Fluid Dynamics
A Comparative Study of Finite-Volume-based Coupled and Segregated Reduced-Order Models for Incompressible Flows in Parametrized Domains
Andrea Buffolini, Davide Oberto and Gianluigi Rozza
This work presents a comparative analysis of Reduced-Order Models (ROMs) applied to incompressible fluid dynamics within geometrically parametrized domains. Two distinct reduced-order solution strategies are investigated and compared: a monolithic coupled solver and a segregated SIMPLE-based
algorithm. Their performance is assessed on two steady, two-dimensional
benchmark cases: a lid-driven cavity flow and a flow past a cylindrical obstacle. The two
algorithms are compared in terms of fields evaluation and aerodynamic coefficients prediction. The computational results highlight a fundamental trade-off between accuracy and numerical efficiency. On the one hand, after an opportune supremizers enrichment, the coupled approach guarantees a faster convergence, despite the need of a larger number of degrees of freedom. On the other hand, the segregated SIMPLE
algorithm yields superior reconstruction accuracy, particularly for lower-dimensional reduced spaces, at the cost of a slower convergence rate.
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Optics
Reduction of hydroxyl groups in optical nanofibers via in-fiber laser heating
Koki Oguri, Ken-ichi Harada, Samuel K. Ruddell et al. (+2 more)
Optical nanofibers fabricated using a standard oxyhydrogen flame exhibit optical losses at wavelengths around 1385~nm due to absorption by embedded hydroxyl groups, posing a challenge for the realization of
quantum electrodynamics systems using ytterbium atoms. Here, we establish a method for the reduction of hydroxyl groups by heating them with a
laser guided within the optical nanofiber under
vacuum conditions. The temperature of the optical nanofiber during heating is estimated by monitoring the phase shift of the transmitted light using an interferometer. As a result, evidence suggesting that hydroxyl groups were desorbed by
laser heating was obtained.
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All authors Koki Oguri, Ken-ichi Harada, Samuel K. Ruddell, Karen E. Webb, Takao Aoki
Fluid Dynamics · Cross-listed from math.NA
A Systematic Analysis of Automatic Differentiation versus Discretization-based Constraints for Physics-Informed PDE Solvers
Xing Guo, Hongwei Tang, Zewei Meng et al. (+3 more)
Physics-informed neural networks (PINNs) represent a growing frontier in using artificial intelligence to solve partial differential equations (PDEs). Automatic differentiation (AD) plays a central role in this paradigm, which is mesh-free and replaces traditional iterative solvers with gradient-based optimization in continuous space. However, the inherent limitations of AD, particularly in handling higher-order derivatives and discontinuous solutions, pose significant challenges for complex problems. This has motivated a growing number of researchers to explore discretization-based constraints as an alternative path. Yet, the respective applicability of these two paradigms remains largely unexplored. In this work, we conduct systematic experiments across a wide spectrum of problems, from simple linear Poisson to high-Mach hypersonic flows with strong discontinuities. Through a rigorous decomposition of approximation, optimization, and truncation errors, we systematically elucidate the fundamental trade-offs and error-governing mechanisms of both paradigms, as well as two representative network architectures: multi-layer perceptron (MLP) and graph neural network (GNN). Our results reveal a consistent trend: as nonlinearity strengthens, the accuracy advantage of discretization-based constraints becomes increasingly pronounced, with smaller optimization errors compensating for the truncation errors. Moreover, the more complex the nonlinearity and boundary conditions, the greater the advantage of GNN over MLP. These insights offer a robust practical guideline for configuring neural PDE solvers in demanding engineering applications. Our source data and code are available at https://github.com/guoxing0809/neuropde_analysis.
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All authors Xing Guo, Hongwei Tang, Zewei Meng, Yidong Zhang, Shaoqiu Xiao, Feng Liu
Optics · Cross-listed from cond-mat.mtrl-sci
Quantifying thermal and driven magnon populations with femtosecond noise correlation spectroscopy
F. S. Herbst, M. A. Weiss, A. Leitenstorfer et al. (+5 more)
Precise knowledge of the total number of
magnons, including both coherent and incoherent (e.g. thermal) excitations, is imperative for the advancement of fundamental
spin-wave physics and the development of next-generation magnonic devices. In particular, quantifying
magnons is key to understanding
magnon transport phenomena, the nonlinear regime, or ultrafast magnetization dynamics. Typically, incoherent
magnons are accessed by frequency-domain techniques, which lack the temporal resolution required for ultrafast processes, while ultrafast time-domain methods are generally sensitive only to the coherent dynamics. In this work, we demonstrate that femtosecond noise correlation spectroscopy enables a fully quantitative, time-domain measurement of both thermal and coherently excited
magnon modes in bismuth-substituted yttrium iron garnet driven by a free-running microwave. We model the experimental data and extract the
magnon number by simulating the
magnon band structure of the sample, the magneto-optical response function, and the optical spot size used in the experiment. Our analysis establishes a connection between
magnon mode calculations and experimentally accessible
magnetic properties and fiducially reproduces the waveform and amplitude of the magneto-optical correlation signal for different experimental conditions. These results open a new pathway towards the optical
tomography of
magnon modes in non-linear or non-
equilibrium conditions and can be readily extended to study ultrafast incoherent dynamics in other condensed matter systems.
