Fluid Dynamics · Cross-listed from astro-ph.SR
Kelvin waves over a differentially rotating spherical shell
T. Boismard and M. Rieutord
Context. Be
stars are presently viewed as B-type
stars surrounded by a disc fueled by the
star itself during episodicexcretion events. The origin of these events are poorly understood.Aims. This article aims to determine whether or not surface equatorial Kelvin waves can be unstable and therefore canplay a role in the triggering of the Be phenomenon.Methods. We first derive an analytical expression for gravito-inertial modes in the shallow-water framework. Then, weinvestigate numerically the
evolution of equatorial Kelvin modes as system parameters vary. The study is extended tothick-layer configurations with a constant density fluid. We then analyze the stability of these modes under differentialrotation and viscous effects.Results. We show that equatorial Kelvin waves still exist in a spherical shell of finite thickness, but that their equatorialconfinement is weaker. At low azimuthal wavenumbers, Kelvin waves are in the inertial waves frequency band and thusget specificities of inertial waves like shear layers associated with singularities of the Poincaré equation. These shearlayers are new dissipative structures for Kelvin waves. When a radial (shellular) differential rotation is imposed, we showthat equatorial Kelvin waves can be destabilised provided that differential rotation and viscosity are in an appropriaterange. The non-monotonic behaviour of the growth rate of the instability is traced back to the rise of a critical layerwhere the fluid azimuthal velocity equals the phase speed of the surface waves.Conclusions. This study provides new insights into the behavior of equatorial Kelvin waves in astrophysics, particularlyin rapidly rotating
stars. The results reinforce the idea that gravito-inertial waves, and more specifically the equatorialKelvin waves, can be unstable and thus be key parts in the mechanisms leading to the Be phenomenon.
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Applied Physics
Experimental demonstration for precisely tuning the focal length of finite-aperture focused beams and vortex
Shiyu Li, Yicheng Feng, Weiwei Cui et al. (+1 more)
High-frequency focused ultrasound is widely used in biomedical applications such as high-resolution imaging, neuromodulation, particle manipulation, and so on. However, dynamic tuning of the focal plane in conventional systems often relies on mechanically adjustable components or array-based control with complex system and high cost. In this work, an optically transparent, planar compact piezoelectric ultrasonic transducer was designed and fabricated by truncating an ideal spherical wavefront with a plane, enabling high-frequency focused ultrasound generation and convenient integration with microscopic platforms. The acoustic field was characterized experimentally at the focal plane under the design frequency and at propagation planes near the design frequency to evaluate the focal tuning. An approximate linear relation between the focal length and driving frequency near the design one is derived theoretically, and the finite-range tuning behavior is interpreted using the stationary-phase condition. Both theory and experiment show that the focal length varies approximately linearly with excitation frequency near the design frequency. Water-tank measurements agree well with the theoretical prediction, confirming the proposed model. This work provides a simple and cost-effective approach for focal tuning in compact high-frequency ultrasound devices.
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All authors Shiyu Li, Yicheng Feng, Weiwei Cui, Zhixiong Gong
Optics
Magnetically Tunable Chiral Phonon Polaritons with Magneto-optical Bound States in the Continuum
Yu Sun, Jue Li, Wei Li et al. (+3 more)
Chiral phonon-polaritonic states are of interest for handedness-dependent light-matter interactions, yet their realization and
magnetic control remain challenging, while direct magneto-optical tunability of
phonon-polaritonic media is limited. Here, we propose a hybrid platform in which an hBN
phonon polariton couples to a
chiral bound state in the continuum supported by a magneto-optical photonic
crystal, enabling strong and selective photonic coupling. The interaction gives rise to pronounced mode splitting and the formation of hybrid states, and their modal composition is quantified by
phonon-proportion analysis and described by a coupling theory. Importantly, the hybridization can be controlled by
magnetic bias through the magneto-optical response of the photonic component, providing control over the modal composition and spectral response. In addition, the hybrid states exhibit handedness-selective absorption under circularly polarized excitation. This work offers a feasible route toward magnetically tunable
chiral phonon-polaritonic devices and hybrid polaritonic functionalities
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All authors Yu Sun, Jue Li, Wei Li, Bo Li, Qinghua Song, Mengyao Li
Instrumentation and Detectors
Projection of purification performance for the RELICS experiment
Jiachen Yu, Kaihang Li, Jingfan Gu et al. (+47 more)
The RELICS (REactor
neutrino LIquid xenon Coherent elastic Scattering) experiment employs a dual-phase
liquid xenon time projection chamber to search for Coherent Elastic
Neutrino-
Nucleus Scattering (CE$\nu$NS) induced by reactor
neutrinos. To detect these sub-keV
nuclear recoils and minimize signal attenuation, it is critical to maintain a sufficiently low
impurity concentration in the detector. This work presents a comprehensive purity
evolution model developed to describe
impurity migration inside the detector. Utilizing measured material outgassing rates as input parameters, the model incorporates non-uniform transport mechanisms of the
impurities, including circulation, vaporization, and condensation. The model is validated using data from a dedicated prototype detector. Based on this validated model, projections for the purification performance of the upcoming RELICS-10 and RELICS-50 detectors are provided.
