Geophysics
Paleomagnetic signatures of core-mantle interactions inferred from top-heavy thermochemical geodynamo simulations
Souvik Naskar, Jonathan E. Mound, Christopher J. Davies et al. (+3 more)
The time-averaged geomagnetic field provides crucial insights into deep Earth dynamics and thermal core-mantle interactions. Paleomagnetic observations and numerical dynamo simulations are equivocal regarding the longitudinal structure of the time-averaged field, though the latter have often considered a generic buoyancy source, which may obscure distinct signatures of thermal and chemical buoyancy that arise near the equator and poles, respectively. In this study, we present a new suite of top-heavy geodynamo simulations, varying the relative strengths of thermal and chemical driving and comparing the resultant
magnetic signatures to observational field models spanning centuries to tens of thousands of years. None of the spatially-averaged measures of field morphology and variability we tested could robustly distinguish between different levels of chemical driving or the presence of heterogeneous outer boundary heat flux. On the other hand, observational constraints requiring longitudinal variations in time-averaged inclination anomaly are readily matched by simulations with heterogeneous outer boundary thermal forcing, in contrast to those with homogeneous mantle heat flux. Longitudinal field structures are reduced, but not erased, by elevated chemical driving, which also promotes the formation and deepening of polar minima in the radial
magnetic field. Our simulations indicate that both the strong heat flux heterogeneity and chemical driving in Earth's core are likely to result in small but persistent departures from the geocentric axial dipole approximation.
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All authors Souvik Naskar, Jonathan E. Mound, Christopher J. Davies, Hannah F. Rogers, Stephen J. Mason, Andrew T. Clarke
Computational Physics
A one-parameter family of realizability-interior closures for odd-order kinetic moment systems
Somdeb Bandopadhyay
Moment closures at odd truncation order present a fundamental difficulty: the standard Gramian closure saturates the realizability boundary, producing only weak hyperbolicity and failing to preserve Maxwellian
equilibrium. We show that every odd-order closure for the one-dimensional kinetic equation decomposes into a boundary term, the Schur complement of the Hankel moment
matrix, and a positive margin above it. An exact
polynomial identity connects this margin to the
eigenvalues of the flux Jacobian, reducing hyperbolicity to a root-splitting problem. A dimensional argument proves that no margin depending only on density, velocity, and temperature can produce a
hyperbolic system for $M \geq 5$. A one-parameter family $C_{\eta,n}$, $\eta \in [0,1]$, built from normalized Schur-complement ratios, reveals that the Morin-McDonald closure is the arithmetic endpoint of this decomposition. The weighted AM-GM inequality makes the accuracy-robustness tradeoff precise: the
geometric endpoint ($\eta = 0$) is 2-4% more accurate on bimodal
benchmarks, while the arithmetic endpoint ($\eta = 1$, Morin-McDonald) provides the most robust hyperbolicity profile. All members share the same
equilibrium Jacobian, whose spectral radius is 13% ($M = 5$) to 29% ($M = 13$) smaller than Grad's closure, allowing larger CFL time steps. A linearized
entropy exists at every tested order, and for a source-compatible choice of the symmetrizer weights, the BGK source dissipates it near
equilibrium. A smooth nonlinear
entropy exists for $M = 3$ but does not for $M = 5$ or $M = 7$ (certified by linear programming). The closure is validated on bimodal and Mott-Smith
benchmarks, where the interpolated family achieves errors 10-40x smaller than the Gramian or Grad closures, and demonstrated in free-transport Riemann problems at $M = 5, 7, 9, 11$ and BGK Riemann problems at $M = 5$ and $9$.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Epitaxial Strain Activates Altermagnetic Spin-Splitting Torques in RuO2(100)
Qi Jia, Seung Gyo Jeong, Seungjun Lee et al. (+10 more)
The altermagnetic nature of rutile RuO2 remains under active debate: bulk measurements indicate a nearly nonmagnetic ground state, whereas thin-film studies have reported
symmetry-dependent transport signatures consistent with altermagnetism. Here, we provide experimental evidence that altermagnetic
spin splitting in RuO2 is a strain-stabilized emergent state rather than an intrinsic bulk property. Angular-resolved
spin-torque measurements reveal a
symmetry-selected
spin Hall response characteristic of altermagnetic
spin splitting, which is strongest in the strained regime but progressively suppressed as the
lattice relaxes toward the bulk limit. Complementary
magnetic measurements further reveal enhanced coercivity and exchange-bias behavior exclusively in strained films, indicating the emergence of a strain-stabilized
magnetic state. First-principles calculations reproduce the strain-dependent
evolution of the Neel order and
spin-split electronic structure, supporting the experimental observations. Together, these results establish altermagnetic
spin splitting in RuO2 as a strain-stabilized emergent state and provide a unified explanation for the long-standing discrepancy between bulk and thin-film observations.
