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Papers

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Physics Physics

physics Watch Physics

Friday 10 April

Atmospheric and Oceanic Physics · Cross-listed from cs.LG

U-Cast: A Surprisingly Simple and Efficient Frontier Probabilistic AI Weather Forecaster

Salva Rühling Cachay, Duncan Watson-Parris and Rose Yu

AI-based weather forecasting now rivals traditional physics-based ensembles, but state-of-the-art (SOTA) models rely on specialized architectures and massive computational budgets, creating a high barrier to entry. We demonstrate that such complexity is unnecessary for frontier performance. We introduce \ours, a probabilistic forecaster built on a standard U-Net backbone trained with a simple recipe: deterministic pre-training on Mean Absolute Error followed by short probabilistic fine-tuning on the Continuous Ranked Probability Score (CRPS) using Monte Carlo Dropout for stochasticity. As a result, our model matches or exceeds the probabilistic skill of GenCast and IFS ENS at $1.5^\circ$ resolution while reducing training compute by over $10\times$ compared to leading CRPS-based models and inference latency by over $10\times$ compared to diffusion-based models. U-Cast trains in under 12 H200 GPU-days and generates a 15-day ensemble forecast in 3 seconds. These results suggest that scalable, general-purpose architectures paired with efficient training curricula can match complex domain-specific designs at a fraction of the cost, opening the training of frontier probabilistic weather models to the broader community.
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Plasma Physics

A Fully Electromagnetic Hybrid PIC-Fluid Model for Predictive Fusion Neutron Yield in Dense Plasma Focus

Yinjian Zhao, Zhe Liu, Qiang Sun et al. (+2 more)

While magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) remain the primary routes toward controlled fusion, progress is still constrained by energy loss, plasma instabilities, and the cost and complexity of large-scale facilities. The Dense Plasma Focus (DPF) device presents a compact, pulsed-power-driven alternative for producing fusion-relevant conditions and neutron emissions. However, the quantitative prediction of neutron yield in DPF devices poses a significant numerical challenge, primarily due to the imperative of self-consistently resolving kinetic ion behavior, electromagnetic energy coupling, and vacuum field evolution. This complexity often impedes a definitive understanding of the underlying neutron production mechanisms. To address this, we develop a fully electromagnetic hybrid simulation framework: ions are advanced kinetically with particle-in-cell, electrons are a quasi-neutral fluid, and Maxwell's equations are solved in both plasma and vacuum. The generalized Ohm law includes resistive, electron pressure-gradient, and Hall terms, with a predictor-corrector update for current density. We apply the model to a non-hollow 180 kA DPF geometry similar to the LLNL configuration. The simulated ion density, ion temperature, and axial electric field reproduce sheath formation, axial rundown, radial compression, and post-pinch expansion. The outer sheath front position agrees with fully kinetic benchmarks within 10% over the available comparison interval. With a compact fit to the D-D fusion cross section, the predicted total neutron yield is 0.296e7, comparable in order of magnitude to reported fully kinetic results at similar currents and nearly two orders of magnitude higher than earlier hybrid results.
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All authors Yinjian Zhao, Zhe Liu, Qiang Sun, Qianhong Zhou, Guangrui Sun

Optics

Local control and lateral nanofocusing of hyperbolic phonon polaritons

Jacob T. Heiden, Haozhe Tong, Yongjun Lim et al. (+6 more)

Phonon polaritons in van der Waals crystals enable exceptional light confinement and control over low-loss nanolight propagation. The polariton wavelength can be controlled by the crystal geometry, isotopic composition, or surrounding environment – for which substrate engineering is particularly effective. However, existing approaches of substrate nanopatterning are binary and offer limited leverage. Here, we demonstrate local control over the wavelength of phonon polaritons in hexagonal boron nitride by employing a sinusoidally corrugated gold surface to smoothly vary the gap between the van der Waals crystal and metallic substrate. The nonuniform gap provides a continuous and nearly threefold local variation of the polariton wavelength across the structure, verified by near-field optical microscopy. Our platform further enables lateral nanofocusing by gradually compressing and decompressing the wavelength of propagating polaritons by a factor of around 2.5 achieved solely through substrate geometry, consistent with our local control experiments and theoretical calculations. Our results push the boundaries of substrate engineering and showcase a powerful method for precise and local tailoring of polaritonic modes.
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All authors Jacob T. Heiden, Haozhe Tong, Yongjun Lim, Heerin Noh, Pablo Alonso-González, Alexey. Y. Nikitin, Seungwoo Lee, Sergey G. Menabde, Min Seok Jang

Atomic Physics · Cross-listed from nucl-ex

Towards better nuclear charge radii

István Angeli, Dimiter L. Balabanski, Paraskevi Dimitriou et al. (+16 more)