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All authors F. S. Herbst, M. A. Weiss, A. Leitenstorfer, M. Lammel, N. Beaulieu, J. Ben Youssef, R. Schlitz, S. T. B. Goennenwein
Optics · Cross-listed from cs.NE
Photonic reservoir computing with dimensionally compressed readout
Gerald Kobi, Mohab Abdalla, Miguel C. Soriano et al. (+1 more)
This work addresses a hardware constraint in reservoir computing: the limited size of the readout layer imposed by systems with a physical readout. We investigate a strategy to accommodate this constraint based on random projection, which compresses high-dimensional reservoir states into a lower-dimensional subspace while preserving key properties of the source space and information- processing capabilities. To evaluate this approach, we compare a small, standalone time delay reservoir against a larger configuration whose output is projected down to match the same restricted readout dimension. Using task-independent metrics, we demonstrate that the distribution of information-processing capacities may differ between the two configurations, even at identical readout sizes. Furthermore, we perform a comprehensive hyperparameter scan to assess how both systems behave under varying physical regimes. Finally, we
benchmark this approach on the standard NARMA10 task, showing that the random projection framework can yield superior performance compared to a standalone constrained reservoir, within specific compression range. These results provide a scalable pathway to bypass physical readout bottlenecks in hardware-based reservoir computing.
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All authors Gerald Kobi, Mohab Abdalla, Miguel C. Soriano, Damien Rontani
Optics
Mechanical quality factor estimation from a nonlinear optical cavity response
Zohran Ali, Davide Tomasella, Daniel Allepuz-Requena et al. (+2 more)
Intrinsic damping rate and quality factor ($Q$) are key parameters in optomechanical systems. However, in high-Q devices, their measurement is often challenging because probe-induced dynamical backaction (DBA) and the need to resolve and accurately track the mechanical resonance limit the performance of state-of-the-art techniques. Here, we introduce an all-optical ringdown method in the unresolved-sideband regime that exploits the nonlinear, time-averaged optical response induced by strong mechanical motion. We derive an analytical model of the time-averaged optical cavity response probed by a weak frequency-scanning
laser. During the
evolution of the mechanical oscillator, the excited motion modulates the Lorentzian lineshape into a double-horned profile whose peak separation enables an accurate estimation of the modulation amplitude. Tracking this response during the mechanical ringdown allows the intrinsic damping rate to be determined without resolving the mechanical oscillation. We apply the method to a density-modulated phononic
crystal membrane placed inside a high-finesse cavity and obtain mechanical quality factors consistent with independent measurements on the same platform. Our method requires a minimal optical setup, while offering an in situ diagnostic and reduced impact from probe-induced DBA and robustness against measurement noise. Finally, the model can describe other resonant systems dispersively coupled to coherent frequency modulations, providing new insights and measurement strategies that expand beyond the optomechanical platform.
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All authors Zohran Ali, Davide Tomasella, Daniel Allepuz-Requena, Alexander Huck, Ulrik Lund Andersen
Fluid Dynamics · Cross-listed from math-ph
Towards Heterogeneous Exascale CFD with a Single Fortran Code Base: OpenMP Target Acceleration of the High-Order Unstructured Solver UCNS3D
Panagiotis Tsoutsanis, Michal Uminski, Christopher Day et al. (+1 more)
Heterogeneous exascale systems are reshaping computational fluid dynamics, yet rewriting mature high-order solvers for accelerators can fragment code bases and weaken reproducibility. We present a single-source OpenMP target modernisation of UCNS3D, a high-order unstructured finite-volume solver for compressible flows. The common CPU/GPU implementation preserves its numerical formulation, Fortran code base, and workflows. Rather than porting isolated kernels, we enable the complete explicit time-advancement path: high-order reconstruction, gradient evaluation, inviscid and viscous fluxes, boundary treatment,
halo exchange, and solution update. The implementation uses persistent target data regions, flat run-time arrays, compile-time sizing of temporary storage, explicit local
algebra, target-callable routines, and GPU-aware MPI with device-resident buffers. These choices address the irregular stencils, complex data structures, and substantial temporary storage of high-order unstructured CFD. Verification using the compressible Taylor-Green
vortex shows CPU and GPU dissipation histories agreeing to machine precision on LUMI and with published reference data. A single-node run on the ARCHER2 GPU platform provides an independent portability check. End-to-end performance is evaluated on fully populated nodes using Taylor-Green
vortex, LM1021 sonic-boom, and NASA high-lift CRM
benchmarks. Relative to the previous production implementation, the refactored CPU path is 1.27-1.67 times faster, while GPU offload delivers same-node speed-ups of 2.71-4.05 and 84-101 percent strong-scaling efficiency. The results show that standards-based OpenMP provides portable, production-scale acceleration without sacrificing numerical fidelity, CPU performance, or software sustainability.
