Chemical Physics · Cross-listed from quant-ph
Experimental Quantification of Spin-Phonon Coupling in Molecular Qubits using Inelastic Neutron Scattering
Stefan H. Lohaus, Kay T. Xia, Yongqiang Cheng et al. (+1 more)
Electronic
spin superposition states enable nanoscale sensing through their sensitivity to the local environment, yet their sensitivity to vibrational motion also limits their coherence times. In molecular
spin systems, chemical tunability and atomic-scale resolution are accompanied by a dense, thermally accessible
phonon spectrum that introduces efficient
spin relaxation pathways. Despite extensive theoretical work, there is little experimental consensus on which vibrational energies dominate
spin relaxation or how molecular structure controls
spin-
phonon coupling (SPC). We present a fully experimental method to quantify SPC coefficients by combining temperature-dependent vibrational spectra from inelastic
neutron scattering with
spin relaxation rates measured by electron paramagnetic resonance. We apply this framework to two model S = 1/2 systems, copper(II) phthalocyanine (CuPc) and copper(II) octaethylporphyrin (CuOEP). Two distinct relaxation regimes emerge: below 40 K, weakly coupled
lattice modes below $50~\mathrm{cm}^{-1}$ dominate, whereas above 40 K, optical
phonons above ~$185~\mathrm{cm}^{-1}$ become thermally populated and drive relaxation with SPC coefficients nearly three orders of magnitude larger. Structural distortions in CuOEP that break planar
symmetry soften the
crystal lattice and enhance anharmonic scattering, but also raise the energy of stretching modes at the molecular core where the
spins reside. This redistributes vibrational energy toward the molecular periphery and out of plane, ultimately reducing SPC relative to CuPc and enabling room-temperature
spin coherence in CuOEP. Although our method does not provide mode-specific SPC coefficients, it quantifies contributions from distinct spectral regions and establishes a broadly applicable, fully experimental link between
crystal structure,
lattice dynamics, and
spin relaxation.
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All authors Stefan H. Lohaus, Kay T. Xia, Yongqiang Cheng, Ryan G. Hadt
Computational Physics · Cross-listed from cs.LG
Structure-Preserving Learning Improves Geometry Generalization in Neural PDEs
Benjamin D. Shaffer, Shawn Koohy, Brooks Kinch et al. (+2 more)
We aim to develop physics foundation models for science and engineering that provide real-time solutions to Partial Differential Equations (PDEs) which preserve structure and accuracy under adaptation to unseen geometries. To this end, we introduce General-Geometry Neural Whitney Forms (Geo-NeW): a data-driven finite element method. We jointly learn a differential operator and compatible reduced finite element spaces defined on the underlying geometry. The resulting model is solved to generate predictions, while exactly preserving physical conservation laws through Finite Element Exterior Calculus. Geometry enters the model as a discretized mesh both through a
transformer-based encoding and as the basis for the learned finite element spaces. This explicitly connects the underlying geometry and imposed boundary conditions to the solution, providing a powerful inductive bias for learning neural PDEs, which we demonstrate improves generalization to unseen domains. We provide a novel parameterization of the constitutive model ensuring the existence and uniqueness of the solution. Our approach demonstrates state-of-the-art performance on several steady-state PDE
benchmarks, and provides a significant improvement over conventional baselines on out-of-distribution geometries.
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All authors Benjamin D. Shaffer, Shawn Koohy, Brooks Kinch, M. Ani Hsieh, Nathaniel Trask
Applied Physics
A bulk acoustic resonator with vertical electrodes for wideband filters
Silvan Stettler, Edgar Navarro-Gesse, Carlos Collado et al. (+2 more)
Radiofrequency (RF) front ends for current and next generation (5G and 6G) wireless communication demand acoustic filters that combine wide bandwidth, high power capability, and thermal stability. Existing surface and bulk acoustic wave (SAW and BAW) technologies face inherent trade-offs between electromechanical coupling, lithographic tunability, and robustness. Here we introduce the bulk acoustic resonator with vertical electrodes (VBAR), a device that combines the advantages of suspended and solidly mounted resonators. VBARs use lithium niobate (LiNbO3) ridges with sidewall electrodes to excite a shear-horizontal bulk acoustic resonance, providing frequency control through lithography in a configuration that is mechanically anchored to the substrate. Fabricated VBARs exhibit electromechanical coupling coefficients exceeding 30% in the 2-4 GHz range, enabling ladder filters with fractional bandwidths of nearly 20%. While further optimization is necessary to minimize losses, the VBAR concept offers an alternative route toward wideband and robust RF filters for next-generation wireless systems.
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All authors Silvan Stettler, Edgar Navarro-Gesse, Carlos Collado, Jordi Mateu, Luis G. Villanueva
Optics · Cross-listed from cond-mat.mes-hall
Single-Emitter Spectra from an Ensemble
Jonah R. Horowitz, Oliver J. Tye, Oliver M. Nix et al. (+5 more)
The heterogeneity in nanoscale emitters hinders efforts to understand their basic photophysics and limits their use in practical applications. Existing methods have difficulty accurately characterizing single-emitter spectra and optical heterogeneity on a statistical scale. Here, we introduce SPICEE (SPectrally Imbalanced Correlations from Ensemble Emission), a spectrally filtered
photon-correlation technique that recovers single-particle emission lineshapes from an ensemble sample. Analytical derivations, numerical modeling, and experiments on a solution ensemble of emitters validate the technique. We apply SPICEE to blue-emitting ZnSeTe
semiconductor nanocrystals relevant to display applications and find that the low color purity in the ensemble spectrum is primarily caused by a small subpopulation of nanocrystals with a distinct emission mechanism. This work demonstrates that SPICEE is a powerful high-throughput tool for accurately characterizing the single-emitter properties of nanoscale systems.
