Instrumentation and Detectors
CMOS Image Sensors for CEvNS Detection at Nuclear Reactors
Santiago Ezequiel Perez, Dario Rodrigues and Miguel Sofo-Haro
In this work we present Complementary Metal-
Oxide-
Semiconductor (CMOS) Image Sensors (CIS) for reactor
neutrino experiments targeting coherent elastic
neutrino-
nucleus scattering (CEvNS). We have developed an active-shielding strategy for physical background reduction along with an analytical model describing the impact of intrinsic detector backgrounds from dark current and readout noise at a given frame rate (fps). Assuming a conservative background of 100 DRU, and a feasible CIS-based detector with $\sim$100g of sensitive silicon mass, 1$e^-$ of readout noise, and 200fps, it can detect CEvNS in less than 50 days at 16 meters from a 3.6 GW thermal reactor core. Improving the detector performance to 0.2$e^-$ readout noise and 1000fps substantially reduces the detection time to about 7 days. These results establish CIS technology as a promising platform for reactor monitoring and precision
neutrino measurements, with thick CMOS sensors featuring parallel and non-destructive readout emerging as particularly attractive candidates for next-generation CEvNS experiments.
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Classical Physics · Cross-listed from cond-mat.stat-mech
Classical fractons with cosmological fixed points
Akash Singh, Dileep P. Jatkar, S. L. Sondhi et al. (+1 more)
Classical fractons are
Hamiltonian systems that can develop attractors after projection onto configuration or shape variables, although the full phase space admits none. We study a scale-invariant, dipole-conserving two-parameter family of fracton
Hamiltonians $H_{\alpha,\beta}$. By separating coordinates into scale and shape, we obtain autonomous shape dynamics that admit fixed points which leave a purely scale
evolution of the form $R(t)\propto |t|^{\alpha/(\alpha-\beta)}$. The shape fixed points, which determine the distribution of the expanding particles, are central configurations of power-law Riesz potentials. The distinguished model $(\alpha,\beta)=(-2,1)$ is unique: its scale
evolution takes the Einstein-de Sitter form $R(t)\propto |t|^{2/3}$, its fixed-point equation is the equal-mass Newtonian central-configuration, its large-$N$ distribution is a homogeneous ball, and its homothetic trajectories admit a zero-energy Newtonian gravitational dual. The fixed points are locally stable, and simulations at moderate $N$ approach them from random initial data. Large $N$ simulations reveal a richer class of fixed-points: bound clusters of approximately fixed physical size retain internal motion, while their centers approach unequal-mass Newtonian central configurations and preserve large-scale homogeneity. A scale-separation
conjecture yields an effective unequal-mass fracton dynamics for the centers and a corresponding zero-energy Newtonian gravitational dual. Trajectories generically exhibit a bidirectional arrow of time: scale and shape complexity grow away from a Janus point, while Boltzmann
entropy grows logarithmically. Together, these features reproduce the salient structure of a flat matter-dominated cosmology. In the distinguished fracton model, all these cosmological analogues emerge as attractor properties, making it a toy model for cosmological dynamics without fine-tuning.
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All authors Akash Singh, Dileep P. Jatkar, S. L. Sondhi, Abhishodh Prakash
Atomic Physics · Cross-listed from hep-ph
Testing Antimatter Couplings with Spectroscopy
Joerg Jaeckel and Lucas Puetter
We investigate how scalar-mediated potentials with Lorentz-violating couplings to Standard Model
fermions affect spectroscopic observables in atoms and highly charged ions. Suitable combinations of an ordinary scalar and a time-like component of a Lorentz violating vector coupling allow for a split into "matter" and "antimatter" couplings, at least in the non-relativistic limit. By considering hydrogen and antihydrogen spectra, we access both matter and antimatter couplings. While relativistic effects alone lift degeneracies in ordinary hydrogen, providing indirect access to antimatter couplings, comparisons with antihydrogen measurements lead to significantly improved sensitivity to the antimatter couplings. In highly charged ions, enhanced relativistic effects further amplify the sensitivity, compensating for reduced experimental precision and larger theoretical uncertainties. We obtain the strongest bounds to date for scalar masses $m_\phi \gtrsim 400\:\mathrm{keV}$. For comparison, we estimate astrophysical constraints on the same parameter space, providing strong bounds even on antimatter couplings, despite
stars being predominantly composed of matter.
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Computational Physics · Cross-listed from stat.ML
Leveraging generative models to assist Monte Carlo sampling
Marylou Gabrié
Sampling high-dimensional probability distributions is a central task in scientific computing, with applications ranging from
Bayesian inference to statistical physics and molecular simulation. Despite decades of methodological developments, two major challenges remain: scaling to high dimensions and efficiently exploring
multimodal distributions characterized by metastable states. Classical approaches such as Markov chain Monte Carlo, tempering methods, or enhanced sampling based on collective variables have achieved major successes, but they also face intrinsic limitations. This tutorial review explores a new paradigm that has recently emerged at the interface of machine learning and computational statistical physics: the use of generative models as tools for sampling. In this context, models such as normalizing flows and
diffusion models are not used in their traditional data-driven setting, but rather as flexible probabilistic models that can assist the sampling of distributions known only up to a normalization constant. This manuscript reviews the early development of this rapidly evolving field and discusses several methodological directions, including exact samplers based on generative models and strategies to train such models in the absence of data. While an exhaustive survey of the literature is not attempted, we present a selection of key ideas and methods, along with a discussion of their strengths and limitations. The review is intended to be an accessible tutorial for both physics and machine learning audiences, and it aims to provide a starting point for researchers interested in exploring this exciting area of research.
