Optics
Lasing Mode Control in ZnO Nanowires Coupled to TiO2 Nanopillars
Daniel Repp, Francesco Vitale, Raja Hoffmann et al. (+4 more)
Nanowire
lasers based on spectrally broad gain materials typically exhibit multimode emission, which limits their utility in applications requiring precisely defined spectral characteristics. In this study, we experimentally demonstrate the selective, narrow-band suppression of individual lasing modes in zinc oxide (ZnO) nanowire
lasers through near-field coupling to titania (TiO2) nanopillars. Our study is based on photoluminescence spectroscopy in the lasing regime, which is complemented by finite-difference time-domain simulations. We show suppression of longitudinal nanowire lasing modes by their resonant coupling to the whispering gallery modes in nanopillars of suitable size. In addition to spectral selectivity of the coupling, we reveal two distinct coupling regimes based on polarization matching between whispering gallery modes and nanowire waveguide modes. These findings demonstrate a promising approach towards engineering the spectral emission properties of nanowire
lasers through tailored photonic architectures.
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All authors Daniel Repp, Francesco Vitale, Raja Hoffmann, Isabelle Staude, Thomas Siefke, Carsten Ronning, Thomas Pertsch
Chemical Physics
Simulation of a Battery Cell on Quantum Computers: Reactions & Transport
Albert J. Pool, Michael Schelling and Birger Horstmann
Simulations of electrochemical materials and systems accelerate technological progress, but are still limited by computational power. In particular,
quantum computing offers prospects for higher resolutions, due to the exponential amount of data that can be stored in a
quantum state. As current
quantum computers are still noisy, we consider a hybrid
quantum-classical
algorithm, that divides the problem into smaller computational tasks. We describe how to implement such an
algorithm for non-linear partial differential equations, the Feynman-Kitaev
Hamiltonian, in a scalable way for an electrochemical system. We show how it can evaluate general electrochemical models and present a
quantum simulation of the Single Particle Model with electrolyte (SPMe) as the first
quantum simulation of a battery
cell.
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Fluid Dynamics · Cross-listed from eess.SY
A partitioned fluid-structure interaction solver for two-phase sloshing and flexible spacecraft dynamics
Umberto Zucchelli, Miguel Alfonso Mendez, Annafederica Urbano et al. (+3 more)
This paper presents a high-fidelity direct numerical simulation (DNS)-fluid-structure interaction (FSI) framework for rigid-
liquid-flexible spacecraft dynamics under microgravity conditions. The
liquid-gas flow is simulated with the incompressible two-phase solver implemented in DIVA, validated against FLUIDICS experiments conducted aboard the International Space Station (ISS). The flexible appendages are described by a rotating assumed-mode plate model that accounts for
geometric stiffening. The fluid and structural operators are coupled through a Dirichlet-Neumann fixed-point
algorithm with Aitken relaxation, and a closed-system mechanical energy balance is used as an a posteriori diagnostic to assess the energy imbalance of the partitioned discretisation. The coupling strategy is validated against an experimental free-decay sloshing
benchmark, and its numerical consistency is assessed through spatial sensitivity studies of the energy-balance defect. Prescribed-motion, rigid open-loop, and flexible open-loop simulations of a
spin-up manoeuvre are compared to isolate the effect of structural feedback on the sloshing response. Reduced
liquid models identified from the different simulation architectures exhibit different predictive capabilities when embedded in the same rigid-flexible plant. A controller synthesized from the reduced model identified from the flexible simulation is replayed in the nonlinear CFD-FSI environment. The reduced model reproduces the principal attitude and actuator responses for the considered manoeuvre but does not recover the detailed nonlinear sloshing-load history. The framework provides a high-fidelity environment for analysing coupled spacecraft dynamics, identifying control-oriented models, and assessing reduced-model-based control strategies beyond their linear design representation.
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All authors Umberto Zucchelli, Miguel Alfonso Mendez, Annafederica Urbano, Sebastien Vincent-Bonnieu, Piotr Wenderski, Francesco Sanfedino
Physics and Society
Dynamics-structure interchangeability in binary opinion models on multiplex networks
Julian Sienkiewicz and Anna Chmiel
We examine the interchangeability between two duplex systems with opinion dynamics: one characterized by different dynamics parameters $a_1$ and $a_2$ on each layer and full node overlap, and the second with the same parameter $a_1$ on both layers but only partial node overlap $r$. We introduce a general framework for identifying the critical line between the ordered and disordered phases, thereby translating one system into another. The description is supported by several examples of opinion dynamics models and a rigorous measure of the distance between the stationary solutions of the rate equations in both settings. Our results show that even large values of $r$ are sufficient to obtain very good correspondence between the two settings.
