Chemical Physics · Cross-listed from cond-mat.stat-mech
Maximum entropy distributions of wavefunctions at thermal equilibrium
Jacob T. Willson, Henrik J. Heelweg and Adam P. Willard
Statistical mechanics reveals that the properties of a macroscopic physical system emerge as an average over an ensemble of statistically independent microscopic subsystems, each occupying a specific microstate. In the study of
quantum systems, these microstates can be chosen to correspond to the pure state wavefunctions of individual
quantum systems. However, the physical principles that govern the distribution of a pure state wavefunction ensemble, even under conditions of thermal
equilibrium, are not well established. For instance, the canonical Boltzmann distribution cannot be applied to wavefunctions because they lack a definite energy. In this manuscript, we present a maximum
entropy principle for the
quantum wavefunction ensemble at thermal
equilibrium, the so-called Scrooge ensemble. We highlight that a constraint on the energy expectation value, or even the shape of the associated eigenstate distribution, fails to yield a valid
equilibrium state. We find that in addition to these constraints, one must also constrain the measurement
entropy to be equal to the Rényi divergence of the ensemble with respect to the Gibbs state, indicating that the Rényi divergence may have uninvestigated physical importance to thermal
equilibrium in
quantum systems.
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Atmospheric and Oceanic Physics · Cross-listed from stat.CO
Adaptive Nonlinear Data Assimilation through P-Spline Triangular Measure Transport
Berent Å. S. Lunde and Maximilian Ramgraber
Non-Gaussian statistics are a challenge for data assimilation. Linear methods oversimplify the problem, yet fully nonlinear methods are often too expensive to use in practice. The best solution usually lies between these extremes. Triangular measure transport offers a flexible framework for nonlinear data assimilation. Its success, however, depends on how the map is parametrized. Too much flexibility leads to overfitting; too little misses important structure. To address this balance, we develop an adaptation
algorithm that selects a parsimonious parametrization automatically. Our method uses P-spline basis functions and an information criterion as a continuous measure of model complexity. This formulation enables gradient descent and allows efficient, fine-scale adaptation in high-dimensional settings. The resulting
algorithm requires no hyperparameter tuning. It adjusts the transport map to the appropriate level of complexity based on the system statistics and ensemble size. We demonstrate its performance in nonlinear, non-Gaussian problems, including a high-dimensional distributed groundwater model.
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Optics · Cross-listed from cond-mat.quant-gas
Anomalous Topological Bloch Oscillations under Non-Abelian Gauge Fields
Chunyan Li, Ce Shang and Boris A. Malomed
Topological Bloch oscillations are a hallmark of
quantum transport phenomenon in which wavepackets undergo oscillatory motion driven by the interplay between an external force and topological edge states and serve as a powerful dynamical probe for the
geometric properties of topological bands.
Spin-orbit coupling (SOC) has also emerged as a crucial ingredient for manipulating
quantum states in materials, with the corresponding gauge fields arising from the Rashba and Dresselhaus interactions. In this work, we investigate the propagation of spinor wavepackets in a honeycomb Zeeman
lattice governed by the Gross-Pitaevskii equation. By tuning the relative strengths of Rashba and Dresselhaus SOC, we engineer a non-Abelian gauge field that drives anomalous topological Bloch oscillations (ATBOs). Unlike conventional topological Bloch oscillation (TBOs), these ATBOs exhibit asymmetric motion, including a freezing effect in one half of the oscillation cycle, which can be tuned by the SOC parameters and external forces. Our findings establish SOC-based non-Abelian gauge fields as a powerful mechanism controlling topological
quantum dynamics, with implications for spintronic devices and
quantum data processing.
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Optics · Cross-listed from quant-ph
Exact Law of Quantum Reversibility under Gaussian Pure Loss
Ammar Fayad
Classical reverse
diffusion is generated by changing the drift at fixed noise. We show that the
quantum version of this principle obeys an exact law with a sharp phase boundary. For Gaussian pure-loss dynamics – the canonical model of continuous-variable decoherence in optical attenuation channels, squeezed-light interferometric sensing, and superconducting bosonic architectures – complete positivity, the requirement that the dynamics remain physical even for systems entangled with an ancilla, creates an exact phase boundary at which the minimum reverse cost vanishes, fixes the reverse-noise budget on both sides, and makes pure nonclassical targets dynamically singular. The minimum reverse cost vanishes exactly at a critical squeezing-to-thermal ratio and is strictly positive away from it, with a sharp asymmetry: below the boundary, standard reverse prescriptions such as the fixed-
diffusion Bayes reverse remain feasible at mild cost; above it, these prescriptions become infeasible, the covariance-aligned generator remains CP-feasible and uniquely optimal, and the cost can be severe. The optimal reverse noise is locked to the state's own fluctuation geometry and simultaneously minimizes the
geometric, metrological, and thermodynamic price of reversal. For multimode trajectories, the exact cost is additive in a canonical set of mode-resolved data, and a globally continuous protocol attains this optimum on every mixed-state interval. If a pure nonclassical endpoint is included, the same pointwise law holds for every $t>0$, but the optimum diverges as $2/t$: exact reversal of a pure
quantum state is dynamically unattainable. These results establish an exact law of
quantum reversibility in the canonical pure-loss setting and provide a sharp
benchmark for broader theories of
quantum reverse
diffusion.