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All authors Jiachen Yu, Kaihang Li, Jingfan Gu, Chang Cai, Guocai Chen, Jiangyu Chen, Huayu Dai, Rundong Fang, Hongrui Gao, Fei Gao, Xiaoran Guo, Jiheng Guo, Chengjie Jia, Gaojun Jin, Fali Ju, Yanzhou Hao, Xu Han, Yang Lei, Meng Li, Minhua Li, Shengchao Li, Siyin Li, Tao Li, Qing Lin, Jiajun Liu, Sheng Lv, Yuanyuan Ren, Chuanping Shen, Lijun Tong, Yuhuang Wan, Jun Wang, Xiaoyu Wang, Wei Wang, Xiaoping Wang, Zihu Wang, Yuehuan Wei, Liming Weng, Xiang Xiao, Lingfeng Xie, Jijun Yang, Litao Yang, Long Yang, Jingqiang Ye, Qian Yue, Yuyong Yue, Tianyuan Zha, Bingwei Zhang, Honghui Zhang, Zhicai Zhang, Yifei Zhao
Optics
Scalable 3D silicon nitride photonic interposer for high-density optical interconnects
Yu Xia, Yuhao Huang, Yuemin Li et al. (+10 more)
Modern computing workloads demand energy-efficient, high-bandwidth interconnects, motivating photonic interposers as an alternative to electrical links. Here we demonstrate a compact 3D silicon nitride (SiN) photonic interposer prototype comprising two routing layers, with the 3D routing scheme optimized by a global optimization
algorithm. The 3D interposer realizes a fully connected 12-node optical network that reduces the total number of intralayer crossings from 495 for all-planar routing to merely 150 (69.7% reduction), below the theoretical lower bound of 153 for all-planar interconnects. Comparing the two schemes, our 3D design achieves a 45.8% reduction experimentally in the average loss per waveguide. The proposed 3D routing architecture also features inherent
symmetry and is scalable to higher node counts, flexible node placements, additional routing layers, and other operating wavelengths, enabling denser, lower-loss photonic interposers for next-generation scale-up and high-performance computing (HPC) systems.
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All authors Yu Xia, Yuhao Huang, Yuemin Li, Jie Wang, Yunqi Fu, Yaoran Huang, Hongjie Liang, Hao Fang, Zheng Li, Mingfei Liu, Yitian Tong, Di Yu, Chao Xiang
Optics
Meter-long broadband chirped Bragg gratings for on-chip dispersion control and pulse shaping
Zhaoting Geng, Yitian Tong, Chuchen Zhang et al. (+12 more)
Precise on-chip dispersion control is essential for advanced integrated photonic technologies, enabling applications ranging from high-speed communications and sensing to signal processing and biomedical imaging. However, existing on-chip dispersion control methods still suffer from substantial loss and a limited dispersion-bandwidth product (DBP) far from application needs. As a result, on-chip systems continue to rely exclusively on off-chip dispersion control solutions provided by optical fiber or bulky free-space optics. To overcome these limitations, we design and fabricate meter-long chirped spiral Bragg gratings (CSBGs) on the ultra-low-loss silicon nitride (SiN) photonic platform for advanced dispersion control. Our device achieves a 10-nanosecond group delay with customizable bandwidths exceeding 10 nanometers within a compact footprint of only 30 $\text {mm} ^2$, surpassing the physical limits of fiber-based grating devices. More importantly, CSBGs can simultaneously possess the characteristics of high stability, low latency, and a large DBP, thanks to the ultra-low-loss SiN platform with a loss of only 0.3 dB/m. Leveraging the precise and stable dispersion profile, we demonstrate high-fidelity pulse shaping and compression of electro-optic frequency combs (EOCs) with a 1-GHz repetition rate centered across the entire reflection bandwidth. The compressed pulse has an on-chip peak (average) power of 21.6 watts (580 milliwatts). Furthermore, we showcase for the first time the application of on-chip pulse-compressed EOC in wavelength-swept coherent anti-Stokes Raman scattering (CARS) microscopy. Our work provides integrated photonics with a long-sought, scalable, and robust solution for high-performance on-chip dispersion control, empowering a new generation of on-chip functionalities.
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All authors Zhaoting Geng, Yitian Tong, Chuchen Zhang, Huajun Tang, Zhenmin Du, Yu Xia, Mingfei Liu, Di Yu, Yuhao Huang, Yaoran Huang, Zheng Li, Tianxiang Dai, Kenneth Kin-Yip Wong, Hongwei Chen, Chao Xiang
General Physics
A possible solution to the mystery of the ANITA anomalous events
Massimo Villata
In 2006 and 2014, the Antarctic Impulsive Transient
Antenna (ANITA), a balloon-borne
radio observatory flying over Antarctica, detected two strange upward-going
radio pulse events that have not yet been explained by our current understanding of physics. These were not signals reflected by the ice and therefore it must have been an air shower originating from a
cosmic ray coming from under the Antarctic ice, but this hypothesis was also ruled out by various data analyses. The CPT
gravity theory and its associated cosmological model, the
lattice Universe, can instead explain those events in a completely natural and spontaneous way, without any additional assumptions beyond general relativity and the expected matter-antimatter
symmetry of the Universe on which they are based. Together with the antihelium candidate events from AMS-02, the anomalous ANITA events can thus lend further validity to a cosmological model that has already achieved considerable success in explaining the accelerated expansion of the Universe, without the need for dark energy. These events thus add to a series of problems unsolved by standard cosmology and physics, but whose solution is straightforward, spontaneous and natural within the framework of CPT
gravity, without the need for ad hoc hypotheses and unknown ingredients.
