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Physics Physics

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Computational Physics

A quantum-assisted latent surrogate model for Bayesian inversion of heterogeneous material properties on NISQ hardware

Dewangga Alfarisy, Catherine F. Higham and Eky Febrianto

Bayesian inversion is widely used in engineering applications, including material characterisation, structural damage identification, and medical diagnostics. These inverse problems are typically ill-posed, because localised variations in material properties must be inferred from noisy observations, and they are computationally intensive, since they often require many evaluations of a high-fidelity forward solver. Quantum computing has recently attracted considerable interest, partly because some near-term algorithms are feasible on NISQ hardware. In particular, PQC combined with classical optimisation enable a hybrid quantum-classical surrogate model. A central obstacle to applying such circuits to inversion is that the discretised parameter and response fields are far too high-dimensional to be embedded in a near-term quantum register. In this work we propose a quantum-assisted latent surrogate model for the Bayesian inversion of inhomogeneous material properties, in which latent compression bridges these high-dimensional fields and the small registers accessible to near-term circuits. The low intrinsic dimensional structure of the spatially varying conductivity and potential fields is exploited by reducing the conductivity through PCA and the response through a convolutional autoencoder. A PQC is then trained to map the latent conductivity to the latent response, and stochastic variational inference is performed entirely in latent space. The methodology is demonstrated on one- and two-dimensional inverse problems under both informative and non-informative priors. We further evaluate the model on IonQ simulator and Rigetti Cepheus-1-108Q, and use a lightweight learned denoising stage that recovers the noiseless accuracy to within a small residual. (The abstract has been shortened to meet arXiv's 1,920-character limit. For the full Abstract, please download the full Article.)
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Computational Physics

A Unified Framework for Bell-Shaped Gaussian Quadratures in Deterministic Boltzmann Solvers

Shanshan Dong, Lu Wang and Guanqing Wang

In this work, we develop a unified theoretical framework that constructs Bell-shaped Gaussian quadratures for deterministic Boltzmann solvers. The proposed framework establishes a general class of bell-shaped weight functions together with the corresponding integral transformations, revealing the common mathematical structure underlying existing generalized Gaussian quadratures. Based on this framework, a unified procedure for constructing discrete velocity sets is developed by combining radial quadratures with appropriate directional quadratures in different velocity-space dimensions. Several existing generalized Gaussian quadratures are naturally recovered as special cases, while the proposed framework provides a systematic route for constructing new quadrature rules based on different bell-shaped weight functions. Extensive benchmark simulations over a broad range of flow regimes demonstrate that the proposed framework achieves high integration accuracy and computational efficiency with significantly fewer discrete velocities than conventional quadrature strategies. Overall, the proposed framework not only unifies existing generalized Gaussian quadratures under a common mathematical foundation but also establishes a general design principle for the systematic development of efficient velocity-space quadratures in deterministic Boltzmann solvers.
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Atmospheric and Oceanic Physics · Cross-listed from astro-ph.EP

Simulations of the Evolving Ozone Layer: Implications for the Early Earth, Exoplanets, and the Search For Life

Akhil Kumar and Gregory J. Cooke

Over 4 billion years, Earth's atmosphere has been transformed from a composition devoid of molecular oxygen (O$_2$) to one where O$_2$ is now 21% of our modern atmosphere by volume. With high quantities of O$_2$, an ozone (O$_3$) layer can form and partially shield the surface from biologically harmful ultraviolet radiation (UV). The evolution of the O$_3$ layer has previously been simulated under the modern Sun by independent groups with separate models. Here, we present simulations of Earth's atmosphere from four open-source one-dimensional (1D) photochemical models and a 3D chemistry-climate model, focussing on O$_3$. We find that the O$_3$ layer thickness exhibits a clear deviation between the 1D models and the 3D model due to several factors, including treatments of O$_2$ photolysis, chemical networks, H$_2$O microphysics and 3D transport. We find that 1D models introduce a bias for unobserved climate states and show how these biases may propagate to calculations of biological UV damage and surface habitability. We show that when applied to specific exoplanet atmospheres, these discrepancies can become more pronounced, propagating through to observational predictions for the next generation of telescopes, such as HWO and LIFE, that will search for habitable and inhabited exoplanets.
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Instrumentation and Detectors

Energy, vertex, and time response of a LiquidO detector with an opaque-scintillator target to Compton-tagged electrons

LiquidO Collaboration: S. Katz, J. T. Moffatt, G. Wendel et al. (+88 more)

