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Physics Physics

physics Watch Physics

Thursday 19 February

Biological Physics · Cross-listed from q-bio.NC

Scaling and tuning to criticality in resting-state human magnetoencephalography

Irem Topal, Anna Poggialini, Marco Dal Maschio et al. (+3 more)

From 1/f noise to neuronal avalanches, evidence of scaling in brain activity has been increasingly linked to tuning to or near criticality. The concept of scaling is intimately related to the renormalization group (RG), in essence providing coarse-grained, simplified descriptions that generalize to classes of diverse physical systems. Following the RG idea, scaling laws have been reported in populations of spiking neurons at microscopic scales. Whether similar scaling principles govern large-scale neural activity in the human brain and how they relate to underlying neural physiology remains unresolved. Here, we analyze large-scale electrophysiological recordings (MEG) of human resting-state brain activity and apply a RG-inspired coarse-graining approach to track collective neural dynamics across spatial scales. We find that multiple observables exhibit robust scale-invariant behavior under coarse-graining: activity variance and correlations grow according to power laws, covariance eigenspectra follow a characteristic scaling relation, and neuronal avalanche statistics remain invariant. Using an analytically tractable neural network model, we show that the observed scaling signatures arise when the system operates slightly below criticality, and that the scaling exponents depend on the excitation-inhibition balance. These findings demonstrate that RG-inspired scaling analysis can uncover signatures of critical dynamics in non-invasive human electrophysiology and suggest a principled route toward estimating excitation-inhibition balance from large-scale brain recordings.
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All authors Irem Topal, Anna Poggialini, Marco Dal Maschio, Daniele De Martino, Oren Shriki, Fabrizio Lombardi

Fluid Dynamics

The influence of body anisotropy on wake characteristics and enstrophy production for prolate ellipsoids at $ \mathrm{Re}_{D} = 10,000 $

Sartaj Tanweer, Mukesh Sharma, Aditya R. Nayak et al. (+3 more)

The flow around prolate ellipsoids is investigated using Large Eddy Simulation (LES) at a Reynolds number of $ \mathrm{Re}_{D} = 10,000 $. Five different aspect ratios are considered, with $ \mathit{AR} = H/D $ varying from 5:1 to 1:1, where $D$ and $H$ represent the minor- and major- axes, respectively. The major axes of the ellipsoids are set perpendicular to the freestream, and the influence of body anisotropy on boundary layer separation, shear layer behaviour, enstrophy production, and local flow topology is examined. Higher body anisotropy leads to early separation of the boundary layer in the equatorial plane, resulting in a wider wake and a monotonic increase in pressure drag and total drag. Positive enstrophy production reaches a maximum approximately $2.5D$ downstream of the ellipsoids independently of body anisotropy. High body anisotropy leads to sustained negative enstrophy production in the near-wake, specifically near the poles of the 5:1 ellipsoid. Negative production occurs due to the distinct behaviour of streamlines near the high curvature pole, where they undergo strong anisotropic contraction in the cross-stream plane. Interactions between the vorticity vector and the intermediate eigenvector of the strain rate tensor are shown to be the primary source of enstrophy production close to the pole, and the intermediate eigenvalue exhibits negative values in this region. The negative production region is shown to be dominated by the unstable focus / compressing (UF/C) topology, which is consistent with findings from other studies that report negative enstrophy production in turbulent flows.
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All authors Sartaj Tanweer, Mukesh Sharma, Aditya R. Nayak, Edwin Malkiel, Michael Twardowski, Siddhartha Verma

Chemical Physics

Förster resonance energy transfer with transient coherent effects

Maximilian Meyer-Mölleringhof, Pablo Martinez-Azcona, Aurélia Chenu et al. (+1 more)

We formulate the weak intramolecular coupling Förster resonance energy transfer theory in a form suitable for calculating ultrafast nonlinear response of molecular systems. We introduce a formally exact time-dependent factorization of the molecular statistical operator into the system and bath components. Combining this factorization with unperturbed environment evolution, we generalize the traditional Förster master equation for the state population probabilities into a complete master equation for the system's reduced statistical operator. The traditional Förster theory applies in the limit where the intermolecular coupling is weak, and the system-bath coupling is strong. Our technique of derivation explicitly leads to a time non-local Förster type master equation, which remains valid also in the limit of vanishing system-bath coupling. The theory predicts a rapid initial coherent evolution of populations arising from a transient initial coherence-dependent term, which induces a slippage of the initial condition that persists during subsequent rate-controlled transfer. Comparison with exact numerical results confirms the clear improvement of the present generalization over earlier formulations of the Förster theory and delineates its range of validity.
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All authors Maximilian Meyer-Mölleringhof, Pablo Martinez-Azcona, Aurélia Chenu, Tomáš Mančal

Atomic Physics · Cross-listed from quant-ph

Shortcuts to Adiabaticity via Adaptive Quantum Zeno Measurements

Adolfo del Campo

Stroboscopic measurements of a time-dependent projector generate a quantum Zeno dynamics whose effective Hamiltonian is the Kato-Avron Hamiltonian for parallel transport, which reduces to counterdiabatic driving in the case of a nonselective measurement of the instantaneous eigenprojectors of the system. The same generator arises under continuous monitoring of a time-dependent observable and under a time-varying complex absorbing potential. Departures from the ideal Zeno limit are governed, in all three settings, by a single positive leakage operator with a dynamical and a purely geometric contribution. Matching the corresponding generators yields a model-independent generalized Schulman relation for the quantum Zeno dynamics in the three scenarios, and a purely geometric bound on the measurement resources needed to steer a subspace along a prescribed path.
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Fluid Dynamics