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Fluid Dynamics
Fluid-Structure Interaction and Underwater Hydrostatic Implosion of Thin-Walled Metallic Cylinders in Semi-Confined Conditions
Bolaji Oladipo, Helio Matos, Arun Shukla et al. (+1 more)
This study presents a comprehensive numerical investigation of the dynamic behavior and fluid-structure interactions (FSI) of metallic cylinders undergoing hydrostatic collapse in semi-confined fluid environments using a structured Arbitrary Eulerian-Lagrangian (ALE) formulation in LS-DYNA. The numerical model reproduces the experimentally measured collapse pressure of 3.69 MPa and predicts the first water hammer peak with a 1.01% error, demonstrating high predictive fidelity. Following validation, the effects of material type (aluminum and titanium), cylinder slenderness ratio (L/D), and confinement diameter on collapse behavior, pressure
evolution, and fluid motion are examined. Titanium cylinders exhibited sharper collapses, higher water hammer pressures exceeding 70 MPa, and greater kinetic and strain energy accumulation than aluminum due to their higher stiffness and yield strength. Lower L/D ratios produced more abrupt collapses, whereas higher L/D ratios promoted more gradual, axisymmetric deformation. Larger confinement diameters intensified jet formation and increased fluid velocities. The simulations provide mechanistic insight into the coupling between structural deformation and surrounding fluid, showing that geometry, material stiffness, and confinement govern collapse-induced energy transfer. Full-field FSI analysis captures key phenomena, including radial jetting, peak fluid velocities, and internal cavitation, that are not evident from pressure-time histories alone. These findings provide quantitative guidance for the design and safety assessment of subsea pressure housings, marine pipelines, and other
underwater structures subjected to extreme hydrostatic loading.
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All authors Bolaji Oladipo, Helio Matos, Arun Shukla, Sumanta Das
Fluid Dynamics
Efficient three-dimensional variational data assimilation of multi-plane PIV data
Uttam Cadambi Padmanaban, Samaresh Midya, Ping He et al. (+2 more)
We perform three-dimensional variational data assimilation (3DVar) using a discrete adjoint approach to optimise the time-averaged momentum equations. The experimental data consist of sparse stereoscopic particle image velocimetry (PIV) measurements collected along $12$ cross-stream planes in the wake of a vehicle-like bluff body at a Reynolds number $Re_L = 5.64 \times 10^5$ based on the streamwise body length. Adjoint localisation is proposed and implemented to reduce the
memory footprint of the discrete adjoint method for spatially-varying control variables in 3DVar by confining the control variable space to a user-defined subdomain. Restricting the control variable to $12$ % of the full control space yields a maximum reduction in peak
memory of $64$ %, while producing assimilated fields of comparable fidelity with respect to mean velocity and the optimised momentum forcing field. The localised adjoint case improves upon the baseline Spalart–Allmaras
turbulence model and recovers the correct asymmetric
topology of the complex three-dimensional (3D) recirculation bubble. The assimilated Reynolds shear stress agrees well with the experiment, and the assimilated mean pressure is shown to be physically consistent when correlated with the in-plane vorticity fields. A data efficiency study is also performed, in which the number of planes provided for assimilation is progressively reduced, demonstrating that the data coverage must extend at least to the end of the primary recirculation bubble to adequately constrain the near-wake dynamics. The efficiency that adjoint localisation affords is crucial for assimilating sparse, experimental data for 3D separated flows on fine meshes that can tackle industrial problems of interest.
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All authors Uttam Cadambi Padmanaban, Samaresh Midya, Ping He, Bharathram Ganapathisubramani, Sean Symon
Plasma Physics
Characterization of a prototype parallel-plate $^{238}$U fission chamber with DD and DT fusion neutron sources
V. Hagenlocker, R.A. Tinguely, X. Wang et al. (+5 more)
The SPARC tokamak will employ $^{238}$U-based fission chambers (FCs) to monitor high-performance deuterium-tritium (DT)
plasma operations, spanning
neutron yield rates from ${\sim}10^{15}$ to ${>}10^{19}$ n/s. This work validates the $^{238}$U FC design, which utilizes a parallel-plate detector geometry and borated polyethylene collimation to prioritize unscattered DD and DT fusion
neutrons. Experimental testing with both DD and DT
neutron generators corroborates vendor-specified efficiencies and demonstrates excellent detector linearity, with measured count rates showing good agreement with OpenMC neutronics simulations. Further characterization confirms the $^{238}$U FC's robustness against SPARC-relevant environmental challenges, including stray
magnetic fields up to 14 mT and possible signal degradation risks associated with $\sim$30 m long cable runs. These results confirm that the $^{238}$U FC, supported by indirect
neutron shielding as well as appropriate pulse height thresholds, provides a reliable solution for fusion power measurements as part of the SPARC
neutron diagnostics suite.
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All authors V. Hagenlocker, R.A. Tinguely, X. Wang, J.L. Ball, B. Buschmann, M. Gatu-Johnson, R. Gocht, P. Raj
Physics and Society · Cross-listed from cs.AI
Interaction Creates Dynamical AI Behavior Absent in Isolation
Bella Xinrui Li, Frank Yingjie Huo and Neil F Johnson
What will happen when AI
agents interact in daily life, e.g. when one AI starts bossing another around? We find a counterintuitive answer that opens new avenues for out-of-
equilibrium Physics. When a boss AI directs a stream of messages at the subordinate AI while ignoring its replies, it drives the subordinate into an alien behavioral state that it would never have exhibited alone. Although the two AIs share the same well-defined (decoding) temperature, the subordinate neither copies its boss nor returns to how it behaves on its own; instead, it adopts an entirely different behavior. The boss's added value is similar to a pre-recorded tape. When the boss listens, they both adopt a similar alien dynamical state. A simple kinetic theory captures the principal effects, such as why the way in which the same messages are delivered will matter in future AI-AI interactions.
