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Physics Physics

physics Watch Physics

Wednesday 24 June

Instrumentation and Detectors

Calibration and Performance of Germanium High Voltage Detectors for SuperCDMS SNOLAB

M.F. Albakry, I. Alkhatib, D. Alonso-González et al. (+141 more)

As SuperCDMS SNOLAB is getting ready to search for low mass dark matter particles, using cryogenic Ge and Si detectors, a set of six of the new SuperCDMS High Voltage (HV) detectors (four Ge and two Si) were tested in the Cryogenic Underground TEst facility (CUTE) at SNOLAB. This provided the first opportunity to gain experience with this new detector type and assess their performance thoroughly under low background conditions. Here we describe the SuperCDMS HV detector concept and discuss some of the newly developed analysis methods and approaches. Focusing on the Ge detectors, we investigate the detector performance under voltage bias (up to 90 V), exercise the low energy (keV to sub-keV range) calibration based on the electron capture peaks generated by the decay of $^{71}$Ge, assess the detector resolution, and demonstrate the unexpected (and encouraging) ability of these detectors to also measure high energy interactions in the hundreds of keV range with good resolution (better than 3% at 356 keV).
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All authors M.F. Albakry, I. Alkhatib, D. Alonso-González, J. Anczarski, T. Aralis, T. Aramaki, A. Ashtari Esfahani, I. Ataee Langroudy, R. Bhattacharyya, A.J. Biffl, P.L. Brink, M. Buchanan, R. Bunker, B. Cabrera, R. Calkins, R.A. Cameron, P. Camus, C. Cartaro, D.G. Cerdeño, Y.-Y. Chang, M. Chaudhuri, J.-H. Chen, R. Chen, J. Cooley, J. Corbett, P. Cushman, R. Cyna, S. Das, K. Dering, S. Dharani, M.L. di Vacri, M.D. Diamond, M. Elwan, S. Fallows, E. Figueroa-Feliciano, S.L. Franzen, G. Gerbier, R. Germond, A. Gevorgian, M. Ghaith, G. Godden, S.R. Golwala, G. Gonzalez, J. Hall, C.A.S. Harms, C. Hays, B.A. Hines, Z. Hong, L. Hsu, M.E. Huber, V. Iyer, M. Jha, V.K.S. Kashyap, M.H. Kelsey, K.T. Kennard, Z. Kromer, A. Kubik, N.A. Kurinsky, J. Leyva, J. Liu, Y. Liu, E. Lopez Asamar, P. Lukens, R. López Noé, R. Mahapatra, J.S. Mammo, A. Mayer, P.C. McNamara, É. Michaud, E. Michielin, K. Mickelson, N. Mirabolfathi, M. Mirzakhani, B. Mohanty, D. Mondal, D. Monteiro, S. Nagorny, J. Nelson, H. Neog, H. Nguyen, J.L. Orrell, M.D. Osborne, S.M. Oser, P. Pakarha, L. Pandey, S. Pandey, R. Partridge, P.K. Patel, D.S. Pedreros, W. Peng, M.A. Penner, W.L. Perry, R. Podviianiuk, M. Potts, S.S. Poudel, A. Pradeep, M. Pyle, W. Rau, A. Rehberg, R. Ren, T. Reynolds, M. Rios, A. Roberts, A.E. Robinson, L. Rosado Del Rio, J.L. Ryan, T. Saab, D. Sadek, B. Sadoulet, S. Salehi, J. Sander, A. Sattari, R.W. Schnee, S. Scorza, B. Serfass, R.S. Shenoy, A. Simchony, P. Sinervo, Z.J. Smith, R. Soni, K. Stifter, M. Stukel, H. Sun, E. Tanner, N. Tenpas, D. Toback, R. Underwood, A.N. Villano, J. Viol, O. Wen, Z. Williams, M.J. Wilson, J. Winchell, J. Xiong, S. Yellin, B.A. Young, B. Zatschler, S. Zatschler, A. Zaytsev, E. Zhang, J. Zheng, L. Zheng, A. Zuniga, M.J. Zurowski

Atmospheric and Oceanic Physics

Sampling sea state using a diffusion model

Jiarong Wu, Bertrand Chapron and Laure Zanna

Sea state prediction is essential for operational maritime applications and coupled earth system modeling, yet current spectral wave models remain computationally prohibitive for many use cases, including online coupling to climate simulations and making probabilistic (ensemble-based) predictions. While deep learning has recently demonstrated strong performance in weather forecasting, existing AI-based wave models are predominantly deterministic and largely limited to bulk variables such as significant wave height, leaving probabilistic sea state estimation largely unexplored. In this work, we propose a diffusion-based generative model for global sea state estimation that conditions on a relatively long history (5 days) of global wind forcing. This generative model directly samples the complex conditional distribution of sea state without autoregressive time-stepping. Unlike prior approaches, our framework naturally extends beyond bulk variables to estimate partition-related variables and derived quantities, such as Stokes drift and mean square slope. Trained on a 30-year global WAVEWATCH-III hindcast, the model achieves substantial computational acceleration compared with numerical spectral models while delivering skillful predictions and a calibrated ensemble spread for the bulk variables. Our results suggest that diffusion-based sea state sampling offers a promising path toward probabilistic wave forecasting and efficient coupling of sea state information into broader earth system models.
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Atmospheric and Oceanic Physics · Cross-listed from math-ph

A new formulation of metriplectic dynamics with an application to quasigeostrophic ocean modeling with advected quantities

