Atomic Physics
Qprop-ND: A Nondipole Extension of the Qprop Package for Strong-Field Laser Physics
Haoyuan He, Zhao-Han Zhang, Karen Z. Hatsagortsyan et al. (+1 more)
The Qprop 3.0 package for the solution of the time-dependent Schrödinger equation for an electron in a
laser field and atomic potential is extended to incorporate nondipole effects related to the
laser wave propagation. The developed code can be used for the simulation of strong field atomic phenomena in the nondipole regime, such as above-threshold ionization, ionization stabilization in high-frequency
laser fields, high-order harmonic generation, when the effects connected with the
magnetic field are non-negligible or when the
laser wavelength is comparable with the atomic size. Similar to the dipole Qprop the wave function is expanded in spherical harmonics, the time-propagation of the wave functions is performed using the Crank- Nicolson approach, and the photoelectron spectra are calculated employing the t-SURFF or i- SURFV methods. The validity and accuracy of the implementation are demonstrated through several illustrative examples.
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All authors Haoyuan He, Zhao-Han Zhang, Karen Z. Hatsagortsyan, Christoph H. KeiteL
Geophysics · Cross-listed from cs.AI
Structural Alignment for Reliable Industrial AI: Bridging Physical Reality, Data, Models, and Human Intent
Lizhi Xiao, Sihong Wu, Victoria Xiao et al. (+5 more)
Artificial intelligence is increasingly deployed in critical industrial domains, including healthcare, energy grids, subsurface exploration, where failures can have severe consequences for human safety, system stability, and economic outcomes. Yet AI is still evaluated primarily through
benchmark accuracy, a model-centric metric that fails to capture the structural complexity and risks of real-world deployment. We propose a framework that views industrial AI reliability as a problem of structural
alignment across four interacting worlds: physical, representational, machine, and human cognitive. These worlds are connected through two interfaces: digitalization, linking physical reality to computational representations, and goal encoding, translating human cognition to the machine objectives. Together, they define the space of admissible solutions. We characterize the solution space through four attributes: existence, non-uniqueness, robustness, and interpretability and show how mismatches arise at interfaces and propagate across worlds to produce reliability failures. Applications to healthcare, energy grids, and subsurface exploration illustrate that although dominant failure modes differ across domains, for example, interpretability in healthcare, robustness in energy grids, and non-uniqueness in subsurface exploration, all originate from a shared structural mechanism. By shifting the focus from model-centric evaluation to system-level
alignment, this framework offers a principled foundation for assessing and governing reliability in industrial AI systems.
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All authors Lizhi Xiao, Sihong Wu, Victoria Xiao, Yiqiao Song, Chen Gu, Jianwei Ma, Xinming Wu, Aimé Fournier
Instrumentation and Detectors
A linear Paul trap to study the equilibrium of charged micron-sized particles in air
Roxen Wilby Kissangou, Marius Romuald Kamsap, Mike Delon Mboumba et al. (+2 more)
We describe and use a macroscopic linear quadrupolar trap to explore the trapping and
equilibrium properties of charged particles. These devices, when operated to trap atomic ions, are at the core of ion based
quantum computer and optical atomic clock. To illustrate the characteristics of few particle trapping, and observe different force balance on a charged particle, a macroscopic linear trap, operating at room condition, is trapping micrometer-sized particles. Compared to atomic or molecular ions, their mass can not be neglected and requires an extra voltage for
gravity force compensation. We show how this compensation can be demonstrated experimentally and that the choice of hollow-core glass spheres has the advantage of a good reproducibility of the experiments, that allows one to deduce with good precision the charge-to-mass ratio of the trapped particle.
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All authors Roxen Wilby Kissangou, Marius Romuald Kamsap, Mike Delon Mboumba, Marie Houssin, Caroline Champenois
Optics
Contactless Continuous-Variable Quantum Optical State Conditioning With Classical MmWave Phase
Niloy Ghosh and Sarang Pendharker
This paper establishes the Heisenberg's picture framework for seamless mmWave-to-photonic data transduction. Based on this framework, contactless modulation of continuous-variable (CV)
quantum optical states with digitally modulated classical mmWave beams is shown for the first time. Our analysis reveals the direct influence of mmWave phase variation on the Wigner-space
evolution of modulated optical coherent and squeezed states. Furthermore, the analysis indicates that classical mmWave phase not only governs the displacement but also modulates the quadrature uncertainty of squeezed states, revealing a novel technique for
embedding information onto multiple
quantum-optical degrees of freedom. This work builds the theoretical and analytical foundation for wireless conditioning of
quantum light without conventional on-chip metallic interconnects and complex electronic control circuitry, thereby opening a key pathway toward seamless bridging of integrated
quantum photonics with emerging mmWave or THz communication technology.