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All authors Jonah R. Horowitz, Oliver J. Tye, Oliver M. Nix, Shaun Tan, Hogeun Chang, Ji Hyun Min, Taehyung Kim, Moungi G. Bawendi
Optics
Gear-based 3D-printed Micromachines Actuated by Optical Tweezers
Alaa M. Ali, Gwenn Ulliac, Edison Gerena et al. (+4 more)
The miniaturization of mechanical mechanisms is crucial to enable the development of compact, high-performance micromachines. However, the downscaling actuation of conventional gears and micromotors has remained limited by the inherent challenges of implementing mechanical/electrical powering. Here, we present the design, fabrication, and characterization of an optomechanical, gear-driven micromachine realized through two-
photon polymerization 3D printing. The actuation is achieved using optical tweezers. The device integrates a microgear transmission system with an optically actuated part, enabling light-controlled micromachines. When illuminated by a highly focused
laser source, the first gear generates rotational torque within the gear assembly, converting optical energy into directional mechanical work that can be transmitted to the coupled gear. We demonstrate the fabrication of micromachines using two-
photon polymerization (2PP)
laser writing, enabling the fabrication of spur gear trains and bevel gears that can produce out-of-plane rotations, which is not achievable with traditional micromachining fabrication techniques. The micromachines are composed of a single gear or a train of two or three gears without any unwanted adhesion between the components, leading to functioning systems. Experimentally, the fabricated micromachines were actuated using optical tweezers, demonstrating continuous gear rotation, effective motion transmission in gear trains, out-of-plane rotations, and the ability to amplify velocity or torque. Optical-tweezer actuation broadens the potential applications of these micromachines, particularly in biomedical and lab-on-a-chip systems, where precise, minimally invasive control at the microscale is essential.
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All authors Alaa M. Ali, Gwenn Ulliac, Edison Gerena, Abdenbi Mohand-Ousaid, Sinan Haliyo, Aude Bolopion, Muamer Kadic
Applied Physics · Cross-listed from cond-mat.mes-hall
Universal reconstructive polarimetry with graphene-metal infrared photodetectors
Valentin Semkin, Kirill Kapralov, Ilya Mazurenko et al. (+8 more)
Recent advent of smart photodetectors, where in-situ tuning of responsivity enables the reconstruction of light intensity, polarization and spectrum by a single device, has revolutionized the field of optoelectronics. So far, most such reconstructive detectors were realized with non-scalable technology of van der Waals stacking. Here, we demonstrate the infrared reconstructive polarimetry with photodetectors based on conventional gated
graphene-metal junctions. The reconstruction exploits the gate tuning of polarization contrast, which enables the determination of both infrared power and polarization angle from photovoltage measurements at two different gate voltages. The physics enabling the polarimetry lies in polarization-dependent shift of the electron hot spot near the contact, and the gate tuning of photosensitive barrier width. We further show the universality of polarization reconstruction, i.e. its feasibility with different geometries of the junction, and with
graphene of different quality, from boron-nitride encapsulated flakes to the scalable chemical vapor deposited films.
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All authors Valentin Semkin, Kirill Kapralov, Ilya Mazurenko, Mikhail Kashchenko, Alexander Morozov, Yakov Matyushkin, Dmitry Mylnikov, Denis Bandurin, Li Lin, Alexey Bocharov, Dmitry Svintsov
Atmospheric and Oceanic Physics
The Design and Performance of Meteorological Sensors for WindBorne Global Sounding Balloons
Jake Spisak, Christopher P. Riedel, Andrey Sushko et al. (+10 more)
WindBorne Systems has developed a constellation of long-duration atmospheric balloons to collect meteorological data across the globe, filling gaps in current in-situ data collection methods. Each Global Sounding Balloon (GSB) is capable of flying for weeks or months and performing dozens of soundings while measuring pressure, temperature, humidity, and GNSS-derived position, altitude, and wind velocity. This data is transmitted to ground via satellite, processed, and made available within minutes of being collected. The current meteorological sensor package has remained largely unchanged since mid-2024 and has flown on thousands of GSBs totaling over one million hours of flight time. Here we present the design and performance of this sensor package. The custom readout architecture and housing allow for data collection across nearly all in-flight conditions while minimizing sources of bias and noise. Uncertainty is characterized via sounding reproducibility studies and in-house calibration of pressure, humidity, and temperature sensors. The calibration and data processing procedures have been optimized and validated by comparison with external
datasets. We present external validation in the form of 1) side-by-side radiosonde launches performed in collaboration with the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography, which show agreement within expected uncertainty limits, and 2) intercomparison studies with European Centre for Medium-Range Weather Forecasts Reanalysis v5, which show an aggregate root mean square difference of: Geopotential height – 14 m; Pressure – 0.36 hPa; Temperature – 0.91 K; Wind speed u – 2.45 m/s; Wind speed v – 2.50 m/s; Relative humidity – 13%.
