well-understood geometrically, its accurate characterization by high-level electronic structure methods is plagued by numerical instabilities. Specifically, standard Coupled Cluster (CC) theory suffers from root bifurcations near Ground State CIs, rendering the “Gold Standard” of chemistry inapplicable where it is needed most. Here, we present QuMorpheus, an open-source computational package that resolves these singularities by implementing a topological framework based on Dissipative Mixed Hodge Modules (DMHM) [P. Saurabh, arXiv:2512.19487 (2025)]. By algorithmically mapping the CC
polynomial equations to a spectral sheaf, we compute the exact Monodromy ($\mu$) invariants of the intersection. We demonstrate that this automated algebraic geometry approach correctly identifies the physical ground state
topology in the Köhn-Tajti model and resolves the intersection seams of realistic chemical systems, including Ethylene and the Chloronium ion ($\mathrm{H_2Cl^+}$). Furthermore, we apply QuMorpheus to the photoisomerization of Previtamin D, proving that the experimentally observed Woodward-Hoffmann selection rules are a direct consequence of a topological “Monodromy Wall” ($\mu=1, \gamma=\pi$) rather than purely energetic barriers. This establishes a general software solution to the “Yarkony Problem,” enabling the robust, automated mapping of global intersection seams in complex molecular systems. The topological stability of these intersections allows for the control protocols discussed in Ref.[P. Saurabh, Submitted to Phys. Rev. X (2025)].
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Applied Physics
Microstructured Electrode-Piezopolymer Interface for Ultrasound Transducers with Enhanced Flexibility and Acoustic Performance
Spencer Hagen{\S}, Dulcce A Valenzuela{\S}, Parag V Chitnis et al. (+1 more)
Ultrasound transducers made from rigid piezoceramics are difficult to adapt for wearable or conformal applications. Piezopolymer-based transducers offer a practical alternative; however, most existing studies focus on piezoelectric materials, while the influence of electrode material and electrode-
polymer interface remains underexplored. This study leverages different interface-engineering strategies to examine the influence of electrode-piezopolymer interface morphology on piezoelectric, dielectric, and acoustic behavior in flexible transducers. Devices were fabricated using silver (Ag), gold (Au),
graphene flakes (GF),
laser-induced
graphene (LIG), and Au-decorated LIG electrodes, enabling comparison across interfacial architectures. LIG-based transducers showed strong acoustic and piezoelectric output due to partial infiltration of the piezopolymer into the porous LIG network, which enhances interfacial contact and stress transfer. Au-based transducers achieved comparable acoustic output. In contrast, dense Ag electrodes and layered GF films provided limited coupling, resulting in reduced electromechanical response. LIG-based transducers exhibited the highest flexibility and durability, retaining stable performance after 10,000 bending cycles and an eight-week aging study, whereas GF, Ag, and Au devices degraded under bending, and Ag electrodes declined over time. These findings demonstrate that engineering the electrode-
polymer interface is critical for high-performance flexible ultrasound transducers and identify LIG as a strong candidate for wearable imaging applications.
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All authors Spencer Hagen{\S}, Dulcce A Valenzuela{\S}, Parag V Chitnis, Shirin Movaghgharnezhad
Computational Physics · Cross-listed from cs.LG
GeoTransolver: Learning Physics on Irregular Domains Using Multi-scale Geometry Aware Physics Attention Transformer
Corey Adams, Rishikesh Ranade, Ram Cherukuri et al. (+1 more)
We present GeoTransolver, a multiscale geometry-aware physics
attention transformer for Computer Aided Engineering (CAE). GeoTransolver extends the Transolver backbone with GALE (Geometry-Aware Latent
Embeddings)
attention, which pairs physics-aware self-
attention on learned state slices with cross-
attention to a shared geometry and global context computed via multi-scale ball queries (inspired by Domino) and reused in every block. Implemented and released in NVIDIA PhysicsNeMo, GeoTransolver persistently projects geometry and global parameters, into physical state spaces to anchor computations to domain structure and operating regimes. We
benchmark on DrivAerML, SHIFT-SUV, and SHIFT-Wing against Domino, Transolver (PhysicsNeMo implementation), and literature-reported AB-UPT, evaluating drag/lift R2 and relative L1 errors on field variables. As an additional nonlinear structural mechanics application, we also report Transolver and GeoTransolver results on bumper-beam and full-vehicle Body-in-White (BIW) crash-dynamics
benchmarks, evaluating relative L2 trajectory error and probe-level kinematic MSE. GeoTransolver delivers improved accuracy, robustness to geometry and regime shifts, and favorable data efficiency; we include DrivAerML ablations and qualitative contour and design-trend results, advancing operator learning for high-fidelity surrogates on complex, irregular, non-linear domains.