Francisco J. Beron-Vera and Erwin Luesink

A general formulation of metriplectic dynamics is presented, where the metriplectic four-bracket is constructed by multiplying two skew-symmetric brackets. The new formulation is then used to introduce irreversibility in a generalized two-dimensional (2D) quasigeostrophic (QG) upper-ocean model involving advected quantities, with the thermal QG model as a special case. By construction, the resulting dynamics ensure the conservation of internal energy and the generation of entropy, in accordance with the first and second laws of thermodynamics. Our metriplectic dynamics formulation allows for a flexible specification of irreversibility, ranging from a type that results in nearly material conservation of potential vorticity to the representation of realistic forcing and dissipation in 2D QG ocean modeling with advected quantities.
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Physics and Society

Low-dimensional Dynamics of the Social Compass Model

Corbit R. Sampson and Juan G. Restrepo

The social compass model has been recently proposed as a model for depolarization in populations where individuals have multiple, possibly correlated, opinions. Previous work has focused on the steady state of this model, but has not addressed the dynamics leading to depolarization. We show that the macroscopic dynamics of the social compass model can be described using the Ott-Antonsen Ansatz and that, for initially clustered opinions, the resulting equations reduce to a finite-dimensional system of ordinary differential equations. We study the linear stability of the polarized state and find a dispersion relation for the growth rate of perturbations from this state. We find that the critical coupling for depolarization depends only on the first inverse moment of the conviction distribution, whereas the rate of depolarization depends on higher moments. Consequently, conviction distributions with the same critical coupling can exhibit vastly different depolarization timescales. We also demonstrate how our analysis can be extended to study depolarization in the presence of community structure.
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Fluid Dynamics

Geometry-Driven Passive Fluid Transport in Paper-Based Microdevices

Mohd Shafiq Nasir, Akimitsu Kugimiya and Muhammad Salman Al Farisi

Channel geometry strongly influences capillary-driven fluid transport in paper-based devices, yet systematic comparative studies correlating geometric design with flow behaviour and analyte confinement remain limited. The present study investigates five distinct channel geometries namely converging-diverging, diverging-converging, wide-to-narrow, circular, and rectangular that was fabricated on cellulose filter paper with a standardized area of 32.5 mm\textsuperscript{2} and analyzed using geometry-adapted extensions of the Lucas–Washburn equation. Pyrene and benz[{\alpha}]anthracene were employed as fluorescent model analytes to enable UV-based quantification of analyte confinement within each geometry. Flow transport times ranged from 23.1 s (circular, fastest) to 65.0 s (diverging-converging, slowest), with corresponding mean velocities of 0.571 and 0.284 mm/s for pyrene respectively, demonstrating that channel geometry strongly influences capillary transport in paper-based devices. Diverging-converging and wide-to-narrow designs produced the greatest analyte confinement by imposing flow retardation and sustained channel acceleration respectively, while circular and rectangular designs yielded relatively uniform velocity distributions and weaker confinement. Cyclodextrin-functionalized chitosan coatings served as a surface chemistry tool to anchor analyte retention at designated preconcentration zones, enabling geometric effects to be isolated and quantified. Computational fluid dynamics simulations, calibrated against experimental flow data and validated through a mesh independence study, reproduced the experimentally observed velocity magnitude distributions across all five geometries, showing semi-quantitative agreement with geometry-adapted Lucas–Washburn predictions.
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Plasma Physics

Integrating Gyrokinetic Flux Predictions with Ideal MHD Stability Boundaries

J. McClenaghan, K. E. Thome, T. F. Neiser et al. (+5 more)

Accurate prediction of pedestal height and width in tokamaks remains a critical issue as it strongly influences the predicted plasma performance of all future reactors. We present an integrated pedestal-stability workflow that combines equilibrium scans with magnetohydrodynamic (MHD) stability analysis using ELITE and GATO and gyrokinetic transport predictions using CGYRO/QLGYRO. The workflow reproduces the characteristic KBM first- and second-stability structure previously identified in gyrokinetic pedestal studies. Applied to spherical tokamaks (STs), the workflow shows good agreement with past studies when low-n peeling stability is included, emphasizing the importance of resolving low-n physics in ST pedestals. Extending the analysis to SPARC-like, high toroidal field plasmas, kinetic ballooning mode (KBM) and microtearing mode (MTM) heat fluxes are found to increase strongly with toroidal field, suggesting that access to the KBM second-stability region may become significantly more difficult in high toroidal field devices. Comparison with global ELITE finite-n analysis at SPARC parameters suggests that the H-mode pedestal lies in an intermediate regime bounded by local KBM second stability on one side and global finite-n ballooning instability on the other, consistent with the EPED picture once global effects are included
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All authors J. McClenaghan, K. E. Thome, T. F. Neiser, J. Candy, F. D. Halpern, T. H. Osborne, S. Saarelma, the MAST-U team

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

Does Aurora Encode Atmospheric Structure? Latent Regime Analysis and Attribution

Emma Kasteleyn and Ana Lucic

ML foundation models are able to emulate atmospheric dynamics accurately and efficiently but operate as opaque “black boxes”. We investigate the internal representations of the Aurora model using spatially pooled PCA and layer-wise relevance propagation (LRP). We find evidence that Aurora's latent space is primarily organized by seasonal cycles, whereas extreme storm events do not form a linearly separable cluster. LRP indicates that the model attends to features consistent with the 3D vertical structure of the Great Storm of 1987. Perturbation tests show masking relevant regions degrades forecasts $3.31\times$ more than random masking. These findings suggest that Aurora learns meteorological coherence and vertical structure without explicit instruction.
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Fluid Dynamics