LiquidO detectors confine scintillation light near its point of production by stochastic scattering in an opaque medium and collect it with a lattice of wavelength-shifting (WLS) fibers. The elementary signal of such a detector is the point-like sub-MeV energy deposition, yet the response to that signal at the center of the detector volume has not been measured against an event-by-event ground truth. To close this gap, we couple BPULSE, a 4-liter prototype LiquidO detector, to a Compton-coincidence calibration setup that selects electron recoils of known energy on a constrained beam axis. The prototype is a 160 mm cube of opaque scintillator with 64 WLS fibers in alternating orthogonal layers at a 20 mm pitch, read out by silicon photomultipliers. Compton scatters of collimated gamma-ray beams from $^{137}$Cs and $^{60}$Co sources are tagged by a NaI(Tl) spectrometer. For 373.4 keV electrons, tagged from $90^{\circ}$ scatters of the $^{137}$Cs beam, the detector collects $19.04 \pm 0.07$ photoelectrons (p.e.). Across four operating points, the two sources at two scattering angles, it responds linearly at $48.3 \pm 1.5$ p.e./MeV. The energy resolution of $(23.4 \pm 0.4)\%$ matches the Poisson statistics of the detected photoelectrons. Collection at both fiber ends and larger sensors would raise the light yield of this target to an estimated 108-124 p.e./MeV. Center-of-mass reconstruction locates each recoil to the width of the delivered 20 mm beam spot, which bounds the intrinsic localization of the detector from above. The arrival time response sets a lower bound of 1.5 ns on the single-scatter start time at the observed $\approx 19$ p.e. light level. This single-scatter response is the building block for reconstructing multi-site events. It constrains the light collection, confinement, and timing models on which reconstruction in future LiquidO detectors will rest.
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All authors LiquidO Collaboration: S. Katz, J. T. Moffatt, G. Wendel, D. F. Cowen, I. Jovanovic, S. Schoppmann, A. S. Wilhelm, J. Apilluelo, L. Asquith, N. P. Barradas, J. L. Beney, M. Berberan e Santos, X. de la Bernardie, T. J. C. Bezerra, M. Bongrand, C. Bourgeois, D. Breton, J. Busto, A. Cabrera, A. Cadiou, E. Calvo, M. de Carlos Generowicz, B. J. Cattermole, E. Chauveau, M. Chen, P. Chimenti, S. Kr. Das, S. Dusini, A. Earle, M. Felizardo, C. Frigerio Martins, J. Galán, J. A. García, A. Gibson-Foster, C. Girard-Carillo, J. J. Gómez-Cadenas, W. C. Griffith, K. Groomes, M. Guitière, F. Haddad, J. Hartnell, A. Holin, I. G. Irastorza, W. Keck, A. Kling, L. Koch, J. F. Le Du, F. Lefevre, P. Loaiza, J. A. Lock, T. Lux, G. Luzón, J. Maalmi, J. P. Malhado, F. Mantovani, J. G. Marques, C. Marquet, M. Martínez, D. Navas-Nicolás, H. Nunokawa, J. P. Ochoa-Ricoux, T. Palmeira, C. Palomares, D. Petyt, P. Pillot, A. Pin, M. S. Pravikoff, S. Richards, M. Roche, N. Rodrigues, R. Rosero, B. Roskovec, M. L. Sarsa, A. Serafini, C. Shepherd-Themistocleous, W. Shorrock, M. Silva, L. Simard, S. R. Soleti, D. Stocco, V. Strati, J. S. Stutzmann, F. Suekane, N. Tuccori, A. Verdugo, B. Viaud, S. M. Wakely, A. Weber, A. W. R. Wong, M. Yeh, F. Yermia

Chemical Physics · Cross-listed from stat.ML

Joint Neural Posterior Estimation and Model Selection for Chemical Reaction Networks

J. Arturo Esquivel, Jorge A. Campos-Gonzalez-Angulo, Sergio Pablo-García et al. (+2 more)

Simulation-based Bayesian inference for Chemical Reaction Networks (CRNs) must simultaneously solve two computationally demanding problems: discriminating between overlapping reaction pathways and estimating reaction rate constants. Classical approaches, such as Sequential Monte Carlo ABC, rely on handcrafted summary statistics and scale poorly across large parameter spaces. To overcome this, we introduce a neural inference architecture. Our pipeline utilizes shared 1D-CNNs and a permutation-invariant Set Attention mechanism to learn low-dimensional summary statistics from variable-length, multi-experiment time-series data. These statistics simultaneously condition a model selection network to compute posterior model probabilities and model-specific conditional Invertible Neural Networks (cINNs) that estimate parameter posterior distributions. We demonstrate the practical utility of our approach on a real protodeboronation example, illustrating how it handles structural ambiguity and extracts kinetic parameters from competing catalyst deactivation pathways.
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All authors J. Arturo Esquivel, Jorge A. Campos-Gonzalez-Angulo, Sergio Pablo-García, Alán Aspuru-Guzik, Vianey Leos-Barajas

Atomic Physics

Information-theoretic measures of electron correlation in a double quantum dot

W. S. Nascimento, A. M. Maniero, F. V. Prudente et al. (+1 more)

In this work, we investigated how variations in spatial confinement affect the electron correlation between two electrons in a symmetric double quantum dot. In strong confinement regime, the ground-state energy can be obtained using the Hartree-Fock method neglecting the electron-electron repulsion term. Under a weaker confinement, the FCI method provides a more accurate description. Using the mutual information as a measure of correlation, we determine the confinement regions where electronic motion is uncorrelated. We conjecture that the Shannon entropy can serve as a qualitative guide to to study the electron correlation. We identified an approximately linear relationship between mutual information and relative correlation energy.
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All authors W. S. Nascimento, A. M. Maniero, F. V. Prudente, Ginette Jalbert

Chemical Physics

Embossing of Tapered, Isometric Micro-Interdigitated Flow Fields for Enhanced Desalination by Faradaic Deionization