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All authors Corey Adams, Rishikesh Ranade, Ram Cherukuri, Sanjay Choudhry
Atomic Physics · Cross-listed from quant-ph
Storage and retrieval of optical skyrmions with topological characteristics
Jinwen Wang, Xin Yang, Yun Chen et al. (+10 more)
Optical skyrmions are topological structures of light whose defining property, the skyrmion number, is robust against perturbations. This makes them attractive for applications in
quantum information storage, where resilience to decoherence is paramount. However, their preservation during coherent storage remains unexplored. We report the first experimental demonstration of storing and retrieving optical skyrmions in a cold $^{87}$Rb vapor using a dual-path electromagnetically induced transparency
memory. Crucially, we show that the skyrmion number remains invariant for storage times up to several microseconds, even when subjected to imbalanced loss between the two paths and substantial perturbations in control beam power. Our work demonstrates the survival of a non-trivial topological invariant in a
quantum memory, marking a significant step towards topologically protected photonic technologies.
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All authors Jinwen Wang, Xin Yang, Yun Chen, Zhujun Ye, Xinji Zeng, Yongkun Zhou, Shuya Zhang, Claire Marie Cisowski, Chengyuan Wang, Katsuya Inoue, Yijie Shen, Sonja Franke-Arnold, Hong Gao
Chemical Physics
Before We Inject: Assessing the Impact of Silica-Based Aerosols on Stratospheric Chemistry via a Kinetic Model Informed by Molecular Dynamics
Dennis Lima, Saif Al-Kuwari and Ivan Gladich
Stratospheric aerosol injection (SAI) has been proposed as a geoengineering strategy to mitigate global warming by increasing Earth's albedo. Silica-based materials, such as diamond-doped silica aerogels, have shown promising optical properties, but their impact on stratospheric chemistry, ozone one in particular, remains largely unknown. Here, we present first-principles molecular dynamics (MD) simulations of the heterogeneous reaction between hydrogen chloride ($\mathrm{HCl}$) and chlorine nitrate ($\mathrm{ClONO_2}$), two main reservoirs of stratospheric chlorine and nitrogen species, on a dry, hydroxylated $\alpha$-quartz silica interface. Our results reveal a barrierless reaction pathway toward the formation of chlorine gas ($\mathrm{Cl}_2$), a major contributor to stratospheric ozone loss. We design a heterogeneous kinetic model informed by our MD simulation and available experimental data: despite the barrierless formation of $\mathrm{Cl_2}$, the higher surface affinities and partial pressures of $\mathrm{HNO_3}$ and $\mathrm{HCl}$ compared to those of $\mathrm{ClONO_2}$ result in a negligible reaction probability, $\gamma_\mathrm{ClONO_2}$, upon chlorine nitrate collision with the silica surface. Since $\gamma_\mathrm{ClONO_2}$ enters as a proportionality constant in the definition of the heterogeneous reaction rate, our kinetic model indicates that the injection of silica-based aerosols may have only a limited impact on stratospheric ozone depletion driven by $\mathrm{HCl}$ and $\mathrm{ClONO_2}$ chemistry. At the same time, our findings also underscore the scarcity of experimental data, the need of better theoretical frameworks for the inclusion of MD results into kinetic models, and the urgency for further experimental validations of silica-based SAI technologies before their deployment in
climate intervention strategies.
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Accelerator Physics
Optimizing the interaction geometry of inverse Compton scattering x-ray sources
C.W. Sweers and O.J. Luiten
Inverse Compton scattering (ICS) is a promising method for generating coherent and tunable x-rays in a compact setup. In this paper, we present a theoretical framework describing the output of an ICS x-ray source for arbitrary interaction angles between pulsed electron and
laser beams, in the Thomson regime. This allows for analytic optimization of the x-ray beam properties by varying the parameters defining the geometry. In general, different x-ray applications require optimization of different x-ray beam properties, such as energy spread for x-ray spectroscopy and angular spread for x-ray scattering measurements. In this paper, we restrict ourselves to optimization of the x-ray brilliance, which is a comprehensive figure of merit for x-ray beam quality. The framework can be used, however, to optimize other x-ray properties. We investigate two specific ICS interaction geometries in particular: head-on scattering of a
laser beam off an electron beam; and scattering of a
laser beam off an electron beam in a co-propagating geometry, interacting under a grazing angle. For head-on scattering we show that a tightly focused, cylindrically symmetric
laser pulse, which balances
laser intensity and interaction time, optimizes the x-ray brilliance. For a co-propagating, grazing angle geometry, an elliptical focus of the
laser pulse is required to mitigate the
geometric reduction of the interaction time. We find that the latter geometry is especially useful for soft x-ray generation.
