Geophysics
Single and Multi-Objective Optimization of Distributed Acoustic Sensing Cable Layouts for Geophysical Applications
Dominik Strutz, Tjeerd Kiers and Andrew Curtis
We present a systematic approach to optimise distributed acoustic sensing (DAS) fibre-optic cable layouts using global optimisation techniques. Our method represents cable geometries using splines, enabling efficient exploration of layouts while respecting physical deployment constraints. The use of evolutionary
algorithms enables single and multi-objective optimisation, taking into account complex design constraints such as terrain, accesibility, exclusion zones and cable length, while allowing efficient parallelisation of the optimisation process. We demonstrate the approach on a real-world case study, optimising the layout of a DAS cable for monitoring slope stability in the Cuolm da Vi area of Switzerland. We adapt design criteria for seismic source location problems, and for ambient noise surface wave
tomography, to account for the unique characteristics of DAS, such as directional sensitivity patterns. The results show significant potential for improvements in source location accuracy and surface wave tomographic resolution by optimising cable layouts, highlighting the potential of this approach for optimising DAS deployments in various geophysical applications.
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Optics
Airy Resonances in Photonic Crystal Superpotentials
Zeyu Zhang, Brian Gould, Maria Barsukova et al. (+1 more)
Airy wavefunctions are associated with one of the simplest scenarios in wave mechanics: a
quantum bouncing ball. In other words, they are the eigenstates of the time-independent Schrodinger equation with a linear potential. In the domain of optics,
laser beams that are spatially shaped as Airy functions (`Airy beams') have been shown to exhibit a prominent lobe that follows a curved path, rather than propagating in a straight line, and which has self-healing properties in the presence of obstacles. Here, we observe the presence of Airy resonances in two-dimensional photonic
crystals composed of a
lattice of holes in a silicon slab. Analogously to electrons in a linear potential, these Airy resonances arise due to a linear spatial variation in the
lattice constant of the holes. We map the electromagnetic description of the photonic
crystal onto a 2D non-Hermitian Schrodinger equation with a linear potential, which we call a `superpotential'. The non-Hermiticity appears in the form of a complex effective mass due to out-of-plane radiation and fundamentally alters the collective optical response of the Airy resonances.
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All authors Zeyu Zhang, Brian Gould, Maria Barsukova, Mikael C. Rechtsman
Instrumentation and Detectors · Cross-listed from quant-ph
Efficient Radiofrequency Sensing with Fluorescence Encoding
Nicole Voce and Paul Stevenson
Optically-active
spin qubits have emerged as powerful
quantum sensors capable of nanoscale magnetometry, yet conventional coherent sensing approaches are ultimately limited by the coherence time of the sensor, typically precluding detection in the sub-MHz regime. We present a broadly applicable fluorescence-encoding method that circumvents coherence-time constraints by transducing time-varying
magnetic fields directly into modulated fluorescence signals. Using nitrogen-vacancy centers in diamond as a model system, we demonstrate shot-noise-limited sensitivity for AC
magnetic fields spanning near-DC to MHz frequencies, with detection bandwidth tunable via optical excitation power. The technique captures complete spectral information in a single measurement, eliminating the need for point-by-point frequency scanning, and allows phase-sensitive multi-frequency detection with Hz-level resolution. This approach transforms
quantum sensors into atomic-scale spectrum analyzers, with immediate applications for low-frequency RF communication, zero-field NMR, and bioelectronic sensing. Our approach is broadly applicable to the expanding class of optically-active
spin qubits, including molecular systems and fluorescent
proteins, opening new sensing regimes previously inaccessible to coherent techniques
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Plasma Physics
Factors Controlling the Statistics of Magnetic Reconnection in MHD Turbulence
M. B. Khan, M. A. Shay, S. Oughton et al. (+9 more)
We study the statistics of dynamical quantities associated with
magnetic reconnection events embedded in a sea of strong background magnetohydrodynamic (MHD)
turbulence using direct numerical simulations. We focus on the relationship of the reconnection properties to the statistics of global turbulent fields. For the first time, we show that the distribution in
turbulence of reconnection rates (determined by upstream fields) is strongly correlated with the magnitude of the global turbulent
magnetic field at the correlation scale. The average reconnection rates, and associated dissipation rates, during
turbulence are thus much larger than predicted by using turbulent
magnetic field fluctuation amplitudes at the dissipation or kinetic scales.
Magnetic reconnection may therefore be playing a major role in energy dissipation in astrophysical and heliospheric
turbulence.