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Optics · Cross-listed from quant-ph
Bridging two families of non-Hermiticity: from non-reciprocal couplings to an imaginary potential using the Lanczos transformation
Li Ge
Two types of non-Hermiticity found in physical systems, i.e., non-reciprocal couplings and complex potentials, have gained considerable interest recently. The former leads to the non-Hermitian skin effect, while the latter gives rise to a range of non-Hermitian
symmetries such as parity-time ($PT$) and particle-hole
symmetries. Although these two non-Hermitian forms have been incorporated in the same models, so far they have been treated as distinct families of non-Hermiticity. In this work, we establish an isospectral mapping between them using the Lanczos transformation. More specifically, we show that a generalized Hatano-Nelson model $H$ with non-reciprocal and spatially varying couplings can be mapped to a tight-binding model $H_L$ with real symmetric couplings and an imaginary on-site potential. This result holds even when the original $H$ already has an imaginary potential and exceptional points. Our work provides a refreshed understanding of the connection between different forms of non-Hermiticity. It also offers an approach to obtaining an intuitive physical understanding of exceptional points in $H_L$ that are elusive in $H$. Finally, our findings also warrant a versatile approach to constructing non-Hermitian systems with a complex potential and a real spectrum, without $PT$
symmetry.
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Optics
A photonic integrated comb engine for ultracold quantum gases
Wei Sun, Xiaoying Yan, Jinbao Long et al. (+18 more)
Cold atoms underpin
quantum sensing, simulation and computation, but their coherent control demands highly stable optical fields whose generation, referencing and power scaling remain formidable integration challenges. While photonic integrated
circuits have yielded compact visible
lasers and high-$Q$ microresonators have enabled chip-scale optical frequency combs, these crucial technologies have largely remained functionally fragmented. Consequently, the coherent manipulation of ultracold
quantum gases using a fully integrated
laser-comb source has yet to be realized. Here we demonstrate a scalable, hybrid-integrated microcomb engine at 780 nm that seamlessly bridges frequency synthesis, atomic referencing and power amplification to achieve
quantum state control of a Bose–Einstein condensate. By self-injection locking of electrically driven III–V
lasers to high-$Q$ Si$_3$N$_4$ microresonators, we generate coherent platicon microcombs featuring 20- and 100-GHz mode spacings. Absolute referencing of the microcomb to an $^{85}$Rb transition actively suppresses long-term frequency drift from over 200 MHz to the 100-kHz level across 2,000 s. A selected comb tooth is subsequently injection-amplified to 102 mW, entirely preserving the microcomb's pristine coherence and stability. We utilize this synthesized field to construct an optical
lattice, drive coherent two-
photon Raman transitions, and prepare stationary
spin–orbit-coupled and Raman-
lattice states within an $^{87}$Rb condensate. By providing a synchronized optical grid, this atom-referenced microcomb can allow multiple optical-control channels to scale without a proportional multiplication of independent frequency references. Our work establishes a fully integrated frequency-synthesis architecture essential for realizing deployable, large-scale atomic
quantum systems.
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All authors Wei Sun, Xiaoying Yan, Jinbao Long, Sanli Huang, Zhixin Duan, Hao Tan, Zhenyuan Shang, Zeying Zhong, Jiahao Sun, Yue Hu, Shichang Li, Baoqi Shi, Yi-Han Luo, Shuyi Li, Chen Shen, Hanqing Liu, Xiangbin Su, Haiqiao Ni, Zhichuan Niu, Shengjun Yang, Junqiu Liu
Chemical Physics · Cross-listed from quant-ph
Decoherence Tuning in Voltage-Driven Plasmonic Cavities
Yuchen Wang, Oliver Tan and Norah M. Hoffmann
Strong light-matter coupling offers a powerful framework for modifying molecular structure, dynamics, and optical response, yet achieving this regime at the single-molecule level remains a central challenge. Scanning Tunneling Microscope Break Junctions (STM-BJ) provide a promising route by combining single-molecule addressability with extreme nanoscale field confinement. However, the metallic environment that enables such confinement also introduces substantial plasmonic and excitonic losses, raising the question of how strong coupling can be realized in a metal-molecule-metal junction. Here, we identify the voltage as the key control parameter. We show that the applied bias not only drives the formation of an interfacial
exciton through resonant charge transport but also suppresses its coupling to metallic loss channels. Simultaneously, the plasmonic cavity retains extreme mode confinement while the availability of modes is moderately tuned by voltage. Together, these results establish voltage-driven STM-BJs as electrically tunable single-molecule plasmonic cavities and open new routes for using the powerful STM-BJ toolbox, including
quantum transport, tracking chemical dynamics, optoelectronics, and molecular-scale
quantum control under strong light-matter coupling.