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All authors Panagiotis Tsoutsanis, Michal Uminski, Christopher Day, David Henty
Instrumentation and Detectors
Review of Hybrid and Opaque Scintillator Technologies Advancing Neutrino and Dark Matter Detectors
Stefan Schoppmann
Organic
liquid scintillators are used since several decades, especially in
neutrino physics. They excel at the detection of low-energy particles where energy and timing information is required. Organic
liquid scintillators have advantages such as high light yield,
radio purity, cost effectiveness, and more. However, they also exhibit disadvantages, most prominently a lack of vertex resolution and particle identification. Various novel ideas have emerged over the course of the last decade to improve the performance of organic
liquid scintillators. Among them are most prominently hybrid and opaque scintillators. In this proceedings, these novel scintillators are reviewed and their current applications in the research fields of
neutrino and dark matter physics are illustrated.
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Instrumentation and Detectors
Ton-scale Xenon Gas TPC for $0\nu\beta\beta$ Search at Atmospheric Pressure
Y. Mei, K. Mistry and D.R. Nygren
We explore aspects of an unorthodox ton-scale xenon gas time projection chamber detector operated at normal temperature and pressure (NTP), designed for $0\nu\beta\beta$ discovery at $\sim10^{27}$ year sensitivity. At fixed active mass, a greater transparency to $\gamma$-ray backgrounds and better track clarity exists at NTP relative to higher density. Operation at NTP also alleviates difficulties with pressure containment and significantly reduces HV requirements. With metre-scale electron tracks at a few MeV, event
topology can be used to efficiently reject the copious $\gamma$-ray backgrounds by factors ranging from 550–1200, largely compensating for the greater surface area of the detector. Event
topology is captured from anode plane signals combined with sensing the secondary ion component arriving at the cathode plane. A molecular gas additive limits
diffusion of the secondary electron tracks to below a cm and provides stable proportional avalanche gain. An energy resolution $\delta$E/E $\leq$ 1% FWHM seems possible. A 100 kg scale demonstrator for this detector technology could lead directly to a ton-scale search.
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Chemical Physics
Low-rank approximation of Moment Tensor Potential enables reducing training set size without loss of accuracy
Anna Bondarenko, Nikita Rybin, Maxim Rakhuba et al. (+1 more)
In this study, we implement a low-rank approximation of Moment Tensor Potential (MTP) based on the tensor train (TT) decomposition. The implemented tensor-factorized MTP (TFMTP) and the original MTP model are actively trained via a MaxVol-based
algorithm during molecular dynamics simulations of a four-component molten salt mixture, LiF-NaF-KF (FLiNaK), and geometry optimizations of a five-component equiatomic Mo-Nb-Ta-W-V random
alloy. We demonstrate that under a 1.5-fold compression, TFMTP requires two times fewer configurations for fitting than the original MTP model, while maintaining an indistinguishable level of accuracy. These actively trained MTP and TFMTP models are further used to evaluate the density and viscosity of FLiNaK at temperatures ranging from 600 to 1200 K, as well as the elastic constants and bulk modulus of the Mo-Nb-Ta-W-V
alloy at zero temperature. For both atomic systems, the differences in physical properties predicted by MTP and TFMTP are negligible.
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All authors Anna Bondarenko, Nikita Rybin, Maxim Rakhuba, Ivan S. Novikov
Applied Physics
Dynamic distortion from discretized coupling feedback in soft-spin Ising machines
Victor H. González and Natalia G. Berloff
Although Ising machines (IMs) have grown in popularity due to their potential as physics-based accelerators for combinatorial optimization problems (COPs), most literature focuses on empirically-obtained
benchmarks with low universality. In this work, we propose dynamic feedback distortion as a universal metric to quantify the effect of coupling field discretization in time-multiplexed IMs. Starting from the transfer functions of realistic hardware, we analytically show how this distortion can be mitigated using a global bias (or choosing the correct discrete coupling element) and injecting coloured noise. Our numerical results show that our mitigation protocols are very effective, especially in complicated energy landscapes (namely tunable Möbius ladders and 2D tiling problems); where an analogue reduction of the distortion leads to a two–three order of magnitude increase in the success rate of complex COPs.
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Optics · Cross-listed from quant-ph
Phase estimation in spontaneous nonlinear interferometry for enhanced quantum imaging
Jonas L. Moos, Cristofero Oglialoro, Enno Giese et al. (+1 more)
Bicolor
quantum imaging can reach, in principle, phase supersensitivity approaching the Heisenberg limit using squeezed light from high-gain parametric down-conversion, but established
quantum-imaging setups typically operate in the low-gain, spontaneous regime, where such scaling is inaccessible. Here, we show experimentally and theoretically that a symmetric nonlinear interferometer, even in the spontaneous regime, retains a phase-sensitivity advantage over configurations where
entanglement is not exploited as a
quantum-metrological resource, although the achievable phase sensitivity remains shot-noise-limited. This advantage appears as a shift of the optimal working point toward the dark fringe, the low-gain signature of the mechanism underlying high-gain supersensitivity. We derive design choices for phase-optimized nonlinear interferometers accordingly, favoring configurations that exploit
entanglement as a metrological resource and specifying their optimal operating point.