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All authors Jake Spisak, Christopher P. Riedel, Andrey Sushko, Michal Adamkiewicz, Joan Creus-Costa, John Dean, Jacob Radford, F. Martin Ralph, Larissa Reames, Anna M. Wilson, Subin Yoon, Vijay Tallapragada, Todd Hutchinson
Medical Physics
Perfusion Imaging and Single Material Reconstruction in Polychromatic Photon Counting CT
Namhoon Kim, Ashwin Pananjady, Amir Pourmorteza et al. (+1 more)
Background: Perfusion computed
tomography (CT) images the dynamics of a contrast
agent through the body over time, and is one of the highest X-ray dose scans in medical imaging. Recently, a theoretically justified reconstruction
algorithm based on a monotone variational inequality (VI) was proposed for single material polychromatic
photon-counting CT, and showed promising early results at low-dose imaging. Purpose: We adapt this reconstruction
algorithm for perfusion CT, to reconstruct the concentration map of the contrast
agent while the static background tissue is assumed known; we call our method VI-PRISM (VI-based PeRfusion Imaging and Single Material reconstruction). We evaluate its potential for dose-reduced perfusion CT, using a digital phantom with water and iodine of varying concentration. Methods: Simulated iodine concentrations range from 0.05 to 2.5 mg/ml. The simulated X-ray source emits
photons up to 100 keV, with average intensity ranging from $10^5$ down to $10^2$
photons per detector element. The number of tomographic projections was varied from 984 down to 8 to characterize the tradeoff in
photon allocation between views and intensity. Results: We compare VI-PRISM against filtered back-projection (FBP), and find that VI-PRISM recovers iodine concentration with error below 0.4 mg/ml at all source intensity levels tested. Even with a dose reduction between 10x and 100x compared to FBP, VI-PRISM exhibits reconstruction quality on par with FBP. Conclusion: Across all
photon budgets and angular sampling densities tested, VI-PRISM achieved consistently lower RMSE, reduced noise, and higher SNR compared to filtered back-projection. Even in extremely
photon-limited and sparsely sampled regimes, VI-PRISM recovered iodine concentrations with errors below 0.4 mg/ml, showing that VI-PRISM can support accurate and dose-efficient perfusion imaging in
photon-counting CT.
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All authors Namhoon Kim, Ashwin Pananjady, Amir Pourmorteza, Sara Fridovich-Keil
Space Physics
Ionospheric Observations from the ISS: Overcoming Noise Challenges in Signal Extraction
Rachel Ulrich, Kelly R. Moran, Ky Potter et al. (+3 more)
The Electric Propulsion Electrostatic Analyzer Experiment (ÈPÈE) is a compact ion energy bandpass filter deployed on the International Space Station (ISS) in March 2023 and providing continuous measurements through April 2024. This period coincides with the
Solar Cycle 25 maximum, capturing unique observations of
solar activity extremes in the mid- to low-latitude regions of the topside ionosphere. From these in situ spectra we derive
plasma parameters that inform space-weather impacts on satellite
navigation and
radio communication. We present a statistical processing pipeline for ÈPÈE that (i) estimates the instrument noise floor, (ii) accounts for irregular temporal sampling, and (iii) extracts ionospheric signals. Rather than discarding noisy data, the method learns a baseline noise model and fits the measurement surface using a scaled Vecchia Gaussian process approximation, recovering values typically rejected by thresholding. The resulting products increase data coverage and enable noise-assisted monitoring of ionospheric variability.
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All authors Rachel Ulrich, Kelly R. Moran, Ky Potter, Lauren A. Castro, Gabriel R. Wilson, Carlos Maldonado
Instrumentation and Detectors
A rapid low-background assay of $^{210}$Pb in archaeological lead
M. Consonni, M. Clemenza, E. Di Stefano et al. (+11 more)
In this work, we present a fast and highly efficient method for the measurement of $^{210}$Pb in metallic archaeological lead using the commercial low-background
liquid scintillation counter Wallac Quantulus 1220 installed at the University of Milano-Bicocca (Italy). By combining an optimized chemical preparation with pulse-shape analysis (PSA), the technique achieves sensitivities at the level of a few $10^2$ mBq/kg within one week of measurement, using sample masses below 1 g. The method enables the simultaneous identification of the $\beta$ decays of $^{210}$Pb and $^{210}$Bi and the $\alpha$ decay of $^{210}$Po, allowing a direct verification of secular
equilibrium within the decay chain. With extended acquisition times, detection limits below 100 mBq/kg are reached after approximately 40 days. This approach provides a rapid, accessible, and reliable tool for the radiopurity screening of lead, and is well suited for quality control and R&D activities in next-generation low-background and rare-event physics experiments. Moreover, the method has the potential to be extended to other materials relevant for low-background applications.