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All authors M. B. Khan, M. A. Shay, S. Oughton, W. H. Matthaeus, C. C. Haggerty, S. Adhikari, P. A. Cassak, S. Fordin, D. O'Donnell, Y. Yang, R. Bandyopadhyay, S. Roy
Instrumentation and Detectors
Characterization of a 28 nm $\textit{smartpixels}$ ASIC With On-Chip ML for Particle Tracking Detectors
Benjamin Parpillon, Anthony Badea, Danush Shekar et al. (+35 more)
We present a 28 nm CMOS pixel readout integrated
circuit implementing in-pixel analog signal processing and on-chip machine learning data filtering for particle tracking detectors. Our ASIC comprises two $32 \times 8$ pixel
matrices with a pixel pitch of $25 \times 25~\mu\mathrm{m}^2$, in which each pixel integrates a charge-sensitive amplifier with synchronous auto-zero offset cancellation and a 2-bit flash ADC with programmable thresholds. Two analog front-end architectures, single-ended and differential, are implemented and characterized. Digitized pixel data are combined into row-wise projections and processed by an on-chip, fully combinational neural network classifier for data reduction. Measurements at room temperature using charge injection demonstrate an equivalent noise charge of $54.6~\mathrm{e}^{-}$ and a threshold dispersion of $\sim$78.2~\unit{\electron} at nominal bias, linear response up to several~\unit{\kilo\electron}, and stable operation at a 10~MHz clock frequency. The neural network output is compared with offline RTL predictions and agrees for $99.06\%$ of $1.5 \times 10^{5}$ test inputs.
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All authors Benjamin Parpillon, Anthony Badea, Danush Shekar, Cristian Gingu, Giuseppe Di Guglielmo, Tom Deline, Sergey Los, Adam Quinn, Michele Ronchi, Daniel Abadjiev, Doug Berry, Arghya Ranjan Das, Jennet Dickinson, Karri DiPetrillo, Farah Fahim, Lindsey Gray, Harshul Gupta, Eliza Howard, David Jiang, Pamela Klabbers, Mira Littmann, Mia Liu, Petar Maksimovic, Nick Manganelli, Corrinne Mills, Mark S. Neubauer, Jannicke Pearkes, Paul Rubinov, Ricardo Silvestre, Morris Swartz, Chinar Syal, Nhan Tran, Amit Trivedi, Keith Ulmer, Mohammad Abrar Wadud, Benjamin Weiss, Jieun Yoo, Eric You
Chemical Physics
Factorized electron-nuclear dynamics with effective complex potential: on-the-fly implementation for H$_2^+$ in a laser field
Julian Stetzler, Sophya Garashchuk and Vitaly A. Rassolov
Conventional theoretical and computational approaches to fully coupled
quantum molecular dynamics, i.e. when both the electrons and
nuclei are treated as
quantum-mechanical particles, are impractical for all but the smallest chemical systems. In this paper we describe the formalism and implementation of the Factorized Electron
Nuclear Dynamics (FENDy) with effective complex potential [J. Chem. Theory Comput. 19 (2023), pp 1393-1408], which goes beyond the established framework of the Born-Oppenheimer approximation or Born-Huang expansion of the molecular wavefunction. This method is based on the exact factorization of the molecular wavefunction, with the
nuclei evolving under a complex time-dependent potential which captures the key features of dynamics in the
nuclear subspace. The complementary electronic component of the molecular wavefunction is normalized to one for all
nuclear configurations. We implement and employ FENDy to model the dynamics of H$_2^+$ molecular ion under a femtosecond
laser pulse. The electronic wavefunction is represented within the standard electronic structure bases without referencing the electronic eigenstates. The
nuclear wavefunction is represented as a
quantum-trajectory ensemble, which in principle circumvents the exponential scaling of the numerical cost with the system size. The challenging evaluation of the gradients on unstructured grids is performed by projection on auxiliary bases.
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Physics and Society · Cross-listed from cs.CY
Fixed Points and Stochastic Meritocracies: A Long-Term Perspective
Gaurab Pokharel, Diptangshu Sen, Sanmay Das et al. (+1 more)
We study group
fairness in the context of feedback loops induced by meritocratic selection into programs that themselves confer additional advantage, like college admissions. We introduce a stylized, yet novel inter-generational model for the setting and analyze it in situations where there are no underlying differences between two populations. When the benefit of the program (or the harm of not getting into it) is completely symmetric, we show that disparities between the two populations will vanish on average in the long term, although in the short term disparities will continue to arise and dissipate cyclically. Further, the time an accumulated advantage takes to dissipate can be significant, and increases as a function of the relative importance of the program in conveying benefits. Interestingly, significant disparities can arise purely due to randomness even from completely symmetric initial conditions, especially when populations are small. The introduction of even a slight asymmetry, where the group that has accumulated an advantage becomes slightly preferred, leads to a completely different outcome. In these instances, starting from completely symmetric initial conditions, disparities between groups arise stochastically and then persist over time, yielding a permanent advantage for one group. Our analysis precisely characterizes conditions under which disparities persist or diminish, with a particular focus on the role of the scarcity of available spots in the program and its effectiveness. We also present extensive simulations in a richer model that further support our theoretical results in the simpler, stylized model. Our findings are relevant for the design and implementation of algorithmic
fairness interventions in similar selection processes.