Variational derivation of a moist thermal rotating shallow water model

Colin J. Cotter, Darryl D. Holm and Oliver D. Street

We introduce a new energy-conserving, moist shallow water model with thermal stratification and rotation. The model is derived from a variational principle, using a Lagrangian expressed in terms of enthalpy. In this model, the latent heat from phase transitions modifies the buoyancy dynamics, which in turn feeds back to alter the vertically integrated hydrodynamic motion. Finally, we generalise this moisture parameterisation to non-hydrostatic Green-Naghdi equations.
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Optics

Generalized vibration curves for apodization and super-resolution in far-field diffraction

Lowell T. Wood

The Cornu spiral, widely used to analyze Fresnel diffraction, is a familiar example of a vibration curve, also known as an amplitude-phase curve or phasor diagram. A related construction appears in discussions of Fraunhofer diffraction, where the aperture function is uniform, making the curve's shape depend solely on phase. When the aperture function varies with position, however, both amplitude and phase determine the geometry. Here, vibration curves are extended to continuous, monotonic, symmetric, nonuniform aperture functions that produce either apodization (broadening of the central maximum with suppression of side maxima) or super-resolution (narrowing of the central maximum with enhancement of side maxima). These generalized vibration curves provide an intuitive visualization of how aperture structure shapes the far-field diffraction pattern. They clarify the mechanisms behind apodization and super-resolution and reveal how phasor rotation at the first diffraction zero provides a signature that characterizes the two effects. This unified perspective serves as a useful pedagogical tool for connecting Fourier transforms, optical diffraction, and vibration curves in the undergraduate and graduate curriculum.
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Optics

Fiber Bragg grating-based acoustic sensing system enabled by ML-trained, sub-picometer-tunable hybrid III-V/SiN lasers

Prabhav Gaur, Premanand Chandramani, Yossef Ehrlichman et al. (+7 more)

Distributed acoustic emission (AE) sensing is critical for early detection of structural degradation, yet conventional electrical sensors are difficult to scale and fiber-based approaches are limited by interrogation complexity and resolution. Here, we report an intelligent fiber Bragg grating (FBG) sensing system enabled by machine learning (ML)-trained hybrid III-V/SiN tunable lasers that achieve uniform, mode-hop-free, sub-picometer wavelength control. A supervised gradient-descent algorithm is used to learn the nonlinear electro-thermal tuning space of Vernier-based external-cavity lasers, enabling continuous tuning with <0.1 pm resolution and <0.5 dB power variation. This capability allows precise alignment to FBG reflection slopes for high-sensitivity acoustic detection. We demonstrate a four-laser interrogation system monitoring 16 FBG sensors distributed across multiple metallic structures, operating over a 35 nm wavelength span. The system autonomously identifies sensor resonances, dynamically tracks spectral shifts, and reconfigures interrogation wavelengths in response to localized acoustic events. Using pencil-lead break tests as calibrated AE sources, we show simultaneous multi-channel detection and adaptive spatial localization. The combination of narrow linewidth (<10 kHz), wide tunability, and ML-driven calibration enables robust, scalable, and high-resolution sensing. This approach establishes a pathway toward fully autonomous, distributed photonic sensing networks for real-time structural health monitoring.
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All authors Prabhav Gaur, Premanand Chandramani, Yossef Ehrlichman, Mohammed Alshamari, Yufei Chu, Abu Mitul, John Simons, Ibrahim G. Yayla, Ming Han, Ashok V. Krishnamoorthy

Optics · Cross-listed from quant-ph

Mechanisms governing photon-pair generation and emission directionality in quantum metasurfaces

Alberto Paniate, Ivano Ruo-Berchera and Francesco Monticone

Metasurfaces are emerging as a promising platform for photon-pair generation through spontaneous parametric down-conversion, thanks to their compactness, integrability, and intrinsic multifunctionality, which enables the engineering of complex quantum states. However, their full potential remains only partially exploited because the physical mechanisms governing key properties of the generated photon pairs, such as generation efficiency and emission directionality, are not yet fully understood. As a result, metasurface designs and experimental configurations are often optimized through trial-and-error procedures. Here, we theoretically investigate the main mechanisms that control photon-pair generation and detection by studying how different pump configurations and measurement geometries affect the generation efficiency, emission directionality, and collection efficiency of the emitted photon pairs. This framework allows us to interpret existing experimental results and to provide general guidelines for the design of metasurfaces and the choice of experimental configurations in future experiments. Finally, we show that substrate thickness and multilayer configurations represent additional degrees of freedom for quantum metasurface design and can be engineered to enhance the generation efficiency and control the emission directionality, providing a new route for the optimization of photon-pair sources based on metasurfaces.
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Instrumentation and Detectors

Production and installation of wavelength-shifting reflective light enhancers for the Short-Baseline Near Detector

