Chemical Physics
Path Integral Methods in Atomistic Modelling: An Introduction
Michele Ceriotti, David E. Manolopoulos, Thomas E. Markland et al. (+1 more)
This book provides an introduction to path integral methods and their application to modeling atomistic processes. The book covers both the foundational theory and recently developed simulation techniques. The text provides a self-contained resource and was originally developed for the CECAM schools on Path Integral Methods.
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All authors Michele Ceriotti, David E. Manolopoulos, Thomas E. Markland, Mariana Rossi
Optics
Picosecond Supercontinuum Generation in All-Normal Dispersion Optical Fibers Enabled by Polarization Instabilities
R. Morel, A. Kudlinski, O. Vanvincq et al. (+4 more)
Supercontinuum generation in all-normal-dispersion optical fibers has so far been predominantly explored under femtosecond pumping conditions. Here, we demonstrate that efficient and broadband supercontinuum generation can also be achieved in the long picosecond regime by pumping a highly birefringent all-normal-dispersion silica-based photonic
crystal fiber at 1064 nm. The observed spectral broadening results from the combined action of polarization modulation instability and cascaded Raman scattering, enabling octave-spanning spectra extending from 600 nm to 1650 nm. These results establish a distinct operating regime for supercontinuum generation and open new perspectives for robust, high-power broadband fiber sources.
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All authors R. Morel, A. Kudlinski, O. Vanvincq, L. Emonin, G. Fanjoux, J. M. Dudley, T. Sylvestre
Physics and Society
Group dynamics shape contagion onsets and multistable active phases under collective reinforcement
Santiago Lamata-Otín, Federico Malizia, Leah A. Keating et al. (+4 more)
Group-based reinforcement can induce discontinuous transitions from inactive to active phases in higher-order contagion models. However, these results are typically obtained on static interaction structures or within mean-field approximations that neglect temporal changes in group composition. Here, we show that group dynamics is not a secondary effect but a central aspect that determines the macroscopic transition class of higher-order contagion processes. We develop an analytically tractable approximate master equation model that effectively interpolates between quenched and mean-field limits through a group composition turnover rate. Our results reveal the rich impact of time-varying structures: it can induce discontinuous phase transition, broaden the bistable region, and at the same time promote or suppress contagion near criticality. Moreover, when real-world turnover rates and group-size heterogeneity are taken into account, the system exhibits a qualitatively richer phase diagram with four distinct dynamical phases, combining continuous or discontinuous transitions with localized or delocalized activity. In localized regimes, we uncover multistable active phases with multiple coexisting active states, which are observed in neither the annealed nor the quenched limits, and extend classical absorbing-active bistability. Finally, we demonstrate that the emergence of discontinuous transitions in real-world systems requires stronger nonlinear reinforcement than previously thought, indicating that simulations in static structures can yield qualitatively misleading predictions.
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All authors Santiago Lamata-Otín, Federico Malizia, Leah A. Keating, Guillaume St-Onge, Vito Latora, Jesús Gómez-Gardeñes, Laurent Hébert-Dufresne
Accelerator Physics
Machine learning-based virtual diagnostics of dielectric laser acceleration
Thilo Egenolf and Oliver Boine-Frankenheim
We present the development of a digital twin-based reconstruction framework for dielectric
laser acceleration (DLA) based on machine-learning-assisted inversion of single-shot electron energy spectra. DLA as a promising candidate for compact electron accelerator designs using optical nearfields in dielectric nanostructures lacks on direct diagnostics on the
laser-electron interaction. Thus, the outgoing electron energy distribution is one of the few experimentally accessible observables. To exploit this information, DLA interaction and mapping on the downstream spectrometer are treated as nonlinear measurement device whose response is described by the
symplectic sixdimensional tracking code DLAtrack6D. This forward simulation model serves as a digital twin mapping
laser-electron interaction parameters onto resulting energy spectra. For diagnostics, we are interested in the inverse mapping represented by a neural network trained by synthetic
datasets generated with the forward simulation model. The reconstruction performance and parameter identifiability of the inverse model are evaluated for parameter ranges relevant to planned experiments at the ARES linac in the SINBAD facility at DESY. Simulation studies demonstrate that the method can recover pulse front tilt angles with an accuracy of about 1 deg and phase offsets with an RMSE of about 0.36 rad corresponding to a difference of 0.4 fs in arrival time. Training with noisy spectra further improves robustness against spectrometer noise. The trained surrogate model evaluates in the millisecond range, enabling shot-to-shot parameter estimation compatible with the 50 Hz repetition rate of ARES. The approach effectively transforms the DLA interaction region into a virtual in situ diagnostics for otherwise inaccessible
laser parameters during experiment and provides a foundation for real-time monitoring and control of future DLA experiments.