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Atomic Physics · Cross-listed from hep-ph
Optimal Calibration-Free Observable for the Nucleon-Coupling Ratio in a Dual-Alkali Comagnetometer for Dark Matter Searches
Yossi Rosenzweig, Yevgeny Kats, Eli Sarid et al. (+3 more)
A dual-alkali single-
cell $^{87}$Rb-$^{39}$K-$^{3}$He comagnetometer can read an
axion-like dark matter signal through two optical rotation channels, encoding the ratio $\mathcal{R}=\xi_n/\xi_p$ of the field's
neutron and
proton spin couplings in their relative response. The inter-species phase difference $\Delta\varphi$ has been proposed as a calibration-free readout that is sensitive to $\mathcal{R}$. Treating the extraction of $\mathcal{R}$ as a statistical estimation problem, we show that the estimate of $\mathcal{R}$ depends on the two channels only through their complex ratio, which splits into $\Delta\varphi$ and an amplitude ratio, of which only $\Delta\varphi$ is insensitive to the relative gain and hence calibration free. For our choice of comagnetometer parameters, above $\sim\!100$ Hz the phase difference alone captures most of the coupling-ratio information. At lower frequencies $\Delta\varphi$ is no longer near-sufficient. Below $\sim\!40$ Hz, the amplitude ratio would improve the precision on $\mathcal{R}$ by a factor of $\gtrsim2$. Recovering that information, however, requires the relative gain to be known sufficiently accurately, so $\Delta\varphi$ remains the robust observable even where it is not the most informative one.
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All authors Yossi Rosenzweig, Yevgeny Kats, Eli Sarid, Menachem Givon, Yonathan Japha, Ron Folman
Atomic Physics
Observation of $\Pi$-symmetry ultralong-range Rydberg molecules
Matthew T. Eiles, Aleksandr Zaitsev, Dominik Dorer et al. (+5 more)
We observe weakly-bound $\Pi$-
symmetry electronic states in the spectroscopy of $^{87}$Rb$(nP_{3/2})$+$^{87}$Rb($5S_{1/2}$) ultralong-range Rydberg molecules. We detect these molecules in Rydberg states having principal
quantum number $13\le n \le 16$. Their $\Pi$-state character is unambiguously identified via their observed multiplet structure: the $2F+1$
magnetic sublevels of the ground-state rubidium atom separate, as in the Zeeman effect, because of the
spin-
spin coupling between the Rydberg and valence electrons. We find a rapid decrease in the molecular binding energy $\propto (n-\mu_{P_{3/2}})^{-11}$, where $\mu_{P_{3/2}}$ is the
quantum defect, indicating that the low-$n$ regime of Rydberg states is ideally suited for studies of $\Pi$-
symmetry molecules. Our observations are in good agreement with Green's function-based calculations for $14\le n\le 16$, with poorer agreement for $n=13$ hinting at the beginning of a breakdown of the
Fermi pseudopotential approach at low $n$.
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All authors Matthew T. Eiles, Aleksandr Zaitsev, Dominik Dorer, Shinsuke Haze, Markus Deiß, S. Efe Gürleyen, Chris H. Greene, Johannes Hecker Denschlag
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Permutation invariant neural network prediction of vacancy formation under deformation and varying chemical environment in FCC high entropy alloys
Tanvir Sohail and Swarnava Ghosh
Vacancy formation energies govern
diffusion, irradiation damage, phase stability, and dynamic failure in high-
entropy alloys (HEAs), yet their strong dependence on local chemical environments and mechanical deformation makes atomistic calculations prohibitively expensive for large-scale studies. Here, we develop an atomistically informed permutation invariant machine learning framework for predicting strain dependent vacancy formation energies in FCC HEAs from local atomic environments. The model employs a vacancy-centered representation constructed from objective
geometric descriptors together with invariants of the local deformation gradient, enabling the coupled effects of chemical disorder and finite deformation to be learned within a unified framework. Atomistic simulations reveal that volumetric deformation is the dominant factor controlling the average variation in vacancy formation energy, whereas shear deformation has a comparatively minor influence. At the same time, substantial site to site variability persists under identical macroscopic loading, demonstrating that local chemical environments govern the statistical distribution of vacancy energetics beyond species-averaged trends. The proposed framework accurately predicts vacancy formation energies across diverse deformation states while providing orders-of-magnitude faster evaluation than direct atomistic simulations. These results establish an efficient route for incorporating stress-dependent defect energetics into multiscale models of
diffusion, irradiation damage, and dynamic failure in chemically complex
alloys.
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Atomic Physics · Cross-listed from cond-mat.quant-gas
Phase-Noise-Induced Heating in Optical Lattices
Jean Paul Nohra, Cyprien Daix, Joris Verstraten et al. (+5 more)
We experimentally and theoretically study the origin of heating in optical
lattices by disentangling the respective roles of intensity and phase noise depending on the
lattice parameters. While intensity noise is widely identified as a major limiting factor, we show that phase noise can become the dominant heating source, especially for light atoms and deep optical
lattices. We provide a simple theoretical framework to predict the phase-noise-induced heating from the power spectral density of the
laser phase noise, which can be measured experimentally. We show that such predictions can accurately reproduce the measured heating rates of lithium-6 atoms in a triangular
lattice. Our approach is readily generalized to other
lattice geometries and atomic species.