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All authors Qi Jia, Seung Gyo Jeong, Seungjun Lee, Denis Tonini, Anand Santhosh, Yifei Yang, Xiangrui Li, Brahmdutta Dixit, Shuang Liang, Yu-Chia Chen, Tony Low, Bharat Jalan, Jian-Ping Wang
Physics and Society
The Allure of Complete Discovery as Passage: Broadening the Range of SETI Research Ideas via Futures Literacy and Triple-Loop Learning
George Profitiliotis
This paper argues that, although it principally refers to extraterrestrial rather than human affairs, SETI's imaginary is a social imaginary proper, as it is implicitly linked in an intrinsic, non-trivial, co-constitutive way to a social imaginary of humanity's future. Specifically, SETI's imaginary is an imaginary of a society of sapient extraterrestrials that makes possible the achievement of a desirable future of humanity through the former's discovery by the latter. Moreover, it argues that the range of SETI research ideas, which get bundled in non-fictional conviction narratives promising SETI's imaginary, is currently limited because actualizing this desirable future state of humanity after such a discovery relies on a "complete discovery". Finally, an intervention is offered in the form of a hands-on workshop for SETI scientists, which could help them reveal, reframe, and rethink the role that this imaginary for a desirable "post-discovery" future of humanity plays in their present research ideas.
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Fluid Dynamics
A Gaussian-based spatially weighted loss formulation for Physics-Informed Neural Networks with Shocks
Kheir-eddine Otmani, Abdelhalim Azzouz, Nourelhouda Groun et al. (+1 more)
Physics-informed neural networks (PINNs) often struggle to resolve shocks because smooth neural representations and globally averaged residual losses tend to underemphasize localized high-gradient regions. We introduce a residual-tracked Gaussian weighting strategy that represents the spatial distribution of the PDE-residual loss through a small number of learnable parameters, without resampling the collocation points or prescribing the shock location. The Gaussian center and width are updated from the evolving PDE residual, allowing the weighting field to follow stationary and moving shocks during training without prior knowledge of their positions or trajectories. The method is assessed using one-dimensional low-viscosity Burgers problems and a two-dimensional Euler Riemann problem with four interacting shocks. For $\nu=5\times10^{-4}$, the relative $L_2$ error decreases from approximately $45\%$ to $13\%$ for the stationary shock and from $33\%$ to $14\%$ for the moving shock, compared with a standard PINN. In the two-dimensional problem, the maximum absolute density error decreases from $1.08$ to $0.62$. These results show that a compact, dynamically localized residual weighting can substantially improve PINN resolution of shock-dominated solutions while retaining the original collocation set and avoiding prescribed shock trajectories.
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All authors Kheir-eddine Otmani, Abdelhalim Azzouz, Nourelhouda Groun, Esteban Ferrer
Optics · Cross-listed from cond-mat.mes-hall
Strong coupling regimes of an organic exciton mirror in a microcavity
Christoph Bennenhei, Lukas Lackner, Moritz Gittinger et al. (+7 more)
The coherent, periodic energy transfer between light- and matter excitations characterizes the strong coupling regime of cavity
exciton-polaritons, resulting, in the simplest case, in a Rabi-doublet in the spectral domain. We demonstrate a peculiar regime of strong light-matter coupling, which arises when photonic cavity modes couple to an ultra-thin excitonic mirror. We embed a 12 nm J-aggregated thin film in an open microcavity and tune the coupling strength from weak to the onset of ultrastrong coupling. At resonance, the excitonic mirror selectively changes dielectric to metallic field boundary conditions adding a 2{\pi} phase, which links optical cavity modes of different order. Our work gives an exciting perspective to ultra-fast cavity switches and photonic devices based on excitonic optical elements.
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All authors Christoph Bennenhei, Lukas Lackner, Moritz Gittinger, Falk Eilenberger, Marvin F. Schumacher, Arne Lützen, Ivan Shelykh, Christoph Lienau, Martin Esmann, Christian Schneider
Fluid Dynamics
Poisoning effect of ammonia on the performance and transport process of proton exchange membrane fuel cells
Yaxian Han, Wei Gao, Yichao Huang et al. (+2 more)
Ammonia is a high-density hydrogen energy carrier and can be decomposed to produce hydrogen for use in fuel
cells. However, a significant challenge in ammonia-decomposition-based fuel
cell applications is the unavoidable presence of trace ammonia
impurity, which can poison the fuel
cell, but the poisoning mechanism remains unclear. To address this, a three-dimensional numerical model of
proton exchange membrane (PEM) fuel
cells with ammonia
impurities is established to explore the transport process and underlying poisoning mechanism. The influences of key factors, including ammonia concentration, operating temperature, operating humidity, and membrane thickness, are studied. The poisoning mechanism is analyzed from the perspectives of the distributions of
proton conductivity, current density, and dissolved water content. The results show that ammonia diminishes the
cell performance by substantially reducing the
proton conductivity of both the PEM and the anode catalyst layer. Higher operating temperatures and higher operating humidity can alleviate ammonia poisoning. Decreasing the membrane thickness can also help to mitigate ammonia poisoning, but may lead to less uniform current distribution.