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All authors M. Consonni, M. Clemenza, E. Di Stefano, N. Ferreiro Iachellini, F. Filippini, A. Gardini, G. Grosso, L. Pattavina, R. Della Pergola, S. Quitadamo, E. Sala, F. Saliu, A. Salvini, L. Trombetta
History and Philosophy of Physics · Cross-listed from astro-ph.CO
Probabilistic inference in very large universes
Feraz Azhar, Alan H. Guth and Mohammad Hossein Namjoo
[Abridged] Some cosmological theories propose that the observable universe is a small part of a much larger universe in which parameters describing the low-energy laws of physics vary from region to region. How can we reasonably assess a theory that describes such a mostly unobservable universe? We propose a
Bayesian method based on theory-generated probability distributions for our observations. We focus on basic principles, leaving aside concerns about practicality. (We also leave aside the measure problem, to discuss other issues.) We argue that cosmological theories can be tested by standard
Bayesian updating, but we need to use theoretical predictions for "first-person" probabilities – i.e., probabilities for our observations, accounting for all relevant selection effects. These selection effects can depend on the observer, and on time, so in principle first-person probabilities are defined for each observer-instant – an observer at an instant of time. First-person probabilities should take into account everything the observer believes about herself and her surroundings – i.e., her "subjective state". We advocate a "Principle of Self-Locating Indifference" (PSLI), asserting that any real observer should make predictions as if she were chosen randomly from the theoretically predicted observer-instants that share her subjective state. We believe the PSLI is intuitively very reasonable, but also argue that it maximizes the expected fraction of observers who will make correct predictions. Cosmological theories will in general predict a set of possible universes, each with a probability. To calculate first-person probabilities, we argue that each possible universe should be weighted by the number of observer-instants in the specified subjective state that it contains. We also discuss Boltzmann
brains, the humans/Jovians parable of Hartle and Srednicki, and the use of "old evidence".
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Optics
Extrinsic Limitations of Stealthy Hyperuniform devices
Yuhao Xu, Miao Chen, Louis Forestier et al. (+3 more)
Hyperuniformity promises an unusual form of wave control: the suppression of elastic scattering over extended angular ranges without periodic order. Here, we present a comprehensive experimental and theoretical study of 2D stealthy hyperuniform metasurfaces operating at optical frequencies. In agreement with theoretical expectations, we observe a pronounced reduction of elastic scattering around the specular direction in metasurfaces fabricated by electron-beam lithography. However, the measured suppression is substantially weaker than that predicted by structure-factor calculations based on ideal stealthy hyperuniform point-pattern generators. We identify and quantitatively analyze the physical origins of this discrepancy and establish realistic performance bounds. By isolating the dominant limiting mechanisms, our results provide practical design guidelines for the implementation of stealthy hyperuniformity in functional devices.
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All authors Yuhao Xu, Miao Chen, Louis Forestier, Franck Carcenac, Laurent Mazenq, Philippe Lalanne
General Physics
Discrete dynamical systems with scaling and inversion symmetries
Vaguiner Rodrigues dos Santos, Enrique Chipicoski Gabrick, Edson Denis Leonel et al. (+1 more)
In this work, we investigate scale invariance in the temporal
evolution and chaotic regime of discrete dynamical systems. By exploiting the close interrelation between scaling and inversion transformations, we formulate scale
symmetry in terms of inversion
symmetry. As applications of our approach, we determine fractal dimensions and compute Lyapunov exponents for paradigmatic dynamical systems using scaling and inversion
symmetries. By comparing our method with standard approaches, we obtain identical numerical values for the Lyapunov exponents using only a small number of iterations. Furthermore, our
geometric-based framework naturally provides access to the fractal dimension. The agreement with standard results demonstrates that the proposed method is efficient and can be effectively employed in the study of dynamical systems.
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All authors Vaguiner Rodrigues dos Santos, Enrique Chipicoski Gabrick, Edson Denis Leonel, Iberê Luiz Caldas
Fluid Dynamics · Cross-listed from math.NA
A space-time LATIN-PGD strategy for solving Newtonian compressible flows
Élise Foulatier, Pierre-Alain Boucard, François Louf et al. (+2 more)
Simulating flow problems is at the core of many engineering applications but often requires high computational effort, especially when dealing with complex models. This work presents a novel approach for resolving flow problems using the LATIN-PGD solver. In this contribution, we place ourselves within the framework of Newtonian compressible and laminar flows. This specific and relatively simple case enables focusing on flows for which a state equation provides a direct relation between pressure and density. It is then possible to use the LATIN solver to set up a pressure-velocity decoupling
algorithm. Moreover, Proper Generalised Decomposition (PGD) is natively included in the solver and yields two independent space-time decompositions for the velocity and the pressure fields. As a first step, the solver is validated on a problem for which an analytical solution is available. It is then applied to slightly more complex problems. The results show good agreement with the literature, and we expect that the solver could be used to compute more complicated material laws in the future.