Nuclear charge radii constitute a physical observable of growing significance across multiple subdisciplines of physics and related fields. Their determination relies on a combination of complementary experimental techniques and advanced theoretical frameworks. Current recommended values are informed by the outcomes of several independent working groups, each employing distinct methodological approaches and evaluation strategies. The present effort is directed toward a more precise and reliable extraction of charge radii, as well as the development of a modern, transparent, and methodologically robust compilation of recommended values.
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All authors István Angeli, Dimiter L. Balabanski, Paraskevi Dimitriou, Dipti, Kieran T. Flanagan, Georgi Georgiev, Mikhail Gorchtein, Paul Gùeye, Fabian Heiße, Andreas Knecht, Kei Minamisono, Wilfried Nörtershäuser, Ben Ohayon, Natalia S. Oreshkina, B.K. Sahoo, Hunter Staiger, Endre Takacs, Xiaofei Yang, Deyan T. Yordanov

Instrumentation and Detectors

Options for RICH detectors based on silica aerogels for the high-momentum range

A.Yu. Barnyakov, V.S.Bobrovnikov, A.R.Buzykaev et al. (+8 more)

Nowadays, several projects of future colliding beam experiments are being considered in the world. Among them are the CEPC (Circular Electron Positron Collider) in China and the FCC (Future Circular Collider) at CERN (Switzerland). To perform experiments on flavor physics in the energy range of the projects an excellent particle identification up to momenta of 30 GeV/c is required. Several concepts of RICH detectors based on aerogel were considered and evaluated with the help of GEANT4 simulation: FARICH (Focusing Aerogel RICH) based on multilayer aerogel with maximal refractive index of 1.008, RICH with Fresnel lens based on aerogel with refractive index of 1.008, RICH based on transparent aerogel fibers with refractive index of 1.008. The results of the simulation are presented. Some results of beam tests at the BINP performed to validate GEANT4 simulation are presented as well.
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All authors A.Yu. Barnyakov, V.S.Bobrovnikov, A.R.Buzykaev, A.V. Chepelev, R.A. Efremov, A.F. Daniluyk, A.A. Katcin, E.A.Kravchenko, I.A. Kuyanov, A.D. Ofitserov, I.V.Ovtin

Optics

A scalable platform for nanometer-scale quantum confinement

Christina M. Spaegele, Mehdi Rezaee, Thomas Werkmeister et al. (+8 more)

Overcoming the limitations of current nanofabrication techniques to achieve nanoscale feature sizes is essential for achieving new regimes of light-matter interactions at extreme frequencies and length scales. Here, we demonstrate a scalable nanofabrication platform capable of producing in-plane feature sizes down to 1.75 nm, pushing the boundaries of current top-down nanofabrication techniques. Using precise thickness control of atomic layer deposition (ALD) and employing widely spaced oxide nanofins, we transform conventional ALD into a surface structuring method that produces nanolaminates with sub-10 nm periodicities over large areas. The resulting nanostructures can be used as a one-dimensional gate array to control charge carriers in two-dimensional materials. As an initial demonstration, we integrate the platform with graphene and perform electron transport measurements. In the presence of the gate array enabled by the nanolaminate, we observe satellite Dirac peaks consistent with band-structure modulation, suggestive of quantum-confinement effects. Our platform paves the way for exploring previously inaccessible regimes of nanoscale light-matter interactions, holding significant promise for applications in short wavelength optics, electronics, and polaritonics.
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All authors Christina M. Spaegele, Mehdi Rezaee, Thomas Werkmeister, Soon Wei Daniel Lim, Kailyn Vaillancourt, Joon-Suh Park, Paul Chevalier, Ido Kaminer, Philip Kim, Federico Capasso, Michele Tamagnone

Biological Physics · Cross-listed from cond-mat.soft

Theory of post-jamming rigidity in feedback-regulated cellular packings

Pawel Gniewek

Budding-cell packings jam before all buds are mechanically constrained, so the post-jamming state is set not by the pressure $P$ alone but also by the fraction $u$ of buds that remain unconstrained. We develop a mean-field theory in these two variables for this regime. Stress feedback suppresses growth on the loaded buds, so continued growth is redirected onto the remaining free ones. As those buds are completed they add contacts that raise the excess coordination without a comparable rise in prestress. We introduce a modified Maxwell count, a bud-depletion relation, and a flux-partition argument to predict the post-jamming coordination, the density at which the reservoir of initially free buds is exhausted, and how strong feedback can stiffen the packing while generating little internal pressure. Because the added contacts raise the rigidity while the prestress stays low, we conclude that feedback-regulated growth provides a distinct mechanism of self-rigidification.
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Optics · Cross-listed from quant-ph

Observing complementary Lucas sequences using non-Hermitian zero modes

Li Ge

The Lucas sequences are integers defined by a homogeneous recurrence relation. They include the well-known Fibonacci numbers, which appear abundantly in nature. The complementary Lucas numbers, defined by the same recurrence relation, are less well-known. In this work, we show that such complementary Lucas sequences can be observed simultaneously on the same physical platform, using zero modes in one-dimensional system(s) coupled to a non-Hermitian reservoir. When the latter consists solely of gain and loss modulated non-Hermiticity, the two Lucas sequences can manifest as a linearly localized edge state and a constant-intensity mode, respectively. When the reservoir features asymmetric couplings as well, more general Lucas sequences can be realized either directly on one sublattice in the reservoir or by reconstructing the wave function on both sublattices. Finally, if we allow, in addition, an alternate frequency detuning in the reservoir, all Lucas sequences can be observed in principle, including the Fibonacci and Lucas numbers.
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Plasma Physics