Impact of Structure-Preserving Discretizations on Compressible Wall-Bounded Turbulence of Thermally Perfect Gases

Alessandro Aiello, Andrea Palumbo, Carlo De Michele et al. (+1 more)

Direct numerical simulations of compressible turbulent channel flow at supersonic and hypersonic Mach numbers are performed using a thermally perfect gas model for CO$_2$. The objective is to assess the role of structure-preserving discretizations of the convective terms in high-enthalpy regimes, with particular emphasis on entropy conservation, kinetic-energy preservation, and consistency with the thermodynamic closure. The comparative analysis of various formulations examines their impact on robustness, thermodynamic fluctuations, and turbulence statistics across a range of Mach numbers. Differences among formulations are found to originate primarily in the treatment of thermodynamic variables and progressively influence the dynamical fields as compressibility effects intensify. In particular, the coupling between entropy consistency and pressure discretization is shown to affect Reynolds stresses and mean flow properties in high-speed regimes. Overall, the results indicate that consistency between the numerical formulation and the thermodynamic model contributes significantly to the reliable simulation of high-enthalpy compressible turbulence. The study systematically assesses entropy-conservative discretizations for thermally perfect gases in wall-bounded flows and examines their impact on thermodynamic-dynamic coupling at high Mach numbers.
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All authors Alessandro Aiello, Andrea Palumbo, Carlo De Michele, Gennaro Coppola

Fluid Dynamics

Learning Flow Distributions via Projection-Constrained Diffusion on Manifolds

Noah Trupin, Rahul Ghosh and Aadi Jangid

We present a generative modeling framework for synthesizing physically feasible two-dimensional incompressible flows under arbitrary obstacle geometries and boundary conditions. Whereas existing diffusion-based flow generators either ignore physical constraints, impose soft penalties that do not guarantee feasibility, or specialize to fixed geometries, our approach integrates three complementary components: (1) a boundary-conditioned diffusion model operating on velocity fields; (2) a physics-informed training objective incorporating a divergence penalty; and (3) a projection-constrained reverse diffusion process that enforces exact incompressibility through a geometry-aware Helmholtz-Hodge operator. We derive the method as a discrete approximation to constrained Langevin sampling on the manifold of divergence-free vector fields, providing a connection between modern diffusion models and geometric constraint enforcement in incompressible flow spaces. Experiments on analytic Navier-Stokes data and obstacle-bounded flow configurations demonstrate significantly improved divergence, spectral accuracy, vorticity statistics, and boundary consistency relative to unconstrained, projection-only, and penalty-only baselines. Our formulation unifies soft and hard physical structure within diffusion models and provides a foundation for generative modeling of incompressible fields in robotics, graphics, and scientific computing.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci

Inelastic Constitutive Kolmogorov-Arnold Networks: A generalized framework for automated discovery of interpretable inelastic material models

Chenyi Ji, Kian P. Abdolazizi, Hagen Holthusen et al. (+2 more)

A key problem of solid mechanics is the identification of the constitutive law of a material, that is, the relation between strain history and stress. Machine learning has lead to considerable advances in this field lately. Here we introduce inelastic Constitutive Kolmogorov-Arnold Networks (iCKANs). This novel artificial neural network architecture can discover in an automated manner symbolic constitutive laws describing both the elastic and inelastic behavior of materials. That is, it can translate data from material testing into corresponding elastic and inelastic potential functions in closed mathematical form. We demonstrate the advantages of iCKANs using both synthetic data and experimental data of the viscoelastic polymer materials VHB 4910 and VHB 4905. The results demonstrate that iCKANs accurately capture complex viscoelastic behavior while preserving physical interpretability. It is a particular strength of iCKANs that they can process not only mechanical data but also arbitrary additional information available about a material (e.g., about temperature-dependent behavior). This makes iCKANs a powerful tool to discover in the future also how specific processing or service conditions affect the properties of materials.
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All authors Chenyi Ji, Kian P. Abdolazizi, Hagen Holthusen, Christian J. Cyron, Kevin Linka

Instrumentation and Detectors

Development and Application of an eV Neutron Polarization for Parity Violation Studies at CSNS Back-n Beamline

Xu Qin, Tianhao Wang, Xuanbo Chen et al. (+26 more)

The dynamic enhancement of symmetry-breaking effects in neutron-nucleus resonances provides a sensitive testing ground for Time-Reversal Invariance Violation (TRIV). Exploiting this mechanism, the Neutron Optics Parity and Time Reversal Experiment (NOPTREX) seeks to elucidate the origin of the universe's baryon asymmetry. Critical to this effort is the precise measurement of Parity Violation (PV) asymmetries, which is essential to calibrate the nuclear parameters required for future TRIV experiments. To facilitate these studies, we developed an eV polarized neutron at the Back-n white neutron beamline of the China Spallation Neutron Source (CSNS). Neutron polarization is generated by an in-situ Spin-Exchange Optical Pumping (SEOP) $^3$He filter. Spin manipulation is performed by an adiabatic spin flipper, while spin polarization is preserved over the flight path by a vacuum transport system equipped with a solenoidal guide field. Experiments successfully measured an asymmetry of approximately $7.8 \pm 2.4$ (stat.) $\pm 0.3$ (sys.) % at the 0.747 eV p-wave resonance of $^{139}$La. These results are in agreement with previous results on this resonance and validate the system's capability for PV measurements.
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All authors Xu Qin, Tianhao Wang, Xuanbo Chen, Changdong Deng, Yongce Gong, Zenghang Huang, Wei Jiang, Zhengquan Liu, Guangyuan Luan, Haotian Luo, Qiuyue Luo, Yongjia Lv, You Lv, Nikolaos Vassilopoulos, Xichao Ruan, William Michael Snow, Kang Sun, Sepehr Samiei, Jian Tang, Shilin Wang, Hongyi Wu, Xiaomin Xiong, Xinyu Yuan, Junpei Zhang, Mofan Zhang, Qiwei Zhang, Qingbo Zheng, Ruirui Fan, Xin Tong