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All authors Élise Foulatier, Pierre-Alain Boucard, François Louf, David Néron, Philipp Junker
Popular Physics
Réflexions sur la puissance motrice du Soleil
Daniel Suchet, Nathan Roubinowitz and Jean-François Guillemoles
A quintessential source of heat, the Sun radiates toward the Earth a power ten thousand times greater than humanity's energy needs. Harnessing this energy bounty, however, requires capturing and converting sunlight. Today, this conversion can be achieved through several families of technologies at varying stages of maturity: photovoltaic
solar, thermal, concentrated
solar power, and more. While their applications differ, all these technologies must meet common fundamental constraints, and as Carnot proposed, one can 'consider in all its generality the principle of producing motion through heat' from the Sun. However, unlike traditional 'heat engines,' the coupling with the hot source here is radiative, introducing specific constraints that must be accounted for. In this presentation dedicated to radiative machines, you will encounter familiar terms as well as particular expressions that will provide the keys to understanding
solar technologies
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Medical Physics · Cross-listed from cs.CV
Multi-head automated segmentation by incorporating detection head into the contextual layer neural network
Edwin Kys and Febian Febian
Deep learning based auto
segmentation is increasingly used in radiotherapy, but conventional models often produce anatomically implausible false positives, or
hallucinations, in slices lacking target structures. We propose a gated multi-head
Transformer architecture based on Swin U-Net, augmented with inter-slice context integration and a parallel detection head, which jointly performs slice-level structure detection via a multi-layer perceptron and pixel-level
segmentation through a context-enhanced stream. Detection outputs gate the
segmentation predictions to suppress false positives in anatomically invalid slices, and training uses slice-wise Tversky loss to address class imbalance. Experiments on the Prostate-Anatomical-Edge-Cases
dataset from The Cancer Imaging Archive demonstrate that the gated model substantially outperforms a non-gated
segmentation-only baseline, achieving a mean Dice loss of $0.013 \pm 0.036$ versus $0.732 \pm 0.314$, with detection probabilities strongly correlated with anatomical presence, effectively eliminating spurious
segmentations. In contrast, the non-gated model exhibited higher variability and persistent false positives across all slices. These results indicate that detection-based gating enhances robustness and anatomical plausibility in automated
segmentation applications, reducing hallucinated predictions without compromising
segmentation quality in valid slices, and offers a promising approach for improving the reliability of clinical radiotherapy auto-contouring workflows.
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Optics
Numerically optimized FROG results for the study of red-shifted spectra in multi-frequency Raman generation
Sakthi Priya Amirtharaj, Zujun Xu, Donna Strickland et al. (+7 more)
When multifrequency Raman scattering is driven in the transient regime by two chirped pump pulses, the resulting anti-Stokes orders exhibit asymmetric spectral broadening toward lower frequencies, leading to a characteristic double-peaked structure in each order. In this Letter, frequency-resolved optical gating (FROG) is used to investigate the spectral
evolution of the first anti-Stokes Raman component. To interpret the observed features, we introduce a double-pulse interference model and employ an adaptive learning-based reconstruction
algorithm using the Adam optimizer to retrieve the temporal field
evolution. The simulation results show good agreement with the experimental measurements. Our analysis indicates that the observed red-shifted spectral component originates from linear Raman processes within the two-
photon dressed-state framework.
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All authors Sakthi Priya Amirtharaj, Zujun Xu, Donna Strickland, Borun Chowdhury, Sagnik Acharya, Priyam Samantray, Anil Prabhakar, Kisor Kumar Sahu, Franz Bamer, S. Swayamjyoti
Space Physics · Cross-listed from astro-ph.IM
X-ray characterization of fully-depleted p-channel Skipper-CCDs for the DarkNESS mission
Phoenix Alpine, Ana M. Botti, Brenda A. Cervantes-Vergara et al. (+11 more)
The Dark matter Nanosatellite Equipped with Skipper Sensors (DarkNESS) mission is a 6U CubeSat designed to search for X-ray lines from decaying dark matter using Skipper-CCDs. Thick, fully-depleted p-channel Skipper-CCDs provide low readout noise and high
quantum efficiency for 1-10 keV X-rays, but their X-ray performance has not yet been demonstrated in the space environment. DarkNESS will operate in low-Earth orbit, where trapped
protons induce displacement damage in the sensor that increases charge-transfer inefficiency and degrades the X-ray energy resolution. This work measures the X-ray line response of Skipper-CCDs before and after
proton irradiation and quantifies the associated degradation. A sensor was exposed to 217 MeV
protons at a fluence of 8.4 x 10^10
protons cm^-2, corresponding to a displacement-damage dose more than an order of magnitude above the three-year expectation for representative mid-inclination and Sun-synchronous low-Earth orbits. A 55Fe source was used to compare the energy resolution of the beam-exposed quadrant to adjacent unexposed quadrants and a non-irradiated reference sensor. These measurements provide a quantitative assessment of radiation-induced spectral degradation in Skipper-CCDs and enable an estimate of the end-of-life X-ray energy resolution expected for DarkNESS operation in low-Earth orbit.
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All authors Phoenix Alpine, Ana M. Botti, Brenda A. Cervantes-Vergara, Claudio R. Chavez, Fernando Chierchie, Alex Drlica-Wagner, Juan Estrada, Erez Etzion, Michael Lembeck, Pilar López Maggi, Joseph Noonan, Brandon Roach, Nathan Saffold, Javier Tiffenberg
Instrumentation and Detectors · Cross-listed from astro-ph.IM
Depth Calibration of Double-sided Strip Germanium Detectors for the Compton Spectrometer and Imager Satellite
Field R. Rogers, Sean N. Pike, Samer Alnussirat et al. (+12 more)
Double-sided strip high-purity germanium detectors with three-dimensional position reconstruction capability have been developed over three decades, with space-based applications in high-energy astrophysics and heliophysics. Position resolution in three dimensions is key to reconstruction of Compton scattering events, including for the upcoming Compton Spectrometer and Imager (COSI) satellite mission. Two-dimensional position reconstruction is enabled by
segmentation of the two detector faces into orthogonal strip contacts, enabling a pixelized analysis. The depth of an interaction cannot be measured directly but must be inferred from the charge collection time difference between the two faces of the detector. Here, we demonstrate for the first time the depth calibration of a detector with the COSI satellite geometry read out using an application specific integrated
circuit (ASIC) developed for the COSI mission. In this work, we map collection time difference to depth using the Julia-based simulation package SolidStateDetectors$.$jl and validate it with comparison to the timing distributions observed in data. We also use simulations and data to demonstrate the depth resolution on a per-pixel basis, with >90% of pixels having <0.9 mm (FWHM) resolution at 59.5 keV and <0.6 mm (FWHM) resolution at 122.1 keV.
