Chemical Physics · Cross-listed from cond-mat.soft
Colloidal shadows reveal hidden solute transport
Haoyu Liu, Zehao Chen and Amir A. Pahlavan
An object releasing a chemical into a surrounding flow leaves behind a plume that encodes the rate of release, but for most solutes, that plume is invisible. Classical transport theory describes this configuration through a self-similar concentration boundary layer whose structure has never been resolved experimentally in forced flow at low Reynolds number: a century of measurements at these conditions has returned integrated transfer rates rather than the field itself. Here we show that both the field and the information it carries are experimentally accessible. Around hydrogel posts photopatterned inside a microfluidic channel, a released solute drives suspended colloidal particles away by diffusiophoresis, i.e., their drift along chemical gradients, carving a particle-free “shadow” downstream. Using a fluorescent solute, we resolve the concentration field around the post and recover the classical self-similar structure of convective mass transfer. For an invisible surfactant, the width of the shadow, benchmarked against a directly imaged solute on the same platform, then serves as a proxy for the dimensionless rate of mass transfer from the post. Finally, comparing two orientations of a triangular post tests a classical prediction by Brenner: the local concentration fields rearrange, yet no orientation dependence of the integrated transfer rate is resolved. For solute–tracer pairs whose diffusiophoretic response is known, colloidal shadows thus turn ordinary tracer particles into quantitative reporters of chemical exchange that cannot be observed directly.
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Instrumentation and Detectors
Fast BIB simulation at a future Muon Collider with generative machine learning
Radha Mastandrea, Shiyu Peng, Benjamin Rosser et al. (+1 more)
Beam-induced background (BIB) from
muon decay products will be an overwhelming and unavoidable background at a future
Muon Collider. In order to develop robust event reconstruction
algorithms, we need large amounts of accurate BIB simulation to test on. BIB simulation is currently compute-limited: the simulated sample presently used for BIB overlay, which statistically represents approximately $10\%$ of a single unique event's worth of simulated BIB, requires on the order of $10^6$ HS23$\cdot$hours to generate and occupies approximately $100$ GB on disk. In this work, we develop the first machine learning models for fast BIB generation in tracking detectors. We consider two classes of architectures: a slower but higher-fidelity tabular
diffusion model, and a faster but lower fidelity circular spline flow model. We find that both classes of architectures produce BIB hits and tracks that closely resemble those of available full simulation hits and tracks, and that the machine learning models can produce BIB in over an order of magnitude less time than what is needed to produce full simulation BIB. We release the model weights with the paper so that the
Muon Collider community can use these fast BIB hits for future R&D.
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All authors Radha Mastandrea, Shiyu Peng, Benjamin Rosser, Matt LeBlanc
Classical Physics
Plasmonics at radio frequencies
Igor I. Smolyaninov, Quirino Balzano, John Mulholland et al. (+2 more)
We demonstrate that low loss
radio frequency plasmon-like surface electromagnetic waves may propagate along rough interfaces between air and highly conductive media, such as water or metal. Unlike the well-known Zenneck wave solutions, these surface waves have mode index larger than 1, so that their propagation properties are generally similar to the properties of surface plasmons in the visible frequency range. The wave impedance of these modes is derived, which demonstrates the need to use special plasmonic inducers or exciters for efficient generation of these novel surface electromagnetic modes. Propagation characteristics of these
radio frequency plasmons were explored both experimentally and theoretically in the cases of water-air and water-ice-air interfaces, and the two-dimensional character of this propagation has been revealed. Other important applications of
radio frequency plasmons were demonstrated, such as communication along metal infrastructure immersed in water, communication along a lake floor,
underwater plasmonic radar, as well as plasmonic communications underground and in the dense jungles.
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All authors Igor I. Smolyaninov, Quirino Balzano, John Mulholland, Viktor A. Podolskiy, Dendy Young
Space Physics · Cross-listed from astro-ph.IM
Continuous Learning of Gravity Field Irregularities Around Small Bodies via Neural Hamiltonian ODEs
Giacomo Acciarini and Dario Izzo
We propose to learn the unknown dynamics in the proximity of a small body directly from tracking data, representing them as a feed-forward neural network embedded in the system
Hamiltonian. The equations of motion form a Neural
Hamiltonian Ordinary Differential Equation, whose variational equations provide exact training gradients: estimation uses position and velocity arcs at realistic noise levels, without acceleration or potential labels, and a continual learning approach warm-starts the network as new data are acquired. The known part of the
Hamiltonian carries whatever is available, from the central term and
spin state to the constant-density model of the imaged shape. We assess the method against a normalized spherical harmonics expansion estimated from identical arcs through the same machinery, on scenarios built on the shapes of Itokawa, 67P, Bennu and Eros. The network remains usable inside the Brillouin sphere: it plans ballistic descents at Itokawa to \SI{4.6}{m} median touchdown error from tracking alone, against 5.1–\SI{48.9}{m} for harmonics of degree 4–12, and to \SI{0.9}{m} with the imaged shape as prior, a configuration that also recovers localised density anomalies invisible to any harmonics degree. The two representations are complementary, and we discuss their combined use across the phases of a small-body mission.