Atomic Physics · Cross-listed from cond-mat.quant-gas

Realization of fractional Fermi seas

Yi Zeng, Alvise Bastianello, Sudipta Dhar et al. (+7 more)

The Pauli exclusion principle is a cornerstone of quantum physics: it governs the structure of matter. Extensions of this principle, such as Haldane's generalized exclusion statistics, predict the existence of exotic quantum states characterized by fractional Fermi seas (FFS), i.e. momentum distributions with uniform but fractional occupancies. Here, we report the experimental realization of fractional Fermi seas in an excited one-dimensional Bose gas prepared through ramping cycles in the interaction strength. The resulting excited yet stable Bose-gas states exhibit Friedel oscillations, smoking-gun signatures of the underlying FFS. The stabilization of these states offers an opportunity to deepen our understanding of quantum thermodynamics in the presence of exotic statistics and paves the way for applications in quantum information and sensing.
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All authors Yi Zeng, Alvise Bastianello, Sudipta Dhar, Zekui Wang, Xudong Yu, Milena Horvath, Grigori E. Astrakharchik, Yanliang Guo, Hanns-Christoph Nägerl, Manuele Landini

Optics

Hologram generation using attention for Fraunhofer diffraction

Dilawer Singh, Antoni J. Wojcik and Timothy D. Wilkinson

Controlling optical wavefronts in the strict far-field regime is a fully global inverse problem. Fraunhofer propagation is a single Fourier transform of the aperture, so every modulator pixel couples to every point of the reconstruction and no spatial locality survives for the convolutional priors that dominate learned holography to exploit. Iterative phase retrieval stagnates and trades computation for quality, and camera-in-the-loop methods remain iterative and near-field. Here we show that this global coupling maps naturally onto self-attention, generating a phase-only hologram in a single forward pass of 12 to 24 ms. On hardware, every simulation-trained method collapses to a common floor between 15.8 and 16.1 dB median PSNR set by model-reality mismatch, despite spanning 27.7 to 56.5 dB median PSNR in ideal simulation. Placing the physical optics inside the training loop, which we call self-attention in-the-loop (SAIL), reaches 19.53 dB median PSNR and exceeds the strongest camera-adapted baseline by 0.79 dB on 18 of 18 targets (0.43 dB on 14 of 18 under a more faithful forward model). Most importantly, we show self-attention allows one shared network to serve 18 targets, and as the task complexity increases, the attention mechanism activates. These results establish self-attention as a scalable framework for far-field holography, and attention-based modeling as a general approach to inverse problems governed by long-range interactions in wave physics.
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Plasma Physics

Characterization of compressible fluctuations in solar wind streams dominated by balanced and imbalanced turbulence: Parker Solar Probe, Solar Orbiter and Wind observations

C.A. Gonzalez, C. Gonzalez and A. Tenerani

Characterizing compressible fluctuations in the solar wind is essential for understanding their role in solar wind acceleration and heating, yet their origin and evolution across different turbulence regimes remain poorly understood. In this study, we carry out a statistical analysis of the properties of compressible fluctuations in solar wind dominated by balanced and imbalanced turbulence. Using in-situ measurements from Wind, Solar Orbiter, and Parker Solar Probe, we investigate the scale dependence of density and magnetic field fluctuations and their correlations with plasma beta and radial distance. Our results indicate that solar wind compressibility is likely affected by both expansion effects and compressible dynamics governed by local plasma conditions. The non-Alfvenic wind is dominated by anti-correlated fluctuations, whereas the Alfvenic wind contains a mixture of correlated and anti-correlated fluctuations, though the latter remain prevalent. While the anti-correlated component is consistent with MHD slow magnetosonic modes, the correlated (fast mode-like) component is not reproduced by predictions from either linear MHD theory or nonlinear models of forced compressible fluctuations. Nevertheless, the dominant slow mode component explains the observed dependence on beta and the enhanced density fluctuations measured by Parker Solar Probe. This further suggests that slow mode waves contribute significantly to the compressible energy budget near the Sun and may play an important role in solar wind heating and acceleration close to the Sun.
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Optics · Cross-listed from quant-ph

Subluminal and superluminal velocities of free-space photons

Konstantin Y. Bliokh

We consider rectilinear free-space propagation of electromagnetic wavepackets using electromagnetic field theory, scalar wavepacket propagation, and quantum-mechanical formalism. We demonstrate that spatially localized wavepackets are inherently characterized by a subluminal group velocity and a superluminal phase velocity, whose product equals $c^2$. These velocities are also known as the 'energy' and 'momentum' velocities, introduced by K. Milton and J. Schwinger. We illustrate general conclusions by explicit calculations for Gaussian and higher-order beams and wavepackets, and also highlight subtleties of the quantum-mechanical description based on the 'photon wavefunction'.
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Instrumentation and Detectors · Cross-listed from hep-ex

Momentum Measurement of Charged Particles in FASER's Emulsion Detector at the LHC

FASER Collaboration: Roshan Mammen Abraham, Xiaocong Ai, Saul Alonso Monsalve et al. (+131 more)

