Optics
Observation of polaritonic flat-band bound states in the continuum in a 2D magnet
Fuhuan Shen, Jiahao Ren, Zhiyi Yuan et al. (+5 more)
Flat-band bound states in the continuum (BICs) are topological states with suppressed group velocity and robustness against radiation loss, offering a powerful platform for the exploration of non-Hermitian, nonlinear, topological phenomena and device applications. Van der Waals (vdW) metasurfaces have recently emerged as promising candidates for sustaining BICs and hybridizing with material transitions. However, the realization of flat-band BICs remains elusive. Here, we experimentally demonstrate polaritonic high-order BICs on a wide-angle flat band utilizing a subwavelength metasurface made of a vdW magnet CrSBr. The large oscillator strength of direct
excitons in CrSBr enables near ultrastrong coupling with BICs, leading to strongly suppressed polaritonic angular dispersions. Remarkably, second-order polaritonic BICs become flat-band across a wide angular range, with corresponding Q factors exceeding 1500. Additionally, we find that these polaritonic BICs vanish in the transverse
magnetic configuration, while leading to fascinating surface
hyperbolic exciton-polaritons within the Reststrahlen band. Our findings underscore CrSBr as an exceptional platform for exploring flat-band photonics and polaritonics, paving the new avenue for advances in next-generation optical and
quantum technologies.
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All authors Fuhuan Shen, Jiahao Ren, Zhiyi Yuan, Kai Wu, Sai Yan, Kunal Parasad, Hai Son Nguyen, Rui Su
Accelerator Physics
RF Applications
Thomas Geoffrey Lucas
Radiofrequency (RF) systems play a critical role in particle accelerators by enabling the acceleration, manipulation, and diagnosis of charged particle beams. At the heart of many of these systems lies the RF cavity, whose effective design requires close collaboration among RF designers, beam physicists, and mechanical engineers. This chapter presents the fundamental principles of RF systems, with particular emphasis on RF cavities, and underscores the interdisciplinary effort involved in their development. The SwissFEL X-ray free-electron
laser at the Paul Scherrer Institut serves as a key example to illustrate these concepts.
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Atomic Physics
Shake-up and shake-off spectra in the electron capture decay of atomic $^7$Be
Mauro Guerra, Inwook Kim, Stephan Friedrich et al. (+33 more)
The most stringent laboratory-based experimental limits on the existence of sub-MeV sterile
neutrinos are currently set by decay spectroscopy of radioactive $^7$Be embedded into superconducting sensors. The systematic uncertainties are dominated by the modeling of the electron shake-up and shake-off spectra that are not based on state-of-the-art atomic theory and do not include electron correlations or relativistic effects. We have used the multiconfiguration Dirac-Fock formalism to obtain correlated wavefunctions ab initio and compute all single and double shake processes in the electron capture decay of atomic $^7$Be. The simulations can explain some but not all of the observed spectral features, likely because the wave functions are modified by the Ta sensor material that the $^7$Be is embedded into. The new models also show that the L/K electron capture ratio of $^7$Be in Ta has previously been slightly underestimated revising the previous value of 0.070(7) to a new value of 0.0756(20).
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All authors Mauro Guerra, Inwook Kim, Stephan Friedrich, Pedro Amaro, Adrien Andoche, Gonçalo Baptista, Connor Bray, Robin Cantor, David Diercks, Spencer L. Fretwell, Abigail Gillespie, Ad Hall, Cameron N. Harris, Jackson T. Harris, Leendert M. Hayen, Paul Antoine Hervieux, Paul Indelicato, Geon Bo Kim, Kyle G. Leach, Annika Lennarz, Vincenzo Lordi, Peter Machule, Andrew Marino, David McKeen, Xavier Mougeot, Daniel Pinheiro, Francisco Ponce, Chris Ruiz, Amit Samanta, José Paulo Santos, Joseph Smolsky, Caitlyn Stone-Whitehead, Joseph Templet, William K. Warburton, Benjamin Waters, Jorge Machado
Optics
Moderate-terahertz-induced plateau expansion of high-order harmonic generation to soft X-ray region
Doan-An Trieu, Duong D. Hoang-Trong, Cam-Tu Le et al. (+5 more)
Extending the high-harmonic cutoff with experimentally accessible fields is essential for advancing tabletop coherent extreme ultraviolet (EUV) and soft X-ray sources. Although terahertz (THz) assistance offers a promising route, cutoff extension at weak, laboratory-accessible THz strengths remain poorly understood. In this report, we comprehensively investigate THz-assisted high-order harmonic generation (HHG) using time-dependent Schrödinger equation simulations supported by classical trajectory analysis and Bohmian-based
quantum dynamics. By mapping the plateau
evolution versus THz strength, we show that even weak THz fields can extend the cutoff, producing a pronounced “fish-fin” structure whose prominent rays saturate near $I_p + 8 U_p$. We trace this extension to long electron excursions spanning several optical cycles before recombination, and provide a fully consistent explanation using both classical analysis and Bohmian trajectories flow. Our findings reveal that this cutoff-extension mechanism is remarkably robust, persisting across different atomic species and remaining insensitive to variations in the driving parameters. These results demonstrate that cutoff control is achievable with laboratory-scale THz fields, offering practical guidelines for engineering coherent high-energy HHG, and providing a robust pathway for tracking ultrafast electron motion in real time.