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All authors Field R. Rogers, Sean N. Pike, Samer Alnussirat, Robin Anthony-Petersen, Steven E. Boggs, Felix Hagemann, Sophia E. Haight, Alyson Joens, Carolyn Kierans, Alexander Lowell, Brent Mochizuki, Albert Y. Shih, Clio Sleator, John A. Tomsick, Andreas Zoglauer
Fluid Dynamics · Cross-listed from astro-ph.SR
Nonlinear interaction between dynamo-generated magnetic fields, mean flows and internal gravity waves in stellar stably-stratified layers: From 3D to 1D
Florentin Daniel, Ludovic Petitdemange, Charly Pinçon et al. (+3 more)
Magnetic fields have been constrained at the surface of several massive and intermediate-mass
stars, but their origin and properties in deep
stellar radiative interiors are still debated, despite recent detections in the core of some red
giant stars. Therefore, the modelling of AM transport in
stellar radiative layers only relies on theoretical and numerical estimates of
magnetic fields. Recent 3D numerical simulations show that a dynamo could occur in deep radiative regions. A realistic setup for understanding AM transport in such layers thus requires to take into account the mutual interactions of IGW and dynamo-generated
magnetic field. We model the dynamics induced by IGW and dynamo in rotating radiative
stellar layers using a simple description applicable to various evolutionary stages. As dynamo action and the propagation of IGW are 3D processes that have characteristic timescales short compared to periods associated with structural
evolution of
stars, we propose a mean-field 1D model by taking advantage of the dynamo coefficients computed from 3D spherical simulations. In this model, the necessary mean shear flow to trigger the dynamo results from the dissipation of monochromatic IGW generated in existing adjacent convective layers, which are expected to drive the formation of an oscillating rotational shear layer, the so-called Shear Layer Oscillation (SLO). In turn,
magnetic effects can act on the mean flow through the Lorentz force. We show that the inclusion of
magnetic fields adds up to the already very complex nonlinear problem and gives rise to the emergence of new dynamical regimes. Particularly, the fast SLO generated very close to the place where IGW are generated is perturbed by
magnetic fields. This dynamical change can filter the wave energy spectrum transmitted towards further layers, with potential influence on the long-term
evolution of the inner rotation.
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All authors Florentin Daniel, Ludovic Petitdemange, Charly Pinçon, Kévin Belkacem, Bruno Longo, Christophe Gissinger
Optics
Impact of interference between two infrared pulses driving high harmonic generation
Sarang Dev Ganeshamandiram, Jahanzeb Muhammad, Marvin Schmoll et al. (+4 more)
Extreme ultraviolet (XUV) interferometry is technically challenging to implement. One approach to generating interference between two XUV pulses relies on driving high-harmonic generation in a gas jet with two collinearly overlapping infrared
laser pulses. We investigate this scheme through a combined experimental and theoretical study, with particular emphasis on the regime of temporal overlap between the driving pulses. A special phase-modulation interferometry technique is implemented to increase the sensitivity for the comprehensive mapping of the strong-field induced high-order nonlinear response. We find that the dynamics arising from the interference of the two electric fields can be adequately described by the non-perturbative model developed by Lewenstein and co-workers.
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All authors Sarang Dev Ganeshamandiram, Jahanzeb Muhammad, Marvin Schmoll, Ronak Shah, Frank Stienkemeier, Giuseppe Sansone, Lukas Bruder
Applied Physics · Cross-listed from cs.RO
SoMA: A Real-to-Sim Neural Simulator for Robotic Soft-body Manipulation
Mu Huang, Hui Wang, Kerui Ren et al. (+5 more)
Simulating deformable objects under rich interactions remains a fundamental challenge for real-to-sim
robot manipulation, with dynamics jointly driven by environmental effects and
robot actions. Existing simulators rely on predefined physics or data-driven dynamics without
robot-conditioned control, limiting accuracy, stability, and generalization. This paper presents SoMA, a 3D Gaussian Splat simulator for soft-body manipulation. SoMA couples deformable dynamics, environmental forces, and
robot joint actions in a unified latent neural space for end-to-end real-to-sim simulation. Modeling interactions over learned Gaussian splats enables controllable, stable long-horizon manipulation and generalization beyond observed trajectories without predefined physical models. SoMA improves resimulation accuracy and generalization on real-world
robot manipulation by 20%, enabling stable simulation of complex tasks such as long-horizon cloth folding.