Statistical equilibrium model for stellarators

Maximilian Ruth, Joshua W. Burby, Wrick Sengupta et al. (+1 more)

In three dimensional toroidal domains without symmetry, the standard magnetohydrodynamic (MHD) equilibrium model used for magnetic confinement fusion does not generally support smooth solutions. Instead, solutions have singular plasma currents on resonant magnetic surfaces that violate the MHD assumption of length-scale separation, further leading to the non- or slow convergence of numerical approximations under refinement. In this work, we present an improved equilibrium principle derived from a statistical model for plasma fluctuations. Instead of being static, we assume that the plasma magnetic field is ergodically and rapidly fluctuating relative to the MHD time scale. By averaging the resulting force, we derive a variational equilibrium problem for the statistical mean magnetic field which depends on fluctuation variance. Then, through asymptotics, numerical simulations, and a Grad-Shafranov type argument, we show that the variational principle supports smooth solutions for specific fluctuation statistics chosen to minimally modify the standard equilibrium modeling paradigm. Physically, this model smooths singular current sheets with a length scale determined by the magnetic field fluctuations.
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All authors Maximilian Ruth, Joshua W. Burby, Wrick Sengupta, Andrew Brown

Atomic Physics

Sub-Doppler laser cooling and optical transport of cesium with static magnetic fields

Tobias Bothwell, Junxin Chen, Brian M. Fields et al. (+16 more)

Laser cooling of alkali atoms typically requires time-varying magnetic fields, introducing unwanted coupling between atom preparation and coherent operations. Here we demonstrate sub-Doppler laser cooling and optical transport of alkali atoms in a fully static magnetic-field configuration. Using a blue-detuned Type-II magneto-optical trap (MOT) operating on the closed $F=3 \rightarrow F'=2$ transition of the D2 line in cesium, we achieve temperatures of 17(1) $\mu$K without changing the magnetic-field gradient between cooling stages. This enables direct loading into a shallow optical lattice and transport over 17 cm within the same static-field environment. In contrast to conventional alkali cooling schemes with dynamic fields, our approach establishes a continuous cooling and transport protocol compatible with static-field platforms. These results validate Type-II cooling as a practical technique for alkali atoms and provide a new route toward continuous-operation architectures in sensing and quantum computing.
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All authors Tobias Bothwell, Junxin Chen, Brian M. Fields, Madeline K. Dawes, Anthony Reiter, Christina C. C. Willis, Jacob Scott, Michael McMaster, Farhad Majdeteimouri, Ilya Vinogradov, Seth Miers, Daniel C. Cole, Kevin Loeffler, Ryan A. Jones, Marin Iliev, Jonathan Gilbert, Eric Copenhaver, Thomas W. Noel, Alexander G. Radnaev

Fluid Dynamics

Universal Relation between Nusselt Number and Bejan Number in Natural Convection

Takuya Masuda and Toshio Tagawa

We propose a universal scaling law linking the Nusselt number (Nu) and the Bejan number (Be) in natural convection. Using entropy generation analysis and boundary-layer scaling, we demonstrate that Be^-1 - 1 = a Nu^b emerges independently of geometry and boundary conditions when transport is governed by a single control parameter. The relation is validated using a canonical square cavity. This result establishes a direct connection between heat transfer and thermodynamic irreversibility, revealing a fundamental constraint in convective transport.
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Optics

High-resolution long-range 3D single-photon imaging with a compact SPAD array

Zunwang Bo, Chenjin Deng, Fei Wang et al. (+6 more)

High-resolution three-dimensional imaging under photon-starved conditions remains challenging. Here, we demonstrate a high-resolution long-range 3D single-photon imaging system based on a digital micromirror device (DMD) and a compact 64 multiply 64 single-photon avalanche diode (SPAD) array. By combining high-resolution spatial modulation with parallel time-resolved detection, the system extends the effective spatial sampling beyond the native detector format while preserving depth information through time-of-flight measurement. In outdoor experiments at a stand-off distance of 670 m, we achieved 3D reconstruction of natural targets with an effective spatial resolution of 256 multiply 256. These results validate the proposed method as an effective approach for high-resolution long-range 3D single-photon imaging using compact SPAD arrays.
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All authors Zunwang Bo, Chenjin Deng, Fei Wang, Wenlin Gong, Yuanhao Su, Yichen Zhang, Mingliang Chen, Chunfang Wang, Shensheng Han

Fluid Dynamics

Effects of Nozzle Roughness on the Streamwise Streaks in Underexpanded Jets – An Experimental Study