R. Acciarri, L. Aliaga-Soplin, R. Alvarez-Garrote et al. (+194 more)

We report on the design, production, and installation of a wavelength-shifting reflective system on the cathode of the Short-Baseline Near Detector (SBND), a liquid argon time projection chamber located along the Fermilab Booster Neutrino Beam. To increase and homogenize scintillation-light collection, 64 double-sided plates were fabricated from FR4, laminated with specular reflector film and coated with 300 $\mu$g/cm$^2$ of tetraphenyl butadiene (TPB) wavelength shifter using controlled physical vapor deposition. The coating uniformity was validated through dedicated measurements of deposited mass and profilometry studies. Because exposure to ambient blue/UV light could degrade the TPB, protective filtering and controlled storage conditions were implemented during handling and installation. The coated plates were assembled between conductive meshes for high-voltage compatibility and installed in situ during detector integration. This system constitutes the largest TPB-coated area deployed in a neutrino detector. It operates in conjunction with SBND's photon detection system, which consists of photomultiplier tubes and X-ARAPUCAs. Early light-collection measurements show high uniformity and light response across the detector, supporting improved triggering, calorimetry, and position reconstruction in SBND.
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All authors R. Acciarri, L. Aliaga-Soplin, R. Alvarez-Garrote, D. Andrade Aldana, C. Andreopoulos, A. Antonakis, S. Balasubramanian, A. Barnard, V. Basque, J. Bateman, M. C. Bazetto, A. Beever, E. Belchior, M. Betancourt, A. Bhat, M. Bishai, A. Blake, B. Bogart, D. Brailsford, A. Brandt, S. Brickner, M. B. Brunetti, L. Camilleri, D. Caratelli, D. Carber, B. Carlson, M. F. Carneiro, W. Castiglioni, R. Castillo Fernandez, F. Cavanna, A. Chappell, H. Chen, S. Chung, R. Coackley, S. Cotton J. I. Crespo-Anadón, C. Cuesta, Y. Dabburi, O. Dalager, M. Dall'Olio, R. Darby, I. de Icaza, M. Del Tutto, Z. Djurcic, S. Dominguez-Vidales, M. Dubnowski, K. Duffy, S. Dytman, A. Ereditato, J. J. Evans, A. Ezeribe, C. Fan, A. Filkins, B. Fleming, W. Foreman, D. Franco, H. Frandini, G. Fricano, I. Furic, A. Furmanski, S. Gao, D. Garcia-Gamez, S. Gardiner, I. Gil-Botella, S. Gollapinni, O. Goodwin, P. Green, W. C. Griffith, L. Hagaman, P. Hamilton, B. Harris, C. Harrison, A. Hergenhan, M. Hernandez-Morquecho, P. Holanda, C. James, R. S. Jones, M. Jung, T. Junk, D. Kalra, G. Karagiorgi, L. Kashur, K. J. Kelly, W. Ketchum, M. King, J. Klein, L. Kotsiopoulou, S. Kr Das, T. Kroupová, V. A. Kudryavtsev, N. Lane, H. Lay, R. LaZur, J.-Y. Li, K. Lin, B. R. Littlejohn, L. Liu, W. C. Louis, X. Lu, X. Luo, A. Machado, P. Machado, C. Mariani, F. Marinho, J. Marshall, C. Martin-Morales, A. Mastbaum, K. Mavrokoridis, N. McConkey, B. McCusker, J. Mclaughlin, K. Mistry, M. Mooney, A. F. Moor, G. Moreno Granados, C. A. Moura, J. Mueller, S. Mulleriababu, A. Navrer-Agasson, M. Nebot-Guinot, V. C. L. Nguyen, F. J. Nicolas-Arnaldos, J. Nowak, S. B. Oh, N. Oza, O. Palamara, N. Pallat, V. Pandey, A. Papadopoulou, H. B. Parkinson, J. Paton, L. Paulucci, Z. Pavlovic, D. Payne, L. Pelegrina-Gutiérrez, O. L. G. Peres, V. L. Pimentel, J. Plows, G. Putnam, X. Qian, R. Rajagopalan, P. Ratoff, H. Ray, M. Reggiani-Guzzo, M. Roda, J. Romeo-Araujo, M. Ross-Lonergan, N. Rowe, P. Roy, A. Sanchez-Castillo, P. Sanchez-Lucas, D. W. Schmitz, A. Schneider, A. Schukraft, H. Scott, E. Segreto, M. Shaevitz, P. Singh, B. Slater, J. Smith, R. Soares, M. Soares-Nunes, M. Soderberg, S. Söldner-Rembold, F. Spagliardi, J. Spitz, M. Stancari, T. Strauss, A. M. Szelc, C. Thorpe, D. Totani, M. Toups, C. Touramanis, L. Tung, G. A. Valdiviesso, R. G. Van de Water, A. Vázquez-Ramos, L. Wan, M. Weber, H. Wei, T. Wester, A. White, A. Wilkinson, P. Wilson, T. Wongjirad, E. Worcester, M. Worcester, S. Yadav, E. Yandel, T. Yang, L. Yates, S. Yebes, B. Yu, H. Yu, J. Yu, B. Zamorano, J. Zennamo, C. Zhang

Fluid Dynamics

Droplet Fusion as a Relaxation Process: Comparison with Shape Recovery of Newtonian and Viscoelastic Droplets