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Plasma Physics
Generation of Whistler Waves by Reflected Electrons and Their Self-Confinement at Quasi-Perpendicular Shocks
Ruolin Wang and Takanobu Amano
We investigate the mechanism of whistler-mode wave generation by shock-reflected electrons at quasi-perpendicular collisionless shocks. By employing Liouville mapping to construct the electron velocity distribution function in the shock and performing linear instability analysis, we explore whistler wave generation by the mirror-reflected electrons near the upstream edge of the shock transition layer. We find that the reflected electrons can excite two distinct instabilities with different propagation directions when both the upstream electron beta $\beta_e$ and Alfven Mach number in the de Hoffmann-Teller frame $M_A/\cos\theta_{bn}$ are sufficiently large, where $M_A$ is \Alfven Mach number and $\theta_{bn}$ is the angle between the upstream
magnetic field and the shock normal. In the parameter regime of Earth's bow shock, the instability threshold condition is roughly given by $M_A/\cos\theta_{bn}\gtrsim50$. Since such shocks are super-critical with respect to the whistler critical Mach number, the generated waves cannot propagate upstream and will accumulate in the transition layer. Furthermore, we find that the pitch-angle scattering by the generated waves may trigger secondary instabilities on the same branch. We suggest that the sequence of instabilities likely happening within the shock transition layer can efficiently scatter the reflected electrons over a broad range of pitch angles. Consequently, the reflected electrons may be confined within the shock by the waves generated by themselves. The self-confinement provides the necessary ingredient of
stochastic shock drift acceleration, which then offers a plausible mechanism for the electron injection into diffusive shock acceleration.
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Fluid Dynamics
Acoustic radiation of thermodiffusively unstable turbulent lean premixed hydrogen-air flames
Francesco G. Schiavone, Guillaume Daviller and Davide Laera
The impact of thermodiffusive effects on combustion noise in turbulent premixed slot jet flames is investigated using Direct Numerical Simulations. Two thermodiffusively unstable lean hydrogen-air flames are compared with a thermodiffusively stable stoichiometric methane-air flame with comparable laminar properties and same
turbulence intensity. The hydrogen cases differ in bulk velocity, chosen to match either the turbulent flame brush length or the bulk velocity of the methane case. Thermodiffusive effects are found to strongly alter both the heat release rate fluctuations, which dominate the far-field acoustic radiation, and the flame surface dynamics. A theoretical framework extending the classical flamelet theory to thermodiffusively unstable flames is proposed and validated, relating the flame-generated sound to the time derivative of the flame surface area and to the stretch factor $I_0$. The analysis identifies flame stretch as a key mechanism promoting noise radiation in thermodiffusively unstable flames. Spectral analyses further show that hydrogen flames exhibit stronger low-frequency heat release rate fluctuations and reduced high-frequency content relative to the methane flame. This is shown to be related to the coupled action of
turbulence and thermodiffusive instabilities, which enhance large-scale flame motions while attenuating small-scale flame annihilation events. Consequently, hydrogen flames radiate more strongly at low frequencies, near the acoustic peak, and exhibit a steeper high-frequency spectral roll-off. Finally, Spectral Proper Orthogonal Decomposition reveals that hydrogen non-equidiffusion intensifies shear layer instabilities between combustion products and ambient air. These results indicate that thermodiffusive effects influence both direct and indirect combustion noise generation mechanisms in hydrogen flames.
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Instrumentation and Detectors
A Sub-electron-noise Skipper-CCD Readout ASIC with Improved Channel-to-channel Isolation and an Integrated Cryogenic Voltage Reference
Fabricio Alcalde Bessia, Claudio Chavez, Troy England et al. (+6 more)
The MIDNA application specific integrated
circuits (ASICs) are a series of skipper-CCD readout chips fabricated in a 65 nm low-power CMOS process that implement a correlated double sampling signal processing chain based on dual-slope integrators. They are capable of working from room to cryogenic temperatures, down to 84 K. The present iteration of the ASIC has been fabricated including several design updates and the addition of an on-chip voltage reference, resulting in improved performance. This work presents the main vulnerabilities solved, the changes carried out, and the resulting performance benefits. Measurements with a skipper-CCD and the ASIC at 140 K showed that the single-electron resolution can be reached by averaging the measured charge in the analog domain using the analog pile-up technique with a readout noise as low as 0.11 erms of equivalent charge for 1200 samples. The channel-to-channel crosstalk was also characterized showing values better than -62 dB.
