Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci
Bond-resolved STM with density-based methods
Emiliano Ventura-Macias, Jose Martinez-Castro, Guillermo Haas et al. (+7 more)
Bond-resolved scanning tunneling microscopy (BRSTM) provides intramolecular contrast with CO-functionalized tips, but its interpretation requires a description of both probe relaxation and orbital-dependent tunneling. We introduce a simulation framework that combines the Full-Density-Based Model (FDBM) for CO-tip relaxation with Chen's derivative rules applied directly to real-space density-functional-theory (DFT) wave functions. We test the method against a series of constant-height BRSTM images of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on Ag(111), acquired in 10~pm tip-height increments, and published data for 1,5,9-trioxo-13-azatriangulene (TOAT) on Cu(111). The simulations reproduce the principal intramolecular contrast features and their
evolution with tip height. The comparison identifies distinct roles for the substrate: it modifies the partially occupied molecular states and probe–sample forces in PTCDA/Ag(111), while its influence on the TOAT/Cu(111) contrast remains relevant even without substantial changes in molecular-orbital occupation. Our framework thus provides a practical and accurate route to interpreting BRSTM images that incorporates, from a single DFT calculation, the separate contributions of electronic structure and CO-tip relaxation.
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All authors Emiliano Ventura-Macias, Jose Martinez-Castro, Guillermo Haas, Jara Trujillo-Mulero, Pablo Pou, Taner Esat, Markus Ternes, Ruslan Temirov, F. Stefan Tautz, Ruben Perez
Chemical Physics
Enhancing Diffusion-Based Sampling with Molecular Collective Variables
Juno Nam, Bálint Máté, Artur P. Toshev et al. (+6 more)
Diffusion-based samplers learn to sample complex, high-dimensional distributions using energies or log densities alone, without training data. Yet, they remain impractical for molecular sampling because they are often slower than molecular dynamics and miss thermodynamically relevant modes. Inspired by enhanced sampling, we encourage exploration by introducing a sequential bias along bespoke, information-rich, low-dimensional projections of atomic coordinates known as collective variables (CVs). We introduce a repulsive potential centered on the CVs from recent samples, which pushes future samples towards novel CV regions and effectively increases the temperature in the projected space. Our resulting method improves efficiency, mode discovery, enables the estimation of free energy differences, and retains independent sampling from the approximate Boltzmann distribution via reweighting by the bias. On standard peptide conformational sampling
benchmarks, the method recovers diverse conformational states and accurate free energy profiles. We are the first to demonstrate reactive sampling using a
diffusion-based sampler, capturing bond breaking and formation with universal interatomic potentials at near-first-principles accuracy. The approach resolves reactive energy landscapes at a fraction of the wall-clock time of standard sampling methods, advancing
diffusion-based sampling towards practical use in molecular sciences.
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All authors Juno Nam, Bálint Máté, Artur P. Toshev, Manasa Kaniselvan, Rafael Gómez-Bombarelli, Ricky T. Q. Chen, Brandon Wood, Guan-Horng Liu, Benjamin Kurt Miller
Atomic Physics
Millimeter Wave Imaging using Autler-Townes Splitting Induced Fluorescence from Rydberg Atoms in Rubidium Vapor
Gour Pati, Daniel Mechael, Frederik K. Fatemi et al. (+1 more)
We demonstrate millimeter wave (mmWave) imaging using Autler-Townes (AT) splitting-induced fluorescence in rubidium vapor. By employing counter-propagating probe and coupling beams, we create a plane of atoms in a dark state that is sensitive to incident mmWave and demonstrate the method with mmWaves resonant with the transition between two neighboring Rydberg states at 91.4 giga hertz. Objects in the mmWave beam path affect the spatial profile of the mmWave field, which, in turn, leads to spatial variation of optical fluorescence at 780 nm. This results in a transduction of the mmWave spatial profile to an optical image that can be acquired by a CCD camera. We demonstrate real-time, diffraction-limited mmWave imaging in transmission geometry, over an effective sensing area of 6.5 cm square with a minimum 600 micro-volt per cm detectable electric field and a rapid 16.4 micro-second response time. In addition, we demonstrate this method with a variety of imaging masks, including 3D-printed
vortex phase plates. Our study provides a pathway for high-speed and high-resolution mmWave imaging with potential applications in security, communications, and scientific research.