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Physics and Society
Structure of Exposure Modeling of Systems to Climate Change Related Hazards
Matthieu Dutel, Adam Abdin, Didier Soto et al. (+1 more)
Physical infrastructures designed for stable
climate conditions support a significant portion of daily human life activities. However,
climate change reshapes the distributions of extreme
climate intensities. As a result, physical infrastructures that may face extreme events exceeding their design thresholds risk damage and require adaptation. A preliminary step to adaptation is to identify exposed infrastructures to
climate hazards. This paper aims to structure the exposure modeling to
climate change hazards by providing an overall methodology. This paper instantiates a framework using the Boolean Exposure Model to assess how physical systems may be exposed to
climate hazards. The framework combines a Boolean System Model for infrastructures and a Boolean Hazard Model informed by extreme value statistics. An illustrative case study quantifies the exposure of road bridges in French administrative units to extreme temperatures. Results indicate increasing exposure across future
climate scenarios and time periods, with spatial non-uniformity. This framework supports multi-level analysis and integrates non-stationary
climate extremes, providing a structured exposure model to facilitate the adaptation of physical systems to
climate change.
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All authors Matthieu Dutel, Adam Abdin, Didier Soto, Anne Barros
Chemical Physics
Experimental and numerical study of shock wave propagation in water generated by pulsed arc electrohydraulic discharges
Wen Chen, Olivier Maurel, Christian La Borderie et al. (+6 more)
The objective of this study is to simulate the propagation of the shock wave in water due to an explosion. The study is part of a global research program on the development of an alternative stimulation technique to conventional hydraulic fracturing in tight gas reservoirs aimed at inducing a distributed state of microcracking of rocks instead of localized fracture. We consider the possibility of increasing the permeability of rocks with dynamic blasts. The blast is a shock wave generated in water by pulsed arc electrohydraulic discharges. The amplitude of these shock waves is prescribed by the electrohydraulic discharges which generate high pressures of several kilobars within microseconds. A simplified method has been used to simulate the injected electrical energy as augmentation of enthalpy in water locally. The finite element code EUROPLEXUS is used to perform fluid fast dynamic computation. The predicted pressure is consistent with the experimental results. In addition, shock wave propagation characteristics predicted with simulation can be valuable reference for design of underwater structural elements and engineering of underwater explosion.
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All authors Wen Chen, Olivier Maurel, Christian La Borderie, Thierry Reess, Antoine Silvestre de Ferron, Mohammed Matallah, Gilles Pijaudier-Cabot, Jacques Antoine, Franck Rey-Bethbeder
Atomic Physics
Raman Transitions in Collinear Laser Spectroscopy for High-Precision Frequency Measurements
Julien Spahn, Hendrik Bodnar, Kristian König et al. (+2 more)
We demonstrate stimulated Raman spectroscopy on dipole-forbidden fine-structure transitions in a fast ion beam. It is applied to the $\mathrm{S}_{1/2}\rightarrow\mathrm{D}_{5/2}$ clock transition in $^{88}\mathrm{Sr}^{+}$ and combined with a subsequent E1 transition to allow for its detection by standard fluorescence detection. Building on this, the $\mathrm{D}_{3/2}\rightarrow\mathrm{D}_{5/2}$ fine-structure splitting is measured directly using a Doppler-free scheme employing two subsequent Raman transitions. These measurements demonstrate a path toward precision collinear
laser spectroscopy of narrow transitions on short-lived isotopes beyond the linewidth limit of conventional electric-dipole spectroscopy, which can be used to probe fundamental aspects of atomic and nuclear physics.
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All authors Julien Spahn, Hendrik Bodnar, Kristian König, Wilfried Nörtershäuser, Robbe Van Duyse
Atomic Physics
Reconstructing Molecular-Ion Quantum States with Two-Color Strong-Field Scattering
Dina S. Eissa, Felipe Morales, Abraham Camacho Garibay et al. (+6 more)
Strong-field ionization of molecules can prepare coherent superpositions of ionic states whose amplitudes and relative phases govern the ensuing ultrafast dynamics, but accessing this information experimentally remains a challenge. Here we introduce two-color strong-field scattering, in which a strong mid-infrared field ionizes the molecule and launches an electron, while a weak second harmonic field resonantly couples vibronic states of the parent ion during the electron's continuum excursion, thereby introducing structural changes on the sub-
laser-cycle timescale. Scanning the relative phase between the two colors controls the ionic
evolution and maps it onto phase-dependent sub-angstrom bond-length changes retrieved from the rescattering signal. Using the example of N$_2$, we apply the two-color setup to probe the coherence between different ionization channels and to reconstruct the initial ionic superposition. Our results establish two-color strong-field scattering as a powerful structural approach to characterize the complex amplitudes of ion
quantum wavepackets.
