Accelerator Physics
Impedance of multilayer cylindrical structures with a material-filled beam region
Erik Kvikne, Elias Métral and Erik Adli
Beam-coupling impedances in material media are relevant for ionization-cooling channels of a future
muon collider, where the beam propagates in matter rather than
vacuum. We extend the cylindrical field-matching formalism for multilayer structures to the case of a material-filled beam region surrounded by external layers with arbitrary electromagnetic properties. Relative to the
vacuum formulation, the usual factor $1/\gamma^2$ is replaced by the material-dependent factor $F=1/\varepsilon_1-\mu_1\beta^2$, and the radial propagation constant is modified accordingly. Analytical expressions are obtained for the monopolar longitudinal and dipolar transverse impedances, with the surrounding structure encoded through reflection coefficients determined by field matching. The formalism reduces to the known
vacuum and perfectly conducting limits in the appropriate cases. Representative calculations are presented for absorber-relevant configurations, illustrating the dependence on the material properties of both the beam region and the surrounding layers. In particular, a finite beam-region conductivity can generate a real impedance component and reverse the sign of the imaginary space-charge impedance, while sufficiently high permittivity can give rise to resonant structures associated with oscillatory radial fields. The effect of finite-conductivity surroundings is also examined, showing the approach towards the perfectly conducting limit as the external conductivity is increased. The applicability of the infinite-length approximation is also discussed by comparison with finite-length mode-matching results.
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Optics
End-to-end meta-imagers: Information-theoretic objectives and generalized focusing optima
Lukas Kienesberger, Zeyu Kuang, Yaxi Liu et al. (+1 more)
Metasurfaces and complex photonic components are increasingly co-designed with computational back-ends via end-to-end optimization, yet such optimizations are expensive and opaque – obscuring the role of the optics and any fundamental performance limits. We develop two information-theoretic objectives, based on Shannon capacity and Fisher information, that isolate the photonic contribution to image formation. Both are closed-form, data-free functions of the transfer
matrix, requiring no training data, and yield designs whose reconstruction quality matches end-to-end optimization. We prove that for both objectives, and for a broader family with a shared mathematical structure, the optimal transfer
matrix is a permutation
matrix: each source's emission is concentrated on a single, distinct detector, a condition we call generalized focusing. This holds regardless of source/detector geometry, as we demonstrate in settings where conventional imaging intuition offers no guidance, including a two-way imager, imaging through a random scattering medium, and Hermite–Gauss mode sorting. The root of this constraint is an "intensity bottleneck": nonnegative intensity measurements admit only Kronecker deltas as a complete orthonormal basis. We further show that this bottleneck, and the generalized-focusing optimum, persist for coherent and partially coherent sources – the constraint is the detector array, not the source coherence.
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All authors Lukas Kienesberger, Zeyu Kuang, Yaxi Liu, Owen D. Miller
Instrumentation and Detectors
A magnetic environment with reproducible spatio-temporal magnetic conditions at picotesla level
Philipp Wunderl, Maximilian Huber, Florian Büttiker et al. (+16 more)
Walk-in, picotesla-scale environments are essential for measurements of biomagnetism and fundamental physics. However, conventional rooms require typical active dynamic compensation, which adds complexity and
magnetic noise. Here, we present a solution that achieves an absolute residual field well below 100$\,$pT within its central measurement volume. Following
magnetic equilibration, this environment achieves picotesla-scale reproducibility. Consequently, optically pumped magnetometers operate at their design noise and drift performance and remain operational during sensor motion without active feedback. A key technique is robotic mapping, which resolves the ultra-low residual field patterns and demagnetization stability. We demonstrate the platform's versatility through high-fidelity adult and fetal magnetocardiography, standing magnetoencephalography, and ultra-low field
magnetic resonance with polarized noble gases in the limit of strongly coupled
spins in a negligible holding field. The achieved passive reproducibility turns the ultra-low
magnetic background into a predictable, correctable property, establishing a novel foundation for next-generation
quantum sensing and precision physics.
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All authors Philipp Wunderl, Maximilian Huber, Florian Büttiker, Jonas Emrich, Peter Ewert, Peter Fierlinger, Reinhard Heckel, Felix Herz, Tobias Jensch, Kim Kölbl, Florian Kuchler, Thorben Lützel, Karin Narushima, René Seiger, Jonas Vögtle, Annette Wacker-Gussmann, Chiara Weckmann, Lena Wunderl, Peisen Zhao
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Activated Migration of Localized Ligand-Field Excitons in Atomically Thin CrCl3
Hyesun Kim, Renlong Liu, Sangho Yoon et al. (+6 more)
Two-dimensional
crystals with densely packed atoms exhibit a range of emerging properties, particularly a wide variety of excitonic behaviors. Thickness-variable layered chromium trihalides with finite surface recombination sites provide an ideal system for understanding how
excitons confined in octahedral ligand fields migrate on nanometer length scales, a regime that defies conventional transport probes. In this work, we demonstrate that Cr3+-derived photoluminescence in CrCl3 is spectrally thickness-independent, but its relaxation dynamics are strongly sensitive to thickness and temperature, thereby indicating significant activated migration. A
diffusion-coupled surface recombination model reveals an effective out-of-plane diffusivity of 4.5 x 10-6 cm2/s for the ligand-field
excitons and a
diffusion activation energy of 130 meV. The latter is comparable to the reorganization energy independently estimated from optical Stokes shifts, suggesting that
exciton transport is coupled to local
lattice relaxation. Furthermore, we show that the relaxation dynamics can be systematically tuned by either enhancing or suppressing surface recombination through controlled surface reactions or encapsulation. This work not only reveals the nanoscopic transport of localized ligand-field
excitons but also establishes a spectroscopic transport probe applicable to various 2D materials.