We present a momentum measurement method based on multiple Coulomb scattering (MCS) in the FASER$\nu$ emulsion detector. The measurement of charged-particle momenta is essential for studying neutrino interactions in the TeV energy range at the FASER experiment. This method exploits the sub-micron spatial resolution and long tracking length of the FASER$\nu$ detector, enabling momentum determination from a few GeV up to a few TeV. The performance was evaluated using Geant4-based Monte Carlo simulations and validated with muon test beam data in the momentum range 100-300 GeV. As a first probe of the method for higher momentum muons, background muons recorded by the FASER$\nu$ detector were examined, showing reconstructed momenta consistent with expectations from their angular spread.
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All authors FASER Collaboration: Roshan Mammen Abraham, Xiaocong Ai, Saul Alonso Monsalve, John Anders, Emma Kate Anderson, Claire Antel, Akitaka Ariga, Tomoko Ariga, Jeremy Atkinson, Florian U. Bernlochner, Tobias Boeckh, Eliot Bornand, Jamie Boyd, Lydia Brenner, Angela Burger, Franck Cadoux, Roberto Cardella, David W. Casper, Charlotte Cavanagh, Shiyang Chen, Xin Chen, Xing Cheng, Kohei Chinone, Dhruv Chouhan, Andrea Coccaro, Stephane Débieux, Ansh Desai, Sergey Dmitrievsky, Radu Dobre, Monica D'Onofrio, Sinead Eley, Yannick Favre, Jonathan L. Feng, Carlo Alberto Fenoglio, Didier Ferrere, Max Fieg, Wissal Filali, Elena Firu, Haruhi Fujimori, Edward Galantay, Ali Garabaglu, Stephen Gibson, Sergio Gonzalez-Sevilla, Yuri Gornushkin, Yotam Granov, Jinjing Gu, Carl Gwilliam, Elie Hammou, Daiki Hayakawa, Michael Holzbock, Shih-Chieh Hsu, Zhen Hu, Giuseppe Iacobucci, Tomohiro Inada, Luca Iodice, Sune Jakobsen, Cesar Jesus-Valls, Arash Jofrehei, Hans Joos, Enrique Kajomovitz, Takumi Kanai, Hiroaki Kawahara, Alex Keyken, Felix Kling, Daniela Köck, Pantelis Kontaxakis, Jelle Koorn, Umut Kose, Peter Krack, Susanne Kuehn, Thanushan Kugathasan, Sebastian Laudage, Lorne Levinson, Botao Li, Jinfeng Liu, Yi Liu, Margaret S. Lutz, Jack MacDonald, Joern Mahlstedt, Toni Mäkelä, Anna Mascellani, Lawson McCoy, Josh McFayden, Andrea Pizarro Medina, Théo Moretti, Keiko Moriyama, Toshiyuki Nakano, Laurie Nevay, Motoya Nonaka, Yuma Ohara, Ken Ohashi, Kazuaki Okui, Hidetoshi Otono, Lorenzo Paolozzi, Annabelle Parry, Pawan Pawan, Brian Petersen, Titi Preda, Markus Prim, Junkai Qin, Michaela Queitsch-Maitland, Juan Rojo, Hiroki Rokujo, André Rubbia, Osamu Sato, Paola Scampoli, Kristof Schmieden, Matthias Schott, Cristiano Sebastiani, Anna Sfyrla, Davide Sgalaberna, Mansoora Shamim, Yosuke Takubo, Noshin Tarannum, Simon Thor, Eric Torrence, Oscar Ivan Valdes Martinez, Svetlana Vasina, Benedikt Vormwald, Chi Wang, Yuxiao Wang, Eli Welch, Aaron White, Monika Wielers, Benjamin James Wilson, Yue Xu, Heng Yang, Lekai Yao, Daichi Yoshikawa, Stefano Zambito, Shunliang Zhang, Yuxuan Zhang, Xingyu Zhao, Zijian Zhao

Applied Physics · Cross-listed from cond-mat.other

Hybrid Surrogate-Based Multi-Objective Optimization of Graded BCC Lattices

Jaswanth V Gurudev and Ratna Kumar Annabattula

Functionally graded BCC lattice structures hold promise for applications requiring simultaneous impact absorption and thermal dissipation, yet existing optimization frameworks rely on raw geometric parameters that are spatially blind to features such as the orientation of design gradients. In this study, we optimize density-graded BCC lattices for concurrent crashworthiness and heat dissipation via surrogate-based goal programming, initially using raw truss diameter as design variables. The lattice is discretized into three zones to achieve optimal dimensionality, and Pareto-optimal designs were identified that improve specific energy absorption and peak stresses during collisions while also enhancing its Nusselt number and pressure drop under forced convection relative to a non-graded lattice. Key insights of the effect of material distribution along the gradation axis on the performance are discussed in detail. We then introduce Physics-Informed Geometric Operators (PIGOs), which are scalar quantities derived from both the diameter profile and the triangulated surface mesh as candidate surrogate design variables. Pearson correlation analysis reveals that the raw diameter variables remain competitive, with the porosity gradient emerging as the most broadly predictive PIGO, strongly capturing both peak stress and pressure drop. The Nusselt number resists prediction by all variables tested, confirming that heat transfer is irreducibly multidimensional in this configuration due to competing surface-area and flow-blockage effects. The PIGO framework is topology-agnostic and extends naturally beyond the three-zone parameterization to finer gradations and alternative lattice topologies.
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Medical Physics