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All authors Mu Huang, Hui Wang, Kerui Ren, Linning Xu, Yunsong Zhou, Mulin Yu, Bo Dai, Jiangmiao Pang
Physics and Society
Patterns in Conflict Dynamics in Yemen and Syria
Moussa Abdou and Neil F. Johnson
Conflict fatalities tend to follow heavy-tailed statistical distributions. A 2005 fusion-fission theory predicts mathematically that for armed groups operating in dynamically evolving clusters within a given conflict, the number of fatalities per conflict event will follow an approximate power-law distribution with exponent near 2.5, with the specific exponent value offering insight into the relative robustness of larger versus smaller clusters of fighters in that armed group. Since Yemen and Syria are current hotspots for future conflict, yet their most recent conflicts (2023-2025) have not been studied at the event level, we use ACLED data to determine their best-fit exponent value as each conflict evolved. We find that the exponent lies between 2.5 and 3.5 predominantly throughout each conflict, which suggests that the fighters in each of these conflicts continued to operate in smaller clusters as the conflict evolved. Moreover, temporary reductions in the exponent value – which suggests a temporary increase in the robustness and involvement of larger clusters of fighters – appear to arise during major crises ahead of the largest battles. Though the lack higher-quality data for these conflicts prevents us from establishing this more firmly, such a temporary reduction in the exponent value hints at its potential use as an early-warning signature.
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Space Physics
Geoelectric Field Caused by Flux Transfer Events in an Ionosphere-Coupled Vlasiator Simulation
Konstantinos Horaites, Markku Alho, Yann Pfau-Kempf et al. (+10 more)
We report on the relationship between flux transfer events (FTEs) at Earth's magnetopause and the geoelectric field that is induced near the FTEs'
magnetic footpoints. We study this system using the global hybrid-Vlasov code Vlasiator, which has recently been extended to model ionospheric physics. We also highlight the significance of 3D
magnetic null points, which in our simulation can separate the FTEs into multiple flux ropes. Near the null points, the coiled FTE
magnetic field lines are rerouted towards Earth, so that the
magnetic footpoints are planted near the Region 1 ionospheric current system. The helicities of the flux ropes are organized by the y-component (GSE) of the
magnetic field at the Earth's magnetopause. This occurs in our simulation due to the absence of a y-component of the interplanetary
magnetic field, which would normally supply the FTE guide field that determines the helicity. We observe Alfvenic, Earthward-flowing field-aligned currents generated near the magnetopause that correlate with the passage of FTEs nearby. These pulses of current coincide with the formation of rotational geoelectric field structures, that appear near the noon meridian and propagate around the auroral oval towards the nightside.
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All authors Konstantinos Horaites, Markku Alho, Yann Pfau-Kempf, Urs Ganse, Abiyot Workayehu, Jonas Suni, Fasil Tesema, Liisa Juusola, Giulia Cozzani, Sanni Hoilijoki, Ivan Zaitsev, Shiva Kavosi, Minna Palmroth
Chemical Physics
FragmentFlow: Scalable Transition State Generation for Large Molecules
Ron Shprints, Peter Holderrieth, Juno Nam et al. (+2 more)
Transition states (TSs) are central to understanding and quantitatively predicting chemical reactivity and reaction mechanisms. Although traditional TS generation methods are computationally expensive, recent generative modeling approaches have enabled chemically meaningful TS prediction for relatively small molecules. However, these methods fail to generalize to practically relevant reaction substrates because of distribution shifts induced by increasing molecular sizes. Furthermore, TS geometries for larger molecules are not available at scale, making it infeasible to train generative models from scratch on such molecules. To address these challenges, we introduce FragmentFlow: a divide-and-conquer approach that trains a generative model to predict TS geometries for the reactive core atoms, which define the reaction mechanism. The full TS structure is then reconstructed by re-attaching substituent fragments to the predicted core. By operating on reactive cores, whose size and composition remain relatively invariant across molecular contexts, FragmentFlow mitigates distribution shifts in generative modeling. Evaluated on a new curated
dataset of reactions involving reactants with up to 33 heavy atoms, FragmentFlow correctly identifies 90% of TSs while requiring 30% fewer saddle-point optimization steps than classical initialization schemes. These results point toward scalable TS generation for high-throughput reactivity studies.
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All authors Ron Shprints, Peter Holderrieth, Juno Nam, Rafael Gómez-Bombarelli, Tommi Jaakkola
Fluid Dynamics
Transition to dilatation-dominated isothermal compressible turbulence
Shadab Alam, Christoph Federrath and Jörg Schumacher
The kinetic energy dissipation rate is of central importance for small-scale statistics in turbulent flows. Here, we report a transition to the dilatation-dominated regime of three-dimensional isothermal fully compressible, homogeneous, isotropic
turbulence by moments of energy dissipation and its components up to order~4 for root-mean-square (rms) Mach numbers $0.1\le M_{\rm rms}\le 10$ and for Reynolds numbers $100\le Re\le 2400$. Our high-resolution numerical simulations show a crossover from incompressible to $M_{\rm rms}$–independent, Burgers
turbulence-like scaling of energy dissipation rate moments with respect to Reynolds number $Re$. This confirms the statistical dominance of shocks for rms Mach numbers $M_{\rm rms}\gtrsim 1$.