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Physics and Society · Cross-listed from q-bio.PE
Predicting success of cooperators across arbitrary heterogeneous environmental landscapes
Amir Kargaran, Kamran Kaveh and Krishnendu Chatterjee
Cooperation is central to the organization of complex biological and social systems. Most theoretical models assume homogeneous environments; in reality, populations inhabit spatially varying landscapes in which the payoffs of cooperation differ across space. Here, we introduce a general framework for the
evolution of cooperation in complex, heterogeneous environments where the benefit of cooperation depends on local environmental quality. Cooperators in environmentally rich sites confer greater benefits than those on poor sites. We show that whether heterogeneity promotes or suppresses cooperation is determined primarily by the spatial organization of environmental states. Across arbitrary environmental landscapes, a single quantity, the spatial correlation index (SCI), predicts the fixation probability of cooperators. Under weak selection, segregated environments enhance cooperation, whereas highly intermixed, checkerboard-like landscapes suppress it. Beyond fixation probabilities, environmental organization also controls evolutionary timescales: segregated landscapes generate long-lived metastable coexistence, whereas intermixed landscapes lead to faster but less successful fixation of cooperators. Together, these results provide a unifying description of how spatial environmental heterogeneity shapes the
evolution of cooperation and suggest measurable predictors of cooperative success in biological and social settings.
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Applied Physics
Thermal Characterization of Buried Interfaces in Multilayer Heterostructures via TDTR with Periodic Waveform Analysis
Mingzhen Zhang, Puqing Jiang and Ronggui Yang
Accurate evaluation of buried thermal interfaces is vital for understanding and optimizing heat dissipation in wide- and ultra-wide-bandgap (WBG/UWBG)
semiconductor devices. Conventional time-domain thermoreflectance (TDTR) typically probes only near-surface transport due to its restricted modulation frequency range. Here, we employ a frequency-tunable periodic waveform analysis TDTR (PWA-TDTR) technique to perform depth-resolved thermal measurements on three representative systems: epitaxial {\epsilon}-Ga2O3/SiC, GaN/Si, and mechanically bonded GaN/diamond. By combining broadband multi-frequency probing with sensitivity-guided joint fitting, we quantitively determine interfacial thermal conductance, layer-specific thermal conductivity, and volumetric heat capacity, without requiring destructive sample preparation. The results reveal that the buried Ga2O3/SiC interface exhibits weak
phonon transmission due to acoustic mismatch; the transition layers in GaN/Si act as
phonon-impedance gradients that redistribute heat flux; and the GaN/diamond boundary remains the dominant thermal bottleneck despite diamond's ultrahigh bulk conductivity. These findings demonstrate that the modulation frequency in PWA-TDTR functions as a tunable probe of depth-dependent
phonon transport, directly linking frequency-domain thermal response to interfacial energy transmission. Overall, this work positions PWA-TDTR as a versatile platform for investigating buried nonmetal-nonmetal interfaces in next-generation high-power and optoelectronic materials.
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Applied Physics
Anisotropic Thermal Characterization of Suspended and Spin-Coated Polyimide Films Using a Square-Pulsed Source Method
Bingjiang Zhang, Dihui Wang, Tao Chen et al. (+2 more)
Polyimide (PI) thin films are widely used in advanced technologies, yet accurate characterization of their thermal properties remains challenging, as evidenced by significant inconsistencies in reported data and an incomplete understanding of heat transfer mechanisms. In this study, we employ an optical Square-Pulsed Source (SPS) technique to simultaneously measure the in-plane and cross-plane thermal conductivities, as well as the volumetric heat capacity, of PI thin films. SPS is a pump-probe method that utilizes a square-wave-modulated pump
laser to induce periodic heating and a probe
laser to detect the thermoreflectance response. Thermal properties are extracted by analyzing amplitude signals across multiple modulation frequencies and
laser spot sizes. Measurements were conducted on both suspended commercial PI films and
spin-coated PI films on fused silica substrates. The results show that
spin-coated films exhibit higher cross-plane thermal conductivity and lower anisotropy compared to suspended films, which we attribute to differences in molecular orientation and substrate interactions. These findings provide new physical insights into anisotropic heat transport in
polymer thin films and demonstrate the SPS technique as a robust tool for probing microscale thermal phenomena in soft materials.
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All authors Bingjiang Zhang, Dihui Wang, Tao Chen, Heng Ban, Puqing Jiang
Plasma Physics
Nonlinear Energy Transfer Analysis between Coherent Modes in Developing Plasma Turbulence
Sandip Das, Lavkesh Lachhvani, Kunal Singha et al. (+4 more)
Energy transfer among various spectral components of fluctuating physical parameters in
plasma occurs due to the nonlinear interactions, but these effects are typically not captured by the traditional linear spectral methods.