Enhanced distribution of molecules in the brain due to oscillations of the interstitial flow

Raghu Raghavan and Richard D. Penn

MRI measurements from a decade-old study of the physical properties of brain tissue observed a dynamic, pulsating fluid flow in the interstitial spaces of the brain attributed to the cardiac cycle. The effects of this cyclic flow pattern on the spatial distribution of molecules in the brain are modeled in this paper. The effects of oscillatory flow on the dispersion or volumetric transmission of a molecule that is advected by this flow is modeled by a mechanism hitherto neglected in the literature. An oscillatory random walk model is used to estimate the spread or effective diffusivity due to the oscillatory advection. Then, respiration effects are also estimated and the additional dispersion of molecules due to this are calculated in our model. Our model indicates that the observed oscillatory flow in the interstitial spaces due to cardiac as well as respiratory pulsatility can induce an effective diffusivity when the spread of the molecule is observed over times long compared with a cycle of the oscillation. This would help explain the high-volume transmission within the interstitium or brain parenchyma found in MRI measurements of a marker infused into the cerebrospinal fluid in human subjects that is well above what would be expected. Interstitial spaces should be viewed as a region of dynamic oscillatory flow driven by cardiac and respiratory cycles. This oscillatory flow could result in a significant dispersion of molecules and explain the higher-than-expected effective diffusion suggested in human studies. It may be possible to augment or slow this flow and concomitant spread by applying external forces.
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Atomic Physics

Parity-Doublet Coherence Times in Optically Trapped Polyatomic Molecules

Paige Robichaud, Christian Hallas, Junheng Tao et al. (+3 more)

Polyatomic molecules provide complex internal structures that are ideal for applications in quantum information science, quantum simulation, and precision searches for physics beyond the Standard Model. A key feature of polyatomic molecules is the presence of parity-doublet states. These structures, which generically arise from the rotational and vibrational degrees of freedom afforded by polyatomic molecules, are a powerful feature to pursue these diverse quantum science applications. Linear triatomic molecules contain $\ell$-type parity doublet states, which are predicted to exhibit robust coherence properties. We optically trap CaOH molecules, prepare them in $\ell$-type parity-doublet states, and realize a bare qubit coherence time of $T_2^* = 0.8(2)$ s. We suppress differential Stark shifts by employing molecular spectroscopy to cancel ambient electric fields, and characterize parity-dependent trap shifts, which are found to limit the coherence time. The parity-doublet coherence times achieved in this work are a defining milestone for the use of polyatomic molecules in quantum science.
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All authors Paige Robichaud, Christian Hallas, Junheng Tao, Giseok Lee, Nathaniel B. Vilas, John M. Doyle

Accelerator Physics

Toward a Fully Autonomous, AI-Native Particle Accelerator

Chris Tennant

This position paper presents a vision for self-driving particle accelerators that operate autonomously with minimal human intervention. We propose that future facilities be designed through artificial intelligence (AI) co-design, where AI jointly optimizes the accelerator lattice, diagnostics, and science application from inception to maximize performance while enabling autonomous operation. Rather than retrofitting AI onto human-centric systems, we envision facilities designed from the ground up as AI-native platforms. We outline nine critical research thrusts spanning agentic control architectures, knowledge integration, adaptive learning, digital twins, health monitoring, safety frameworks, modular hardware design, multimodal data fusion, and cross-domain collaboration. This roadmap aims to guide the accelerator community toward a future where AI-driven design and operation deliver unprecedented science output and reliability.
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Optics · Cross-listed from cond-mat.mes-hall

Perturbative sensing of nanoscale materials with millimeter-wave photonic crystals

Kevin K. S. Multani, Zhurun Ji, Wentao Jiang et al. (+7 more)

We introduce millimeter-wave silicon photonic crystal cavities as a versatile platform for the perturbative sensing of nanoscale materials. This dielectric-based platform is compatible with strong magnetic fields, opening avenues for studying quantum materials in extreme environments where superconducting cavities cannot operate. To establish the platform's performance, we cryogenically characterize a silicon photonic crystal cavity at 4.3 K, achieving a total quality factor exceeding $10^5$ for a 96 GHz mode. As a proof-of-concept for its sensing capabilities, we position a hexagonal boron nitride-multilayer graphene (hBN-MLG) heterostructure at an electric-field antinode of the cavity and measure the perturbative response at room temperature. The heterostructure induces a significant change in the cavity's resonance, from which we extract a total sample conductivity of approximately $5.1\times10^6$~S/m. These results establish silicon photonic crystal cavities as a promising platform for sensitive, on-chip spectroscopy of nanoscale materials at millimeter-wave frequencies.
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All authors Kevin K. S. Multani, Zhurun Ji, Wentao Jiang, Siyuan Qi, Akasha G. Hayden, Gitanjali Multani, Sharon Ruth S. Platt, Emilio A. Nanni, Zhi-Xun Shen, Amir H. Safavi-Naeini

Atomic Physics

High-precision Penning-trap spectroscopy of the ground-state spin structure of HD+

Charlotte M. König, Matthew Bohman, Fabian Heiße et al. (+10 more)