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All authors Gaurab Pokharel, Diptangshu Sen, Sanmay Das, Juba Ziani
Space Physics · Cross-listed from astro-ph.SR
Characterization of the Trans-Alfvénic Region Using Observations from Parker Solar Probe
Subash Adhikari, Riddhi Bandyopadhyay, Joshua Goodwill et al. (+14 more)
Close to Earth the
solar wind is usually super-Alfvénic, i.e. the speed of the
solar wind is much larger than the Alfvén speed. However, in the lower coronal regions, the
solar wind is mostly sub-Alfvénic. With the Parker
Solar Probe (PSP) crossing the boundary between the sub- and super-Alfvénic flow, Bandyopadhyay et al. (2022) performed a
turbulence characterization of the sub-Alfvénic
solar wind with initial data from encounters 8 and 9. In this study, we re-examine the
turbulence properties such as
turbulence amplitude, anisotropy of the
magnetic field variance, intermittency and switchback strength extending with PSP data for encounters 8-19. The later orbits probe lower altitudes and experience sub-Alfvénic conditions more frequently providing a greater statistical coverage to contrast sub- and super-Alfvénic
solar wind. Also, by isolating the intervals where the
solar wind speed is approximately equal to the Alfvén speed, we explore the transition in more detail. We show that the amplitude of the normalized
magnetic field fluctuation is smaller for the sub-Alfvénic samples. While
solar wind
turbulence in general is shown to be anisotropic, the sub-Alfvénic samples are more anisotropic than the super-Alfvénic samples, in general. Further, we show that the sub- and super-Alfvénic samples do not show much distinction in terms of intermittency strength. Finally, consistent with prior results, we find no evidence for polarity reversing > 90 degrees switchbacks in the sub-Alfvénic
solar wind
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All authors Subash Adhikari, Riddhi Bandyopadhyay, Joshua Goodwill, William H. Matthaeus, David Ruffolo, Panisara Thepthong, Peera Pongkitiwanichakul, Sohom Roy, Francesco Pecora, Rohit Chhiber, Rayta Pradata, Arcadi Usmanov, Michael Stevens, Samuel Badman, Orlando Romeo, Jiaming Wang, Melvyn L. Goldstein
Chemical Physics
Analysis of divergent dynamics of exactly factorized electron-nuclear wavefunctions
Julian Stetzler, Sophya Garashchuk and Vitaly A. Rassolov
The Exact Factorization (XF) of molecular wavefunctions can be viewed as an 'electronic wavepacket' framework for
quantum dynamics. It is an appealing alternative to the conventional non-adiabatic dynamics, unfolding in the space of coupled electronic eigenstates. However, implementation of the non-linear XF equations for general systems presents a formidable challenge: the XF counterparts to the non-adiabatic coupling involve division by the
nuclear probability density, which leads to severe numerical instabilities in the low-density regions of space. In case of the non-adiabatic dynamics the effect of coupling is relatively smooth, but this theoretical framework becomes impractical when numerous electronic states are involved. In this paper the origin of the XF-specific challenge is analyzed analytically. We demonstrate that the problem arises when the factorized wavefunction diverges, even without the explicit coupling of the Born-Huang electronic states used to describe the molecular wavefunction. Using a 'minimal' model of the photodissociation, we derive expressions for the XF dynamics and locate the source of the XF instability. We analyze the dependence of this instability on the
nuclear wavefunction bifurcation in the stationary and moving frames of reference, the latter associated with the
quantum trajectory ensemble describing the
nuclear XF wavepacket in a compact form. We show that the near-singular behavior persists in the moving frame and in the atomic basis representation of the electronic wavefunction. This model and insight into the root of the XF implementation challenge will help to address the issue, leading to further development of the XF methods.
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Atomic Physics
Letokhov-Chebotayev intracavity trapping spectroscopy of H$_2$
Wim Ubachs, Frank M.J. Cozijn, Meissa L. Diouf et al. (+3 more)
In the early days of
laser spectroscopy Letokhov and Chebotayev proposed a scheme for measuring narrow spectral lines where the resolution is not restricted to Doppler effects because the molecules are entrained in a standing-wave light field. Now, such one-dimensional trapping in the intensity maxima of an intracavity field, slightly detuned from resonance, is experimentally demonstrated in the measurement of the very weak S(0) (2-0) quadrupole overtone transition in H$_2$ at 1189 nm. The trapping manifests as an extremely narrow absorption feature at the predicted zero-
recoil position, a 70 kHz shift from the blue-
recoil component observed in Lamb-dip spectroscopy. A quantitative analysis of the saturation and trapping conditions supports the findings.
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All authors Wim Ubachs, Frank M.J. Cozijn, Meissa L. Diouf, Clement Lauzin, Hubert Jóźwiak, Piotr Wcisło
Atomic Physics · Cross-listed from quant-ph
Angular Geometry of Atomic Multipole Transitions
Wesley C. Campbell
A simple way to calculate Rabi frequencies is outlined for interactions of atomic or
nuclear multipole moments with
laser fields that focuses on their relative geometry. The resulting expression takes the form of a dot product between the
laser polarization and a vector spherical harmonic, thereby naturally connecting to the multipole's far-field spontaneous-emission pattern and providing a way to visualize the interaction. Since the vector spherical harmonics are not yet a standard tool in
quantum science, their relevant properties are reviewed. This approach is illustrated in the calculation of a variety of beam effects, yielding both perturbative corrections and some nontrivial cases with non-vanishing coupling.