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All authors Doan-An Trieu, Duong D. Hoang-Trong, Cam-Tu Le, Sang Ha, Ngoc-Hung Phan, F. V. Potemkin, Van-Hoang Le, Ngoc-Loan Phan
Biological Physics · Cross-listed from cond-mat.soft
Negative Pressure and Cavitation Dynamics in Plant-like Structures
Olivier Vincent
It is well known that a solid (e.g. wood or rubber) can be put under tensile stress by pulling on it. Once a critical stress is overcome, the solid breaks, leaving an empty space. Similarly, due to internal cohesion, a
liquid can withstand tension (i.e. negative pressure), up to a critical point where a large bubble spontaneously forms, releasing the tension and leaving a void (the bubble). This process is known as cavitation. While water at negative pressure is metastable, such a state can be long-lived. In fact, water under tension is found routinely in the plant kingdom, as a direct effect of dehydration, e.g. by evaporation. In this chapter, we provide a brief overview of occurrences of water stress and cavitation in plants, then use a simple thermodynamic and fluid mechanical framework to describe the basic physics of water stress and cavitation. We focus specifically on situations close to those in plants, that is water at negative pressure nested within a structure that is solid, but porous and potentially deformable. We also discuss insights from these simple models as well as from experiments with artificial structures mimicking some essential aspects of the structures found within plants.
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Optics
Multi-wavelength UV Upconversion in Lanthanides assisted by Photonic Crystals
Damien Rinnert, Emmanuel Drouard, Antonio Pereira et al. (+6 more)
Upconversion luminescence consists of the absorption of low-energies
photons followed by the emission of a higher energy
photon. The process has mainly been studied in lanthanides to upconvert monochromatic near-infrared excitation to near-infrared or visible light, and has been exploited only to a limited extent to upconvert broad excitations to ultra-violet. In addition, upconverting near-infrared and visible light to ultra-violet is crucial for applications such as
solar-to-fuel conversion or environmental remediation. However, upconversion luminescence is limited by the low absorption cross-sections of lanthanides. In this work, we engineered Bloch modes in a photonic
crystal to assist a multi-wavelength upconversion mechanism and demonstrated a 28-fold enhancement of ultra-violet upconversion luminescence of Yb3+-Tm3+ doped thin films. Materials were selected and optimized to design nanostructures without parasitic absorption losses. The
geometric parameters of the photonic
crystals were scanned to match a slow-light resonance with an excited-state transition of Tm3+ and thus enhance incident visible light absorption. Ultra-violet light extraction was also enhanced by photonic
crystal Bloch modes. Each of these two contributions were quantified and the measured photonic band structures were well reproduced by electromagnetic simulations.
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All authors Damien Rinnert, Emmanuel Drouard, Antonio Pereira, Celine Chevalier, Aziz Benamrouche, Benjamin Fornacciari, Hai Son Nguyen, Gilles Ledoux, Christian Seassal
Fluid Dynamics
Libby-Fox perturbations and the semi-analytic adjoint solution for laminar viscous flow along a flat plate
Carlos Lozano and Jorge Ponsin
The properties of the solution to the adjoint two-dimensional boundary layer (BL) equations on a flat plate are investigated from the viewpoint of Libby-Fox theory, which describes the algebraic perturbations to the Blasius boundary layer. The adjoint solution is obtained from the Green's function of the perturbation equation as a sum over the infinite perturbation modes of the Blasius solution. The explicit representation of the adjoint solution allows us to derive constraints on the
eigenvalues and eigenfunctions, explicitly compute the Adjoint Transport Convection (ATC) term and evaluate flow sensitivities for shape design, initial-value perturbations, and active flow control. The extension of the analysis to the case with non-zero pressure gradient, corresponding to the Falkner-Skan solution, is also briefly discussed.
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History and Philosophy of Physics · Cross-listed from nucl-th
Tribute to Tullio Bressani, Bogdan Povh and Toshimitsu Yamazaki
Avraham Gal
In this HYP2025 talk I pay tribute to Tullio Bressani (1940-2024), Bogdan Povh (1932-2024) and Toshimitsu Yamazaki (1934-2025), all of whom made lasting contributions to shaping up Strangeness
Nuclear Physics. Yoshinori Akaishi's (1941-2025) record is also noted.