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All authors Fabricio Alcalde Bessia, Claudio Chavez, Troy England, Hongzhi Sun, Andrew Lathrop, Davide Braga, Miguel Sofo-Haro, Juan Estrada, Farah Fahim
Medical Physics
Machine learning reconstruction of digit bone Raman spectra enables noninvasive transcutaneous detection of systemic osteoporosis
Mohammad Hosseini, Sadia Afrin, Anthony Yosick et al. (+2 more)
Osteoporosis, a major global epidemic, often goes undetected until a fracture occurs, largely due to poor access to screening using gold standard methods, such as dual-energy X-ray absorptiometry (DXA). As a potential nonionizing radiation alternative, we present a transcutaneous spatially offset Raman spectroscopy (SORS) approach combined with machine learning (ML) to recover bone spectra through overlying soft tissue and extract diagnostic information. In a human cadaveric study spanning normal, osteopenic, and osteoporotic donors, we acquired paired Raman measurements from transcutaneous fingers at multiple spatial offsets (0, 3, and 6 mm) and from the corresponding exposed finger bones. Using this paired
dataset, supervised machine-learning models were trained to reconstruct exposed-bone Raman spectra from transcutaneous measurements, enabling direct recovery of bone biochemical signatures from transcutaneous tissue. The ML predicted bone spectra preserved physiologically meaningful Raman features and demonstrated statistically significant differences between normal and osteoporotic groups across four key Raman-derived metrics (p < 0.05), representing, to our knowledge, the first demonstration of transcutaneous Raman discrimination between clinically established bone-health categories in a human cadaveric study. The ML-predicted spectra further correlated with distal-radius DXA T-scores (r = 0.73, RMSECV = 1.4), approaching the performance achieved using exposed-bone measurements (r = 0.9, RMSECV = 0.8). Finally, preliminary in vivo measurements from two volunteers revealed clear bone-related transcutaneous spectral features consistent with cadaveric data, supporting translational feasibility. Together, these results establish a foundation for nonionizing radiation, transcutaneous Raman assessment of bone health using supervised spectral extraction from accessible measurement sites
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All authors Mohammad Hosseini, Sadia Afrin, Anthony Yosick, Hani Awad, Andrew J. Berger
Instrumentation and Detectors · Cross-listed from quant-ph
XCOM: Full Mesh Network Synchronization and Low-Latency Communication for QICK (Quantum Instrumentation Control Kit)
Diego Martin, Luis H. Arnaldi, Kenneth Treptow et al. (+5 more)
Quantum computing experiments and testbeds with large
qubit counts have until recently been a privilege afforded only to large companies or
quantum technologies where scaling to hundreds or thousands of
qubits does not require a substantial increase in
quantum control hardware (neutral atoms, trapped ions, or
spin defects). Superconducting and
spin qubit testbeds critically depend on scaling their control systems beyond what a single electronics board can provide. Multi-board control systems combining RF, fast DC control, bias, and readout require precise synchronization and communication across many hardware and firmware components. To address this, we present XCOM, a network that synchronizes QICK boards and the absolute clocks governing
quantum program execution to within 100 ps, free of drift and loss of lock. XCOM also provides deterministic, all-to-all simultaneous data communication with latency below 185 ns. Like QICK itself, XCOM is compatible with a broad range of
qubit technologies and is designed to scale to large systems.
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All authors Diego Martin, Luis H. Arnaldi, Kenneth Treptow, Neal Wilcer, Sho Uemura, Sara Sussman, David I Schuster, Gustavo Cancelo
Optics
Temporal dynamics of Levy flights of photons in a three-dimensional geometry for hot vapor
Ricardo V. M. de Almeida Filho, Joao C. de Aquino Carvalho, Thierry Passerat de Silans et al. (+2 more)
Multiple scattering of light by resonant vapor is characterized by Lévy-type superdiffusion with a step size distribution $P(x) \propto 1/x^{1+\alpha}$, with $0 < \alpha < 2$. The Lévy parameter $\alpha$ was measured from $P(x)$, steady fluorescence, frequency-dependent fluorescence and time-resolved transmission, where the latter was observed for quenched disordered media, not yet for annealed disordered media. Here we report first measurements of this quantity from time-resolved fluorescence for
photons that are forward diffused from light pulses exciting a hot rubidium vapor, a medium characterized by annealed disorder, where correlations between the
photon steps are absent. Also, the vapor is contained in a three-dimensional geometry, a turned cylinder with respect of the incident
photon direction. We show experimentally that $\alpha$ can be extracted from this setup, and the results are consistent with those given by the steady frequency-dependent forward fluorescence. Theoretical simulations are consistent with these results. Also, our simulations show the validity of the one-dimensional theories for our actual geometry and other three-dimensional ones, as thin and thick disks, and a measurement of the number of steps that the
photon performed before leaving the medium.
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All authors Ricardo V. M. de Almeida Filho, Joao C. de Aquino Carvalho, Thierry Passerat de Silans, Marcio H. G. de Miranda, Michelle O. Araújo
Biological Physics
Resolving Scale-Dependent Diffusivity in the Brain Extracellular Space
Quentin Gresil, Ivo Calaresu, Finn L. Sebastian et al. (+4 more)
Transport through the
brain extracellular space has traditionally been summarized by effective
diffusion coefficients measured over specific observation ranges. Whether local mobility remains predictive as the same molecule explores larger distances remains unresolved. Here, we track individual ultrashort carbon nanotubes in three dimensions within living hippocampal tissue, following their motion from nanometre to micrometre scales. Using freely diffusing nanotubes in water as an experimental reference, we resolve trajectory-specific crossover lengths beyond which instantaneous diffusivity decreases, with slice-level medians of 0.67 $\mu$m in the pyramidal layer and 0.52 $\mu$m in the radiatum. The pyramidal layer combines higher short-time diffusivity with an approximately twofold larger post-crossover restriction exponent than the radiatum ($\vartheta$ = 0.77 versus 0.38). This decoupling of local mobility from larger-scale exploration is incompatible with a scale-independent rescaling of transport, showing that effective extracellular diffusivity must be interpreted relative to the scale of exploration.