Haohan Gong and Shengkai Wang

The present study investigated the formation of streamwise streaks in underexpanded jets from round sonic nozzles, based on direct experimental observation using high-speed schlieren imaging and PLIF methods. The effect of geometric perturbations of the nozzle exit on the streamwise flow structure was examined through a series of comparative experiments. Underexpanded jets were generated in a vacuum chamber using phi-4 mm nozzles of two different configurations: (a) a "smooth" nozzle, shaped and polished by a high-quality commercial lathe machine; and (b) nozzles with artificially introduced sinusoidal perturbation of various wavenumbers on the circular contour of the exit. In the case of the "smooth" nozzle, experiments were repeated following a 60-degree rotation of the nozzle along its axis, and a similar rotation in the streak patterns was observed. This suggests that the streamwise streaks most likely originated from geometric perturbations caused by the minute roughness at the nozzle exit. In the latter case, the effects of modal distribution of geometric perturbation on the streaks were further investigated. The results showed that the low-wavenumber (k < 5) perturbations exhibited much smaller growth rates of streamwise streaks - likely dominated by residual roughness similar to the "smooth" case - compared to higher-wavenumber (k = 6 and 7) perturbations, where the streak patterns were observed to correlate geometrically with the perturbed nozzle exit contour. Results from the present study should prove useful in enhancing the current understanding of noise patterns in supersonic wind tunnel tests, where nozzles are critical components.
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Thursday 9 April

Biological Physics

Engineering quantum optical responses of microtubules through tryptophan-network simulations and ultraviolet spectroscopy

Lea Gassab and Travis J. A. Craddock

Microtubules host dense ultraviolet-absorbing aromatic networks, suggesting an opportunity to engineer their optical response for biotechnology. Here we assess the feasibility of tuning microtubule fluorescence by combining an excitonic radiative-coupling model with molecular-dynamics-derived microtubule-like assemblies and steady-state absorbance and fluorescence measurements in microplate geometries. Simulations quantify how positional and orientational fluctuations reshape radiative rates and quantum yield, and predict how perturbing the tryptophan network by removing a specific site, adding an extra tryptophan at candidate binding pockets, or using mixed modification fractions can modulate emission. Experiments on porcine tubulin dimers and taxol-stabilized microtubules support these trends: polymerization enhances microtubule quantum yield at 280 nm and yields bounded changes at 295 nm due to scattering, while added L-tryptophan reproducibly quenches microtubules at both wavelengths. Together, theory and experiment provide evidence for chemically addressable tuning of microtubule quantum yield and motivate design rules for engineered microtubule photonics.
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Instrumentation and Detectors

Toward Neutrino and Dark Matter Detection with Ancient Minerals: TEM Study of Heavy-Ion Tracks in Olivine

Andrew Calabrese-Day, Emilie LaVoie-Ingram, Kathryn Ream et al. (+5 more)

Solar, supernova, and atmospheric neutrinos, and possibly weakly interacting massive particle (WIMP) dark matter, have been interacting in the Earth beneath our feet for billions of years. The ”paleo-detector” technique seeks to detect and characterize the induced crystalline defects from these events, in particular from energetic nuclear recoils, which in some minerals can be preserved on these timescales. Such defects can manifest as nuclear recoil tracks, on the order of a few nanometers wide and extending up to hundreds of microns in length, which can be detected with nanoscale-resolution microscopy. In order to test the feasibility of the paleo-detector technique and to study the formation and morphology of track defects in promising mineral candidates like olivine, we use ion irradiation to artificially implant tracks to effectively mimic astrophysical particle interactions. We present a study of heavy-ion track width as a function of depth, which we relate to ion energy, in an olivine crystal irradiated with 15 MeV Au$^{+5}$ using scanning transmission electron microscopy (STEM). Unlike previous studies, which measure tracks at the surface of the irradiated sample, we instead take measurements at various target depths via focused ion-beam sectioning of the irradiated sample. No etching techniques are used to enhance the tracks. In addition, we provide a comparison to predictions from simulations using SRIM software and previous results with a variety of ion species and energies. Notably, we find that a significant change in track continuity across the energy range studied (0.4-12.9 MeV) is indicative of the transition between electronic and nuclear stopping power dominance, consistent with the simulations' predictions. Overall, the tracks produced in olivine indicate that this mineral is an attractive candidate for paleo-detection, with robust track creation at the MeV scale.
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All authors Andrew Calabrese-Day, Emilie LaVoie-Ingram, Kathryn Ream, Hannah Ross, Joshua Spitz, Patrick Stengel, Kai Sun, Alexander Takla

Applied Physics · Cross-listed from cs.CV

Data-Driven Automated Identification of Optimal Feature-Representative Images in Infrared Thermography Using Statistical and Morphological Metrics

Harutyun Yagdjian and Martin Gurka

Infrared thermography (IRT) is a widely used non-destructive testing technique for detecting structural features such as subsurface defects. However, most IRT post-processing methods generate image sequences in which defect visibility varies strongly across time, frequency, or coefficient/index domains, making the identification of defect-representative images a critical challenge. Conventional evaluation metrics, such as the signal-to-noise ratio (SNR) or the Tanimoto criterion, often require prior knowledge of defect locations or defect-free reference regions, limiting their suitability for automated and unsupervised analysis. In this work, a data-driven methodology is proposed to identify images within IRT datasets that are most likely to contain and represent structural features, particularly anomalies and defects, without requiring prior spatial information. The approach is based on three complementary metrics: the Homogeneity Index of Mixture (HI), which quantifies statistical heterogeneity via deviations of local intensity distributions from a global reference distribution; a Representative Elementary Area (REA), derived from a Minkowski-functional adaptation of the Representative Elementary Volume concept to two-dimensional images; and a geometrical-topological Total Variation Energy (TVE) index, also based on two-dimensional Minkowski functionals, designed to improve sensitivity to localized anomalies. The framework is validated experimentally using pulse-heated IRT data from a carbon fiber-reinforced polymer (CFRP) plate containing six artificial defects at depths between 0.135 mm and 0.810 mm, and is further supported by one-dimensional N-layer thermal model simulations. The results demonstrate robust and unbiased ranking of image sequences and provide a reliable basis for automated defect-oriented image selection in IRT.
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Physics Education