Optics
Fast compression of pure-quartic solitons in nonlinear optical fibers via shortcuts to adiabaticity
Chengyu Han, Qian Kong, Ming Shen et al. (+1 more)
Pure-quartic
solitons (PQSs) supported by negative fourth-order dispersion have recently attracted considerable interest. In this work, we study both adiabatic and nonadiabatic compression of PQSs in nonlinear optical fibers with pure quartic dispersion in the presence of distributed gain and loss. Within a variational framework, we show that, for weak constant gain, the adiabatic compression dynamics can be mapped onto the motion of an effective particle in a slowly deformed potential, providing an intuitive physical picture. To overcome the long propagation distance required by conventional adiabatic condition, we exploit shortcuts to adiabaticity (STA) based on inverse engineering and derive analytical gain-loss profiles, with appropriate boundary conditions that realize a prescribed fast compression over a shorter propagation distance. Numerical simulations confirm the theoretical predictions and indicate a minimum propagation distance below which noticeable waveform distortion emerges. Compared with standard adiabatic references, the STA design significantly reduces the required compression distance while maintaining high-fidelity PQS
evolution.
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All authors Chengyu Han, Qian Kong, Ming Shen, Xi Chen
Biological Physics
Magnetic Nanoparticles as Label-Free Dual-Function Nanoheaters and Nanothermometers
Alejandro Venegas-Gomez, Pablo Palacios-Alonso, Cristina C. Carrizo et al. (+6 more)
Heat generation and temperature reading at the nanoscale have attracted increasing
attention due to their direct relevance in thermal therapeutic approaches. Consequently, huge progress has been made toward the design of dual-function nanoplatforms that integrate heating and thermometry capabilities at the nanoscale. However, in most cases, dual nanoheater nanothermometer platforms rely either on specifically engineered materials or on complex readout schemes, which limits translational potential due to complex implementation procedures. To overcome these challenges, we present a methodology for directly extracting temperature information based on dynamical magnetization measurements of cobalt ferrite
magnetic nanoflowers. We demonstrate that these nanocrystals monitor temperature changes through variations in their magnetization cycles measured under alternating
magnetic fields. Importantly, this thermometric functionality is preserved after surface functionalization and under chemical variations in the nanoparticle environment. Interestingly, we show that we can simultaneously generate heat and report temperature changes within the same
agent. This is thanks to the photothermal conversion of cobalt ferrite nanoparticles subjected to near infrared irradiation and the tight reported relationship between magnetization dynamics and Brownian relaxation. Together, these results establish cobalt ferrite
magnetic nanoparticles as a label-free platform for simultaneous heat generation and intrinsic temperature readout, enabling real-time nanoscale thermal control.
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All authors Alejandro Venegas-Gomez, Pablo Palacios-Alonso, Cristina C. Carrizo, Julieta Velasco Martínez-Pardo, Olmo Gómez-Rubio, Sedef Ozel-Okcu, Rafael Delgado-Buscalioni, Sebastian A. Thompson, Francisco J. Teran
Chemical Physics
Algebraic Geometry for Spin-Adapted Coupled Cluster Theory
Fabian M. Faulstich and Svala Sverrisdóttir
We develop and numerically analyze an algebraic-
geometric framework for
spin-adapted coupled-cluster (CC) theory. Since the electronic
Hamiltonian is SU(2)-invariant, physically relevant
quantum states lie in the
spin singlet sector. We give an explicit description of the SU(2)-invariant (
spin singlet) many-body space by identifying it with an Artinian commutative ring, called the excitation ring, whose dimension is governed by a Narayana number. We define
spin-adapted truncation varieties via
embeddings of graded subspaces of this ring, and we identify the CCS truncation variety with the Veronese square of the Grassmannian. Compared to the
spin-generalized formulation, this approach yields a substantial reduction in dimension and degree, with direct computational consequences. In particular, the CC degree of the truncation variety – governing the number of homotopy paths required to compute all CC solutions – is reduced by orders of magnitude. We present scaling studies demonstrating asymptotic improvements and we exploit this reduction to compute the full solution landscape of
spin-adapted CC equations for water and lithium hydride.
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Physics and Society
Evolutionary Dynamics of Reputation-Based Voluntary Prisoner's Dilemma Games
Chen Shen, Zhao Song, Xinyu Wang et al. (+4 more)
Cooperation underlies many natural and artificial systems. While voluntary participation can sustain cooperation without informational assumptions, real interactions are rarely anonymous, leaving the joint effects of participation and reputation insufficiently understood. We propose a reputation-based voluntary Prisoner's Dilemma in which
agents incur a monitoring cost to inspect opponents and decide whether to exit an interaction for a fixed incentive to avoid exploitation or to default to cooperation or defection. We show that reputation-conditioned exit generates multiple coexistence pathways that sustain cooperation across population structures. In well-mixed populations, cooperation persists through stable mixed coexistence, whereas in structured populations, exit-incentive-dependent regimes emerge, including local cyclic dominance and persistent oscillations. Together, these results extend voluntary participation frameworks and underscore the role of exit-incentive design in cooperative multi-
agent systems.