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Applied Physics · Cross-listed from cs.LG
Toward Reliable Railway-Bogie Response Prediction Using Multifidelity TDNN and Physics-Informed Residual Learning
Gyeolhee Lee, Moosun Kim, Taewook Kwon et al. (+3 more)
Railway engineers need simulation models that predict vehicle responses across operating scenarios that cannot be tested exhaustively. Agreement with representative measurements provides essential evidence, but calibration at a limited set of conditions does not guarantee accuracy elsewhere. We present a multifidelity railway-bogie response-correction method that treats multibody simulation histories as low-fidelity information and roller-rig measurements as high-fidelity evidence. This method combines an experiment-anchored fidelity assignment with physics-informed discrepancy learning for multichannel bogie-response histories. A time-delay neural network (TDNN) represents the condition-dependent simulation trend, and development-fitted amplitude
alignment defines the low-fidelity baseline. A residual-correction network then models the reproducible response component not explained by this baseline and adds it to the baseline. An effective dynamic-balance equation constrains the learned discrepancy by representing differences in inertia, damping, stiffness, and external forcing between the simulated and physical systems. The training objective combines this constraint with residual matching, temporal smoothness, and a combined channel-2 acceleration loss selected using displacement-acceleration consistency evidence. For the evaluated reconstruction case, the corrected response gives a mean coefficient of determination of 0.8197, a mean normalized root-mean-square error (NRMSE) of 4.6055 %, and a mean normalized mean absolute error (NMAE) of 1.9297 %. These results provide initial evidence of accurate response prediction at the held-out 385 km/h condition.
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All authors Gyeolhee Lee, Moosun Kim, Taewook Kwon, Jaehun Kim, Changsung Jeon, Dongjin Lee
Atomic Physics
SI-Traceable Calibration and Performance Benchmarking of a Terahertz Photomixer Transmitter-Receiver System Using a Rydberg Atomic Sensor
Alisher Duspayev, Kaitlin R. Moore, Georg Raithel et al. (+1 more)
Accurate calibration of electromagnetic field strength in the terahertz (THz) frequency regime remains challenging due to the limited availability of SI-traceable field sensors. Here we demonstrate SI-traceable calibration and performance benchmarking of a commercial photomixer-based THz transmitter-receiver system operating near 204 GHz using Rydberg electric-field sensing in a thermal atomic vapor. The THz electric field is extracted from the Autler-Townes (AT) effect of the cesium $17D_{5/2}\rightarrow18P_{3/2}$ Rydberg transition. We measure the strength of AT-split lines as a function of THz detuning from resonance to find the on-resonant Rabi frequency, which, together with atomic transition dipole moments and fundamental constants, yields the THz electric field. The atomically measured field calibrates the photomixer transmitter field and power, while simultaneous measurements with a commercial InGaAs photomixer receiver calibrate the receiver's current-to-field responsivity and convert its current-noise floor into an absolute noise-equivalent THz electric-field sensitivity. Our study demonstrates that Rydberg atomic sensors provide a practical method for SI-traceable calibration and benchmarking of THz transmitter and receiver systems, and for the establishment of a quantitative link between state-of-the-art and absolute atom-based THz sensors.
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All authors Alisher Duspayev, Kaitlin R. Moore, Georg Raithel, David A. Anderson
Accelerator Physics
Physics-Informed Drift Diagnosis for Laser-Plasma Accelerator Operations
Ou Labun, Calin Hojbota, Mara Klebonas et al. (+4 more)
Laser-
plasma accelerators (LPAs) sustain accelerating gradients of order $100\,\mathrm{GV/m}$, but routine operation remains difficult: electron beam metrics drift over an operating shift, and the root physical cause is often invisible to the available diagnostics. We formulate LPA operation as a latent state-space model in which three effective interaction-point variables, the normalized
laser amplitude $a_0$, the normalized
plasma electron density $\tilde n_e$ and the residual pulse chirp $\mathcal{C}$, are inferred from routine electron beam observations by an extended Kalman filter. The emission model, which maps the latent state to the diagnostics, is kept structurally separate from the {transition} model, which describes how the latent state evolves between shots. The separation supports diagnosis in two stages, one asking which latent variable moved and one asking what moved it. The implemented emission model is a toy model, yielding an expected performance in line with current facilities and using 3D blow-out regime dependencies where relevant. We conduct synthetic sessions to test the effectiveness of the detection and attribution protocols, finding that attribution is limited by excitation rather than by shot count or diagnostic resolution. Because the construction needs only a set of physical latent variables, an emission model and a family of hardware-derived transition models, it transfers to other drift-prone subsystems. We argue that the accuracy of the whole procedure is limited by the emission model rather than by the inference method.