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All authors Jonas L. Moos, Cristofero Oglialoro, Enno Giese, Markus Gräfe
Computational Physics · Cross-listed from cond-mat.stat-mech
Emergent Equilibrium Structure Along a Critical Cluster Recursion
Shuo Wei, Abbas Ali Saberi and Youjin Deng
Critical universality does not determine the microscopic conditional structure of a probability measure. We study a bicolored cluster recursion constrained to remain critical at every generation, with no
equilibrium spin measure or fixed coupling imposed. In both two and three dimensions, the resulting history-dependent sequence develops a common Ising/Fortuin–Kasteleyn (FK) compatibility structure: the second-shell dependence of a one-site conditional law is strongly suppressed, nearest-neighbor effective couplings move progressively toward one another near the critical Ising value, and cluster and interface observables organize around the corresponding FK geometry. An exact cluster-coloring factorization singles out $q=2$ as the point where the residual connectivity weight disappears from the two-color
spin marginal. Thus
equilibrium-compatible conditional structure can emerge along a trajectory that remains critical throughout.
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Fluid Dynamics · Cross-listed from math.NA
A new formulation of Discontinuous Galerkin method for interface capturing approaches
W. Herri, K. Benmoussa, R. Bouydou et al. (+1 more)
In computational fluid dynamics, the numerical simulation of free-surface flows using interface capturing approaches (level set, pseudo-concentration) requires accurate resolution of a transport equation. In the present work, this equation is solved using a new formulation of the Lesaint–Raviart discontinuous Galerkin method, which is particularly suitable for problems without inflow boundaries. The motion is described by the incompressible Navier–Stokes equations with surface tension, discretized using the standard $P2-P1$ Taylor–Hood finite element method in space. Surface tension effects are represented using the so-called Continuum Surface Force model. Finally, the proposed approach is implemented and tested on several
benchmarks, including the single rising bubble and the Rayleigh–Taylor instability.
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All authors W. Herri, K. Benmoussa, R. Bouydou, D. Yakoubi
Chemical Physics
Strong Evidence for Formation of Hydroxyl Anion via 2-Particle-1-Hole Feshbach Resonances
Siddique Ali, Meenakshi Rana, Soumya Ghosh et al. (+3 more)
This study investigates the formation of the hydroxyl anion (OH$^-$) via dissociative electron attachment in 2-propanol as a model system for studying both organic and inorganic molecules. Using high-level CAP-EOM-EA-CCSD calculations and advanced ToF mass spectrometry, we demonstrate that OH$^-$ formation at electron energies between 7 and 11 eV is dominated by two-particle-one-hole (2p-1h) Feshbach resonances. The potential-energy curves reveal a dense
manifold of anionic states coupled through numerous avoided crossings, facilitating nonadiabatic population transfer during C-OH bond dissociation. Survival-probability analysis identifies a subset of six long-lived resonances that persist long enough to drive fragmentation, with states 25 and 28 acting as primary drivers by funneling the attached electron into the localized $\sigma^*(\mathrm{C{-}OH})$ antibonding orbital. These theoretical predictions are confirmed by experimental observations of a prominent OH$^-$ yield peaking at 8.6 eV, supporting a site-specific fragmentation mechanism that generalizes to the broader class of molecules.
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All authors Siddique Ali, Meenakshi Rana, Soumya Ghosh, Narayan Kundu, Aryya Ghosh, Dhananjay Nandi
Optics
Planar metal-semiconductor Yagi-Uda type antennas for tunable narrow-linewidth quantum dot emitters
Ievgen Brytavskyi, Andreas Kitzmüller, Santanu Manna et al. (+13 more)
Tunable photonic architectures that improve the extraction efficiency of light from embedded epitaxial
quantum dots across a wide spectral range are key enablers for developing bright sources of single and indistinguishable
photons. In this study, we experimentally demonstrate planar multilayer
antenna structures consisting of epitaxially grown AlGaAs and InGaAs membranes containing
quantum dots sandwiched between metallic Au (or Ag) reflector and director layers together with Al$_2$O$_3$ spacer layers. We show that the linewidths and fine-structure splitting of the neutral
exciton emission remain comparable to those measured in the corresponding unprocessed samples, demonstrating that the fabrication process preserves the optical quality of the emitters. In addition to broadband operation, we demonstrate that the planar architecture is compatible with electrical tuning via integrated diode structures, and strain tuning using piezoelectric actuators. In spite of limitations related to optical losses in the ultrathin metallic layers, the demonstrated fabrication simplicity, scalability, and compatibility with tunable
quantum emitters establish planar
antennas as a promising platform for solid-state
quantum photonic devices.