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Fluid Dynamics
Three-dimensional mesh adaptation in PFEM
Thomas Leyssens, Jonathan Lambrechts and Jean-François Remacle
Chaotic free surface flows are challenging problems to simulate numerically, mainly due to the significant changes in geometry and frequent topological changes. Methods that track the
evolution of the fluid in a Lagrangian formulation are a natural choice. One such method is the Particle Finite Element Method (PFEM). As a hybrid particle-based and mesh-based method, PFEM leverages advantages from both approaches. The equations of motion are solved on a mesh using the finite element method and the obtained velocity field is used to displace the nodes of this mesh, considered as particles carrying all the relevant information across time steps. To avoid element distortion, the mesh is frequently re-generated. This introduces some challenges: How can the new shape of the domain be detected? How can the quality of the elements be kept acceptable? Can adaptive mesh refinement increase the accuracy and efficiency of the solver? Can PFEM simulations be performed in the presence of complex boundary geometries? In this work, three contributions to the geometry and mesh component of PFEM are introduced for three-dimensional free surface flow simulations. First, we propose a different domain reconstruction approach than the classically used alpha-shape procedure, namely through the use of the advected boundary from the previous time step as a predicate to represent the new shape of the domain. Second, an adaptive refinement procedure is proposed in two steps: refinement of the boundary surface followed by quality-based node insertion in the bulk. Third, an approach for managing boundaries in complex geometries is presented. A series of applications is shown to demonstrate the interest of the approach.
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Instrumentation and Detectors · Cross-listed from cs.LG
Inverse Autoregressive Flows for Zero Degree Calorimeter fast simulation
Emilia Majerz, Witold Dzwinel and Jacek Kitowski
Physics-based machine learning blends traditional science with modern data-driven techniques. Rather than relying exclusively on empirical data or predefined equations, this methodology embeds domain knowledge directly into the learning process, resulting in models that are both more accurate and robust. We leverage this paradigm to accelerate simulations of the Zero Degree Calorimeter (ZDC) of the ALICE experiment at CERN. Our method introduces a novel loss function and an output variability-based scaling mechanism, which enhance the model's capability to accurately represent the spatial distribution and morphology of particle showers in detector outputs while mitigating the influence of rare artefacts on the training. Leveraging Normalizing Flows (NFs) in a teacher-student generative framework, we demonstrate that our approach not only outperforms classic data-driven model assimilation but also yields models that are 421 times faster than existing NF implementations in ZDC simulation literature.
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Instrumentation and Detectors
Design and Modeling of a Simple-Structured Continuously Variable Transmission Utilizing Shape Memory Alloy Superelasticity for Twisted String Actuator
Chanchan Xu, Shuai Dong and Xiaojie Wang
Twisted String Actuators (TSAs) are widely used in robotics but suffer from a limited range of Transmission Ratio (TR) variation, restricting their efficiency under varying loads.To overcome this, we propose a novel lightweight, simple-structured Continuously Variable Transmission (CVT) mechanism for TSA utilizing Shape
Memory Alloy (SMA) superelasticity. The CVT mechanism consists solely of a pair of highly lightweight superelastic SMA rods connecting the ends of twisted strings. These rods deform under external loads, adjusting the inter-string distance to enable continuous TR variation.We develop a comprehensive theoretical model that integrates three critical nonlinearities
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Applied Physics · Cross-listed from cond-mat.stat-mech
Optimal navigation in a noisy environment
Abhijit Sinha, Sandeep Jangid, Tridib Sadhu et al. (+1 more)
Navigating toward a known target in a noisy environment is a fundamental problem shared across biological, physical, and engineered systems. Although optimal strategies are often framed in terms of continuous, fine-grained feedback, we show that efficient
navigation emerges from a far simpler principle: natural wandering punctuated by intermittent course corrections. Using a controlled robotic platform, active Brownian particle simulations, and scaling theory, we identify a universal trade-off between noise-induced deviation and the finite cost of reorientation, yielding an optimal course correction frequency governed by only a few system parameters. Despite their differing levels of complexity, our experiment and theory collapse onto common quantitative signatures, including first-passage time distribution and non-Gaussian angular dispersion. Our results establish intermittent course-correction as a minimal and robust alternative to continuous feedback, offering a unifying guiding principle for point-to-point
navigation in complex environments.
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All authors Abhijit Sinha, Sandeep Jangid, Tridib Sadhu, Shankar Ghosh
Chemical Physics
Finite-Temperature Thermally-Assisted-Occupation Density Functional Theory, Ab Initio Molecular Dynamics, and Quantum Mechanics/Molecular Mechanics Methods
Shaozhi Li and Jeng-Da Chai
Recently, thermally-assisted-occupation density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] has been demonstrated to be an efficient and accurate electronic structure method for studying the ground-state properties of large multi-reference (MR) systems at absolute zero. To explore the thermal
equilibrium properties of large MR systems at finite electronic temperatures, in the present work, we propose the finite-temperature (FT) extension of TAO-DFT, denoted as FT-TAO-DFT. Besides, to unlock the dynamical information of large MR systems at finite temperatures, FT-TAO-DFT is combined with ab initio molecular dynamics, leading to FT-TAO-AIMD. In addition, we also develop FT-TAO-DFT-based
quantum mechanics/molecular mechanics (QM/MM), denoted as FT-TAO-QM/MM, to provide a cost-effective description of the thermal
equilibrium properties of a QM subsystem with MR character embedded in an MM environment at finite temperatures. Moreover, the FT-TAO-DFT, FT-TAO-AIMD, and FT-TAO-QM/MM methods are employed to explore the radical nature and infrared (IR) spectra of n-acenes (n = 2–6), consisting of n linearly fused benzene rings, in
vacuum and in an argon (Ar)
matrix at finite temperatures. According to our calculations, for n-acenes at 1000 K or below, the electronic temperature effects on the radical nature and IR spectra are very minor, while the
nuclear temperature effects on these properties are noticeable. For n-acene in an Ar matrx at absolute zero, the Ar
matrix has minimal impact on the radical nature of n-acene, while the co-deposition procedure of n-acene and Ar atoms may affect the IR spectrum of n-acene.