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Biological Physics · Cross-listed from math.AP
The Naito–Okuda–Ouyang Biconcave Red Blood Cell Profile as a Finite-Energy Unbranched Weak Immersion with Point-Force Residues
Hao Wu
The axisymmetric profile \(\sin\psi(\rho)=c_0\rho\log(\rho/\rho_B)\) introduced by Naito, Okuda, and Ouyang is an exact solution of the unconstrained Helfrich shape equation for every \(\rho>0\), but its mean
curvature diverges logarithmically at the dimple center. A covariant local analysis shows that in Cartesian graph coordinates the immersion is nondegenerate and belongs to \(W^{2,p}\) for every finite \(p\); it is \(C^{1,\alpha}\) for every \(\alpha<1\), but neither \(C^{1,1}\) nor \(C^2\). The conformal factor has a finite nonzero limit, so the point has branch multiplicity one and is not a branch point in the sense used in weak-immersion compactness theory. The Helfrich energy is finite, whereas the complete Euler–Lagrange operator carries the distributional residue \(\E_{\CH}=4\pi c_0\delta_p\) under the convention specified below. Hence the profile is a classical solution on the punctured surface and a finite-energy weak immersion, but it is not a free weak critical point of the unforced Canham–Helfrich functional. Stationarity is restored after adding the corresponding point-force potential or under a pinned-point constraint. Area and volume multipliers cannot cancel the Dirac residue. The apparent sign discrepancy between the shape equation used in the original papers and the modern convention is explained by the opposite definition of mean
curvature. These results delimit precisely what can and cannot be inferred from modern existence and regularity
theorems for Canham–Helfrich minimizers.
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Chemical Physics · Cross-listed from quant-ph
Broadband and Large-Multimode Quantum Optical Storage with Rare-Earth Ions in Solids
Yisheng Lei, Senthil Kumar Kuppusamy, Idris Tlemsani et al. (+6 more)
Broadband
quantum memory devices are essential elements for future
quantum networks. Here we propose a broadband
quantum memory scheme called Hole Anti-hole Grating Echo
Memory (HAGEM) for rare-earth ions in solids, which can be implemented with most of the present rare-earth ions hosted in various types of solids. Using HAGEM, a
quantum memory device with one billion temporal modes per second can be developed with current available technologies. To validate the
memory protocol, we conducted some proof-of-concept experiments. We provide a Eu$^\text{{3+}}$ molecular complex with special hyperfine level structures of which the hyperfine level separations are in a specific mathematical correlation that can be obtained by harnessing chemical engineering. Using the proposed
memory protocol and material, we experimentally demonstrate a single-mode
quantum optical storage efficiency of 14.9% and a
memory bandwidth of 200MHz, which can easily be extended to a few GHz. In addition, a multi-mode storage of four temporal modes is achieved with a storage efficiency of 1.3%. Broadband & large-multimode
quantum memory device with a long storage time enabled by HAGEM integrating with the current available entangled
photon pair source and tunable delay lines, a
quantum repeater network with an
entanglement distribution rate on the order of 1kHz - 10kHz can be created with a communication distance around 100km. This will greatly facilitate the development of
quantum networks in near future.
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All authors Yisheng Lei, Senthil Kumar Kuppusamy, Idris Tlemsani, Suma Al-Hunaishi, Pengrui Jiao, Olaf Fuhr, Mario Ruben, Philippe Goldner, Diana Serrano
Optics
Physical Fidelity of Wave-Based Inverse Problems under Broken Time-Reversal Symmetry
Haiyan Ou, Jiajia Duan, Edmund Y. Lam et al. (+1 more)
Modern coherent imaging commonly treats defocus interference as an undesirable artifact to be suppressed. Here, we show that this interference is instead a deterministic projection shadow associated with broken time-reversal
symmetry (TRS) under finite-aperture observation. The resulting non-
unitary observation operator imposes irretrievable information loss, making this shadow an unavoidable coherent residual. We demonstrate that suppressing this residual beyond the measurement support can yield physically inconsistent reconstructions by assigning unconstrained components within the null space, thereby disrupting the propagation of the reconstructed complex field. We term this failure mode physical overfitting and introduce the complex-field TRS residual metric, R_TRS(z). By using the measured axial
evolution of the projection shadow as a z-resolved physical reference, the metric extends fidelity assessment from two-dimensional (2D) detector-plane agreement to propagation-resolved three-dimensional (3D) complex-field consistency. These results establish a physical constraint on phase-space
retrieval and wave-based inverse reconstruction.
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All authors Haiyan Ou, Jiajia Duan, Edmund Y. Lam, Bingzhong Wang
Medical Physics
GenMC: Real-Time Generative Monte Carlo Surrogate for Quantitative Photoacoustic Imaging
Mengjie Shi, Feng He, Tom Vercauteren et al. (+1 more)
Photoacoustic (PA) imaging provides molecular and functional information about tissue, such as blood oxygen saturation (sO2), yet its clinical translation is hindered by inaccurate quantification. A major source of error is the spectral colouring effect, in which wavelength-dependent optical attenuation distorts the local optical fluence. Monte Carlo (MC) simulation is the gold standard for modelling light transport, but its computational demand precludes real-time use. Here, GenMC is presented, a deep generative framework based on a conditional generative
adversarial network that estimates optical fluence distributions from tissue anatomy and literature-derived optical properties, with anatomical priors obtained from co-registered ultrasound images. Trained on MC-generated synthetic
datasets, GenMC produces high-fidelity fluence maps in under 30 ms per frame, a four-orders-of-magnitude speed-up over conventional MC simulation, and reaches peak signal-to-noise ratios of up to 36.24 dB in vivo, outperforming UNet and Pix2Pix baselines. Validation in blood-mimicking phantoms and in 37 human volunteers spanning Fitzpatrick skin types III-V demonstrates improved accuracy, robustness, and physiological consistency of sO2 estimation. By enabling real-time, accurate, and reproducible quantification of tissue oxygenation, GenMC addresses a critical barrier to quantitative PA imaging and offers a general strategy for rapid, high-fidelity approximation of light transport in tissue.