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All authors Gour Pati, Daniel Mechael, Frederik K. Fatemi, Renu Tripathi
Biological Physics
Exosome-mediated chemotaxis optimizes leader-follower cell migration
Louis González and Andrew Mugler
Cells frequently employ extracellular vesicles, or exosomes, to signal across long distances and coordinate collective actions. Exosomes diffuse slowly, can be actively degraded, and contain
stochastic amounts of molecular cargo. These features raise the question of the efficacy of exosomes as a directional signal, but this question has not be systematically investigated. We develop a theoretical and computational approach to quantify the limits of exosome-mediated chemotaxis at the individual
cell level. In our model, a leader
cell secretes exosomes, which diffuse in the extracellular space, and a follower
cell guides its migration by integrating discrete exosome detections over a finite
memory window. We combine analytical calculations and
stochastic simulations and show that the chemotactic velocity exhibits a non-monotonic dependence on the exosome cargo size. Small exosomes produce frequent but weak signals, whereas large exosomes produce strong but infrequent encounters. In the presence of nonlinear signal transduction, this tradeoff leads to an optimal cargo size that maximizes information throughput, as quantified by the average speed of the follower
cell. Using a reduced one-dimensional model, we derive closed-form expressions coupling the optimal cargo size to follower speed as a function of secretion rate,
memory time, and detection sensitivity. These results identify molecular packaging and
memory integration as key determinants of exosome-mediated information transmission and highlight general design principles for optimization of migration under guidance by discrete and diffusible signaling particles.
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Biological Physics · Cross-listed from cond-mat.soft
Modelling of magnetic vortex microdisc dynamics under varying magnetic field in biological viscoelastic environments
Andrea Visonà, Robert Morel, Hélène Joisten et al. (+2 more)
Magnetically driven microparticles provide a versatile platform for probing and manipulating biological systems, yet the physical framework governing their actuation in complex environments remains only partially explored. Within the field of cellular magneto-mechanical stimulation,
vortex microdiscs have emerged as particularly promising candidates for developing novel therapeutic approaches. Here, we introduce a simplified two-dimensional model describing the magneto-mechanical response of such particles embedded in viscoelastic media under varying
magnetic fields. Using a Maxwell description of the medium combined with simplified elasticity assumptions, we derive analytical expressions and support them with numerical simulations of particle motion under both oscillating and rotating
magnetic fields. Our results show that rotating fields typically induce oscillatory dynamics and that the transition to asynchronous motion occurs at a critical frequency determined by viscosity and stiffness. The amplitude and phase of this motion is governed by the competition between
magnetic and viscoelastic contributions, with particle motion being strongly impaired when the latter dominate. Energy-based considerations further demonstrate that, within the frequency range explored of few tens of Hertz, no heat is generated – distinguishing this approach from
magnetic hyperthermia – while the elastic energy transferred to the surrounding medium is, in principle, sufficient to perturb major cellular processes. This work provides a simple framework to anticipate the first-order influence of rheological properties on magnetically driven microdisc dynamics, thereby enabling a better understanding of their impact in
cells or extracellular materials and bridging the gap between experimental observations and theoretical modelling.
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All authors Andrea Visonà, Robert Morel, Hélène Joisten, Bernard Dieny, Alice Nicolas
Atomic Physics
Fabrication of an atom chip for Rydberg atom-metal surface interaction studies
O. Cherry, J. D. Carter and J. D. D. Martin
An atom chip has been fabricated for the study of interactions between $^{87}$Rb Rydberg atoms and a Au surface. The chip tightly confines cold atoms by generating high
magnetic field gradients using microfabricated current-carrying wires. These trapped atoms may be excited to Rydberg states at well-defined atom-surface distances. For the purpose of Rydberg atom-surface interaction studies, the chip has a thermally evaporated Au surface layer, separated from the underlying trapping wires by a planarizing polyimide dielectric. Special
attention was paid to the edge roughness of the trapping wires, the planarization of the polyimide, and the grain structure of the Au surface.