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All authors Yaxian Han, Wei Gao, Yichao Huang, Tianyou Wang, Zhizhao Che
Optics
Exact modes, hybridization and polarization rotation of electromagnetic fields propagating in topological insulating slab
Sebastián Filipini, Mauro Cambiaso, Alberto Martín-Ruiz et al. (+1 more)
We study electromagnetic waves in slab waveguides with a topological
insulator core characterized by a topological magnetoelectric parameter (ME). TIs are electrically insulating in the bulk with robust conducting states at their boundaries. Their electromagnetic response is described by an
axion-like $\Theta$ term that modifies Maxwell's electrodynamics, leading to rich and unconventional phenomena, as the topological ME effect. All supported modes are exact hybrid modes with nonvanishing longitudinal field components. This hybridization is a consequence of the boundary conditions produced by the $\Theta$ term and is absent in topologically trivial, reciprocal and non-
chiral slab waveguides. Modifications to the propagation condition and modes are shown for the asymmetric slab. The detailed solution of the exact modes, coupling of modes and the dispersion relations is made for the symmetric slab. By solving the full $\Theta$-electrodynamics nonperturbatively, we derive the modal dispersion relations and explore polarization rotation and power transfer between modes. Our approach reveals qualitative and quantitative deviations from standard coupled-mode theory and captures new signatures of the topological ME response. Due to the smallness of the $\Theta$-effects, we perform a perturbative analysis of mode propagation, based on writing a general solution as a superposition of exact modes of $\Theta$-ED but expanding to first non-vanishing order. Also, we apply coupled-mode theory, that is predicated on building solutions as superpositions of modes of ordinary electrodynamics that fail to satisfy the boundary conditions imposed by the $\Theta$-term but compensate at the expense of modifying the field profiles. These findings provide a comprehensive framework for light control in topological photonics and potential routes to experimentally probe the ME effect in guided settings.
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All authors Sebastián Filipini, Mauro Cambiaso, Alberto Martín-Ruiz, Luis F. Urrutia
Applied Physics · Cross-listed from cs.RO
From Rubble Simulation to Active Magnetic Mapping: Quantum Sensing for Disaster Response
Samuel Tovey, Stefan Prestel and Hiroshi Yamauchi
Locating survivors of building collapses within the first 72 hours is a critical challenge in disaster response, and existing sensing modalities provide only partial information about the structure beneath the rubble. This paper proposes drone-based
quantum magnetometry as a complementary modality and develops a simulation pipeline spanning rubble physics, sensor-array deployment, and active spatial reconstruction. We use Unreal Engine to generate a steel-reinforced concrete parking-garage collapse and compute the induced
magnetic field via a per-triangle dipole approximation, establishing that meaningful
magnetic structure is recoverable in the sub-pT to sub-nT range from roughly 1 m above the roofline. Then, we feed sparse multi-sensor samples into a Gaussian Process Regression back-end driven by
Bayesian active sampling and validate the pipeline across multiple independent collapse realizations; a three-sensor array optimizes the trade-off between gradient resolution and
UAV payload constraints, and active sampling reaches peak structural correlation in roughly $100$ samples. Together, these results indicate that
quantum-grade sensing could become a useful tool for drone-based structural analysis and potentially void detection in collapsed buildings.
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Optics · Cross-listed from cond-mat.mes-hall
High-Performance Nanophononic Resonators in Self-Suspended WSe$_2$ Domes and Drums
Jens-Christian Drawer, Bo Han, Edson Rafael Cardozo de Oliveira et al. (+7 more)
Van der Waals materials are ideally suited for the implementation of high-frequency nanophononic resonators with atomically flat interfaces. Here, we present two versatile van der Waals-based nanophononic architectures: First, we introduce self-supporting nano-domes of WSe$_2$ as a scalable platform for the simultaneous generation of hundreds of high-quality nanoacoustic resonators with resonance frequencies in the 100 GHz range. Second, we engineer self-supporting nano-drums that reach record-high working frequencies for 2D-
semiconductor transducers beyond 1 THz. Through optical pump-probe spectroscopy experiments and photoelastic linear chain model calculations, we gain a detailed understanding of the intricate interplay between phononic mode hybridization across
heterostructures, the differences between modes close to the center and edge of the acoustic Brillouin zone, and the temporal structure of the photoelastic response. Both architectures have potential applications in low-cost nanoacoustic probing and the ultrafast modulation of
quantum emitters in two-dimensional
semiconductors. While nano-drums surpass the THz frequency barrier, nano-domes appear as an accessible, low-cost alternative for developing scalable nanophononic technologies.
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All authors Jens-Christian Drawer, Bo Han, Edson Rafael Cardozo de Oliveira, Chushuang Xiang, Vita Solovyeva, Kenji Watanabe, Takashi Taniguchi, Norberto Daniel Lanzillotti-Kimura, Christian Schneider, Martin Esmann
Accelerator Physics
Dispersion Suppression for Wedge-Based Final Cooling at a 10 TeV Muon Collider
Inci Karaaslan, Karri DiPetrillo, David Neuffer et al. (+2 more)
Achieving a luminosity of $\gtrsim 10^{34} cm^{-2} s^{-1}$ in a $10 \text{ } TeV$
Muon Collider, given the short lifetime of a
muon, requires reducing the 6D emittance of the
muon beam through a process known as ionization cooling. In the final stage of this cooling process, the transverse emittance must be reduced to $22 \text{ } \mu m$, typically by allowing longitudinal emittance growth up to downstream acceptance limits. While the current International
Muon Collider Collaboration designs involve $40 \text{ } T$ solenoids to reach the transverse emittance target, such high-field solenoids come with several challenges, including mechanical stress management, quench protection, and potential limitations in relying on High Temperature
Superconductor technology. Designed as an alternative to using such solenoids while simultaneously reaching target transverse emittance, the previously proposed wedge-based, reverse emittance-exchange cooling scheme requires excellent dispersion suppression. In this study, we design and simulate a dispersion suppressor channel for the wedge-based final cooling design that reduces dispersion in the target direction to a target value of $D_x \sim 0.001 \text{ } m$.