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All authors Quentin Gresil, Ivo Calaresu, Finn L. Sebastian, Benjamin Flavel, Jana Zaumseil, Laurent Groc, Laurent Cognet
Plasma Physics
J. Griff-McMahon, V. Valenzuela-Villaseca, C. A. Walsh et al. (+9 more)
Self-generated
magnetic fields are commonly produced in high-power
laser-
plasma interactions. These fields can inhibit
plasma heat-flow which makes them important in inertial fusion and controlled laboratory astrophysics experiments. In this work, we characterize the time
evolution of self-generated
magnetic fields using multi-view
proton tomography at two timings. Tomographic reconstructions of the
magnetic field show a clear transition from fields located close to the target at early time to more extended coronal fields at later time. The tomographic inversion and mesh radiography also enable a direct measurement of the
magnetic-flux
evolution. Comparisons with extended-MHD simulations show only moderate agreement in field structure, but good agreement in
magnetic flux. This suggests that the field generation model is largely correct under these conditions, while the
magnetic transport model requires additional development to reproduce the observed field structure.
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All authors J. Griff-McMahon, V. Valenzuela-Villaseca, C. A. Walsh, S. Malko, B. McCluskey, K. Lezhnin, H. Landsberger, L. Berzak Hopkins, G. Fiksel, M. J. Rosenberg, D. B. Schaeffer, W. Fox
Geophysics
Improving moment tensor solutions under Earth structure uncertainty with simulation-based inference
A. A. Saoulis, T.-S. Pham and A. M. G. Ferreira
Bayesian inference represents a principled way to incorporate Earth structure uncertainty in full-waveform moment tensor inversions, but traditional approaches generally require significant approximations that risk biasing the resulting solutions. We introduce a robust method for handling theory errors using simulation-based inference (SBI), a machine learning approach that empirically models their impact on the observations. This framework retains the rigour of
Bayesian inference while avoiding restrictive assumptions about the functional form of the uncertainties. We begin by demonstrating that the common Gaussian parametrisation of theory errors breaks down under minor ($1-3 \%$) 1-D Earth model uncertainty. To address this issue, we develop two formalisms for utilising SBI to improve the quality of the moment tensor solutions: one using physics-based insights into the theory errors, and another utilising an end-to-end deep learning
algorithm. We then compare the results of moment tensor inversion with the standard Gaussian approach and SBI, and demonstrate that Gaussian assumptions induce bias and significantly under-report moment tensor uncertainties. We also show that these effects are particularly problematic when inverting short period data and for shallow, isotropic events. On the other hand, SBI produces more reliable, better calibrated posteriors of the earthquake source mechanism. Finally, we successfully apply our methodology to two well studied moderate magnitude earthquakes: one from the 1997 Long Valley Caldera volcanic earthquake sequence, and the 2020 Zagreb earthquake.
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Applied Physics · Cross-listed from quant-ph
Quantum and classical approaches to the optimization of highway platooning: the two-vehicle matching problem
Chinonso Onah, Agneev Guin, Carsten Othmer et al. (+2 more)
Aerodynamic drag reduction on highways through vehicle platooning is a well-known concept, but it has not yet seen systematic uptake, arguably because of significant technological and legislative obstacles. As a low-tech entry point to real multi-vehicle platooning, "Windbreaking-as-a-Service" (WaaS) was introduced recently. Here we use a QUBO formulation to study classical metaheuristics such as simulated annealing and tabu search, together with emerging
quantum heuristics including
quantum annealing and variants of the
Quantum Approximate Optimization
Algorithm (QAOA). These heuristic solvers do not guarantee optimality, but they traverse the same higher-order landscape using
polynomial memory. They can also be parallelized aggressively, and efficient classical post-processing can be used in hybrid workflows to return only valid schedules. This paper therefore positions QUBO as a common
language that allows heterogeneous classical,
quantum, and hybrid solvers to address the optimization of highway platooning.
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All authors Chinonso Onah, Agneev Guin, Carsten Othmer, J. A. Montañez-Barrera, Kristel Michielsen
Fluid Dynamics
Geometric Dynamics of Turbulence: A Minimal Oscillator Structure from Non-local Closure
Alejandro Sevilla
Turbulence remains one of the central open problems in classical physics, largely due to the absence of a closed dynamical description of the Reynolds stress. Existing approaches typically rely either on local constitutive assumptions or on high-dimensional statistical representations, without identifying a minimal set of dynamical variables governing the cascade response. Here we show that the non-local stress response implied by the Navier-Stokes equations admits a systematic reduction onto a low-dimensional anisotropic sector of the turbulent cascade. This reduction leads to a minimal dynamical system with the structure of a damped oscillator, arising from the coupling between the leading angular mode and its nonlinear transfer to higher-order sectors. Within this framework, classical turbulent behaviors – including inertial-range scaling, shear-driven transport, and wall-bounded logarithmic profiles – emerge as different realizations of the same underlying dynamical structure. Universal quantities such as the Kolmogorov constant and the von Kármán constant appear as leading-order consequences of internal consistency conditions applied across homogeneous and shear-driven regimes. These results suggest that
turbulence admits a minimal dynamical backbone governed by non-local cascade response, providing a unified perspective that connects spectral transfer, anisotropy, and mean-flow interaction within a single reduced framework.
