Computational Physics · Cross-listed from math.NA
Variance Reduction in the Fokker-Planck Particle Method for Rarefied Gases using Quasi-Random Numbers
Lukas Netterdon, Veronica Montanaro, Manuel Torrilhon et al. (+1 more)
The Fokker-Planck (FP) particle method accelerates rarefied-gas simulations by replacing the binary collisions of the commonly used Direct Simulation Monte Carlo (DSMC) method with a drift=
diffusion process. Like all particle methods, the FP method is inherently
stochastic, which leads to statistical fluctuations in macroscopic quantities and necessitates large particle numbers for accurate results. In this work, we investigate the use of quasi-random numbers, which sample distributions more evenly and thereby reduce the variance. To preserve the low-discrepancy structure across time steps, we employ the Array Randomized Quasi-Monte Carlo (Array-RQMC) technique. We combine the FP method with Array-RQMC and compare it in homogeneous and inhomogeneous problems with other commonly used variance-reduction techniques. The proposed FP-Array-RQMC approach achieves improved convergence rates compared with pseudo-random sampling and yields smaller
estimator errors for sufficiently large particle numbers.
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All authors Lukas Netterdon, Veronica Montanaro, Manuel Torrilhon, Hossein Gorji
Chemical Physics
Quantum-Electrodynamical Time-Dependent Density Functional Theory Description of Molecules Interacting with Light
Yetmgeta Aklilu, Tiany Yang, Cody Covington et al. (+1 more)
We study light-mediated interactions between spatially separated molecules using real-time
quantum electrodynamical time-dependent density functional theory based on the Pauli-Fierz
Hamiltonian. An ultrashort delta-kick excitation selectively perturbs a single molecule, while a second, distant molecule remains initially unexcited. In free space, the excitation stays localized and no response is observed in the second molecule. In contrast, when both molecules are coupled to the same cavity mode, the initial excitation induces coherent dynamics in the distant molecule through the shared quantized electromagnetic field.
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All authors Yetmgeta Aklilu, Tiany Yang, Cody Covington, Kalman Varga
Computational Physics
Differentiable quantum-trajectory simulation of Lindblad dynamics for QGP transport-coefficient inference
Lukas Heinrich and Tom Magorsch
We study parameter estimation for the transport coefficients of the
quark-
gluon plasma by differentiating open-
quantum-system-based Monte Carlo simulations of quarkonium suppression. The underlying simulator requires solving a Lindblad equation in a large
Hilbert space, which makes parameter estimation computationally expensive. We approach the problem using gradient-based optimization. Specifically, we apply the score-function gradient
estimator to differentiate through discrete jump sampling in the Monte Carlo wave-function
algorithm used to solve the Lindblad equation. The resulting
stochastic gradient
estimator exhibits sufficiently low variance and can still be estimated in an embarrassingly parallel manner, enabling efficient scaling of the simulations. We implement this gradient
estimator in the existing open-source quarkonium suppression code QTraj. To demonstrate its utility for parameter estimation, we infer the two transport coefficients $\hat{\kappa}$ and $\hat{\gamma}$ using gradient-based optimization on synthetic
nuclear modification factor data.
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Optics · Cross-listed from quant-ph
Vacuum Torque Without Anisotropy: Switchable Casimir Torque Between Altermagnets
Zixuan Dai and Qing-Dong Jiang
Casimir torque is conventionally associated with explicit breaking of rotational
symmetry, arising from material dielectric anisotropy,
geometric asymmetry, or externally applied fields that themselves break rotational invariance. Here we demonstrate a fundamentally different mechanism: an axially symmetric
magnetic field can generate a Casimir torque by inducing an axially asymmetric Casimir energy - and can even reverse the torque's sign. Focusing on two-dimensional altermagnets, we show that a
magnetic field applied perpendicular to the plane - while preserving in-plane rotational
symmetry - activates an orientation-dependent
vacuum interaction through the combined crystalline
symmetry $\mathrm{C_n T}$ inherent to altermagnetic order. The resulting torque emerges continuously and scales quadratically with the
magnetic field strength. We further analyze its temperature and distance dependence, revealing scaling behaviors that are qualitatively different from those found in uniaxial bulk materials. Our results identify time-reversal
symmetry breaking as a powerful route for engineering both the sign and strength of Casimir torque and establish altermagnets as an exciting platform for exploring phenomena driven by
vacuum quantum fluctuations.