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All authors Dina S. Eissa, Felipe Morales, Abraham Camacho Garibay, Vyacheslav Leshchenko, Cosmin I. Blaga, Misha Ivanov, Pierre Agostini, Maria Richter, Louis F. DiMauro
Medical Physics
Physics-informed self-supervised generation of digital brain MRI phantoms from weighted images using differentiable MRI simulation
Kseniya Belousova, Anna Konanykhina, Zilya Murzina et al. (+2 more)
Purpose: To develop a physics-informed, self-supervised framework for generating digital
brain MRI phantoms directly from conventional weighted MR images without requiring ground-truth parametric maps or anatomical segmentation. Methods: The framework predicts T1, T2, and
proton density (PD) maps from T1-, T2-, and PD-weighted images and reconstructs the input images through an MRI signal model. Three generative architectures (variational autoencoder (VAE), generative
adversarial network (GAN), and flow-based model) were compared. Models were pretrained on 3,739 synthetic
brain slices generated using digital phantoms and an analytical MRI signal model, followed by fine-tuning on 90 real
brain slices from three healthy volunteers. The best-performing architecture was subsequently fine-tuned using the differentiable MR-Zero numerical MRI simulator and evaluated on 30 held-out real slices. Results: The flow-based model demonstrated the highest overall performance and preserved fine anatomical details better than the VAE and GAN. After analytical-model fine-tuning, it achieved MS-SSIM values of 0.955-0.985 and PSNR values of 26.68-32.63 dB across T1-, T2-, and PD-weighted images. Fine-tuning with MR-Zero increased T1-weighted reconstruction quality from 0.955 to 0.977 (MS-SSIM) and from 26.68 to 30.60 dB (PSNR), and provided high robustness of metrics across different MR image weightings. The resulting digital phantoms also enabled simulation of images using previously unseen acquisition protocols. Conclusion: The proposed framework enables physics-informed generation of reusable digital
brain MRI phantoms from weighted images using limited real-world data. Combining synthetic pretraining with differentiable numerical MRI simulation provides a practical approach for physically grounded MRI data augmentation without requiring reference parametric maps.
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All authors Kseniya Belousova, Anna Konanykhina, Zilya Murzina, Walid Al-Haidri, Ekaterina Brui
Fluid Dynamics
A Conservative Multi-Level Adaptive Velocity-Space Method for the Discrete Unified Gas-Kinetic Scheme
Weijie Ren, Hang Yu, Zhengyu Tian et al. (+2 more)
Multiscale gas flows often span a wide range of Knudsen numbers, within which the flow varies from near-continuum to highly rarefied and strongly nonequilibrium states. Such flows require kinetic solvers that remain accurate across the entire range. The discrete unified gas-kinetic scheme (DUGKS) provides such a unified description, but its computational cost and
memory consumption are dominated by the size of the discrete velocity space. To alleviate this bottleneck, this work improves the DUGKS with multi-level adaptive velocity-space discretization (MLVS-DUGKS), reducing velocity-space redundancy while preserving accuracy and conservation. This method identify the velocity-space requirements of each physical
cell from its distribution function, and then groups these requirements into a small number of representative velocity spaces. This organization retains sensitivity to different local flow states without constructing an independent velocity space for every physical
cell. A linear moment-constrained correction is incorporated to maintain discrete compatibility and conservative data transfer between representative velocity spaces.
Benchmark simulations spanning near-continuum to highly rarefied regimes show close agreement with the uniform-velocity-space DUGKS (UVS-DUGKS). For the computationally demanding cases, the average number of discrete velocity points is reduced by approximately one order of magnitude, yielding speedups of 6.67–7.51 and GPU-
memory reductions by factors of 6.15–6.88. A threshold study further shows that the actual computational performance is governed by a balance between velocity-space compression and cross-level coupling overhead. The MLVS-DUGKS thus provides an accurate, conservative, and computationally efficient framework for multiscale nonequilibrium-flow simulations.
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All authors Weijie Ren, Hang Yu, Zhengyu Tian, Wenjia Xie, XiaoQiang Fan
Optics · Cross-listed from quant-ph
An Exact Polynomial Task-Risk Bridge for Time-Multiplexed Photonic Quantum Reservoirs
Yuqi Zhang, Tianyu Zhou, Yilun Jiang et al. (+2 more)
Time-multiplexed (TDM) photonic reservoirs are usually judged by their scores on a few
datasets, which say little about a chip's overall performance, and designed by enumerating candidate
circuits and simulating each one, which is inefficient and gives no guarantee of finding a good structure. For a time-unrolled passive linear network with data-modulated gates or sources and a ridge readout, we derive an exact bridge from the task to the prediction risk in three steps. (i) Task features: the finite-shot risk depends on the time series only through finitely many statistics of its training windows and their correlations with the target, selected by the encoding and the optical paths. (ii) Encoding: every output moment is a
polynomial in the features of the data-modulated sites, with degree and support bounded by tuples of optical paths. Gate encoding reads the characteristic function and creates interactions across time lags; squeezing encoding reads the moment-generating function and displacement encoding low-order moments, and with quadrature receivers they yield only additive and linear models, respectively, for every
topology. (iii) Readout: for homodyne, heterodyne and
photon-number receivers the risk closes exactly, and its dependence on the number of shots is an explicit sum over signal-to-noise modes; threshold clicks admit finite-dictionary approximations with certified error. Parts of the network that share no light carry independent states, which a receiver combines only through measurement events that join them. Checks on seven
datasets confirm every exact statement to machine precision. The three steps thus yield a useful space of candidate TDM architectures, pruned by exact statements rather than by trial simulation, which can in future guide the selection of TDM chips for target requirements.