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Plasma Physics
Lagrangian Formulation of the Snowplow Model and Operating Point for Z pinch Devices
Miguel Cárdenas, Alejandro Nettle and Leandro Núñez
We write down the lagrangian for the snowplow model of the Z pinch system. Then, we develop the Euler-Lagrange equations to find out the corresponding equations of motion. Next, we set a criterion for quantitatively estimating the performance of Z pinch devices. Finally, we apply this criterion to a specific Z pinch system.
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Plasma Physics
Loading non-Maxwellian Velocity Distributions in Particle Simulations
Seiji Zenitani, Shunsuke Usami and Shuichi Matsukiyo
Numerical procedures for generating non-Maxwellian velocity distributions in particle simulations are presented. First, Monte Carlo methods for an $(r,q)$ distribution that generalizes flattop and kappa distributions are discussed. Then, two rejection methods for the regularized kappa distribution are presented, followed by a comparison in the $\kappa$ space. A simple recipe is proposed for the subtracted kappa distribution. Properties and numerical recipes for the ring and shell distributions with a finite Gaussian width are discussed. The ring and shell Maxwellians are further introduced as alternatives to the ring and shell distributions. Finally, methods for the super-Gaussian and the filled-shell distributions are presented.
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Atomic Physics · Cross-listed from quant-ph
Optimal and efficient inference tools for field tracking with precessing spins
Klaudia Dilcher, Piotr Bania, Diana Mendez-Avalos et al. (+3 more)
Precise, real-time monitoring of
magnetic field
evolution is important in applications including
magnetic navigation and searches for physics beyond the standard model. One main field-monitoring technique, the
spin-precession magnetometer (SPM), observes electron,
nucleus, colour centre, or
muon spins as they precess in response to their local
magnetic field. Here, we study
Bayesian signal-recovery methods for SPMs in the free-induction decay (FID) mode. In particular, we study tracking of field changes well within the coherence time of the
spin system, and thus well beyond the response bandwidth, as in [R. Jiménez-Martínez et al., Phys. Rev. Lett. 120, 040503 (2018)]. We derive the
Bayesian Cramér-Rao bound that dictates the ultimate precision in estimating the Larmor frequency, which we show to be attained by the computationally expensive prediction error method (PEM). Relative to this
benchmark, we show that the extended Kalman filter (EKF) and cubature Kalman filter (CKF) offer near-optimal tracking that is also computationally efficient, with the use of the latter giving better results only for a large
spin number. Focusing thus on the EKF, we show that it is sufficient to accurately track fluctuating and unknown transient signals. Our methods can be easily adapted to other types of sensors undergoing nonlinear dissipative dynamics and experiencing intrinsic Gaussian-like
stochastic noises.