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Optics · Cross-listed from cs.ET
SEPhIA: <1 laser/neuron Spiking Electro-Photonic Integrated Multi-Tiled Architecture for Scalable Optical Neuromorphic Computing
Matěj Hejda, Aishwarya Natarajan, Chaerin Hong et al. (+4 more)
Research into optical spiking neural networks (SNNs) has primarily focused on spiking devices, networks of excitable
lasers or numerical modelling of large architectures, often overlooking key constraints such as limited optical power, crosstalk and footprint. We introduce SEPhIA, a photonic-electronic, multi-tiled SNN architecture emphasizing implementation feasibility and realistic scaling. SEPhIA leverages microring resonator modulators (MRMs) and multi-wavelength sources to achieve effective sub-one-
laser-per-spiking
neuron efficiency. We validate SEPhIA at both device and architecture levels by time-domain co-simulating excitable CMOS-MRR coupled
circuits and by devising a physics-aware, trainable optoelectronic SNN model, with both approaches utilizing experimentally derived device parameters. The multi-layer optoelectronic SNN achieves classification accuracies over 90% on a four-class spike-encoded
dataset, closely comparable to software models. A design space study further quantifies how photonic device parameters impact SNN performance under constrained signal-to-noise conditions. SEPhIA offers a scalable, expressive, physically grounded solution for neuromorphic photonic computing, capable of addressing spike-encoded tasks.
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All authors Matěj Hejda, Aishwarya Natarajan, Chaerin Hong, Mehmet Berkay On, Sébastien d'Herbais de Thun, Raymond G. Beausoleil, Thomas Van Vaerenbergh
Computational Physics · Cross-listed from quant-ph
Quantum Grid Path Planning Using Parallel QAOA Circuits Based on Minimum Energy Principle
Jun Liu
To overcome the bottleneck of classical path planning schemes in solving NP problems and address the predicament faced by current mainstream
quantum path planning frameworks in the Noisy Intermediate-Scale
Quantum (NISQ) era, this study attempts to construct a
quantum path planning solution based on parallel
Quantum Approximate Optimization
Algorithm (QAOA) architecture. Specifically, the grid path planning problem is mapped to the problem of finding the minimum
quantum energy state. Two parallel QAOA
circuits are built to simultaneously execute two solution processes, namely connectivity energy calculation and path energy calculation. A classical
algorithm is employed to filter out unreasonable solutions of connectivity energy, and finally, the approximate optimal solution to the path planning problem is obtained by merging the calculation results of the two parallel
circuits. The research findings indicate that by setting appropriate filter parameters,
quantum states corresponding to position points with extremely low occurrence probabilities can be effectively filtered out, thereby increasing the probability of obtaining the target
quantum state. Even when the
circuit layer number p is only 1, the theoretical solution of the optimal path coding combination can still be found by leveraging the critical role of the filter. Compared with serial
circuits, parallel
circuits exhibit a significant advantage, as they can find the optimal feasible path coding combination with the highest probability.
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Optics
Strong interlayer coupling and chiral flat-band cascades in twisted bilayer gratings
Daegwang Choi, Soon-Jae Lee, Seung-Woon Cho et al. (+5 more)
From atomic
crystals to macroscopic material structures, twisted
bilayer systems have emerged as a promising route to control wave phenomena. In few-layer van der Waals (vdW) materials, however, the intrinsically weak interlayer coupling typically demands fine control of small twist angles to reach magic-angle conditions. Here, we show that one-dimensional photonic
crystal bilayers can overcome this limitation by accessing a regime of strong interlayer coupling – comparable to intralayer coupling. This strong coupling enables flat-band formation over a broad angular range even at large twist angles. We experimentally realize this regime by stacking WS$_2$ gratings using a two-step lithography method, resulting in ultra-wide
chiral flat-band cascades in magic-angle twisted
bilayer gratings. Our work not only provides a platform for designing photonic applications with tunable localization but also explores a new regime of physics unattainable in conventional solid-state based moiré systems.
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All authors Daegwang Choi, Soon-Jae Lee, Seung-Woon Cho, Chan Bin Bark, Seik Pak, Dong-Jin Shin, Moon Jip Park, Su-Hyun Gong
Physics and Society
Monthly Rural-Urban Scaling of Road Accidents in England, Wales and Scotland (2019-2023)
Isabel Copsey, Quentin Hanley and Jack Sutton
Road traffic accidents remain a major public health challenge worldwide, with urbanisation and population density identified as key factors influencing risk. This study analyses monthly accident data from 2009 to 2023 across 632 parliamentary constituencies in England, Wales, and Scotland, using an area-normalised approach based on population density. Segmented power law models consistently identified breakpoints separating sublinear rural from superlinear urban scaling behaviours. Seasonal variation in scaling exponents was pronounced in rural regions but less evident in urban ones.