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Biological Physics · Cross-listed from cond-mat.soft
Spatiotemporal Chaos and Defect Proliferation in Polar-Apolar Active Mixture
Partha Sarathi Mondal, Tamas Vicsek and Shradha Mishra
Chaotic transitions in inertial fluids typically proceed through a direct energy cascade from large to small scales. In contrast, active systems, composed of self propelled units, inject energy at microscopic scales and therefore exhibit an inverse cascade, giving rise to distinctly unconventional flow patterns. Here, we investigate an active mixture consisting of both apolar and polar self driven components, a setting expected to display richer behaviours than those found in living
liquid crystal (LLC) systems, where the apolar constituent is passive. Using numerical solutions of the corresponding hydrodynamic equations, we uncover a variety of complex dynamical states. Our results reveal a non-monotonic response of the apolar species to changes in the density and activity of the polar component. In an intermediate regime, reminiscent of LLC-induced disorder, the system develops a dynamically disordered phase characterised by high-density, chaotically evolving band-like structures and by the continual creation and annihilation of half integer topological defects. We show that this regime exhibits spatiotemporal chaos, which we quantify through two complementary measures: the spectral properties of density fluctuations and the maximal Lyapunov exponent. Together, these findings broaden the understanding of complex transitions in active matter and suggest potential experimental realisations in bacterial suspensions or synthetic microswimmer assemblies.
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Fluid Dynamics · Cross-listed from cond-mat.soft
Dynamics of Marangoni-Driven Elliptical Janus Particles
Pabitra Masanta, Ratan Sarkar, Punit Parmananda et al. (+1 more)
We investigate the spontaneous motion of an elliptical Janus particle, driven by Marangoni forces, on a water surface to understand how particle shape and size influence its dynamics. The Janus particle is one-half infused with a substance such as camphor, which lowers the surface tension upon release onto the water surface. The resulting surface tension gradient generates Marangoni forces that propel the particle. For fully camphor-infused (non-Janus) particles, previous studies have shown that motion occurs along the short axis of the ellipse. However, for Janus particles, our experiments reveal a much richer steady-state dynamics, depending on both the particle's eccentricity and size. To understand these dynamics, we develop a numerical model that captures the connection between the spatio-temporal
evolution of the camphor concentration field and the Marangoni force driving the particle. Using this model, we simulate the motion of particles with varying eccentricities - from nearly circular to highly elongated shapes. The simulations qualitatively reproduce all the trajectories observed in experiments and provide insights into how particle geometry influences the dynamics of chemically driven anisotropic particles. With the help of the numerical model, we compute a full phase diagram characterising the dynamical states as a function of surfactant properties.
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All authors Pabitra Masanta, Ratan Sarkar, Punit Parmananda, Raghunath Chelakkot
Optics · Cross-listed from quant-ph
Localization and coherent control of 25 nuclear spins in Silicon Carbide
Pierre Kuna, Erik Hesselmeier-Hüttmann, Phillip Schillinger et al. (+7 more)
Optically addressable
spin defects are excellent candidate platform for
quantum sensing and
quantum network.
Nuclear spins coupled to color centers naturally enable long lived
quantum memories and local
qubits registers. To fully leverage this potential precise characterization of the surrounding
nuclear-
spin environment augmented with refined DFT models is required. In this work, we report angstrom-level 3D localization of 25
nuclear spins around a single V2 center in 4H Silicon Carbide. Utilizing specially placed robust
nuclear memory as a highly efficient readout ancilla for readout, we apply correlation based spectroscopy and by selecting multi-
spin chains up to length four, we access and characterize extended
nuclear spin cluster. Using the coupling map we reconstruct their couplings to the central electron
spin and neighboring
nuclei. This work paves the way towards advanced
quantum register applications on Silicon Carbide platform.