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History and Philosophy of Physics
From Hole Theory to Quantum Field Theory: Relativistic Fermions and the Role of Ettore Majorana (1933-1937)
Francesco Vissani
Between 1933 and 1937, the treatment of relativistic
spin-1/2 particles, initially rooted in Hole theory, evolved into the modern framework of
quantum field theory. This paper reconstructs the crucial stages of that transition by examining the formal and physical progress of the numerous authors who shaped the field's modern formalism. This historical study traces the development of fermionic field theory in full, beginning with the foundational work of the 1920s, focussing on the results of the 1930s, and concluding with the influential synthesis of Wolfgang Pauli in 1941, the content of which has shaped the subsequent tradition. Within this framework, particular emphasis is given to Ettore Majorana's 1937 quantisation procedure and argument for anti-commuting fermionic
quantum fields. This study demonstrates that Majorana's work was not merely a technical variant, but the definitive rejection of the concept of negative energy solutions, whose conceptual clarity and educational value remain vital today.
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Data Analysis and Statistics · Cross-listed from cs.CL
Compressing Transformer Language Models via Matrix Product Operator Decomposition: A Case Study on PicoGPT
Younes Javanmard, Tanmoy Pandit and Masoud Mardani
Transformer-based
language models achieve strong performance across NLP tasks, but their quadratic parameter scaling with hidden dimension makes deployment on resource-constrained hardware expensive. We study
Matrix Product Operator (MPO) decomposition as a principled compression method for
transformers. MPO factorises weight
matrices into chains of low-rank cores, with approximation quality controlled by the bond dimension chi. We replace every nn.Linear layer in PicoGPT, a GPT-2-style character-level
language model with about 1M parameters, with an MPOLinear module parameterised as an MPO chain. Cores are initialised either by TT-SVD from pretrained dense weights or from random initialisation, and trained using standard PyTorch autograd without a custom backward pass. We derive balanced factorisation schemes for the five distinct weight shapes in PicoGPT and evaluate bond dimensions chi in {4, 8, 16, 32} on Tiny Shakespeare. MPO compression achieves up to 13x compression per
transformer block at chi = 4. At chi = 16, the model uses 191,872 parameters instead of 1,020,224 while retaining 97.7% of baseline
token accuracy (51.6% vs 52.8%). Reconstruction error follows the expected trend and is lower for three-site than two-site factorisations at the same bond dimension. The chi = 8 model gives the best accuracy per parameter, exceeding the dense baseline by 2.7x on this metric. These results show that MPO parameterisation is a practical and theoretically grounded alternative to low-rank methods and unstructured
pruning for
transformer compression.
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Fluid Dynamics · Cross-listed from math.AP
Bifurcations of solitary waves in a coupled system of long and short waves
James Hornick and Dmitry E. Pelinovsky
We consider families of solitary waves in the Korteweg–de Vries (KdV) equation coupled with the linear Schrödinger (LS) equation. This model has been used to describe interactions between long and short waves. To characterize families of solitary waves, we consider a sequence of local (pitchfork) bifurcations of the uncoupled KdV
solitons. The first member of the sequence is the KdV
soliton coupled with the ground state of the LS equation, which is proven to be the constrained minimizer of energy for fixed mass and momentum. The other members of the sequence are the KdV
solitons coupled with the excited states of the LS equation. We connect the first two bifurcations with the exact solutions of the KdV–LS system frequently used in the literature.
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Computational Physics · Cross-listed from quant-ph
SesQ: A Surface Electrostatic Simulator for Precise Energy Participation Ratio Simulation in Superconducting Qubits
Ziang Wang, Shuyuan Guan, Feng Wu et al. (+6 more)
An accurate and efficient numerical electromagnetic model for superconducting
qubits is essential for characterizing and minimizing design-dependent dielectric losses. The energy participation ratio (EPR) is the commonly adopted metric used to evaluate these losses, but its calculation presents a severe multiscale computational challenge. Conventional finite element method (FEM) requires 3D volumetric meshing, leading to prohibitive computational costs and
memory requirements when attempting to capture singular electric fields at nanometer-thin material interfaces. To address this bottleneck, we propose SesQ, a surface integral equation simulator tailored for the precise simulation of the EPR. By applying discretization on 2D surfaces, deriving a semi-analytical multilayer Green's function, and employing a dedicated non-conformal boundary mesh refinement scheme, SesQ accurately resolves singular edge fields without an explosive growth in the number of unknowns. Validations with analytically solvable models demonstrate that SesQ accelerates capacitance extraction by roughly two orders of magnitude compared to commercial FEM tools. While achieving comparable accuracy for capacitance extraction, SesQ delivers superior precision for EPR calculation. Simulations of practical transmon
qubits further reveal that FEM approaches tend to significantly underestimate the EPR. Finally, the high efficiency of SesQ enables rapid iteration in the layout optimization, as demonstrated by minimizing the EPR of the
qubit pattern, establishing the simulator as a powerful tool for the automated design of low-loss superconducting
quantum circuits.