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All authors Chen Shen, Zhao Song, Xinyu Wang, Lei Shi, Matjaž Perc, Zhen Wang, Jun Tanimoto
Applied Physics · Cross-listed from cond-mat.mes-hall
Enhanced Terahertz Photoresponse via Acoustic Plasmon Cavity Resonances in Scalable Graphene
Domenico De Fazio, Sebastián Castilla, Karuppasamy P. Soundarapandian et al. (+11 more)
Precise control and nanoscale confinement of terahertz (THz) fields are essential requirements for emerging applications in photonics,
quantum technologies, wireless communications, and sensing. Here, we demonstrate a polaritonic cavity enhanced THz photoresponse in an
antenna coupled device based on chemical vapor deposited (CVD) monolayer
graphene. The dipole
antenna lobes simultaneously serve as two gate electrodes, concentrate the impinging THz field, and efficiently launch acoustic
graphene plasmons (AGPs), which drive a strong photo-thermoelectric (PTE) signal. Between 6 and 90 K, the photovoltage exhibits pronounced peaks, modulating the PTE response by up to 40%, that we attribute to AGPs forming a Fabry Pérot THz cavity in the full or half
graphene channel. Combined full wave and transport thermal simulations accurately reproduce the gate controlled plasmon wavelength, spatial absorption profile, and the resulting nonuniform electron heating responsible for the PTE response. The lateral and vertical maximum confinement factors of the AGP wavelength relative to the incident wavelength are 165 and 4000, respectively, for frequencies from 1.83 to 2.52 THz. These results demonstrate that wafer scalable CVD
graphene, without hBN encapsulation, can host coherent AGP resonances and exhibit an efficient polaritonic enhanced photoresponse under appropriate gating,
antenna coupling, and AGP cavity design, opening a route to scalable, polarization and frequency selective,
liquid nitrogen cooled, and low power consumption THz detection platforms based on plasmon thermoelectric transduction.
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All authors Domenico De Fazio, Sebastián Castilla, Karuppasamy P. Soundarapandian, Tetiana Slipchenko, Ioannis Vangelidis, Simone Marconi, Riccardo Bertini, Vlad Petrica, Yang Hao, Alessandro Principi, Elefterios Lidorikis, Roshan K. Kumar, Luis Martín-Moreno, Frank H. L. Koppens
Computational Physics · Cross-listed from math.NA
A robust and stable hybrid neural network/finite element method for 2D flows that generalizes to different geometries
Robert Jendersie, Nils Margenberg, Christian Lessig et al. (+1 more)
The deep neural network multigrid solver (DNN-MG) combines a coarse-grid finite element simulation with a deep neural network that corrects the solution on finer grid levels, thereby improving the computational efficiency. In this work, we discuss various design choices for the DNN-MG method and demonstrate significant improvements in accuracy and generalizability when applied to the solution of the nonstationary Navier-Stokes equations. We investigate the stability of the hybrid simulation and show how the neural networks can be made more robust with the help of replay buffers. After an initial single-step training, we run the hybrid simulation for extended periods and compute new reference solutions of the neural network perturbed state for each step. By retraining on this data, the error caused by the neural network over multiple time-steps due to distributional shift can be effectively reduced without the need for a differentiable numerical solver. Furthermore, we compare multiple neural network architectures, including recurrent neural networks and
Transformers, and study their ability to utilize more information from an increased temporal and spatial receptive field.
Transformers allow us to make use of information from
cells outside the predicted patch even with unstructured meshes while maintaining the locality of our approach. This can further improve the accuracy of DNN-MG without a significant impact on performance.
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All authors Robert Jendersie, Nils Margenberg, Christian Lessig, Thomas Richter
Physics and Society · Cross-listed from q-bio.PE
Adaptive dynamics of eco-evolutionary repeated games: Effect of reward and punishment
Prosanta Mandal, Suman Chakraborty, Vaibhav Madhok et al. (+1 more)
Long-term evolutionary processes can strongly influence common-pool resource conservation by generating new traits or behaviours that modify the feedback between population strategies and the resource state. Here we develop an eco-evolutionary framework in which individuals repeatedly interact with the same opponent and follow direct reciprocity through reactive strategies. The strategic dynamics is coupled to a renewable common resource and analyzed using adaptive dynamics. After our exhaustive non-linear dynamical analysis of $2\times2$ strategic games, we focus on comparative and combined usefulness of institutional incentives in the form of rewards and punishments in preventing the Tragedy of the Commons even when defection dominates in the replete resource state. We also report possibility of robust stable oscillations – emerging via
Hopf bifurcation – in resource state and population strategies.
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All authors Prosanta Mandal, Suman Chakraborty, Vaibhav Madhok, Sagar Chakraborty
Fluid Dynamics
Numerical investigation of unsteady flow in a reversible pump-turbine
Chirag Trivedi
Hydropower is an important source of renewable energy that provides clean energy. Pump-turbine type hydraulic turbine is widely used to mitigate the intermittent energy demand and store a large-scale energy. Pump-turbine operates in reverse mode in pump mode to store energy. Flow conditions in turbine mode and pump mode operations is substantially different. This study investigates the unsteady flow field in the model pump-turbine. A computational model of the pump-turbine was created, and the model included hexahedral mesh of 58.19 million nodes. Total verification and validation error was 7.7%. Three operating conditions in turbine mode and four in pump mode were simulated. Flow characteristics, such as blade loading, time-dependent pressure fluctuations, frequency spectra, radial and tangential velocity were investigated. The frequency spectra revealed amplitude of frequencies up to tenth harmonics of the blade passing frequency in pump mode. The higher harmonic frequencies can potentially reach the high mode eigen frequencies and increase the risk of resonance. Flow field analysis in the draft tube indicted the strong presence of Dean
vortices causing highly asymmetric flow at the runner inlet in pump mode operation. This study provides essential insights into the complex flow phenomena and advances the understanding of unsteady flow behaviour in pump-turbines.