Plasma density fluctuations measured in the Inverse Mirror
Plasma Experimental Device (IMPED) have signatures of nonlinear mode interactions among various instability modes, i.e. Rayleigh-Taylor (RT) and Drift-Wave (DW) modes. In this paper, the energy transfer among these modes as a result of nonlinear wave interactions (through the quadratic coupling processes) have been investigated in detail. The existing computational methods for single field model such as Ritz method and Kim method have been explored to understand the dynamics of nonlinear interaction between coherent modes. Both methods are applied and validated in simulation as well as experimental data from IMPED for coherent modes in
plasma. We find that the validity and applicability of the methods depend on the statistical nature of the data, particularly higher-order moments such as kurtosis, and on spatial stationarity. Energy transfer analysis using these methods reveals primarily the transfer of energy from a RT mode and a mix mode of DW and RT to a comparatively low-frequency DW mode, demonstrating the capability of the method to quantify spectral energy transport between the coherent modes.
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All authors Sandip Das, Lavkesh Lachhvani, Kunal Singha, Rosh Roy, Tanmay Karmakar, Daniel Raju, Prabal Chattopadhyay
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Depth-Resolved Thermal Conductivity of HFCVD Diamond Films via Square-Pulsed Thermometry
Kexin Zhang, Xiaosong Han, Ershuai Yin et al. (+3 more)
The integration of high-thermal-conductivity diamond films onto silicon carbide (SiC) substrates offers a promising pathway for thermal management in high-power electronic devices. Here, we investigate the depth-dependent thermal conductivity of a ~5 {\mu}m-thick diamond film grown on SiC by hot-filament chemical vapor deposition (HFCVD) using square-pulsed source (SPS) thermometry. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) reveal pronounced grain coarsening from the nucleation interface to the film surface. By combining frequency-dependent thermal penetration with a depth-resolved thermal transport model, we quantitatively reconstruct the thermal conductivity profile. The thermal conductivity increases sharply from ~60 W m^(-1) K^(-1) near the nucleation region to ~200 W m^(-1) K^(-1) at the surface, directly reflecting the underlying microstructural
evolution. These results provide a physically grounded understanding of graded heat transport in HFCVD diamond and offer practical guidance for engineering diamond-based thermal management layers for next-generation power devices.
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All authors Kexin Zhang, Xiaosong Han, Ershuai Yin, Xin Qian, Junjun Wei, Puqing Jiang
Plasma Physics · Cross-listed from astro-ph.HE
Acoustic instability at shock-wave precursors
Antonio Capanema, Pasquale Blasi and Emanuele Sobacchi
Magnetic field amplification is an integral part of the process of particle acceleration at non-relativistic shocks. It is necessary to reach the maximum energies required by observations, especially in
supernova remnants, thought to be sources of the bulk of
Galactic cosmic rays. Such amplification can be caused by the acoustic instability that develops when small density perturbations interact with the
cosmic-ray pressure gradient in the upstream of a
cosmic-ray-modified shock. The vorticity induced by the nonlinear development of the instability may lead to
turbulence, which amplifies the pre-existing
magnetic fields. To study this phenomenon, we use the PLUTO code to carry out 2D (and some 3D) magnetohydrodynamical simulations of the
evolution of small density perturbations in the presence of an assigned
cosmic-ray pressure gradient. Adopting more realistic values of Mach number and
cosmic-ray acceleration efficiency than previously assumed in the literature, we show that the acoustic instability can transform small density perturbations into large nonlinear structures while the fluid crosses the precursor region of a
cosmic-ray-modified shock. We study the power spectrum of turbulent
magnetic fluctuations that may be important to scatter particles. We comment on the possible constructive interference between acoustic and non-resonant streaming instabilities. We discuss limitations of previous and current numerical investigations in accessing spatial scales where
turbulence is expected to turn nonlinear, and outline perspectives for future investigations.
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Fluid Dynamics
Heat transport in magnetohydrodynamic duct flow regimes with conducting and insulating walls
Andreu Queralt McBride, Dmitry Krasnov, Yuri Kolesnikov et al. (+1 more)
The flow of a
liquid metal (LM) in a rectangular duct segment, subject to a uniform transverse
magnetic field and uniform heating at the side walls is explored in an ample parameter space using Direct Numerical Simulation (DNS). We modify electrical wall conductivity, (either highly conducting or perfectly insulating) and investigate the effects of the buoyancy force, both in horizontally and vertically orientated ducts. In the latter case, it may be directed either with the flow or against the flow, creating backflow regions. In this parameter space and with the presence of
vortex promoters at the inlet of the duct we identify $4$ types of flow. We calculate the Nusselt number $Nu(t)$ for each of them and study the statistical properties to compare their heat transfer capabilities in future fusion reactor blankets.