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All authors Ziang Wang, Shuyuan Guan, Feng Wu, Xiaohang Zhang, Qiong Li, Jianxin Chen, Xin Wan, Tian Xia, Hui-Hai Zhao
Optics · Cross-listed from quant-ph
Photon-triplets for quantum optics generated by a phase-matched third-order difference-frequency mixing in a KTiOPO4 bulk crystal pumped at 532 nm
Gaspar Mougin-Trichon, Veronique Boutou, Corinne Felix et al. (+2 more)
We report implementation and modelling of an efficient
photon-triplets generation experiment based on a difference-frequency-mixing of two picosecond beams at 532 nm and 1491 nm in a type II phase-matched KTP
crystal. The
photon-triplets flux was measured as a function of the energy of the two incident beams using a coincidence protocol. A maximal flux of 11.6
photon-triplets per second was achieved. These experimental data were satisfactorily described by a semiclassical model based on the
quantum fluctuations of
vacuum and the classical equations of nonlinear optics.
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All authors Gaspar Mougin-Trichon, Veronique Boutou, Corinne Felix, David Jegouso, Benoit Boulanger
Computational Physics
Structured force reformulation of many-body dispersion: towards effective atom–atom decomposition and surrogate modeling
Zhaoxiang Shen, Raúl I. Sosa, Stéphane P.A. Bordas et al. (+2 more)
We present a structured force reformulation of the many-body dispersion (MBD) model that enables a physically consistent decomposition of forces into pairwise components. By introducing a many-body correlation
matrix that scales dipole–dipole interactions, we derive unified expressions for the MBD energy, force, and Hessian. This reformulation reveals a natural structure for effective atom–atom force decomposition and provides a promising foundation for interpretable analysis and machine learning surrogate modeling of MBD interactions.
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All authors Zhaoxiang Shen, Raúl I. Sosa, Stéphane P.A. Bordas, Alexandre Tkatchenko, Jakub Lengiewicz
Plasma Physics
The FreeGSNKE Pulse Design Tool (FPDT): a computational framework for evolutive plasma scenario and control design
K.Pentland, N. C. Amorisco, A. Ross et al. (+8 more)
We present the FreeGSNKE Pulse Design Tool (FPDT), an open-source, Python-based computational framework that enables in silico testing and predictive design of tokamak
plasma scenarios and control strategies. The FPDT couples the FreeGSNKE evolutive
equilibrium solver with a virtual
Plasma Control System (PCS) containing modular and customisable controllers. Given a set of user-defined waveforms and control parameters, the virtual PCS uses feedback and feedforward control to modulate
plasma current, position, and shape, while adhering to machine safety limits on poloidal field coil currents and voltages. The resulting framework allows simulation of the controlled dynamic
evolution of
plasma equilibria, along with the currents in both active poloidal field coils and passive conducting structures, under the assumption of axisymmetry. The FPDT can be used to develop
plasma scenarios, test control schemes, calibrate control parameters, and perform uncertainty quantification studies, thereby reducing iterative and expensive experimental testing on a physical tokamak. The FPDT is machine-agnostic and can be customised to implement different control
algorithms tailored to the specific tokamak of interest. Here, we outline the overall framework and validate its performance on
plasma discharges on the MAST Upgrade tokamak in the `flat-top' phase. We demonstrate excellent quantitative agreement between the FPDT simulations, the desired control waveforms, and the experimental shot data. With this extension to the FreeGSNKE open-source suite of codes we aim to encourage more reproducible and collaborative research in
plasma modelling and control.
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All authors K.Pentland, N. C. Amorisco, A. Ross, P. Cavestany, T. Nunn, A. Agnello, G. K. Holt, G. McArdle, C. Vincent, J. Buchanan, S. J. P. Pamela
Fluid Dynamics · Cross-listed from cond-mat.soft
Bubbles in highly porous media: Clogging and unclogging at constrictions
J.M.P. Beunen, T. Lappan, P. Malgaretti et al. (+3 more)
Gas bubble transport through highly porous transport layers (PTLs) is a key process in electrochemical devices such as
proton exchange membrane water electrolyzers, where bubbles generated at catalyst surfaces must migrate through complex porous networks. To understand this process, we focus on model systems, namely the motion of single, paired and multiple bubbles in capillaries and study these by combining analytical modeling, three-dimensional color-gradient
lattice Boltzmann simulations, and X-ray radiography. For single bubbles, we derive an analytical expression for the critical Bond number separating passage from clogging and show that, in the low deformation regime, it accurately predicts this transition in circular capillaries. Extending the study to bubble pairs, we uncover additional clogging and unclogging pathways, including hydrodynamic unclogging driven by pressure buildup in the interbubble film, and coalescence-induced clogging and unclogging. By mapping our results as functions of confinement ratio and Bond number, we define distinct dynamical regimes that control bubble passage. Experiments on bubble chains rising through highly porous nickel foams confirm the predicted clogging and unclogging mechanisms.