Instructor Framing and Incentives Shape Physics Students' Engagement and Learning Gains from an Inquiry-Based Electrostatics Tutorial on the Method of Images

Jaya Shivangani Kashyap, Robert P. Devaty and Chandralekha Singh

The method of images (MoI) is a valuable technique for solving certain electrostatic boundary value problems consisting of charge density near conductor(s). We developed and validated an inquiry-based tutorial on MoI to help students learn to identify the problems related to the concept. We implemented the inquiry-based tutorial accompanied by pretest and posttest, across three instructors' classes to evaluate student learning. We also conducted think-aloud interviews with advanced physics students, which helped us gain insights into their problem-solving strategies, evaluate their understanding developed through the tutorial and make necessary refinements to the MoI tutorial. The study identified common student difficulties, which were subsequently integrated into the inquiry-based tutorial as a guide to provide support to students. We found that advanced students have common difficulties related to physics concepts similar to those found in introductory physics courses. The performance difference in the pretest administered after lecture-based instruction and the posttest administered after working through the tutorial reflects students' ability to apply what they learned from the inquiry-based tutorial compared to traditional lecture. Another important and unanticipated finding reveals how instructor's framing about inquiry-based instructional tasks can have a significant impact on student motivation, engagement, and performance. Overall, this iterative multi-year design-based comparative research with mixed-method triangulation provides valuable insights on the challenges involved in such studies that educators and researchers alike can greatly benefit from.
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Data Analysis and Statistics

New Deep Learning Data Analysis Method for PROSPECT using GAPE: Genetic Algorithm Powered Evolution

M. Adriamirado, A. B. Balantekin, C. Bass et al. (+40 more)

We propose a genetic algorithm powered evolution (GAPE) method to create deep learning solutions for energy and position estimation for reactor antineutrino interactions in the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT) at the highly enriched High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. We also apply GAPE to create classification models to distinguish signatures of inverse beta decay (IBD) interactions of reactor antineutrinos from common background types. The GAPE method can also be adopted for optimization of other types of problems that utilize machine learning (ML) models for particle physics applications. When applied in the PROSPECT context, we find that the models selected by GAPE can, in some cases, outperform the traditional models previously used for PROSPECT data analysis. In particular, when benchmarked against conventional PROSPECT neutrino identification pathways using the same underlying information, the classifier offers the promise of improving the signal-to-background ratio by nearly 2.8 times. Performance biases uncovered during initial IBD classifier validation were primarily caused by differences in time-dependent response between background and signal training datasets. Biases were effectively mitigated through a data-period-specific training regimen, offering a pathway towards realizing an unbiased IBD signal classifier for future reactor neutrino datasets.
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All authors M. Adriamirado, A. B. Balantekin, C. Bass, O. Benevides Rodrigues, E. P. Bernard, N. S. Bowden, C. D. Bryan, T. Classen, A. J. Conant, N. Craft, A. Delgado, G. Deichert, M. J. Dolinski, A. Erickson, M. Fuller, A. Galindo-Uribarri, S. Ghosh, S. Gokhale, C. Grant, S. Hans, A. B. Hansell, T. E. Haugen, K. M. Heeger, B. Heffron, A. Irani, J. Koblanski, C. E. Lane, B. R. Littlejohn, A. Lozano Sanchez, J. Maricic, F. Machado, M. P. Mendenhall, A. M. Meyer, R. Milincic, P. E. Mueller, H. P. Mumm, R. Neilson, C. Roca, R. Rosero, D. Venegas-Vargas, J. Wilhelmi, M. Yeh, X. Zhang

Chemical Physics · Cross-listed from astro-ph.EP

The Fate of Frozen Carbonated Water at Europa-like Conditions

Swaroop Chandra, William T.P. Denman and Michael E. Brown

We present the results of experiments probing the retention of CO2 in crystalline water ice, frozen sodium chloride (NaCl) brines, and flash-frozen carbonated water using diffuse reflectance infrared spectroscopy. Characteristic absorptions alluding to the formation of clathrate hydrates in crystalline ices and frozen brines are observed. NaCl in frozen brines does not affect qualitatively affect the formation of clathrate hydrates. Generation and stability of clathrates in crystalline ice transiently subjected to pressure-temperature (P-T) conditions in the stability region is observed, despite conditions being unviable at the onset of freezing. Retention of CO2 in flash-frozen carbonated water is observed to be dependent on the temperature of the substrate during freezing. The state of CO2 retained in the resulting ices differs from clathrate hydrates, as inferred from the respective infrared spectra. Both mechanisms of CO2 retention are stable up to 140 K and under evacuated conditions. In the context of Europa, the P-T states traversed by the samples plausibly represent the typical conditions around endogenous CO2 if it is indeed transported from the subsurface ocean to the surface while being retained in ice/frozen brines and/or liquid emerging on the surface. However, the absorptions of CO2 in the laboratory infrared spectra do not match those detected on the leading side of Europa by the NIRSpec instrument on board JWST. Therefore, it is unlikely that the endogenous CO2 observed at the surface of Europa is sourced directly from the ocean, unless additional processes affect the observed bands of CO2 on Europa.
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Optics · Cross-listed from nlin.PS