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All authors Ou Labun, Calin Hojbota, Mara Klebonas, Mike Downer, Rafal Zgadzaj, Phil Franke, Lance Labun
Biological Physics · Cross-listed from quant-ph
Computational framework for quantum state tomography of spin ensembles
Jiwoo Seo and Vesna F. Mitrović
We present
Tomography-NMR, an open-source Python package that reconstructs
quantum density
matrices from spectroscopic measurement data. The package implements a complete analysis pipeline for two-
qubit quantum state
tomography based on the product operator formalism: raw time-domain signals are
Fourier-transformed into frequency-domain spectra, spectral peak intensities are mapped to expansion coefficients of the density
matrix, and the full
quantum state is reconstructed. Three integration methods are provided for different use cases: direct peak height measurement and fixed-parameter numerical integration require no theoretical reference and are suited to unknown states, achieving fidelities of approximately 98% on a
benchmark set of known states, while a systematic parameter optimization against a known target state achieves reconstruction fidelities exceeding 99% for the same
benchmark states. While the detailed theoretical framework for
quantum state
tomography is well established, the practical procedures for extracting density
matrices from experimental spectra are often inadequately documented in the literature and obscured within proprietary software. This package addresses that gap by providing a fully transparent, reproducible implementation of every analysis step, from spectral preprocessing to density
matrix visualization. The software has been validated on experimentally prepared two-
qubit states measured via
nuclear magnetic resonance (NMR) spectroscopy of coupled $^{31}$P
nuclei. Average reconstruction fidelities range from 0.975 to 0.995 across a
benchmark set of 20 two-
qubit states, including the computational basis states, Bell states, and the outputs of three fundamental
quantum gates (CNOT, H, and T). Although developed for NMR, the modular architecture facilitates adaptation to other spectroscopic platforms and alternative measurement protocols.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
High-fidelity k$\cdot$p representations of first-principles electronic band structures through covariant renormalization
Kristian Berland
The k$\cdot$p method can be applied directly to first-principles energies and momentum
matrix elements, but the resulting models converge slowly with the number of bands and are inexact wherever the underlying
Hamiltonian is nonlocal. We show that both limitations can be largely removed by renormalizing the
eigenvalue spectra of the Hermitian momentum
matrices. These spectra are gauge invariant, and are identical along
symmetry-related directions; hence scaling the recurring magnitudes provides a modest set of parameters that preserves degeneracies and
crystal symmetry without needing to construct a
symmetry-adapted basis. We choose to renormalize the models against reference
eigenvalues and band velocities on rays out of a high-
symmetry point. For GaP, a 15-band model can reproduce the band structure in the near-gap reference regions within a few meV. For zincblende and wurtzite AlN, similar accuracy requires 30- or 85-band models, which in the case of zincblende is traced to the strong warping in the [110] direction. The scheme readily generalizes to rocksalt PbTe, which includes
spin-orbit coupling, and has $L$-centered valence- and conduction-band extrema. Further, we demonstrate, for GaP, how compact four-band
Hamiltonians can be obtained by downfolding within the same renormalization scheme. Moreover, by changing the fitting regime to encompass the entire Brillouin zone, the scheme can be used to generate full-zone models that reproduce the density of states. A practical use of the method is illustrated with a 59-band k$\cdot$p model for GaP, which can be evaluated on meshes far denser than the reference calculation, that in turn can be used both to resolve fine features in the density of states and to compute the hole conductivity at low temperature.
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Optics · Cross-listed from cond-mat.str-el
Sub-cycle doublon-holon dynamics in one-dimensional Mott insulators revealed by two-color high-harmonic spectroscopy
Lance Hatch, Aditya Verma, Eric Schultz et al. (+7 more)
Solid-state high-harmonic spectroscopy is becoming an emerging tool for probing nonequilibrium many-body dynamics. Yet, direct measurements of strongly driven, sub-optical-cycle dynamics in correlated materials during high-harmonic emission remain largely unexplored. Here, we measure high-harmonic emission chirp in a prototypical one-dimensional Mott
insulator, which encodes strongly driven doublon-holon dynamics at sub-optical-cycle timescales. We observe a positive chirp for above band gap harmonics, indicating that high harmonics are dominated by doublon-holon recombinations. We further show a harmonic order-dependent dephasing, which can be understood through different doublon-holon excursion distances associated with each harmonic. These results reveal coherent doublon-holon dynamics and their ultrafast dephasing in Mott
insulators, which is relevant to other nonequilibrium light-induced phenomena, such as Floquet engineering.