Fourier-based cross-spectral analysis of yearly cycles revealed systematic phase shifts: rural exponents lagged pre-exponential factors by 4.5 months, while urban exponents were 2.7 months out of phase, producing a 5.3 month shift between rural and urban exponents. These findings highlight the importance of pre-exponentials-defined as the expected density of accidents at unit population density-as comparable descaled metrics, revealing both long-term national declines and recurring seasonal peaks. Notably, the phase offsets suggest structurally distinct causes of rural and urban accident risk, with urban regions exhibiting increasing acceleration in accident scaling, potentially linked to growth in vehicle numbers, size, and weight. Residuals, modelled with the Type I Generalised Logistic Distribution (GLD), captured skewness and heterogeneity more effectively than normal assumptions. Geospatial mapping highlighted persistent urban hotspots alongside rural and coastal constituencies with systematically lower accident densities than predicted. Together, these findings advance understanding of how density and urbanisation shape accident risk and provide evidence to support more targeted road safety interventions and policy planning.
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Plasma Physics
GyroSwin: 5D Surrogates for Gyrokinetic Plasma Turbulence Simulations
Fabian Paischer, Gianluca Galletti, William Hornsby et al. (+5 more)
Nuclear fusion plays a pivotal role in the quest for reliable and sustainable energy production. A major roadblock to viable fusion power is understanding
plasma turbulence, which significantly impairs
plasma confinement, and is vital for next-generation reactor design.
Plasma turbulence is governed by the nonlinear gyrokinetic equation, which evolves a 5D distribution function over time. Due to its high computational cost, reduced-order models are often employed in practice to approximate turbulent transport of energy. However, they omit nonlinear effects unique to the full 5D dynamics. To tackle this, we introduce GyroSwin, the first scalable 5D neural surrogate that can model 5D nonlinear gyrokinetic simulations, thereby capturing the physical phenomena neglected by reduced models, while providing accurate estimates of turbulent heat transport. GyroSwin (i) extends hierarchical
Vision Transformers to 5D, (ii) introduces cross-
attention and integration modules for latent 3D$\leftrightarrow$5D interactions between electrostatic potential fields and the distribution function, and (iii) performs channelwise mode separation inspired by nonlinear physics. We demonstrate that GyroSwin outperforms widely used reduced numerics on heat flux prediction, captures the turbulent energy cascade, and reduces the cost of fully resolved nonlinear gyrokinetics by three orders of magnitude while remaining physically verifiable. GyroSwin shows promising scaling laws, tested up to one billion parameters, paving the way for scalable neural surrogates for gyrokinetic simulations of
plasma turbulence.
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All authors Fabian Paischer, Gianluca Galletti, William Hornsby, Paul Setinek, Lorenzo Zanisi, Naomi Carey, Stanislas Pamela, Johannes Brandstetter
Fluid Dynamics
Symmetry-breaking bifurcations and sub-harmonic lock-in of a flexible splitter plate in cylinder wake flow
Baiyang Song, Huan Ping, Wenli Chen et al. (+2 more)
This paper investigates the flow past a flexible splitter plate attached to the rear of a fixed circular cylinder at a low Reynolds number of 150. A systematic exploration of the plate length ($L/D$), flexibility coefficient ($S^{*}$), and mass ratio ($m^{*}$) reveals new laws and phenomena. The large-amplitude vibration of the structure is attributed to a resonance phenomenon induced by fluid-structure interaction. The modal decomposition indicates that resonance arises from the coupling between the first and second structural modes, where the excitation of the second structural mode plays a critical role. Due to the combined effects of added mass and periodic stiffness variations, the two modes become synchronized, oscillating at the same frequency while maintaining a fixed phase difference of $\pi/2$. This further results in the resonant frequency being locked at half of the second natural frequency, which is approximately three times the first natural frequency. A reduction in plate length and an increase in mass ratio are both associated with a narrower resonant locking range, while a higher mass ratio also shifts this range toward lower frequencies. A
symmetry-breaking bifurcation is observed for cases with $L/D\leq3.5$, whereas for $L/D=4.0$, the flow remains in a steady state with a stationary splitter plate prior to the onset of resonance. For cases with a short flexible plate and a high mass ratio, the shortened resonance interval causes the plate to return to the
symmetry-breaking stage after resonance, gradually approaching an
equilibrium position determined by the flow field characteristics at high flexibility coefficients.
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All authors Baiyang Song, Huan Ping, Wenli Chen, Yong Cao, Dai Zhou
Geophysics
Effects of Wall Roughness on Coupled Flow and Heat Transport in Fractured Media
Alessandro Lenci, Yves Méheust, Maria Klepikova et al. (+2 more)
Heat transfer in fractured media is governed by the interplay between advective transport along rough-walled fractures and conductive transport, both within the fractures and in the surrounding low-permeability
matrix. Flow localization induced by aperture heterogeneity, combined with
matrix conduction, gives rise to anomalous thermal behavior. To capture these effects, we develop a
stochastic modeling framework that couples a time-domain random walk (TDRW) representation of advective and conductive transport in the fractures with a semi-analytical model of conductive heat exchange with the
matrix.