Md Habibur Rahman, Sadia Afrin and Kyle C. Smith

Engineered transport architectures can improve electrolyte distribution and active-material utilization in porous electrodes, yet their implementation remains limited by fabrication methods that compromise precision, throughput, active-material preservation, or scalability. Here, an integrated embossing-calendering method is introduced to pattern Prussian blue analog (PBA) porous electrodes with embedded, micro-interdigitated flow fields (e$\mu$-IDFFs) for electrochemical desalination. This non-subtractive, roll-to-roll compatible method forms channels by controlling plastic deformation while simultaneously calendering the electrode, preserving active material and reducing patterning time by 100-fold relative to mechanical milling. Indentation experiments and a closed-form model further show that embossing requires 15-fold less force than stamping, while electrode microstructures show local densification beneath embossed channels. PBA electrodes are embossed with novel e$\mu$-IDFFs that use continuous width-tapering with isometric flow paths that promote uniform electrolyte distribution, increase rate capability, and reduce polarization. Compared with e$\mu$-IDFFs patterned using less scalable means and non-isometric flow paths, these e$\mu$-IDFFs desalinate seawater-salinity feeds near to potable levels with 1.5-fold of its thermodynamic energy efficiency and water recovery. Brackish desalination benefits similarly. Tapered, isometric e$\mu$-IDFFs and the embossing method introduced to pattern them are readily translated other electrochemical energy storage and separations systems.
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Optics

Engineering Color and Angular Stability in Building-Integrated Photovoltaics Using Metal-Oxide Photonic Glasses

Sinan Genc, Talat Ozden and Alpan Bek

Coloring building-integrated photovoltaics poses a dilemma: absorptive pigments cost photocurrent, while ordered photonic structures are iridescent. Amorphous photonic glasses, disordered packings of high-index nanospheres, are proposed to avoid both, yet their angle-independent color has rarely been quantified on a realistic module stack. A non-absorbing scatterer needs a high index with visible transparency, which the Moss rule caps near 2.35. Coupling Mie scattering, the Percus-Yevick structure factor, the exact phase function, and two-flux transfer with absorption and refraction at the front glass, we fix four target colors that a crowd-sourced naming survey calls unambiguously blue, green, gold, and terracotta, and map the recipes reaching them across four metal oxides, four encapsulants, two cell technologies, and wide ranges of particle size, packing fraction, and layer number. All four are reached in a laminated three-layer coating, to within DeltaE00 of 0.8 to 2.5, but not from one oxide: transparent TiO2 renders the blue and only pale warm tones; the green, gold, and terracotta require the blue-band absorption of V2O5, and the low-contrast oxides turn grey at the warm end. The encapsulant governs the color, and the cell technology does not. Disorder does not confer angle independence: the colors hold for an observer moving under a fixed sun but drift by DeltaE00 of 5 to 18 over the day, terracotta least, and a facade lit from above and viewed from below shifts every color towards the blue. Oxide, layer number, and facade geometry must therefore be designed together.
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Chemical Physics

Ensuring Complete Consistency between Hops and Wavefunction Propagation in Fewest-Switches Surface Hopping

Jonathan R. Mannouch

Fewest-switches surface hopping (FSSH) is a popular and versatile approach for performing dynamical simulations beyond the Born-Oppenheimer approximation, in which nonadiabatic effects are incorporated through stochastic hops of the active potential energy surface. However, the FSSH algorithm does not ensure that hops are completely consistent with the underlying electronic wavefunction dynamics. This can lead to significant errors as well as requiring small propagation time steps, which can significantly compromise the computational efficiency of the method. These problems are known to be particularly severe at so-called trivial crossings, for which the nonadiabatic coupling is entirely localized at the crossing point. Here, we solve the trivial-crossing problem by developing a fully-consistent hopping-probability formula, which generates attempted hops that match the time-evolution of the wavefunction across any size time step by construction. A state-tracking algorithm is also utilized to ensure that attempted hops are always accepted at trivial crossings. Through application to systems that contain extremely challenging trivial crossings, we demonstrate that this hopping scheme is capable of obtaining highly accurate results, even when large propagation time steps are used.
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Medical Physics

Direct correlation of intravoxel incoherent motion imaging based on implicit neural representations and histopathology in pediatric Wilms tumors: can it differentiate between subtypes?

G.C. Arends, M. Fitski, J. Harbers et al. (+8 more)

Wilms tumor (WT) is a heterogeneous pediatric renal malignancy. Invasive procedures to establish histology prior to pre operative treatment are not recommended by the International Society of Pediatric (SIOP) Oncology Renal Tumor Study Group, yet different tissue components are associated with different responses to therapy (SIOP Umbrella protocol). Intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) may improve subtype differentiation before surgery as a noninvasive radiographic biomarker by capturing both diffusion and perfusion characteristics, as opposed to the conventionally used apparent diffusion coefficient (ADC). The objective of this study is to evaluate the discriminative performance of IVIM MRI in differentiating WT subtypes. IVIM provides quantitative parameters that disentangle the diffusion coefficient (D), incoherent blood flow (pseudodiffusion Dstar) and perfusion fraction (f). This retrospective study included thirthy children with WT. Standardized 1.5T MRI with 10 b value diffusion weighted imaging (DWI) was performed. IVIM parameters were estimated using a selfsupervised implicit neural representations network and were correlated with histopathology via a patient specific 3D printed cutting guide. Statistical analyses included mixed models, receiver operating curve analysis, and logistic regression. Thirty lesions were MRI histopathology correlated on slice level. Significant subtype differences were observed for Dstar stromal versus epithelial (p = 0.024), regressive tumors (p = 0.031) and mixed WT tumors (p = 0.043). ADC showed no significant subtype differences. Direct MRI histopathology correlation enabled differentiation between stromal subtype and epithelial, mixed and regressive subtype on macroscopic slice level using Dstar.
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All authors G.C. Arends, M. Fitski, J. Harbers, J.N. van der Beek, R.R. de Krijger, M.M. van den Heuvel-Eibrink, A.F.W. van der Steeg, F.F.J. Simonis, E. Versteeg, A.S. Littooij, C.M.W. Tax