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All authors Yuqi Zhang, Tianyu Zhou, Yilun Jiang, Tian Chen, Hao Tang
Physics and Society · Cross-listed from quant-ph
A technological capability scale for civilizations from the Kardashev and Barrow scales
Volkan Gurses
We introduce a technological capability scale that ranks civilizations by the control operations they can perform per second. A control operation is defined as setting one binary degree of freedom of matter to a specified value, whatever its previous state. Building on constructor theory, we sort them into construction and its special cases on information media, namely processing, storage and transfer. The index $\Xi = K + B$ adds to the Kardashev index $K$ an efficiency index $B$ of energy per operation, measured from the thermal floor at the microwave background temperature. The Kardashev scale gives the ceiling for resets of thermally random bits with heat radiated into the present sky, and the Barrow scale gives the floor, which for such a reset is the thermal floor at the heat-rejection temperature at every level. Since 1950 the energy per logic operation has fallen 11.7 orders of magnitude, around 5 through miniaturization. Humanity, at $K = 0.73$, computes with CMOS logic gates at $B = -0.78$ in primary energy. We describe the ultimate technology, at $\Xi = 7.58$, which would dissipate the conjectured largest power $c^5/4G$ into an uncharged, non-rotating black hole near its largest mass in de Sitter space.
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Medical Physics · Cross-listed from q-bio.QM
Uncertainty Quantification in Cardiac Model Personalisation from Ultrafast Ultrasound
Camilla Ferrario, Maelys Venet, Olivier Villemain et al. (+1 more)
Cardiac model personalisation requires inferring mechanical parameters that are not directly measurable in vivo. Ultrafast ultrasound shear wave elastography (SWE) enables non-invasive tracking of myocardial stiffness dynamics over the cardiac cycle, providing a target for personalisation. However, mapping these observations to subject specific model parameters remains ill-posed, as multiple parameter sets can reproduce the same stiffness dynamics. We formulate SWE-informed personalisation as a statistical inference problem using simulation-based inference (SBI). Using a subject-adapted 0D cardiovascular model and neural posterior estimation, we estimate model-conditional posterior distributions over active stiffness scale k0, contraction rate kATP, and relaxation rate kSR, conditioned on SWE-derived curve features and subject specific context. Among six healthy volunteers, four passed objective prior-support diagnostics and were retained for quantitative posterior analysis. Curve-level RMSE against the observed SWE target decreased from 12.61 $\pm$ 5.55 kPa for the prior predictive median to 1.14 $\pm$ 0.38 kPa for the posterior predictive median, an 89.7 $\pm$ 4.2% reduction. Posterior analysis revealed parameter-specific uncertainty, k0-kATP compensation, weaker constraint of kSR, and the importance of prior-predictive diagnostics for assessing whether each subject is represented within the modelled SWE feature space. These results support SBI for uncertainty aware SWE-based personalisation, while identifying prior support and forward-model adequacy as key diagnostics.
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All authors Camilla Ferrario, Maelys Venet, Olivier Villemain, Maxime Sermesant
Optics
Generating Vector-Vortex $\gamma$ Photons by Nonlinear Compton Scattering
Yong-Zheng Ren, Mamutjan Ababekri, Jun-Lin Zhou et al. (+8 more)
Vector-
vortex photons, characterized by a nonseparable coupling between polarization and orbital angular momentum (OAM), offer opportunities for optical manipulation,
quantum communication, nuclear photonics, etc. However, their generation in the $\gamma$-ray regime remains challenging. Here, we put forward a novel method to generate vector-
vortex $\gamma$
photons via nonlinear Compton scattering in elliptically polarized
laser pulses. We reveal that tailoring
laser ellipticity directs the multiphoton absorption to coherently populate OAM modes with opposite winding numbers, $\pm \ell$, tied to orthogonal circular polarizations, producing nonseparable
spin-OAM
photon states. For a linearly polarized
laser of moderate intensity (dimensionless amplitude $a_0 \sim 1$), the mode-pair concurrence–a 0-to-1 measure of
spin-OAM
entanglement–reaches unity for MeV $\gamma$
photons, realizing maximally nonseparable radial- or azimuthal-type vector-
vortex states. The
laser amplitude further controls the accessible OAM spectrum. Our method offers a route to MeV vector-
vortex photons, opening a new avenue for nuclear-scale structured photonics and high-energy
quantum information.