Matrix trapping times follow a Lévy-Smirnov distribution derived from first-passage theory, capturing the heavy-tailed dynamics typical of fractured systems. Heat flux at the fracture-
matrix interface is computed via a nonlocal convolution integral based on Duhamel's principle, accounting for thermal
memory effects. The model is validated against analytical
benchmarks and finite-element simulations. Monte Carlo simulations over
stochastic aperture fields quantify the influence of fracture closure, correlation length, and Péclet number. Results reveal a transition from superdiffusive to subdiffusive regimes, driven by the competition between advective transport along preferential paths, dispersion induced by aperture variability, and
matrix-driven heat conduction. In the long-time regime, heat exchange exhibits a characteristic $t^{-1/2}$ decay. At early times, limited thermal penetration into the
matrix leads to weaker interfacial fluxes, underscoring the role of
matrix thermal inertia. The proposed framework enables physically consistent and computationally efficient simulations of thermal transport in complex fractured systems, with implications for geothermal energy, subsurface thermal storage, and engineered heat exchange in low-permeability environments.
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All authors Alessandro Lenci, Yves Méheust, Maria Klepikova, Vittorio Di Federico, Daniel M. Tartakovsky
Atomic Physics · Cross-listed from hep-ph
Muonium Hyperfine Splitting Uncertainty Revisited
Michael I. Eides
Uncertainty of the theoretical prediction for the hyperfine splitting in the ground state of muonium is considered. It is compared with the respective discussion in the two most recent CODATA adjustments of the fundamental physical constants.
Computational Physics · Cross-listed from quant-ph
End-to-End Quantum Algorithm for Topology Optimization in Structural Mechanics
Leonhard Hölscher, Oliver Ahrend, Lukas Karch et al. (+5 more)
Topology optimization is a key methodology in engineering design for finding efficient and robust structures. Due to the enormous size of the design space, evaluating all possible configurations is typically infeasible. In this work, we present an end-to-end, fault-tolerant
quantum algorithm for
topology optimization that operates on the exponential
Hilbert space representing the design space. We demonstrate the
algorithm on the two-dimensional Messerschmitt-Bölkow-Blohm (MBB) beam problem. By restricting design variables to binary values, we reformulate the compliance minimization task as a combinatorial satisfiability problem solved using Grover's
algorithm. Within Grover's oracle, the compliance is computed through the finite-element method (FEM) using established
quantum algorithms, including block-encoding of the stiffness
matrix,
Quantum Singular Value Transformation (QSVT) for
matrix inversion, Hadamard test, and
Quantum Amplitude Estimation (QAE). The complete
algorithm is implemented and validated using classical
quantum-
circuit simulations. A detailed complexity analysis shows that the method evaluates the compliance of exponentially many structures in
quantum superposition in
polynomial time. In the global search, our approach maintains Grover's quadratic speedup compared to classical unstructured search. Overall, the proposed
quantum workflow demonstrates how
quantum algorithms can advance the field of computational science and engineering.
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All authors Leonhard Hölscher, Oliver Ahrend, Lukas Karch, Carlotta L'Estocq, Marc Marfany Andreu, Tobias Stollenwerk, Frank K. Wilhelm, Julia Kowalski
Computational Physics · Cross-listed from quant-ph
Universal initial state preparation for first quantized quantum simulations
Jack S. Baker, Gaurav Saxena and Thi Ha Kyaw
Preparing
symmetry-adapted initial states is a principal bottleneck in first-quantized
quantum simulation. We present a universal approach that efficiently maps any
polynomial-size superposition of occupation-number configurations to the first-quantized representation on a digital
quantum computer. The method exploits the Jordan–Schwinger Lie
algebra homomorphism, which identifies number-conserving second-quantized operators with their first-quantized action and induces an equivariant bijection between Fock occupations and $\mathfrak{su}(d)$ weight states within the Schur–Weyl decomposition. Operationally, we deterministically prepare an superposition of target Schur labels and apply the inverse
quantum Schur transform. For $L$ configurations of $N$ particles over $d$ modes prepared to accuracy $\epsilon$, the most efficient variant of the
algorithm runs with non-Clifford gate complexity $\mathrm{poly}(L, N, \log d, \log \epsilon^{-1})$. The protocol applies universally to
fermions,
bosons, and Green's paraparticles in arbitrary single-particle bases. Resource estimates establish practicality within leading first-quantized pipelines, with statistics-aware specializations promising further reductions.