Atmospheric and Oceanic Physics · Cross-listed from astro-ph.IM

Establishing baseline model performances for optical turbulence forecasting

M. De Sepibus, E. Masciadri, C. Weinberger et al. (+4 more)

Accurate forecasting of optical turbulence (OT) is useful to optimise telescope scheduling and maximising observing efficiency, as the performance of adaptive optics systems strongly depends on turbulence conditions. While various numerical weather prediction and machine learning models are developed to predict these complex turbulence properties, properly evaluating their added value requires well-defined baseline reference models. This study establishes baseline performance thresholds for key astroclimatic parameters using two distinct models: one forecasting the parameter average over a specific timescale, and the other forecasting the temporal evolution over the same specific timescale. We apply these frameworks to extensive, multi-year datasets from the sites of the Very Large Telescope (VLT) and the Large Binocular Telescope (LBT) and discuss the possibility of extrapolating reference values of forecast performances for other sites based on their optical turbulence statistical characteristics. Our results show that baseline predictive accuracy varies according to the observing site, the specific parameter, the chosen timescale, and the forecasting approach. Therefore, an OT forecasting model's accuracy cannot be quantified in absolute terms, but relatively to the baseline.
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All authors M. De Sepibus, E. Masciadri, C. Weinberger, A. Otarola, S. Miesske, C. Veillet, S. Ragland

Optics

Probing topological edge states in multilayer dielectric photonic nanostructures

Eva Otero, Ivan Toftul, Michael Scalora et al. (+3 more)

Topological photonics has recently attracted a significant attention, leading to many theoretical studies and predictions. However, direct experimental demonstrations of topology-driven effects, particularly in nanostructures, are rarely proven. In this work, we experimentally investigate multilayer photonic nanostructures composed of alternating subwavelength dielectric layers, arranged according to the topological Su-Schrieffer-Heeger model. By engineering different edge truncations, we probe different supported topological phases. Our theoretical predictions and experimental measurements reveal strong field confinement at the surface exclusively in the configuration supporting topological edge states, providing their localized character and topological origin. First, we demonstrate enhanced absorption in an ultrathin absorbing overlayer deposited on the surface when the topological surface mode is present, highlighting the potential for surface-sensing applications. Second, we observe enhanced second-harmonic generation in reflection from the surface, demonstrating the potential of topological states for surface enhanced nonlinear optics enabled by the strong localization of the electromagnetic field at the interface.
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All authors Eva Otero, Ivan Toftul, Michael Scalora, Jose Trull, Crina Cojocaru, Yuri Kivshar

Fluid Dynamics

Some generalizations of the tornado model

S. N. Artekha

A possible mechanism of tornado generation is associated with the Schwarzschild criterion for convective instability. The supercooled cloud-air mixture near the axis starts to descend and, due to the super adiabatic temperature gradient, the overheated near-surface air mass rises. The complete system of equations for full model includes equations for the stream function, for the azimuthal velocity component, and for the change in density. The refined model considers rotating convection within the framework of ideal hydrodynamics. The simplest model uses a separate equation for the stream function and can be applied to the initial stage of vortex generation. Within the framework of the simplest model, an analytical solution is combined from 8 linear dependencies by height. Rotation increases due to the conservation of angular momentum. Within the framework of the refined model, some unidirectional differential rotation arises, but it depends on boundary conditions (can be local). The full model studies the tornado development as rotating convection from the very beginning to the quasi-stationary stage. Velocity components increase in a coordinated manner. Two cases are considered: a single whirlwind and a two-eyed tornado. Radial flows converge towards the central part of the tornado near the earth surface, and there is an outflow from the "wall" to the axis and to the periphery near the top of the tornado. The maximum vertical velocity component is achieved at a certain radial distance at a certain height. The maximum azimuthal velocity component is achieved in the tornado "wall". Tornado generation criteria are discussed.
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Chemical Physics · Cross-listed from cond-mat.stat-mech

Extending the mean first-passage-time formalism to the reconstruction of high free-energy barriers: A top-start approach

Ying Jiang and Ivan Saika-Voivod

Rare events, such as crystal nucleation in mildly supercooled liquids, are characterized by waiting times that can be much longer than the timescale of the underlying microscopic dynamics. The mean first-passage time (MFPT) formalism [J. Wedekind and D. Reguera, J. Phys. Chem. B 112, 11060 (2008)] provides a route to reconstruct one-dimensional free-energy profiles from the MFPT and steady-state distribution measured along a reaction coordinate, but conventional implementations become inefficient for sufficiently high barriers because spontaneous crossings are rarely observed. We introduce a "top-start" extension that initiates trajectories near the barrier top and reconstructs the free-energy profile from their subsequent evolution away from the barrier toward lower-free-energy regions. We establish the equivalence between the top-start and two-region constructions using a Markov-chain transition-matrix formulation. We validate the method using one-dimensional random-walk simulations across low, medium, and high free-energy barriers, with transition-matrix calculations providing an exact benchmark for the corresponding discretized models. The top-start reconstruction remains accurate in the high-barrier regime where conventional MFPT sampling becomes prohibitively inefficient.
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Chemical Physics · Cross-listed from cs.LG

Does Pretraining Teach Chemical Language Models Chemistry?