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All authors Yong-Zheng Ren, Mamutjan Ababekri, Jun-Lin Zhou, Feng Wan, Qian Zhao, Zhong-Peng Li, Kun Xue, Ya-Qing Huang, Zhao-Hui Chen, Zhong-Feng Xu, Jian-Xing Li
Classical Physics
Similarities between the speed limit in relativity and the sound barrier in inviscid fluid flows
F Salmon
The Prandtl-Glauert-Lorentz transformation establishes a deep mathematical correspondence between compressible potential flow theory and special relativity. Despite being implicit in the aerodynamic literature since the early twentieth century, this analogy remains largely unrecognised across the two communities and has never been surveyed in a unified manner. This review presents, in a self-contained and pedagogical framework accessible to both communities, the historical, mathematical, and applied dimensions of this correspondence. After tracing the parallel developments that gave rise to compressible aerodynamic theory and special relativity, we establish the formal equivalence between the Lorentz transformation and the Prandtl-Glauert coordinate change, and reinterpret relativistic concepts such as time dilation, the Doppler effect, and the Lorentz factor within the acoustic framework. Thanks to the added mass concept, we finally extend this analogy and show that the whole mathematical framework of special relativity is exactly mirrored by the linearised compressible potential flow theory.
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Classical Physics · Cross-listed from math.AP
Multi-material flow with a new viscoelastic model
Sébastien Boyaval
We study a new quasilinear system of balance laws (i.e. conservative first-order PDEs with source terms) for the numerical simulation by a front-capturing approach of viscoelastic athermal multi-material flows with sharp interfaces (like a mixture of immiscible fluids and solids). It naturally extends with an energy balance that is meaningful to stability and thermodynamics. In particular, the unequivocal definition of solutions to Cauchy problems can be guaranteed in some cases, thanks to a symmetric-
hyperbolic formulation.
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Physics and Society
Hybrid epidemic simulation framework coupling equation-based and individual-based models
Jaeyoung Kwak, Michael H. Lees, Chin Chun Ooi et al. (+1 more)
Mass gathering events like concerts, sports matches, and festivals bring many people into close contact within a short period, creating localized bursts of infection that can shape epidemic outcomes across an entire city. To evaluate how these transient transmission events translate into broader urban impacts, we developed a simulation model linking event-scale contact dynamics with citywide commuting networks. Using Madrid, Spain, as a case study, we compared several types of gatherings and examined how their effects changed under different levels of disease transmissibility. We found that mass gatherings consistently amplified outbreak magnitude, accelerated progression, advanced district-level arrival times, and synchronized spatial spread. Remarkably, while the initial seed size generated at the event accounted for much of this acceleration, post-event transmission conditions provided complementary predictive signal regarding invasion timing. These findings demonstrate that mitigating transmission during mass gatherings can yield downstream public health benefits by delaying broader spatial spread. More generally, this multiscale framework offers a tool to evaluate how temporary, localized contact shifts produce longer-lasting consequences for urban populations.
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All authors Jaeyoung Kwak, Michael H. Lees, Chin Chun Ooi, Wentong Cai
Fluid Dynamics
Equal-response probing with replicate calibration identifies scaling relations from noisy observations of complex systems
Dingbang Yan, Zhaoyue Xu and Hua-Dong Yao
Dimensionless descriptions of complex physical systems can sometimes be reduced further when multiple input groups combine into a single composite scaling coordinate. Identifying such structure from noisy response evaluations is difficult because apparent departures may reflect either genuine response structure or evaluation noise. Here we develop equal-response probing with replicate calibration to assess whether two dimensionless inputs support a one-group representation under prescribed directional and collapse tolerances. Equal-response geometry provides a candidate coordinate without direct numerical differentiation, while a second stage evaluates the accuracy of the resulting one-dimensional collapse. Replicate evaluations estimate the noise contribution to both stages, enabling reducible, not-red and unresolved outcomes. We evaluate the framework across eight model-based
benchmark regimes spanning rough-pipe flow,
cell-monolayer wound closure, microfluidic droplet generation and column buckling. Six regimes satisfy both criteria and two fail both, while known reduced coordinates are recovered in exact-reduction
benchmarks. Controlled synthetic tests assess false-alarm behaviour, sensitivity to structural departures and noise calibration. These results show how replicate-calibrated equal-response probing distinguishes regime-specific scaling structure from variation attributable to evaluation noise while retaining an unresolved outcome when evaluation noise precludes a definitive verdict at the prescribed tolerances.