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All authors Lance Hatch, Aditya Verma, Eric Schultz, Hanjun Yang, Priscila Rosa, Genda Gu, Igor Zaliznyak, Giulio Vampa, Laimei Nie, Hanzhe Liu
Accelerator Physics
Coupling periodic-cell and finite-bunch dynamics for structured photocathodes
Dmitry Bazyl and Igor Zagorodnov
Patterning a photocathode with submicrometre features can enhance nonlinear photoemission by concentrating the optical field, but the surface geometry can also increase the transverse momentum spread of the emitted electrons. Resolving nanoscale surface fields across an injector-scale illuminated area within a full rf gun simulation is computationally demanding. To couple these scales, we developed an approach which combines a self-consistent finite flat-cathode calculation with the particle-resolved difference between matched structured and flat periodic calculations. The finite calculation determines the macroscopic bunch
evolution and space-charge field. The periodic difference determines the local change caused by the surface. For a finite but relatively small test problem, comparison with a fully resolved finite-array WarpX calculation gives differences of 1.3% in rms energy spread and less than 0.1% in projected normalized emittance. We then apply the method to representative FEL photoinjector parameters with a 100 pC emitted source distributed over more than half a million periods, and track the composed bunch through an L-band rf gun and solenoid. The initial difference between the projected horizontal and vertical emittances becomes much smaller after rf acceleration and solenoid focusing. At 1.52 m downstream of the cathode, the projected emittances are nearly equal and exceed those of the matched flat-cathode reference by less than 2% in both planes. The central-slice emittances exceed the reference values by approximately 3% horizontally and 5% vertically.
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Computational Physics · Cross-listed from cond-mat.str-el
Block entropy area based non-local fermionic mode optimization with gradient disentanglers
Miklós Antal Werner, Gero Friesecke, Andor Menczer et al. (+2 more)
We introduce a systematic block
entropy area based mode optimization
algorithm for many-body
quantum states of interacting
fermions represented by
matrix product states. From the gradient of a global cost function, the block
entropy area, a long-ranged, non-interacting effective disentangler
Hamiltonian is formed. We then simulate the time-dependent Schrödinger equation driven by the disentangler
Hamiltonian by employing the time-dependent variational principle based on projector splitting, and minimize the cost function. The combination of the density
matrix renormalization group with this gradient-based
entanglement minimization forms an efficient low-rank iterative ground-state
algorithm that also provides an optimized single-particle basis for
matrix product state representation. We demonstrate the method on two-dimensional
lattice models of interacting
fermions and the Fe${_4}$S${_4}$ cluster, and show its robustness and superiority over earlier protocols using nearest-neighbor mode rotations and reorderings.
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All authors Miklós Antal Werner, Gero Friesecke, Andor Menczer, Kornél Kapás, Örs Legeza
Optics
Designing metallo-dielectric antennas for cryogenic applications
Siwei Luo, Tim Hebenstreit, Alexey Shkarin et al. (+3 more)
We present the design of cryogenic metallo-dielectric
antennas tailored to single organic emitters, where the choice of host material imposes specific constraints on the
antenna geometry. Using dibenzoterrylene (DBT) in para-dichlorobenzene (p-DCB}) as a model system, we show that
photon collection efficiencies exceeding 90% can be achieved for arbitrary dipole orientations of the fluorescent molecule. The
antenna design is intrinsically broadband and tolerant to emitter positioning within the structure. We further provide concrete fabrication guidelines for the full
antenna architecture, and experimentally demonstrate its operating principle by recording a back-focal-plane image (BFP) of a single molecule inside a fabricated
antenna.
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All authors Siwei Luo, Tim Hebenstreit, Alexey Shkarin, Jan Renger, Tobias Utikal, Stephan Götzinger
Atomic Physics
Nondipole Coulomb effects in strong x-ray field ionization
Haoyuan He, Karen Z. Hatsagortsyan and Christoph H. Keitel
Atomic ionization in superintense x-ray fields is studied through numerical solutions of the time-dependent Schrödinger equation including nondipole corrections. The role of the Coulomb potential of the atomic core in the nondipole regime is analyzed for a linearly polarized
laser field. In the considered high-frequency and high-intensity stabilization regime, the photoelectron spectra are dominated by a near-zero-energy structure, while above-threshold ionization peaks are suppressed. Two sub-regimes in the nondipole case are identified based on the scaling of the Coulomb momentum transfer, when the Coulomb effect during the interaction with the
laser field is either significant or minor. The Coulomb influenced regime sets in within the realm of relatively low field strengths, high
laser frequencies, and long pulse durations. An intuitive model explaining the distinct features in the photoelectron momentum distributions and the Coulomb effect scaling is provided.