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All authors Andreu Queralt McBride, Dmitry Krasnov, Yuri Kolesnikov, Jörg Schumacher
Fluid Dynamics
Stability of Diffusive Shear Layers
Stefan S. Nixon and Philipp P. Vieweg
As one of the cornerstones of fluid mechanics, stability analyses provide essential physical insights into the growth of perturbations and eventual transition to
turbulence. However, classical \enquote{frozen-time} stability analyses implicitly assume a time-independence of their base flow and thus fail for \enquote{rapidly} diffusing shear layers. Here, we propose a self-similar ansatz to naturally incorporate the \enquote{diffusive} base-state expansion into the stability operator. Our approach reveals two competing physical mechanisms: an \enquote{expansion wind} delays the Kelvin-Helmholtz instability whereas a diminishing effective viscosity sustains this instability far beyond classical predictions. Direct numerical simulations confirm that our framework accurately captures the instability's extended lifespan, growth rate, and spectral
topology, eventually revising the timeline of shear-induced mixing fundamentally.
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Atomic Physics
Energies and lifetimes of the 9p and 10p excited states in atomic francium
Pierre Lassègues, A. Chakraborty, R.P. de Groote et al. (+29 more)
We present the first measurement of 9p 2P1/2,3/2 and 10p 2P1/2,3/2 excited levels absolute wavenumbers and radiative lifetime in francium. We used the Collinear Resonance Ionization Spectroscopy (CRIS) technique, applied on a beam of 221Fr atoms. Prior to this work, no experimental data existed for francium p-states with n > 8. The results provide a precision experimental test of relativistic coupled-cluster theory for the heaviest alkali, showing good agreement for lifetimes and relative excitation energies, despite a residual global offset in absolute energies.
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All authors Pierre Lassègues, A. Chakraborty, R.P. de Groote, B.K. Sahoo, O. Ahmad, C.M. Fajardo-Zambrano, A. McGlone, J. Warbinek, A. Ajayakumar, M. Athanasakis-Kaklamanakis, M. Au, J. Berbalk, D. Bettaney, B. van den Borne, T.E. Cocolios, M. Duggan, K.T. Flanagan, R.F. Garcia Ruiz, D. Gonzalez-Acevedo, A. Kastberg, Á. Koszorús, L. Lalanne, K.M. Lynch, D.T. McElroy, G. Neyens, L. Nies, L. Quanjel, A. Raggio, J.R. Reilly, J. Snikeris, S.G. Wilkins, X.F. Yang
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Enhancing Laser Surface Texturing through Advanced Machine Learning Techniques
Christoph Zwahr, Frederic Schell, Tobias Steege et al. (+1 more)
Laser material processing has emerged as a versatile and indispensable tool in various industries, including manufacturing, healthcare, and materials science. However, the interaction of a
lasers with surfaces is highly dependent on a large number of factors, including properties of the
laser source such as pulse duration, wavelength and pulse form, as well as properties of the material such as surface roughness, heat capacity and thermal conductivity. Therefore, the optimization of
laser texturing processes in regards to specific target geometries while maintaining texture quality and process efficiency is a time consuming task that requires experienced operators with expert knowledge of the process and its components. The complex and nonlinear relationships between the various process,
laser and material parameters and the resulting surface topography or functionality are challenging to model analytically. Therefore, the fabrication of large numbers of different parameter variations are typically required to enable empirical modeling and process optimization. Machine learning offers a promising approach to overcoming these challenges, particularly when the interrelations between process parameters are not well understood. It enables effective process optimization, surface property prediction, and automated monitoring-tasks that previously required expert knowledge. This chapter demonstrates the application of machine learning to
Laser Surface Texturing techniques. Using
algorithms such as neural networks and random forests, surface roughness can be predicted based on
laser parameters and material data. This facilitates faster process optimization, reduces experimental effort, and enables predictive visualization - all while maintaining high accuracy.
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All authors Christoph Zwahr, Frederic Schell, Tobias Steege, Andrés Fabián Lasagni
Atomic Physics
Experimental Determination of the $D1$ Magic Wavelength for $^{40}$K
Guy Hay Kalifa, Dor Kopelevitch, Amir Stern et al. (+1 more)
Neutral-atom arrays offer a promising path for
quantum simulation, yet the potential of fermionic $^{40}$K remains largely constrained by state-dependent light shifts that degrade cooling and detection fidelities. This problem can be resolved by working at a magic wavelength, where the differential light shift vanishes. We report the first experimental determination of the magic wavelength for the D1 transition in fermionic $^{40}$K at 1227.54(4) nm. Using in-trap loss spectroscopy in a wavelength-tunable optical tweezer, we map the differential AC Stark shift across a range of trapping powers and wavelengths. By converting these shifts to differential scalar polarizabilities, we find excellent agreement with relativistic all-order calculations.
Benchmark measurements at 1064.49 nm further quantify the intensity-sampling systematics inherent to standard trapping wavelengths, contrasting with the “mechanically clean” environment provided by the magic condition. Our results provide an important step toward high-fidelity in-trap D1 cooling, fluorescence imaging, and light-assisted loading, establishing a robust path toward scaling fermionic neutral-atom arrays for
quantum information science.