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All authors Jean Paul Nohra, Cyprien Daix, Joris Verstraten, Maxime Dixmerias, Tim de Jongh, Bruno Peaudecerf, Fabrice Gerbier, Tarik Yefsah
Optics
Active Control of Extreme Ultraviolet Photon Flux and Resolution with a Plane Ruled Reflection Grating Spectrometer that Measures Diverging High-Harmonics
Caleb H. DeWitt, Nnamdi C. Okey, Griffin W. Hancock et al. (+1 more)
High harmonic generation is a versatile tabletop source for the investigation of ultrafast dynamics with atomic fidelity and few-femtosecond time resolution. However, intensity modulations in the high harmonic spectra due to an alternating peak-and-valley structure in femtosecond extreme ultraviolet (XUV) sources can lead to significant distortions in measured XUV absorption spectra. We report a broadband extreme ultraviolet (XUV) spectrometer with a plane ruled reflection grating that can be spectrally adjusted on the fly using a motorized iris aperture in the entrance slit to control the divergence of the XUV beam prior to its dispersive detection. The effective divergence is tuned between 0.03 to 1.9 milli-radian with concomitant variation in the detected XUV
photon counts of 1.0 $\times$ 10$^6$
photons/s/eV to 1.5 $\times$ 10$^7$ near 40 eV. Metallic samples of Fe (10 nm) and Ti (10 nm) deposited on Si$_3$N$_4$ membranes (100 nm) are measured under these conditions, with a spectral coverage of > 30 eV and a resolution of up to 500 meV. A volcano plot between signal-to-noise ratio (SNR) and spectral resolution determines the trade-off point in measuring elemental near-edge absorption spectra of thin film samples. Consistent with ray tracing simulations, we show that this design parameter offers on-demand high resolution or high SNR configurations for the rapid acquisition of XUV absorption spectra of thin film solid-state samples, especially strongly correlated materials.
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All authors Caleb H. DeWitt, Nnamdi C. Okey, Griffin W. Hancock, Aditi Bhattacherjee
Optics
Harnessing bound states in the continuum for quantum and nonlinear photonics in silicon nitride microresonators
Eduardo C. Lima, Marco Clementi, Alice Viola et al. (+4 more)
In this work we theoretically and experimentally investigate bound states in the continuum (BICs) in a reconfigurable integrated photonic structure, focusing on spontaneous four-wave mixing. We consider a configuration in which only one mode, the idler, is tuned to the BIC condition, and show that suppressing the radiative loss of this single mode profoundly reshapes the overall nonlinear dynamics. In particularly, we realize electrically tunable Friedrich-Wintgen BICs with Q > 10^6 in an interferometrically coupled silicon-nitride microresonator. Although inaccessible through linear excitation, the BIC is populated by four-wave mixing and read out through its radiative
photon partner. In the low-gain regime, we investigate the spectral, correlation, and coherence properties of the generated
photon pairs, revealing distinctive signatures in the signal-idler correlations and an extracted signal whose coherence time approaches the intrinsic-loss-limited lifetime of the dark idler. In the high-gain regime, making one mode participating in optical parametric amplification a BIC enhances the parametric gain by 12 dB and lowers the oscillation threshold by 1.6 dB. These results establish BICs as a tool for mode-selective lifetime engineering, enabling control over both biphoton wavepackets and the threshold dynamics of integrated parametric devices.
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All authors Eduardo C. Lima, Marco Clementi, Alice Viola, Matteo Galli, Daniele Bajoni, Marco Liscidini, Massimo Borghi
Optics
Optomechanical Levitation and Control of High Aspect Ratio Silicon Nanorods
Zhenan Chen, Sophie Sanghera, Yanhui Hu et al. (+7 more)
Nano- and micro-particles levitated by optical, electrical or
magnetic fields are a new frontier in precision sensing and for tests of fundamental physics. For optically levitated anisotropic particles it is possible to control their translation,
alignment and rotation. We report on the levitation and characterization of nanofabricated, high uniformity, high aspect ratio, high refractive index silicon cylinders, with diameters as low as 50 nm and lengths up to 1500 nm. We are able to tune their oscillation frequencies from 10 kHz to over 1 MHz, and exert huge optical torque to generate high rotation rates. These optically levitated silicon nanorods will enable precision torque sensing, and when pushed to smaller sizes, tests of
quantum physics through the generation of angular momentum superposition states.
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All authors Zhenan Chen, Sophie Sanghera, Yanhui Hu, James Sabin, Maryam Nikkhou, Alex Gee, David Burt, Qiongyuan Wu, Joseph Kelly, James Millen
Atmospheric and Oceanic Physics
Evaluating Explainable AI Methods for Geoscientific Regression: Insights from Applications and the Lorenz-63 System
Ieuan Higgs, Todd Jones, Kieran Hunt et al. (+1 more)
As artificial intelligence (AI) systems transition from research prototypes to operational tools in Earth system science and
forecasting, establishing trust in their predictions becomes increasingly important. Although model inputs and outputs are observable, the internal decision-making of modern AI models remains complex and hard to interpret, earning them the label “black boxes.” Explainable artificial intelligence (XAI) offers techniques to provide insight into these processes. However, most XAI methods were developed for classification tasks, raising questions about their suitability for the regression problems that dominate geoscientific applications. We review XAI approaches through this lens, organising them into a structured framework and examining both their theoretical foundations and practical behaviour. To ground this discussion, we apply a selection of methods to a machine learning emulator of the Lorenz 1963 system, an archetypal chaotic model that provides a tractable, physically meaningful setting for exposing the limitations and failure modes of general-purpose XAI in regression contexts. We then survey how these and related methods have been applied across a variety of Earth system sciences. We further situate XAI within the model development lifecycle, linking methodological choices to the needs of different stakeholder groups across operational Earth system science. We close by identifying gaps in existing methodologies and outlining a forward-looking research agenda, with practical recommendations for the responsible, effective use of XAI in regression applications of geoscientific modelling and
forecasting.