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All authors Hyesun Kim, Renlong Liu, Sangho Yoon, Hyunjong Lim, Takashi Taniguchi, Kenji Watanabe, Jonghwan Kim, Changgu Lee, Sunmin Ryu
Applied Physics · Cross-listed from cs.LG
When Does Depth Matter For In-Context Learning? Adaptive Inference in Deep Transformers
Ravin Raj and Gautam Reddy
Transformers perform computations through many successive
attention and feedforward blocks, allowing them to learn complex correlations between a large collection of coupled variables. When does stacking successive
attention-feedforward computations over many layers provide a computational advantage over a single
transformer block? We address this question by examining in-context learning in generalized linear
attention transformers. We first introduce a general theory of distributed inference in such
transformers, subject to constraints on communication and depth. We show that such systems can exploit internal representations (`function vectors') to infer a latent context variable at increasingly finer scales over its layers. For an in-context linear regression task, the theory predicts that while one-layer
transformers without feedforward blocks are optimal for Gaussian priors over the context variable, multi-layer
transformers are superior for non-Gaussian, tree-like priors. Trained linear
attention transformers reproduce quantitative predictions from the theory. Using causal key-patching experiments, we verify that function vectors in intermediate layers mediate adaptive routing of information. Our results suggest that depth and feedforward blocks enable
transformers to implement adaptive inference, and this is advantageous when the distribution over latent variables has hierarchical structure.
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Chemical Physics
Ionization Potentials at Mean-Field Computational Cost: The Extended Koopmans' Framework for pCCD
Seyedehdelaram Jahani, Katharina Boguslawski and Paweł Tecmer
We introduce a mean-field-like computational model for calculating ionization potentials (IPs) based on the pair Coupled Cluster Doubles (pCCD) wave function. Specifically, our model combines the extended Koopmans'
theorem (EKT) with the advantages of a variationally orbital-optimized (oo)-pCCD ansatz. The computational cost of the EKT(pCCD) method is negligible (O(N^3)) as the response 1- and 2-particle reduced density
matrices used to construct the generalized Fock
matrix are readily available after an oo-pCCD calculation. We benchmarked our new computational model for IPs of atoms, small molecules, and a set of organic acceptor molecules against experimental and theoretical reference data. The EKT(pCCD) model significantly improves upon the modified Koopmans' approach [J. Chem. Phys. 162, 184110 (2025)], and the obtained IPs are comparable to those of computationally more expensive IP-EOM-pCCD-based models, approaching CCSD(T) reference values (with a mean error of 0.05 eV). Most importantly, the EKT(pCCD) approach is almost independent of the basis set size, and reliable IPs are already obtained with small basis sets.
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Optics · Cross-listed from cond-mat.mes-hall
Optical vortex probe of loop-current chirality in moiré materials
Nobuhiko Yokoshi and Akihito Kato
We propose a
symmetry-resolved optical probe of intrinsic loop-current chirality in moiré materials, with twisted
bilayer graphene as a representative realization. Interlayer interference generates
chiral electronic circulation on triangular plaquettes, giving rise to an intrinsic
geometric chirality that enters the second-order response through a $C_3$-selected angular harmonic of the Berry
curvature and can be isolated by the orbital-angular-momentum difference $\Delta\ell$ of interfering optical
vortex beams. When moiré $C_3$
symmetry is preserved, the intrinsic contribution appears in the $\Delta\ell=3$ channel of the helicity-dependent dc photocurrent, whereas $C_3$-breaking perturbations activate additional channels. These results establish angular-momentum-resolved nonlinear optics as a route to probing
geometric chirality in moiré and other
symmetry-engineered
quantum materials.
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Space Physics
Deflective Sunshades: conceptual design and origami-inspired folding strategy
Benedetta Marazzato, Jonas Seiler, Harry Holt et al. (+5 more)
Space-based
solar radiation management has been proposed as a direct means of modulating Earth's radiative balance by reducing incident
solar flux. A prominent concept consists of large sunshades operating near the Sun-Earth L1 region. However, feasibility is constrained by a fundamental lower bound on the required mass, arising from the coupled requirements of achieving sufficient insolation reduction while maintaining dynamical
equilibrium under
solar radiation pressure (SRP). We introduce a class of sunshades, termed deflective, designed to shape the effective SRP through macroscopic surface geometry. By employing inclined reflective elements, these systems redirect incident radiation to simultaneously control flux attenuation and the resulting momentum exchange, enabling the use of conventional high-reflectivity materials (e.g., aluminium films). The concept admits multiple geometrical realizations, including conical, pyramidal, and louvered (venetian-blind) configurations. A conical configuration is then studied in more detail as a representative implementation of this broader design principle. To improve its packaging efficiency and scalability, we consider a distributed constellation of units and propose a flat-folding strategy based on a Miura-Ori pattern adapted to the conical geometry finding its optimal configuration parameters resulting in a favourable geometry.