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All authors Guy Hay Kalifa, Dor Kopelevitch, Amir Stern, Yoav Sagi
Fluid Dynamics
Learning step-level dynamic soaring in shear flow
Lunbing Chen, Jixin Lu, Yufei Yin et al. (+3 more)
Dynamic soaring enables sustained flight by extracting energy from wind shear, yet it is commonly understood as a cycle-level maneuver that assumes stable flow conditions. In realistic unsteady environments, however, such assumptions are often violated, raising the question of whether explicit cycle-level planning is necessary. Here, we show that dynamic soaring can emerge from step-level, state-feedback control using only local sensing, without explicit trajectory planning. Using deep reinforcement learning as a tool, we obtain policies that achieve robust omnidirectional
navigation across diverse shear-flow conditions. The learned behavior organizes into a structured control law that coordinates turning and vertical motion, giving rise to a two-phase strategy governed by a trade-off between energy extraction and directional progress. The resulting policy generalizes across varying conditions and reproduces key features observed in biological flight and optimal-control solutions. These findings identify a feedback-based control structure underlying dynamic soaring, demonstrating that efficient energy-harvesting flight can emerge from local interactions with the flow without explicit planning, and providing insights for biological flight and autonomous systems in complex, flow-coupled environments.
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All authors Lunbing Chen, Jixin Lu, Yufei Yin, Jinpeng Huang, Yang Xiang, Hong Liu
Optics · Cross-listed from quant-ph
Permutationally symmetric molecular aggregates
Sricharan Raghavan-Chitra, Arghadip Koner and Joel Yuen-Zhou
Linear optical spectra of molecular aggregates are often approximated by classical optics methods such as the discrete-dipole approximation (DDA), coherent
exciton scattering (CES), and coherent potential approximation (CPA), where the only
quantum-mechanical input to the calculation is the linear susceptibility of the monomers. However, the limits of validity of these classical optics methods remain opaque. Here, starting from a
quantum mechanical
Hamiltonian for the aggregate, we identify a limit where DDA/CPA/CES is exact: all-to-all coupled permutationally symmetric aggregates of $N \to \infty$ monomers. The permutational
symmetry of this molecular version of the Lipkin-Meshkov-Glick model, which is closely related to that of the molecular polariton problem of many identical molecules coupled to a single-cavity mode, allows us to borrow recent techniques developed for the latter. In particular, we identify a $1/N$ expansion that corrects the classical optics limit with finite $N$ corrections to the linear response of the aggregate. These corrections feature as Raman-like transitions of a single monomer. We illustrate these findings with calculations on the very physically-relevant setup of a homodimer. Our findings clarify how
quantum optical features that go beyond classical optics can already be present in simple arrays of
quantum emitters such as molecular aggregates.
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Chemical Physics
Velocity Formulations for Hyper-Rayleigh Scattering Optical Activity Spectroscopy: Addressing the Origin-dependence Problem
Andrea Bonvicini, Sonia Coriani and Benoît Champagne
The theory of hyper-Rayleigh scattering optical activity (HRS-OA) spectroscopy has previously been described within the length formulation of the pure electric-dipole and mixed (electric-dipole/
magnetic-dipole and electric-dipole/electric-quadrupole) first hyperpolarizabilities required for the description of this process. In this work, we provide an alternative formulation of these pure and mixed hyperpolarizabilities. This new formulation made use of the velocity form of the electric-dipole and electric-quadrupole moment operators that enter in the quadratic response functions. A one-to-one correspondence is found for the gauge-origin shifts obtained in the two formulations. These relations ensure the origin-independence of the theory also for the velocity formulation. Furthermore, even though the basis set dependence of the velocity formulation is more significant compared to the length one, the former is origin-independent by design. This property makes it particularly suitable for calculations of HRS-OA invariants using approximated (variational or not) wavefunctions.
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General Physics
Small-System Group: Thermodynamics as a Complete Self-Similarity Limit
Amilcare Porporato and Lamberto Rondoni
We revisit the Rayleigh–Riabouchinsky paradox in dimensional analysis by making explicit the bridge between thermodynamics and the mechanical interpretation of temperature. Boltzmann's constant $k_B$ acts as a dimensional unifier, leading to an augmented $\Pi$-
theorem with an additional dimensionless group that encodes system size. In the macroscopic thermodynamic limit this small-system group, $\Pi_B = k_B/(c\,\ell^3)$ – the inverse heat capacity of a control volume of size $\ell^3$ in units of $k_B$ – becomes irrelevant as the response becomes self-similar with respect to it, recovering Rayleigh's formulation. Under suitable conditions, macroscopic limits make the fluctuations of the observables of interest negligible compared to their expected values, hence the state of a system is characterized by a reduced set of parameters. We thus recast thermodynamics as the complete-similarity limit of statistical mechanics with respect to $\Pi_B$, which also controls thermodynamic fluctuations. We also discuss second-order phase transitions from the viewpoint of incomplete similarity.