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Fluid Dynamics
Two-Color LIF investigation of mixing during droplet impact onto a thin liquid film
Hatim Ennayar and Jeanette Hussong
A two-color
laser-induced fluorescence (2C-LIF) technique is presented for investigating droplet impact on thin
liquid films, enabling simultaneous, spatially and temporally resolved measurements of film thickness and scalar concentration. The method is applied to water droplets impacting thin
liquid films over a range of Reynolds numbers, Weber numbers and dimensionless film thicknesses, providing direct access to early-time mixing processes during impact. To quantify scalar transport within the
liquid film, the reconstructed concentration fields are evaluated using a coefficient-of-variaton (CV) approach, providing a quantitative measure of mixture homogeneity. This enables identification of the transition from inertia-dominated convective transport to
diffusion-controlled mixing. Based on this analysis, an empirical correlation describing the
evolution of CV as a function of Reynolds number and film thickness is formulated. Finally, the applicability of the 2C-LIF method is demonstrated for binary ethanol-water films, where additional transport mechanisms influence and modify the mixing dynamics.
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Fluid Dynamics
Scale by scale analysis of magnetoconvection with uniform wall-normal and wall-parallel magnetic fields at low magnetic Reynolds number
Jake Ineson, Aleksander Dubas and Alex Skillen
Rayleigh-Bénard convection under an imposed inductionless
magnetic field is analysed statistically from the perspective of single-point and multi-scale energy budgets. The data is obtained from direct numerical simulations with a Rayleigh number of $10^6$, a Prandtl number of $1$ and Hartmann numbers of $0$, $20$, $40$ and $80$. Wall-parallel and wall-normal
magnetic fields are considered as two separate cases. The initial analysis focuses qualitatively on the influence of the
magnetic field upon the coherent structures. A central contribution of this work is the interpretation of these structural modifications through magnetohydrodynamically modified turbulent kinetic energy budgets. For example, in the wall-normal case, the thinning of the thermal plumes can be attributed to the damping of the pressure-
diffusion mechanisms due to the Lorentz dissipation. In the wall-parallel configuration, Joule dissipation induces a pressure-strain redistribution mechanism that preferentially transfers kinetic energy from the wall-normal velocity component to the field-perpendicular, wall-parallel velocity component but less so to the field-parallel velocity component. This description is then extended to scale-space by considering budgets relating second- and third-order structure functions. Here, the anisotropy is accounted for by analysing directional structure functions. Despite the anisotropy, the Lorentz force appears as an isotropic sink damping intermediate and large scales of motion. The result of this is a lack of transfer between scales of motion and hence a flow with suppressed small-scale
turbulence. These results establish a link between qualitative observations and long-term energy balances, providing new insight into magnetoconvective
turbulence and informing future modelling and theoretical approaches to such flows.
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Chemical Physics
Data-driven construction of machine-learning-based interatomic potentials for gas-surface scattering dynamics: the case of NO on graphite
Samuel Del Fré, Gilberto A. Alou Angulo, Maurice Monnerville et al. (+1 more)
Accurate atomistic simulations of gas-surface scattering require potential energy surfaces that remain reliable over broad configurational and energetic ranges while retaining the efficiency needed for extensive trajectory sampling. Here, we develop a data-driven workflow for constructing a machine-learning interatomic potential (MLIP) tailored to gas-surface scattering dynamics, using nitric
oxide (NO) scattering from highly oriented pyrolytic graphite (HOPG) as a
benchmark system. Starting from an initial ab initio molecular dynamics (AIMD)
dataset, local atomic environments are described by SOAP descriptors and analyzed in a reduced feature space obtained through principal component analysis. Farthest point sampling is then used to build a compact training set, and the resulting Deep Potential model is refined through a query-by-committee active-learning strategy using additional configurations extracted from molecular dynamics simulations over extended ranges of incident energies and surface temperatures. The final MLIP reproduces reference energies and forces with high fidelity and enables large-scale molecular dynamics simulations of NO scattering from graphite at a computational cost far below that of AIMD. The simulations provide detailed insight into adsorption energetics, trapping versus direct scattering probabilities, translational energy loss, angular distributions, and rotational excitation. Overall, the results reproduce the main experimental trends and demonstrate that descriptor-guided sampling combined with active learning offers an efficient and transferable strategy for constructing MLIPs for gas-surface interactions.