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All authors Inci Karaaslan, Karri DiPetrillo, David Neuffer, Diktys Stratakis, Katsuya Yonehara
Atmospheric and Oceanic Physics
Event-Aware Loss Design for Forecasting of Convective Precipitation and Lightning
ChangJae Lee, Heecheol Yang and Byeonggwon Kim
Accurate
forecasting of high-impact weather, specifically extreme precipitation and lightning, remains a significant challenge in numerical weather prediction (NWP) due to the complexity of atmospheric microphysics. While deep-learning models have shown promise in large-scale
forecasting, they often suffer from systematic under-prediction of rare, high-intensity events and localized convective showers when optimized with conventional loss functions like Mean Squared Error (MSE). This study proposes an Event-Aware multi-task deep-learning post-processing framework designed to improve the representation of convective processes by leveraging lightning observations. The model jointly predicts precipitation amount, rainfall probability, and lightning occurrence using a shared-backbone Patch-cGAN (Conditional Generative
Adversarial Network) architecture. To address the rare event problem, we introduce a lightning-informed loss-weighting strategy that element-wisely multiplies the MSE component by a spatial weight map derived from observed lightning strikes, forcing the model to prioritize accuracy in convective regions during training. Evaluations conducted over the Korean Peninsula during the 2025 Summer demonstrate that our framework outperforms standard AI
benchmarks and conventional NWP models, particularly at intense rainfall thresholds (40 mm/6 h). Furthermore, the model exhibits superior skill in predicting lightning compared to conventional lightning parameterization and instability-index-based methods. These results indicate that integrating physical event indicators into the loss formulation effectively guides models to learn the meteorological signatures of deep convection, offering a pathway toward more reliable extreme weather
forecasting.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Impact of sintering conditions on the dielectric properties of TiO2 ceramics for metamaterialsapplications at terahertz frequencies
Djihad Amina Djemmah, Delphine Gourdonnaud, Faycal Bouamrane et al. (+3 more)
Titanium dioxyde (TiO2) is a promising dielectric material for the realization of metamaterials operating in the terahertz (THz) range. Indeed, these necessitate a high permittivity and low loss material. In this paper, we compare the processes of fabrication and the results of characterisation of bulk TiO2 pellets. From the results of this characterization, we have numerically designed 2D all dielectric metamaterials (ADM) showing that they may exhibit negative or near-zero effective index. Our previous simulations show that the relative permittivity epsilon has to be around 100, while the loss tangent has to be lower than 0.02. We have thus compared conventional sintering (CS) vs spark
plasma sintering (SPS), and investigated the effect of post-sintering annealing on the loss to satisfy these two criteria. The samples were characterized by THz Time Domain Spectroscopy (THz-TDS). One of the samples exhibits a loss tangent as low as 0.006, with a permittivity epsilon = 103. These results highlight the importance of the fabrication process on the EM properties of bulk TiO2, and demonstrate that it is a promising material for the development of metamaterial in the THz band.
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All authors Djihad Amina Djemmah, Delphine Gourdonnaud, Faycal Bouamrane, Jean-Francois Roux, Pierre-Marie Geffroy, Eric Akmansoy
Optics · Cross-listed from eess.IV
Improving Richardson–Lucy Deconvolution with Diffusion Priors for Fluorescence Microscopy
Hao Chen and Scott S. Howard
Richardson–Lucy (RL) deconvolution improves fluorescence microscopy images by recovering details lost to diffraction. It estimates the fluorescence signal most likely to have produced the measured
photon counts under a Poisson imaging model. However, deconvolution remains ill-posed, especially at low
photon counts, when weak biological structures become difficult to distinguish from shot noise and the prior strongly influences the reconstruction. RL recovers structure in early iterations but can amplify noise and become unstable, while regularizers such as total variation (TV) reduce these artifacts at the cost of oversmoothing. Instead, we learn a prior from real fluorescence microscopy images and use its gradient within an inverse-problem framework. The prior is estimated using an unconditional score-based
diffusion model trained on a large microscopy
dataset. At each step, the learned prior guides RL toward plausible specimen structures, while RL enforces Poisson consistency with the measured counts. Across diverse biological samples and cellular morphologies, the framework reduces RL noise amplification while better preserving weak structures at low
photon counts.
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Physics and Society
Exact Solution of Granovetter's Threshold Model for a Finite Population
José F. Fontanari
The Granovetter threshold model formalizes collective behavior by assuming that individual
agents face a binary decision to join a movement, doing so only when the number of already active participants reaches or exceeds an intrinsic, personal threshold. In this work, we derive an exact analytical expression for the probability that a cascade halts with precisely $k$ active
agents in a finite population of size $N$ triggered by a single initial instigator, and use this result to obtain the scaling corrections that govern the system near its critical boundaries. By parameterizing individual threshold heterogeneity via a Beta distribution with shape parameters $\alpha$ and $\beta$, we map how these micro-level predispositions aggregate into macro-level collective outcomes. Here, a small $\alpha$ represents a high proportion of low-threshold, highly susceptible
agents, while a small $\beta$ marks a significant density of high-threshold, conservative individuals. In the infinite-population limit, a phase transition occurs at the critical parameter $\alpha = 1$, which separates an inactive phase from a regime of widespread mobilization. For a power threshold distribution ($\beta = 1$), the system exhibits a discontinuous, first-order phase transition where the active fraction jumps abruptly from 0 to 1, and the finite-size critical scaling window contracts as $N^{-1/2}$. In stark contrast, when the population features a persistent density of high-threshold
agents ($\beta < 1$), the system undergoes an infinite-order phase transition characterized by an exceptionally smooth, continuous onset of collective activity, causing the finite-size critical region to contract at a drastically slower rate proportional to $(\ln N)^{-1}$. These analytical findings establish a mathematical
benchmark for finite-size effects in behavioral cascades.