Mohammad Moein Naderi, Zhangli Peng and Huan-Xiang Zhou

Biomolecular condensates formed by phase separation often exhibit viscoelastic behavior, yet their shape recovery and fusion dynamics are frequently interpreted using purely viscous models. Here, we develop a unified theoretical and computational framework to quantify how viscoelasticity governs these two processes. We combine analytical theory for small-deformation shape recovery with axisymmetric finite-element simulations based on the Oldroyd-B constitutive model to systematically investigate both shape recovery and droplet fusion under comparable conditions. Our results show that, although both processes are driven by capillary forces, they are fundamentally distinct in their underlying physics. Shape recovery is governed by global viscocapillary relaxation of a single connected interface and follows single- or multi-exponential decay depending on the relative magnitude of the viscocapillary timescale and the stress relaxation time. In contrast, droplet fusion is intrinsically a multistage process involving localized curvature-driven neck formation, rapid bridge expansion, and a transition to global relaxation. We demonstrate that viscoelasticity introduces an additional intrinsic timescale that governs the competition between capillary driving and stress relaxation, characterized by the Deborah number. This leads to enhanced intermediate-stage fusion dynamics and modified relaxation behavior compared to Newtonian droplets. Furthermore, we show that the presence of an exterior fluid introduces additional hydrodynamic dissipation, significantly slowing the fusion process. Finally, we compare the computationally predicted droplet fusion in the Newtonian and viscoelastic cases with a stretched-exponential empirical formula. Deviations observed in viscoelastic regimes highlight the limitations of purely viscous descriptions and the need for models incorporating stress relaxation.
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Optics

Routes to Chaos in Class-B laser Dimer Necklaces

J. Diaz-Avila, A. A. Macias Infante, B. R. Jaramillo-Avila et al. (+1 more)

Linear $\mathcal{PT}$-symmetric dimer necklaces use cyclic coupling to organize phase-locked modes, while class-B laser–resonator dimers use carrier inversion to destabilize gain–loss dynamics and produce routes to chaos. We study a cyclic necklace of class-B laser–resonator dimers to determine how inter-dimer coupling and cyclic phase constraints modify carrier-mediated instabilities. The carrier inversion turns the necklace into an amplitude–phase–carrier system whose active-site gain controls intensities, while the linewidth-enhancement factor shifts phases. We derive the real dynamical equations, identify uniform fixed points above threshold, and classify their phase configurations under cyclic closure. Even necklaces support full synchronization, a uniform $\pi$ shift, and two alternating phase configurations; odd necklaces support only the first two. Linear stability of these configurations partitions the coupling plane into sixteen possible regions, including one region with no stable uniform fixed point. Long-time simulations for representative two- and three-dimer necklaces show stable lasing, multistability, and irregular lasing controlled by pump ratio and coupling strengths. Increasing the pump ratio expands stable domains and suppresses the region without stable uniform fixed points.
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All authors J. Diaz-Avila, A. A. Macias Infante, B. R. Jaramillo-Avila, B. M. Rodriguez-Lara

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

Challenging the $p$-type Paradigm: Intrinsic $n$-type Mobility in Antiferromagnetic Cr$_2$O$_3$

Á. A. Carrasco Álvarez and S. Poncé

Chromium oxide (Cr$_2$O$_3$) is widely considered a $p$-type transparent conducting oxide despite ongoing debate regarding its intrinsic transport character. Here, we resolve this question by computing phonon-limited electron and hole mobilities using the ab initio Boltzmann transport equation. We find that electron mobility systematically exceeds hole mobility over a wide temperature range, demonstrating that Cr$_2$O$_3$ is intrinsically $n$-type. Analysis of scattering mechanisms reveals that scattering with phonons affects electrons and holes similarly, and that the mobility asymmetry originates from the electronic structure, namely the larger effective mass and multi-valley character of the valence band. The intrinsic $n$-type character, combined with moderate hole mobility, enables bipolar transport and revises the role of Cr$_2$O$_3$ in transparent electronics. Additionally, our results on mobility complement previous studies on defect formation indicating that the commonly observed $p$-type behavior is extrinsic. These insights provide a complete chemical-transport paradigm for Cr$_2$O$_3$, re-evaluating its role in functional transparent electronic and magneto-optoelectronic applications
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Optics · Cross-listed from quant-ph

Complex frequency-dependent quadrature squeezing in semiconductor lasers

Daniele Nello, Giuseppe Patera and Lorenzo Columbo

We present a comprehensive study of quadrature squeezing in a quantum well laser based on a fully quantum Langevin approach. We compute the frequency-resolved squeezing map of the laser field and identify optimal squeezing curves, revealing, for the first time to our knowledge, both frequency-dependent squeezing and complex or hidden squeezing in a semiconductor laser. We further analyse the role of the linewidth enhancement factor (alpha-factor) in the emergence of these features. Our results establish semiconductor lasers as a platform for the generation of non-classical light and open new perspectives for their application in quantum communication and sensing.
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Fluid Dynamics · Cross-listed from cond-mat.soft

Odd Diffusion in Three-Dimensional Isotropic Media

Viola Zixin Zhao, Andres Franco Valiente and David T. Limmer

Odd diffusion is a hallmark of chiral active matter, generating currents transverse to density gradients. Existing theories rely on a linear antisymmetric transport coefficient that exists only in two dimensions, raising the question of whether odd diffusion can occur in isotropic three-dimensional systems. Here we show that such transport is possible through a nonlinear constitutive law. Symmetry considerations reveal that the three-dimensional Levi-Civita tensor permits a leading order isotropic odd current at second order in the density gradient expansion and only in multicomponent systems. The resulting transport generates boundary-driven rotational currents, finite vorticity, and enstrophy despite the absence of external torques or preferred directions. We show how such a constitutive law derives from a microscopic model of particles interacting through nonreciprocal three-body forces using the Dean–Kawasaki coarse-graining procedure. These results establish a minimal framework for odd transport in isotropic three dimensions.
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Data Analysis and Statistics

Interpreting "Interpretability" and Explaining "Explainability" in Machine Learning in Physics