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Geophysics · Cross-listed from astro-ph.EP
Decameter-sized Earth Impactors – II: A Bayesian Inference Approach to Meteoroid Ablation Modeling
Ian Chow and Peter G. Brown
Small asteroids and large meteoroids frequently impact the Earth, though their physical and material properties remain poorly understood. When observed as fireballs in Earth's atmosphere, these properties can be inferred from their ablation and fragmentation behavior. The 2022 release of previously classified United States Government (USG) satellite sensor data has provided hundreds of new fireball light curves, allowing for more detailed analysis. Here we present a new
Bayesian inference method based on dynamic nested sampling that can robustly estimate these objects' physical parameters from their observed light curves, starting from relatively uninformative, flat priors. We validate our method against seven USG sensor-observed fireballs with independent ground-based observations and demonstrate that our results are consistent with previous estimates. We then apply our technique to $13$ decameter-size Earth impactors to conduct the most detailed population-level study of their structure and material strength to date. We identify three structurally distinct groups within the decameter impactors. The first group are primarily structurally homogeneous, weak objects which catastrophically disrupt below $\sim1.5$ MPa. The second group are heterogeneous objects which progressively fragment starting from $\sim1$ MPa typically up to $\sim3-8$ MPa. The third group are strong aggregates which remain mostly intact until $9-10$ MPa. Our results also suggest that decameter-size asteroids fragment in two distinct phases: an initial phase at $\sim0.04-0.09$ MPa and a second at $\sim1-4$ MPa. While decimeter- to meter-size objects typically lose most of their mass in the initial phase, larger decameter-size objects instead lose most of their mass in the second phase.
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Chemical Physics
Analysis of the Rankine attraction term in an equation of state based on the London dispersion force
P.M. Biesheuvel
The attraction term in an equation of state for gases, $-a c^2$, proposed by Rankine in 1854, is generally related to the London dispersion force via the equation for the second virial coefficient, $B_2$, given by $B_2 = 2\pi N_0 \int_0^\infty \left(1- \exp \left(-\omega / kT\right)\right) r^2 \text{d}r$, where $\omega$ is the attraction energy between two molecules in the gas. This equation works very well to describe $B_2$ and thus $a=B_2 RT$ as function of temperature, but the derivation is complicated. Here we present two other methods to derive $B_2$ and thus $a$ from the London equation, which have a more intuitive background. (The more simple of the two we expect must be available in literature.) We analyze these three models for the gas argon at temperatures between 150 and 900 K. All three methods fit the data quite closely while an analytical approximation fits data even better. The temperature dependence of $a$ is well described by a proportionality of $a$ with a term $1+T^*/T$ where $T^*$ is a constant that depends on the type of gas.
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Physics and Society
Causal Entropy, Control and Leadership Dynamics
Sam Turley and Matthew Turner
Collective motion in animal groups provide examples of emergent, decentralised coordination. Here, we examine a bottom-up model of collective behavior based on Future State Maximisation (FSM). In this model
agents seek to maximise the diversity of their future visual states over a finite time horizon. We further assume that a subset of
agents have a directional bias, e.g. towards different destinations. We observe swarm fragmentation on increasing (i) the strength of these preferences, or (ii) the difference in preferred directions, or (iii) the number of biased
agents. Depending on these factors, biased
agents can leave the swarm alone, leaving behind all other
agents, or they can entrain some fraction of the group to leave with them. We further study the role of a classical nearest-neighbor
alignment term on cohesion. Notably, we identify the existence of an finite, optimal coupling strength that suppresses fragmentation and maximises the flock cohesion. Our results demonstrate that FSM can be successfully combined with classical flocking rules, offering a flexible framework for modeling intelligent collective systems.
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Optics
VCSEL-based CPO for Scale-Up in A.I. Datacenter. Status and Perspectives
Manuel Kohli and Jean Teissier
The drastic increase of bandwidth demands in AI datacenters requires new solutions with low power consumption and high bandwidth densities. Further increasing the total bandwidth with copper interconnects is challenging, thus it is crucial to introduce optics into the scale-up network. For this purpose, the most important metrics are the energy efficiency of the total link in addition to the spatial bandwidth-density and reach. With the inefficiency of copper traces at high speeds, transitioning to co-packaged optics is no longer optional but essential. Here, we show that the mature VCSEL technology offers the ideal combination of low-cost, low-latency, high-reliability, and energy efficiency at all bitrates, thanks to their unique versatility and high wall-plug-efficiency. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible.
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Plasma Physics
Relativistic electron dynamics in ultra-intense lasers
Amol R Holkundkar
These lectures at Winter School on Intense
Laser Science (WiSILS-2024) at IIT Jodhpur, India, will focus on the Relativistic charge particle dynamics in ultra-intense
laser pulses. We will be learning about the relativistic equations of motion, Radiation-Reaction, Thomson scattering, Ponderomotive scattering, and its usage as the potential diagnostic tool. A simulation code LEADS will address the relativistic electron dynamics in the intense-
laser pulse.