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All authors Mengjie Shi, Feng He, Tom Vercauteren, Wenfeng Xia
Computational Physics
Optimal limits on weak integrability breaking and protected thermal memory near qutrit exchange
Hanbing Liang and Fujun Liu
Although integrability does not universally require a continuous one-site
symmetry, we rigorously prove that every jointly analytic, regular Yang-Baxter deformation of the qutrit exchange interaction necessarily retains a nontrivial, analytically varying one-site charge. Breaking this local
symmetry imposes a fundamental physical constraint on approximate conservation, governed by the optimal uniform bound $\delta^3 \le C\varepsilon$ that explicitly relates the minimal one-site
symmetry defect $\delta$ to the local current-conservation residual $\varepsilon$. While breaking all one-site charges strictly forbids an exact integrable completion, an optimally compensated nearest-neighbor interaction saturates this cubic limit and anomalously extends the guaranteed infinite-temperature energy-current correlation window to order $|\lambda|^{-3}$ in the perturbation strength $\lambda$. Furthermore, we reveal a fundamental resonance obstruction for intrinsic conversion perturbations that strictly prevents any exact first-order repair of a broken one-site charge on any finite ring. Nevertheless, we demonstrate that the complete eight-dimensional charge
memory matrix remains thermodynamically protected and approaches the identity for timescales $t=o(|\lambda|^{-3/2})$, a robust feature of the full infinite-temperature dynamics when the thermodynamic limit is taken before weak coupling.
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Medical Physics
Non-circular scan trajectories for reducing cone-beam artifacts in Gamma Knife CBCT images: a simulation study
Alexandra Alain-Beaudoin, Håkan Nordström, Luc Beaulieu et al. (+1 more)
Objective. Gamma Knife cone-beam computed
tomography (CBCT) images are deteriorated by cone-beam artifacts whose magnitude increases along the superior direction. In this study, a novel scan trajectory compatible with the Gamma Knife CBCT system is optimized to reduce cone-beam artifacts, with the aim to replace the current 200-degree single-arc scan. Approach. Data sampling analysis with tomographic incompleteness maps indicates the level of undersampling across the field of view based on the geometry of the system and of a scan trajectory. Moreover, CBCT simulations are performed from a virtual phantom with disks aligned along the axial direction and from a CT reconstruction of a stereotactic end-to-end validation (STEEV) phantom. CBCT projections are simulated for a given scan trajectory through a polychromatic forward projection model with added noise and scatter, then the CBCT image is reconstructed using an iterative
algorithm which minimizes weighted least squares. Main results. Both the incompleteness analysis and the CBCT simulations indicate adding lines to the current single-arc trajectory is more efficient to reduce cone-beam artifacts than adding more arcs, both in terms of number of additional projections and new artifacts. A line-arc-line trajectory with source axial steps of 3.5 mm removes virtually all cone-beam artifacts. The widths of the cone-beam artifacts created by the disks show a positive correlation between the artifact magnitude and the incompleteness value. Significance. A line-arc-line scan trajectory is promising to reduce cone-beam artifacts of the Gamma Knife CBCT images while being a compatible and reasonable trajectory for the current system design.
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All authors Alexandra Alain-Beaudoin, Håkan Nordström, Luc Beaulieu, Joakim da Silva
Physics Education
Determination of the Charge of Electron Using Faraday's Law of Electrolysis
Vladimir Ya. Kezerashvili and Roman Ya. Kezerashvili
We propose a simple experiment for measuring the charge of the electron based on Faraday's law of electrolysis, assuming the known value of Avogadro's number. The experimental setup consists of electrolytic
cells connected in series, so that the same electric current passes through each electrolyte. By measuring the mass deposited at the electrodes and relating it to the total electric charge transferred through the electrolyte using Faraday's law, the charge of the electron can be determined. The experiment requires only standard laboratory equipment, and its performance and analysis are within the skills and knowledge of most students taking
algebra-based general physics courses. It is therefore particularly suitable for instructional laboratories in high schools and two- and four-year colleges. We demonstrate that students can obtain a reasonable value for the charge of the electron from simple measurements, providing a direct experimental connection between Faraday's law, Avogadro's number, and the electron charge.
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Instrumentation and Detectors
Study of the properties of sustainable materials for shielding against ionizing radiations
Julien Faivre
The SuShi project aims at determining how sustainable materials can be used to shield against ionizing radiations. This contribution presents a comparison of the effect of concrete and rammed raw earth on
photons. For energies around the MeV, where interactions by Compton scattering dominate, changes in the material composition have virtually no effect. The density difference results in 20% more thickness needed for earth to achieve the same flux attenuation as concrete. The same value is found for higher energies, where
photons produce electromagnetic showers. Below 0.1 MeV, material composition and earth moisture content matter but the attenuation is much larger.