We present high-precision spectroscopy of the ground-state hyperfine structure of HD$^+$ at 4~T. We determine the bound-electron $g$ factor, $g_{e,\mathrm{bound}} = -2.002\,278\,540\,96(40)$, to a relative uncertainty of $2\times$10$^{-10}$, the most precise determination of a bound-electron $g$ factor of a molecular ion to date. The experimental value agrees with recently developed ab initio theory that now includes quantum-electrodynamical effects up to order $\alpha^5$ and has reduced the theoretical uncertainty by three orders of magnitude [O. Kullie et al., Phys. Rev. A 112 052813 (2025)]. In addition, we extract the scalar spin-spin interaction coefficients $E_4$~=~925\,395.758(41)$\,$kHz (electron-proton) and $E_5$~=~142\,287.821(22)$\,$kHz (electron-deuteron), which show a moderate tension with another state-of-the-art theoretical prediction [M. Haidar et al., Phys. Rev. A 106 042815 (2022)].
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All authors Charlotte M. König, Matthew Bohman, Fabian Heiße, Jonathan Morgner, Tim Sailer, Bingsheng Tu, Klaus Blaum, Sven Sturm, Dimitar Bakalov, Hugo D. Nogueira, Jean-Philippe Karr, Ossama Kullie, Stephan Schiller

Biological Physics

Tunable asymmetric swimming in biflagellate microswimmers

Benjamin J. Walker, Clément Moreau, Tommie L. Robinson et al. (+4 more)

Many biological microswimmers can modulate their swimming gait to achieve directional control of motility, especially when performing steering towards specific directional cues. This can be achieved without the need for obvious morphological or structural asymmetries in the form of the organism, or in the number or organisation of propulsion-generating appendages such as cilia. In this work, we identify and validate a core principle of asymmetric turning in biflagellate microswimmers: propulsive forces interact constructively to drive translation whilst interacting destructively to drive rotation. We explore the ramifications of this tunable biflagellar swimming mechanism across a range of systems, from a simple, back-of-the-envelope model to a detailed computational representation of an exemplar swimmer. This leads to a markedly general quantitative relation between key drivers of asymmetry, such as ciliary beat frequency, and the curvature of emergent trajectories. We discuss how the model green alga Chlamydomonas reinhardtii, which actuates its two cilia in a symmetric breaststroke for forward swimming, may exploit this feature for phototaxis. Finally, we validate our predictions in a Chlamydomonas-inspired robophysical model, implementing closed-loop control to achieve phototactic turning.
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All authors Benjamin J. Walker, Clément Moreau, Tommie L. Robinson, Zhaochen J. Xu, Daniel I. Goldman, Eamonn A. Gaffney, Kirsty Y. Wan

Plasma Physics

Kinetic route to helicity-constrained decay

Dion Li

Through two-dimensional, three-velocity-component particle-in-cell simulations of freely decaying subion turbulence, intermittent localized regions with $\mathbf{E} \cdot \mathbf{B} \neq 0$ are found, in the early electron-scale interaction phase, to be statistically associated with decreases in $|H_{V_s}|$, the fixed-gauge structure-integrated magnetic-helicity diagnostic. This structure-level behavior coincides with a decline of the Saffman helicity-variance plateau value $I_H$. Motivated by these observations, we propose a source-compensated, history-dependent helicity density that satisfies an exact local balance identity by construction, enabling Saffman-type two-point correlation integrals, which, under standard flux-decorrelation assumptions, can exhibit intermediate-scale plateaus that are roughly time independent. In the simulations, such plateaus are observed to remain approximately invariant over the measured kinetic interval even as $I_H$ evolves during the early kinetic stage. Under approximate single-scale self-similarity, the plateau behavior of the magnetic integral is consistent with the two-dimensional decay constraint $BL \sim \text{const}$. For initially net-helical configurations, we observe rapid development of mixed-signed magnetic-helicity patches and a decrease of the global fractional helicity, such that the decay over the kinetic interval is again most consistent with the cancellation-dominated scaling constraint.
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Atomic Physics

The Stark effect in molecular Rydberg states: Calculation of Rydberg-Stark manifolds of H$_2$ and D$_2$ including fine and hyperfine structures

Ioana Doran, Leon Jeckel, Maximilian Beyer et al. (+2 more)

We present a general theoretical treatment and calculations of the fine and hyperfine structures in the spectra of high-$n$ molecular Rydberg states in static uniform electric fields. The treatment combines (i) multichannel quantum-defect theory and long-range polarization models to determine the field-free energies of $n\ell$ Rydberg states of the molecules ($\ell$ is the orbital-angular-momentum quantum number of the Rydberg electron), (ii) a matrix-diagonalization approach to calculate the Stark shifts including their hyperfine structure, and (iii) sequences of angular-momentum frame transformations to predict the line positions and intensities in Stark spectra as they would be observed in single or multiphoton excitation sequences. To clarify how the molecular rotation and the nuclear spins influence the fine and hyperfine structure of molecular Rydberg-Stark spectra, we compare calculated spectra of ortho-D$_2$ with a D$_2^+$ ion core in the rotational ground state ($N^+=0$) for total nuclear spins $I$ of 0 (i.e., without hyperfine structure) and 2 (i.e., with hyperfine structure) with the corresponding spectra of para-H$_2$ with an H$_2^+$ ion core in the first excited rotational state ($N^+=2$) but zero nuclear spin ($I=0$). The calculations show that the hyperfine interaction alone does not significantly modify the Stark effect, but splits each Stark state by almost exactly the hyperfine Fermi-contact splitting of the ion core. In contrast, the effect of the molecular rotation, which is coupled both to the ion-core electron spin by the magnetic spin-rotation interaction and to the Rydberg-electron orbital motion by the core-polarization and charge-quadrupole interactions, induces Stark-state specific splittings that significantly differ from the spin-rotation splitting of the ($N^+=2$) ion core.
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All authors Ioana Doran, Leon Jeckel, Maximilian Beyer, Christian Jungen, Frédéric Merkt