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Physics Education
"What If I Had Participated?" A Machine Learning-Based Counterfactual Analysis of Non-Participants' Success Potential in STEM Competitions: The Case of the German Physics Olympiad
Paul Tschisgale and Knut Neumann
STEM student competitions aim to identify capable, science-interested students and further support them in developing their STEM-related abilities and interests. When such students do not participate, they may appear to be missed not only by the competition but by this form of support altogether; unless they are reached through other competitions. The present study therefore investigated to what extent students who would likely have succeeded in the German Physics Olympiad are missed by it. The study sample comprised 282 Olympiad participants and 1,103 non-participants from academic-track secondary schools, all assessed on 31 indicators spanning sociodemographic background, cognitive abilities, self-related beliefs, motivational variables, personality traits, vocational interests, and prior participation across other STEM competitions. Three machine learning models (elastic net, random forest, gradient boosting) were trained on the participant sample to predict first-round success based on those indicators. The elastic net was found to perform best. Although predictive accuracy was modest, the model proved well-calibrated, supporting valid group-level inferences. Only a few variables predicted success: mathematics skills, physics- and engineering-related skills, and having skipped a grade were positive predictors, whereas conventional vocational interests were a negative predictor. When applied to the non-participants, the model identified 43 students (3.9%) as potentially successful. Crucially, 74% of these students had previously entered at least one selective STEM competition, leaving only 11 students (ca. 1% of all non-participants) entirely unreached by the selective STEM competition system. These findings indicate that the majority of potentially successful non-participants are not absent from the selective STEM competition system but are engaged by it through other domains.
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Optics
Nonlinear Quantum Optics in Epsilon-Near-Zero Nanospheres: a Macroscopic Quantum Electrodynamics Approach
Sonia Alipour and Marco Ornigotti
We present a theoretical framework for handling
quantum nonlinear processes in epsilon-near-zero (ENZ_ nano spheres, based on macroscopic
quantum electrodynamics and the resonant states (RSs) expansion of the Green's tensor in nano cavities. Using third-harmonic generation (THG) as a case study, we derive analytical expressions for the generation efficiency, and the
quantum fluctuations of the generated nonlinear field, as a function of different
quantum states of the impinging pump field. Finally, we discuss how to generalise this theoretical framework to arbitrarily
quantum nonlinear processes in photonic nanostructures.
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Classical Physics
Generalized reverberation theory in diffuse sound fields: Introducing mean residual free path for macroscopic and microscopic unification
Toshiki Hanyu
Sabine's foundational theory established the cornerstone of modern architectural acoustics. However, it fails to predict zero reverberation time in perfectly absorptive rooms. Eyring subsequently addressed this issue by proposing a new formula, which Knudsen later extended to incorporate air absorption. Nevertheless, Eyring's underlying approach contains fundamental theoretical contradictions. To resolve these flaws, the author previously introduced macroscopic and microscopic models for a revised reverberation theory; however, their mathematical unification, rigorous derivation from differential equations, and the mechanism behind Eyring's underestimation remained unclarified. This paper presents a comprehensive generalization and mathematical foundation of the revised theory. The macroscopic model is derived directly from fundamental energy differential equations, incorporating air absorption and a generalized mean residual free path. By reformulating the microscopic model as a sequential convolution process, its fundamental consistency with the macroscopic model is mathematically demonstrated. Crucially, it is shown that Eyring's underestimation can be interpreted as stemming universally from the structural omission of temporal variance expansion ({\sigma}_{n}^{2}=n{\sigma}^{2}) inherent to multiple reflections, regardless of the assumed probability distribution. Finally, ray-tracing simulations validate the scale-invariant accuracy of the proposed theory. Ultimately, this mathematically consistent framework establishes the theoretical limit for future generalized theories in non-diffuse sound fields.
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Atomic Physics
Potential-energy surfaces of water and its molecular ions up to H$_2$O$^{3+}$
Giorgio Visentin and Agapi Emmanouilidou
We compute the potential-energy surfaces for molecular ions up to H$_2$O$^{3+}$ with any combinations of outer-valence, inner-valence and core holes. To obtain the potential-energy surfaces, we consider several ab initio techniques based on the CASSCF method and
benchmark them with respect to the literature. We thus identify the techniques which produce accurate potential-energy surfaces as a function of the two bond lengths and the angle between the two bond lengths. These potential-energy surfaces will be used in future studies of the interaction of water with free-electron
laser pulses. Furthermore, the techniques employed in this work in the context of water can be used to obtain the potential-energy surfaces of other triatomic molecules.