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Plasma Physics
Alfvénic high-frequency oscillations at the pedestal of JET plasmas
Leonor Roque, Paulo Rodrigues, Emilia R. Solano et al. (+2 more)
Long-lived ($\sim 10$ s) high-frequency oscillations (HFOs, $50-450$ kHz) near the
plasma edge have been reported and experimentally described in L-H transition studies at JET and AUG. In this work, we show that these HFOs are a general phenomenon observed in various
plasma scenarios and compositions (H$^1$, D, D-He$^3$, D-T) under different heating schemes, including pure Ohmic, ICRH and NBI. We demonstrate that dominant axisymmetric ($n=0$) HFOs are Global Alfvén eigenmodes (GAEs) tied to the shear-Alfvén continuum (SAC) minima arising at the
plasma edge due to the sharp decrease of the density and increase of the safety factor. This hypothesis is corroborated by the remarkable agreement found between the measured frequencies of HFOs and the SAC minima computed by the ideal MHD code CSMISH for a comprehensive set of JET pulses. This result, along with the fact that HFOs are observed over long time windows and across a variety of
plasma scenarios, makes them convenient MHD constraints for accurate
equilibrium reconstruction near the edge. In view of this pragmatic application, we derive a first-order analytic expression for the two lowest coupled branches of the $n=0$ SAC, disclosing their dependence (and, consequently, that of the HFOs) on the
plasma density, safety factor, and elongation profiles. In addition, we discuss the nature of $n\neq 0$ HFOs observed along with the dominant $n=0$ HFOs.
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All authors Leonor Roque, Paulo Rodrigues, Emilia R. Solano, JET contributors, The Eurofusion Tokamak Exploitation Team
Chemical Physics
From $\langle n \rangle$ to $n$: Separating multi-particle dynamics by intensity cycling
Pavel Malý, František Trojánek, Petr Malý et al. (+1 more)
We address the interpretation of transient spectroscopy signals proportional to average excitation number in terms of discrete number of excitations. Building on our recent intensity cycling approach, we derive a general scheme to isolate multi-particle dynamics from any transient signal under minimal assumptions. The key result is a general formula expressing the extracted nonlinear signal terms by multi-excitation propagators. We demonstrate the approach on
exciton transport and annihilation in organic nanoparticles, and carrier recombination in silicon nanocrystals.
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All authors Pavel Malý, František Trojánek, Petr Malý, Jérémie Léonard
Fluid Dynamics
Dynamical and statistical properties of large scales in turbulence
A. Alexakis, M. E. Brachet, S. Fauve et al. (+1 more)
We present a review of results concerning the properties of scales larger than the forcing scale in turbulent flows. In three-dimensional
turbulence, when the power driving the flow is injected at a well-defined scale, the injection scale separates the small-scale range, where the Kolmogorov cascade takes place, from the large-scale range across which the mean energy flux is zero, suggesting that these modes are in
equilibrium. We show that, in the case of spatially periodic forcing involving only a few modes, an equipartition energy spectrum is generated at large scales, and we discuss the deviations from equipartition observed with more complex forcings. In two-dimensional
turbulence, the injection scale separates the direct enstrophy cascade toward small scales from the inverse energy cascade toward large scales. Because of the inverse cascade, one would not expect
equilibrium statistical physics tools to be suitable for describing the large-scale structures. Yet this is precisely the situation in which such tools have been most widely used. We indeed show that the bifurcations observed between different largescale regimes of two-dimensional
turbulence, both in experiments and in direct numerical simulations, can be qualitatively described by the Truncated Euler equations, whose solutions satisfy statistical
equilibrium.
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All authors A. Alexakis, M. E. Brachet, S. Fauve, F. Pétrélis
Chemical Physics
On the Electronic Path-Integral Normal Modes of the Spin-Mapping Representation of Nonadiabatic Dynamics
Lauren E. Cook, James R. Rampton and Timothy J. H. Hele
Nonadiabatic Matsubara dynamics has been proposed in both the Meyer-Miller-Stock-Thoss (MMST) and
spin-mapping representations, whereby the dynamics are truncated in the higher path-integral normal modes of the nuclear degrees of freedom, but no truncation is performed in the electronic variables. In contrast to single-surface Matsubara dynamics, these methods do not appear to conserve the
Quantum Boltzmann Distribution (QBD) for general systems. Recently, it was shown that truncating in the electronic path-integral normal modes of the MMST representation does not lead to conservation of the QBD for a single trajectory or accurate computation of a correlation function. Here, the electronic path-integral normal modes in the
spin-mapping representation are investigated. We focus on a two-level system although we expect our findings to be applicable to any number of electronic states. We find, perhaps surprisingly, that the higher normal modes of the
spin-vector $z$-component, the difference in state populations, are constrained by the QBD, that the time-evolved state population observable is a function of only the
spin-mapping centroid, and that the full $N$-bead computational results are replicated using only the
spin-mapping centroid, leading to accurate, QBD conserving dynamics. While at present these results are not a generally-applicable method, we believe this may explain the recent success of
spin-mapping approaches compared to MMST approaches, %To our knowledge, this is the first method obtaining conservation of the QBD when truncating in electronic normal modes and should aid the future derivation of highly accurate and
Quantum Boltzmann conserving nonadiabatic dynamics methods.