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All authors Klaudia Dilcher, Piotr Bania, Diana Mendez-Avalos, Aleksandra Sierant, Morgan W. Mitchell, Jan Kolodynski
Optics
Linear and nonlinear optical tuning with Sb$_2$S$_3$-based metasurfaces
Amin Zamani, Meibao Qin, Gabriel Sanderson et al. (+11 more)
Here, we experimentally demonstrate the unique properties of Sb$_2$S$_3$ metasurfaces on monolithic and hybridised Sb$_2$S$_3$-Si platforms. Their advantages are particularly pronounced in the telecommunication spectral range, where both phases remain nearly lossless together with a large and stable refractive index contrast compared to other counterparts. The monolithic metasurface enables transmission modulation depths of up to 92% and resonance shifts as large as $\sim$150~nm at the telecommunication wavelengths through
laser-induced phase transitions from amorphous to $\sim$ 50% polycrystalline states. Furthermore, we demonstrate that integrating a silicon overlayer introduces high-Q hybrid resonances with enhanced near-field confinement, enabling comparable modulation, experimentally, with nearly half the
laser switching power required as compared to the monolithic structure. Beyond linear optical switching, the broad resonance tunability of the Sb$_2$S$_3$ metasurface, together with the strong third-order nonlinearity of these materials, provides a promising platform for tunable nonlinear light generation. By exciting the Sb$_2$S$_3$ metasurfaces with a fixed broadband pump, we experimentally demonstrate tunable third-harmonic generation emission over a $\sim$40~nm spectral range through phase-change transition. Such tunability provides a versatile route for integrating Sb$_2$S$_3$ with intrinsically highly nonlinear materials to enable the combination of large optical tunability and efficient nonlinear light generation. We have proven this concept via our hybrid Sb$_2$S$_3$-Si platform, which shows a threefold enhancement in tunable THG emission arising from the combined nonlinear responses of Sb$_2$S$_3$ and silicon, and benefiting from enhanced electromagnetic field confinement enabled by the metasurface's high-Q resonances.
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All authors Amin Zamani, Meibao Qin, Gabriel Sanderson, Lu Zhang, Sara Moujdi, Qiwei Miao, Ze Zheng, Mohammadhossein Momtazpour, Christopher J. Mellor, Wending Zhang, Ting Mei, Zakaria Mansouri, Lei Xu, Mohsen Rahmani
Fluid Dynamics
Is the transition to unsteadiness in the wake of slender bodies an artefact of boundary conditions ?
David Fabre
This work considers the transition to unsteadiness in the wake of 2D slender bodies, and questions the relevance of the generally accepted scenario involving a region of absolute instability within the near wake. The case of a thin plate at zero incidence is first considered. Despite the absence of absolute instability region, global stability analysis reveals the existence of numerous unstable
eigenvalues organized along a characteristic "arc-branch" whose properties significantly depends upon the size of the numerical domain. These arc-branch modes are explained as resulting from a non-local pressure perturbation spuriously generated at the outlet of the domain due to the no-stress boundary condition, which then triggers the shedding of vortical structures at the trailing edge of the plate. The case of NACA0012 wing profiles at small incidences is then considered. Global stability analysis reveals that both the non-local spurious feedback mechanism and the classical local feedback mechanism are active. Trying to suppress the spurious feedback by enlarging the size of the numerical domain is shown to be inefficient. On the other hand, filtering methods suppressing the exponential spatial growth of perturbations, with either a sponge or a complex mapping, are found to be efficient. Thanks to these ideas, the critical Reynolds number and Strouhal number at onset can eventually be computed and are mapped for incidences in the range $ \alpha \in [0^o - 5 ^o]$. It is postulated that the non-local feedback mechanism evidenced here could be at play in other strongly convective flows.
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Geophysics
Quantifying the form-flow-saltation dynamics of aeolian sand ripples
J.M. Nield, M.C. Baddock, G.F.S. Wiggs et al. (+9 more)
Ripples are the most fundamental and ubiquitous aeolian bedforms formed on sandy surfaces, but their small size and fast response times make them inherently difficult to measure. However, these attributes also make ripples excellent flow indicators, and they have been used extensively in planetary locations for this purpose. Here, we use terrestrial
laser scanning to measure ripple morphometry and celerity coincidently, as well as saltation height above rippled surfaces. We find that although ripple height and wavelength respond linearly to increased shear velocity, under strong winds ripple celerity exhibits a non-linear increase. This relationship at high wind speeds is also reflected in the response of aerodynamic roughness and saltation dynamics, with a greater maximum saltation height present over ripple lee slopes. Importantly, when using ripple patterns as indicators of flow conditions, celerity or height should be used in preference to wavelength as their dynamics respond faster to changing wind speed. In planetary and stratigraphic settings where measuring celerity is not possible, wavelength should be considered as indicative of consistent wind conditions rather than the full range of sand transporting wind speeds.