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All authors Benedetta Marazzato, Jonas Seiler, Harry Holt, Dolf Huybrechts, Richard Murchie, Leone Costi, Jai Grover, Dario Izzo
Physics and Society
Targeting Behavior or Intention? Intervention Strategies in Expressed-Private Opinion Dynamics
Barbara Kamińska, Arkadiusz Jędrzejewski and Katarzyna Sznajd-Weron
Exogenous interventions, including economic incentives, can be used to promote behavioral change and the adoption of new products or practices. They may act on different levels, either directly affecting customers' behavior (expressed level) or changing intentions (private level). The key question is which intervention strategy is more effective: targeting the expressed or the private level. Although expressed-private opinion (EPO) models are especially suitable for addressing this problem, they have not yet been used in this context. To fill this gap, we extend previous
agent-based EPO models by incorporating exogenous interventions and compare different intervention strategies. We analyze the resulting model using a mean-field approximation, complemented by Monte Carlo simulations on a complete graph. Our results show that there is no universal answer to whether an intervention should target the expressed or the private opinion. The effectiveness of an intervention depends on the adoption level at the moment of its introduction. Interventions acting on the expressed level are more effective when adoption is still low, whereas interventions acting on the private level are more effective when adoption is already high and the goal is to support internal acceptance and reduce dissonance. Moreover, the model shows that high adoption is accompanied by low dissonance between expressed and private opinions, which is consistent with self-congruity theory. This agreement provides theoretical support for the model and strengthens its policy implications.
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Atomic Physics · Cross-listed from quant-ph
Quantum enhancement and Doppler suppression of Kasevich-Chu atom interferometer with motional squeezing states
Dongyang Yu, Yubin Wang, Fong En Oon et al. (+1 more)
Hybridization of internal and external atomic degrees of freedom in a Kasevich-Chu interferometer enables the possibility to enhance the sensitivity significantly even under
quantum-standard limit. By introducing motional squeezing state as an input, we systematically derive the computational framework of
quantum and classical Fisher information of two measurement protocols for arbitrary strength of Doppler effects. Through maximizing the corresponding classical Fisher information, we obtain the optimal control parameters and the corresponding
quantum Fisher information. For population measurement, the largest sensitivity can be as large as four times than the semi-classical limit through enlarging the atom coherence length. For joint measurement of population and position, the competition between
quantum enhancement and Doppler suppression induces two three behaviors, in one regime, the
quantum enhancement dominates even in presence of strong Doppler broadening effects where the sensitivity is significantly enhanced; while in another regime, an optimal squeezing parameter is observed where the classical Fisher information reaches the maximum. Our results clearly demonstrate the robustness of external
quantum enhancement against Doppler suppression. Our proposal can be readily applied to gravimeter of mobile platform where decoherence from noise will damage the many-body
entanglement of internal
spin squeezing.
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All authors Dongyang Yu, Yubin Wang, Fong En Oon, Qiang Lin
Instrumentation and Detectors
Gaseous Tritium Activity Monitoring with Scintillators (GaTAMoS)
Florian Priester, Alexander Marsteller, Johanna Wydra et al. (+1 more)
We present a novel device for the inline activity monitoring of gaseous tritium, named Gaseous Tritium Activity Monitoring with Scintillators (GaTAMOS). Unlike established methods that often rely on
liquid scintillation or plastic scintillators with limited chemical resistance, this system utilises a chemically inert, inorganic Terbium-activated Gadolinium Oxysulfide (Gd2O2S:Tb) ceramic. A specialised soldering technique was developed to join the ceramic scintillator to a stainless-steel flange, achieving a
vacuum-tight seal fully compatible with high-purity tritium applications. The device was characterised using pure tritium gas, demonstrating a linear response and high sensitivity across a dynamic range from < 1 kBq to >10 GBq. A key advantage of the ceramic material over organic alternatives is its high tolerance to aggressive cleaning
agents. We demonstrate that the inevitable tritium
memory effect can be significantly mitigated by flushing the
cell with ethanol, removing >95% of residual contamination within minutes. The proposed system offers a compact, robust, and cost-effective alternative to ionisation chambers or BIXS systems for process monitoring in tritium handling facilities.
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All authors Florian Priester, Alexander Marsteller, Johanna Wydra, Robin Größle
Biological Physics
Oscillating concentrations suppress condensate coarsening
Mathias S. Heltberg, Lukas H. Kristensen, Mogens H. Jensen et al. (+1 more)
Living
cells utilize condensates to spatially concentrate molecules in response to dynamic signals. For instance,
nuclear condensates respond to oscillations in transcription factor levels in the nucleoplasm, including those involved in repairing multiple DNA breaks. To understand how oscillating signals affect condensates, we analyze a theoretical model using numerical simulations and analytical theory. While passive dynamics would drive all molecules into a single condensate, we find that sufficiently fast oscillations stabilize multiple droplets, allowing control of their sizes. We thus reveal a new behavior of chemically active droplets, which could be exploited in synthetic applications.