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All authors J.M.P. Beunen, T. Lappan, P. Malgaretti, O. Aouane, K. Eckert, J. Harting
Instrumentation and Detectors
Process Development and First Cryogenic Operation of Compact Germanium Ring-Contact HPGe Prototypes
Kunming Dong, Shasika Panamaldeniya and Dongming Mei
Rare-event experiments such as LEGEND-1000 require high-purity germanium (HPGe) detectors with excellent energy resolution, low electronic noise, and scalable low-background packaging. The germanium ring-contact (GeRC) concept addresses this need through a recessed ring-and-groove electrode geometry intended to preserve point-contact-like low-capacitance signal formation in larger
crystals. However, reliable GeRC fabrication has remained unproven because the non-planar groove geometry complicates machining, surface recovery, conformal passivation, and especially the eventual formation of a robust lithium-diffused outer contact. We report the fabrication and first cryogenic operation of two compact n-type GeRC process-validation prototypes produced from in-house HPGe
crystals at the University of South Dakota. An optimized workflow was developed for core drilling, groove cutting, non-planar polishing, conformal amorphous-germanium (a-Ge) encapsulation, Al patterning, and GeRC-specific cryogenic mounting. Two independent sputtering systems were used to test whether the thin-film sequence remains operable across substantially different deposition environments. At 77~K, both devices biased stably, showed an inferred depletion onset near 340~V from a pulser-based capacitance proxy consistent with electrostatic modeling, and produced identifiable full-energy peaks from $^{241}\mathrm{Am}$ and $^{137}\mathrm{Cs}$. These results establish a proof-of-principle process and readout baseline for geometry-specific GeRC development. They do not yet constitute a deployment-ready large-mass GeRC technology, but they define the foundation for the next step: integrating conformal lithium-paint deposition and controlled
diffusion on the ring-and-groove
topology.
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Atmospheric and Oceanic Physics
Remote Influences of Land Surface Temperature and their Implications for Sea Surface Temperature Patterns
Bosong Zhang and Timothy M. Merlis
The spatial pattern of sea surface temperature (SST) plays a central role in shaping the
climate system, yet the influence of land surface temperature (LST) on large-scale SST patterns remains understudied. Using a state-of-the-art coupled
climate model, we investigate the
climate response to regional abrupt LST warming and time-dependent ramped-warming. We find that regional LST warming can substantially alter the mean-state SST pattern, with the response depending strongly on the location of land warming. In particular, warming over South America strengthens the zonal SST gradient across the tropical Pacific, producing a more La Niña-like mean state. Enhanced land warming increases the zonal contrast in diabatic heating, which excites stationary Rossby wave responses that strengthen alongshore winds and coastal upwelling in the eastern tropical Pacific, providing a dynamical pathway linking regional land warming to changes in the equatorial Pacific mean state. Similar remote SST responses occur for warming over North America, which is accompanied by cooling in the North Pacific, and over Central Africa, which is accompanied by cooling in the tropical Atlantic. In contrast, warming over the Maritime Continent and Tibetan Plateau produces little systematic change in large-scale SST patterns. These results demonstrate that regional LST changes can exert a substantial and geographically dependent influence on remote ocean temperatures. They further suggest that biases in both the mean state and warming trends of LST may contribute to biases in simulated SST patterns in historical simulations, highlighting the importance of accurately representing LST in
climate models.
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Plasma Physics
Simulation Design for Velocity-Controlled Spatio-Temporal Drivers in Laser Wakefield Acceleration
Chiara Badiali, Rafael Almeida, Thales Silva et al. (+1 more)
Velocity-controlled spatio-temporal (ST)
laser drivers offer a route to tailoring
laser-
plasma interactions by allowing the velocity of the intensity peak to be controlled independently of the envelope group velocity. In this work, we present a simulation-design workflow for PIC modelling of subluminal velocity-controlled ST pulses in OSIRIS based on a Maxwell-consistent spectral construction expressed as a superposition of exact
vacuum solutions, and we describe its discrete k-space representation for numerical initialisation. We then examine wakefield excitation with velocity-controlled drivers, showing how the ST geometry couples the effective longitudinal extent of the high-intensity region to the transverse scale and deriving scaling guidelines for near-resonant excitation in the subluminal regime. Finally, we discuss the
geometric constraints that make long-distance simulations costly, including focus-envelope slippage and strong transverse expansion, and we show that continuous wall injection can reproduce the intended
vacuum propagation while substantially reducing the transverse domain size. Together, these results provide practical guidelines for accurate and computationally efficient PIC simulations of velocity-controlled ST drivers in wakefield-relevant regimes.