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All authors Ieuan Higgs, Todd Jones, Kieran Hunt, Anna-Louise Ellis
Chemical Physics
The origin of carotenoid triplets in purple photosynthetic bacteria
Juan J. Romero, Andrew Gall, Viola D'mello et al. (+4 more)
Photosynthetic
antenna proteins harvest light energy while at the same time protecting the organism against photodamage. Carotenoid molecules are essential in the latter process, efficiently quenching unwanted (bacterio)chlorophyll excited states created after
photon absorption. (Bacterio)chlorophyll triplets, formed by inter-system crossing, are particularly significant, since in the absence of carotenoid quenching, they sensitise the highly oxidative singlet oxygen. In light-harvesting complex 2 (LH2) from Rhodoblastus acidophilus, the pathways that populate carotenoid dark and triplet states remain controversial, involving bacteriochlorophyll-to-carotenoid triplet-triplet transfer and/or generation of triplets by the carotenoid molecules themselves through singlet fission. Transient absorption has been central to understanding photoprotection in these organisms, but spectral congestion limits the separation of the overlapping species needed to discriminate between these pathways. By applying femtosecond stimulated resonance Raman spectroscopy (FSRRS) in different resonance conditions to this
protein, in combination with an extension of global analysis to four dimensions (wavenumber, time, intensity and resonance condition), we separate each component of the carotenoid dark-state
manifold together with its kinetics. An entangled triplet pair S*/1(TT) is observed, which lives about 60 ps, some eight times longer than in solution. However, this stabilisation does not open a pathway to separated triplets or to carotenoid-BChl a heterofission. Triplet-triplet transfer from bacteriochlorophyll a to carotenoid is also resolved under BChl a excitation, and fits cleanly as a single 2100 ps component. The carotenoid triplet in LH2 is thus produced by photoprotective triplet-triplet transfer from BChl a, and not by singlet fission.
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All authors Juan J. Romero, Andrew Gall, Viola D'mello, Cristian Ilioaia, Andrew A. Pascal, Bruno Robert, Manuel J. Llansola-Portoles
Medical Physics
An Angular Spectrum Method for Nonlinear Propagation in Heterogeneous Tissue with Immersed Sources for Ultrasound
Gianmarco Pinton
A modified angular spectrum method (ASM) is developed for three-dimensional nonlinear acoustic propagation through heterogeneous tissue, targeting transcranial and therapeutic ultrasound. First, a consistent obliquity correction is applied to both the linear and nonlinear operators of the split-step update. The attenuation and dispersion filter carries a per-mode k/kz factor on the full wavenumber-frequency grid, so each component accumulates absorption and phase over its true path length dz/cos(theta), while the Burgers coefficient is scaled by the power-weighted mean beam obliquity. Second, the retarded-time Burgers update is discretized with a second-order Kurganov-Tadmor central-upwind flux using MUSCL reconstruction and SSP-RK2 time integration, composed with diffraction and attenuation through Strang splitting with adaptive CFL sub-cycling, resolving fully developed shocks without the temporal refinement that the CFL coupling imposes on FDTD. Third, a plane-by-plane source-injection scheme decomposes deeply curved bowl transducers into axial slices injected at their correct propagation depths, preserving the aperture-dependent shock-formation distance. Phase-and-amplitude screens derived from skull CT data model transcranial aberration and insertion loss, and three enhanced absorbing-boundary treatments reduce boundary reflections by a factor of 2.4. Analytical validation reproduces the baffled-piston far-field pattern to 0.014 RMS and the focused-piston focal pressure to within 2.3 percent. In a transcranial
benchmark through an ex vivo human skull, the ASM matches the Fullwave 2 focal-plane intensity to 1.1 percent RMS and predicts a 5.4 dB through-skull insertion loss. For a bowl transducer (R = 80 mm, f0 = 1 MHz), the ASM matches the Fullwave 2 focal depth to within 2.3 percent with 9x less
memory and 2.9x less wall time.