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All authors Pierre Kuna, Erik Hesselmeier-Hüttmann, Phillip Schillinger, Felix Gloistein, István Takács, Viktor Ivády, Wolfgang Knolle, Jawad Ul-Hassan, Jörg Wrachtrup, Vadim Vorobyov
Optics
Non-Hermitian Exceptional Topology on a Klein Bottle Photonic Circuit
Ze-Sheng Xu, J. Lukas K. König, Andrea Cataldo et al. (+8 more)
Non-Hermitian physics has unlocked a wealth of unconventional wave phenomena beyond the reach of Hermitian systems, with exceptional points (EPs) driving enhanced sensitivity, nonreciprocal transport, and topological behavior unique to non-Hermitian degeneracies. Here, we present a scalable and reconfigurable silicon photonic integrated
circuit capable of emulating arbitrary non-Hermitian time
evolution with high precision. Using this programmable platform, we implement a two-band non-Hermitian
Hamiltonian defined on a Klein-bottle
topology a nonorientable parameter space that enables exceptional phases forbidden on orientable
manifolds. Through an on-chip amplitude-and-phase reconstruction protocol, we retrieve the full complex
Hamiltonian at multiple points in parameter space and experimentally map the associated
Fermi arc where the imaginary
eigenvalue gap closes. The orientation of the measured
Fermi arc reveals a nontrivial exceptional
topology: it implies the presence of same-charge EPs (or an EP monopole) that cannot annihilate locally on the Klein bottle. Our results demonstrate the first photonic realization of exceptional
topology on a nonorientable
manifold and establish a versatile platform for exploring exotic non-Hermitian and topological models relevant to classical and
quantum photonics.
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All authors Ze-Sheng Xu, J. Lukas K. König, Andrea Cataldo, Rohan Yadgirkar, Govind Krishna, Venkatesh Deenadayalan, Val Zwiller, Stefan Preble, Emil J. Bergholtz, Jun Gao, Ali W. Elshaari
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Reductive Contact and Dipolar Interface Engineering Enable Stable Flexible CsSnI3 Nanowire Photodetectors
Letian Dai, Wanru Chen, Quanming Geng et al. (+4 more)
Lead-free tin-based halide perovskites are attractive for flexible and environmentally benign optoelectronics, but their application is limited by the rapid oxidation of Sn2+ to Sn4+ and poor operational stability. Here, we report a flexible CsSnI3 nanowire photodetector that achieves both high near-infrared photoresponse and long-term stability through synergistic aluminium-substrate contact engineering and dipolar interface modification. A 0.2 mm anodized aluminium foil serves as the flexible substrate, where localized
laser ablation exposes metallic aluminium regions that act as reductive sites, effectively suppressing Sn2+ oxidation during nanowire growth. Simultaneously, a polar interlayer of 3-fluoro-2-nitroanisole is introduced to improve energy-level
alignment, suppress interfacial deprotonation, and enhance charge extraction. The resulting device exhibits a responsivity of 0.39 A W-1, a specific detectivity of 1.38 * 10^13 Jones, and a wide linear dynamic range of 156 dB under 850 nm illumination. Moreover, the device retains over 85% of its initial photocurrent after 60 days in ambient air and maintains 94% of its initial photocurrent after 1000 bending cycles. This work establishes an effective strategy for stabilizing Sn-based perovskites toward high-performance flexible optoelectronic devices.
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All authors Letian Dai, Wanru Chen, Quanming Geng, Ying Xu, Guowu Zhou, Nuo Chen, Xiongjie Li
Computational Physics · Cross-listed from astro-ph.IM
The AI Scaling Wall of Diminishing Returns: Of LLMs, Electric Dogs, and General Relativity
Hemant Shukla
LLMs are hitting the scaling wall - compute grows 10-100x while accuracy barely moves. This note quantifies the slowdown and argues that the next leap in AI will come not from bigger models, but from smarter, more efficient ones.
Computational Physics
An immersed boundary method for the discrete velocity model of the Boltzmann equation
Longqing Ge, Qingdong Cai, Yonghao Zhang et al. (+1 more)
Computational modeling and simulation of fluid-structure interactions constitute a fundamental cornerstone for advancing aerospace engineering endeavors. This paper addresses the notion and implementation of the immersed boundary method for the discrete velocity model of the Boltzmann equation. The method incorporates the Maxwell gas-surface interaction model into the construction of ghost-
cell particle distribution functions, facilitating meticulous characterization of velocity slip and temperature jump effects within a Cartesian grid framework, which ultimately achieves accurate prediction of aerodynamic parameters. This study presents two principal advancements. First, an upwind-weighted compact interpolation strategy is developed in physical space, which ensures numerical stability and robustness for arbitrary geometries without relying on large stencils or normal-direction projections. Second, a cut-
cell correction methodology is proposed in velocity space to address the degradation of quadrature accuracy caused by surface discontinuities. The resulting framework is equally applicable to both two- and three-dimensional problems without requiring any dimension-specific modifications. Rigorous analysis is provided to prove that the approach maintains second-order accuracy across both physical and velocity space, while ensuring robust numerical stability. Comprehensive numerical experiments demonstrate that the solution
algorithm achieves the designed accuracy and delivers precise predictions comparable to body-conformal solvers, while retaining the simplicity, flexibility, and scalability of the Cartesian grid method. The proposed approach provides a unified and physically consistent immersed boundary framework for simulating dynamic interactions between non-
equilibrium flows and structural components across a wide range of flow regimes.