Rikab Gambhir, Luisa Lucie-Smith and Jesse Thaler

We review the concepts of interpretability and explainability as they apply to machine learning in physics. We define interpretability as concerning the structural transparency of a model (the ability to understand or approximate its inner workings) and explainability as concerning the scientific content of a model (the ability to map it onto domain knowledge). We discuss the trade-offs each entails (interpretability vs. expressivity; explainability vs. adaptability), the contexts in which each is needed, and the intrinsic and post-hoc tools available for achieving them. Throughout, we emphasize that machine-learned models are subject to the same scientific questions as classical models, differing only in scale, and that interpretability and explainability are best understood as deliberate modeling choices rather than inherent properties. We also emphasize the importance of task specification and intervention plans as a core aspect of model design.
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Plasma Physics · Cross-listed from astro-ph.GA

Latent thermal instability

Prakriti Pal Choudhury and Archie F. A. Bott

Multiscale temperature fluctuations are abundant in the intracluster medium (ICM) outside of galaxy cluster cores ($\sim 100~{\rm kpc}$). Their origin is often attributed to turbulent stirring by subhalos or accreting baryons crossing the virial radius. However, their apparent resistance to mixing and thermal conduction in a collisional medium has not been explained. We propose a new mechanism by which steady-state temperature fluctuations can form and persist outside the cluster core. Local thermal instability, or Field instability, is used to explain filamentary condensates in cluster cores but is usually dismissed outside them because thermal conduction should suppress instability. In weakly collisional or collisionless plasmas, however, thermal conduction can be anomalously suppressed by heat-flux-driven plasma instabilities triggered in presence of a local magnetic field, leading to two effects: (i) condensates form in a new parameter regime that overlaps with conditions outside the core, and (ii) condensates reach a steady state as in the hydrodynamic limit. This extends the regime of instability-driven fluctuations to over $\gtrsim50\%$ (depending on hot plasma temperature) of the cluster. We use one-dimensional hydrodynamic simulations of condensates to test our analytical ideas.
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Plasma Physics

Single-Shot Intensity-Correlation Diffractive X-ray Imaging of ICF Plasmas

Kenan Qu, Daniel Bhatti and Nathaniel J. Fisch

X-ray radiography of inertial confinement fusion plasmas is currently limited to several-micron resolution by geometric blur, diffraction, and photon-throughput tradeoffs. We propose single-shot intensity-correlation diffractive imaging (IDI) as a lensless route to submicron plasma turbulence measurements under low-self-emission conditions. Rather than relying on physical apertures, IDI reconstructs plasma morphology by Fourier transforming the spatial correlations of chaotic far-field speckles via the Hanbury Brown-Twiss effect. The Fourier phase is retrieved by applying bispectral closure-phase constraints derived from third-order intensity correlations. We demonstrate this submicron capability in a numerical simulation using a $50~\mathrm{keV}$ x-ray probe scattered by a spiral plasma structure.
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Instrumentation and Detectors

Application of surface coating for radon mitigation in rare-event searches

Florian Jörg, Guillaume Eurin and Hardy Simgen

Rare-event searches offer a powerful avenue for investigating some of the most fundamental questions in modern physics, most prominently the particle nature of dark matter and the possible Majorana nature of the neutrino. Often, their dominant source of background comes from the radioactive noble gas radon emanating from materials. We report on a novel strategy to mitigate this background by the application of coating layers. A method for electroplating of copper was developed that showed a thousandfold reduction of the $^{222}$Rn emanation rate from a $^{226}$Ra-implanted stainless steel sample.
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Applied Physics · Cross-listed from cs.RO

Morphology-Specific Closed-Loop Control of Logarithmic-Spiral Continuum Arms via Online Jacobian Error Compensation

Partha Datta, Yi Jin, Wei Lin et al. (+1 more)

Logarithmic spirals are ubiquitous in biological appendages and provide an attractive morphology for continuum manipulators capable of reaching, wrapping, and grasping. Recently reported logarithmic-spiral robots demonstrated scalable fabrication and versatile grasping but lacked inverse kinematics and closed-loop control. This work presents the first morphology-specific closed-loop task-space control framework for logarithmic-spiral continuum arms. A segmented tendon-driven model with a centerline backbone and equilateral tendon routing is developed in MuJoCo to capture tapered compliance and contact dynamics. An analytical task-space Jacobian is derived directly from the logarithmic-spiral kinematics and combined with online Jacobian error compensation using a Broyden secant update and Kalman-filter estimation. The resulting controller continuously corrects modeling errors arising from nonlinear deformation, contact, and geometric mismatch. The framework is validated through planar and spatial simulations, including trajectory tracking, attitude regulation, disturbance rejection, three-dimensional position tracking, and simultaneous position-orientation control. Compared with a piecewise-constant-curvature (PCC) baseline, the proposed method consistently reduces tracking errors, suppresses attitude drift, and maintains a bounded Jacobian estimation error. The controller is further applied to morphology-enabled manipulation tasks, including obstacle-assisted reach-wrap-release motions, adaptive whole-arm grasping, and cooperative multi-arm object handling. Results demonstrate that combining logarithmic-spiral morphology with online Jacobian compensation enables accurate, robust, and scalable control of highly underactuated continuum manipulators. The proposed framework establishes a physics-grounded baseline for future hardware implementation and learning-augmented soft robotic control.
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All authors Partha Datta, Yi Jin, Wei Lin, C. Chase Cao