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Physics Education
A bottom-up taxonomy of student discourse with a Socratic AI physics tutor
Syed Furqan Abbas Hashmi and N. Sanjay Rebello
Large
language model (LLM) tutors are being deployed in introductory physics courses at a scale that produces transcript corpora far larger than traditional qualitative coding can absorb. A central question for physics education research (PER) is empirical and prior to any claim about effectiveness: what do students actually say to these tutors? We address this question for one Socratic AI tutor deployed in an introductory calculus-based mechanics course by building a bottom-up taxonomy of student discourse. Each student turn is assigned an emergent free-text label by an LLM coder using the surrounding conversational context; near-paraphrase labels are then consolidated into a smaller set of discourse categories using a similarity-based grouping procedure. The procedure is validated against a stratified human-coded sample. The resulting taxonomy of 357 categories is strikingly concentrated: the top 25 categories cover roughly half of all student turns, and two thematic bands: equation-handling and meta-procedural requests together dominate the head of the distribution. The substantive contribution is the taxonomy itself: a description of the discourse PER researchers can expect to encounter when students work with an AI tutor of this design, including a striking prevalence of meta-procedural turns in which students cede strategic control to the tutor
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Medical Physics
Measurements Automatically Extracted from Zero Echo Time MRI Using Deep Learning Image Segmentation and Geometric Modeling Agree with Expert Manual Readings
Jack Consolini, Eric A. Bogner, Meghan Sahr et al. (+3 more)
Computed
tomography (CT) remains the reference for 3D osseous morphometry in femoroacetabular impingement (FAI) but requires ionizing radiation and manual measurement. Zero echo time (ZTE) MRI visualizes cortical bone and yields FAI angles that agree with CT, but automated angle extraction remains limited. We developed and validated automated FAI angle computation from ZTE MRI and assessed agreement with expert manual measurements in a cross-sectional study (level of evidence, 3). Pelvic ZTE MRI was acquired in 73 participants (mean age 36.8 +/- 18.5 years; 51 women, 22 men), yielding 135 hips. nnU-Net was trained on 100 manually curated hips to segment the femur, pelvis, and three osseous landmarks. Custom
geometric algorithms computed alpha, femoral neck-shaft, Tonnis, coronal and sagittal center-edge, and acetabular version angles from inferred
segmentations. Measurements on 35 test hips were compared with the mean of two radiologists' manual measures using intraclass correlation (ICC) and Bland-Altman analysis. Dice exceeded 0.96 for bone and ranged from 0.65 to 0.83 for landmarks. Median landmark error was 0.38 mm (femoral head), 0.82 mm (lateral acetabulum), and <2.5 mm (medial acetabulum, greater trochanter). Interrater ICC was excellent for acetabular version, coronal center-edge, and Tonnis (>=0.82) but poor for alpha and femoral neck-shaft. Model versus rater-mean agreement was excellent for acetabular version, coronal center-edge, and Tonnis (0.92-0.96), good for mid-acetabular sagittal center-edge (0.74), and fair for alpha (0.45) and femoral neck-shaft (0.55). Model Bland-Altman limits of agreement were narrower than interrater limits for most angles. Fully automated morphometric assessment from ZTE MRI is feasible and performs comparably to expert readers for most coverage and version angles.
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All authors Jack Consolini, Eric A. Bogner, Meghan Sahr, Matthew F. Koff, Kevin M. Koch, Hollis G. Potter
Atmospheric and Oceanic Physics
Finite-Response Complementarity in Fluctuation Constraints on Climate Sensitivity
Zaibo Zhao and Yongwen Zhang
Equilibrium climate sensitivity (ECS) is a zero-frequency susceptibility, whereas historical globalmean temperature variability samples a finite, forced projection of the
climate system. We test whether information missed by a scalar fluctuation-
memory coordinate reappears in a finite CO2 response. After conditioning both ECS and the finite response on {\Psi}, CMIP5 residuals are nearly uncoupled (C5 = 0.154), whereas CMIP6 shows strong complementarity (C6 = 0.593, p = 0.00288). A two-mode
stochastic response model attributes this contrast to hidden-response spread that is visible in the finite response but poorly projected onto {\Psi}. The CMIP6 residual direction defines a first-order correction and yields a HadCRUT5 conditional ECS estimate centered at 3.00 K. Thus the weakened CMIP6 fluctuation constraint does not imply that susceptibility information is lost: part of it is recovered through a complementary finite-response projection.
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Chemical Physics
Beyond the Four-Decade DIIS Default:Auxiliary-Curvature Acceleration of Self-Consistent-Field Calculations
Peng Bao and Qiang Shi
Direct inversion in the iterative subspace (DIIS), introduced in 1980, remains the practical default for accelerating Hartree-Fock and Kohn-Sham self-consistent-field (SCF) calculations. Many later methods improve robustness or iteration count, but the near-zero overhead of DIIS makes a broad reduction in total wall time difficult. We introduce AURORA-SCF (auxiliary-
curvature unified Riemannian orbital-response acceleration), which evaluates energy and gradient only with the requested target
Hamiltonian while obtaining most orbital
curvature from an independent valence-STO-3G model. A target-level, transported L-BFGS history corrects the model mismatch; a shifted
matrix-free solve, trust region, and geodesic orbital update control the step. In 16 direct CPU RHF pairs spanning 137-1484 atomic orbitals, AURORA-SCF was faster in every case, reducing mean wall time by 26.2% and target J/K builds by 33.3%. In a separate set of 63 converged, energy-matched density-fitted GPU pairs spanning seven molecules, closed- and open-shell formalisms, and HF, PBE, B3LYP, and M06-2X, it was again faster in every included pair, with mean reductions of 26.5% in wall time and 31.9% in target J/K builds. Focused direct CPU and GPU sweeps show mean wall-time reductions of 30-34%. These results establish a specific advance beyond the four-decade DIIS default: transferred, secant-corrected
curvature can reduce total SCF wall time, not merely iteration count, without changing the target stationary equations. The same optimization pattern also suggests a route to faster orbital optimization elsewhere in
quantum chemistry and to multifidelity optimization across scientific computing.
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Computational Physics · Cross-listed from math.NA
Mesh-Based Filtering to Alleviate Time-Step Restrictions in Runge–Kutta Discontinuous Galerkin Methods in Spherical-polar Coordinates: Application to the Euler Equations
Joseph Hunter, Eirik Endeve and Yulong Xing
We propose a mesh-based filtering approach to alleviate the severe timestep restrictions arising in explicit Runge–Kutta discontinuous Galerkin (RKDG) methods formulated in spherical-polar coordinates. The filter enables stable
evolution on the original logically Cartesian mesh while using larger time steps associated with an auxiliary merged mesh constructed to eliminate the extreme
cell anisotropies produced by converging coordinate lines near coordinate singularities. The filter is implemented as a sequence of post-processing operations applied within an $s$-stage RK time integrator, making it straightforward to incorporate into existing structured-mesh DG frameworks. We analyze the filter in one spatial dimension and prove that the filtered RKDG method is equivalent to evolving the RKDG discretization on a nonuniform mesh obtained by merging selected elements of the underlying uniform mesh. This equivalence implies that the filtered method inherits the accuracy and stability properties of the corresponding RKDG discretization on the merged mesh. We apply the mesh-based filter to an existing RKDG method for the Euler equations in spherical-polar coordinates and demonstrate, through selected two- and three-dimensional examples, its effectiveness in accelerating simulations through significantly larger stable timesteps.