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All authors Longqing Ge, Qingdong Cai, Yonghao Zhang, Tianbai Xiao
Computational Physics · Cross-listed from quant-ph
Tree tensor network states represent low-energy states faithfully
Thomas Barthel
Extending corresponding results for
matrix product states [Verstraete and Cirac, PRB 73, 094423 (2006); Schuch et al. PRL 100, 030504 (2008)], it is shown how the approximation error of tree tensor network states (TTNS) can be bounded using Schmidt spectra or Rényi
entanglement entropies of the target
quantum state. Conversely, one obtains bounds on TTNS bond dimensions needed to achieve a specific approximation accuracy. The result implies that efficient TTNS approximations exist if $\alpha<1$ Rényi
entanglement entropies for single-branch cuts obey an area law, as in ground and low-energy states of certain gapped systems on tree graphs.
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Optics · Cross-listed from quant-ph
Passive quantum state transfer in a dispersion-engineered waveguide
Zeyu Kuang, Oliver Diekmann, Lorenz Fischer et al. (+2 more)
High-fidelity state transfer is fundamentally limited by time-reversal
symmetry: one
qubit emits a
photon with a certain temporal pulse shape, whereas a second
qubit requires the time-reversed pulse shape to efficiently absorb this
photon. This limit is often overcome by introducing active elements. Here, we propose an alternative solution: by tailoring the dispersion relation of a waveguide, the
photon pulse emitted by one
qubit is passively reshaped into its time-reversed counterpart, thus enabling perfect absorption. We analytically derive the optimal dispersion relations in the limit of small and large
qubit-
qubit separations, and numerically extend our results to arbitrary separations via multiparameter optimization. We further propose a spatially inhomogeneous waveguide that renders the state transfer robust to variations in
qubit separations. In all cases, we obtain near-unity transfer fidelity (>= 98%) that is robust against imperfections in parameter values and propagation loss. Our dispersion-engineered waveguide provides a compact and passive route toward on-chip
quantum networks, highlighting dispersion as a powerful resource in waveguide
quantum electrodynamics.
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All authors Zeyu Kuang, Oliver Diekmann, Lorenz Fischer, Stefan Rotter, Carlos Gonzalez-Ballestero
Optics
Deterministic exciton confinement in 2D semiconductors via local dielectric engineering for scalable quantum light sources
Raziel Itzhak, Alex Hayat and Ilya Goykhman
Single-
photon emitters are essential building blocks for
quantum communication and photonic
quantum technologies. However, realizing scalable, on-chip SPEs on a CMOS-compatible platform remains a significant challenge. Here, we propose and theoretically demonstrate a scalable approach to
exciton confinement in two-dimensional
semiconductors via local dielectric engineering. By introducing a high-dielectric-constant nanopillar above or beneath the 2D material, we create a spatially varying dielectric environment that can support localized
exciton states, enabling deterministic, lithography-compatible single-
photon emission without relying on strain, defects, or etching of the 2D layer. Using numerical solutions to the 2D excitonic Schrodinger equation, we quantify the resulting confinement through binding energies, wavefunction profiles, and a spatial confinement parameter. These results offer a practical and scalable route for integrating 2D-based
quantum emitters into photonic platforms, paving the way for next-generation
quantum optoelectronic devices.
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Computational Physics · Cross-listed from cs.LG
NeuralCrop: Combining physics and machine learning for improved crop modelling
Yunan Lin, Sebastian Bathiany, Maha Badri et al. (+6 more)
Global gridded crop models (GGCMs) are crucial for projecting
climate impacts on agricultural productivity and assessing associated risks to food security. However, state-of-the-art GGCMs are subject to substantial uncertainties arising from reduced representations of complex processes. Projected increases in the frequency and severity of
climate extremes require more reliable agricultural yield simulations. Recent machine learning approaches trained on observational data provide alternatives to GGCMs, but remain under-constrained due to sparse observations and show poor out-of-distribution generalization. Here we introduce NeuralCrop, a differentiable hybrid GGCM that combines the strengths of an advanced process-based GGCM (LPJmL) with data-driven components. NeuralCrop is first trained to reproduce its underlying fully process-based version, before it is fine-tuned on observational flux data of physiological variables. Evaluation against held-out flux-tower observations from European wheat and US maize sites shows 32.6-45.2% reductions in mean normalized root-mean-square error for daily carbon and water fluxes. Although fine-tuned only on physiological variables, NeuralCrop improves temporal correlations with independent yield records across 71.4% of the cultivated area for European wheat and 84.0% for the US Corn Belt during 1981-2019. It performs highly competitively compared to GGCMI Phase~3 models. NeuralCrop reproduces yield anomalies more accurately across a range of soil-moisture conditions and especially for extreme drought conditions. For large-scale, long-term simulations, NeuralCrop runs nearly two orders of magnitude faster than the CPU-based LPJmL baseline model, mainly thanks to GPU acceleration. Our results highlight end-to-end hybrid crop modelling as a promising avenue for improving crop simulations and informing food security assessments under
climate change.