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All authors J.M. Nield, M.C. Baddock, G.F.S. Wiggs, J. Best, K.T. Christensen, P. Delorme, A. Valdez, N.R. Bristow, M.H.T. Hipondoka, D.P. Goss, N.S. Wallum, P. Claudin
Plasma Physics
Towards fully predictive gyrokinetic full-f simulations: validation and triangularity studies in TCV
A. C. D. Hoffmann, T. N. Bernard, M. Francisquez et al. (+6 more)
Designing economical
magnetic confinement fusion power plants motivates computational tools that can estimate
plasma behavior from engineering parameters without direct reliance on experimental measurement of the
plasma profiles. In this work, we present full-$f$ global gyrokinetic (GK)
turbulence simulations of edge and scrape-off layer
turbulence in tokamaks that use only
magnetic geometry, heating power, and particle inventory as inputs. Unlike many modeling approaches that employ free parameters fitted to experimental data, raising uncertainties when extrapolating to reactor scales, his approach directly simulates
turbulence and resulting profiles through GK without such empirical adjustments. This is achieved via an adaptive sourcing
algorithm in Gkeyll that strictly controls energy injection and emulates particle sourcing due to neutral recycling. We show that the simulated kinetic profiles compare reasonably well with Thomson scattering and Langmuir probe data for Tokamak à Configuration Variable (TCV) discharge #65125, and that the simulations reproduce characteristic features such as blob transport and self-organized electric fields. Applying the same framework to study triangularity effects suggests mechanisms contributing to the improved confinement reported for negative triangularity (NT). Simulations of TCV discharges #65125 and #65130 indicate that NT increases the $E \times B$ flow shear (by about 20% in these cases), which correlates with reduced turbulent losses and a modest change in the distribution of power exhaust to the vessel wall. While the physical models contain approximations that can be refined in future work, the predictive capability demonstrated here, evolving multiple profile relaxation times with kinetic electron and ion models in hundreds of GPU hours, indicates the feasibility of using Gkeyll to support design studies of fusion devices.
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All authors A. C. D. Hoffmann, T. N. Bernard, M. Francisquez, G. W. Hammett, A. Hakim, J. Boedo, R. Rizkallah, C. K. Tsui, the TCV team
Optics
General model and modulation strategies for Sagnac-based encoders
Federico Berra, Matías Rubén Bolaños, Alberto De Toni et al. (+6 more)
In recent decades, there has been an increasing demand for faster modulation schemes. Electro-optic modulators are essential components in modern photonic systems, enabling high-speed control of light for applications ranging from telecommunications to
quantum communication. Conventional inline and Mach-Zehnder modulators, while widely adopted, are limited by bias drift, high operating voltages, and polarization-mode dispersion. Sagnac loop-based modulators have recently emerged as a promising alternative, offering inherent stability against environmental fluctuations and eliminating the need for active bias control. In this work, we present a comprehensive model of the Sagnac modulator that captures both intensity and polarization modulation. We analyze the role of asymmetry in the loop, highlighting its impact on the achievable repetition rate, and propose modulation strategies to overcome these constraints. Finally, we investigate the symmetric Sagnac configuration and demonstrate practical techniques for achieving robust modulation while mitigating experimental challenges. Our results establish the Sagnac modulator as a versatile and stable platform for next-generation photonic and
quantum communication systems.
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All authors Federico Berra, Matías Rubén Bolaños, Alberto De Toni, Kannan Vijayadharan, Costantino Agnesi, Marco Avesani, Andrea Stanco, Paolo Villoresi, Giuseppe Vallone
Chemical Physics · Cross-listed from cond-mat.mes-hall
Neuromorphic heat transport effects in a molecular junction
Renai Chen and Galen T. Craven
Understanding energy transport at the nanoscale is an open and fundamental challenge in the molecular sciences with direct implications for the design of new electronics, computing devices, and materials. While nanoscale energy transport under steady-state conditions has been studied extensively, there is much less known about energy transport under time-dependent driving forces, particularly in the far-from-
equilibrium regime. In this work, we use nonequilibrium molecular dynamics simulations and
stochastic thermodynamics to investigate energy transport in a well-studied nanoscale system, a molecular junction, subjected to a time-periodic temperature gradient. The primary observation is that molecular junctions can exhibit heat transport hysteresis, a phenomenon in which the heat flux through a system depends not only on the instantaneous value of a time-dependent temperature bias but also on the temporal history of that bias. The presented findings illustrate that molecular junctions can exhibit the specific
memory effect, heat transport hysteresis, that is essential for the design of thermal neuromorphic computers. This work elucidates a potential pathway toward the realization of such devices.