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All authors Chiara Badiali, Rafael Almeida, Thales Silva, Jorge Vieira
Chemical Physics
A reduced-cost two-component relativistic equation-of-motion coupled cluster method for the double electron attachment problem
Sujan Mandal, Tamoghna Mukhopadhyay and Achintya Kumar Dutta
We present a computationally efficient relativistic formulation of the equation-of-motion coupled-cluster (EOM-CC) method for the double electron attachment (DEA) problem. In this work, the exact two-component
Hamiltonian within the atomic mean-field approximation is employed, yielding results that are in close agreement with the corresponding four-component calculations. However, canonical DEA-EOM-CCSD calculations become prohibitively expensive for heavy elements and large basis sets due to the substantial
memory requirements associated with the complex-valued 3p1h excitation
manifold. To address this limitation, we introduce a new state-specific frozen natural spinor basis that significantly reduces the virtual space through two controllable truncation thresholds. Furthermore, the use of Cholesky decomposition for the two-electron integrals provides an additional reduction in
memory requirements. The performance of the proposed approach is demonstrated through calculations of double ionization potentials and excitation energies for group-12 and group-14 heavy elements. Vertical excitation energies for heavy chalcogen dimers are also presented. In addition, a range of diatomic spectroscopic constants is evaluated for group-13 hydrides. Finally, the method is applied to predict the singlet-triplet gaps of dihalocarbenes, indicating that an accurate description of these systems may require excitation
manifolds beyond the 3p1h space.
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Computational Physics
Pulgon-tools: A toolkit for analysing and harnessing symmetries in quasi-1D systems
Yu-Jie Cen, Sandro Wieser, Georg K. H. Madsen et al. (+1 more)
Pulgon-tools is an open-source software package providing building blocks for the analysis and modeling of quasi-one-dimensional (quasi-1D) periodic systems based on line-group theory. While mature libraries exist for space-group detection in three-dimensional
crystals, an automated and structure-based identification of line groups has so far been lacking. We present software that integrates four complementary components within a consistent line-group framework: (i) structure generation, (ii)
symmetry detection, (iii) irreducible representations (irreps) and character tables and (iv) harmonic interatomic force constants (IFCs) correction. This paper introduces the general code structure and several examples that illustrate some relevant applications of the program.
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All authors Yu-Jie Cen, Sandro Wieser, Georg K. H. Madsen, Jesús Carrete
Optics · Cross-listed from cond-mat.str-el
Superradiant Charge Density Waves in a Driven Cavity-Matter Hybrid
Luka Skolc, Sambuddha Chattopadhyay, Filip Marijanović et al. (+4 more)
Optical cavities enable strong, long-range, light-matter interactions that can drive collective ordering phenomena, such as superradiant self-organization in ultracold atomic gases. Extending these ideas to solid-state electron systems could enable continuous-wave optical control of electronic order, but is impeded by the mismatch between optical wavelengths and electronic length scales. Here, we propose a platform for realizing superradiant charge density waves (sCDWs) in doped, driven transition-metal dichalcogenides coupled to an optical cavity. A nanoscale grating generates electric fields at large in-plane optical momenta, allowing cavity
photons to couple efficiently to electronic density fluctuations through
exciton-polaron processes. Using a linear-stability analysis, we determine the threshold for superradiant ordering and map out the driven phase diagram. We show that tuning the grating periodicity to match the enhanced electronic density fluctuations - such as those near Wigner crystallization - substantially lowers the required pump intensity. Our results establish a novel route toward cavity-controlled electronic order in
quantum materials.
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All authors Luka Skolc, Sambuddha Chattopadhyay, Filip Marijanović, Qitong Li, Jonathan Keeling, Benjamin L. Lev, Eugene Demler
Applied Physics
Monolithic piezo-magnonic-MEMS for efficient modulation of RF signals
M. Cocconcelli, A. Angotti, P. Florio et al. (+3 more)
Compact, low-power analog RF components are essential for next-generation microwave electronics and wireless systems. We demonstrate an all-electric integrated piezo-magnonic microelectromechanical system that enables efficient voltage control of GHz
spin-wave signals via magnetoelastic coupling. Exploiting the large strain in a CoFeB magnonic waveguide integrated on a silicon bridge with piezoelectric actuation, very large values of the magnetoelectric field (up to $30\,\mathrm{mT}$ at $30\,\mathrm{V}$) are obtained, thus achieving reversible phase and amplitude control of propagating
spin waves. In the static regime, we achieve either up to $4\pi$ phase modulation or $\approx 50\,\mathrm{dB}$ amplitude attenuation with drive voltages below $20\,\mathrm{V}$ at $7\,\mathrm{GHz}$. Leveraging the bridge's first bending resonance ($\approx 17\,\mathrm{kHz}$) yields resonant enhancement of the phase modulation efficiency. This allows us to achieve a $2\pi$ phase swing with just $2.2\,\mathrm{V}$ drive and power consumption of $\approx 6\,\mu\mathrm{W}$. Our results highlight piezo-magnonic MEMS as a promising new class of devices for reconfigurable RF front ends and analog signal processors.