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Biological Physics
Density-dependent growth emerges from Bayesian adaptation of phenotype
Manish Kumar Gupta, Arnab Barua and Haralampos Hatzikirou
Classical models often describe early tumor expansion as exponential growth, yet experimental and clinical evidence shows that tumor populations can deviate systematically from this behavior, exhibiting density dependent proliferation, cooperative low-density growth, intermediate growth optima, and finite upper growth bounds before resource limitation or spatial crowding dominate. These observations raise a common question: why should the per capita growth rate depend on population size? Here, we propose that sensing mismatch provides a mesoscopic link between environmental change and density dependent proliferation. We model the
cell as a
Bayesian adaptive
agent whose coarse grained phenotype evolves on an intrinsic regulatory landscape, while environmental sensing reweights phenotypic states according to how well they account for the extracellular signal statistics generated by the population. In the weak phenotype signal correlation regime, the stationary phenotype distribution is Gaussian, with its mean displaced from the proliferative optimum by a population size-dependent baseline information mismatch. This displacement produces a quadratic penalty in the per capita growth rate. Coupling the framework to a receptor ligand decoding model, we show that basal readout error and nonlinear receptor saturation make the mismatch nonmonotonic in population size. This single structure gives rise to an intermediate proliferation optimum, an Allee survival threshold, a tissue specific capacity, and superlinear scaling at low density. A phase diagram in the phenotype signal coupling and readout-error plane partitions growth into regulated, uncontrolled, and arrested regimes. Thus, density dependent proliferation need not be imposed phenomenologically, but can emerge from cellular sensing and inference.
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Computational Physics · Cross-listed from math.NA
A fast scheme for the homogeneous Boltzmann equation based on lifting and tensor train approximation
Kun Huang, Yingda Cheng and Irene M. Gamba
We propose a fast deterministic scheme for the space-homogeneous Boltzmann equation that exploits the low-rank structure of the velocity distribution. This paper consists of two independent contributions. The first is a lifting-projection (LP) scheme, inspired by the approach in the recent theoretical breakthroughs \cite{guillen2025landau, imbert2026monotonicity, guillen2025landau2} on the well-posedness of the Landau and Boltzmann equations. In particular, the approach lifts the nonlinear 3D Boltzmann equation to the 6D linear Kac master equation, advanced over a single time step, and projected back to its marginal in 3D. The second contribution is a low-rank tensor method for evaluating the collision operator, in which the lifted solution is represented in tensor train (TT) format and computed via a TT cross approximation
algorithm with interpolation, complemented by a TT-friendly conservation correction that enforces conservation of mass, momentum, and energy. When the solution is low-rank in velocity, the method scales linearly in $n$ when cubic interpolation is used (and quadratic in $n$ when spectral interpolation is used), where $n$ is the number of grid points in each velocity direction. Therefore, our methods offer significant computational savings over existing deterministic solvers in such cases. Numerical experiments on 2D and 3D
benchmarks, including the BKW exact solution and anisotropic initial data, confirm the computational scaling, the expected order of accuracy and verify the effectiveness of the conservation correction.
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Medical Physics
On the link between optoacoustic imaging and selective photothermolysis
Sergio Contador, Rodrigo Rojo, Alvaro Jimenez et al. (+1 more)
Selective photothermolysis (SP) is widely used in clinical and cosmetic dermatology to remove unwanted skin structures. Careful
laser parameter selection results in safe and effective target removal. Nevertheless, parameter selection relies on a trial-and-error process based on visual inspection of the immediate skin response. This process is highly dependent on the practitioner experience and can be time-consuming. SP and optoacoustic imaging (OI) share many physical principles. However, the possibility of using OI to improve
laser parameter selection in SP has not been studied before. Here, we explore the relationship between OI and SP theoretically and through clinical in-human trials with a focus on tattoo removal. Our results demonstrate a strong correlation between OI signals acquired before and after treatment with the immediate clinical endpoint, suggesting that OI could be used as a tool for optimal parameter selection and reduced treatment duration in tattoo removal and other SP treatments.