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Chemical Physics · Cross-listed from quant-ph
A Periodic Orbit Trace Formula for Quantum Scrambling: The Role of the Normally Hyperbolic Invariant Manifold
Stephen Wiggins
Out-of-Time-Order Correlators (OTOCs) quantify
quantum information scrambling, but their connection to localized phase-space structures, such as chemical transition states, requires formal development. We derive a leading-order semiclassical expansion for the local microcanonical OTOC in systems with an index-1 saddle point, expressing the scrambling rate as a coherent sum over unstable periodic orbits on the Normally
Hyperbolic Invariant
Manifold (NHIM). Valid in the semiclassical limit and the intermediate-time regime before the Ehrenfest time, our derivation utilizes the Normal Form theory of the transition state, which transforms the
Hamiltonian near the saddle into an integrable (though generally non-separable) form dependent on conserved actions. We outline the derivation of the microcanonical trace, the semiclassical propagator for integrable systems, the factorization of the stability
matrix, and the Schur complement reduction of the stationary phase approximation. Our result extends periodic-orbit trace methods to scrambling observables, yielding a local instability exponent {\Lambda}(J) governing the leading semiclassical growth window. As a special case, when the observation time coincides with the intrinsic periods of the contributing orbits, the trace sum reduces to an effective 1.5{\Lambda} scaling, resulting from the competition between local
hyperbolic growth and wavepacket dilution. This simplified form is conditional; the full expansion retains a coherent sum over orbit periods. Finally, we discuss how the dependence of the instability on transverse actions establishes a theoretical mechanism for mode-selective control of scrambling, and outline a numerical evaluation strategy to test these predictions.
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Data Analysis and Statistics · Cross-listed from hep-ex
Cross-Domain Transfer with Particle Physics Foundation Models: From Jets to Neutrino Interactions
Gregor Krzmanc, Vinicius Mikuni, Benjamin Nachman et al. (+1 more)
Future AI-based studies in particle physics will likely start from a foundation model to accelerate training and enhance sensitivity. As a step toward a general-purpose foundation model for particle physics, we investigate whether the OmniLearned and ParticleViT foundation models pretrained on diverse high-$Q^2$ simulated and real $pp$ and $ep$ collisions retain useful knowledge to a few-GeV fixed-target
neutrino experiment. We process MINERvA
neutrino–
nucleus scattering events and evaluate pretrained models on two types of tasks: regression of available energy and binary classification of charged-current pion final states ($\mathrm{CC1\pi^{\pm}}$, $\mathrm{CCN\pi^{\pm}}$, and $\mathrm{CC1\pi^{0}}$). Pretrained OmniLearned and ParticleViT models outperform similarly sized models trained from scratch at the same compute budget, with the largest gains for OmniLearned on regression and for ParticleViT on classification. When the same
transformer architecture is instead initialized from unrelated text pretraining (BERT), this advantage appears only marginally for classification in terms of compute efficiency and not in any way for regression. These results suggest that particle-level foundation models acquire inductive biases that generalize across large differences in energy scale, detector technology, and underlying physics processes, pointing toward detector-agnostic inference in particle physics.
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All authors Gregor Krzmanc, Vinicius Mikuni, Benjamin Nachman, Callum Wilkinson
Optics · Cross-listed from quant-ph
Chiral state conversion near an exceptional point: speed-noise competition
Qing-Wei Wang
One intriguing property of non-Hermitian systems is the breakdown of adiabatic
theorem and
chiral state conversion as the system dynamically encircles exceptional points. However, the subtle dependence of the
chiral dynamics on the loop geometry, the starting point, the encircling speed and especially the noise has not been studied systematically. Here we propose a non-chirality degree $\chi_c$ to measure the chirality quantitatively and analyze it in dynamics without noise by exact solution and dynamics with noise by numerical integration. The exact dynamics starting from the broken phase show chirality oscillations, which are extremely sensitive to noise when the speed is small. The encircling speed and the noise strength are found to compete with each other in determining $\chi_c$, resulting in two distinguished limits, namely the noisy limit and the clean limit. The critical boundary between the two limits satisfies a simple scaling law, which could be explained in terms of first-order perturbation theory and the condition number of the transfer
matrix. Our findings reveal the essential role played by noise in non-Hermitian dynamics and are relevant for both theoretical and experimental investigations.
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Plasma Physics
Estimating coil features from an equilibrium
Eduardo Rodriguez and Wrick Sengupta
We present an explicit theoretical framework for constructing artificial modular coils for
vacuum stellarator fields based solely on
equilibrium properties, achieved through the formulation of a current potential defined on flux surfaces. Contours of constant Boozer toroidal angle can be directly interpreted as proxy coils, and so we demonstrate that key measures of coil complexity (particularly coil non-planarity) are strongly governed by local
magnetic field properties. This approach shows promise as predictor for more realistic coil configurations, providing both a pathway towards deeper understanding of
equilibrium-coil relationships and a potential practical proxy for coil design.
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Applied Physics · Cross-listed from cond-mat.supr-con
Nanoscale electrothermal-switch superconducting diode for electrically programmable superconducting circuits
Tianyu Li, Jiong Li, Chong Li et al. (+13 more)
Superconducting diodes enable dissipationless directional transport, yet achieving electrical tunability and scalability remains a major challenge for
circuit-level integration. Here, we demonstrate an electrothermal-switch superconducting diode in which a gate-controlled nanoscale hotspot dynamically breaks inversion
symmetry in a superconducting nanowire. This mechanism gives rise to two coexisting nonreciprocal transport regimes-one associated with a nonreciprocal superconducting-to-normal transition and the other with ratchet-like
vortex dynamics-both originating from the same electrothermal-switch process. The diode exhibits efficiencies up to 42% and 60% for the two regimes, respectively, and can be electrically switched on, off, or reversed in polarity in situ by applying a small gate current. These capabilities enable programmable superconducting
circuits that realize electrically reconfigurable full-wave and half-wave rectification. The lithography-compatible design, high performance, and gate-controlled functionality establish a scalable platform for programmable superconducting electronics and hybrid
quantum systems.