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Geophysics · Cross-listed from gr-qc
Thick Lunar Crust Amplifies Deci-Hertz Gravitational-Wave Signal
Lei Zhang, Han Yan, Xian Chen et al. (+1 more)
Gravitational waves (GWs) in the $0.01\sim1$ Hz band encode unique signatures of the early universe and merging compact objects, but they are beyond the reach of existing observatories. Theoretical models suggest that the Moon could act as a resonant detector, but the unknown influence of its rugged surface and heterogeneous interior poses a challenge to the accurate modeling of its response. Here, we address this long-standing uncertainty by constructing the first high-resolution, two-dimensional model of the lunar GW response, more realistic than previous ones. We achieve this by combining high-fidelity spectral-element simulations with the analytical power of normal-mode perturbation theory, thereby resolving topographical effects down to 2 km grid spacing while maintaining the capacity to discern global free-oscillation patterns. This dual-methodology approach not only recovers the expected predominant quadrupole ($l=2$) oscillation mode, but also exposes a systematic signal amplification in thick-crust regions. This enhancement is traced by our normal-mode analysis to a mode-coupling process, in which the original quadrupolar oscillation induced by the passing GW distributes energy into a series of higher-order modes, the hybridized eigenmodes of a laterally heterogeneous Moon. In certain narrow frequency ranges, we observe up to tenfold amplification spanning into the deci-hertz band, highlighting the power of numerical simulations in resolving these structurally fine-tuned features for designing future detectors. Our work establishes the Moon as a resonant GW detector albeit its complex topographical structures, and the resulting amplification maps provide quantitative guide for the optimal landing site selection.
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All authors Lei Zhang, Han Yan, Xian Chen, Jinhai Zhang
Computational Physics · Cross-listed from astro-ph.GA
Simulations of multi-phase gas in and around galaxies
Max Gronke and Evan Schneider
Multiphase gas – ranging from cold molecular clouds ($\lesssim 100\,$K) to hot, diffuse
plasma ($\gtrsim 10^6\,$K) is a defining feature of the interstellar, circumgalactic, intracluster, and intergalactic media. Accurately simulating its dynamics is critical to improving our understanding of
galaxy formation and
evolution, however, due to their multi-scale and multi-physics nature, multiphase systems are highly challenging to model. In this review, we provide a comprehensive overview of numerical simulations of multiphase gas in and around
galaxies. We begin by outlining the environments where multiphase gas arises and the physical and computational challenges associated with its modeling. Key quantities that characterize multiphase gas dynamics are discussed, followed by an in-depth look at idealized setups such as turbulent mixing layers, cloud-wind interactions, thermal instability, and turbulent boxes. The review then transitions to less idealized and/or larger-scale simulations, covering radiative
supernovae bubbles, tall box simulations, isolated
galaxy models including
dwarf and Milky Way-mass systems, and cosmological zoom-in simulations, with a particular focus on simulations that enhance resolution in the
halo. Throughout, we emphasize the importance of connecting scales, extracting robust diagnostics, and comparing simulations to observations. We conclude by outlining persistent challenges and promising directions for future work in simulating the multiphase Universe.
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Atomic Physics
A Robust Strontium Tweezer Apparatus for Quantum Computing
Marijn Venderbosch, Rik van Herk, Zhichao Guo et al. (+11 more)
Neutral atoms for
quantum computing applications show promise in terms of scalability and connectivity. We demonstrate the realization of a versatile apparatus capable of stochastically loading a 5x5 array of optical tweezers with single $^{88}$Sr atoms featuring flexible
magnetic field control and excellent optical access. A custom-designed oven,
spin-flip Zeeman slower, and deflection stage produce a controlled flux of Sr directed to the science chamber. In the science chamber, featuring a
vacuum pressure of $3 \times 10^{-11}$ mbar, the Sr is cooled using two
laser cooling stages, resulting in $\sim 3 \times 10^5$ atoms at a temperature of 5(1) $\mu$K. The optical tweezers feature a $1/e^2$ waist of 0.81(2) $\mu$m, and loaded atoms can be imaged with a fidelity of $\sim 0.997$ and a survival probability of $0.99^{+0.01}_{-0.02}$. The atomic array presented here forms the core of a full-stack
quantum computing processor targeted for
quantum chemistry computational problems.