Homoclinic and heteroclinic solutions of the nonlinear Schrödinger equation with a complex Wadati potential

Sathyanarayanan Chandramouli, Patrick Sprenger and Mark A. Hoefer

Stationary solutions asymptoting to nonlinear plane waves of the nonlinear Schrödinger equation with a PT-symmetric, complex linear potential are characterized. The potential includes both a spatially varying gain-loss profile and a repulsive real part, generated by a Wadati potential function,that support the existence of homoclinic and heteroclinic solutions that asymptote to the same or different, respectively, nonlinear plane waves in the far field. Asymptotic analysis and numerical simulations are used to examine solution existence, bifurcations, and structure. Such solutions play an important role in resonant nonlinear wave generation of dispersive media with localized gain and loss.
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Computational Physics · Cross-listed from cs.SI

Hierarchical Community Detection in Bipartite Networks

Tania Ghosh and Kevin E. Bassler

Many bipartite networks exhibit hierarchical community structure, but existing community detection methods are not well-suited for detecting hierarchy. They also do not effectively handle weighted bipartite networks. In this work, we introduce a novel modularity-based objective function, called the generalized bipartite modularity density, Qbg, specifically designed for hierarchical community detection in bipartite systems. The framework incorporates a tunable resolution parameter that enables systematic exploration of community structure across multiple scales. It leverages resolution-limit behavior in bipartite networks as a tool to uncover hierarchical organization without projecting the network or altering its intrinsic bipartite topology. We evaluate the method using a hierarchical synthetic bipartite benchmark and apply it to two empirical networks. In all cases, Qbg recovers established mesoscale structure while revealing additional hierarchical and fine-scale organization beyond that detected by conventional bipartite approaches. These results establish Qbg as a flexible, interpretable, and resolution-aware framework for hierarchical community detection in bipartite networks.
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Instrumentation and Detectors · Cross-listed from astro-ph.IM

Development of the New Optical Sensor for IceCube-Gen2

Delaney Butterfield and Chris Wendt

A new digital optical module (DOM) has been developed for the proposed expansion to the IceCube detector at the South Pole, IceCube-Gen2. The "Gen2-DOM" has 4 times the integrated photon sensitivity of the current IceCube DOMs and has built off the design features of the IceCube Upgrade modules. The Gen2-DOM has up to 18 4" photomultiplier tubes (PMTs) in a borosilicate glass pressure vessel, arranged in a uniform 4$\pi$ angular distribution. The mechanical design has been optimized to fit into a reduced borehole diameter which, in turn, will reduce drilling costs during installation. Each PMT has a dedicated readout board, designed to increase sensitivity to high-energy events aligned with the science goals of IceCube-Gen2. Internal storage enables multi-level triggering schemes with reduced overall flow of data on the long cables. Twelve prototypes of the Gen2-DOM will be deployed in the IceCube Upgrade in the 2025-2026 austral summer. This article will focus on the current status of design development and initial performance testing results.
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Medical Physics · Cross-listed from eess.IV

PSIRNet: Deep Learning-based Free-breathing Rapid Acquisition Late Enhancement Imaging

Arda Atalik, Hui Xue, Rhodri H. Davies et al. (+4 more)

Purpose: To develop and evaluate a deep learning (DL) method for free-breathing phase-sensitive inversion recovery (PSIR) late gadolinium enhancement (LGE) cardiac MRI that produces diagnostic-quality images from a single acquisition over two heartbeats, eliminating the need for 8 to 24 motion-corrected (MOCO) signal averages. Materials and Methods: Raw data comprising 800,653 slices from 55,917 patients, acquired on 1.5T and 3T scanners across multiple sites from 2016 to 2024, were used in this retrospective study. Data were split by patient: 640,000 slices (42,822 patients) for training and the remainder for validation and testing, without overlap. The training and testing data were from different institutions. PSIRNet, a physics-guided DL network with 845 million parameters, was trained end-to-end to reconstruct PSIR images with surface coil correction from a single interleaved IR/PD acquisition over two heartbeats. Reconstruction quality was evaluated using SSIM, PSNR, and NRMSE against MOCO PSIR references. Two expert cardiologists performed an independent qualitative assessment, scoring image quality on a 5-point Likert scale across bright blood, dark blood, and wideband LGE variants. Paired superiority and equivalence (margin = 0.25 Likert points) were tested using exact Wilcoxon signed-rank tests at a significance level of 0.05 using R version 4.5.2. Results: Both readers rated single-average PSIRNet reconstructions superior to MOCO PSIR for dark blood LGE (conservative P = .002); for bright blood and wideband, one reader rated it superior and the other confirmed equivalence (all P < .001). Inference required approximately 100 msec per slice versus more than 5 sec for MOCO PSIR. Conclusion: PSIRNet produces diagnostic-quality free-breathing PSIR LGE images from a single acquisition, enabling 8- to 24-fold reduction in acquisition time.
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All authors Arda Atalik, Hui Xue, Rhodri H. Davies, Thomas A. Treibel, Daniel K. Sodickson, Michael S. Hansen, Peter Kellman