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Fluid Dynamics
A Conservative Hybrid Eulerian-Lagrangian Method with Persistent Structure Tracking for Multiscale Cavitation
Mahdi Lavari and Aswin Gnanaskandan
Hybrid Eulerian Lagrangian methods for multiscale cavitation represent grid resolved vapor structures in an Eulerian formulation and unresolved bubbles in a Lagrangian description, requiring transitions between the two representations as structures evolve. Existing approaches typically treat these transitions as local
geometric operations, while resolved structures are identified independently at each time step, limiting the use of temporal history in representation changes. This work presents a conservative hybrid Eulerian Lagrangian framework with embedded, on the fly persistent structure tracking. Resolved vapor structures are detected using connected component labeling and reconciled across processor boundaries through a deterministic parallel procedure. Successive observations are associated using physics informed predictions of structure position and size, maintaining persistent identities and histories through birth, death, breakup, coalescence, and representation transitions. The retained history enables history aware Eulerian to Lagrangian transition criteria and initialization of Lagrangian bubbles with the radius and radius rate information required by the bubble dynamics model. Conservative bidirectional transfer operators preserve vapor mass and linear momentum while preventing simultaneous representation of the same vapor volume. Canonical tests verify persistent tracking through fragmentation, coalescence, and close crossings, repeated representation switching, conservation of mass and momentum, and deterministic parallel behavior.
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Plasma Physics
Experimental Plasma Density Profiles Determined Through Measurements of the Magnetosonic Wave Speed
Cameron Kuchta, Jan Egedal, Abhishek Mhatre et al. (+4 more)
Information on
plasma density in laboratory
plasmas is commonly acquired using either Langmuir probes or optical diagnostics. Here, we present an alternative approach, inferring the density profile from
magnetic measurements of a
plasma wave. In particular, during the process of creating a reconnecting current layer for
magnetic reconnection experiments in the Big Red Ball, the reconnection drive first launches a large amplitude fast magnetosonic wave. The propagation of the wavefront is measured with high spatial and temporal resolutions by in situ
magnetic diagnostics. Given a known uniform background
magnetic field strength and the known dispersion relation of the wave, we here show how the characteristics of the wavefront can be applied to determine the initial
plasma density profile.
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All authors Cameron Kuchta, Jan Egedal, Abhishek Mhatre, Paul Gradney, Joseph Olson, Xinyu Yu, Cary B. Forest
Computational Physics
Stress-Testing Dynamical and Generative Downscaling Using Subseasonal Extreme Precipitation Forecasts
Mauricio Lima, Marika Koukoula, Romain Pilon et al. (+4 more)
Coarse spatial resolution limits the ability of subseasonal prediction models to resolve extreme precipitation. Downscaling with either dynamical or deep generative models can overcome this issue, but the comparative performance of these models for extremes across different atmospheric regimes remains poorly understood. In this work, we evaluate the Weather Research and
Forecasting (WRF) model against a
diffusion-based generative model by downscaling two physically distinct, extreme precipitation events up to lead times of 3 weeks. For a fair comparison with WRF, which can downscale boundary conditions from different driving models without model-specific training, the
diffusion model is trained in an unpaired fashion. Both approaches improve upon the raw European Centre for Medium-Range Weather Forecasts forecasts, in comparison to fused rain gauge-radar observations in Switzerland (CombiPrecip), but exhibit regime-dependent strengths. WRF achieves the highest probabilistic skill for a multicell, non-stationary event. Conversely, the
diffusion model is more consistent across different performance metrics for the two events, outperforming WRF in a more stationary supercell event. These results demonstrate that explicit dynamical modeling can add value for specific precipitation events for subseasonal lead times, and that generative downscaling adds value more broadly in different situations.
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All authors Mauricio Lima, Marika Koukoula, Romain Pilon, Monika Feldmann, Erwan Koch, Daniela I.V. Domeisen, Tom Beucler
Data Analysis and Statistics · Cross-listed from astro-ph.IM
Bayesian Superiority in On/Off analysis
Gleb Babenov and Petr Satunin
We present a detailed comparison of
Bayesian criteria with three non-informative priors - flat, Jeffreys, and scale-invariant - for testing a signal against an unknown background and compare them with the classical frequentist Li-Ma approach in the On/Off problem. We perform Monte Carlo simulations for various background levels and evaluate the Li-Ma and
Bayesian criteria by their Type I error rates. We then simulate a nonzero signal and compare the criteria in terms of Type II error rates. We find that both the Li-Ma criterion and the
Bayesian criterion with the Jeffreys prior control Type I error well, excluding the case of small background $b < 0.5$; the
Bayesian criterion with the Jeffreys prior is statistically more powerful than the Li-Ma criterion for $b \lesssim 40$.
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Physics Education
Questioning your brilliance in physics: Differential shifts in fixed mindsets by grade and gender
Fargol Seifollahi, Christian D. Schunn and Chandralekha Singh
Students' domain-specific mindsets and their beliefs about their capacity to improve through effort play a crucial role in shaping their experiences and decisions to persist in STEM disciplines. Physics is generally seen as a field requiring innate brilliance, which can reinforce fixed mindsets, particularly after initial setbacks in performance that are common in introductory university courses. In this study, we examine changes in fixed mindsets and potential gender differences in an introductory calculus-based physics course. Our sample consisted of 508 students with an average age of 18, predominantly White, with men comprising the majority. Based upon survey response distributions, three distinct mindset categories were identified: Hesitant, Hopeful, and Confident, describing how strongly students rejected a fixed mindset in physics. The results suggested large gender differences in distributions at the high and low-end groups. We also found an overall decline toward fixed mindsets across the course, and logistic regressions controlling for initial mindsets showed that women were significantly more likely than men to shift away from the Confident category. While the majority of men tended to stay within the Confident category, the majority of women moved away from it. Particularly, this differential shift was seen among students receiving Bs or Cs, the most commonly awarded grades in this course. Furthermore, there were relatively small differences in the probability of change within men as a function of grades received, whereas women showed marked declines toward fixed beliefs with either a B or C. Our findings provide empirical evidence for the dynamic, grade-sensitive nature of students' mindsets in a calculus-based physics course.