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All authors Marijn Venderbosch, Rik van Herk, Zhichao Guo, Jesús del Pozo Mellado, Max Festenstein, Deon Janse van Rensburg, Ivo Knottnerus, Yu Chih Tseng, Alexander Urech, Robert Spreeuw, Florian Schreck, Rianne Lous, Edgar Vredenbregt, Servaas Kokkelmans
Atomic Physics
Resonant X-Ray Difference-Frequency Seeding of Inner-Shell X-Ray Lasers
Carles Serrat
We analyze a class of inner-shell x-ray
laser systems in which the initial conditions of the emission are set by a resonant x-ray difference-frequency drive. Using a microscopic density-
matrix framework, we show that two coherent x-ray fields at frequencies $\omega_1$ and $\omega_2$, with $\omega_1-\omega_2=\omega_0$, can induce a phase-locked coherence on a core-level transition at $\omega_0$ without requiring an external field or nonlinear susceptibility at that frequency. In the presence of population inversion, this driven coherence sets the phase and temporal onset of the amplified field, while gain remains governed by conventional inner-shell lasing mechanisms. We refer to this operating regime as a resonant x-ray difference-frequency
laser (re-XDFL). The analysis demonstrates that difference-frequency-driven coherence provides a physically consistent route to controlled inner-shell x-ray
laser emission beyond purely ASE-initiated operation.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
Electronic structure, phase stability, and transport properties of the AlTiVCr lightweight high-entropy alloy: A computational study
Christopher D. Woodgate, Hubert J. Naguszewski, Nicolas F. Piwek et al. (+1 more)
We investigate the thermodynamics and phase stability of the AlTiVCr lightweight high-
entropy alloy using a combination of ab initio electronic structure calculations, a concentration wave analysis, and atomistic Monte Carlo simulations. In
alignment both with experimental data and with results obtained using other computational approaches, we predict a $\textrm{B2}$ (CsCl) chemical ordering emerging in this
alloy at comparatively high temperatures, which is driven by Al and Ti moving to separate sublattices, while V and Cr express weaker site preferences. The impact of this $\textrm{B2}$ chemical ordering on the electronic transport properties of the
alloy is investigated within a Kubo-Greenwood linear response framework and it is found that, counter-intuitively, the
alloy's residual resistivity increases as the material transitions from the $\textrm{A2}$ (disordered bcc) phase to our predicted $\textrm{B2}$ (partially) ordered structure. This is understood to result primarily from a reduction in the density of electronic states at the
Fermi level induced by the chemical ordering. At low temperatures, our atomistic Monte Carlo simulations then reveal subsequent sublattice orderings, with the ground-state configuration predicted to be a fully-ordered, single-phase structure with vanishing associated residual resistivity. These results give fresh, insight into the atomic-scale structure and consequent physical properties of this well-studied, technologically relevant material.
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All authors Christopher D. Woodgate, Hubert J. Naguszewski, Nicolas F. Piwek, David Redka
Optics
Integrated Photonic Quantum Computing: From Silicon to Lithium Niobate
Hui Zhang, Yiming Ma, Yuancheng Zhan et al. (+6 more)
Quantum technologies have surpassed classical systems by leveraging the unique properties of superposition and
entanglement in
photons and matter. Recent advancements in integrated
quantum photonics, especially in silicon-based and lithium niobate platforms, are pushing the technology toward greater scalability and functionality. Silicon
circuits have progressed from centimeter-scale, dual-
photon systems to millimeter-scale, high-density devices that integrate thousands of components, enabling sophisticated programmable manipulation of multi-
photon states. Meanwhile, lithium niobate, thanks to its wide optical transmission window, outstanding nonlinear and electro-optic coefficients, and chemical stability, has emerged as an optimal substrate for fully integrated photonic
quantum chips. Devices made from this material exhibit high efficiency in in generating, manipulating, converting, storing, and detecting
photon states, thereby establishing a basis for deterministic multi-
photon generation and single-
photon quantum interactions, as well as comprehensive frequency-state control. This review explores the development of integrated photonic
quantum technologies based on both silicon and lithium niobate, highlighting invaluable insights gained from silicon-based systems that can assist the scaling of lithium niobate technologies. It examines the functional integration mechanisms of lithium niobate in electro-optic tuning and nonlinear energy conversion, showcasing its transformative impact throughout the photonic
quantum computing process. Looking ahead, we speculate on the developmental pathways for lithium niobate platforms and their potential to revolutionize areas such as
quantum communication, complex system simulation,
quantum sampling, and optical
quantum computing paradigms.
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All authors Hui Zhang, Yiming Ma, Yuancheng Zhan, Yuzhi Shi, Zhanshan Wang, Leong Chuan Kwek, Anthony Laing, Ai Qun Liu, Xinbin Cheng
Data Analysis and Statistics · Cross-listed from stat.ME
Variational Dimension Lifting for Robust Tracking of Nonlinear Stochastic Dynamics
Yonatan L. Ashenafi
Nonlinear
stochastic motion presents significant challenges for
Bayesian particle tracking. To address this challenge, we propose a lifting framework that constructs a higher-dimensional linear
stochastic representation of nonlinear state-space models. The resulting surrogates enable the use of computationally efficient linear filtering techniques while retaining a direct connection to the underlying nonlinear dynamics. The paper derives the necessary conditions for such transformations using Ito's lemma and variational calculus, and illustrates the method on a bistable cubic motion model, radial Brownian process model, and a logistic model with multiplicative noise. Simulations confirm that the transformed linear systems, when projected back, accurately reconstruct the nonlinear dynamics and, in distinct regimes of stiffness and singularity, yield tracking accuracy competitive with conventional filters, while avoiding their structural instabilities.