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Fluid Dynamics
Stochastic Modeling and Upscaling of Hydrodynamic Transport in Geological Fractures
Alessandro Lenci, Yves Méheust, Marco Dentz et al. (+1 more)
Characterizing hydrodynamic transport in fractured rocks is essential for carbon storage and geothermal energy production. Multiscale heterogeneities lead to anomalous solute transport, featuring breakthrough curve (BTC) tailing and nonlinear growth of plume spatial moments. We focus on purely advective transport within synthetic geological fractures with prescribed relative closure $\sigma_a/\langle a \rangle$ and correlation length $L_\mathrm{c}$. We adopt a
stochastic approach with multiple fracture realizations for each set of
geometric parameters. Steady-state depth-averaged Stokes flow is solved under the lubrication approximation. Flow heterogeneity is organized over the correlation length $L_\mathrm{c}$. The ensemble-averaged velocity PDFs are insensitive to $L_\mathrm{c}$ but strongly influenced by $\sigma_a/\langle a \rangle$, particularly their low-velocity power-law scaling. A time-domain random walk (TDRW) simulation is used to compute plume spatial moments and outlet BTCs. The mean longitudinal plume position scales linearly with time at both early and late stages. The variance shows ballistic scaling at early times and a late-time behavior controlled by the low-velocity power law of the velocity PDF, with exponent $\alpha$ strongly influenced by $\sigma_a/\langle a \rangle$. The properties of the BTCs are also controlled by $\alpha$, including the broadening of the peak as $\sigma_a/\langle a \rangle$ increases, and the scaling of the power-law tails. Advective transport is also modeled using a one-dimensional continuous-time random walk (CTRW) that relies only on the velocity PDF, flow tortuosity, and flow correlation length. The CTRW reproduces the TDRW results and provides analytical predictions for the asymptotic transport scalings.
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All authors Alessandro Lenci, Yves Méheust, Marco Dentz, Vittorio Di Federico
Chemical Physics
Effective Core Potentials for calculations of continuum spectra of molecules using the molecular R-matrix method
Zdenek Masin, Jakub Benda, Martin Crhan et al. (+4 more)
Implementation of Effective Core Potentials (ECPs) into the molecular scattering suite UKRmol+ is presented together with a set of calculations for a range of targets relevant for
plasma modeling. Continuum description in scattering and photoionization calculations for large targets or high-energy electrons often requires the use of numerical continuum functions and the associated molecular integrals. We derive expressions for ECP integrals over B-spline type orbitals using their momentum-space representation and describe their implementation. Sample calculations are presented for electron collision from bromine molecule (Br$_2$), silicon tetrabromide (SiBr$_4$) and tungsten hydride (WH) as well as photoionisation of methyl iodide (CH$_3$I).
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All authors Zdenek Masin, Jakub Benda, Martin Crhan, Gregory S. J. Armstrong, Anna Nelson, Sebastian Mohr, Jonathan Tennyson
Optics
Bulk plasmons in elemental metals
Dario A. Leon, Claudia Cardoso and Kristian Berland
The spectral properties, momentum dispersion, and broadening of bulk plasmonic excitations of 26 elemental metals are studied from first principles calculations in the random-phase approximation. Spectral band structures are constructed from the resulting momentum- and frequency-dependent inverse dielectric function. We develop an effective analytical representation of the main collective excitations in the dielectric response, extending our earlier model based on multipole-Padé approximants (MPAs) to incorporate both momentum and frequency dependence [MPA($\q$)]. With this representation, we identify plasmonic quasiparticle dispersions exhibiting complex features, including non-
parabolic energy and intensity dispersions, discontinuities due to anisotropy, and overlapping effects that lead to band crossings and anti-crossings. Comparing with available experimental data, mainly in the optical limit, we find good agreement with the computed spectra. The results for elemental metals and their effective MPA($\q$) representation establish a reference point that can guide both fundamental studies and practical applications in plasmonics and spectroscopy.
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Optics
Advanced mirror shapes for mode enhancement in plano-concave cavities
William James Hughes and Peter Horak
Optical cavities are frequently used in
quantum technologies to enhance light matter interactions, with applications including single
photon generation and
entanglement of distant emitters. The Fabry-Pérot resonator is a popular choice for its high optical access and large emitter-mirror separation. A typical configuration, particularly for emitters that should not be placed close to the mirror surface like trapped ions and Rydberg atoms, features two spherical mirrors placed around a central emitter, but this arrangement can put demanding requirements on the mirror
alignment. In contrast, plano-concave cavities are tolerant to mirror misalignment and only require the manufacture of one curved mirror, but have limited ability to focus light in the centre of the cavity. Here we show how mirror shaping can overcome this limitation of plano-concave cavities while preserving the key advantages. We demonstrate through numerical simulations that simple mirror shaping can increase coupling between a plano-concave cavity and a central emitter by an order of magnitude, even rivalling misalignment-sensitive concave-concave counterparts for achievable interaction strength. We use these observations to establish the conditions under which plano-concave cavities with shaped mirrors could improve the performance and practicality of emitter-cavity systems.