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Atomic Physics
Impact of Raman lasers beam profile inhomogeneities on a spaceborne quantum accelerometer
Benoit Kaczmarczuk, Gabriel Ducasse, Louis Pagot et al. (+2 more)
We report on the study of the impact of
laser beam profile inhomogeneities on the acceleration measurements of a
quantum accelerometer in space. This sensor uses a low ballistic expansion source based on delta-kick collimated Bose-Einstein condensates, and an interferometer configuration based on a sequence of Raman double diffraction beamsplitters, best suited to the microgravity environment. We characterize both phase and intensity fluctuations in terms of power spectral densities and calculate their impact on the interferometer phase, averaging over all trajectories of the atoms, via numerical simulations based on randomly drawn
laser profiles as well as via analytical treatments. We show that high quality optics, such as those realized for gravitational wave detectors, combined with large initial size atomic sources, will allow to reduce interferometer phase bias and fluctuations to the order of 1 mrad corresponding to accelerations in the low 10 -12 m.s -2 range.
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All authors Benoit Kaczmarczuk, Gabriel Ducasse, Louis Pagot, Quentin Beaufils, Franck Pereira dos Santos
Fluid Dynamics
Surface gravity wave-mean flow interaction with comparable spatial scales. Part II: two-way coupling and wave-wave interactions
Basile Gallet
We consider narrow-band deep-water surface
gravity waves propagating above a background flow whose spatial scale is comparable to the wavelength. We focus on the regime where the background-flow speed is comparable to the Stokes drift of the waves to derive a two-way coupled model between the fast waves and the slow background flow. Nonlinear wave interactions arise at the same asymptotic order as the two-way coupling and must therefore be included in the derivation. The resulting model consists of a nonlinear version of the reduced wave equation obtained in part I, coupled to a Craik-Leibovich equation governing the
evolution of the background flow. The model describes the
evolution of the wave field and background flow over the slow turnover frequency of the background flow, thus saving the computational burden of temporally resolving the fast wave frequency. The inviscid model exactly conserves wave action, mechanical energy and horizontal momentum, while the viscous model exactly conserves horizontal momentum. The coupling terms are cast in compact form for ease of physical interpretation and numerical implementation.
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Plasma Physics
Physics-Informed Neural Networks to Infer the Perpendicular Energy Conductivity in the Scrape-Off Layer of Stellarator Devices
J. Gallego, P. Protopapas, A. Bustos et al. (+6 more)
In this work, we develop an inverse Physics-Informed Neural Network (PINN) framework to infer the dependence of the scrape-off layer (SOL) perpendicular heat conductivity on
plasma density and temperature, $\kappa_\perp(n,T)$. The method combines radial profile measurements of electron density and temperature with the residual of a reduced one-dimensional SOL transport equation, so that the inferred conductivity is constrained by both the measurements and the underlying transport model. Three neural networks are trained simultaneously: two reconstruct the temperature and density profiles as functions of the radial coordinate and transported power, while a third represents the effective conductivity as a function of the local density and temperature. The framework is first validated using synthetic data generated from a prescribed conductivity function, allowing the inferred $\kappa_\perp(n,T)$ to be compared directly with the ground truth. The model recovers the imposed functional dependence with errors below $10~\%$ in the data-constrained region. Bootstrap resampling is shown to provide a practical indicator of prediction reliability and consistency. A scan in the number of
plasma profiles used for training and the number of radial measurement positions per profile identifies a practical trade-off between reconstruction accuracy and data availability. Finally, the method is applied to an experimental
dataset from the TJ-II stellarator obtained with the helium-beam diagnostic. This exploratory application provides an initial estimate of the effective SOL conductivity and illustrates the potential of inverse PINNs for extracting transport information from
plasma edge measurements.
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All authors J. Gallego, P. Protopapas, A. Bustos, A. Alonso, S. Barquero, A. Baciero, I. Rivera, J. A. Moríñigo, R. Mayo-García
Instrumentation and Detectors · Cross-listed from eess.SP
Multi-Threshold Sampling: Signal Space, Sampling Operators, and First Recorded Crossing-Time Distributions
Ao Qiu and Qingguo Xie
Multi-threshold (MT) sampling records crossing times at selected thresholds for parameter estimation and waveform reconstruction. We develop a mathematical framework that defines the signal space and sampling operators and maps the signal distribution to the distribution of recorded crossings. The framework distinguishes model mismatch, signal noise, threshold mismatch, and threshold noise. Finite point measures accommodate variable crossing counts and preserve multiplicity after time quantization.