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All authors Sergio Contador, Rodrigo Rojo, Alvaro Jimenez, Juan Aguirre
Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci
Orientation Mapping via Dictionary Indexing of AC-STEM Kikuchi patterns using Open-source Software
Shamail Ahmed, Johannes Haust, Felix Gruber et al. (+5 more)
The properties of polycrystalline materials are strongly influenced by the spatial arrangement and orientations of individual grains within the microstructure, making nanoscale characterization of grain orientation essential. This is also often the case for small grains in the nm regime explored using scanning transmission electron microscopy (STEM). Automated
crystal orientation mapping (ACOM) is traditionally performed using spot-like diffraction patterns. In contrast, orientation mapping based on transmission Kikuchi diffraction (TKD) using an aberration-corrected (AC) convergent STEM probe remains relatively underexplored, despite its superior orientation sensitivity and higher spatial resolution. In this work, we present an open-source software-based template-matching approach for orientation mapping using AC-STEM TKD. A master pattern (a simulated angular distribution of Kikuchi band intensities on the unit sphere) is first generated through a dynamical simulation implemented in open-source software. This resulting pattern is subsequently imported into another open-source package for
geometric simulations and orientation indexing. We demonstrate the capability of the proposed method by applying it to orientation mapping in BaZr0.4Ce0.4Y0.1Yb0.1O3-{\delta} (BZCYYb4411) fuel-
cell material and LiNiO2 (LNO) lithium-ion battery cathode material. The best-matched simulated patterns exhibit strong agreement with experimental data, even under the challenging conditions with limited diffraction space available for matching.
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All authors Shamail Ahmed, Johannes Haust, Felix Gruber, Celina Becker, Juergen Belz, Andreas Beyer, Laura-Alena Schaefer, Kerstin Volz
Optics
Sensitivity of Fitting High Order Zernikes
Gregg M. Gallatin
The sensitivity of fitting Zernike coefficients to wavefront data due to an error or uncertainty in the exact position of the edge of the wavefront data is derived. The results indicate that fitting higher and higher order Zernikes rapidly becomes a useless exercise unless the true edge of the wavefront data is known with sufficient precision.
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Physics and Society
Collective variables for homophily-driven network rewiring dynamics
Sören Nagel, Stefanie Winkelmann, Péter Koltai et al. (+2 more)
Stochastic network rewiring processes, in which edges dynamically rewire based on fixed node attributes, are widely used in applications ranging from social dynamics to neuroscience and form an important component of adaptive network modelling. In this paper, we identify low-dimensional collective variables (CVs) that capture the essential macroscopic behavior of such time-evolving networks and enable reduced-order descriptions of their dynamics. To this end, we apply the data-driven transition
manifold approach to homophily-driven rewiring models, in which edges preferentially connect nodes with similar attributes. For two representative models, we find that the optimal CV is a consensus measure quantifying the fraction of edges whose incident nodes differ by less than a certain threshold. Building on the learned CV, we construct reduced macroscopic models using a data-driven approach based on sparse regression and through an analytical derivation using graphons. The latter yields a closed-form
evolution equation for the consensus measure and analytically validates the identified CV.
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All authors Sören Nagel, Stefanie Winkelmann, Péter Koltai, Nataša Djurdjevac Conrad, Marvin Lücke
Computational Physics · Cross-listed from cond-mat.supr-con
First-Principles Quantum-Spectral framework for Elementary Vortex Pinning in superconductors
Haozhe Shi, Yuncheng Xie, Tong Zhang et al. (+2 more)
The critical current of a type-II
superconductor is controlled by
vortex pinning, whose microscopic input is the elementary pinning force. Scanning tunneling spectroscopy has shown that a defect pins a
vortex by reorganizing the Caroli–de Gennes–Matricon (CdGM) states in its core, but why this spectral reorganization amounts to a pinning force has lacked a
quantum-mechanical, first-principles account. Here we establish a transferable first-principles computational framework for elementary
vortex pinning, in which defect-resolved DFT/Wannier electronic structures are embedded into a finite-box projected Bogoliubov–de Gennes free-energy formalism to convert quasiparticle spectral reorganization into
vortex-pinning energies and forces. Using this framework, we confirm that the defect-induced reorganization of the
vortex-core spectrum is the microscopic origin of the elementary pinning force. The force is evaluated as a finite-box
vortex-insertion free energy whose four-configuration subtraction isolates the meV-scale interaction from much larger backgrounds. With the superconducting gap scale and
vortex-core profile fixed from experiments, the FeSe Fe-site vacancy reproduces the microscopic STM force scale together with the measured spectral reorganization. All five point defects in FeSe and FeTe pin attractively, with FeTe Fe-site vacancy strongest. Elementary
vortex pinning thereby becomes a computable electronic-structure quantity, opening the first-principles screening of point defects toward higher critical currents.
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All authors Haozhe Shi, Yuncheng Xie, Tong Zhang, Weibin Chu, Xin-Gao Gong
Optics
Hybrid deep learning-based phase diversity method for wavefront reconstruction
Y. Rodimkov, A. Kotov, K. Burdonov et al. (+4 more)
The efficiency of high-power
laser systems is limited by wavefront distortions in the beam, particularly non-common path aberrations, which reduce the peak intensity at the focal plane. Compensating for these aberrations requires the calibration of the adaptive optics system. Conventional calibration methods rely on a time-consuming iterative optimization that is highly sensitive to initial conditions. While deep learning-based models offer high speed, they often demonstrate insufficient accuracy. In this work, we present a hybrid wavefront reconstruction method that combines a convolutional neural network to generate an initial estimate of the wavefront distortions, with the L-BFGS (Limited-
memory Broyden-Fletcher-Goldfarb-Shanno)
algorithm for its subsequent refinement. In numerical simulations, the method achieved an efficiency of $\sim 0.99$ in 80% of the cases for a root-mean-square (RMS) of wavefront distortions ranging from 0 to $1.3\lambda$. In a physical experiment, for initial wavefront distortions with RMS values from 0.15 to $0.6\lambda$, the method achieved an efficiency of $\sim 0.75$. As a result, focusing with a Strehl ratio of $0.96 \pm 0.02$ was attained within 2 to 4 iterations of the
algorithm, confirming the applicability of the method for the fast and accurate calibration of adaptive optics systems under real experimental conditions.