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All authors Tianyu Li, Jiong Li, Chong Li, Peiyuan Huang, Nuo-Zhou Yang, Wuyue Xu, Wen-Cheng Yue, Yang-Yang Lyu, Yihuang Xiong, Xuecou Tu, Tao Tao, Xiaoqing Jia, Qing-Hu Chen, Huabing Wang, Peiheng Wu, Yong-Lei Wang
Optics · Cross-listed from quant-ph
Geometric phase-assisted simple phase compensation enabling quantum key distribution using phase-shifted Bell states
Ayan Kumar Nai and G. K. Samanta
Entanglement-based
quantum key distribution (QKD) relies on the distribution of high-fidelity maximally entangled Bell states, typically generated via spontaneous parametric down-conversion (SPDC). In practical systems, unwanted relative phases arise from birefringence, pump-beam contributions, imperfect
photon-pair generation, transmission through physical channels, and collection, transforming Bell states into phase-shifted states. This degrades interference visibility, increases the
quantum bit error rate (QBER), and limits secure key generation. Conventional compensation techniques, such as birefringent
crystals, interferometric stabilization, and spatial light modulators, are often impractical in real-world deployments. Here, we demonstrate a simple and versatile phase-compensation scheme that can be implemented at either the source or the receiver to eliminate arbitrary relative phases in Bell states. We theoretically and experimentally quantify the dependence of QBER in the BBM92 protocol on the relative phase and show that
geometric-phase-based control can effectively restore
entanglement quality. In a proof-of-concept experiment using a nondegenerate polarization Bell state, we achieve a fidelity exceeding 95% and reduce QBER below the 11% security threshold required for secure QKD. This robust approach enables practical phase control in entangled-
photon systems and can be extended to time-bin QKD via time-polarization mapping, offering a promising route toward stable, low-QBER
quantum communication.
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Fluid Dynamics
Recurrent bifurcations of stability spectra for steep Stokes waves in a deep fluid
Sergey Dyachenko, Robert Marangell and Dmitry E. Pelinovsky
We study the modulational stability problem for the traveling periodic waves (called Stokes waves) in an infinitely deep fluid by using pseudo-differential operators in conformal variables. We derive the criteria and the normal forms for four bifurcations which are repeated recurrently when the steepness of the Stokes wave is increased towards the highest wave with the peaked profile. The four bifurcations are observed in the following order: (a) new figure-8 bands appearing at each extremal point of speed, (b) degeneration of figure-8 bands resulting in vertical slopes, (c) new circular bands around the origin appearing at each period-doubling bifurcation, and (d) reconnection of figure-$\infty$ bands at each extremal point of energy. Our work uses the analytic theory of Stokes waves developed previously for Babenko's equation. The novelty of our work is the analytic extension of the modulational stability problem for singular pseudo-differential operators in terms of the Floquet parameter. The derivation of the normal form uses some structural assumptions which are known to be true for the Stokes waves. For the first and second bifurcation cycles, we compute numerically with a higher-order accuracy the actual values of wave steepness for which the structural assumptions are satisfied and the numerical coefficients of the normal forms to show the excellent agreement between the normal form theory and the numerical approximations of the spectral bands.
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Applied Physics · Cross-listed from cond-mat.mes-hall
Ian Babich, Timofey M. Savilov, Natalia A. Mamchik et al. (+14 more)
The advent of van der Waals (vdW)
heterostructures has enabled formation of bespoke materials with atomic precision, where numerous
quantum and topological phenomena have already been discovered. This atomic-layer tunability, however, comes at a cost: individual 2D layers must be picked up, moved, and placed in a deterministic manner while keeping their interfaces atomically clean. Recent advances in machine learning and robotics place even stronger emphasis on the deterministic aspect of vdW assembly. Current
polymer-based transfer methods satisfy neither the determinism nor cleanliness requirements. To this end, solutions are needed where adhesion can be dynamically and deterministically controlled without leaving organic contamination. Here, we present a
polymer free transfer technique employing thin muscovite (mica)
crystals. Temperature control over mica adhesion enables deterministic pick-up, stacking, and release of 2D materials, while their crystalline, inorganic nature ensures pristine interfaces and suppresses strain. Fully compatible with existing fabrication workflows, this approach enables the assembly of demanding vdW
heterostructures, including those with exposed conductive layers, moiré superlattices and suspended membranes. Our method represents a promising strategy for vdW
heterostructure fabrication toward its automatization.
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All authors Ian Babich, Timofey M. Savilov, Natalia A. Mamchik, Kristina Vaklinova, Nansi Zhou, Denis S. Baranov, Dmitrii A. Litvinov, Virgil Gavriliuc, Yue Yuan, Amoz Chua, Kenji Watanabe, Takashi Taniguchi, Mario Lanza, Maciej Koperski, Kostya S. Novoselov, Alexey I. Berdyugin, Makars Šiškins