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Atmospheric and Oceanic Physics
State transitions in land-vegetation systems emerge at Paris Agreement warming levels in CMIP6
Pouriya Alinaghi, Sybren Drijfhout, Joran Angevaare et al. (+2 more)
Using an automatic detection workflow applied to the Coupled Model Intercomparison Project Phase 6 (CMIP6) ensemble under future emission scenarios, we identify 47 abrupt and more gradually developing state transitions in the land-vegetation component of the Earth system, classified into 9 categories. Over the Amazon, we find state transitions via vegetation dieback alongside greening cases; the contrast between them is traced primarily to differences in precipitation: models showing dieback experience either a larger absolute decline in precipitation, or one that translates more efficiently into soil moisture loss, particularly near the surface, while in greening models the CO$_2$ fertilization effect wins out where the soil moisture loss remains weaker. The precipitation decline in dieback-prone models appears driven through a weakening of moist convection. Across these Amazon cases, models with dynamic vegetation undergo dieback, whereas greening is confined to models with prescribed vegetation distributions. African cases include greening over eastern-central Africa and the Congo basin, and an abrupt soil-moisture drying also over the Congo. At high latitudes, boreal forest expands, while permafrost thaws once the regional above-zero temperatures persist for more than half the year. Additional categories cover transitions to a reduced snow-cover state over northeastern North America, increased vegetation biomass near the Tibetan Plateau and southeastern Asia, and increased leaf-area index over the northeast Northern America. Of particular concern, a global warming of 2$^\circ$C or below, within reach of the Paris Agreement targets, is already enough to trigger the onset of the majority of the identified categories in CMIP6.
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All authors Pouriya Alinaghi, Sybren Drijfhout, Joran Angevaare, Chris Jones, Andy Wiltshire
Optics
Dynamically reconfigurable THz quantum walk comb laser through subharmonic excitation
Valerio Digiorgio, Robert Matthew Gray, Marco Raffa et al. (+5 more)
On-chip frequency combs are increasingly relevant to both
laser science and applications. Broad bandwidths and flat-top spectral envelopes are especially desirable for precision spectroscopy and dense wavelength-division multiplexed communications. Toward these goals, active microwave modulation has emerged as a powerful strategy for generating, stabilizing, and reconfiguring frequency combs at the source. However, practical challenges associated with high-frequency modulation imposes an upper bound on the accessible cavity free spectral ranges. Here, we demonstrate a subharmonic locking scheme in a
quantum walk comb
laser, a recently introduced platform for broadband and highly controllable comb states. Using a THz ring
quantum cascade
laser, we realize
quantum walk comb formation under strong microwave injection at successive subharmonics of the cavity round-trip frequency, tuning the comb spacing from 15.8 to 1.58 GHz. The resulting states arise from fast-gain dynamics and nonlinear microwave mixing in the
laser cavity. Through two-tone injection, we exploit this mixing to dynamically control the comb bandwidth and spectral shape. These results establish subharmonic excitation as a route to broadband, reconfigurable
semiconductor comb generation in high-FSR cavities.
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All authors Valerio Digiorgio, Robert Matthew Gray, Marco Raffa, Paolo Micheletti, Alexander Dikopoltsev, Mattias Beck, Jérôme Faist, Giacomo Scalari
Instrumentation and Detectors · Cross-listed from astro-ph.IM
WST, the Wide-field Spectroscopic Telescope: dispersing elements
Andrea Bianco, Michele Frangiamore, Anna Brucalassi et al. (+7 more)
The Wide-field Spectroscopic
Telescope (WST) is a proposed 12-m class facility entirely dedicated to spectroscopic surveys, combining a high-multiplex multi-object spectrograph operating at low (MOS-LR) and high (MOS-HR) spectral resolution with a
giant panoramic integral-field spectrograph (IFS), all three operating in parallel. Diffraction gratings are the key dispersing elements of all three instruments and, given the very large number and size of the units required, drive critical trade-offs in throughput, feasibility and production cost. This paper reviews the two grating technologies under consideration for WST, Volume Phase
Holographic Gratings (VPHG) and binary (lithographic, surface-relief) gratings, summarizing their working principles and the parameters that control their diffraction efficiency. We then present the current baseline grating parameters and vendor results for each instrument: low-dispersion, VPHGs for the IFS; a four-arm GRISM layout for MOS-LR; and two competing high-resolution disperser architectures (8M16D and 16M4D) for MOS-HR, where binary gratings show a promising path to diffraction efficiencies beyond what is achievable with VPHGs. We conclude with the main open challenges, chiefly the mass production of hundreds of grating units within cost and schedule and the next steps foreseen to consolidate the disperser baseline for WST.