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All authors Y. Rodimkov, A. Kotov, K. Burdonov, S. Perevalov, V. Volokitin, I. Meyerov, A. Soloviev
Atomic Physics
Collisions and Stopping of Fast Charged Particles in Matter
Francesc Salvat
This text is intended to offer a consistent presentation of the theory of collisions and stopping of charged particles in matter, limited to the range of intermediate kinetic energies where atomic aggregation effects are relatively unimportant and processes such as the creation of particle-antiparticle pairs are not likely to occur. The first three Chapters contain introductory material on the classical description of electromagnetic fields in matter, an overview of
quantum wave equations for a particle in a central potential, and an account of elementary atomic-structure models. Chapters 4 and 5 are devoted to the classical and
quantum theories of elastic collisions of charged particles with atoms. The theory of inelastic collisions and stopping is split into two parts: first, collisions with atoms are considered within the plane-wave Born approximation in Chapter 6, which includes a derivation of the Bethe stopping power formula; second, the theory of inelastic collisions in dense materials is based on the dielectric formalism, which is formulated for the electron gas, and extended to arbitrary materials by means of optical-data models in Chapter 7. Chapter 8 offers a detailed review of the theory of stopping, starting with the classical study by Bohr and ending with derivations of the Bloch and Barkas corrections to the stopping power. Chapter 9 deals with general aspects of transport theory, including derivations of energy-straggling distributions and multiple-scattering distributions, which are the basis for condensed simulation schemes of charged particle transport. Finally, Chapter 10 describes the Fortran programs elastic and sbethe, which implement the main theoretical models presented in the preceding Chapters and are distributed as ancillary information.
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Instrumentation and Detectors · Cross-listed from cond-mat.other
Brillouin Light Scattering Spectroscopy of Propagating Magnons at Sub-Kelvin Temperatures
David Schmoll, Nikolai Kuznetsov, Phillip Rehberger et al. (+8 more)
Coupling light to
magnetic excitations in the form of
spin waves underpins both the optical study of magnetism and emerging schemes for
quantum transduction, positioning the quanta of these excitations,
magnons, as promising carriers for hybrid
quantum networks. However, exploiting them in the
quantum regime requires millikelvin temperatures to suppress thermal
magnon populations, thereby confining such experiments to dilution refrigerators. There,
magnons can already be excited and read out electrically, yet an optical interface required for microwave-to-optical
photon conversion has been missing. Here, we demonstrate the first optical detection of coherently driven, propagating
spin waves via Brillouin Light Scattering (BLS) spectroscopy inside a dilution refrigerator. By simultaneously recording the optical and electrical responses of the same
spin-wave mode in a yttrium iron garnet film, we find that the BLS spectra track the electrically measured transmission across a range of applied
magnetic fields. For the lowest optical power of 7.9 {\mu}W that still enabled
spin-wave detection, we measured a global
equilibrium sample temperature of 510 mK via a resistance thermometer, while numerical modelling of the
laser-induced heating yields a maximum local temperature of 900 mK at the focal spot. This brings free-space optical access to
magnons into the sub-kelvin regime, representing a milestone towards
magnon-mediated
quantum transduction in hybrid
quantum systems.
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All authors David Schmoll, Nikolai Kuznetsov, Phillip Rehberger, Franz Vilsmeier, Roman Verba, Denys Slobodianiuk, Rostyslav O. Serha, Khrystyna O. Levchenko, Sebastiaan van Dijken, Andrii V. Chumak, Sebastian Knauer
Atomic Physics
Coupling of negative-positive trapped-ion pairs
Daniel Kienzler
Direct motional coupling of opposite-charge trapped-ion pairs could provide a pathway to extend ultra-low temperatures and
quantum control to negative ions that lack the suitable electronic energy structures required for direct
laser cooling. Because positive and negative ions cannot be confined within a single electrostatic potential well, I investigate a configuration where single ions are trapped in close proximity within separate potential wells to couple their motion. I analytically and numerically evaluate the electrostatic trapping requirements. As a concrete implementation, I present an optimized segmented surface Paul trap design to couple an antimatter hydrogen molecular ion ($\bar{H}_2^-$) and a beryllium ion ($^9 Be^+$). A motional coupling frequency of 5 kHz can be achieved at an ion-ion separation of $35 \mu m$, with an ion height of $50 \mu m$, axial trap frequencies of 4 MHz, and static trap voltages with a magnitude of $\approx 20 V$. Finally, I outline three applications for this technique:
quantum logic spectroscopy of $\bar{H}_2^-$ for matter-antimatter comparisons, the preparation of cold neutral deuterium atoms via near-threshold photo-detachment of $D^-$ for optical trapping, and
quantum information processing using equal-mass opposite-charge ion pairs.