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All authors Ievgen Brytavskyi, Andreas Kitzmüller, Santanu Manna, Gabriel Undeutsch, Christian Weidinger, Thomas Oberleitner, Ailton J. Garcia, Jr., Saimon Filipe Covre da Silva, Josef Resl, Raphael Joos, Robert Sittig, Michael Jetter, Simone L. Portalupi, Peter Michler, Armando Rastelli
Optics · Cross-listed from quant-ph
Momentum-Space-Engineered Spatial Photonic Ising Machine for Long-Range Interactions
Haijun Zhou, Hengyang Li, Maolin Wang et al. (+4 more)
Long-range Ising models (LRIMs) with dense nonlocal and competing interactions are central to statistical physics,
quantum simulation, and complex networks. Although the spatial photonic Ising machine (SPIM) exploits intrinsic optical parallelism for Ising computation, its ability to faithfully encode dense long-range couplings and capture the resulting thermodynamic signatures remains underexplored. Here, we present a momentum-space-engineered SPIM framework that maps prescribed long-range coupling kernels onto momentum-space masks for parallel
Hamiltonian evaluation. Based on a high-fidelity optical field propagation model, the annealing dynamics of LRIMs with power-law and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions are systematically investigated. For the power-law model, we investigate the modulation of the estimated critical temperature by the decay exponent {\sigma} and coupling cutoff radius R. For the RKKY model, we reproduce diverse ordered states induced by complex competing long-range interactions. A proof-of-principle experiment demonstrates the physical feasibility of our approach. This framework broadens the class of many-body systems accessible to the SPIM platform.
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All authors Haijun Zhou, Hengyang Li, Maolin Wang, Yunru Chen, Yingxiong Qin, Xiahui Tang, Gang Xu
Computational Physics · Cross-listed from cs.LG
Constitutive State-Space Modeling of Path-Dependent Plasticity: A Resolution-Consistent and Parallelizable Computational Framework
Rui Barreira, Taylan Soydan, Francesco Scipione et al. (+2 more)
Data-driven constitutive models for path-dependent plasticity are commonly formulated using nonlinear recurrent neural networks, whose sequential state
evolution limits parallel training and whose predictions may depend on the discretization of the applied strain path. We introduce a Constitutive State Space (CSS) model that reformulates structured state-space dynamics as an incremental constitutive operator. The strain increment is decomposed into magnitude and direction: the loading direction drives the latent state-space system, while the increment magnitude enters the zero-order-hold discretization of its continuous-time linear recurrence. This mechanics-tailored construction guarantees stationarity under zero increments, strongly reduces sensitivity to strain-path resolution, and retains the parallel-scan structure of S5 for efficient training on long constitutive histories. The CSS and Minimal State
Cell (MSC) architectures are compared for four multiaxial path-dependent material models including isotropic J2 plasticity, pressure-sensitive foam plasticity, and combined isotropic-kinematic hardening. CSS matches or exceeds the prediction accuracy of the MSC, including one order of magnitude lower validation losses for the plastically incompressible materials. Importantly, CSS maintains low errors across large changes in strain-path discretization, whereas the MSC error increases substantially when evaluated at coarser resolutions than used for training. CSS trains substantially faster and requires fewer strain-stress pairs to attain comparable or better accuracy. Analysis of the learned state further reveals latent structure consistent with the dimensionality of the underlying physical constitutive models. These results establish mechanics-tailored structured state-space dynamics as a computational framework for efficient and discretization-robust data-driven constitutive modeling.
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All authors Rui Barreira, Taylan Soydan, Francesco Scipione, Miguel A. Bessa, Dirk Mohr
Applied Physics
An integrated viscoelastic modeling framework combining analytical and FEM approaches: Application to WSe2 coatings
Mohamed Bensalem, Fateh Bahadur, Yue Wang et al. (+2 more)
This work presents an integrated methodology combining analytical and finite element FEM based viscoelastic modeling for characterizing the nanoindentation response of coatings. The proposed framework combines two complementary modeling approaches: an analytical model based on the Burgers formulation to analyze nanoindentation load displacement data and extract rheological parameters, and a numerical FEM model implemented in ABAQUS using a 2D axisymmetric indenter coating substrate configuration with viscoelasticity represented through Prony series. An automated inverse optimization routine employing the Nelder Mead simplex
algorithm minimizes the discrepancy between experimental and simulated responses. The methodology is demonstrated and validated on WSe2 coatings, showing an agreement between the analytical predictions, FEM simulations, and experimental measurements. Despite the
geometric simplifications, the FEM approach provides accurate predictions while maintaining high computational efficiency of time dependent mechanical behavior. The proposed framework provides a robust tool for characterizing viscoelastic behavior from nanoindentation data while enabling access to internal stress and strain fields, thereby offering deeper insight into plastic deformation, crack initiation, and failure mechanism.