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Optics
Biorthogonality of Guided Modes in Non-Hermitian Electromagnetism
Amgad Abdrabou, M. A. Swillam, Şahin K. Özdemir et al. (+1 more)
Biorthogonality plays a central role in the analysis of non-Hermitian photonic systems, where modal expansions generally require both right and left eigenstates. While these concepts are straightforward within scalar and coupled-mode descriptions, their interpretation in the full vectorial Maxwell framework is less transparent. In particular, the standard electromagnetic modal orthogonality relation derived from unconjugated Lorentz reciprocity involves both electric and
magnetic fields and differs in form from the biorthogonality relations obtained from conventional adjoint-operator arguments. Here, we establish the connection between these two formulations for non-Hermitian waveguiding systems with gain and loss. Starting from the full vectorial electric-field wave equation, we formulate the guided-mode problem as a quadratic
eigenvalue problem in the propagation constant, construct its adjoint, and identify the corresponding left eigenmodes. We show that the left eigenmode is related to the complex conjugate of the backward-propagating electric-field mode and demonstrate that the resulting electric-field biorthogonal pairing is equivalent to the mixed electric–
magnetic field relation obtained from unconjugated Lorentz reciprocity. The framework also clarifies the electromagnetic meaning of modal normalization, its connection to self-orthogonality at exceptional points, and the recovery of conventional conjugated modal orthogonality in the lossless limit. These results provide a unified operator-theoretic interpretation of electromagnetic biorthogonality and Lorentz reciprocity and establish a direct connection between the left/right eigenstate
language of non-Hermitian physics and the reciprocity-based modal framework of classical electromagnetism.
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All authors Amgad Abdrabou, M. A. Swillam, Şahin K. Özdemir, R. El-Ganainy
Fluid Dynamics
Effects of Corner Radius and Knudsen Number on Rarefied Gas Flow in a Lid-Driven Cavity
Peiliang Yan and Chuang Wen
Finite corner
curvature is commonly omitted when rarefied cavity flows are represented using idealised geometries. This study examines how downstream corner rounding affects lid-driven cavity flow over 0.5 $\le$ Kn $\le$ 5. Direct simulation Monte Carlo calculations were performed for normalised corner radii of Rc = 0, 0.10 and 0.20. The model was assessed through published
benchmark data and a local grid-sensitivity test. Velocity fields, centreline profiles, area-averaged speed, translational temperature, number density and temperature anisotropy were analysed. A single primary
vortex persisted across all cases. Corner rounding modified the local turning of the downstream return flow but caused little change in the wider circulation. The root-mean-square differences between the rounded and sharp-cornered centreline velocity profiles remained below 0.007. The area-averaged normalised speed increased in all rounded configurations, with a maximum change of approximately 2.5%. The thermodynamic response showed a stronger dependence on rarefaction. Corner rounding reduced the mean temperature non-uniformity at Kn = 0.5 and 1, but increased it at Kn = 2 and 5. Changes in the mean density deviation remained within approximately 1.3%, while the mean translational-temperature anisotropy varied from about -3% to 2.4%. The results show that the sharp-corner approximation captures the global velocity structure under the conditions studied, but can omit local flow changes and small thermodynamic responses associated with finite corner
curvature.
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Atomic Physics
Sub-Doppler cooling of trapped ions using optical tweezers
Bas Gerritsen, Liam J. Bond, Jiri Minář et al. (+3 more)
We propose a sub-Doppler cooling scheme for trapped-ion
crystals in Paul traps. The combination of a hollow tweezer and microwave drive creates an effective two-level system which is cooled through attractive Sisyphus cooling. For ${}^{171}\rm{Yb}^+$ ions, we numerically identify optimal parameters for one- and two-ion
crystals, and investigate the cooling rate in ion
crystals with up to three ions. Our cooling scheme utilizes a single ion addressed with a tweezer to achieve sub-Doppler cooling of the $N$ axial motional modes perpendicular to the tweezer propagation direction, does not rely on the Lamb-Dicke regime and uses off-resonant light. We reach $1/e$ cooling times for the center of mass mode of $\tau_{\rm com}<2$ ms, and a steady-state excitation number of $\bar{n}_{\rm{com}}\approx 0.7$. Our scheme is well-suited as an intermediate stage between Doppler cooling and ground-state sideband cooling, and can be readily realized in trapped-ion platforms.