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All authors Yunan Lin, Sebastian Bathiany, Maha Badri, Maximilian Gelbrecht, Philipp Hess, Brian Groenke, Jens Heinke, Christoph Müller, Niklas Boers
Plasma Physics
Thermal wakefield structure in plasma acceleration processes: insights from fluid models and PIC simulations
Daniele Simeoni, Andrea Renato Rossi, Gianmarco Parise et al. (+2 more)
We focus on the process of
plasma acceleration in the presence of non-negligible thermal effects, wherein a driver of relativistic electrons perturbs a warm neutral
plasma and generates a wakefield structure. We study the acceleration process via numerical simulations based on fluid models with different thermal closure assumptions, and also provide systematic comparisons against ground-truth data coming from particle-in-
cell (PIC) simulations. The focus of the analysis is on the first electron depletion bubble after the driver, where we provide a detailed characterization of its size and the electromagnetic fields developed inside. Our results are instrumental in determining the correct thermal closure assumption to be used in fluid models for the numerical simulations of
plasma acceleration processes, as well as elucidating the corresponding limits of applicability.
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All authors Daniele Simeoni, Andrea Renato Rossi, Gianmarco Parise, Fabio Guglietta, Mauro Sbragaglia
Optics
The Zero-Frequency Limit of Spherical Cavity Modes: On the Formal Endpoint at v=1
Mustafa Bakr and Smain Amari
The transverse
magnetic (TM) modes of a spherical cavity satisfy a dispersion relation connecting the angular
eigenvalue $\nu$ to the resonant frequency through zeros of the spherical Bessel function derivative. Analytic continuation of this dispersion relation to $\nu = -1$ yields a formal zero-frequency endpoint where $j_{-1}(x) = \cos x / x$ admits the root $x = 0$. We examine this limit in detail, showing that while the mathematics is well-defined, the endpoint does not correspond to a physical electromagnetic mode. The positivity of the angular Sturm-Liouville operator restricts physical
eigenvalues to $\nu \geq 0$, placing $\nu = -1$ outside the admissible spectrum. We demonstrate that all electromagnetic field components vanish in this limit, even though the underlying Debye potential $\Pi = \cos(kr)/kr$ remains non-trivial and exhibits a monopole-type singularity at the origin. This distinction between potential and field reflects the kernel structure of the curl-curl operator for spherically symmetric configurations. The analysis clarifies the boundary between propagating electromagnetic modes and static field configurations in spherical geometry, connecting the formal endpoint to longstanding questions about mode counting in cavity quantization.
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Instrumentation and Detectors
Evaluation of the Front-End FERS 5202 Readout System for Muon Radiography Applications
R.M.I.D Gamage, F. Ambrosino, L. Cimmino et al. (+2 more)
This work presents a comprehensive characterization of the FERS 5202 front-end readout unit when processing signals from Silicon Photo-multipliers (SiPMs). The readout system's performance is characterized in terms of its charge resolution, dynamic range, and noise performance at the single photoelectron level, which is critical for applications requiring detection of low-light signals such as medical imaging, high-energy physics experiments and
photon counting applications. The evaluation encompassed both fundamental performance metrics and practical implementation scenarios using Hamamatsu MPPC devices. This work aims to provide valuable reference data not only for our intended
muon radiography application but also for the broader scientific community employing SiPMs in diverse experimental contexts.
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All authors R.M.I.D Gamage, F. Ambrosino, L. Cimmino, G. Nyitrai, G. Saracino
Optics
A Novel Noise Analysis Method for Frequency Transfer System by Using ADEV Combine with EMD-WT
Xuan Yang. Junhui Li, Bin Luo, Ziyang Chen et al. (+1 more)
In precision frequency transfer systems, stringent requirements are imposed on the phase stability of transmitted signals. Throughout the transmission process, the inherent challenges of long-haul signal propagation inevitably introduce multiple noise components, including but not limited to thermal noise, phase fluctuations, and environmental interference. The system incline to use the conventional evaluation index - Allan deviation (ADEV) to reflect the system stability in order to evaluate the noise level. Whereas, ADEV can only provide numerical expression and lacks the time-frequency details. Therefore, a complete evaluation system is required by the system. In this paper, we present a groundbreaking integration of ADEV and wavelet transformed empirical mode decomposition (EMD-WT), establishing a novel analytical framework that enables simultaneous characterization of noise types and time-frequency domain properties. This synergistic approach achieves unprecedented dual-domain resolution in noise discrimination in frequency transfer systems.
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All authors Xuan Yang. Junhui Li, Bin Luo, Ziyang Chen, Hong guo
Space Physics · Cross-listed from astro-ph.SR
Alfvénic solar wind intervals observed by Solar Orbiter: Exploiting the capability of the SWA plasma suite and source region investigation
R. D'Amicis, J. M. Raines, S. Benella et al. (+32 more)
Fast and slow
solar wind have distinct properties linked to their
solar sources.Alfvénic slow wind complicates the usual speed-based classification, especially at intermediate speeds.