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All authors Mohamed Bensalem, Fateh Bahadur, Yue Wang, Nabil Daghbouj, Tomas Polcar
Chemical Physics · Cross-listed from quant-ph
Implementing QESEM's High-Accuracy Error Mitigation on a Quantum Computer: a Water Potential Energy Surface Study
Renato Olarte Hernandez, Emanuele Rossi, Sonia Coriani et al. (+5 more)
Quantum error mitigation (QEM) is essential for extracting chemically accurate results from near-term
quantum hardware. Many widely used QEM methods rely on uncontrolled heuristics whose bias depends on the specific
circuit and noise realization. In this work, we employ QESEM—a characterization-based, unbiased quasi-probabilistic mitigation method—on IBM's Aachen
quantum processor to compute the ground-state potential energy surface (PES) of the symmetrically-stretched water molecule. We consider a classically-optimized, single-layer perfect-pairing tiled
unitary product state ansatz. We map this ansatz to an 8-
qubit register corresponding to a (4,4) active space and the STO-3G basis set. Compared to the statevector reference, we find that raw QPU results typically overestimate the ground-state energy by around 500~mHa across the scanned geometries. On the other hand, QESEM-mitigated results fall approximately within 100~mHa, 30~mHa, or “chemical accuracy” ($\sim$1.5~mHa), depending on the target precision. We
benchmark QESEM at both loose (0.1~Ha) and tight (0.01~Ha) precision targets, evaluating both individual and merged batches of runs. As the precision target is tightened, the accuracy improves systematically, matching or exceeding results reported in the literature. We further quantify the sampling cost of these results, reporting the number of shots required at each precision level. Our results show how, with the current levels of hardware error, reaching the highest accuracies demands substantial QPU time. The results demonstrate that the characterization-based, unbiased error mitigation provided by QESEM allows to measure quantitatively meaningful potential energy surfaces on current
quantum hardware. Concurrently, they highlight the sampling overhead associated with QEM, which remains a central bottleneck en route to larger chemical problems and higher precision.
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All authors Renato Olarte Hernandez, Emanuele Rossi, Sonia Coriani, Karl Michael Ziems, Erik Kjellgren, Jacob Kongsted, Tali Shnaider, Stephan P. A. Sauer
Chemical Physics
Mixed quantum-classical evolution in open molecular systems
Michael Galperin and Abraham Nitzan
We consider a mixed
quantum-classical formulation for open nonequilibrium molecular systems. We employ the pseudoparticle nonequilibrium Green's function (PP-NEGF) method as a fully
quantum description and a starting point for introducing classical
nuclear dynamics for an open system. We use this formulation to derive a density-
matrix equation of motion describing the
quantum-classical
evolution. We compare our results with previous formulations and highlight important differences related to the nonequilibrium and open character of the molecular system. We also analyze the approximations needed to reduce full
quantum-classical dynamics to the fewest-switches surface hopping (FSSH) method and show that these approximations are unreasonable when adiabatic surfaces come close to each other.
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Atomic Physics
Magnetic characterization of electronic components for portable atomic sensors using a zero-field optically pumped magnetometry platform
Hyeonjae Kim, Sangkyung Lee, Sin Hyuk Yim et al. (+2 more)
We present a zero-field optically pumped magnetometry platform for
magnetic characterization of a photodetector (PD) board and a resistance temperature detector (RTD) used in a portable atomic magnetometer. For each component, the static
magnetic field along the measurement axis is determined from the shift in the center of the dispersive response, while response distortion caused by off-axis
magnetic-field components is assessed from the absorptive admixture.
Magnetic-field noise is evaluated based on the quadrature difference in the amplitude spectral density (ASD). The platform achieved a -3 dB bandwidth of 71.5 Hz and a median ASD of 57.6 $\mathrm{fT}/\sqrt{\mathrm{Hz}}$ over 20-70 Hz. For the unpowered PD board, static
magnetic fields of approximately 8 nT in magnitude and opposite signs were measured in the front- and back-facing orientations. The back-facing orientation also exhibited a degraded dispersive response consistent with
magnetic-field inhomogeneity. The
magnetic-noise contributions associated with the PD board were estimated at 36.0 and 63.2 $\mathrm{fT}/\sqrt{\mathrm{Hz}}$ in the front- and back-facing orientations, respectively. By contrast, operation of the RTD readout generated a static
magnetic field of -0.6 nT, with no measurable response degradation or additional
magnetic-field noise. These results provide guidance for the design and placement of electronic components in portable atomic magnetometers targeting sensitivities below 0.1 $\mathrm{pT}/\sqrt{\mathrm{Hz}}$.
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All authors Hyeonjae Kim, Sangkyung Lee, Sin Hyuk Yim, Taek Jeong, Younghoon Lim
Applied Physics · Cross-listed from quant-ph
Qubit-Based Benchmarking of InP HEMT LNAs: Readout Fidelity Versus Power Consumption
Junjie Li
High-fidelity single-shot readout of superconducting
qubits is essential for fault-tolerant
quantum computation. Without a
quantum-limited amplifier such as a Josephson parametric amplifier, the cryogenic high-electron-mobility-transistor (HEMT) low-noise amplifier (LNA) at the 4 K stage is the dominant noise source in the readout chain. HEMT LNAs are conventionally characterized by Y-factor measurements of the noise temperature $T_N$, independently of the
quantum measurement they ultimately serve. Here we present a
qubit-in-the-loop benchmarking method. The method uses the two-dimensional IQ histogram of single-shot readout as a direct figure of merit. We apply it to three state-of-the-art cryogenic InP HEMT LNAs with 53%, 60%, and 70% channel indium content, together with a commercial reference amplifier. The 60% and 70% devices have similar $T_N$ in Y-factor measurements, both lower than the 53% device. The 70% device has the highest gain, but
qubit readout SNR and assignment fidelity $\mathcal{F}_a$ instead peak at 60%. Using this method, we map $\mathcal{F}_a$ against HEMT LNA dc power consumption for each device. $\mathcal{F}_a$ does not simply saturate with increasing power. For several devices it declines above a device-dependent power well below typical operating points. For the 60% device, which has the highest overall $\mathcal{F}_a$, about 1~mW is needed to maintain $\mathcal{F}_a > 85\%$. Across all four devices, $\mathcal{F}_a > 80\%$ is reached with as little as about 0.3~mW, roughly an order of magnitude below typical operating points. These results establish a
qubit-referenced benchmarking methodology and provide practical guidance for amplifier selection and bias in power-constrained multi-
qubit readout systems.