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Classical Physics · Cross-listed from cs.LG
A Physical Theory of Backpropagation: Exact Gradients from the Least-Action Principle
Antonino Emanuele Scurria
Backpropagation is typically presented as a symbolic procedure: a backward pass topologically distinct from inference, with non-local error signals and synchronous global clocking, features with no clear analog in physical reality. Existing physics-inspired alternatives recover gradients only approximately, in vanishing-perturbation limits, or under weight-
symmetry constraints incompatible with feedforward architectures. In this paper, we address this gap by deriving exact backpropagation from Hamilton's least-action principle. By recasting the forward dynamics in continuous time and adapting a Lagrangian formalism for non-conservative systems to the resulting flow, we unify inference and gradient computation within a single variational framework on a doubled phase space, whose two conjugate fields jointly encode activations and sensitivities. A single global Lagrangian governs the dynamics: the task loss enters as a
symmetry-breaking perturbation of the forward
manifold, and credit assignment emerges as the tension that develops between the conjugate states. Inference and gradient computation thus unfold simultaneously through local interactions, requiring no separate backward
circuit. Ultimately, standard backpropagation is recovered exactly as the discrete-time projection of this continuous flow. This perspective unifies the formalism of physics with backpropagation, opening a principled pathway for applying tools from classical mechanics -
symplectic geometry, Noether's
theorem, path-integral methods - to the analysis of learning dynamics. As a downstream consequence, it also points toward analog and neuromorphic substrates in which learning is
embodied in the hardware itself.
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Optics
Electrically reconfigurable dipolar polaritons with highly tunable nonlinearity in a homobilayer microcavity
Baixu Xiang, Yubin Wang, Guihan Wen et al. (+9 more)
Active control over optical nonlinearity in solid-state systems is central to unlocking exotic many-body phenomena and photonic devices. While
exciton-polaritons in transition metal dichalcogenides (TMDs) offer a promising platform, their practical utility is impeded by fixed interactions and a trade-off between nonlinearity and oscillator strength. Here, we report electrically tunable dipolar polaritons in a dual-gated
bilayer MoS2 microcavity, demonstrating in situ reshaping of the dispersion and modulation of the light-matter coupling strength via the
quantum-confined Stark effect. Crucially, this electrical control yields a seven-fold enhancement of the polariton-polariton interaction strength. This enhancement arises from the combined tuning of the effective
exciton-
exciton interaction and the excitonic Hopfield coefficient. In addition, electrostatic doping provides an independent knob to continuously drive a strong-to-weak coupling crossover. Our findings establish dual-gated TMD homobilayer as a versatile platform for on-chip, dynamically reconfigurable nonlinear light-matter physics.
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All authors Baixu Xiang, Yubin Wang, Guihan Wen, Yitong Li, Hao Wen, Zengde She, Haiyun Liu, Kenji Watanabe, Takashi Taniguchi, Timothy C. H. Liew, Zhiyuan Sun, Qihua Xiong
Optics · Cross-listed from cond-mat.mtrl-sci
Energy-Transfer-Enhanced Emission and Quantum Sensing of VB- Defects in hBN-PbI2 Heterostructures
Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio et al. (+6 more)
Spin defects in two-dimensional materials hold significant potential for
quantum information technologies and sensing applications. The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has attracted considerable
attention as a
quantum sensor due to its demonstrated sensitivity to temperature,
magnetic fields, and pressure.1 However, its applications have thus far been limited by inherently dim photoluminescence (PL). By fabricating a van der Waals
heterostructure with a sensitizing donor layer, lead iodide (PbI2), we effectively enhance the PL intensity from the VB- by 5-45x, while maintaining compatibility with other
heterostructures and vdW optoelectronic platforms. The type-I band
alignment at the heterojunction enables efficient
exciton migration while suppressing back-electron transfer, and the strong spectral overlap between the PbI2 emission and defect absorption supports efficient fluorescence resonance energy transfer. Ab initio density functional theory (DFT) predicts a
photon-ratcheting mechanism that boosts absorption and emission while maintaining
magnetic resonance (ODMR) contrast through minimal hybridization. Experimentally, the
heterostructure exhibits enhanced continuous-wave ODMR sensitivity and functions as a precise probe of external
magnetic fields. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, highlighting a new strategy for engineering their optical and
magnetic responses.
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All authors Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio, Feihong Chu, Prabhu Swain, Georg Fantner, Andras Kis, Oleg Yazyev, Aleksandra Radenovic
Fluid Dynamics · Cross-listed from math.NA
A new Energy Equation Derivation for the Shallow Water Linearized Moment Equations
Julian Koellermeier
Shallow Water Moment Equations (SWME) are extensions to the well-known Shallow Water Equations (SWE) for the efficient modeling and numerical simulation of free-surface flows. While the SWE typically assume a depth-averaged vertical velocity profile, the SWME allow for vertical variations of the velocity profile. The SWME therefore assume a
polynomial profile and then derive additional
evolution equations for the
polynomial coefficients via higher order depth integration. In this work, we perform a new systematic derivation of the energy equation for a specific variant of the SWME, called the Shallow Water Linearized Moment Equations (SWLME). The derivation is based on the standard SWE energy equation derivation and includes the skew-symmetric formulation of the model. The new systematic derivation is beneficial for the extension to other SWME variants and their numerical solution.
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