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All authors Mathias S. Heltberg, Lukas H. Kristensen, Mogens H. Jensen, David Zwicker
History and Philosophy of Physics
Timekeeping Beyond Human Whim: A Critical Analysis of Strong Conventionalism about Clocks
Matias Slavov
Conventional elements play an integral role in measuring time. Clocks unavoidably require a chosen standard of synchrony. The periodic process selected for the standard is not imposed upon us in any way. Conventionalism, in this regard, offers an insightful perspective on temporal measurement. The strong formulation of this doctrine is, however, questionable. After elaborating on strong conventionalism, it will be argued that it has three downsides: (i) it fails to properly distinguish between highly stable natural processes and complete randomness, as periodicities differ in terms of regularity; (ii) it does not explain that a clock actually measures something, to wit, parts of its own path along its worldline in spacetime; (iii) and relatedly, it omits the distinction between a temporal interval as a physical quantity and the arbitrarily chosen unit of time, leaving the distinction between temporal quantities and units a mystery. This article does not claim that strong conventionalism is incorrect; rather, considering the critical arguments against it, we may conclude that it remains an incomplete theory of what clocks measure.
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Computational Physics · Cross-listed from cs.LG
PhysGuard: Fisher-Guided Gradient Projection for Sim-to-Real Neural PDE Surrogates
Changjian Zhou, Junfeng Fang, Negin Yousefpour et al. (+3 more)
Neural operator models trained on simulation data often lose accuracy when applied to experimental measurements due to the sim-to-real gap. Standard fine-tuning with limited real data can reduce this gap, but it may also damage the core physics-relevant representations learned during pretraining. Although knowledge-preserving adaptation has been widely investigated in
vision or
language tasks, it remains unclear whether these methods are suitable for neural operators whose architectures and protected knowledge are fundamentally different. Neural operators need to preserve core-scale physical structures rather than semantic or visual features. We propose PhysGuard, a physics-preserving framework for accurate sim-to-real adaptation of neural operators. Specifically, PhysGuard uses the empirical Fisher Information
Matrix computed on simulation data to identify physics-critical parameter directions, then restricts fine-tuning updates to directions that do not interfere with them. A layer-wise Gram-
matrix formulation makes this efficient for models with millions of parameters, while an adaptive threshold automatically determines the protected subspace size. A spectral probe experiment shows that the dominant Fisher directions are strongly associated with low-frequency output structures. Experiments on
benchmark across four neural operator architectures and different physical systems show that PhysGuard performs strongly on most evaluation metrics compared to baselines. The benefits are most evident under severe domain shift, where it reduces low-frequency error by up to 32% compared to standard fine-tuning while maintaining adaptability. Our code is available at https://github.com/Data-Driven-Computational-Geotechnics/PhysGuard.
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All authors Changjian Zhou, Junfeng Fang, Negin Yousefpour, Peng Wu, Bin Yan, Guillermo A. Narsilio
Atomic Physics · Cross-listed from cond-mat.quant-gas
Ultracold atomic lattice systems for simulating topological phases: A review
Bei-Bei Wang, Xiao-Dong Lin, Jinyi Zhang et al. (+1 more)
Owing to rapid recent progress, ultracold atomic
lattice systems for simulating topological phases are now at a pivotal stage, evolving from established paradigms into increasingly versatile and programmable
quantum simulators. In this review, we survey recent experimental advances across four major classes of platforms: optical
lattices, including optical
lattices with
laser-assisted tunneling and optical Raman
lattices; synthetic
lattices in momentum or internal-state space; Floquet-engineered
lattices; and optical tweezer arrays, all of which offer distinct capabilities for realizing and probing topological matter. For each class, we highlight representative experimental breakthroughs, the topological models that have been realized, and the advanced detection and characterization techniques employed, emphasizing how these complementary approaches collectively expand the frontier of
quantum simulation. We also discuss emerging directions in strongly correlated and nonequilibrium topological phases, and conclude with an outlook on future prospects.
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All authors Bei-Bei Wang, Xiao-Dong Lin, Jinyi Zhang, Long Zhang
Fluid Dynamics
Learning Interface Breakup: A Geometry-Conditioned Latent Surrogate for Spray Formation
Julius H Ramlau, Friedrich Hastedt, Tolga Birdal et al. (+3 more)
Designing spray nozzles requires predicting how geometry shapes transient two-phase breakup, but high-fidelity volume-of-fluid (VOF) simulations with adaptive mesh refinement (AMR) are too expensive for iterative design exploration. Standard surrogate models are also challenged by this setting because both the
liquid–gas interface and the underlying adaptive discretization evolve across time and geometries. We introduce a geometry-conditioned latent surrogate trained on 797 two-phase nozzle simulations that addresses this by encoding the AMR
cell-density field, rather than the full multi-channel flow state, as a compact proxy for where the solver concentrates resolution. From this representation, the model reconstructs transient density
evolution and nozzle geometry, and a lightweight second stage recovers the remaining flow variables. On held-out simulations, the method accurately captures key interface dynamics while reducing inference time to 0.045 seconds per trajectory, corresponding to a speed-up of more than $6\times10^4$ relative to Basilisk CFD. These results suggest that AMR refinement structure can serve as a compact and learnable representation for geometry-conditioned surrogate modeling of transient two-phase flows.