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Physics and Society
The Maintenance and Necessity of Universal Rules: Scale, Hierarchy, the Cost of Justice, and Civilizational Development
Li Tuobang
Building upon previous research, this paper further explores the topological foundations for maintaining universal rules within ultra-large-scale societies. It finds that in small-scale societies, absolute egalitarianism and the rule of law can be compatible through peer monitoring within a fully connected network. However, in ultra-large-scale societies, to maintain high-dimensional rules capable of protecting innovation and property rights, a complex hierarchical structure including "high-fragility" nodes must be constructed. Through quantitative analysis of power structures, this paper proves that a flattened, two-tier structure inevitably leads to the degradation of the rule of law. Only a social
topology with sufficient hierarchical depth can escape the deathly trap of the Leviathan while expanding in scale, thereby sustaining the dynamic
evolution of civilization.
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Optics
Three-Dimensional Volumetric Reconstruction of Native Chilean Pollen via Lens-Free Digital In-line Holographic Microscopy
J. Staforelli-Vivanco, V. Salamanca-Levi, B. Muñoz-Cepeda et al. (+5 more)
This study presents a methodology for the three-dimensional volumetric reconstruction and morphological characterization of native Chilean pollen grains using lens-free Digital In-line
Holographic Microscopy (DLHM). A 532 nm point source, a 3.45 $\mu$m pixel pitch CMOS sensor and a source–sample distance of $0.46$ mm with a $25$ mm stand-off give a magnification of $\simeq 55\times$ and an effective pixel of 62.9 nm. Wavefronts of Anthemis cotula, Gevuina avellana and Conium maculatum were reconstructed by the Kirchhoff-Helmholtz transform, yielding volumes from $3780.2 \pm 18$ to $4320.5 \pm 15$ $\mu$m$^3$ and sphericities from $0.76 \pm 0.03$ for the echinate A. cotula to $0.89 \pm 0.02$ for G. avellana. Three independent targets make these reconstructions traceable. Certified polystyrene microspheres ($\varnothing = 20.0$ $\mu$m) make the source–sample distance an optically retrieved quantity, the 2.5D height map returning $2068$ $\mu$m$^3$ against an analytical $2094.4$ $\mu$m$^3$. A human erythrocyte, reconstructed with a haemoglobin refractive-index increment taken from the literature rather than fitted, returns $88.9$ fL with a $2.36$ $\mu$m rim and a $1.03$ $\mu$m dimple, within physiological range. Finally, transport-of-intensity
retrieval on bright-field micrographs from a separate, independently calibrated instrument reproduces the projected morphology of G. avellana, though no volume follows from it. These results support label-free "digital fingerprints" for automated melissopalynology in a South American biodiversity hotspot.
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All authors J. Staforelli-Vivanco, V. Salamanca-Levi, B. Muñoz-Cepeda, R. Jofré-Cerda, C. Valdés-Cruces, M. Rondanelli-Reyes, I. Lamas, J. M. Troncoso
Chemical Physics
Automated Analysis of DFT Output Files for Molecular Descriptor Extraction and Reactivity Modeling
Yu-Chien Huang, Dennis Chung-Yang Huang and Yun-Cheng Tsai
Understanding the relationship between molecular structure and chemical reactivity or properties is fundamental to rational molecular design. Linear free energy relationships (LFERs), particularly Hammett analysis, have long served as powerful tools in organic chemistry. Recently, these approaches have been enhanced by incorporating computationally derived parameters, enabling broader applicability across diverse molecules and reactions. To facilitate and scale this process, we present DFTDescriptorPipeline, a fully automated workflow for extracting
quantum chemical descriptors from Gaussian log files and constructing structure-property and structure-reactivity relationships using multivariate linear regression (MLR) models. We validate the workflow across four case studies, including photoswitchable molecules and catalytic reactions. In each case, the models provide interpretable results, demonstrating the versatility of this approach and its relevance to a wide range of chemical contexts. We anticipate that this platform will serve as a generalizable framework for integrating
quantum chemical calculations into data-driven molecular design.
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Chemical Physics
Cooperative Chemical Reactions in Optical Cavities: A Complex Interplay of Mode Hybridization, Timescale Balance, and Pathway Interference
Yaling Ke
Harnessing strong light-matter interactions to control chemical reactions in confined electromagnetic fields offers a promising route toward deepening our understanding of chemical dynamics at the collective
quantum-mechanical level, with potential implications for future chemical synthesis paradigms. Achieving this goal, however, requires an in-depth mechanistic understanding of the underlying dynamical processes. As a step in this direction, we present a systematic and numerically exact
quantum dynamical study of cooperative reaction dynamics inside an optical microcavity. Using a hierarchy of model systems with increasing complexity, we elucidate how cavity-modified reactivity emerges from-and is highly sensitive to-subtle structural and environmental variations. Our models consist of optically dark reactive molecules, each represented by a symmetric double well potential, coupled to infrared-active non-reactive intramolecular or solvent vibrational modes, as well as their respective dissipative environments. Our results demonstrate that cavity-induced rate modifications arise from a delicate interplay among mode hybridization in strong-coupling regimes, the dynamical balance of all participating energy exchange processes, and
quantum interference between multiple fluctuation-dissipation-mediated reaction pathways enabled by collective cavity coupling. By continuously tuning a single system parameter or introducing molecular collectivity, we observe qualitatively distinct rate modification profiles as functions of the cavity frequency, including resonant rate enhancement, resonant rate suppression, hybridization-induced peak splitting, and, notably, asymmetric Fano-type line shapes in which enhancement peaks and suppression dips coexist within a narrow resonance window, highlighting the important role of
quantum interference in cavity-modified chemical reactivity.