Solar Orbiter's
Solar Wind Analyzer (SWA) offers unique capabilities to investigate how Alfvénic slow wind differs from fast wind and relate these differences to their
solar origins. In September 2022,
Solar Orbiter observed several Alfvénic streams: one fast wind, three Alfvénic slow wind (AS1, AS2, AS3), and a moderate fast (FH) interval. We analyze these streams, combining
plasma parameters from all SWA sensors with
magnetic field measurements from the Magnetometer (MAG). A spectral analysis of
magnetic and velocity fluctuations is used to characterize Alfvénicity. The
magnetic connectivity of each stream to its
solar source is examined using Potential Field Source Surface extrapolation combined with ballistic backmapping from the spacecraft.
Proton velocity distribution functions show anisotropies and field-aligned beams characteristic of Alfvénic streams, while electron pitch-angle distributions reveal clear strahl populations. Oxygen and carbon charge-state ratios are low in fast wind but higher in AS1-AS3, consistent with slow wind origins.
Magnetic connectivity suggests the fast wind originates from a large coronal hole; AS1 links to a pseudostreamer with high expansion factor; AS2, AS3, and FH connect to a negative-polarity coronal hole whose field lines cross a pseudostreamer that later dissipates. Spectral analysis indicates near energy equipartition in all intervals except AS2. The combined SWA observations offer key insights into the physical processes shaping Alfvénic
solar wind streams. Our results reinforce that the simple fast/slow wind classification is inadequate for linking
solar wind to sources, and suggest that Alfvénicity relates to the
solar source conditions.
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All authors R. D'Amicis, J. M. Raines, S. Benella, M. Velli, O. Panasenco, G. Nicolaou, C. J. Owen, R. M. Dewey, P. Louarn, A. Fedorov, S. T. Lepri, B. L. Alterman, D. Perrone, R. De Marco, R. Bruno, L. Sorriso-Valvo, O. S. Dhamane, Y. Rivera, O. R. Kieokaew, D. Verscharen, G. Consolini, S. Yardley, V. Réville, D. Telloni, D. Baker, G. Lewis, G. Watson, C. Anekallu, K. Darwish, L. Prech, S. Livi, T. Horbury, G. Mele, V. Fortunato, F. Monti
Instrumentation and Detectors · Cross-listed from quant-ph
Precision Bounds for Characterising Quantum Measurements
Aritra Das, Simon K. Yung, Lorcan O. Conlon et al. (+6 more)
Quantum measurements, alongside
quantum states and processes, form a cornerstone of
quantum information processing. However, unlike states and processes, their efficient characterisation remains relatively unexplored. We resolve this asymmetry by introducing a comprehensive framework for efficient detector estimation that reveals the fundamental limits to extractable parameter information and errors arising in detector analysis - the detector
quantum Fisher information. Our development eliminates the need to optimise for the best probe state, while highlighting aspects of detector analysis that fundamentally differ from
quantum state estimation. Through proofs, examples and experimental validation, we demonstrate the relevance and robustness of our proposal for current
quantum detector technologies. By formalising a dual perspective to state estimation, our framework completes and connects the triad of efficient state, process, and detector
tomography, advancing
quantum information theory with broader implications for emerging technologies reliant on precisely calibrated measurements.
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All authors Aritra Das, Simon K. Yung, Lorcan O. Conlon, Ozlem Erkilic, Angus Walsh, Yong-Su Kim, Ping K. Lam, Syed M. Assad, Jie Zhao
Optics
High efficiency and compact lithium niobate non-resonant recirculating phase modulator and its applications
Feiyu Wang, Liheng Wang, Mingrui Yuan et al. (+12 more)
High modulation efficiency and a compact footprint are critical for next-generation electro-optic (EO) modulators. We introduce a new class of non-resonant recirculating phase modulators (PMs) that boosts modulation efficiency by repeatedly modulating the optical field within a single, non-resonant waveguide, while fundamentally removing the loop-length matching constraint that has limited prior recirculating schemes. This architectural breakthrough simultaneously enables a much smaller device footprint and an extended low-V$\pi$ bandwidth, without relying on narrowband resonances. Building on this concept, we experimentally demonstrate both a Mach-Zehnder modulator (MZM) and a cascaded PM, and verify their versatility in finite impulse response (FIR) filtering and optical frequency comb (OFC) generation. The recirculating MZM operates as a 4-tap rectangular-window FIR filter with 110 GHz bandwidth in a compact 2.889$\times$0.58 mm$^2$ footprint. The cascaded PM achieves a 3.40 GHz low-V$\pi$ bandwidth, a 110 GHz resonant EO bandwidth, and a V$\pi$L of 0.7 V$\cdot$cm, and generates 20 OFC lines under a 33 dBm microwave drive. These results demonstrate, for the first time, a practical and highly efficient non-resonant recirculating modulation platform, laying the groundwork for scalable high-order mode recirculating modulators (RMs) and opening new opportunities in optical communications, sensing, and microwave photonics.
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All authors Feiyu Wang, Liheng Wang, Mingrui Yuan, Zhen Han, Binjie Wang, Yong Zheng, Pu Zhang, Yongheng Jiang, Huifu Xiao, Mei Xian Low, Aditya Dubey, Thach Giang Nguyen, Guanghui Ren, Arnan Mitchell, Yonghui Tian