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All authors Julius H Ramlau, Friedrich Hastedt, Tolga Birdal, Ehecatl-Antonio del Río Chanona, Nausheen S Basha, Omar K Matar
Optics
THz near-field nanoscopy employing coherent synchrotron radiation
Alexander Veber, Maria Eleonora Temperini, Ljiljana Puskar et al. (+1 more)
We demonstrate that the coherent synchrotron radiation (CSR) can be used for the scattering type near-field scanning optical microscopy (s-SNOM). Using a commercially available s-SNOM coupled to a synchrotron source we perform THz imaging and spectroscopy experiments in the spectral range of 25-55 cm-1 and spatial resolution of 60 nm. It is shown that the same optical configuration can be used for nanoscopy in the range of 25 to 4000 cm-1. Conducting experiments across the THz, far-, and mid-IR spectral ranges within a single setup offers a unique capability for the ultrabroadband characterization of complex materials in both life and material sciences at the nanoscale.
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All authors Alexander Veber, Maria Eleonora Temperini, Ljiljana Puskar, Ulrich Schade
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Lattice Matching Dictates the Growth Mode and Quality of Deuterium Crystallization in Confined Spherical Shells
Peng Bi, Yu-Shen Wan, Wei Zhang et al. (+3 more)
Cryogenic hydrogen isotope fuel layers with high structural integrity and atomic-scale smoothness are prerequisites for symmetric implosion and ignition in inertial confinement fusion (ICF). Using deuterium (D$_2$) as model fuel, we perform large-scale molecular dynamics simulations with a Feynman-Hibbs corrected Silvera-Goldman potential to describe
nuclear quantum effects at low temperatures, systematically investigating D$_2$ crystallization inside spherical ablator capsules. By varying substrate
lattice constant from 3.1 angstrom to 3.9 angstrom, we demonstrate that
lattice matching dictates the transition from coherent epitaxial growth to polycrystalline formation, establishing it as the primary design principle for high-performance targets. When the substrate
lattice closely matches the
equilibrium hexagonal-close-packed (HCP) spacing of cryogenic D$_2$ (approximately 3.5 angstrom), D$_2$ forms coherent layer-by-layer epitaxial growth consistent with Ostwald's stepwise nucleation theory, yielding HCP-dominated near-single
crystals with minimal dislocations and ultra-smooth inner surfaces. In contrast, large
lattice mismatch destabilizes coherent growth and causes island-like growth, producing polycrystalline structures with mixed HCP/FCC phases, elevated defects, and greatly increased surface roughness. Radial stress analysis shows that interfacial stress from mismatch localizes within 2-3 molecular layers near the interface, triggering subsequent defect-mediated growth. These findings highlight substrate
lattice matching in regulating confined solid growth and crystallization quality, establish it as a key principle for ablator inner-surface engineering in ICF cryogenic targets, and offer atomic guidance for growing high-quality single-
crystal deuterium-tritium (DT) fuel layers with optimal smoothness.
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All authors Peng Bi, Yu-Shen Wan, Wei Zhang, Jian Chen, Yong Yi, Qi-Feng Chen
Optics
Higher-Order Modes Are More Robust: The Origin of Bending Insensitivity in Multimode Fibers and Its Exploitation for Imaging
Xiangqian Chen, Long He, Qiankai Xia et al. (+4 more)
Multimode fibers (MMFs) hold great promise for minimally invasive imaging, yet their extreme sensitivity to bending perturbations severely hinders practical applications. Starting from mode coupling theory, we theoretically prove and experimentally verify that higher-order modes exhibit significantly greater bending robustness than lower-order modes. We reveal that bending-induced changes in the output speckle arise predominantly from alterations in the mode effective propagation constants, whereas the modal power redistribution caused by inter-modal coupling is negligible. Since the bending-induced changes are dominated by alterations in the mode effective propagation constants, which are inherently independent of the input field, and the modal power redistribution caused by inter-modal coupling is negligible, it follows that, under moderate bending, the perturbation imposed by bending on light propagation inside the fiber is independent of the input field distribution. Based on this input-independent bending perturbation property, we propose a physics-inspired dual-encoder neural network. The network separately extracts features from a reference speckle pattern (corresponding to a circular field input) and an information-carrying speckle pattern acquired under the same fiber state, then employs a differential fusion module to decouple the image information from environmental perturbations, and subsequently recovers the image after excluding the perturbation. Our method significantly enhances the anti-bending capability of MMF imaging systems, offering a new paradigm that integrates physical insights with deep learning for robust fiber-optic imaging.