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Computational Physics
Gradient-based optimization of exact stochastic kinetic models
Francesco Mottes, Qian-Ze Zhu and Michael P. Brenner
Stochastic kinetic models describe systems across biology, chemistry, and physics where discrete events and small populations render deterministic approximations inadequate. Parameter inference and inverse design in these systems require optimizing over trajectories generated by the
Stochastic Simulation
Algorithm, but the discrete reaction events involved are inherently non-differentiable. We present an approach based on straight-through Gumbel-Softmax estimation that maintains exact
stochastic simulations in the forward pass while approximating gradients through a continuous relaxation applied only in the backward pass. We demonstrate robust performance on parameter inference in
stochastic gene expression, first recovering kinetic rates of telegraph promoter models from both moment statistics and full steady-state distributions across diverse and challenging synthetic parameter regimes, then inferring the kinetic parameters of a four-state promoter model from experimental single-molecule RNA timecourse measurements. We further apply the method to inverse design in
stochastic thermodynamics, optimizing non-
equilibrium currents in an interacting particle system under kinetic resource constraints and recovering known analytical bounds. The ability to efficiently differentiate through exact
stochastic simulations provides a foundation for systematic scalable inference and rational design across the many domains governed by continuous-time Markov dynamics.
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Fluid Dynamics
Caustics of finitely dense inertial particles
C. Rajarshi and Rama Govindarajan
Estimating collision rates is of immense importance in particle-laden flows. An economical way of doing this is to directly identify incidences of caustics, or extreme clustering, by tracking particle velocity gradients in the neighborhoods of individual particles. The objective of this work is two-fold. (i) We find conditions under which caustics form, in point-
vortex flow and in two-dimensional
turbulence. While caustics are known to form in regions of strain, we show that the velocity
alignment with strain directions is key. Particles must remain in compressional strain throughout the process to form caustics, whereas survivor particles: which visit high strain but do not form caustics, briefly go through extensional strain during the early part of the process. This enables survivor particles to attain significantly straighter paths, and to move faster, whereas caustics particles follow paths of high
curvature and move slower. As a result, caustics particles stay longer in high-strain regions than survivors. (ii) We ask about the effect of finite particle density, where the particle is denser than the background fluid. We show that finite-density particles need to sample stronger background strain than infinite-density ones to trigger caustics, but our other findings are universal across particle density.
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Optics
Anomalous Tip-Sample Distance Behavior on the Tip-Enhanced Raman Spectroscopy of Graphene in Ambient Conditions
André G. Pereira, Raul Corrêa, Bianca Carneiro et al. (+5 more)
Tip-Enhanced Raman Spectroscopy (TERS) combines Raman spectroscopy with scanning probe microscopy to overcome the spatial resolution limitation imposed by light diffraction, offering a primary optical technique for the comprehensive study of two-dimensional (2D) materials. In this work, we investigate an anomalous decay profile of the TERS intensity of the
graphene 2D band as the tip-sample separation changes, observations enabled by high TERS efficiency and accuracy in tip-approach and tip-retract procedures. The anomalous results can be properly described by the addition of an ad hoc deformation to the effective tip-sample distance, rationalized here as due to the presence of a
liquid meniscus formed via capillary forces.