Leif Sieben and Yoel Zimmermann

Chemical language models (CLMs) are pretrained on large corpora of molecules with the aim of learning representations that transfer to diverse downstream tasks. Here, we systematically study the effects of pretraining using a series of such CLMs across 64 molecular property prediction datasets. We find that the downstream gains of pretraining in CLMs do not scale and performance saturates below gradient-boosting baselines. Across the regimes evaluated, only supervised pretraining on traditional physico-chemical descriptors consistently improves downstream performance for the CLMs tested whereas some forms of pretraining result in models worse than a randomly initialized encoder. While models can resolve molecular structure well, they do so no better than a randomly initialized model, suggesting that, at best, CLMs learn descriptor-like properties in addition to low-level token statistics during pretraining, but surprisingly little chemistry beyond what classical molecular features already capture.
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Instrumentation and Detectors

The Energetic Particle Detector Instrument on ELFIN

Colin Wilkins, Ryan Caron, Ethan Tsai et al. (+24 more)

We present the design methodology, implementation, and data products of the Energetic Particle Detector (EPD) instrument on-board the Electron Losses and Fields Investigation (ELFIN) dual SmallSat mission. ELFIN was designed to study the time-evolution of energetic particle distributions in Earth's magnetosphere, having operated in polar Low Earth Orbit (LEO) from 2018 to 2022. Each satellite's instrument payload contained a pair of detector heads to sense differential-directional fluxes of 50 keV to $\sim$5 MeV electrons (EPDE), and 50 keV to $\sim$2 MeV atomic ions (EPDI), with an energy resolution better than 50% ($\Delta E/E<0.5$). The satellites were spinning with a nominal period of 2.8 s in a plane containing Earth's background magnetic field, with particle counting intervals subdivided into 16 consecutive spin sectors. Each EPD was paired with a three-axis Fluxgate Magnetometer (FGM) sampled at 80 Hz for local pitch-angle determination. Each detector head operated on the principle of pulse-height analysis (PHA) in solid state media, collimated by a rectangular 22.5$^\circ$ field of view and entrance aperture. The EPDE contained a stack of 6 silicon detectors (0.7 cm total thickness) with 0.15 cm$^2$ str geometric factor, with ion contamination mitigated by an aperture foil and digital coincidence logic. The EPDI contained a stack of 2 silicon detectors (0.1 cm total thickness) with 0.03 cm$^2$ str geometric factor, with electron contamination mitigated by a magnetic broom stage and digital anti-coincidence logic. The total assembled mass, volume, and power required for the EPD detector heads and circuit boards were 939 g, 10$\times$9.8$\times$8.4 cm$^3$, and 2.3 W, respectively. We describe each EPD design element alongside instrument data products and processing.
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All authors Colin Wilkins, Ryan Caron, Ethan Tsai, Chris Shaffer, Patrick Cruce, Maxwell Chung, Andrei Runov, Jiang Liu, Drew Turner, Yuri Shprits, Wen Li, Michael Lawson, Emmanuel Masongsong, Cindy Russell, Eric Grimes, Jiashu Wu, Matthew Allen, Jessica Artinger, Alex Flemming, Brayden Hesford, Laura Iglesias, James King, Austin Norris, Carter Pedersen, Daniel Thomlinson, Wynne Turner, Vassilis Angelopoulos

Optics

Mode locking by phase-sensitive amplification

Francesco De Lucia, Yifan Sun, Georges Semaan et al. (+4 more)

Mode locking is the mechanism by which lasers organize many optical modes into stable trains of ultrashort pulses. It underpins optical frequency combs, precision timing and spectroscopy, and provides the phase-coherent waveforms required for applications ranging from strong-field physics to optical frequency metrology. Conventional pulse-forming mechanisms select pulse amplitude without fixing its phase relative to an external optical reference, leaving pulse formation and optical-phase stabilization as separate functions. Phase-sensitive amplification offers a different possibility: the optical reference can participate directly in pulse formation. Here we demonstrate this principle in a continuously pumped oscillator. Kerr-induced phase evolution and cavity detuning turn pump-referenced parametric gain into a power-dependent discriminator that supports stable single-soliton operation. Roundtrip-resolved interferometry reveals that the soliton optical phase remains referenced to the master laser modulo $\pi$. These results establish phase-sensitive mode locking, in which pulse-amplitude selection and optical-phase referencing arise from the same coherent nonlinear feedback.
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All authors Francesco De Lucia, Yifan Sun, Georges Semaan, Clement Dupont, Nicolas Englebert, Simon-Pierre Gorza, François Leo

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

Direct growth of crystalline spinel GaON films: A wide-bandgap mixed-anion semiconductor

Baikui Li, Zecheng Yang, Wenhao Yin et al. (+5 more)