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Physics and Society · Cross-listed from cs.SI
Machines in the Crowd? Measuring the Footprint of Machine-Generated Text on Reddit
Lucio La Cava, Luca Maria Aiello and Andrea Tagarelli
Generative Artificial Intelligence is reshaping online communication by enabling large-scale production of Machine-Generated Text (MGT) at low cost. While its presence is rapidly growing across the Web, little is known about how MGT integrates into social media environments. In this paper, we present the first large-scale characterization of MGT on Reddit. Using a state-of-the-art statistical method for detection of MGT, we analyze over two years of activity (2022-2024) across 51 subreddits representative of Reddit's main community types such as information seeking, social support, and discussion. We study the concentration of MGT across communities and over time, and compared MGT to human-authored text in terms of social signals it expresses and engagement it receives. Our very conservative estimate of MGT prevalence indicates that synthetic text is marginally present on Reddit, but it can reach peaks of up to 9% in some communities in some months. MGT is unevenly distributed across communities, more prevalent in subreddits focused on technical knowledge and social support, and often concentrated in the activity of a small fraction of users. MGT also conveys distinct social signals of warmth and status giving typical of
language of AI assistants. Despite these stylistic differences, MGT achieves engagement levels comparable than human-authored content and in a few cases even higher, suggesting that AI-generated text is becoming an organic component of online social discourse. This work offers the first perspective on the MGT footprint on Reddit, paving the way for new investigations involving platform governance, detection strategies, and community dynamics.
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Accelerator Physics
Sextupole reduction via chaos suppression at the National Synchrotron Light Source II
Yongjun Li, Minghao Song, Yoshiteru Hidaka et al. (+2 more)
We revisit the nonlinear
lattice design approach for the National Synchrotron Light Source II (NSLS-II) storage ring. By suppressing chaos, we identify alternative sextupole configurations to the original design, which relied on the conventional strategy of simultaneously minimizing Resonance Driving Terms (RDT) and Amplitude-Dependent Detuning (ADD). These alternatives achieve comparable performance while requiring fewer sextupoles. A detailed comparison of two representative solutions is presented and supported by experimental validation. Our results show that the dynamic aperture correlates more strongly with global chaos than with individual RDTs, and that the importance of minimizing ADD may have been overstated in earlier design strategies.
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All authors Yongjun Li, Minghao Song, Yoshiteru Hidaka, Victor Smaluk, Timur Shaftan
Fluid Dynamics
On internal wave whispering gallery modes in channels and critical-slope wave attractors
Nimrod Bratspiess, Eyal Heifetz and Leo R. M. Maas
Internal waves are an important feature of stratified fluids, both in oceanic and lake basins and in other settings. Many works have been published on the generic feature of internal wave trapping onto planar wave attractors and super-attractors in 2&3D and the exceptional class of standing global internal wave modes. However, most of these works did not deal with waves that escape trapping. By using continuous
symmetries we analytically prove the existence of internal wave Whispering Gallery Modes (WGMs), internal waves that propagate continuously without getting trapped by attractors. WGMs neutral stability with respect to different perturbations enable whispering gallery beams, a continuum of rays propagating together coherently. The systems' continuous
symmetries also enable projection onto 2D planes that yield effective 2D billiards preserving the original dynamics. By examining rays deviating from these WGMs in
parabolic channels we discover a new type of wave attractor which is located along the channel instead of across it as in previous works. This new wave attractor leads to a re-understanding of WGMs as sitting at the border between the two basins of attraction. Finally, both critical-slope wave attractors and whispering gallery beams are used to propose explanations for along-channel energy fluxes in submarine canyons and
tidal energy intensification near critical slopes.
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Optics
A Langevin Model-Based Magneto-Optic Response SuperParamagnetic Nanoparticles Recorded with a Michelson Interferometer Setup
Syed Azer Reza and Maarij Syed
In this paper, we provide expressions for the detected optical irradiance for magneto-optic characterization of superparamagnetic nanoparticles (SPNs) in solution imparting Faraday rotation (FR) to an optical beam passing through the sample solution. For our analysis, we assume a Langevin model for SPN samples and show the presence of odd and even harmonics for SPN samples characterized with a Michelson interferometer. This optical geometry is potentially useful in understanding nonlinear SPN FR behavior as a result of particle aggregation-based scattering effects.
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Fluid Dynamics
Subcritical transition and multistability in liquid metal magnetoconvection with sidewalls
Matthew McCormack, Andrei Teimurazov, Olga Shishkina et al. (+1 more)
The motionless conducting state of
liquid metal convection with an applied vertical
magnetic field confined in a vessel with insulating side walls becomes linearly unstable to wall modes through a supercritical pitchfork bifurcation. Nevertheless, we show that the transition proceeds subcritically, with stable finite-amplitude solutions with different
symmetries existing at parameter values beneath this linear stability threshold. Under increased thermal driving, the branch born from the linear instability becomes unstable and solutions are attracted to the most subcritical branch, which follows a quasiperiodic route to chaos. Thus, we show that the transition to
turbulence is controlled by this subcritical branch and hence, turbulent solutions have no connection to the initial linear instability. This is further quantified by observing that the subcritical
equilibrium solution sets the spatial
symmetry of the turbulent mean flow and thus, organises large-scale structures in the turbulent regime.
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All authors Matthew McCormack, Andrei Teimurazov, Olga Shishkina, Moritz Linkmann