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All authors André G. Pereira, Raul Corrêa, Bianca Carneiro, Cassiano Rabelo, Thiago L. Vasconcelos, Vitor Monken, Luiz Gustavo Cançado, Ado Jorio
Chemical Physics · Cross-listed from cond-mat.soft
Onset of stripe order in classical fluids: Lessons from lattice-gas mixtures
Gabriele Costa and Santi Prestipino
When two molecular species with mutual affinity are mixed together, various self-assembled phases can arise at low temperature, depending on the shape of like and unlike interactions. Among them, stripes – where layers of one type are regularly alternated with layers of another type – hold a prominent place in materials science, occurring e.g. in the structure of superconductive doped antiferromagnets. Stripe patterns are relevant for the design of functional materials, with applications in optoelectronics, sensing, and biomedicine. In a purely classical setting, an open question pertains to the features that spherically-symmetric particle interactions must have to foster stripe order. Here we address this challenge for a
lattice-gas mixture of two particle species, whose
equilibrium properties are exactly determined by Monte Carlo simulations with Wang-Landau sampling, in both planar and spherical geometry, and for equal chemical potentials of the species. Somewhat surprisingly, stripes can emerge from largely different off-core interactions, featuring various combinations of repulsive like interactions with a predominantly attractive unlike interaction. In addition to stripes, our survey also unveils
crystals and
crystal-like structures, cluster
crystals, and networks, which considerably broaden the catalog of possible patterns. Overall, our study demonstrates that stripes are more widespread than generally thought, as they can be generated by several distinct mechanisms, thereby explaining why stripe patterns are observed in systems as diverse as cuprate materials, biomaterials, and nanoparticle films.
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Chemical Physics
DDCCNet: Physics-enhanced Multitask Neural Networks for Data-driven Coupled-cluster
P. D. Varuna S. Pathirage and Konstantinos D. Vogiatzis
We present the data-driven coupled-cluster deep network (DDCCNet), a family of multitask, physics-enhanced deep learning architectures designed to predict coupled-cluster singles and doubles (CCSD) amplitudes and correlation energies from lower-level electronic structure methods. The three DDCCNet variants (termed as v1, v2, and v3) progressively incorporate architectural refinements ranging from parallel subnetworks for t_1 and t_2 amplitudes to feature-partitioned blocks and physics-enhanced intermediate prediction layers that are structured in accordance with coupled-cluster equations to enhance physical consistency and multitask learning efficiency. These models jointly learn correlated amplitude patterns while
embedding symmetry and orbital-level interactions directly into the network structure. Applied to methanol conformers, CO2 clusters, and small organic molecules, DDCCNet_v2 delivered the most accurate and transferable performance, achieving chemically precise correlation energies across diverse molecular systems. Collectively, DDCCNet establishes a scalable, physically grounded framework that unifies machine learning and ab initio theory for efficient, data-driven electronic structure prediction.
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Fluid Dynamics
Curvature-weighted spectra anticipate dissipation peaks in decaying three-dimensional turbulence
Satori Tsuzuki
We investigate the robustness of a
curvature-weighted spectral precursor to dissipation in freely decaying three-dimensional incompressible
turbulence. Building on our recent work in Physical Review Fluids on the Taylor–Green
vortex, we analyze direct numerical simulations using the shell-summed curl-of-vorticity spectrum, denoted here by $\mathcal{C}_{4}(k,t)$ and equivalent to a $k^4$-weighted energy spectrum in the modal incompressible sense. Extending the study across multiple initial conditions – multi-mode ABC flows, a randomized low-wavenumber ABC field, the Taylor–Green
vortex, and the Kida–Pelz flow – we find a consistent temporal ordering: the characteristic time associated with the advance and saturation of the peak wavenumber of $\mathcal{C}_{4}(k,t)$ precedes the dissipation-peak time, which in turn precedes the characteristic time associated with the peak scale of the nonlinear energy-flux spectrum. We further probe Reynolds-number and scale-separation effects using Taylor–Green simulations at additional viscosities: the precursor ordering persists when adequate scale separation and resolution are maintained, but can change in the low-$R_\lambda$/limited-scale-separation regime. Throughout, we use explicit inspection of
curvature-weighted spectra to distinguish physical peak
evolution from cutoff-proximate artifacts. These results support robustness over the deterministic decaying-flow initial conditions examined here and clarify the practical role of Reynolds number, scale separation, and resolution when using
curvature-weighted spectral diagnostics in decaying
turbulence.