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All authors Andrea Bianco, Michele Frangiamore, Anna Brucalassi, Dimitri Buffat, Corentin Cudennec, Kjetil Dohlen, Alexandre Jeanneau, David Lee, Will Saunders, Andrea Tozzi
Optics · Cross-listed from quant-ph
Demonstration of an LLO CV-QKD system over 12 km of optical fiber
Christiano M. S. Nascimento, Artur A. Matoso, Gustavo C. Amaral et al. (+1 more)
Continuous-variable
quantum key distribution (CV-QKD) promises high rates and seamless integration with classical beams within a single optical fiber. Over the years, implementations have been performed by transmitting a local oscillator reference along with the
quantum channel, opening security loopholes for eavesdroppers and limiting potential applications. Here, we report on a Gaussian CV-QKD implementation using fully independent transmitter and receiver
lasers (local-oscillator sources) over a 12 km fiber spool. The system was experimentally evaluated using logical frames containing approximately $10^7$ coherent states, each composed of ten independently processed subframes of approximately $10^6$ states, and security was assessed in both asymptotic and finite-size regimes under a trusted-device model. The full-fledged classical post-processing is capable of recovering the channel parameters and extracting secret key rates of 5.11 Mbit/s in the asymptotic regime and 4.67 Mbit/s in the finite-size regime, showing good agreement with theoretical predictions. This work establishes the foundation for metropolitan fiber deployment of CV-QKD under strict security constraints.
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All authors Christiano M. S. Nascimento, Artur A. Matoso, Gustavo C. Amaral, Guilherme P. Temporão
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Homojunction-induced thermopower enhancement in polymer films
Zhen Xu, Hui Li, Guangzheng Zuo et al. (+7 more)
It has been more than twenty years since conductive
polymers began to receive
attention as an emerging thermoelectric material. However, the trade-off between electrical conductivity ({\sigma}) and thermopower (S) has proven to be a major challenge that has obstructed their use in actual devices. Here we report the discovery that the thermopower of the p- and n-type legs of organic thermogenerators can be substantially enhanced, without significant deterioration of {\sigma}, by constructing an in-plane segmented structure consisting of a homojunction with different doping levels on either side. In such segmented layers, the S is abnormally higher than the average value of the constituent parts when applying a forward temperature gradient (heating the heavily doped counterpart), while it is lower upon a reverse temperature gradient. Typically, for a two-stage segmented film of p-type PDPP-Se, an abnormally large S of 210 uV K-1 and {\sigma} of 2.5*10^4 S m-1 are obtained, resulting in a large power factor (PF) of 1100 uW m-1 K-2 and a record ZT of 1.36 at room temperature. The enhanced thermopower is attributed to an additional voltage developed at the homojunction under heating as explained by kinetic Monte Carlo simulations. This finding provides a breakthrough approach to the modulation of thermoelectric transport properties of conductive
polymers.
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All authors Zhen Xu, Hui Li, Guangzheng Zuo, Xiaojuan Dai, Jincheng Liao, Guofeng Cheng, Jian Song, Wenqing Zhang, Martijn Kemerink, Lidong Chen
Atomic Physics
Quantum sensing of radiofrequency fields using cold Rydberg atoms in a super-molasses trap
Romain Granier, Anthony El Bekai, Miguel Angel Cifuentes Marín et al. (+12 more)
We demonstrate the
quantum sensing of radiofrequency fields based on cold Rydberg atoms in a super-molasses trap, without the need for
magnetic coils. Our approach combines the metrological advantages of cold atoms with a metal-free dielectric sensor head minimizing perturbations to the electromagnetic environment, a feature that was previously restricted to vapor-
cell-based devices. Moreover, the absence of inductive loads allows to rapidly alternate between the cooling phase and the Rydberg excitation, leading to trap-loss spectroscopy signals one order of magnitude narrower than for conventional magneto-optical traps. This enables self-calibrated microwave power measurements with an unprecedented dynamic range of 43dB, opening the door to new perspectives of applications in calibration measurements. We also report a scale factor linearity better than 1%, the absence of drifts over several tens of minutes leading to a 3$\mu$V/cm resolution, and the possibility to retrieve the ellipticity of the applied microwave field. By demonstrating a cold-atom metrological platform in a compact dielectric sensor head, this work paves the way for new applications in the field of radiofrequency measurements with Rydberg atoms, and in other fields of
quantum sensing based on cold atoms such as magnetometry, gravimetry or inertial
navigation.
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All authors Romain Granier, Anthony El Bekai, Miguel Angel Cifuentes Marín, Cédric Blanchard, Nassim Zahzam, Yannick Bidel, Alexandre Bresson, Vilius Atkočius, Chester Camm, Florence Concepcion, Konstantinos Karakostas, Matt Himsworth, Alexander Jantzen, Alexis Bonnin, Sylvain Schwartz
Optics · Cross-listed from cond-mat.quant-gas
Crossing over universal scaling laws in two-dimensional driven dissipative condensates
Q. Fontaine, F. Helluin, M. Escalera et al. (+8 more)
In low dimensional systems, fluctuations are enhanced and prevent the spontaneous breaking of continuous
symmetries. As a result, spatial and temporal correlation functions decay at large distances and long times. A well established example is given by two-dimensional bosonic condensates at
equilibrium, which do not display long-range order of the coherence but algebraic decay belonging to the Berezinski-Kosterlitz-Thouless universality class. In contrast, the universal behaviors of non-
equilibrium bosonic condensates are more diverse and many open questions remain. Here, we explore the spatio-temporal coherence properties of two-dimensional driven-dissipative polariton condensates in
semiconductor optical microcavities. By tuning microscopic parameters, we observe a cross-over between two scaling laws that we attribute to the Edwards-Wilkinson (EW) and the Kardar-Parisi-Zhang (KPZ) universality classes. We demonstrate the collapse of the measured first-order correlations onto the EW and KPZ universal scaling functions and obtain critical exponents, well matching the values predicted theoretically. Our results highlight the intrinsic non-
equilibrium nature of polariton condensates and establish them as a platform of choice for controlled exploration of the two-dimensional KPZ universality class.
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All authors Q. Fontaine, F. Helluin, M. Escalera, D. Pinto Dias, A. Lemaître, M. Morassi, M. Wouters, A. Minguzzi, L. Canet, S. Ravets, J. Bloch