Computational Physics · Cross-listed from cond-mat.mtrl-sci

Including sample shape in micromagnetics with 3D periodic boundary conditions

Frederik Laust Durhuus, Andrea Roberto Insinga and Rasmus Bjørk

Periodic boundary conditions (PBCs) for computing magnetic fields in repeating magnetic structures, e.g. in micromagnetic simulations, are typically imposed using the quasi periodic macrogeometry approach, where many copies of the simulated domain are introduced. This can be computationally problematic, especially if the simulated domain is incommensurate with the desired sample shape. In this work, we present a formal proof that for sufficiently large magnetic samples, only the average magnetisation gives non-negligible shape effects. Using this insight, we develop a simple, computationally efficient modification of existing implementations which incorporates shape effects in PBC methods.
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Atmospheric and Oceanic Physics

CERBERUS: A Three-Headed Decoder for Vertical Cloud Profiles

Emily K. deJong, Nipun Gunawardena, Kevin Smalley et al. (+2 more)

Atmospheric clouds exhibit complex three-dimensional structure and microphysical details that are poorly constrained by the predominantly two-dimensional satellite observations available at global scales. This mismatch complicates data-driven learning and evaluation of cloud processes in weather and climate models, contributing to ongoing uncertainty in atmospheric physics. We introduce CERBERUS, a probabilistic inference framework for generating vertical radar reflectivity profiles from geostationary satellite brightness temperatures, near-surface meteorological variables, and temporal context. CERBERUS employs a three-headed encoder-decoder architecture to predict a zero-inflated (ZI) vertically-resolved distribution of radar reflectivity. Trained and evaluated using ground-based Ka-band radar observations at the ARM Southern Great Plains site, CERBERUS recovers coherent structures across cloud regimes, generalizes to withheld test periods, and provides uncertainty estimates that reflect physical ambiguity, particularly in multilayer and dynamically complex clouds. These results demonstrate the value of distribution-based learning targets for bridging observational scales, introducing a path toward model-relevant synthetic observations of clouds.
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All authors Emily K. deJong, Nipun Gunawardena, Kevin Smalley, Hassan Beydoun, Peter Caldwell

Optics

Unlocking the O-Band Coherent Transmission: high-power, broadband soliton microcomb

Dmitrii Stoliarov, Nikolay G. Pavlov, Aleksandr Donodin et al. (+15 more)

The O-band (1260-1360 nm), located near the minimum chromatic dispersion of standard single-mode fiber, is an important transmission window for short-reach data-center interconnects. Its broader use is limited by the availability of scalable multi-wavelength, high-power and low-noise light sources. Here we demonstrate a high-power O-band soliton microcomb architecture combining an 834 GHz self-injection-locked (SIL) Si3N4 microcomb spanning 1050-1650 nm with a single-stage bismuth-doped phosphosilicate fiber amplifier. The system delivers > 0 dBm per carrier for 21 O-band comb lines over a 100 nm bandwidth, exhibiting low-noise operation and a 5 dB variation in amplifier gain. We validate the amplified source in a 25-km coherent WDM transmission experiment using 32-GBd dual-polarisation 64-QAM. Comb carriers spanning the O-band are characterised under simultaneous WDM loading, yielding an aggregate GMI-estimated throughput of 7.23 Tb/s and a post-FEC throughput of 6.94 Tb/s. This approach establishes a practical route towards broadband, high-power O-band microcomb sources for multi-terabit optical interconnects.
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All authors Dmitrii Stoliarov, Nikolay G. Pavlov, Aleksandr Donodin, Daniel J. Elson, Vitaly Mikhailov, Jiawei Luo, Sergey Koptyaev, Robert Emmerich, Ruben S. Luis, Hideaki Furukawa, Colja Schubert, Ronald Freund, Yuta Wakayama, Takehiro Tsuritani, David J.DiGiovanni, John D.Jost, Maxim Karpov, Sergei K. Turitsyn

2604.08767 · 9 Apr · We conducted a 25-km single-span coherent WDM transmission experiment using amplified carriers from a single SIL microcomb source. Comb lines spanning the O-band were simultaneously modulated and transmitted through the fibre, extending the original back-to-back characterisation to a system-level demonstration of broadband coherent transmission under simultaneous WDM loading

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Chemical Physics

Cryogenic hydrogen embrittlement of 316plus (EN 1.4420) stainless steel at 77 K and 20 K