Stochastic crossing, timing, and selection operators and their associated Markov kernels describe the sampling process. For nonhomogeneous Poisson
photon arrivals and deterministic MT sampling, we derive the exact cumulative distribution function (CDF) of the first recorded crossing time at a specified threshold within a recorded-time interval. Under additional regularity and local monotonicity conditions, this CDF admits a one-dimensional
Fourier representation. For a scintillation pulse model, numerical CDFs and standard deviations of the first recorded crossing time agree with independent Monte Carlo simulations, providing a quantitative basis for comparing threshold settings. The framework provides a foundation for MT performance evaluation, parameter estimation, waveform reconstruction, and sampler design.
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Chemical Physics
Breaking Water at Graphene Defects
Samuel G. H. Brookes, IniOluwa C. Popoola, Fabian Berger et al. (+3 more)
Water dissociation at solid surfaces underpins processes ranging from corrosion and catalysis to electrochemistry and photovoltaics. Defects often serve as reactive sites for dissociation, yet how solvation influences water dissociation at such sites remains poorly understood. Here, we use state-of-the-art machine-learned interatomic potentials to explore water dissociation at defective
graphene-water interfaces. We show that solvation qualitatively changes the reaction mechanism at a
graphene single vacancy (SV), opening pathways that are absent for an isolated water molecule. Whereas the gas-phase process proceeds via a single concerted channel, the solvated SV splits water through two competing pathways: a basic route forming SV-H and OH-(aq), and an acidic route forming SV-OH and H3O+(aq). These lower-barrier pathways produce distinct chemisorbed intermediates that enhance
graphene-water adsorption. Accordingly, even a simple carbon vacancy gives rise to unexpectedly rich interfacial chemistry, coupling surface chemistry to interfacial charge and wettability, with implications for carbon functionalization and nanofluidic transport.
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All authors Samuel G. H. Brookes, IniOluwa C. Popoola, Fabian Berger, Kara D. Fong, Angelos Michaelides, Christoph Schran
Fluid Dynamics
Surface gravity wave-mean flow interaction with comparable spatial scales. Part I: reduced wave equations
Basile Gallet and Alexandre Tlili
We consider deep-water surface
gravity waves propagating above a background flow whose spatial scale is comparable to the wavelength, focusing on the regime where the flow is slow compared to the group velocity of the waves. We introduce an "equivalent solvability condition" method to construct reduced equations, demanding that, upon multiple-timescale expansion, the reduced equations share the same leading-order solution and first solvability condition as the original system. This approach turns the full 3D problem into a 2D reduced equation for the wave field. We derive such reduced equations for broad-band waves above a depth-invariant background flow, and for narrow-band waves above a fully 3D background flow. In the latter case the reduced equation takes the form of a Schrodinger equation involving the near-surface vorticity of the background flow only, with the impact of the near-surface horizontal flow divergence shown to be subdominant. Beyond the reduction in spatial dimensionality, the latter reduced equation describes the
evolution of the wave field over the slow advective timescale of the background flow, thereby eliminating the computational burden of time-resolving the fast wave period. We illustrate the capabilities of the reduced equations through an analytical solution for the weak scattering of a wave packet by a patch of organized flow, followed by numerical solutions for stronger scattering of a wave packet by a patch of disorganized flow.
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Optics
Heterogeneously Integrated Efficient and Widely Tunable Lasers at 795 nm for Rubidium-Based Quantum Technologies
Max Kiewiet, Stijn Cuyvers, Tom Reep et al. (+8 more)
Scaling
quantum processors and optical atomic clocks fundamentally requires orders-of-magnitude reductions in the size, weight, power, and cost of optical control systems. Photonic integration of
lasers is critical to fulfill these requirements. At the near-infrared wavelengths required for atomic clocks and
quantum computing through manipulation of rubidium atoms,
laser integration is hindered by difficulty in light coupling and poor heat dissipation. Here, we introduce a wafer-scalable method utilizing micro-transfer printing to integrate GaAs-based amplifiers in etched recesses, directly butt-coupled to silicon nitride waveguides. We demonstrate extended-cavity single-mode
lasers using this integration approach. Our compact microgear
laser achieves a narrow 3 kHz fundamental linewidth at an on-chip output power of >22 mW – a record for a single-mode heterogeneously integrated
laser in the 780-800 nm band – with a wall-plug efficiency of 9.4%, showcasing the high-power and efficiency potential of this integration approach. Additionally, we demonstrate a widely tunable
laser leveraging Vernier filters to achieve lasing with 9 nm coarse tuning, a quasi-continuous fine-tuning range exceeding 140 GHz, and a mode-hop-free tuning range of 45 GHz. Our scalable integrated
laser toolkit shows great promise for replacing macroscopic external-cavity diode
lasers in next-generation
quantum technologies and optical atomic clocks.