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Applied Physics · Cross-listed from cond-mat.mes-hall
Capacitance sensing in bilayer graphene with gate reflectometry
Tamás Kalmár, Gergő Fülöp, Bálint Szentpéteri et al. (+5 more)
In the search for topological states in bilayer
graphene, capacitance measurement methods are widely utilized in bridge type readouts or source-drain reflectometry setups. In this paper we demonstrate an alternative readout method based on gate reflectometry. We probe the capacitance of a BLG flake encapsulated between hBN and WSe$_2$ through a lumped-element LC resonator coupled to the top gate electrode of the
heterostructure. The microwave readout reliably tracks the opening of a displacement field-induced band gap in the device. Compared to simultaneous DC transport measurements, the RF signal proves to be less affected by the percolating transport channels caused by sample disorder. Furthermore, we use the gate based readout to identify a small-angle
alignment between the hBN and BLG flake. From the fixed frequency microwave readout, we extract the device capacitance change between the insulating and metallic state of the bilayer and utilize a comprehensive capacitance network model to explain its origin. Finally, we propose an advanced, multiplexed double-resonator readout scheme capable of simultaneously measuring top and bottom gate capacitances to extract the layer polarizability of the system. This work establishes gate reflectometry as a highly scalable and powerful methodology for exploring topological phases and internal charge dynamics in van der Waals
heterostructures.
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All authors Tamás Kalmár, Gergő Fülöp, Bálint Szentpéteri, Olivér Kürtössy, Kenji Watanabe, Takashi Taniguchi, Szabolcs Csonka, Péter Makk
Chemical Physics
Non-equilibrium cavity pumping of electronic molecular polaritons
Yassir El Moutaoukal, Rosario R. Riso and Henrik Koch
Strong light-matter coupling in optical cavities offers a non-invasive route to modify molecular properties, and it is usually reached by collectively coupling many molecules to the same mode. Here we consider the photonic counterpart of the collective regime, in which a single molecule interacts with a cavity mode holding many
photons, a steady state of the pumped cavity. Since the eigenstates of the Pauli-Fierz
Hamiltonian carry no transverse electric field, such a state cannot be described as an excited state of the light-matter system. We therefore constrain the
photon number of the strong coupling QED Hartree-Fock wave function with a Lagrange multiplier and self consistently minimize the energy with respect to all parameters. The constrained reference carries the field of a coherent state with an average number of
photons, generated by a cavity mode whose effective free-field frequency is lowered by the multiplier. We apply this framework to benzene and a benzene-water complex, where the pumped cavity polarizes the molecules and modifies their interaction as with a static classical field. For hydrogen peroxide, the field can reshape the torsional potential and the far-infrared torsional spectrum. The classical driven field limit thus emerges from a quantized mean field description, and the
photon density becomes a control parameter for cavity-modified chemistry.
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Physics and Society
Measuring the impact of hits
Matúš Medo and Liudmila Rozanova
Many real systems can be represented as growing networks where new nodes and links gradually emerge. The Barabási-Albert model for growing networks, and many models inspired by it, are based on the idea that nodes compete for links. However, the strength and the very presence of this competition have not been tested. We propose a robust statistical approach to quantify how strongly nodes compete for links, and apply it to data from various real systems—commenting on online news and cinema attendance data. We find a range of possible behaviors, from the perfectly elastic case, where new entrants shape network growth in a way that leaves the rest of the system unaffected, to an intermediate case where new entrants measurably affect the rest. Perfect competition is never observed. These findings have direct implications for complex systems modeling and e-commerce applications.
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Computational Physics · Cross-listed from cs.LG
E3J: An Efficient and Open-Source Backend for Euclidean Equivariant Operations on GPU and TPU
Olivier Peltre, Armand Picard, Adrien Pichard et al. (+6 more)
We present e3j, a fast Euclid-equivariance backend for
geometric deep learning applications with JAX bindings for GPU and TPU. Leveraging both optimized CUDA and Pallas kernels and algorithmic improvements, the library achieves state-of-the-art throughput and runtime on both forward and backward paths. On a machine learning interatomic potential (MLIP) use case, it outperforms established backends, measuring up to 34% speed-up over cuEquivariance on water box NPT simulation using MACE, while remaining fully open source. E3j achieves over 80% efficiency over the H100 maximum
memory bandwidth on tensor product operations, and in many cases more than doubles throughput of message passing convolutions forward compared to previously available backends. In addition, with the release of dedicated Pallas TPU kernel, e3j opens the possibility of large scale equivariant deep learning workloads on TPU architectures, which has so far been difficult to achieve. Our
benchmarks show that e3j also achieves over 80% of a TPUv6e
memory bandwidth, up to one order of magnitude more than e3nn-jax. The library is available on GitHub, PyPI and is released under an open source Apache 2.0 license.