W. Li, A. Zafra, L. Armendariz et al. (+4 more)

This paper presents the first experimental characterisation of combined hydrogen-temperature effects in 316plus (EN 1.4420), a new austenitic stainless steel for liquid hydrogen (LH2) storage. Uniaxial tensile tests were conducted at room temperature (RT), 77 K and 20 K on uncharged and hydrogen-precharged specimens, complemented by fractography and EBSD-based quantification of strain-induced martensite (SIM). 316plus exhibited cryogenic strengthening at 77 K and 20 K by enhanced SIM formation. Hydrogen did not influence strength at RT or 77 K and caused a modest decrease (~10%) at 20 K, keeping 316plus at the upper bound of cryogenic strength for 316L. The presence of hydrogen resulted in significant reductions in ductility at all temperatures, being most severe at 77 and 20K (~40-50%). Hydrogen suppressed SIM at 20 K, but SIM fraction did not correlate with ductility reduction. Despite the combined effect of temperature and hydrogen, 316plus retained notable ductility (reduction in area ~30%).
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All authors W. Li, A. Zafra, L. Armendariz, Z. Wang, W. Bailey, E. Martinez-Pañeda, S. Afshan

Chemical Physics

Active Learning for Generalizable Detonation Performance Prediction of Energetic Materials

R. Seaton Ullberg, Megan C. Davis, Jeremy N. Schroeder et al. (+5 more)

The discovery of new energetic materials is critical for advancing technologies from defense to private industry. However, experimental approaches remain slow and expensive while computational alternatives require accurate material property inputs that are often costly to obtain, limiting their ability to efficiently predict detonation performance across a vast chemical space. We address this challenge through an active learning strategy that integrates density functional theory calculations, thermochemical modeling, message-passing neural networks, and Bayesian optimization. The resulting high-throughput workflow iteratively expands the training dataset by selecting new molecules in a targeted manner that balances the exploration of broad chemical space with the exploitation of promising high-performing candidates. This approach yields the largest publicly available database of potential CHNO explosives drawn from an initial pool of more than 70 billion candidates and a generalizable surrogate model capable of accurately predicting detonation performance (R$^2$ > 0.98). Feature importance analysis on this largest-to-date dataset reveals that oxygen balance is the dominant driver of detonation performance, complemented by contributions from local electronic structure, density, and the presence of specific functional groups. Cheminformatics analysis highlights how energetic materials with similar performance metrics tend to cluster in distinct chemical spaces offering a clearer direction for future synthesis studies. Together, the surrogate model, database, and resulting chemical insights provide a valuable foundation for high-throughput screening and targeted discovery of new energetic materials spanning diverse and previously unexplored regions of chemical space.
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All authors R. Seaton Ullberg, Megan C. Davis, Jeremy N. Schroeder, Andrew H. Salij, M. J. Cawkwell, Christopher J. Snyder, Wilton J. M. Kort-Kamp, Ivana Matanovic

Applied Physics · Cross-listed from quant-ph

Frequency resolved optical gating using parametric amplification for characterizing ultrafast temporally multimode squeezed states

Elina Sendonaris, Thomas Zacharias, Robert Gray et al. (+2 more)

Temporally multimode squeezed states have been a topic of recent interest due to their applications in quantum communication, information processing, and sensing. Characterizing the mode shapes is crucial for effectively manipulating these states, but current mode shape and state characterization techniques necessitate constraining assumptions and complicated experimental setups. Here, we propose a characterization technique that simultaneously recovers the complex temporal mode shapes and quadrature variances of ultrafast multimode squeezed states based on frequency resolved optical gating (FROG) using an optical parametric amplifier (OPA). FROG is a promising tool for quantum state characterization due to its flexibility of implementation and high temporal resolution. Using an OPA as the nonlinear process in FROG has the benefit of amplifying weak quantum states to a detectable level while preserving quantum information. Numerical simulations demonstrate the recovery of the mode shapes and levels of squeezing and anti-squeezing of ultrafast multimode squeezed states. This scheme offers a practical experimental approach to measuring arbitrary temporal mode shapes and characterizing large-scale multimode ultrafast Gaussian quantum states.
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All authors Elina Sendonaris, Thomas Zacharias, Robert Gray, James Williams, Alireza Marandi

Atomic Physics · Cross-listed from cond-mat.quant-gas

Immiscible to miscible quenching instabilities in two-dimensional binary Bose-Einstein condensates

Lauro Tomio, S. Sabari, Arnaldo Gammal et al. (+1 more)

Immiscible to miscible quenching transitions (IMQT) in homogeneous Bose-Einstein condensate are investigated, considering rubidium isotopes $^{85}$Rb and $^{87}$Rb confined in a two-dimensional (2D) circular box, under two different initial configurations. These IMQT instabilities, triggered by sudden reductions in the two-body interspecies scattering length $a_{12}$, are explored under two distinct initialconditions, highlighting the critical role of nonlinear dynamics in their evolution. The numerical simulations indicate that the instability dynamics are primarily driven by the production of large vortices and the propagation of sound waves (phonons), with sound wave excitations prevailing in the long-term evolution. The compressible and incompressible parts of the kinetic energy spectra, in terms of the wave number $k$, are confronted with the classical Kolmogorov scaling, $k^{-5/3}$ for turbulence, which is observed in the onset of instabilities. Before reaching the ultraviolet dissipation region at small scales, the IMQT spectra exhibit a bottleneck effect, indicating a clear departure from classical scaling behavior. In the time asymptotic miscible regime, it is observed that the vorticity and sound-wave production remain practically stable. In this regime, for both cases investigated, a linear relation is also recognized between the miscibility parameter and the initial IMQT configuration.
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All authors Lauro Tomio, S. Sabari, Arnaldo Gammal, R. K. Kumar