Atomic Physics

Infinite-time surface flux for full-dimensional three-body breakup dynamics

Jinzhen Zhu

We derive an infinite-time surface-flux formulation for full-dimensional three-body breakup dynamics in intense laser fields. The method is designed as a post-pulse extension of time-dependent surface flux (tSurff) calculations for systems with two asymptotic fragments, with helium double ionization and dissociative ionization of $\hydroplus$ as representative applications. Standard tSurff calculations avoid projection on very large boxes, but the spectra still contain a field-free tail after the laser pulse; converging this tail by direct propagation can be expensive for slow particles, narrow resonances, and long-range Coulomb channels. Here the post-pulse time integrals are rewritten as resolvents of the field-free one-particle ionic Hamiltonians and of the full field-free three-body Hamiltonian. The resulting expressions separate the already available tSurff amplitudes from stationary correction terms that can be evaluated from saved wave functions in the inner and single-ionization regions. The formulation gives a common theoretical structure for electron-electron breakup in helium and electron-nuclear breakup in $\hydroplus$, and it is compatible with the spectral decompositions and MPI-parallel workflow of the tRecX framework. This provides a practical route to tSurff+iSurff calculations of correlated three-body spectra without long post-pulse propagation and without solving a large complex linear system independently for every final momentum.
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Data Analysis and Statistics · Cross-listed from cs.LG

\chisao{}: A GPU-Native Parallel Optimizer for Multimodal Black-Box Functions via Convergence-Anticonvergence Oscillation

Ira Wolfson

Finding all modes of a multimodal black-box function is a fundamental challenge in optimization, Bayesian inference, and scientific computing. Existing approaches – basin-hopping, CMA-ES, multistart gradient descent – operate sequentially and cannot exploit the massive parallelism of modern GPU hardware. We introduce \chisao{} (Convergence-Halt-Invert-Stick-And-Oscillate), a GPU-native population optimizer that runs an entire sample batch simultaneously and exploits a deliberate convergence-anticonvergence oscillation cycle to escape local traps while freezing confirmed modes. The structural move is asymmetric: samples that reach true peaks are frozen (“stuck”) and preserved, while the rest keep exploring via momentum-based anti-convergence and stochastically smoothed gradients. Adaptive reseeding via two complementary strategies (Repulse Monkey and Golden Rooster) maintains population diversity throughout. On all 42 functions of the Simon Fraser University optimization benchmark suite across dimensions $d \in \{2, 4, 8, 16, 32, 64\}$, \chisao{} achieves 100% mode recovery where all CPU baselines collapse at $d \geq 8$ on the hardest multimodal functions, at up to \textbf{$34\times$} speedup over basin-hopping on functions where all methods succeed (Michalewicz $d=64$) and up to \textbf{$39\times$} on unimodal functions (Rotated Hyper-Ellipsoid $d=64$, pure GPU dividend). All benchmarks evaluate the objective by value alone – gradients come from finite differences – so the reported speedups are a derivative-free worst case. Under substantial likelihood noise ($\sigma_{\mathrm{noise}}$ up to 1.0), mode detection remains 100% reliable. The algorithm is available as a standalone open-source Python package on PyPI.
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Optics

Microparticles manipulation with a three-dimensional closed optical trap

Chunyu Zhang, Xinran Fang, Pengcheng Mao et al. (+1 more)

Gaussian optical tweezers have strong phototoxicity to bioactive substances and it is difficult to achieve capture and manipulation of multiple particles. Moreover, vortex optical tweezers face several challenges, such as weak axial confinement and dependence on complex optical elements like a spatial light modulator (SLM). Therefore, we design and construct a novel three-dimensional (3D) "optical spindle trap" (OST) system that does not require a SLM. By employing intracavity mode modulation and a simple extra-cavity lens modulation, we generate a fully enclosed 3D dark potential well with zero central intensity. Experimental results demonstrate that the system achieves stable trapping of single or multiple micrometer-sized particles with excellent 3D confinement and enables the trapping of mouse hepatocytes under low-power conditions. The system exhibits high physical stability. Its closed dark-field structure can also reduce phototoxic damage to biological samples. Furthermore, the dimensions of the optical trap can be flexibly tuned to suit various application scenarios. This study provides a novel, highly efficient, gentle, and low-cost optical trap platform for biomedicine and micro/nanoscale manipulation.
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All authors Chunyu Zhang, Xinran Fang, Pengcheng Mao, Dongxu Zhao

Chemical Physics

Converging on bound states in coupled-channel calculations

C. Ruth Le Sueur, James F. E. Croft and Jeremy M. Hutson

We develop a robust algorithm for locating bound states in coupled-channel calculations. Bound states exist at energies where an individual eigenvalue of a log-derivative or ratio matching matrix passes through zero. We describe an algorithm to identify the required eigenvalue of the matching matrix over the full range of energy where it exists. This allows much simpler programming than previous methods. We also consider the choice of the matching distance $R_\textrm{match}$, where the matching matrix is defined; coupled-channel methods are most efficient if $R_\textrm{match}$ is chosen to be in the classically allowed region for all channels that support bound states of interest, but not very close to a node in the wavefunction.
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Optics