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Data Analysis and Statistics · Cross-listed from astro-ph.CO
Evaluating state-of-the-art cloud quantum computers for quantum neural networks in gravitational waves data analysis
Maria-Catalina Isfan, Laurentiu-Ioan Caramete and Ana Caramete
In this work, we explore the possibility of using
quantum computers provided for usage in cloud by big companies (such as IBM, IonQ, IQM
Quantum Computers, etc.) to run our
quantum neural network (QNN) developed for data analysis in the context of LISA Space Mission, developed with the Qiskit library in Python. Our previous work demonstrated that our QNN learns patterns in gravitational wave (GW) data much faster than a classical neural network, making it suitable for fast GW signal detection in future LISA data streams. Analyzing the fees from hardware providers like IBM
Quantum, Amazon Braket and Microsoft Azure, we found that the fees for running the first segment of our QNN sum up to \$2000, \$60000, and \$1000000 respectively. Using free plans, we succeed to run the 3-
qubit feature map of the QNN for one random data sample on {\fontfamily{qcr} \selectfont ibm\_kyoto} and {\fontfamily{qcr}\selectfont IQM
Quantum Computers\_Garnet}
quantum computers, obtaining a fidelity of 99%; we could also run the first prediction segment of our QNN on {\fontfamily{qcr} \selectfont ibm\_kyoto}, implemented for 4
qubits, and obtained a prediction accuracy of 20%. We queried providers such as IBM
Quantum, Amazon Braket, Pasqal, and Munich
Quantum Valley to obtain access to their plans, but, with the exception of Amazon Braket, our applications remain unanswered to this day. Other major setbacks in using the
quantum computers we had access to included Qiskit library version issues (as in the cases of IBM
Quantum and IQM
Quantum Computers) and the frequent unavailability of the devices, as was the case with the Microsoft Azure provider. All the results presented in this paper were accumulated in 2024.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Binding Energies of Charged Particles on Dielectric Surfaces in Liquid Nitrogen
Ashok Timsina and Wolfgang Korsch
A new approach for determining the binding energies of charged particles, such as ions and electrons, on dielectric surfaces in cryogenic
liquids is introduced. The experimental technique outlined in this paper is employed to observe the buildup of charged particles on nonconductive surfaces using the electro-optic Kerr effect. The initial results of binding energy measurements on surfaces of deuterated tetraphenyl butadiene (dTPB)-coated and uncoated polymethyl methacrylate (PMMA) in
liquid nitrogen are presented. Under these conditions, the ions or electrons displayed binding energies of less than 1 meV. Although these findings were obtained in
liquid nitrogen, the methodology is not limited to cryogenic
liquids and is applicable to a wide variety of fluids, with no essential dependence on temperature.
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Plasma Physics
XFEL Imaging Techniques for High Energy Density and Inertial Fusion Energy Research at HED-HiBEF
Alejandro Laso Garcia, Mikhail Mishchenko, Victorien Bouffetier et al. (+53 more)
The imaging platform developed at the High Energy Density - Helmholtz International Beamline for Extreme Fields (HED-HiBEF) instrument at the European XFEL and its applications to high energy density and fusion related research are presented. The platform combines the XFEL beam with the high-intensity short-pulse
laser ReLaX and the high-energy nanosecond-pulse
laser DiPOLE-100X. The spatial resolution is better than 500 nm and the temporal resolution of the order of 50 fs. We show examples of blast waves and converging cylindrical shocks in aluminium, resonant absorption measurements of specific charged states in copper with ReLaX and planar shocks in polystyrene material generated by DiPOLE-100X. We also discuss the possibilities introduced by combining this imaging platform with a kJ-class
laser.
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All authors Alejandro Laso Garcia, Mikhail Mishchenko, Victorien Bouffetier, Gabriel Perez-Callejo, Karen Appel, Alexey Arefiev, Carsten Baehtz, Erik Brambrink, Mihail Cernaianu, Domenico Doria, Tobias Dornheim, Gillis M. Dyer, Nicolas Fefeu, Eric Galtier, Thomas Gawne, Petru V. Ghenuche, Sebastian Goede, Johannes Hagemann, Marie-Luise Herbert, Hauke Höppner, Lingen Huang, Oliver Humphries, Mae Jones, Dimitri Khaghani, Thomas Kluge, Jayanath Koliyadu, Dominik Kraus, Hae Ja Lee, Julian Lütgert, Mikako Makita, Jean-Paul Naedler, Bob Nagler, Motoaki Nakatsutsumi, Quynh Nguyen, Alexander Pelka, Thomas R. Preston, Chong Bing Qu, Sripati V. Rahul, Lisa Randolph, Ronald Redmer, Martin Rehwald, Hans G. Rinderknecht, Angel Rodriguez-Fernandez, Joao J. Santos, Ulrich Schramm, Michal Smid, Cornelius Strohm, Jergus Strucka, Minxue Tang, Patrik Vagovic, Milenko Vescovi, Long Yang, Karl Zeil, Ulf Zastrau, Thomas E. Cowan, Toma Toncian
Optics · Cross-listed from quant-ph
Tripartite quantum correlations obtained by post-selection from twin beams
Pavel Pavlicek, Jan Perina Jr., Vaclav Michalek et al. (+2 more)
Spatially-resolved
photon counting of a twin beam performed by an iCCD camera allows for versatile tailoring the properties of the beams formed by parts of the original twin beam. Dividing the idler beam of the twin beam into three equally-intense parts and post-selecting by detecting a given number of photocounts in the whole signal beam we arrive at the idler fields exhibiting high degrees of nonclassicality and being endowed with tripartite
quantum correlations. Nonclassicality is analyzed with the help of suitable nonclassicality witnesses and their corresponding nonclassicality depths. Suitable parameters are introduced to quantify
quantum correlations. These parameters are analyzed as they depend on the field intensity. The experimental photocount histograms are reconstructed by the maximum-likelihood approach and the obtained
photon-number distributions are compared with a suitable model in which the original twin beam is approximated by an appropriate multi-mode Gaussian field and undergoes the corresponding beams' transformations.