Mixed-anion semiconductors offer opportunities for bandgap engineering beyond conventional multication alloys, but competing phases and disorder complicate their synthesis and the identification of their electronic properties. Gallium oxynitride (GaON) could connect the technologically important GaN and Ga2O3 systems, yet establishing a clear relation between its crystal structure, composition and bandgap remains challenging. Here we report the direct growth of crystalline spinel gamma-GaON films by nitrogen-plasma-assisted pulsed-laser deposition. Varying the nitrogen and oxygen supply yields monoclinic beta-Ga2O3, predominantly disordered films and crystalline spinel GaON. Complementary diffraction, atomic-resolution microscopy and elemental analysis establish the spinel structure and nitrogen incorporation. Temperature-dependent photocurrent spectroscopy reveals a clear redshift of the crystalline gamma-GaON response, supporting assignment of a band-edge transition near 4.3 eV at room temperature. These results open opportunities to investigate mixed-anion wide-bandgap semiconductor physics and develop heterostructures.
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All authors Baikui Li, Zecheng Yang, Wenhao Yin, Zijing Wu, Haitao Zhao, Yunwei Sheng, Honglei Wu, Jiannong Wang

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

A Transferable Machine-Learned Potential Enabling Large-Scale Copper-Carbon Simulations from Equilibrium to Extreme Conditions

Feiyu Zhou, Wei Qiu, Yan Chen et al. (+4 more)

Cu-C materials and interfaces are central to diamond thermal management, metallization, graphene growth and carbon-coating technologies, but atomistic simulations across these applications require a potential that describes metallic Cu, diverse carbon bonding, heterogeneous Cu-C interactions and close atomic encounters. Here we develop NEP-CuC, a transferable neuroevolution potential trained on a dataset of 2,727 uniformly relabelled configurations selected from a heterogeneous Cu-C candidate pool. Disagreement within an ensemble of five independently trained models provides an internal indicator of model sensitivity. A Ziegler-Biersack-Littmark (ZBL) correction describes short-range nuclear repulsion, while a runtime D3(BJ) correction supplements dispersion-sensitive calculations. Tests on source-derived held-out and independent external datasets, together with structural, elastic, defect, interfacial, vibrational and finite-temperature transport benchmarks, establish broad but property-dependent physical fidelity across elemental Cu, diverse carbon environments and heterogeneous Cu-C configurations. Large-scale simulations of amorphous-carbon formation and orientation-dependent shock compression of Cu further test transferability under strongly non-equilibrium conditions. For Cu/diamond interfaces, the same potential describes deposition, annealing and tensile response: preparation history leaves persistent differences in interphase structure, while the mean peak nominal tensile stress at 500 K decreases from $12.35\pm0.71$ to $6.65\pm0.98$ GPa as the incident Cu energy during the initial deposition stage increases from 1 to 50 eV. NEP-CuC provides an atomistic framework for linking processing, interfacial structure and physical response across Cu-C systems, with direct relevance to Cu/diamond thermal-management interfaces, diamond metallization and non-equilibrium Cu-C processing.
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All authors Feiyu Zhou, Wei Qiu, Yan Chen, Jiahui Liu, Yilun Liu, Shengying Yue, Penghua Ying

Optics

Continuous-wave 148.4 nm Generation in Quasi-phase Matched BaMgF4

Yuanzhuang Bu, Xiangting Wang, Ruiyin Gu et al. (+6 more)

We report continuous-wave (CW) vacuum-ultraviolet (VUV) generation at 148.4 nm by second-harmonic generation of 296.8-nm fundamental light in quasi-phase matched (QPM) BaMgF4 (BMF). At the incident power of 170 mW, a VUV output power of approximately 31 pW can be obtained. The quadratic dependence of the signal on the incident power in the QPM region and its attenuation in the ambient environment support the identification of VUV generation. The polarization dependence shows a sine-function shape with a 15% output attenuation from the maximum to the minimum. These results highlight the potential of BMF as a nonlinear medium for CW VUV generation.
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All authors Yuanzhuang Bu, Xiangting Wang, Ruiyin Gu, Chongtai Liu, Luxin Jiang, Xinqing Ding, Ke Zhang, Yongkai Li, Kemi Xu

Physics and Society

Directed percolation in higher-order social dilemmas

Pablo Villegas and Sandro Meloni

Multiplayer social dilemmas on hypergraphs show a variety of emergent phenomena, which has been attributed to group interactions. Here we test whether pairwise dynamics can reproduce them as well. We derive the mesoscopic Langevin equation of a testbed model and find the operator content of absorbing phase transitions: a directed-percolation line, a tricritical point, and a first-order region whose spinodal is the explosive transition. In our analysis, three-player games only set the values of the Landau coefficients. We construct a strictly pairwise model with short-lived memory, in which every event involves at most two entities, that reproduces these coefficients term by term and has exactly the same mean-field fixed points. Simulations confirm that the two dynamics share mean-field critical and tricritical scaling and the size of the critical mass, and that a purely three-player game on a two-dimensional triangular lattice lies in the directed-percolation class. For these games, the explosive transition and the critical mass therefore do not require group interactions, and the critical behavior is that of the pairwise theory.
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Physics and Society

Social Norm Diffusion in Societies: Simple or Complex?