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All authors M. Cocconcelli, A. Angotti, P. Florio, N. Pellizzi, F. Maspero, R. Bertacco
Space Physics · Cross-listed from astro-ph.SR
Solar energetic particles and their association with radio emissions
Diana E. Morosan, Anshu Kumari, Immanuel Jebaraj et al. (+6 more)
Energetic particle populations are ubiquitous throughout the Universe. In our
solar system, the most prominent sources of energetic particles are
solar flares or collisionless shocks often driven by huge eruptions of magnetised
plasma called coronal mass ejections (CMEs). Remotely, low energy electrons from the Sun can be observed as
solar radio bursts that are produced by accelerated electron beams undergoing beam-
plasma interactions. There are still many open questions on the generation of
solar energetic particles (SEP): how and where are SEPs accelerated during
solar flares and CMEs and how they escape the
solar atmosphere? Another important question is: what is the link between the
solar radio bursts and the observed SEPs at spacecraft? SKA can provide high-resolution
radio images combined with spectroscopic observations to determine the acceleration time, trajectory and escape of low energy electrons from the
solar corona. The synergy between SKA and current space missions will help investigate
solar activity and energetic particles across a wide range of wavelengths and particle energies. Particle data from spacecraft can be used to make a connection between
radio bursts and SEPs by comparing SEP inferred injection times and energies to those of electrons generating
radio bursts at the Sun.
Radio observations in turn can be used to distinguish between
flare and shock acceleration since different
radio bursts pinpoint towards different energetic processes. Since the acceleration region and origin of SEPs of various properties is still largely debated,
radio observations have the potential to be an invaluable tool in unraveling these processes.
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All authors Diana E. Morosan, Anshu Kumari, Immanuel Jebaraj, Eduard P. Kontar, Mugundhan V., Ketaki Deshpande, Nina Dresing, Puja Majee, Divya Paliwal
Atomic and Molecular Clusters · Cross-listed from cond-mat.mes-hall
Geometry-controlled competition between axis centering and detwinning in fivefold-twinned gold nanoparticles
Silvia Fasce, Diana Nelli, Luca Benzi et al. (+2 more)
Fivefold-twinned metal nanoparticles host a central wedge disclination that strongly influences their mechanical and catalytic properties. Yet the atomistic mechanisms governing the stability, migration, and annihilation of this topological defect remain incompletely understood. Here we present a systematic molecular dynamics study of gold Marks decahedra in which the fivefold axis is artificially brought close to the surface by controlled
geometric modifications. By generating concave and convex morphologies with varying axis depth, we uncover a geometry-controlled competition between axis centering and detwinning. Concave geometries promote surface
diffusion that restores fivefold
symmetry, either by recentering the original disclination or by nucleating a new subsurface axis through collective atomic rearrangements. In contrast, convex structures with a shallow axis undergo rapid detwinning within the first nanoseconds via surface glide, leading to single-twin or fully FCC configurations. Remarkably, positioning the axis just two atomic layers beneath the surface suppresses detwinning and restores stability. Our results demonstrate that surface
curvature and defect depth critically regulate disclination mobility and twin stability, providing a mechanistic framework to understand the structural
evolution of multi-twinned nanoparticles and to guide the controlled design of defect-engineered nanomaterials.
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All authors Silvia Fasce, Diana Nelli, Luca Benzi, Georg Daniel Förster, Riccardo Ferrando
Plasma Physics · Cross-listed from cond-mat.stat-mech
Ergotropic rearrangement of phase space density
Michele Campisi
The explicit expression of ergotropy (a.k.a. available energy) of a classical system is known for the case when the system phase space density is continuous and with no plateaus. Here we provide the general expression of ergotropy that applies without those limitations. It easily follows upon casting the ergotropy problem as a function rearrangement problem. This leads to the notion of "ergotropic rearangement" which generalises that of "symmetric decreasing rearrangement" (an advanced topic of measure theory). We apply it to investigate the fate of classical ergotropy in the thermodynamic limit, and find that any density of the form $\rho=f(H_0)$ is asymptotically passive, where $H_0$ is the system
Hamiltonian and $f$ a generic function.
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Chemical Physics
Perspective of Fermi's golden rule and its generalizations in chemical physics
Seogjoo J. Jang, Goun Kim and Young Min Rhee
This perspective provides a succinct history of
Fermi's golden rule (FGR), overview of its derivation, assumptions, and representative forms. Major applications of FGR, mostly in the field of chemical physics, are reviewed. These illustrate the broad applicability and success of FGR. Ambiguities and open issues encountered in practical applications of FGR are clarified. Recent advances in generalizations of FGR and computational methods for practical applications are addressed.