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Fluid Dynamics
Weakly nonlinear dynamics of a follower-force active filament in simple shear flow
Ory Schnitzer
We employ weakly nonlinear theory to investigate how an externally imposed simple shear flow affects the onset of spontaneous dynamics of an inertialess active filament deforming in Stokes flow. The filament, clamped to a wall at one end, is subjected to a compressive "follower force" applied tangentially at its free end. By extending my earlier weakly nonlinear analysis of the shear-free case (J. Fluid Mech., 1007 A65, 2025), we derive a generalized amplitude equation governing the near-onset dynamics under weak shear. Analysis of the amplitude equation shows that, besides inducing a steady deflection, the shear damps the filament's intrinsic oscillations. This damping arises from a subtle nonlinear resonance between the shear and the intrinsic oscillations, scales quadratically with the shear rate, and is anisotropic—stronger in the flow direction than normal to it. Without shear, stable whirling states, where the filament tip traces a circular orbit in a plane parallel to the wall, and unstable planar-beating states are known to simultaneously emerge at a critical follower-force value, with circular whirling typically observed beyond this threshold. Shear breaks this degeneracy, driving a sequence of dynamical transitions: from circular to elliptical whirling, then to transverse beating (normal to the shear), and ultimately to steady deflection.
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Fluid Dynamics
Micro-convection mass transfer following bubble coalescence on a solid wall
Zahra Saadat, Michele Cattani, Amin Soltani et al. (+1 more)
The Volume-of-Fluid implementation in the \href{basilisk.fr}{Basilisk} flow solver is employed to study mass transfer after coalescence-induced jump-off of bubbles on solid substrates at four combinations of bubble radius ($R_m=150$ and 25 $\mu$m, hydrogen-water properties) and Schmidt number ($\text{Sc}=210$ and 1). The results show a relatively strong downward entrainment of low-concentration
liquid, induced by a rapid movement of the bubble interface at approximately 0.5 to 1 inertio-capillary time units after the moment of coalescence. At $\text{Sc}=210$, this leads to a highly local increase of the Sherwood number at a core region (roughly an area of radius $R_m/2$) below the south pole of the merged bubble, which persists long after the bubble departure due to the slow
diffusion at large $\text{Sc}$. The enhancement factor of the Sherwood number is highly dependent on the state of the mass-transfer boundary layer at the moment of coalescence, increasing with smaller boundary layer thicknesses. Shortly after the jump-off, the velocity of the bubble is considerably damped and rapidly approaches its free-rise terminal velocity. The effect of micro-convection on the wall mass transfer coefficient at this stage is insignificant when isolated, similar to what is reported in the literature for purely buoyancy-driven bubble rise – but slightly stronger.
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All authors Zahra Saadat, Michele Cattani, Amin Soltani, Pourya Forooghi
Chemical Physics
First-order Degenerate Symmetry-Adapted Perturbation Theory
Dominik Cieśliński, Tijs Karman, Anthony Scemama et al. (+2 more)
Degenerate electronic states govern the photophysics of excimers and the molecular dynamics near conical intersections. In regions where potential energy surfaces are degenerate or nearly degenerate, intermolecular interactions mix the corresponding electronic configurations. We introduce a first-order degenerate formulation of
symmetry-adapted perturbation theory (dSAPT) with weak
symmetry forcing that quantifies the mixing in terms of electrostatic and exchange (Pauli repulsion) contributions. We compare two alternative ways of resolving the degeneracy, in which antisymmetry is enforced either after or before diagonalization of the first-order eigenproblem. Using CASSCF monomer wave functions, we apply dSAPT to two model spatially degenerate systems, H$_2$–F(${}^2P$) and H$_2$–NO(${}^2\Pi$), and show that exchange effects contribute significantly to configuration mixing already at intermediate intermolecular separations. For the H$_2$–NO(${}^2\Pi$) complex, we further demonstrate that second-order dispersion energy is essential for qualitatively reproducing the angular dependence of the diabatic mixing angle. Finally, using water and benzene excimers with monomers described either by CASSCF or CIS wave functions, we show that Pauli repulsion controls delocalization of the excitation at short intermolecular separations.