Claudia Lorenzetti, Aron Szekely, Daniele Vilone et al. (+1 more)

Social norms are a fundamental component of society, shaping how we communicate, cooperate, and avoid conflict. Despite their ubiquitous presence and profound influence on behaviour, questions remain about how they spread from person to person and whether they are adopted. Using an evolutionary game-theoretic model, we study whether simple or complex contagion processes characterise how social norms spread. Crucially, contagion type is endogenous and emerges from the model. We also vary cultural conformism, the cost of following a norm, and network topology to assess the generality of our results. We show that social norms in our model can spread through simple contagion when a new norm is low in cost and cultural conformism is low, while norms spread through complex contagion when the new norm is costly and cultural conformism is high.
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All authors Claudia Lorenzetti, Aron Szekely, Daniele Vilone, Giulia Andrighetto

Optics

Continuous-wave 148.4-nm generation in strontium tetraborate for nuclear absorption spectroscopy

Hanlin Wang, Zhouzhi Tan, Conghui Huang et al. (+13 more)

Continuous-wave light near 148.4 nm enables direct absorption spectroscopy of the thorium-229 nuclear transition. We demonstrate single-pass frequency doubling in strontium tetraborate, delivering an estimated 8.1 nW at 920 mW pump power. At this power, oxygen admission leaves a background of 1.22 kHz, corresponding to an estimated signal-to-background ratio of 3.8 x 10^4 after current-integration calibration. Several crystals grown by top-seeded solution growth produce polarization-dependent VUV signals. Temperature scans reveal distinct maxima among specimens cut from one boule and among positions within a specimen. The source sustains operation over 33.3 h. In a separate 3-h record acquired with 1-ms gates, local referencing achieves near-Poisson averaging, reaching a fractional Allan deviation of 3.5 x 10^-5 at 1000 s. These results establish a practical VUV source for stable, long-duration spectroscopy of weak nuclear absorption.
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All authors Hanlin Wang, Zhouzhi Tan, Conghui Huang, Jinming Liu, Xuan Fan, Runzhe Yang, Meng Wang, Tung-Hsun Chung, Yong-Heng Huo, Yin Hang, Zhiwei Jiao, Heng Tu, Lei Zhang, Xu-Fei Yin, Pengfei Wang, Zhiqiang Zhang

Optics · Cross-listed from math-ph

Spectral Theory of an Exactly Solvable Quantum-Optical Oscillator

Sam Johar and Joseph Kraisler

We study a one-dimensional single-excitation model of a scalar photon field coupled to a continuum of two-level atoms with quadratic density. The resulting matrix Hamiltonian has an unbounded spatially varying coupling and is not semibounded. We prove that it is essentially self-adjoint and determine its spectrum explicitly. The continuous spectrum is the half-line $(-\infty,\Omega]$, where $\Omega$ is the atomic resonance frequency, while the spectrum above $\Omega$ consists of a strictly increasing sequence of simple eigenvalues. These eigenvalues are characterized by the interlaced zeros of the Airy function and its derivative and satisfy \begin{align*} \omega_n = \left(\frac{3\pi g n}{4}\right)^{1/2} + \frac{\Omega}{4} + O(n^{-1/2}). \end{align*} The analysis is based on a nonlinear spectral reduction that yields a confining massless relativistic oscillator above $\Omega$ and an inverted oscillator below $\Omega$.
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Optics

Orbital Angular Momentum Transfer and Beam-Quality Limits in Fork-Grating Electron Diffraction

P.K. Tsiopa and S.S. Baturin

We analyze fork-grating generation of electron vortex beams beyond the ideal single-mode approximation. The incident beam is described as a paraxial Gaussian ensemble with finite transverse momentum spread and a first electromagnetic Hartree phase accumulated before the grating. Within Fresnel propagation we derive an analytical expression for each diffraction order and determine the corresponding orbital-angular-momentum statistics. The mean OAM of a selected order remains fixed by the topological rule, $\langle L_z\rangle_m=mp\hbar$, while its variance is set by the residual transverse momentum spread of the beam prepared at the grating. For the Gaussian mixture, the transverse purity is $\mathcal P_{\perp,m}=[1+2(\Delta L_{z,m}/\hbar)^2]^{-1}$. The observed annular profile is governed by a separate propagation-dependent blurring scale, so a beam can retain well-defined mean OAM while having low transverse purity or a partially filled vortex minimum. Within the radial phase-screen approximation, the Hartree self-field modifies the propagated profile while preserving the full-plane OAM moments and transverse purity.
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Accelerator Physics

Phase Memory Controls Radiative Depolarization Near an Isolated Spin Resonance

Zhe Duan

Radiative depolarization near spin resonances in electron storage rings is conventionally described by correlated-sideband and local resonance-density theories, but a quantitative description of the crossover between them has remained lacking. Here we derive a unified finite-memory response from stochastic spin dynamics near an isolated resonance. By separating the coherent resonance contribution from stochastic fluctuations, we show that the connected correlation of the accumulated resonance-relative spin phase determines the leading off-center weak-resonance depolarization rate. Both conventional theories emerge as controlled asymptotic limits of this response, which also captures the surviving synchrotron phase memory governing the crossover. Monte Carlo spin tracking validates the predicted rates throughout the crossover and reproduces the recurrence-induced generalized-sideband structure. More broadly, the connected-correlation formulation provides a basis for extending radiative depolarization theory to more general stochastic spin-orbit dynamics in storage rings.
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Atomic Physics

Theory of Sub-Doppler Spectroscopy of Alkali Metal Vapors in the Field of Counterpropagating Bichromatic Laser Beams: Probe Beam Regime