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Atomic Physics · Cross-listed from cond-mat.quant-gas
Simulating cavity QED with spin-orbit coupled Bose-Einstein condensates revisited
Muhammad S. Hasan and Karol Gietka
Simulating cavity
quantum electrodynamics in synthetic platforms offers a route to studying light–matter physics without real
photons. We reassess the frequently invoked analogy between harmonically trapped,
spin–orbit-coupled atoms and the
quantum Rabi and Dicke models, with particular emphasis on squeezing and
entanglement. A single non-interacting atom realizes the
quantum Rabi
Hamiltonian exactly, up to elementary
spin and phase-space rotations. For $N$ non-interacting atoms, however, the center-of-mass mode is only one member of a complete orthonormal set containing $N-1$ relative modes. We prove that, after all modes are included, the
spin–
spin terms generated by the collective mode cancel exactly against those generated by the relative modes. Equivalently, the original
Hamiltonian is a sum of independent one-particle
Hamiltonians and therefore cannot create interparticle
entanglement from a separable state. Contact interactions invalidate this cancellation but do not remove the relative modes or turn the exact many-body
Hamiltonian into a Dicke model. A one-mode Dicke description can arise only as a controlled low-energy approximation after all relevant relative excitations have been shown to be spectrally suppressed. We discuss this distinction together with experimental scales, finite temperature, and possible mode-selection strategies. We also distinguish the single-particle interference underlying density fringes from the interaction-stabilized stripe supersolid observed in many-body condensates.
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Applied Physics · Cross-listed from cs.RO
A Foldable and Agile Soft Electromagnetic Robot for Multimodal Navigation in Confined and Unstructured Environments
Zhihao Lv, Xiaoyong Zhang, Mengfan Zhang et al. (+5 more)
Multimodal locomotion is crucial for an animal's adaptability in unstructured wild environments. Similarly, in the human gastrointestinal tract, characterized by viscoelastic mucus, complex rugae, and narrow sphincters like the cardia,
multimodal locomotion is also essential for a small-scale soft
robot to conduct tasks. Here, we introduce a small-scale compact, foldable, and robust soft electromagnetic
robot (M-SEMR) with more than nine locomotion modes designed for such a scenario. Featuring a six-spoke elastomer body embedded with
liquid metal channels and driven by Laplace forces under a static
magnetic field, the M-SEMR is capable of rapid transitions (< 0.35 s) among different locomotion modes. It achieves exceptional agility, including high-speed rolling (818 mm/s, 26 BL/s), omnidirectional crawling, jumping, and swimming. Notably, the
robot can fold to reduce its volume by 79%, enabling it to traverse confined spaces. We further validate its
navigation capabilities on complex terrains, including discrete obstacles, viscoelastic gelatin surfaces, viscous fluids, and simulated biological tissues. This system offers a versatile strategy for developing high-mobility soft
robots for future biomedical applications.
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All authors Zhihao Lv, Xiaoyong Zhang, Mengfan Zhang, Xiaoyu Song, Xingyue Liu, Yide Liu, Shaoxing Qu, Guoyong Mao
Geophysics · Cross-listed from cs.LG
Physics-Informed Neural Networks for Predicting Hydrogen Sorption in Geological Formations: Thermodynamically Constrained Deep Learning Integrating Classical Adsorption Theory
Mohammad Nooraiepour, Mohammad Masoudi, Zezhang Song et al. (+1 more)
Accurate prediction of hydrogen sorption in fine-grained geological materials is essential for evaluating underground hydrogen storage capacity, assessing caprock integrity, and characterizing hydrogen migration in subsurface energy systems. Classical isotherm models perform well at the individual-sample level but fail when generalized across heterogeneous populations, with the coefficient of determination collapsing from 0.80-0.90 for single-sample fits to 0.09-0.38 for aggregated multi-sample
datasets. We present a multi-scale physics-informed neural network framework that addresses this limitation by
embedding classical adsorption theory and thermodynamic constraints directly into the learning process. The framework utilizes 1,987 hydrogen sorption isotherm measurements across clays, shales, coals, supplemented by 224 characteristic uptake measurements. A seven-category physics-informed feature engineering scheme generates 62 thermodynamically meaningful descriptors from raw material characterization data. The loss function enforces saturation limits, a monotonic pressure response, and Van't Hoff temperature dependence via penalty weighting, while a three-phase curriculum-based training strategy ensures stable integration of competing physical constraints. An architecture-diverse ensemble of ten members provides calibrated uncertainty quantification, with post-hoc temperature scaling achieving target prediction interval coverage. The optimized PINN achieves R2 = 0.9544, RMSE = 0.0484 mmol/g, and MAE = 0.0231 mmol/g on the held-out test set, with 98.6% monotonicity satisfaction and zero non-physical negative predictions. Physics-informed regularization yields a 10-15% cross-lithology generalization advantage over a well-tuned random forest under leave-one-lithology-out validation, confirming that thermodynamic constraints transfer meaningfully across geological boundaries.
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All authors Mohammad Nooraiepour, Mohammad Masoudi, Zezhang Song, Helge Hellevang
Fluid Dynamics · Cross-listed from math.AP
Finite-Time Weak Singularities and the Statistical Structure of Turbulence in 3D Incompressible Navier-Stokes Equations
Chio Chon Kit
This paper provides a rigorous mathematical analysis of the global regularity problem for the 3D incompressible Navier-Stokes (NS) equations, specifically addressing the conditions under which smooth initial data may lead to a loss of regularity. By departing from traditional phenomenological
turbulence models and focusing strictly on the mechanical energy transport equation, we derive a fundamental critical condition, $\boldsymbol{u}\cdot\nabla E = 0,$ where $E = \frac12|\boldsymbol{u}|^2 + p$ is the specific mechanical energy, which characterizes the transition from laminar to turbulent flow.