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All authors Max Kiewiet, Stijn Cuyvers, Tom Reep, Konstantinos Akritidis, Gaudhaman Jeevanandam, Manuel Reza, Roelof Jansen, Pol Van Dorpe, Günther Roelkens, Kasper Van Gasse, Bart Kuyken
Fluid Dynamics
Low inertia limit of elasto-inertial turbulence
Shoaib Kamil, Sarath Sankar Suresh, Jose M. Lopez et al. (+1 more)
Pipe and channel flows of viscoelastic fluids display chaotic dynamics at unusually low speeds, a phenomenon referred to as elasto-inertial
turbulence, EIT. First reported in experiments a century ago, recent theoretical studies and model computations predict a variety of scenarios for the phenomenon's origin, ranging from hoop stress modes to center modes and to Tollmien-Schlichting waves. Lacking experimental confirmation, the relevant scenario in actual flows of
polymer solutions remains unknown. We here determine the transition threshold of EIT in pipe experiments, covering three decades in elasticity number. Across this entire parameter range, the transition features center mode structures at onset. Eventually the instability diverges at a lower inertia (upper elasticity) limit, which is a robust signature of this center mode scenario. Finally, we report the first experimental observation of a traveling wave in viscoelastic pipe flow, and the sequences of localized structures found, are in excellent agreement with a center mode traveling wave, the "arrowhead" solution, discovered in model simulations.
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All authors Shoaib Kamil, Sarath Sankar Suresh, Jose M. Lopez, Björn Hof
Optics
Temporal Localisation of Waves from Imaginary Line-Gap Topology
Carlos Camacho, Tom Sheppard, Joshua Feis et al. (+4 more)
For non-Hermitian
Hamiltonians, gain, loss, and non-reciprocity produce complex
eigenvalues which, in turn, facilitate different kinds of topological phases. One example is the imaginary line-gap phase, where
eigenvalues cannot lie on the real line. This notion was recently shown to explain the robust temporal localisation of waves in photonic
quantum walks and time-varying metamaterials. In these systems, waves localise around a time interface between topologically inequivalent mediums. At the core of this phenomenon is a $\mathcal{PT}$-symmetric two-mode model, where the non-trivial
topology arises due to the $\mathbb{Z}_2$ classification of the AI
symmetry class. In this work, we study two-mode models in all non-Hermitian
symmetry classes. We find that robust temporal localisation generically follows as a physical consequence of imaginary line-gap
topology according to a simple diagnostic: at least one of time-reversal
symmetry ($\mathcal{T}^{\hspace{0.05em}2} = 1$) and particle-hole
symmetry ($\mathcal{C}^2 = 1$) must be present. Our results provide a comprehensive
symmetry-based guide to the observation of the topologically protected temporal localisation of waves.
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All authors Carlos Camacho, Tom Sheppard, Joshua Feis, Oliver Ashfield, Alexander Szameit, Frank Schindler, Hannah M. Price
Applied Physics · Cross-listed from nlin.CD
Linear Response Predicts Cusp-Pair Births in Networks with a Localized Cubic
Kanchan Sarkar
Linear response is cheap to measure; the bistability boundaries it organizes are not. For a passive network with one localized cubic, the driving-point receptance $G$ fixes the period-one cusp set at fundamental-harmonic order: cusps lie on a fixed phase contour of $G$, a tangency of that contour under parameter variation creates a pair, and its
curvature separates a gap opening from an isolated loop. For a two-mode absorber the linear prediction locates a
benchmark birth coupling to $0.3\%$, and to $0.03\%$ once a third-harmonic correction of scale $|G(3\Omega)/G(\Omega)|$ is included.
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Instrumentation and Detectors
High-Speed Semi-FE Readout Module for ATLAS MDT at HL-LHC: Design and Production-Level Characterization
Yao Teng, Xueye Hu, Yuxiang Guo et al. (+5 more)
The High-Luminosity upgrade of the Large
Hadron Collider (HL-LHC) introduces increased demands on the ATLAS
Muon Spectrometer, particularly in terms of data throughput, timing distribution and system reliability. The Phase-II Chamber Service Module (CSM) is a key component of the upgraded Monitored Drift Tube (MDT) trigger and readout system, providing a high-speed interface between the front-end electronics and the backend systems. This paper describes the design and implementation of the Phase-II CSM, together with its validation. The results show that the CSM supports two independent optical uplinks, each operating at a line rate of 10.24 Gbps, together with clock distribution and slow control in the expected operating environment. Integration with small-diameter MDT (sMDT) chambers and tests with the prototype L0MDT trigger system are also presented. The CSM boards are now in production and will be used for installation and integration during the upcoming LHC Long Shutdown.
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All authors Yao Teng, Xueye Hu, Yuxiang Guo, Shaghayegh Emami, Thomas Baer, Thomas Schwarz, Junjie Zhu, Bing Zhou