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All authors Bas Gerritsen, Liam J. Bond, Jiri Minář, Arghavan Safavi-Naini, Robert J. Spreeuw, Rene Gerritsma
History and Philosophy of Physics · Cross-listed from quant-ph
Unbounded Operators, Physicality, and Modality in Quantum Theories
Zhonghao Lu
In this paper, I address the problem regarding the physicality of
Hilbert space in
quantum mechanics, a topic brought into focus by Carcassi et al.'s paper "The unphysicality of
Hilbert spaces" recently. I argue for the physicality of the
Hilbert space in
quantum mechanics, and demonstrate that there are inevitable ambiguity and arbitrariness if we want to identify the set of physical states with a proper subset of it. Moreover, I distinguish the ontological and modal reading of physicality from the pragmatic and operational reading of physicality, and then develop what I call the hierarchical view of physicality. According to this view, physicality is not a monolithic concept, but a layered one that admits degrees. I show the connection between the concept of physicality and modal metaphysics, and finally explain how it can be used to address the interpretational problem of
quantum field theory brought by the existence of inequivalent representations.
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Physics and Society
Bifurcation and Multistability in a Collective-Risk Public Goods Game with Quorum-Activated Protection
Shulan Li, Xiaogang Li, Jun he et al. (+2 more)
The danger of collective risk in a public goods game could provide an effective escape route from the tragedy of the commons. Existing studies usually embed risk mitigation in the contribution itself, whereas many real systems rely on a separate costly and non-excludable protective activity that requires a participation quorum. Whether such protection can evolve and persist remains unclear. Here, we formulate an $N$-player public-goods game with ordinary cooperators, defectors, and protective cooperators. Defectors endogenously increase a saturating probability of collective failure, whereas protective cooperators incur an additional cost and reduce this risk for all group members once their number reaches the quorum. Replicator analysis and numerical bifurcation calculations yield three main findings. First, protective cooperation gains an advantage when the focal participant completes the quorum and the resulting expected loss reduction exceeds its additional cost. This advantage varies non-monotonically with group composition. Second, when a single protective cooperator cannot activate protection, protection effectiveness does not enter its first-order invasion fitness at full defection; greater effectiveness cannot overcome the rare-invasion barrier when full defection is locally asymptotically stable. Third, a boundary saddle–node bifurcation creates a saddle and a locally asymptotically stable coexistence
equilibrium of defectors and protective cooperators. When full cooperation and full defection are also locally asymptotically stable, three attractors coexist, and the numerically observed evolutionary outcome depends on the initial population composition. These results distinguish the effectiveness of activated protection from its ability to become established from rarity.
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All authors Shulan Li, Xiaogang Li, Jun he, Lei Shi, Attila Szolnoki
Computational Physics · Cross-listed from cond-mat.stat-mech
Optimal Evasion from a Resetting Searcher
Ami Taitelbaum, Matan Shporer, Shlomi Reuveni et al. (+1 more)
Returning to a familiar location can help a searcher find its target—but how should the target move to avoid being found? We address this question for a resetting Brownian searcher and a mobile target fluctuating around a home location. Keeping the target's typical exploration range fixed, we find that the mean capture time is maximized at an intermediate correlation time: rapid motion promotes encounters, whereas slow motion leaves the target effectively stationary. Between these extremes, persistent excursions away from the searcher's reset point can substantially delay capture. Analytical limiting results explain this optimum, while numerical solutions reveal an approximately linear relation between the maximal mean capture time and the optimal correlation time across many decades. These findings identify temporal correlations as a resource for evasion, allowing a target to prolong survival by changing how it moves rather than where it roams.
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All authors Ami Taitelbaum, Matan Shporer, Shlomi Reuveni, Michael Assaf
Plasma Physics · Cross-listed from cs.LG
Probabilistic and Geometry Aware Neural Surrogate of Scrape Off Layer Plasma Simulations
Gabriele Gianuzzo, Stefan Dasbach, Fleur Hendriks et al. (+2 more)
Fast surrogates for tokamak boundary-
plasma simulation are typically deterministic regressors mapping a global operating point to a flattened vector of
cell values. Near the divertor detachment transition the steady state is not reliably single-valued. A point estimate must average over qualitatively different
plasma states, and it arrives with no statement of confidence. Moreover, the flattened vector representation discards the
geometric structure of the SOLPS-ITER mesh. This work addresses both problems. We unroll the curvilinear mesh into three fixed-size image tensors whose layout preserves
cell adjacency and inverts exactly, letting a convolutional network act on the geometry without loss of information. A conditional flow matching model, well suited to highly sensitive systems, is then trained on this representation. The result is an efficient, scalable surrogate that captures multiple plausible outcomes even at sensitive operating points. Along a gas-puff scan, the predictive distribution splits into a hot and a cold mode across an early regime transition. A further check on synthetic data with an injected bifurcation of known size confirms the model recovers both branches rather than their average.