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Computational Physics
Electromagnetic Scattering by a Finite Metallic Circular Cylinders Set
Matthieu Elineau, Lucille Kuhler and Alexandre Chabory
The problem of electromagnetic scattering by cylinders is an old problem that has been studied in many configurations. The present publication provides a theoretical study on a not yet investigated general case: the set of finite metallic circular cylinders. A model which takes into account both the finiteness of the cylinders and their electromagnetic coupling is provided. The total field is written in a two dimensional problem in terms of cylindrical harmonics and is used to define current densities which are integrated in a three dimensional problem. The finiteness is taken into account assuming current densities that are identical from those of the two dimensional problem. Coupling effects are naturally taken into account via the
matrix formulation of the boundary condition that binds together the cylindrical harmonic coefficients. The proposed closed-form is valid for great cylinder lengths and any cylinder radii. Numerical experiments are also provided in various configurations in order to evaluate the accuracy of the model. The model computational times happens to be 5 orders of magnitude shorter than a full-wave reference simulation, without significant loss of accuracy.
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Physics and Society
The electricity system value of the local acceptance of onshore wind in Europe
James Price, Guillermo Valenzuela-Venegas, Oskar Vågerö et al. (+11 more)
The large-scale deployment of wind power is central to Europe`s energy transition but faces challenges due to its social and environmental impacts on communities. Here we assess how the tolerance of local stakeholders to such impacts translates across spatial scales to shape the cost and design of the continent`s net-zero electricity system using a soft-linked modelling framework. We find that lower impact tolerance can reduce the role of onshore wind in Europe reaching net-zero by up to 84% relative to a future where wind enjoys higher acceptance, with other low carbon sources needing to be scaled up to compensate. This translates into total European electricity system costs increasing by between 2-14% while some countries see costs escalating by 20% or more. Our results show that the local acceptance of onshore wind is a key structural driver of the system and highlight the system value of policies to promote it.
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All authors James Price, Guillermo Valenzuela-Venegas, Oskar Vågerö, Marianne Zeyringer, Monika Bucha, Ruihong Chen, Adrienne Etard, Andrea N. Hahmann, Alena Lohrmann, Russell McKenna, Christian Mikovits, Evangelos Panos, Meixi Zhang, Luis Ramirez Camargo
Instrumentation and Detectors
Sensitivity enhancement techniques for cryogenic calorimeters in the NUCLEUS experiment
M. Cappelli, A. Wallach, H. Abele et al. (+62 more)
Phonon-mediated cryogenic calorimeters find application in rare event searches due to their intrinsically low energy threshold. Achieving optimal sensitivity for these kinds of detectors is crucial for signal identification, leading to various optimization techniques. In this work, we present two complementary methods to increase the sensitivity of cryogenic detectors read out by transition-edge sensors, developed and tested in the context of the
NUCLEUS experiment. The first procedure maps the signal-to-noise ratio of the device across a wide range of operating points, to identify the configuration with maximal sensitivity to be used during data taking. The second method exploits the double readout of the detector, combining the information from different channels with a two-dimensional optimum filter analysis that effectively lowers the energy threshold. By combining both techniques at the same time, we obtain a baseline resolution of $2.94\pm0.05_{\text{stat}}\pm0.74_{\text{syst}}$~eV using a CaWO$_4$ based detector, achieving a promising result ahead of the first run of
NUCLEUS at the experimental site.
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All authors M. Cappelli, A. Wallach, H. Abele, G. Angloher, B. Arnold, M. Atzori Corona, A. Bento, E. Bossio, F. Buchsteiner, J. Burkhart, F. Cappella, N. Casali, R. Cerulli, A. Cruciani, G. Del Castello, M. del Gallo Roccagiovine, S. Dorer, A. Erhart, M. Friedl, S. Fichtinger, V.M. Ghete, M. Giammei, C. Goupy, J. Hakenmüller, D. Hauff, F. Jeanneau, E. Jericha, M. Kaznacheeva, H. Kluck, A. Langenkämper, T. Lasserre, D. Lhuillier, M. Mancuso, R. Martin, B. Mauri, A. Mazzolari, L. McCallin, H. Neyrial, C. Nones, L. Oberauer, L. Peters, F. Petricca, W. Potzel, F. Pröbst, F. Pucci, F. Reindl, M. Romagnoni, J. Rothe, N. Schermer, J. Schieck, S. Schönert, C. Schwertner, L. Scola, G. Soum-Sidikov, L. Stodolsky, A. Schröder, R. Strauss, R. Thalmeier, C. Tomei, L. Valla, M. Vignati, M. Vivier, P. Wasser, A. Wex, L. Wienke