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Optics
Dipole-quadrupole model and multipole analysis of resonant membrane metasurfaces
Izzatjon Allayarov, Andrey B. Evlyukhin and Antonio Calà Lesina
Membrane-metasurfaces, formed by periodic arrangements of holes in a dielectric layer, are gaining
attention for their easier manufacturing via subtractive techniques, unnecessity of substrates, and access to resonant near-fields. Despite their practical relevance, their theoretical description remains elusive. Here, we present a semi-analytical dipole-quadrupole model for the multipole analysis of numerically-obtained reflection and transmission spectra in metasurfaces excited at arbitrary angles. Dipole models are generally sufficient to study traditional metasurfaces made of solid nanostructures. However, the inclusion of electric and
magnetic quadrupoles is necessary to study membrane-metasurfaces, which offer an ideal platform to showcase our method. We demonstrate the importance of choosing the optimal position of a symmetric membrane-metasurface's unit
cell to ensure the sufficiency of the dipole-quadrupole approximation. We show that our formalism can explain complex phenomena arising from inter-multipole interference, including
lattice anapole and generalized Kerker effects, Fano resonances, and quasi-bound states in the continuum. We also present the applicability of the method to membrane-metasurfaces with non-centrosymmetric unit
cells (e.g., conical holes and surface voids). By enabling a deeper insight into the coupling mechanisms leading to the formation of local and collective resonances, our method expands the electromagnetics toolbox to study, understand, and design conventional and membrane-metasurfaces.
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Atomic Physics
Lithium Faraday Filter: Some Like It Hot
Maximilian Luka, Yijun Wang, Denis Uhland et al. (+1 more)
Magnetically induced rotation of linearly polarized light near an atomic resonance, combined with Doppler-broadened absorption windows, enables narrowband transmission of optical frequencies. An ultra-narrowband lithium vapor Faraday filter at about 671 nm is investigated experimentally and theoretically. The resulting Faraday filter transmittance is demonstrated using a lithium heat pipe oven under longitudinal
magnetic fields ranging from 0 to 300 G. Optimization of the lithium Faraday filter performance reveals an optimal operating point at 264 {\deg}C and an external
magnetic field of 269 G, yielding a peak transmission of approx. 82%. The lithium D$_1$- and D$_2$-transitions are only 10 GHz apart and temperature broadening leads to an overlap of the isotopes D-lines. Thus, the applied theoretical model needs to consider both transitions simultaneously. For this purpose, we extended an existing Python library (ElecSus), which now allows for the calculation of the atomic susceptibilities of lithium.
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All authors Maximilian Luka, Yijun Wang, Denis Uhland, Ilja Gerhardt
Optics
Interference-induced cavity resonances and imaginary Rabi splitting
Anael Ben-Asher, Antonio I. Fernandez-Dominguez and Johannes Feist
Polaritons are usually described within single-mode cavity QED models. However, nanophotonic environments typically involve several modes that spectrally overlap and interfere, giving rise to sharp dip features such as Fano profiles in the electromagnetic spectral density. Here, we identify these features as interference-induced resonances, effective electromagnetic modes with complex, non-Hermitian couplings to
quantum emitters. We show that these modes hybridize with emitters to form polaritons even when the system parameters do not satisfy the single-mode strong-coupling criterion. Moreover, the resulting polaritons differ in their decay rates, a phenomenon we term imaginary Rabi splitting. Extending the analysis to ensembles, we find that coupling to interference-induced resonances produces long-lived polaritons that can outlast excitonic dark states. Numerical simulations of a realistic hybrid metallodielectric platform confirm these predictions and demonstrate their robustness against disorder and loss. Our results reveal a new polaritonic regime beyond the single-mode description, offering new opportunities for controlling light-matter interactions in complex electromagnetic environments.