Spectral contraction from Gaussian beams to Helmholtz waves

A. Dominguez-Cruz and B. M. Rodriguez-Lara

We introduce the ratio between the transverse Helmholtz length and the paraxial Gaussian-beam width as the physical parameter governing the contraction from separable Gaussian beams to transverse Helmholtz waves. For a fixed transverse Helmholtz shell within the paraxial angular spectrum, the large-Rayleigh-range limit drives our optical scale ratio towards zero, while the higher-modal-order limit preserves the shell, transforming the isotropic and astigmatic paraxial oscillator eigenvalue problems into the transverse Helmholtz unit-shell eigenvalue problem. As our optical scale ratio vanishes, it realizes the algebraic Inönü-Wigner contraction of the isotropic Gaussian-beam $\mathrm{su}(2)$ algebra to the quadratic fixed-shell realization of the transverse Helmholtz $\mathrm{e}(2)$ algebra; conversely, finite nonzero values parametrize the Cayley-Klein deformation. Under the joint limit of vanishing scale ratio and higher modal order, paraxial Hermite-, Laguerre-, Ince-, and Boyer-Wolf-Gaussian beams undergo a spectral contraction in which their two modal numbers fix the shell and determine the single separation parameter labeling the corresponding Cartesian, Bessel, Mathieu, and Weber transverse Helmholtz waves, while preserving parity. Our spectral contraction extends to the wave operators, symmetry algebras, separation operators, separated equations, and separation spectra.
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Chemical Physics · Cross-listed from cond-mat.mes-hall

Quantum Back-Action Expands the Excitonic Hilbert Space in a Soft Polar Semiconductor

Arnab Ghosh, Patrick Brosseau, Priya Nagpal et al. (+4 more)

Electronic excitations in solids are commonly described within a hierarchy in which the excitonic Hamiltonian is defined first and the lattice acts later through renormalization, relaxation, and dephasing. This picture assumes that the optically accessible excitonic manifold is already present at the moment of photoexcitation. Here we show that this assumption fails in a soft polar semiconductor. Using femtosecond coherent multidimensional spectroscopy on lead-halide perovskite nanocrystals, we observe quantum back-action between an electronic excitation and a collective lattice-polarization field that expands the excitonic Hilbert space in real time. The optical pulse first prepares an excitonic polarization, X1. A second configuration, X2, emerges only after the polaron field develops, while coherent X1-X2 coupling appears at later times. State formation and coherence formation are therefore resolved as distinct stages of quasiparticle formation. In contrast, CdSe quantum dots exhibit the conventional limit in which excitonic states and couplings are present at time zero and are only weakly perturbed by phonons. The observed diagonal and anti-diagonal splittings increase with nanocrystal size and correlate with radiative oscillator strength, opposite to expectations from simple quantum confinement. A dynamical polaron-field model describes the lattice polarization as an order parameter that expands the optically accessible manifold and generates time-dependent coherent coupling. These results show that strong system-bath coupling can actively create excitonic states and the coherent manifold in which they evolve.
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All authors Arnab Ghosh, Patrick Brosseau, Priya Nagpal, Dmitry N. Dirin, Rui Tao, Maksym V. Kovalenko, Patanjali Kambhampati

Plasma Physics

Laser-intensity-spike-dominated hot electron generation from two-plasmon decay instability driven by moderate-bandwidth pulses

C. Yao, Z. H. Cai, X. Wang et al. (+34 more)

Our direct-drive-relevant experiments on the low-coherence Kunwu laser facility identify two-plasmon decay (TPD) as the primary source of hot electrons, and demonstrate for the first time that broadband laser pulses enhance TPD. Using particle-in-cell simulations, we attribute this TPD enhancement and the consequent hot electron production to stochastic intensity spikes inherent in broadband laser fields, robust in both weakly- and strongly-driven regimes. These findings suggest that mitigating hot electron generation requires suppressing these intensity spikes.
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All authors C. Yao, Z. H. Cai, X. Wang, X. C. Wang, H. R. Yin, Z. A. Zhu, C. W. Lian, Y. Ji, X. Jiang, S. M. Xu, Y. Y. Yao, L. Y. Yang, J. N. Zhang, D. Meng, T. Peng, H. Wen, C. Z. Xiao, K. Y. Meng, J. Li, R. Yan, P. Yuan, Z. Zhang, L. Hao, Q. Jia, W. Feng, H. H. An, H. Y. Liu, Z. Y. Xie, P. P. Wang, C. Wang, A. Lei, X. H. Zhao, Z. H. Fang, W. Wang, Y. Q. Gu, Y-K. Ding, J. Zheng

Fluid Dynamics

Interfacial Spectral Memory as a State Variable for Finite-Depth Salt-Finger Exchange

Sriram P. Kalathoor

Thermohaline interfaces in the ocean are often treated through local double-diffusive favorability, yet finite interfaces can also inherit roughness from prior waves, stirring, intrusions, and earlier mixing events. Such inherited geometry can matter because salt fingering does not develop from a flat abstract surface in many geophysical settings. We use controlled three-dimensional direct simulations to test whether the spectral state of a finite rough interface changes the pathway by which salt-finger activity develops between adjacent layers. The density ratio, diffusivity ratio, Prandtl number, interface thickness, roughness amplitude, domain, resolution, and analysis window are held fixed; only the imposed roughness spectrum and, for one pair, the realization are changed. Broad low-mode memory produces the largest cumulative salt exchange and the earliest finite-depth contact. High-annulus memory remains localized and intermediate-scale dominated. Mixed memory produces delayed scale transfer and scalar-rich structure that is robust in integrated exchange and broad-memory measures across a second realization, while local plume timing and probe amplitudes remain realization-sensitive. The simulations therefore support treating interfacial spectral memory as an additional state variable for finite-depth double-diffusive exchange, complementary to local thermodynamic descriptors.
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