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All authors Pavel Pavlicek, Jan Perina Jr., Vaclav Michalek, Radek Machulka, Ondrej Haderka
Fluid Dynamics
Experimental study on gravity currents flowing on heated walls
Stefano Lanzini, Massimo Marro, Mathieu Creyssels et al. (+2 more)
We present an experimental study on steady
gravity currents advancing along a heated wall. The current is generated by a mixture of air and carbon dioxide continuously supplied at the channel inlet. To have a complete point-wise characterization of the flow, simultaneous high-frequency measurements of two velocity components, CO_2 concentration, and temperature are performed. An experimental protocol is presented to reconstruct the local fluid density and to estimate turbulent vertical and horizontal fluxes of CO_2, temperature, and buoyancy. The reliability of both the flow measurements and of the estimate of convective heat flux exchanged at the wall is assessed through integral balances of \textnormal{CO}$_2$ mass, enthalpy, and buoyancy, performed at different distances from the source. Three wall-heating conditions are considered: an adiabatic case, a moderately heated case, and a strongly heated case. In the heated experiments, a convectively unstable boundary layer forms near the wall, capped by a stably stratified region. The influence of this condition on the first- and second-order flow statistics profiles is examined. Although wall heating influences the vertical shear, the Brunt-Vaisala frequency, and both shear and buoyancy production of turbulent kinetic energy within the stably-stratified region characterized by an almost constant vertical gradient of streamwise velocity, neither the gradient Richardson number nor the flux Richardson number exhibits a clear trend in this region with the imposed wall heat flux.
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All authors Stefano Lanzini, Massimo Marro, Mathieu Creyssels, Alexandre Azouzi, Pietro Salizzoni
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Correlated domain and crystallographic orientation mapping in uniaxial ferroelectric polycrystals by interferometric vector piezoresponse force microscopy
Ruben Dragland, Jan Schultheiß, Ivan N. Ushakov et al. (+2 more)
Ongoing advances in scanning probe microscopy techniques are continually expanding the possibilities for nanoscale characterization and correlated studies of functional materials. Here, we demonstrate how a recent extension of piezoresponse force microscopy (PFM), known as interferometric vector PFM, can be utilized for simultaneously mapping the local crystallographic orientations and the domain structure of distributed grains in uniaxial ferroelectric polycrystals. By shifting the
laser beam position on the cantilever, direction-dependent piezoresponse signals are acquired analogous to classical vector PFM, but without the need to rotate the sample. Using polycrystalline ErMnO$_{3}$ as a model system, we demonstrate that the reconstructed piezoresponse vectors correlate one-to-one with the crystallographic orientations of the micrometer-sized grains, carrying grain-orientation and domain-related information. We establish a versatile approach for rapid,
multimodal characterization of polycrystalline uniaxial ferroelectrics, enabling automated, high-throughput reconstruction of polarization and grain orientations with nanoscale precision.
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All authors Ruben Dragland, Jan Schultheiß, Ivan N. Ushakov, Roger Proksch, Dennis Meier
Plasma Physics
The Geometry of Flux Surfaces with Quasi-Poloidal Symmetry
Rishin Madan, Wrick Sengupta, Elizabeth J. Paul et al. (+4 more)
Quasi-poloidal (QP)
magnetic fields have desirable properties for confining
plasma: no radial drift of guiding centres (with positive implications for neoclassical transport), zero Pfirsch-Schlüter current, and a lower level of damping for poloidal flows. Despite their attractive properties, QP fields are not amenable to the near-axis expansion, a major theoretical tool for understanding toroidal fields. In this paper, we provide a novel framework for defining and understanding QP flux surfaces. This framework relies on a simplification that transforms the task of finding a quasi-poloidal flux surface from a 3D problem to a 2D problem. This simplification also applies to asymmetric
magnetic mirrors with desirable properties. We sketch how this 2D problem can form the basis of an efficient optimisation problem for finding QP flux surfaces. We leverage this 2D problem for theoretical understanding: for instance, we identify a route to finding QP flux surfaces that are naturally flat mirrors (Velasco et al. 2023). The reduced model is qualitatively checked against numerically optimised QP
equilibria. These numerical solutions only satisfy QP approximately, but we predictably find that local discrepancies with the reduced model correspond to significant local QP errors, anomalous parallel currents, and field lines deviating from geodesics.