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Chemical Physics
Marcus Theory and The Condon Approximation Revisited I: E-SHAKE and Seam Sampling
D. Vale Cofer-Shabica, Jennifer R. DeRosa and Joseph E. Subotnik
Marcus theory is the workhorse of theoretical chemistry for predicting the rates of charge and energy transfer. Marcus theory overwhelmingly agrees with experiment – both in terms of electron transfer and triplet energy transfer – for the famous set of naphthalene-bridge-biphenyl and naphthalene-bridge-benzophenone systems studied by Piotrowiak, Miller, and Closs. That being said, the agreement is not perfect, and in this manuscript, we revisit one key point of disagreement: the molecule C-13-ae ([3,equatorial]-naphthalene-cyclohexane-[1,axial]-benzophenone). To better understand the theory-experiment disagreement, we introduce and employ a novel scheme to sample the seam between two diabatic electronic states (E-SHAKE) through which we reveal the breakdown of the Condon approximation and the presence of a conical intersection for the C-13-ae molecule; we also predict an isotopic effect on the rate of triplet-triplet energy transfer.
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Optics
Ideal Optical Antimatter using Passive Lossy Materials under Complex Frequency Excitation
Olivia Y. Long, Peter B. Catrysse, Seunghoon Han et al. (+1 more)
The original concept of left-handed material has inspired the possibility of optical antimatter, where the effect of light propagation through a medium can be completely cancelled by its complementary medium. Despite recent progress in the development of negative-index metamaterials, losses continue to be a significant barrier to realizing optical antimatter. In this work, we show that passive, lossy materials can be used to realize optical antimatter when illuminated by light at a complex frequency. We further establish that one can engineer arbitrary complex-valued permittivity and permeability in such materials. Strikingly, we show that materials with a positive index at real frequencies can act as negative-index materials under complex frequency excitation. Using our approach, we numerically demonstrate the optical antimatter functionality, as well as double focusing by an ideal perfect lens and superscattering. Our work demonstrates the power of temporally structured light in unlocking the promising opportunities of complementary media, which have until now been inhibited by material loss.
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All authors Olivia Y. Long, Peter B. Catrysse, Seunghoon Han, Shanhui Fan
Classical Physics
Advanced creep modelling for polymers: A variable-order fractional calculus approach
José Geraldo Telles Ribeiro and Americo Cunha Jr
Polymer-based plastics exhibit time-dependent deformation under constant stress, known as creep, which can lead to rupture or static fatigue. A common misconception is that materials under tolerable static loads remain unaffected over time. Accurate long-term deformation predictions require experimental creep data, but conventional models based on simple rheological elements like springs and dampers often fall short, lacking the flexibility to capture the power-law behaviour intrinsic to creep processes. The springpot, a fractional calculus-based element, has been used to provide a power-law relationship; however, its fixed-order nature limits its accuracy, particularly when the deformation rate evolves over time. This article introduces a variable-order (VO) springpot model that dynamically adapts to the evolving viscoelastic properties of polymeric materials during creep, capturing changes between glassy, transition and rubbery phases. Model parameters are calibrated using a robust procedure for model identification based on the cross-
entropy (CE) method, resulting in physically consistent and accurate predictions. This advanced modelling framework not only overcomes the limitations of the fixed-order models but also establishes a foundation for applying VO mechanics to other viscoelastic materials, providing a valuable tool for predicting long-term material performance in structural applications.