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All authors Xiangqian Chen, Long He, Qiankai Xia, Jialiang Lv, Yuxuan Luan, Lixin Xu, Peijun Yao
Optics
Temporal Faraday effect enabled by Floquet-induced chirality
Neng Wang and Guo Ping Wang
The Faraday effect is a hallmark of nonreciprocal light-matter interactions and traditionally requires
magnetic bias or intrinsically
chiral media. Here we introduce a temporal
chiral metamaterial in which an effective
chiral response is generated entirely by Floquet modulation, without
magnetic fields or structurally
chiral constituents. The medium is realized by periodically rotating the principal axes of the permittivity and permeability tensors in time. Using a nonlocal temporal effective medium theory derived from
Hamiltonian homogenization, we show that the resulting
chiral parameter is an odd function of the wavevector, giving rise to intrinsic nonreciprocity despite Onsager-symmetric constitutive relations. This Floquet-induced chirality produces a temporal Faraday effect, in which the polarization plane of a linearly polarized wave rotates continuously in time. The direction and magnitude of the rotation are programmable through the modulation sequence and remain invariant under both spatial and temporal reversal. Our work establishes Floquet-induced chirality as a fundamentally new mechanism for nonreciprocal light control and opens a route to reconfigurable polarization manipulation in time-modulated photonic systems.
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Space Physics
Beyond Mean Solar Wind Conditions: Turbulence-Aware Forecasting of the AE Index
Cara L. Waters, Christopher H. K. Chen and Mathew J. Owens
The auroral electrojet (AE) index is a key indicator of high latitude geomagnetic activity and is widely used in operational space weather monitoring, yet
forecasting AE from upstream
solar wind conditions remains challenging due to nonlinear coupling, internal magnetospheric dynamics, and multiscale variability. We test whether incorporating
solar wind
turbulence improves short timescale AE forecasts beyond models based only on mean
solar wind and interplanetary
magnetic field parameters. Two gradient boosted decision tree (XGBoost) models are developed using near-Earth
solar wind observations: a baseline model using standard mean parameters and a
turbulence-aware model that additionally includes measures of fluctuation amplitude, intermittency, and Alfvenic structure. Both models achieve peak performance at short lead times, with correlations exceeding 0.8 at 60 minutes. However, while the baseline model exhibits a clear skill peak at 75 minutes, the
turbulence-aware model maintains comparable skill across 60-90 minute horizons, indicating reduced degradation with lead time. The
turbulence-aware model also provides consistent improvements over both the baseline and persistence and, critically, improves forecast robustness for high-impact events. Cost-loss analysis shows that, for the baseline model, economic value decreases systematically with increasing AE threshold and the range of cost-loss ratios yielding positive value narrows. In contrast, the
turbulence-aware model maintains an approximately constant zero-value cost-loss threshold across all event levels, indicating stable economic usefulness even for extreme AE conditions. This demonstrates that
turbulence provides complementary, scale-dependent information beyond mean
solar wind parameters, improving both forecast performance and decision-relevant value for operational space weather applications.
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Fluid Dynamics · Cross-listed from quant-ph
Fully Quantum Algorithm for the 1-dimensional linear Lattice Boltzmann Method
Mohammed Bediche, Matthijs van Waveren, Denis Ricot et al. (+1 more)
A fully
quantum algorithm for solving the one-dimensional linear advection-
diffusion equation using the
Lattice Boltzmann method as a numerical procedure is presented in this work. We start by presenting a state of the art of the current usage of
quantum algorithms for solving ordinary and partial differential equations. We then describe two
algorithms for the one-dimensional
Lattice Boltzmann method with two degrees of freedom. The first one is an existing hybrid
quantum-classical
algorithm with measurements at each time step, and the second one is our improved version, viz. a fully
quantum algorithm where only one measurement is needed at the end of the
algorithm. The fully
quantum algorithm is first executed on a
quantum simulator and then compared with a classical approach. Subsequently, the fully
quantum algorithm is run on a
quantum system with 133
qubits to investigate the effect of noise and the depth of the
circuit on the output state. We find fluctuations in the final result due to the decoherence noise of the
qubits.
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All authors Mohammed Bediche, Matthijs van Waveren, Denis Ricot, Pierre Sagaut
Optics
Continuous-Wave SOFISM with SPAD Array Detection
Lior M. Beck, Tali Dadosh, Anabel Chen et al. (+2 more)
We present a continuous-wave (CW) implementation of super-resolution optical fluctuation imaging with image scanning microscopy (SOFISM) using a pixelated single-
photon avalanche diode (SPAD) detector camera. In a scanning-based geometry, SOFISM requires fluorescence fluctuations on timescales compatible with the pixel dwell time while maintaining sufficient signal under confocal excitation. Photoswitchable fluorophores in an aqueous switching buffer containing the glucose oxidase-catalase oxygen-scavenging system (GLOXY) and mercaptoethylamine (MEA) were therefore used to promote blinking and reduce photobleaching. Correlation analysis of sparse-emitter measurements showed that Alexa Fluor 647 (AF647) exhibits microsecond-scale fluctuation dynamics suitable for CW SOFISM and guided the choice of imaging conditions for scanned samples. Frame rate and delay accumulation were optimized from detector-pair subset variability using a mean-to-STD criterion. The optimal binning time was 2.5 $\mu$s, underscoring the advantage of SPAD-based detection for resolving the relevant fluctuation dynamics. The method was demonstrated on HeLa
cell microtubules labeled with AF647, yielding improved spatial resolution in the constructed SOFISM images compared with the corresponding ISM images. Additional super-resolved images from samples labeled with CF568 and Alexa Fluor 555 (AF555) showed the approach is readily generalizable to other fluorophores. These results establish CW SOFISM as a practical fluctuation-based super-resolution method for confocal microscopy.