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All authors Olivier Peltre, Armand Picard, Adrien Pichard, Miguel Bragança, Luca Giacomoni, Valentin Heyraud, Zachary Weller-Davies, Christoph Brunken, Jules Tilly
Space Physics
Spectral Properties of Solar Wind Charge Exchange from Earth's Magnetospheric Boundaries: MHD and Test Particle Simulations
A. Ramachandran, R. T. Desai, H. L. Norman et al. (+6 more)
The Solar Wind Charge Exchange (SWCX) mechanism, where X-rays can be generated through interactions between heavy, highly charged solar wind ions and neutral atoms, offers an opportunity to observe the large-scale transfers of energy and momentum through the Sun-Earth system. In this study, we simulate SWCX signatures from Earth's outer boundaries using Gorgon global magnetohydrodynamic (MHD) simulations combined with kinetic particle-based simulations which we call the X-ray Imaging of the Magnetosphere (XIM) framework. The XIM-predicted emissivities agree with the predictions of the MHD model, producing enhanced emissions from the magnetosheath and cusp regions, but several differences are apparent. Compared with MHD, XIM shows enhanced structuring in the magnetosheath and notable enhanced emissions along the magnetopause associated with betatron acceleration. The results also evidence species-specific spatial variations, which are shown to vary compared to anticipated relative abundances in the solar wind and ion-specific properties. These simulations provide new insights into the underlying dynamics of SWCX at the Earth's outer boundaries, which can be used to understand what might be observed using X-ray observatories in space, such as the recently launched SMILE mission.
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All authors A. Ramachandran, R. T. Desai, H. L. Norman, Y. Tong, D. Bewicke, S. Nitti, J. A. Carter, J. P. Eastwood, J. P. Chittenden
Applied Physics · Cross-listed from cond-mat.supr-con
Low-Temperature Stabilization of $\delta$-NbN Superconducting Thin Films through Energy-Selective Ion Beam Sputtering
Yifan Liu, Junwoo Lee, Mingyu Xu et al. (+3 more)
Achieving high-quality superconducting thin films at low temperatures is a central challenge for scalable
quantum device integration and Complementary Metal-Oxide-
Semiconductor (CMOS)-compatible fabrication. Here, we demonstrate a room-temperature magnetron sputtering approach for synthesizing niobium nitride (NbN) thin films using a novel energy-selective ion source that enables independent control of ion energy and ion flux. This capability provides a powerful route to precisely tailor surface kinetics and crystallization pathways, overcoming longstanding limitations in stabilizing high-quality NbN at reduced temperatures. The resulting films were characterized by superconducting transport measurements, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Compared with conventional reactive sputtering, ion beam-assisted growth yields a substantial narrowing of the transition width at the superconducting temperature, indicating improved phase purity and electronic homogeneity. Furthermore, this work introduces energy-selective ion control as a general, non-
equilibrium route to stabilize metastable superconducting phases at low temperatures, offering a new design paradigm for thin-film
quantum materials.
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All authors Yifan Liu, Junwoo Lee, Mingyu Xu, Weiwei Xie, Robert J. Cava, Qi Hua Fan
Biological Physics · Cross-listed from cond-mat.soft
Quorum sensing with density-enhanced motility and size regulation
Itay Azizi
Motivated by biological systems and my previous studies of quorum sensing with density-enhanced motility, I study a model of density-enhanced size and motility, in which both particle size and motility increase when the local density (over a distance larger than particle diameter) exceeds the global density. The emergent structures along different size ratios are spots, holes, bands and labyrinths controlled by several distinct observations. First, the characteristic pattern length scale is controlled by the sensing radius and remains approximately independent of the size ratio. Second, the total area occupied by the particles decreases with increasing size ratio. Third, the active fraction barely depends on the size ratio. These results demonstrate how both particle size and motility can couple microscopic regulation to large-scale pattern formation. I conclude by discussing possible extensions of the model.
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Fluid Dynamics
Handling geometric singularities efficiently with the immersed-boundary method: application to riblets
Stefano Cipelli, Alessandro Chiarini, Maurizio Quadrio et al. (+2 more)
We present an enhancement of classical immersed boundary methods for the direct numerical simulation of the incompressible Navier-Stokes equations, designed to efficiently cope with geometrical singularities. The method, while general, is described here in the context of the flow over a plane wall covered by small longitudinal riblets. The enhancement consists in prescribing that the solution near the boundary matches the steady Stokes solution. In this way, sharp corners, where velocity gradients are strongest and viscous effects dominate, become tractable with grids comparable to those necessary for a smooth wall. The method requires the availability of a local Stokes solution, that can be obtained either analytically or numerically. Two test cases are discussed: the laminar flow over one riblet, which allows to measure protrusion heights, and a fully turbulent channel flow with ribbed walls. In both cases, the method reproduces reference results at a substantially lower computational cost.
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All authors Stefano Cipelli, Alessandro Chiarini, Maurizio Quadrio, Davide Gatti, Paolo Luchini