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All authors Samuel Del Fré, Gilberto A. Alou Angulo, Maurice Monnerville, Alejandro Rivero Santamaría
Fluid Dynamics
A Novel Approach for Direct Measurement of the Stretch Factor in Laminar Premixed Hydrogen-Air Flames Affected by Thermodiffusive Instabilities
Marcel Marburger, Christoph Möller, Andrew MacFarlane et al. (+5 more)
This study introduces a novel experimental configuration using OH-PLIF imaging to directly determine the stretch factor ($I_0$) in laminar premixed hydrogen flames transitioning from a quasi-stable to a thermodiffusively unstable regime. A rod-anchored V-flame is stabilised in a laminar premixed reactant flow. Near the anchoring rod, the mildly strained flame remains quasi-stable, exhibiting a smooth surface and a well-defined inclination angle ($\theta_{\mathrm{s}}$) to the main flow. This stable branch is associated with a burning rate $S_{\mathrm{s}}$. Farther downstream, the flame abruptly transitions to a regime dominated by thermodiffusive (TD) instabilities, characterised by cellular structures and a wrinkled surface. The distance between this transition and the anchor decreases with increasing equivalence ratio. This TD-unstable branch exhibits a larger mean flame-surface angle ($\theta_{\mathrm{u}}$), enabling direct determination of the flame-speed increase, $S_{\mathrm{u}}/S_{\mathrm{s}}$. It is assumed that this ratio represents the normalised flame consumption speed, $S_{\mathrm{c}}/S_{\mathrm{L}}$. Determination of $I_0$ additionally requires the increase in flame-surface area caused by the thermodiffusive instabilities. Three complementary methods are therefore used to evaluate the surface area of the TD-unstable branch ($A$) relative to a smooth reference area ($A_0$), yielding consistent trends in $A/A_0$ over the investigated equivalence-ratio range. The resulting $I_0$ values, with the main uncertainty arising from $A$, decrease monotonically with increasing equivalence ratio, from about 1.1–1.3 at $\phi=0.35$ to 0.8–0.9 at $\phi=0.40$, consistent with theoretical predictions. Additional numerical simulations in a reduced two-dimensional representation reproduce the same transition behaviour and yield qualitatively consistent results.
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All authors Marcel Marburger, Christoph Möller, Andrew MacFarlane, Max Schneider, Benjamin Traut, Christian Hasse, Andrea Gruber, Andreas Dreizler
Fluid Dynamics
Characterization of coherent flow structures in brain ventricles
Halvor Herlyng and Shawn C. Shadden
The dynamic flow of cerebrospinal fluid (CSF) in
brain ventricles exhibits flow features on several scales, both spatially and temporally. Most analysis of this complex flow and the accompanying transport has used instantaneous (Eulerian) flow variables. Such analysis makes understanding of unsteady transport challenging. Here, we analyze
brain ventricular CSF flow both in a Eulerian sense and from the Lagrangian perspective – a time-integrated view of the flow. With geometries generated from imaging data, we model CSF flow in adult human and embryonic zebrafish
brain ventricles. In the human
brain we model flow governed by cardiovascular pulsations, CSF secretion and motile cilia. The flow driven by cardiovascular pulsations is derived from a damped linear elastic model of
brain ventricle deformations, as a result of applying displacement boundary conditions derived from experimental data. In the zebrafish
brain we consider flow driven solely by motile cilia. The tissue and flow models are implemented and solved with finite element methods. We use the resulting velocity fields to compute finite-time Lyapunov exponent (FTLE) fields and use these fields to characterize Lagrangian coherent structures, which can be approximated by ridges in the FTLE fields. These coherent structures demonstrate prominent flow features in the
brain ventricles congruent with findings in experimental research. In the human
brain ventricles, we also investigate the role of inertia by comparing flow models governed by the Navier-Stokes and the Stokes equations. Comparisons show that solving the Stokes equations is adequate to compute integrated flow variables like stroke volumes, but that the Stokes approximation fails to resolve intricate features of flow and advective transport that are present in the solution to the Navier-Stokes equations, features that could be important to elucidating transport.
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Instrumentation and Detectors
A Low-Complexity 200 Mbit/s Full-Duplex Digital Link Over a Single Coaxial Cable for Laboratory Instrumentation
Michael Wiebusch
Modern full-duplex communication systems, such as Gigabit Ethernet, enable high data rates over challenging transmission media but require sophisticated circuitry and non-trivial digital interfaces. For laboratory instrumentation, the objective may instead be to achieve moderate-bandwidth full-duplex communication over short, well-controlled coaxial cables with minimal
circuit and interface complexity. We present a low-complexity bidirectional digital interconnect that enables simultaneous transmission and reception of baseband logic signals over a single coaxial cable. The
circuit combines a discrete passive resistive hybrid providing line termination and directional separation, a single logic gate as line driver, and a commercial differential receiver used as a comparator. No modulation,
transformer coupling, adaptive calibration, or active analog or digital echo cancellation is required. The design target is full-duplex operation at 200 MBit/s over 10 m of standard RG-178 cable. An analytical treatment of the hybrid network determines the system parameter that maximizes the differential signal amplitude at the receiver, while
circuit simulations predict the deterministic timing errors resulting from imperfect directional separation. Experimental measurements confirm the predicted deterministic jitter and show good agreement with the simulation results. For typical laboratory coaxial cables up to 10 m, the measured peak-to-peak edge timing error remains below 1.2 ns. A bidirectional transmission experiment with randomized data demonstrates a clearly open eye diagram. It was found that the transceiver inherently provides loopback functionality when the transmission line is left open. The proposed approach provides a simple, protocol-independent bidirectional physical link which may be useful in laboratory instrumentation where cable routing is constrained.