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All authors Lior M. Beck, Tali Dadosh, Anabel Chen, Inna Goliand, Dan Oron
Chemical Physics
Estimating the disjoining pressure of liquid nanofilms from molecular dynamics simulations via implicit treatment of the bulk liquid phase
Jianzhou Wang, Zufeng Zuo, Denvid Lau et al. (+5 more)
The commonly adopted constant bulk
liquid density approximation for estimating disjoining pressure in
liquid nanofilms, although justified by the low compressibility of
liquids, can introduce significant errors in its evaluation. We hypothesize that the bulk
liquid density is a thermodynamic state variable that depends on film thickness and local pressure, and should therefore be determined self-consistently to accurately capture interfacial forces under confinement. A thermodynamically consistent molecular dynamics simulation framework is developed by coupling a surface-tension-based formulation with bulk equations of state obtained from independent simulations. An iterative
algorithm is employed to simultaneously determine bulk
liquid density, film thickness, and disjoining pressure. The method is applied to water and argon nanofilms, and results are benchmarked against conventional constant-density approaches and alternative computational routes based on chemical potential calculation. The proposed framework provides a computationally efficient and thermodynamically rigorous route for evaluating disjoining pressure without requiring explicit full coexisting system simulations. Incorporating density variations significantly improves the accuracy and consistency of predicted disjoining pressures. For water nanofilms, a 3.6% deviation in density can lead to up to 77% overestimation of disjoining pressure at a thickness of 12 Å, whereas the effect is weaker but still non-negligible for argon. The proposed framework restores the inverse-cubic scaling with film thickness predicted by Hamaker theory and reduces discrepancies between independent computational methods. Overall, the results demonstrate that self-consistent treatment of bulk thermodynamics is essential for quantitatively reliable evaluation of surface forces in confined fluid systems.
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All authors Jianzhou Wang, Zufeng Zuo, Denvid Lau, Yuzhu Wang, Pinqiang Mo, Yukun Ji, Liyuan Yu, Yafan Yang
Optics
Upper bound to optical forces through the multipolar control of optical beams
Enrique Ayllón-García, Iker Gómez-Viloria, Quimey Pears Stefano et al. (+6 more)
Optical tweezers enable the manipulation of microscopic objects using light, yet the fundamental limits to the optical forces that can be exerted on matter remain unknown. Here we derive a general upper bound to the maximum optical force that can be applied to a particle, based on an expansion of electromagnetic fields into well-defined helicity multipolar modes. This method finds the optimal force for any kind of fields external to the particle, including evanescent fields. We apply the method to homogeneous spherical particles in a stable trap and identify the field distributions that saturate this bound for the trapping stiffness. We further provide experimentally accessible strategies to approach these optimal conditions, including configurations using counterpropagating and single-beam traps. Experiments demonstrate a threefold enhancement of trapping forces relative to conventional designs, while theoretical predictions indicate that order-of-magnitude improvements are achievable for larger particles and high angular momentum beams. Our results establish fundamental design principles for maximizing optical forces and define the ultimate limits of optical manipulation.
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All authors Enrique Ayllón-García, Iker Gómez-Viloria, Quimey Pears Stefano, Jason T. Francis, Ángel Cifuentes, Ásier Mongelos-Martinez, Shah Jee Rahman, Miguel Varga, Gabriel Molina-Terriza
Optics
Octave bandwidth 3D-Printed Couplers for Low-Loss Thin-Film Lithium Tantalate Circuits
Erik Jung, Xinyu Ma, Jan Brandes et al. (+9 more)
Low-loss, broadband photonic integrated
circuits (PICs) are critical enablers for optical communications, photonic computing, and
quantum applications. Lithium tantalate on
insulator (LTOI) is an emerging photonic platform offering a wide transparency window and strong Pockels effect, and thereby enabling efficient electro-optic modulation and high data rates. Here, we present the first implementation of efficient out-of-plane
polymer coupling interfaces fabricated via 3D direct
laser writing for both fully etched strip and partially etched rib LTOI waveguides, achieving ultra-low coupling losses of 0.9 dB (strip) and 1.25 dB (rib) per interface. Both coupler types exhibit a 3 dB optical bandwidth spanning more than an octave from 850 nm to 1740 nm and maintain stable operation under 1 W optical input power. Combined with on-chip waveguides exhibiting propagation losses below 0.1 dB/cm, these characteristics represent a key step toward unlocking the full potential of LTOI for high-speed optical signal processing with an unprecedented degree of parallelism. In addition, the octave-spanning bandwidth enables efficient interfacing of both the fundamental and second-harmonic signals, making the platform highly attractive for second harmonic generation based
quantum squeezing applications.