A. M. Mikhailov and D. V. Brazhnikov

Sub-Doppler resonances observed in miniature cells ($V \ll 1 cm^3$) with Rb or Cs atoms in the field of counterpropagating bichromatic laser beams are of interest for the creation of a miniature quantum frequency standard (QFS) of the optical range. However, a theory of these resonances that takes into full account the real structure of energy levels in an atom has not yet been constructed, which would make it possible to obtain explicit analytical expressions for the absorption coefficient of the medium. This paper addresses this gap using the density matrix formalism and the algebra of irreducible tensor operators. Namely, we obtained an analytical expression for the absorption coefficient of the probe beam in the presence of a more intense counterpropagating beam (pump-probe regime). Moreover, the calculations were carried out for arbitrary parameters of laser beam polarization, arbitrary angular momenta of optical dipole transitions in the atom and various relaxation processes. The constructed theory allows us to correctly take into account the simultaneous action of various nonlinear optical effects, in contrast to the simplified three-level model of the atom, and also to investigate the partial contribution of each of them to the overall observed resonant circuit. The analysis performed, in particular, made it possible to predict an increase in the amplitude of the sub-Doppler resonance when using counterpropagating light beams with opposite circular polarizations in relation to the configuration of counterpropagating beams with orthogonal linear polarizations, which is often used in practice.
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Chemical Physics · Cross-listed from cond-mat.soft

Ionic gradients shape the spatial organization and dynamics of supramolecular polymers

Claudio Perego, Annalisa Cardellini, Andrea Tagliabue et al. (+1 more)

Living supramolecular materials such as microtubules and actin filaments assemble and function in dynamic, heterogeneous environments, subject to chemical concentration gradients. Their rapid and precise response to such gradients—via aggregation, disassembly, or autonomous motion—underlies the fine spatiotemporal control typical of living systems. Reproducing such responsiveness in synthetic materials is a central challenge in materials science and requires a molecular-level understanding of how gradients couple to supramolecular structure and dynamics, which remains difficult to access experimentally. To this end, we combine implicit-solvent coarse-grained molecular dynamics (MD) with the constant chemical potential MD (C${\mu}$MD) technique to investigate, at molecular resolution, the coupling of two prototypical supramolecular polymer models with externally imposed ionic concentration gradients. Despite their contrasting responses to homogeneous ionic conditions, both systems undergo pronounced spatial reorganization under the gradient, generating regions of locally enhanced supramolecular activity that are inaccessible to homogeneous systems with the same overall content of self-assembling species. Crucially, the local supramolecular dynamics is largely determined by the local concentrations, consistent with the formation of local quasi-equilibria: this direct connection between spatial composition and supramolecular activity emerges as a common governing principle across the two models. These findings shed light on the spatially complex supramolecular response that can be triggered by chemical gradients, and show how a single gradient simulation can encode this response across a continuous range of local chemical environments, thus providing a general strategy to investigate and design materials operating under spatially heterogeneous conditions.
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All authors Claudio Perego, Annalisa Cardellini, Andrea Tagliabue, Giovanni M. Pavan

Atomic Physics

Collision inside an atom: quantum ion-atom dynamics

Arijit Das, Yufeng Wang, Marcin Welter et al. (+6 more)

Rydberg atoms occupy a central role in quantum science; their loosely bound outer electron gives rise to properties that enable quantum information processing1 or the formation of exotic molecular bonds2. Beyond these roles, they have been proposed as a neutral platform for the observation of quantum effects in collisions and reactions of the ionic core with neutral particles3, 4, a long-standing goal of ion-based chemistry and physics. However, all of the experimental results so far could be explained using a classical description of the internuclear motion5. Here we demonstrate cold collisions inside a Rydberg helium atom, achieved by merging helium Rydberg and ground-state helium beams and imaging individual scattering events. We resolve the fully quantum-coherent motion and observe matter-wave diffraction and tunnelling-driven shape resonances down to collision energies of 90 mK. In the case of identical helium nuclei, we demonstrate a new regime of identical-particle Mott interference6, where quantum statistics begin to govern the total scattering cross section. For distinct isotopes, we show the breakdown of the Born-Oppenheimer approximation and benchmark parameter-free, state-of-the-art theory. We directly measure the helium isotope ionization-energy difference to be 15.0 +/- 0.1 K. Our experiments establish Rydberg atoms as a platform for the direct observation of quantum dynamics with a general class of ions, atoms and molecules.
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All authors Arijit Das, Yufeng Wang, Marcin Welter, Karl Horn, Dawid Dąbrowski, Michał Przybytek, Julia Narevicius, Michał Tomza, Edvardas Narevicius

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

A Topological Spin on Racetrack Memory

Benjamin Zingsem

Magnetic racetrack memory requires localized carriers that combine rapid motion, resistance to perturbations and a detectable signal. Here we show how a 360{\deg} domain wall in a hollow ferromagnetic tube combines these properties within a single continuous magnetic shell. Two successive magnetization reversals form a bound object whose surrounding domains point in the same direction. Analytical energetics and micromagnetic simulations establish its finite separation, recovery from tested perturbations and current driven transport without microscopic Dzyaloshinskii-Moriya interaction or a maintaining field. The texture's winding resists unwinding while radial rotation carries an energy cost, providing a specific control over stability. Relative rotation of the constituent spins accounts quantitatively for additional displacement during current onset. The wall supports motion at hundreds of metres per second, with transient velocities approaching one kilometre per second at stronger drive. A prepared seven-bit pattern retains its carriers and local readout contrast after pulsed transport and recovery. Curved-track and differential-current tests identify radial stiffness and drive uniformity as controls for intact motion. These results establish a physical basis for fast, locally distinguishable tubular magnetic bits and identify a continuous switching pathway that can be targeted by tailored excitation.
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