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Chemical Physics
Beyond the Training Domain: Robust Generative Transition State Models for Unseen Chemistry
Samir Darouich, Jacob W. Toney, Weiliang Luo et al. (+3 more)
Transition states (TSs) govern the rates and outcomes of chemical reactions, making their accurate prediction a central challenge in computational chemistry. Although recent machine-learning models achieve near chemical accuracy in the prediction of TS structures and the associated reaction barriers for small organic reactions, their ability to generalize beyond the training domain remains largely unexplored. Here, we introduce targeted
benchmarks to probe chemical and structural novelty in generative TS prediction. Building on Transition1x, a large-scale
dataset of reactions involving small organic molecules, we construct curated extensions incorporating controlled elemental substitutions and diverse transition-metal complexes (TMC). These
benchmarks reveal fundamental limitations of generative models in the generalization to previously unseen elements. As a result, they produce unphysical geometries and large energetic errors, even for reactions structurally similar to well-predicted organic systems. To address this challenge, we introduce a self-supervised pretraining strategy based on
equilibrium conformers that exposes generative TS models to novel chemical environments prior to targeted fine-tuning. Across the newly proposed
benchmarks, self-supervised pretraining substantially improves TS prediction for previously unseen systems, lowering the median RMSD of TS geometries on T1x-TMC reactions from 0.39 to 0.19 $\mathring{A}$ and reducing fine-tuning data requirements by up to 75%, enabling reliable performance even in low-data regimes. Overall, the integration of generative TS models with self-supervised pseudo-reaction pretraining provides an efficient, scalable, and chemically robust framework for elucidating TSs well beyond the small organic molecule domain, establishing a foundation for investigating complex and catalytically relevant reaction landscapes.
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All authors Samir Darouich, Jacob W. Toney, Weiliang Luo, Johannes Kästner, Mathias Niepert, Heather J. Kulik
Optics
Mode Conversion of Hyperbolic Phonon Polaritons in van der Waals terraces
Byung-Il Noh, Sina Jafari Ghalekohneh, Mingyuan Chen et al. (+7 more)
Electromagnetic hyperbolicity has driven key functionalities in nanophotonics, including super-resolution imaging, efficient energy control, and extreme light manipulation. Central to these advances are
hyperbolic polaritons - nanometer-scale light-matter waves - spanning multiple energy-momentum dispersion orders with distinct mode profiles and incrementally high optical momenta. In this work, we report the mode conversion of
hyperbolic polaritons across different dispersion orders by breaking the structure
symmetry in engineered step-shape van der Waals (vdW) terraces. The mode conversion from the fundamental to high-order
hyperbolic polaritons is imaged using scattering-type scanning near-field optical microscopy (s-SNOM) on both hexagonal boron nitride (hBN) and alpha-phase molybdenum trioxide (alpha-MoO3) vdW terraces. Our s-SNOM data, augmented with electromagnetic simulations, further demonstrate the alteration of polariton mode conversion by varying the step size of vdW terraces. The mode conversion reported here offers a practical approach toward integrating previously independent different-order
hyperbolic polaritons with ultra-high momenta, paving the way for promising applications in nano-optical
circuits, sensing, computation, information processing, and super-resolution imaging.
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All authors Byung-Il Noh, Sina Jafari Ghalekohneh, Mingyuan Chen, Jialiang Shen, Eli Janzen, Lang Zhou, Pengyu Chen, James Edgar, Bo Zhao, Siyuan Dai
Physics and Society · Cross-listed from cs.SI
Segregation Before Polarization: How Recommendation Strategies Shape Echo Chamber Pathways
Junning Zhao, Kazutoshi Sasahara and Yu Chen
Social media platforms facilitate echo chambers through feedback loops between user preferences and recommendation
algorithms. While algorithmic homogeneity is well-documented, the distinct evolutionary pathways driven by content-based versus link-based recommendations remain unclear. Using an extended dynamic Bounded Confidence Model (BCM), we show that content-based
algorithms – unlike their link-based counterparts – steer social networks toward a segregation-before-polarization (SbP) pathway. Along this trajectory, structural segregation precedes opinion divergence, accelerating individual isolation while delaying but ultimately intensifying collective polarization. Furthermore, we reveal that reposting appears connective by circulating content beyond direct follow links, yet it simultaneously reinforces echo chambers because it amplifies small, latent opinion differences that would otherwise remain inconsequential. These findings suggest that mitigating polarization requires stage-dependent algorithmic interventions, shifting from content-centric to structure-centric strategies as networks evolve.