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All authors Erik Jung, Xinyu Ma, Jan Brandes, Caghan Ünlüer, Shabnam Taheriniya, Seongmin Jo, Philipp Schmidt, Eric Biedert, Liam McRae, Julian Rasmus Bankwitz, Frank Brückerhoff-Plückelmann, Wolfram Pernice
Applied Physics · Cross-listed from stat.AP
Calibrating the Brody exponent as a quantitative measure of short-range exclusion in 2D spatial point processes
Dawid Kucharski
The Brody distribution, originally a phenomenological interpolation between Poisson and Wigner level-spacing statistics in
quantum chaos, is calibrated here as a quantitative measure of short-range exclusion in 2D spatial point processes. Two results form the core. First, the 2D complete-spatial-randomness baseline is recalibrated to $\beta=0.96\pm0.15$, correcting the inappropriate 1D Poisson reference. Second, an empirical $\beta$–$r_{\text{excl}}$ calibration is validated against the effective hard-core radius with Spearman $\rho=0.988$. The framework is demonstrated on 58 manufactured surfaces (10 materials, 10 processes), phase-extracted interferometric profilometry of a certified roundness standard, and 2D binary
embeddings of
prime numbers. A sparse-integer control proves the
prime $\beta=2.15$ signal is genuinely arithmetic ($\Delta\beta=+0.68$ over random-integer control), while a Cantor-
embedding null result ($\beta=1.40$, TOST $p<0.01$) demonstrates that 2D exclusion is
embedding-created rather than intrinsic. Density-thinning experiments establish that $\beta$ captures exclusion strength rather than point density, while absolute values are density-dependent. A distinct CSR baseline for binary fields at low fill fraction is identified, with a decision table provided. The $\beta$–$r_{\text{excl}}$ calibration, the CSR baseline correction, and the control protocols together constitute a calibrated measurement framework for reproducible characterisation of short-range exclusion in 2D spatial point processes.
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Fluid Dynamics
Engine position effects on contrail evolution for a realistic aircraft configuration
Rémy Annunziata, Nicolas Bonne and François Garnier
This study investigates the influence of representative engine positions on contrail
evolution during the
vortex and dissipation regimes, using three-dimensional simulations of a realistic aircraft geometry. Large Eddy Simulations are employed, coupled with an Eulerian microphysical bulk model, and initialized using fields obtained from prior Reynolds-Averaged Navier-Stokes simulations. This approach enables a consistent transition from near-field jet-
vortex interactions to far-field wake dynamics. Three engine placements are examined under two atmospheric stratifications and two relative humidity conditions. The results reveal that engine position influences the onset and
evolution of
vortex instabilities, alters the descent of the
vortex pair, and leads to slight changes in the distribution of particles within the wake. Despite these aerodynamic differences, the microphysical properties of the contrails tend to converge over time for the parameters and configurations covered in this study. From a broader perspective, engine placement strongly influences initial contrail formation and early
vortex-regime dynamics. At later stages, these differences largely disappear, as
vortex dynamics and atmospheric conditions dominate over the initial dilution changes induced by engine position.
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Optics
Optomechanical parametric control of mid-infrared photons via molecular vibrational polariton
Ryoko Sakuma, Koji Sakai, Hajime Okamoto et al. (+2 more)
Controlling mid-infrared (MIR)
photons using well-developed telecom photonic platforms would enable new functionalities in molecular and
quantum photonics. However, establishing efficient interactions between MIR and telecom
photons remains challenging due to their large spectral separation and weak nonlinear coupling. Here, we demonstrate optomechanical control of MIR
photons mediated by vibrational polaritons, enabling
photon-
photon interaction between MIR and telecom fields across distant spectral regions. Using a Fabry-Pérot cavity incorporating a vibrationally active
polymer, we observe telecom-driven dissipation enhancement of MIR
photons at 9.5 $\mu$m with a modulation depth of 1% under a 4 mW pump. The linear power dependence, mixing-ratio dependence, and detuning response consistently indicate a MIR and telecom
photon-
photon conversion enabled by strong light-matter coupling. This approach establishes a polaritonic optomechanical platform for bridging disparate spectral regimes and provides a dissipation-engineered route toward hybrid MIR photonics and
quantum transduction.
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All authors Ryoko Sakuma, Koji Sakai, Hajime Okamoto, Motoki Asano, Hiroshi Yamaguchi
Plasma Physics
The Effect of Anomalous Resistivity on Tearing Instability
D. Tsiklauri
We study the modification of classical tearing instability due to anomalous resistivity by incorporating a variable, second-order resistivity model into the resistive magnetohydrodynamics (MHD) framework. We evaluate the resulting {weakly non-linear boundary-layer scaling laws under a localized current-feedback mechanism}. By extending the {inner-layer analysis to capture localized current feedback}, we resolve localized spatial singularities ($\delta$ and $\delta'$) at the threshold boundary. These singularities generate unexpected matching jump conditions, demonstrating an early-stage phase-slip layer that forces a
hyperbolic, time-dependent growth rate divergence prior to macroscopic saturation. Physical estimates for fusion devices and
solar flares prove that this {consistent weakly non-linear matching formulation} triggers an abrupt transition into the explosive reconnection regime, offering an exact analytical resolution to the long-standing
solar and tokamak
flare/disruption “trigger problem,” respectively. Finally, a comparative analysis using a truncated linear expansion of the threshold model regularizes the singular behavior, confirming that the explosive finite-time singularity is uniquely driven by the higher-order non-linear current feedback.
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