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Instrumentation and Detectors · Cross-listed from astro-ph.IM
On-Sky Single-photon Time resolution of 35 ps with White Rabbit synchronization: towards the measurement of the size of a White Dwarf star
F. Izraelevitch-Patitucci, S. Tolila, I. Ellafi et al. (+7 more)
The IC4
Stars (Intensity Correlation for
Stars) project aims to measure the diameter of the white
dwarf star Sirius B, using Intensity Interferometry. In this work we present our latest efforts and the milestones achieved in the last year. We report laboratory characterization of the single-
photon detectors, TDC and synchronization electronics. We describe an observation campaign where we demonstrated on-sky time resolution below 35 ps RMS, synchronizing two TDCs using the White Rabbit protocol and a 30 m telecom fiber. We developed the data acquisition of the raw time tags, and an
algorithm to compute the second-order correlation function.
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All authors F. Izraelevitch-Patitucci, S. Tolila, I. Ellafi, J.-P. Rivet, M. Hugbart, G. Labeyrie, O. Lai, A. Zmija, W. Guerin, R. Kaiser
Fluid Dynamics
Implementation and Extension of the Variance-Reduced BGK Method in PICLas
Leon Teichröb, Félix Garmirian and Marcel Pfeiffer
Traditional particle-based kinetic methods, such as DSMC, suffer from prohibitive computational cost in low-signal flows, where the deviation from thermodynamic
equilibrium is small and statistical noise overwhelms the signal of interest. The Variance-Reduced BGK-DSMC scheme is further advanced and implemented to support this class of flows in the open-source gas-kinetics framework PICLas. Modified versions of flow
estimators and collision operators enhancing stability are developed. The Shakhov and Ellipsoidal Statistical models for BGK are demonstrated, along with entirely new features such as adaptive
equilibria, variable particle weights and domain axisymmetry. The implementation is validated using synthetic
benchmarks, 1D, 2D and axisymmetric simulations. Comparison of VRBGK to BGK simulations shows exact agreement of the models. A further comparison with an analytical solution of thermal transpiration in a microchannel showcases the low-signal efficiency of the method as well as newly proposed features.
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Applied Physics · Cross-listed from quant-ph
A Candidate Framework for Free-Space Quantum Key Distribution based on Geometrical-Configuration Modulation
Yu-Ming Bai, Yu-Xuan Liu, Ming-Han Ding et al. (+1 more)
This paper proposes a candidate framework for free-space
quantum key distribution (QKD) based on geometrical-configuration modulation (GM). In the minimal implementation considered here, Alice coherently splits a single
photon emitted from one source into two spatial output modes with a tunable separation, and uses the source separation $R$ as the GM variable that defines the prepared single-
photon spatial superposition state. Bob records the single-
photon detection coordinate in the far field or
Fourier plane, providing the correlated data used for soft-input information reconciliation. Based on this physical mechanism, we first establish an $R-x$ protocol model in which the source separation $R$ and the single-
photon detection coordinate $x$ are random variables, and further propose an $R-\Delta x$ extension based on the difference variable $\Delta x$ between adjacent accepted detection events to mitigate slowly varying center drift in free-space links. The framework specifies state preparation, far-field conditional probabilities, soft-input information generation, parameter estimation, reconciliation, and asymptotic candidate key-rate formulas. A complete composable security analysis further requires derive an explicit computable upper bound on Eve's information from experimentally observed parameters, together with finite-key analysis and experimental validation under free-space conditions. The proposed candidate framework (GM-QKD) provides a modulation approach based on spatial degrees of freedom in which the source geometry serves as the modulation variable.
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All authors Yu-Ming Bai, Yu-Xuan Liu, Ming-Han Ding, Jun-Lin Li
Instrumentation and Detectors
Positron Emission Tomography with quantum-entangled Compton events: first imaging results at clinically relevant activities
Mihael Makek, Ana Marija Kožuljević, Tomislav Bokulić et al. (+4 more)
In Positron Emission
Tomography, a potential, yet unutilized enhancement, may come from exploiting the
quantum entanglement of the annihilation quanta, inscribed in the correlation of their polarizations. To investigate this, we built a PET demonstrator capable of measuring polarization correlations of annihilation quanta by their Compton scattering, based on single-layer scintillator polarimeters. We present a detailed study of the imaging of two $^{68}$Ge line sources, 45 MBq each, to extract the spatial resolution and assess image quality. The results show that a spatial resolution of 2.5$\pm$0.1 mm is obtained using single-pixel events, while resolutions obtained with polarization-correlated Compton events range from 3.6$\pm$0.3 mm to 4.9$\pm$0.3 mm, depending on data selection criteria. We also found that the polarization-correlated Compton events exhibit up to 20% higher average signal to random background ratio compared to the single-pixel events. We also present the first imaging of the NEMA NU-4 phantom filled with a $^{68}$Ga solution of 378 MBq initial activity, successfully combining polarization-correlated events with conventional single-pixel event selection. Based on the extracted spatial resolution, signal-to-background, signal-to-noise, contrast, and contrast-to-noise ratio, we estimate that up to 10% sensitivity increase may be attained by exploiting the polarization-correlated events, while preserving a high image quality.
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All authors Mihael Makek, Ana Marija Kožuljević, Tomislav Bokulić, Darko Grošev, Zdenka Kuncic, Siddharth Parashari, Luka Pavelić