Chemical Physics

Proton transfer and hydronium formation in ionized water

Ivo S. Vinklárek, Sebastian Trippel, Michal Belina et al. (+4 more)

Aqueous radiation chemistry emerges through ultrafast proton transfer and ion-radical formation with unexplored energy-redistribution dynamics steering the subsequent reactions. We performed a time-resolved disruptive-probing experiment on pure water dimer, (H$_2$O)$_2$, to disentangle the elementary post-ionization reactions. Through kinetic-energy-resolved ion imaging, we unraveled the dynamics in the (H$_2$O)$_2^+$ ground state: at low-energy ($\sim$0.05~eV) ultrafast proton transfer ($\sim$19~fs) is followed by H$_3$O$^+$+OH fragmentation ($\sim$360~fs). At higher energies, proton transfer becomes hindered ($\sim$60~fs) while the subsequent fragmentation becomes faster ($\sim$210~fs), eventually ($>0.15$~eV) merging into coupled dynamics ($\sim$100~fs). Additionally, we observed H$_2$O)$_2^+$ stabilization proceeding through a Zundel-like structure. These timescales and product energies reveal how ion-radical formation in ionized hydrogen-bonded networks shapes reactivity in aqueous dynamics.
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All authors Ivo S. Vinklárek, Sebastian Trippel, Michal Belina, Luisa Blum, Hubertus Bromberger, Petr Slavíček, Jochen Küpper

Applied Physics · Cross-listed from cond-mat.soft

Tracking the Brownian motion of DNA-functionalized magnetic nanoparticles for conformation analysis beyond the optical resolution limit

Christian Janzen, Fabian Schmid-Michels, Yahya Shubbak et al. (+6 more)

Brownian motion provides access to hydrodynamic properties of nanoscale objects independent of their optical resolvability. Here, we present a diffusion-based approach to infer effective particle size distributions of DNA-functionalized magnetic nanoparticles (MNPs), consisting of a magnetic core and a polystyrene shell, in a regime where direct geometric sizing is limited by optical diffraction. Using multi-particle tracking microscopy, we analyze the Brownian dynamics of MNPs grafted with double-stranded DNA (dsDNA) of varying contour length under low-salt conditions. A physically motivated model is introduced that relates dsDNA contour length to an effective hydrodynamic diameter via an attenuated corona description. The measured diffusion coefficient distributions exhibit a systematic and monotonic dependence on dsDNA length in quantitative agreement with the model. While the tracked objects are predominantly dsDNA-mediated agglomerates rather than isolated nanoparticles, clustering does not obscure the length-dependent signal. Instead, the dsDNA corona determines the hydrodynamic scaling, whereas agglomeration mainly introduces an offset and distribution broadening. These results demonstrate that Brownian dynamics enables robust readout of biomolecular length scales even far below the optical resolution limit. The distribution-based approach is inherently tolerant to polydispersity and aggregation, making diffusion-based tracking a simple and promising strategy for future biotechnological and biomedical assays.
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All authors Christian Janzen, Fabian Schmid-Michels, Yahya Shubbak, Melanie Wegener, Karl-Josef Dietz, Inga Ennen, Rico Huhnstock, Arno Ehresmann, Andreas Hütten

Computational Physics · Cross-listed from astro-ph.HE

Modeling of Relativistic Plasmas with a Conservative Discontinuous Galerkin Method

James Juno, Grant Johnson, Alexander Philippov et al. (+3 more)

We present a new method for solving the relativistic Vlasov–Maxwell system of equations, applicable to a wide range of extreme high-energy-density astrophysical and laboratory environments. The method directly discretizes the kinetic equation on a high-dimensional phase-space grid using a discontinuous Galerkin finite element approach, yielding a high-order, conservative numerical scheme that is free from the Poisson noise inherent to traditional Monte-Carlo methods. A novel and flexible velocity-space mapping technique enables the efficient treatment of the wide range of energy scales characteristic of relativistic plasmas, including QED pair-production discharges, instabilities in strongly magnetized plasmas surrounding neutron stars, and relativistic magnetic reconnection. Our noise-free approach is capable of providing unique insight into plasma dynamics, enabling detailed analysis of electromagnetic emission and fine-scale phase-space structure.
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All authors James Juno, Grant Johnson, Alexander Philippov, Ammar Hakim, Alexander Chernoglazov, Shuzhe Zeng

Plasma Physics

Tolerances to driver-witness misalignment in a quasilinear plasma wakefield accelerator

T. C. Wilson, J. Farmer, K. Lotov et al. (+1 more)

Plasma-based accelerators offer high accelerating gradients and scalability through staging or long plasma sources, which makes them good candidates for future accelerator and collider concepts. Proton-driven accelerators in particular have the potential to bring particles to high energy in a single stage. In the quasilinear regime - where the plasma wake is only partially evacuated - a witness bunch of electrons drives a cavitated wake, which acts to preserve the emittance of the portion of the witness inside this self-blowout. In the case of a misalignment between the driver and witness, this behaviour can persist, but its effectiveness is reduced. In this paper, we study transverse witness dynamics in this regime, and develop analytical models to describe the witness motion, and develop a metric to estimate emittance preservation based on a single parameter which estimates the density of the witness after phase mixing. Particle in cell simulations using the AWAKE Run 2c baseline parameters show excellent agreement with the predictive models developed. This work allows alignment constraints to be set both for the AWAKE experiment and other wakefield acceleration schemes operating in the quasilinear regime.
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All authors T. C. Wilson, J. Farmer, K. Lotov, A. Pukhov