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All authors Rishin Madan, Wrick Sengupta, Elizabeth J. Paul, Mohammed Haque, Richard Nies, José Luis Velasco, Amitava Bhattacharjee
Fluid Dynamics
Rigid Body Dynamics in Ambient Fluids
Marcel Padilla, Aviv Segall and Olga Sorkine-Hornung
We present a novel framework for rigid body dynamics in ambient media, such as air or water, enabling the reproduction of complex motion phenomena of objects without requiring computational fluid dynamics simulations. Our method computes the added mass of the fluid and estimates dynamic pressure forces from the surface slip velocity, replacing shape-specific drag and lift coefficients with a geometry-driven pressure computation. A physically motivated flow separation criterion then estimates where the fluid detaches from the body surface, governed by a single free parameter with a clear physical interpretation. Our method is the first within the rigid body dynamics context to reproduce the full range of falling plate behaviors: fluttering, tumbling, chaotic and steady modes, as well as phenomena such as the Magnus effect and the flight dynamics of an American football (tight spiral pass paradox). The resulting
algorithm requires only surface force evaluations at runtime and integrates seamlessly into existing physics engines for fast simulation.
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Optics
Understanding Optical Anisotropy in Multilayer {\gamma}-InSe and {\epsilon}-GaSe
Jason Lynch, Zexuan Liu, Sergiy Krylyuk et al. (+3 more)
Low-dimensional media have exhibited optical anisotropy that is unachievable in traditional 3D media due to the asymmetry of their strong, in-plane covalent bonds and weak out-of-plane van der Waals interactions. As a result, 2D media are promising building blocks for ultrathin devices such as polarimeters, polarized light sources, and active polarizers. III-VI
semiconductors possess a rare property in the class of multilayered
semiconductors, which is that their fundamental
excitons are oriented out-of-plane. This allows them to exhibit phenomena such as transparency in the visible range while also being emissive in the visible and near-infrared ranges. Here, we report the first experimental values for the anisotropic refractive indices of {\gamma}-InSe and {\epsilon}-GaSe, and we observe the effects of the out-of-plane
excitons on the c-axis refractive index. It is found that both materials exhibit moderate optical anisotropy for multilayered
semiconductors. The complex, anisotropic refractive index of {\gamma}-InSe and {\epsilon}-GaSe enables the accurate simulation of these media, allowing for the design of high-performance, ultra-compact optoelectronic devices.
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All authors Jason Lynch, Zexuan Liu, Sergiy Krylyuk, Huairuo Zhang, Albert Davydov, Deep Jariwala
Biological Physics · Cross-listed from q-bio.PE
Nonlinear competition avoidance favors coexistence in microbial populations
Mattia Mattei, David Soriano-Paños and Alex Arenas
Bacteria regulate their motility through a variety of mechanisms, including quorum sensing (QS) and other density-dependent responses mediated by diffusible signals. While nonlinear density-dependent motility is well known in active-matter theory to generate nonequilibrium spatial patterns, its consequences for the coexistence of growing, interacting species remain less explored. Here we develop a minimal spatially structured model for two strongly competing species in which local demographic interactions are coupled to an escape response: each species increases its motility nonlinearly (sigmoidal) with the local abundance of its competitor. We show that this sigmoidal motility regulation promotes optimal spatial self-organization and can sustain long term coexistence via segregation, even in parameter regimes that yield competitive exclusion in well-mixed Lotka-Volterra dynamics. On two-dimensional
lattices, the interplay between demographic competition and density-dependent motility generates a range of emergent patterns, including regimes in which the weaker competitor counterintuitively has higher total abundance. Overall, our results identify nonlinear, competitor-induced motility as a fundamental mechanism capable of sustaining coexistence in competing microbial populations.
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Atomic Physics · Cross-listed from quant-ph
Ultra Compact low cost two mode squeezed light source
Shahar Monsa, Shmuel Sternklar and Eliran Talker
Quantum-correlated states of light, such as squeezed states, constitute a fundamental resource for
quantum technologies, enabling enhanced performance in
quantum metrology,
quantum information processing, and
quantum communications. The practical deployment of such technologies requires squeezed-light sources that are compact, efficient, low-cost, and robust. Here we report a compact narrowband source of two-mode squeezed light at 795 nm based on four-wave mixing in hot 85Rb atomic vapor. The source is implemented in a small, modular architecture featuring a single fiber-coupled input, an electro-optic phase modulator combined with a single Fabry-Perot etalon for probe generation, and two free-space output modes corresponding to the signal and conjugate fields. Optimized for low pump power, the system achieves up to -8 dB of intensity-difference squeezing at an analysis frequency of 0.8 MHz with a pump power of only 300 mW. The intrinsic narrowband character of the generated
quantum states makes this source particularly well suited for atomic-based
quantum sensing and
quantum networking, including interfaces with atomic
quantum memories. Our results establish a versatile and portable platform for low-SWaP squeezed-light generation, paving the way toward deployable
quantum-enhanced technologies.
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