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Optics
Phonon-modulated Kerr nonlinearity in ultrathin 2H-MoTe2
Shaoxiang Sheng, Yang Luo, Chenyu Wang et al. (+8 more)
Controlling nonequilibrium responses in optically driven
quantum materials is essential for advancing applications in energy conversion, ultrafast electronics, and
quantum computation. Nonlinear optical spectroscopy serves as a powerful tool to investigate ultrafast electron and
phonon dynamics in these systems; however, conventional nonlinear approaches often require intense
laser pulses (> 10 GW/cm2) and typically encounter a strong background. Here, we introduce a phase-sensitive nonlinear spectroscopic technique that operates at low
laser powers (~ 10 kW/cm2, pulse energies ~ 10 pJ) and enables real-time monitoring and active control of coherent
phonons in a few-layer (three to five) thick 2H-MoTe2. Upon excitation with ultrashort (~ 10 fs) pump pulses, we achieve displacive excitation of coherent
phonons, which periodically modulate the Kerr nonlinearity of the material, leading to cross-phase modulation (XPM) of a delayed probe pulse. This phase modulation induces spectral broadening and oscillations in the center of mass (COM) of the probe spectrum in time, enabling the detection of subtle nonlinear optical responses in a background-free manner. The nonlinear response can be selectively amplified or attenuated by adjusting the strength of the pump pulse, which controls the distribution of photoexcited carriers in the electronic bands. By combining two-color nondegenerate pump-probe measurements and time-dependent density-functional theory (TDDFT) calculations, we directly resolve the coupled nonequilibrium electronic and
phonon dynamics. A dual-pump pulse scheme enables precise control of
phonon oscillations, allowing selective activation or suppression of specific
phonon modes and correspondingly the modulation of the Kerr nonlinearity.
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All authors Shaoxiang Sheng, Yang Luo, Chenyu Wang, Sayooj Sateesh, Yaxian Wang, Marko Burghard, Sayantan Patra, Bhumika Chauhan, Ashish Arora, Sheng Meng, Manish Garg
Data Analysis and Statistics
Taikan Suehara, Takahiro Kawahara, Tomohiko Tanabe et al. (+1 more)
We study the performance of the Particle
Transformer (ParT) for jet
flavor tagging using ILD full simulation events (1M jets) as well as fast simulation samples (10M and 1M jets). We perform 3-category ($b/c/d$), 6-category ($b/c/d/u/s/g$), and 11-category trainings (including
quark–antiquark separation), incorporating multivariate
hadron particle identification information from $dE/dx$ and time-of-flight. For $b$/$c$ tagging, we observe a factor of 5–10 improvement over previous BDT-based taggers, and we obtain reasonable performance for strange tagging and
quark/antiquark separation. The 10M-jet fast simulation study indicates that further gains are possible with higher training statistics.
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All authors Taikan Suehara, Takahiro Kawahara, Tomohiko Tanabe, Risako Tagami
Applied Physics · Cross-listed from quant-ph
Comparing optical-microwave conversion and all-microwave control schemes for a transmon qubit
Volodymyr Monarkha, Massimo Borrelli, Reza Hajitashakkori Kenari et al. (+13 more)
We report a comparative study on transmon
qubit control using (i) conventional attenuated coaxial microwave line and (ii) an optical control system using modulated
laser light delivered over telecommunications optical fiber to a photodiode located at the 1K stage of a dilution cryostat. During each experiment, we performed repeated measurements of the energy relaxation and coherence times of a transmon
qubit using one of the control signal delivery methods. Each measurement run spanned 20 hours of measurement time and from these
datasets we observe no measurable effect on coherence of the
qubit compared to random coherence fluctuations. Our results open up the possibility of large scale integration of the optical
qubit control system.
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All authors Volodymyr Monarkha, Massimo Borrelli, Reza Hajitashakkori Kenari, Mohammad Kobba, Eugenio Cataldo, Beer de Zoeten, Mahnaz Zarrinfar, Kamal Pandey, Abhinand Pusuluri, Filippo D. Michelacci, Eliot Jouan, Bennett Sprague, Simon Groeblacher, Thierry C. van Thiel, Robert Stockill, Russell E. Lake
Optics
Inverse design of a spatial demultiplexer for free-space optical communications: direct optimization over turbulence statistics
Nicolas Barré
Atmospheric
turbulence severely limits the coupling of received optical wavefronts into single-mode fibers in satellite-to-ground free-space optical links. Spatial demultiplexing receivers address this challenge by distributing the incoming field across a bundle of single-mode fibers whose outputs are recombined coherently, relaxing the requirements on wavefront correction. In this work, we investigate the design of such receivers from two complementary angles. We first compare the power coupling statistics achieved by several modal bases and show that the spatial support of the modes matters far more than the specific choice of basis, questioning the relevance of mode-selective approaches for this application. We then present the inverse design of a compact two-plane refractive system optimized directly over an ensemble of
turbulence realizations using
stochastic gradient descent, with no constraint imposed on the input modal decomposition. The optimized system significantly improves over direct coupling into the fiber bundle, approaches the performance of an ideal modal projection, and remains competitive across a broad range of
turbulence conditions.
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Instrumentation and Detectors
Spatial resolution improvement of PICOSEC Micromegas precise timing detectors
F.M. Brunbauer, R. Aleksan, Y. Angelis et al. (+47 more)
The combination of a Cherenkov radiator with a semi-transparent photocathode and a Micromegas based amplification stage allows PICOSEC Micromegas detectors to achieve a time resolution of better than 15ps. While tileable prototypes with 10x10 channels feature 1x1 cm^2 readout pads, finer readout granularity can be used to improve the spatial resolution. We report on the study of high readout granularity PICOSEC Micromegas prototypes which achieve around 0.5mm spatial resolution with 3.5mm large pads. No significant improvement was found when readout pad size was further reduced to 2.2mm. The timing resolution of the leading pad was found to be slightly degraded but remained better than 20ps for a medium granularity prototype. The achieved spatial resolution can enable PICOSEC Micromegas to be used as precise timing and moderate resolution tracking detector simultaneously.