Optics

Stimulated interactions of low-energy free-electrons with light

Fatemeh Chahshouri, Sven Ebel, Mitja Funk et al. (+1 more)

Free-electron interactions with light and matter have long served as a cornerstone for exploring the quantum and ultrafast dynamics of material excitation. In recent years, this paradigm has evolved from a classical description of radiation and acceleration toward a fully quantum framework, transforming our understanding of light-matter interactions at the single-electron level. These advances have opened new opportunities in high-resolution imaging, ultrafast spectroscopy, interferometry, and the coherent shaping of electron wavepackets. This review surveys stimulated interactions between slow electrons and light, encompassing free-space and near-field mediated mechanisms. We discuss how free-space optical fields coherently modulate electron momentum and energy, and how near-field coupling in nanophotonic and plasmonic structures enables strong, phase-matched, efficient momentum exchange with the electron wavepacket. We further describe electron recoil, which is significant in the slow-electron regime, and temporal and spatial wavepacket shaping that enhances coupling efficiency and extends access to quantum-coherent regimes. Building on these foundations, we outline emerging frameworks including hybrid optical-electrostatic modulation, ponderomotive laser-based aberration correction, and optical electron interferometry. By unifying these developments, stimulated electron-light interactions provide a versatile route to precise beam control, quantum-state engineering, and tailored light-matter coupling, with implications for ultrafast spectroscopy, nanoscale metrology, attosecond pulse generation, electron-photon entanglement, and the creation of nonclassical states of light.
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All authors Fatemeh Chahshouri, Sven Ebel, Mitja Funk, Nahid Talebi

Classical Physics · Cross-listed from nlin.CD

Design of low-energy transfers in cislunar space using sequences of lobe dynamics

Naoki Hiraiwa, Mai Bando, Yuzuru Sato et al. (+1 more)

Dynamical structures in the circular restricted three-body problem (CR3BP) are fundamental for designing low-energy transfers, as they aid in analyzing phase space transport and designing desirable trajectories. One of these dynamical structures, lobe dynamics, can be exploited to achieve local chaotic transport around celestial bodies. This study proposes and fully validates a systematic method for designing low-energy transfers by combining multiple sequences of lobe dynamics, building upon the authors' prior preliminary framework. A graph-based framework is developed to explore possible transfer paths between departure and arrival orbits, reducing the complexity of the combinatorial optimization problem for fuel-efficient transfer design. Using this graph, low-energy transfer trajectories are constructed by connecting chaotic orbits within lobes. The resulting optimal trajectory in the Earth–Moon CR3BP is then converted into an optimal transfer in the bicircular restricted four-body problem via multiple shooting. This transfer is compared with existing optimal solutions to demonstrate the effectiveness of the proposed method.
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All authors Naoki Hiraiwa, Mai Bando, Yuzuru Sato, Shinji Hokamoto

Plasma Physics

Self-Consistent Dynamics of Electron Radiation Reaction via Structure-Preserving Geometric Algorithms for Coupled Schrödinger-Maxwell Systems

Jacob Matthew Molina and Hong Qin

Classically, a charged particle in a magnetic field emits radiation, losing momentum and experiencing the Abraham-Lorentz (AL) / Landau-Lifshitz (LL) radiation reaction (RR) force. However, at atomic scales and outside the range of their applicability, the AL/LL equations fail and RR destroys the coherent state of an electron-undermining the very concept of a RR force. This process can be described by the coupled Schrödinger-Maxwell (SM) system under appropriate limits, but the system's nonlinear complexity has long limited purely analytical studies. We present geometric structure-preserving algorithms for the SM system that preserve gauge invariance, symplecticity, and unitarity on the discrete space-time lattice, which are implemented in our Structure-Preserving scHrodINger maXwell (SPHINX) code. By constructing coherent states from the Landau levels, SPHINX simulates the fully-coupled nonlinear dynamics of an electron coherent state, the energy partition evolution, and decoherence/relaxation of the electron wave packet in time due to RR. These simulations indicate that, in an external magnetic field, an electron prepared in an atomic-scale coherent state can radiate strongly, rapidly losing coherence and dispersing into a decoherent wave packet. Additionally, we also present the fully-coupled nonlinear evolution of the non-degenerate ground- and first-excited Landau levels themselves to understand how the coupled SM system modifies the well-known ideal (i.e., Schrödinger-only) dynamics of the Landau Levels. With appropriate boundary conditions, simulations show that the Landau levels are renormalized into stationary dressed eigenstates with constant electromagnetic and kinetic energies. This opens a new computational window into RR physics and advances modeling of extreme-field phenomena in fusion plasmas, astrophysics, and next-generation laser experiments
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Optics · Cross-listed from quant-ph

Organic molecules as single-photon sources

Alexey Shkarin and Stephan Götzinger

The development of single-photon sources has been nothing but rapid in recent years, with quantum emitter-based systems showing especially impressive progress. In this article, we give an overview of the developments in single-photon sources based on single molecules. We will introduce polycyclic hydrocarbons as the most commonly used emitter systems for the realization of an organic solid-state single-photon source. At cryogenic temperatures this special class of fluorescent molecules demonstrates remarkable optical properties such as negligible dephasing, indefinite photostability, and high photon rates, which make them attractive as fundamental building blocks in emerging quantum technologies. To better understand the general properties and limitations of these molecules, we discuss sample preparation and relevant emitter parameters such as absorption and emission spectra, lifetime, and dephasing. We will also give an overview of light extraction strategies as a crucial part of a single-photon source. Finally, we conclude with a look into the future, displaying current challenges and possible solutions.
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