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All authors Dominik Cieśliński, Tijs Karman, Anthony Scemama, Michał Hapka, Piotr S. Żuchowski
Plasma Physics
Dual-decomposition multi-GPU particle-in-cell method for cylindrical plasmas: Batched Fourier-mode multigrid and balanced particle slabs
Yinjian Zhao, Xi Chen and Yingjie Chen
Three-dimensional electrostatic particle-in-
cell (PIC) simulations combine irregular particle operations with a globally coupled Poisson solve, whose preferred parallel decompositions conflict. We introduce a dual-decomposition multi-GPU method: complete azimuthal
Fourier modes are owned during the field solve, whereas spatial slabs own particles. Exact full-spectrum diagonalization and batched
matrix-free
geometric multigrid keep collectives outside the V-cycle, after which every GPU reconstructs the full field. Peer migration,
cell reordering, warp-aggregated deposition, and capacity-constrained dynamic cuts restore particle locality and balance. CPU/GPU Poisson solutions agree to relative L2 errors below 6.9e-16; all 65 physical modes on eight V100 GPUs are solved in 9.350 ms with relative errors below 8.2e-15. For an identical 512*128*400 problem containing 707,788,800 particles per species, the complete PIC loop reaches 0.149108 s per step and strong-scales from five to eight GPUs with 91.81% efficiency. A separate cross-resolution production study shows approximately threefold aggregate particle-update and Poisson-
cell throughput relative to a single RTX 5090 calculation; this measures refined-problem capability rather than a hardware speedup or formal convergence order.
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Applied Physics
Boundary-induced medium mapping enables air-equivalent acoustic propagation and perfect absorption in water
Mingyu Duan, Xiangjun Peng, Ying-Jing Qian et al. (+1 more)
The extreme water-air impedance contrast (~3600) has long acted as a fundamental barrier separating airborne and
underwater acoustics. Here, we overcome this barrier with flexible boundaries, which establish a direct physical mapping between disparate acoustic media, enabling a water-filled channel to emulate air-equivalent wave propagation. Through vibroacoustic coupling, the effective wave velocity is rescaled in an approximately nondispersive manner, producing slow waves with tunable attenuation. Leveraging this concept, we demonstrate broadband
underwater sound absorption at a deep-subwavelength thickness approaching the causal limit. Our findings reveal that acoustic media can be reshaped via boundary dynamics rather than bulk composition, paving the way for transplanting acoustic functionalities and metamaterial design across distinct media.
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All authors Mingyu Duan, Xiangjun Peng, Ying-Jing Qian, Tian Jian Lu
Biological Physics
On the variational framework employing optimal control for biochemical thermodynamics
Adam Moroz and David Ian Wimpenny
The maximum energy dissipation principle can be successfully applied to describe a range of basic nonlinear models. The application of the general variational framework (Moroz, 2008, 2009, 2010) has been illustrated for basic linear schemes. The study presented in the paper shows how the kinetic processes at this level of the biomolecular and biophysical phenomena can be effectively described in terms of the maximum energy dissipation principle and its variational formulation. On the basis of this approach, a range of Lagrangians was proposed for basic nonlinear dissipative kinetic models. The results of this study show that the framework is in agreement with nonlinear
equilibrium thermodynamics.
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Applied Physics
Physics-Constrained Inverse Estimation of Irradiation-Induced Strain in He-H Ion-Implanted 4H-SiC Using Nanoindentation and Finite Element Modeling
M. Bensalem, N. Daghbouj, J.Duchon et al. (+8 more)
Nanoindentation is widely used to evaluate the mechanical properties of irradiated materials however its potential for quantifying irradiation induced subsurface strain remains underexplored. In this work, an integrated experimental numerical framework based on a physics constrained inverse modeling approach is employed to estimate the magnitude of a depth dependent irradiation induced strain distribution in single
crystal 4H SiC following sequential He and H ion implantation. The approach combines depth sensing nanoindentation, finite element modeling FEM, and a simplex based inverse optimization routine to calibrate a physically motivated eigenstrain profile derived from ion damage simulations. The strain field is assumed to follow a lognormal distribution consistent with independently determined damage profiles SRIM, and is implemented in the FEM model through a depth dependent thermal expansion formulation. By minimizing the squared error between simulated and experimental force displacement curves, the peak tensile strain is estimated to be 0.91, accompanied by an effective Young s modulus of 310 GPa and a yield strength of 16.4 GPa. Independent validation using nano beam precession electron diffraction N PED confirms good agreement between the reconstructed and experimentally measured out of plane strain profiles in both magnitude and spatial distribution. The results demonstrate that nanoindentation, when combined with physics based inverse modeling, can provide a practical tool for quantifying irradiation-induced strain and residual stress in
nuclear ceramics. This methodology offers a complementary approach to diffraction based techniques for assessing subsurface damage in ion irradiated materials relevant to advanced
nuclear systems.
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All authors M. Bensalem, N. Daghbouj, J.Duchon, B.S. Li, A.T. AlMotasem, S. Magalhaes, A. Yie, F. Munnik, Xin Ou, W.J. Weber, T. Polcar