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All authors Gabriele Gianuzzo, Stefan Dasbach, Fleur Hendriks, Sven Wiesen, Vlado Menkovski
Biological Physics · Cross-listed from cond-mat.soft
Position-dependent friction in protein folding from a GLE derived with a non-stationary localized projection distribution
Salma Salem, Lucas Tepper, Benjamin J. A. Héry et al. (+3 more)
The Generalized Langevin Equation (GLE) is an integro-differential equation of motion for a general observable of a many-body system and is rigorously derived using the projection operator formalism. In the standard derivation, a stationary canonical phase space distribution is used for the projection. Here, we derive a novel class of GLEs using a non-stationary projection distribution that constrains the initial ensemble to a hypersurface in phase space on which the observable has a fixed value $A_0$. As a result, all GLE parameters, and in particular the
memory friction kernel, depend on $A_0$ and can be extracted from short simulations that do not sample the entire phase space. Applying this non-stationary GLE to
protein folding trajectories, we find for villin and an $\alpha$-helical poly-alanine segment that the total friction is higher in the folded state. These results demonstrate that observable-dependent friction effects are non-negligible and can be accounted for using non-stationary GLEs derived by constrained projection schemes.
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All authors Salma Salem, Lucas Tepper, Benjamin J. A. Héry, Henrik Kiefer, David D. Girardier, Roland R. Netz
Instrumentation and Detectors
CBM T0 Detector Performance Study with Light Ions (4He, 12C) and the DOGMA Readout System
Yevhen Kozymka, Thomas Bergauer, Maximilian von Buelow et al. (+14 more)
This paper presents the realization and performance of the CBM T0 detector system. Built upon an approximately 70 {\mu}m thin polycrystalline CVD (pcCVD) diamond sensor with pad metallization, the detector is mounted on a flexible
vacuum manipulator and operates entirely under passive cooling. Interfaced with the DOGMA readout architecture, the system successfully meets all operational requirements for CBM. It demonstrates a high detection efficiency (near 100%) and a timing precision below 50 ps RMS across a broad range of beam species, from light ions (such as Carbon) to heavy ions (such as Gold). The DOGMA readout features two distinct data paths: a high-precision TDC path routing data directly to the global CBM DAQ, and a secondary path deliver in real-time rate measurements crucial for online beam quality monitoring and fast beam abort logic. Finally, detailed performance studies conducted with light-ion beams at EBG MedAustron are discussed.
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All authors Yevhen Kozymka, Thomas Bergauer, Maximilian von Buelow, Henrik Flörsheimer, Jochen Frühauf, Tetyana Galatyuk, Harald Handerkas, Henning Heggen, Mladen Kis, Sergey Linev, Jerzy Pietraszko, Christian Joachim Schmidt, Luca Schramm, Michael Traxler, Michael Träger, Felix Ulrich-Pur, Robert Visinka
Physics Education
Network lexical analysis of student integration of music and physics knowledge
W. Brian Lane and Emily E. Pipkin
Introductory physics students benefit from learning to integrate new physics knowledge with prior knowledge related to their interests. Writing assignments that offer high epistemic agency can foster this integration, and provide rich artifacts for qualitative analysis. Physics education researchers are increasingly interested in studying such artifacts using computer-based textual analysis. In this paper, we use lexical methods to look for evidence of knowledge integration in written assignments from a Physics of Music course. These assignments require students to communicate to an external audience a clear and cohesive narrative that synthesizes concepts from music and physics. To apply this methodology, we first establish a lexicon of music, physics, and integrated keywords that 10 students used across 6 writing assignments. Then, we visualize this word usage in a series of network diagrams based on which keywords were used in proximity to each other in each assignment. We find that students most strongly connected ideas from music and physics using keywords related to the physical structure of sound (sound, frequency, and wave). Applying these methods to each assignment
prompt and its resulting student submissions, we find that, in assignments with a lower degree of epistemic agency (assessed qualitatively by our experience teaching the course), students primarily followed the example of integration modeled by the assignment
prompt, but in assignments with a higher degree of epistemic agency, they explored music-physics integration to a greater degree. We use this analysis to offer a pedagogical contribution to introductory physics courses centered around students' interests, a theoretical contribution by illustrating a means of quantifying epistemic agency, and a methodological contribution that complements textual analysis and offers the scalability sought in such approaches.
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Optics
Channel closing in strong-field photoemission from tip arrays
Leon Brückner, Jonas Heimerl, Constantin Nauk et al. (+1 more)
Ultrafast photoemission is a promising avenue for the development of petahertz electronics. For such devices, identifying the precise emission mechanism and quantifying the local field strength at the emission site are of utmost interest. While this information can be extracted from electron energy spectra or the scaling of the emission rate with peak intensity, such measurements are not always technically feasible and a clear interpretation of the results can be challenging. Here, we demonstrate channel closing as a precision gauge for the local enhanced optical nearfield strength. Channel closings originate from a field-induced upshift of the
vacuum level, which leads to a small decrease of the emission yield with increasing intensity. We report the first experimental observation of such channel closings in the photoemission rate from an array of nanometer-sharp gold tips. Our data are well matched by simulated yields, enabling us to precisely measure the local, field-enhanced optical nearfield at the tip array in situ. We expect this method to be a versatile diagnostic tool for the characterization of lightwave optoelectronic devices, as it suffices to measure currents only.
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All authors Leon Brückner, Jonas Heimerl, Constantin Nauk, Peter Hommelhoff