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Fluid Dynamics
Relation between the moments of longitudinal velocity derivatives and of dissipation in turbulence
Ping-Fan Yang, Haitao Xu and Alain Pumir
In homogeneous and isotropic
turbulence, measurements of the longitudinal velocity derivative, $\partial_1 u_1$, make it possible to estimate a surrogate of the rate of energy dissipation per unit mass, $\epsilon$: $\epsilon_s = 15 \nu (\partial_1 u_1)^2 $, where $\nu$ is the fluid viscosity, in the sense that the averages of $\epsilon$ and $\epsilon_s$ are equal. We show here that the $n^{th}$ moments of the fluctuations $\epsilon$ and $\epsilon_s$, for $n > 2$, are not exactly proportional to each other, and that the expression for the moment $\langle \epsilon_s^n \rangle$ for $ n \ge 3$ involves in addition to a term proportional to $\langle \epsilon^n \rangle$, other contributions involving the invariant of the strain tensor, $\SSs$: ${\rm tr}( \SSs^3)$. The contribution of this term depends on the distribution of the dimensionless ratio $\mathcal{R} \equiv {\rm tr}(\SSs^3)/{\rm tr}(\SSs^2)^{3/2}$. We find, however, that the relation obtained by assuming that $\mathcal{R}$ is uniformly distributed in the interval $-1/\sqrt{6} \le \mathcal{R} \le 1/\sqrt{6}$, which is obtained when the
matrix $\SSs$ has a Gaussian distribution, differs by no more than a few percents from the exact distribution.
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Medical Physics
Quantum Sensing MRI for Noninvasive Detection of Neuronal Electrical Activity in Human Brains
Yongxian Qian, Ying-Chia Lin, Seyedehsara Hejazi et al. (+12 more)
Neuronal electrical activity underlies human cognition including perception,
attention,
memory,
language, and decision-making. Yet its direct, noninvasive measurement in the living human
brain remains a fundamental challenge. Existing neuroimaging techniques, including electroencephalography (
EEG), magnetoencephalography (MEG), and functional
magnetic resonance imaging (fMRI), are limited by trade-offs in sensitivity and spatial or temporal resolution. Here we propose
quantum sensing MRI (qsMRI), a noninvasive approach that enables direct detection of neuronal firing-induced
magnetic fields using a clinical MRI system. qsMRI exploits endogenous
proton (1H)
nuclear spins in water molecules as intrinsic
quantum sensors and decodes time-resolved phase information from the free induction decay signals to infer neuronal
magnetic fields. We validate qsMRI through simulations, phantom experiments, and human studies at rest and during motor tasks, and provide open experimental procedures to facilitate independent rigorous validation. We further present a case study demonstrating potential applications to neurological disorders. qsMRI represents, to our knowledge, the first-in-human application of
quantum sensing on a clinical MRI platform and may lay the foundation for a non-BOLD functional imaging modality capable of probing neuronal firing dynamics in both cortical and deep
brain regions.
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All authors Yongxian Qian, Ying-Chia Lin, Seyedehsara Hejazi, Kamri Clarke, Kennedy Watson, Xingye Chen, Nahbila-Malikha Kumbella, Justin Quimbo, Abena Dinizulu, Simon Henin, Yulin Ge, Arjun Masurkar, Anli Liu, Yvonne W. Lui, Fernando E. Boada
Data Analysis and Statistics · Cross-listed from hep-ph
PanopTag: Simultaneously Tagging All Jets in a Particle Collision Event
Umar Sohail Qureshi, Brendon Bullard and Ariel Schwartzman
Jet tagging, identifying the origin of jets produced in particle collisions, is a critical classification task in high-energy physics. Despite the revolutionary impact of deep learning on jet tagging over the past decade, the paradigm has remained unchanged. In particular, jets are classified independently, one at a time. This single-jet approach ignores correlations, overlaps, and wider event context between jets. We introduce PanopTag, a new paradigm for jet tagging that departs from traditional single-jet tagging approaches. Rather than classifying jets independently, PanopTag simultaneously tags all jets by employing an encoder-decoder architecture that uses jet kinematics as queries to cross-attend to particle flow object
embeddings. We evaluate PanopTag on heavy-
flavor $(b/c)$-tagging and demonstrate remarkable performance improvements over state-of-the-art single-jet baselines that are only accessible by exploiting event-level features and correlations between jets.
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Chemical Physics · Cross-listed from cond-mat.str-el
Ab Initio Many Body Quantum Embedding and Local Correlation in Crystalline Materials using Interpolative Separable Density Fitting
Junjie Yang, Ning Zhang, Shunyue Yuan et al. (+3 more)
We present an efficient implementation of ab initio many-body
quantum embedding and local correlation methods for infinite periodic systems through translational
symmetry adapted interpolative separable density fitting, an approach which reduces the scaling of the calculations to only linear with the number of k-points. Employing this methodology, we compute correlated ground-state coupled cluster energies within density
matrix embedding and local natural orbital correlation frameworks for both weakly and strongly correlated solids, using up to 1000 k-points. By extrapolating the local correlation domains and k-point sampling we further obtain estimates of the full coupled cluster with singles, doubles, and perturbative triples ground-state energies in the thermodynamic limit.
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All authors Junjie Yang, Ning Zhang, Shunyue Yuan, Jincheng Yu, Hong-Zhou Ye, Garnet Chan