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All authors F.M. Brunbauer, R. Aleksan, Y. Angelis, S. Aune, J. Bortfeldt, M. Brunoldi, J. Datta, D. Desforge, G. Fanourakis, D. Fiorina, K. J. Floethner, M. Gallinaro, F. Garcia, I. Giomataris, K. Gnanvo, Q. Huang, F.J. Iguaz, D. Janssens, A. Kallitsopoulou, I. Karakoulias, M. Kovacic, P. Legou, M. Lisowska, J. Liu, M. Lupberger, I. Maniatis, M. Micetic, H. Muller, E. Oliveri, T. Papaevangelou, M. Pomorski, L. Ropelewski, K. Salamon, D. Sampsonidis, L. Scharenberg, T. Schneider, E. Scorsone, L. Sohl, N. Shankman, M. van Stenis, Y. Tsipolitis, S.E. Tzamarias, A. Utrobicic, I. Vai, R. Veenhof, P. Vitulo, X. Wang, S. White, Z. Zhang, Y. Zhou
Plasma Physics
Quantum Kinetics of Fast-Electron Inelastic Collisions in Partially-Ionized Plasmas
Yeongsun Lee, Pavel Aleynikov and Jong-Kyu Park
Fast electrons in partially ionized
plasmas lose energy through inelastic collisions with bound electrons. While the mean energy loss is well described by stopping-power theory, fluctuations associated with discrete excitation and ionization events produce energy straggling and an additional longitudinal
diffusion in momentum space. We incorporate this effect into fast-electron kinetics through a derived Fokker-Planck operator whose coefficients are obtained from ab initio
quantum many-body simulations. We demonstrate that neglecting inelastic energy
diffusion in partially ionized D-Ar
plasmas can underestimate primary runaway-electron generation by several orders of magnitude.
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Applied Physics
Fueling Dynamics towards Tunable Liquid Metal Machine
Jingyi Li, Minghui Guo, Ju Wang et al. (+2 more)
Self-propelled
liquid metal-aluminum hybrid machines represent a promising class of autonomous motion systems capable of sustained movement without external power sources. While interactions between machines and their environment inevitably occur, the fundamental question of how spatial confinement affects the motion dynamics and the controllability of speed, direction, and lifetime of such
liquid metal machines (LMMs) remains underexplored. Understanding these confined dynamics is essential for practical applications. Here, we present a comprehensive investigation of the non-symmetrical fueling principle governing the direction-tuning effect in LMMs. By confining LMMs within one-dimensional semi-open channels, we thoroughly disclose their impact and turning dynamics with different end obstacles throughout their lifecycle, with particular focus on fuel region morphological
evolution, overall motion, and local flow characteristics after reaction times exceeding one hour. Utilizing ultra-high-speed imaging techniques, we systematically clarify how fuel region
evolution and end-obstacle interactions influence
symmetry-breaking mechanisms and reciprocating dynamics. Our findings reveal complex interactions between material properties, charge transfer processes, and fluid dynamics during end-turning processes, establishing a theoretical foundation for LMM driving dynamics. Beyond the theoretical mechanisms, we further demonstrate that LMM exhibits efficient heat and mass transfer capabilities, paving the way for applications in controlled transport systems and autonomous robotics.
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All authors Jingyi Li, Minghui Guo, Ju Wang, Xi Zhao, Jing Liu
Physics and Society · Cross-listed from eess.SY
Assessing performance tradeoffs in hierarchical organizations using a diffusive coupling model
Lorenzo Zino, Mengbin Ye and Brian D.O. Anderson
We study a continuous-time dynamical system of nodes diffusively coupled over a hierarchical network to examine the efficiency and performance tradeoffs that organizations, teams, and command and control units face while achieving coordination and sharing information across layers. Specifically, after defining a network structure that captures real-world features of hierarchical organizations, we use linear systems theory and perturbation theory to characterize the rate of convergence to a consensus state, and how effectively information can propagate through the network, depending on the breadth of the organization and the strength of inter-layer communication. Interestingly, our analytical insights highlight a fundamental performance tradeoff. Namely, networks that favor fast coordination will have decreased ability to share information that is generated in the lower layers of the organization and is to be passed up the hierarchy. Numerical results validate and extend our theoretical results.
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Fluid Dynamics
Streamwise periodic solver to simulate turbulent flow in finned channels with uniform isothermal walls
Nitish Anand, Praharsh Pai Raikar and Carlo De Servi
Assessment of the thermo-hydraulic performance of heat exchangers using computational fluid dynamics is a challenging task. The intricate geometries of a heat exchanger require a fine discretization of the flow passage, which consequently leads to high computational costs. A streamwise periodic flow model can significantly reduce this cost, particularly for heat exchangers featuring repeating structures. This manuscript presents the streamwise-periodic turbulent source terms for flows in channels with isothermal walls, along with the implementation of the corresponding periodic flow solver in the open-source CFD-Suite, SU2. The accuracy of the implemented solver was verified by comparing its predictions against those of a full fin array simulation for the test case of offset circular fins. The results show that the streamwise periodic flow solver accurately reproduces the solutions of the full array simulation under both laminar and turbulent flow conditions.
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