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Data Analysis and Statistics · Cross-listed from cond-mat.stat-mech
Non-Normal Eigenvector Amplification in Multi-Dimensional Kesten Processes
Virgile Troude and Didier Sornette
Heavy-tailed fluctuations and power law statistics pervade physics, finance, and economics, yet their origin is often ascribed to systems poised near criticality. Here we show that such behavior can emerge far from instability through a universal mechanism of non-normal eigenvector amplification in multidimensional Kesten processes $x_{t+1}=A_t x_t+\eta_t$, where $A_t$ are random interaction
matrices and $\eta_t$ represents external inputs, capturing the evolving interdependence among $N$ coupled components. Even when each random multiplicative
matrix is spectrally stable, non-orthogonal eigenvectors generate transient growth that renormalizes the Lyapunov exponent and lowers the tail exponent, producing stationary power laws without
eigenvalues crossing the stability boundary. We derive explicit relations linking the Lyapunov exponent and the tail index to the statistics of the condition number, $\gamma\!\sim\!\gamma_0+\ln\kappa$ and $\alpha\!\sim\!-2\gamma/\sigma_\kappa^2$, confirmed by numerical simulations. This framework offers a unifying
geometric perspective that help interpret diverse phenomena, including
polymer stretching in
turbulence,
magnetic field amplification in dynamos,
volatility clustering and wealth inequality in financial systems. Non-normal interactions provide a collective route to scale-free behavior in globally stable systems, defining a new universality class where multiplicative feedback and transient amplification generate critical-like statistics without spectral criticality.
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Chemical Physics
Marcus Theory and The Condon Approximation Revisited II: The Horror of Triplet Energy Transfer
Jennifer R. DeRosa, Tian Qiu, D. Vale Cofer-Shabica et al. (+1 more)
We investigate the applicability of the Condon approximation (i.e. the notion that the diabatic coupling is invariant to geometry) in the context of both electron transfer (ET) and triplet energy transfer (TET) and compare the two cases. Although it is well appreciated that diabatic couplings usually arise from the interactions of electronic wavefunction tails, we show that ET tails are very different from TET tails. Using a simple model problem, our analysis explains in detail why the rates of TET decays with twice the rate of ET, while also leading to the hypothesis that the smaller diabatic couplings found for TET (versus ET) should imply more sensitivity to non-Condon fluctuations. As an example, for the classic sets of molecules investigated by Closs, we show that the Condon approximation is indeed less applicable for TET than for ET.
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All authors Jennifer R. DeRosa, Tian Qiu, D. Vale Cofer-Shabica, Joseph E. Subotnik
Medical Physics
Collagen and myocyte interplay in cardiac volume overload: a multi-constituent growth and remodeling framework
Ludovica Maga, Mathias Peirlinck and Lise Noël
Hearts subjected to volume overload (VO) are prone to detrimental anatomical and functional changes in response to elevated mechanical loading, ultimately leading to heart failure. Experimental findings now emphasize that organ-scale changes following VO cannot be explained by myocyte growth alone, as traditionally proposed in the literature. Collagen degradation, in particular, has been associated with VO and assumed to play a central role in both its acute and chronic stages. This hypothesis, however, remains to be substantiated by comprehensive mechanistic evidence, and each constituent contribution to myocardial growth and remodeling (G&R) processes is yet to be quantified. In this work, we present a multi-constituent G&R framework that integrates a mixture-based constitutive model within the kinematic growth formulation. This framework enables us to mechanistically assess the relative contributions of collagen and myocyte changes to alterations in tissue properties, ventricular dimensions, and growth phenotype. Our numerical results confirm that collagen remodeling affects the passive mechanical response of the myocardium, whereas myocytes predominantly influence the extent and phenotype of VO-induced growth. Importantly, collagen degradation exacerbates myocyte hypertrophy, revealing a synergistic interplay that accelerates the left ventricular eccentric growth and thereby promotes systolic dysfunction. This work constitutes an important step towards an integrated characterization of the early compensatory stages of VO-induced cardiac G&R.
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Fluid Dynamics
Verification of Convergent-Divergent Nozzle Designs in Propulsion Aerospace Applications
Noah L. Estrada, Marc A. Cantu, Arturo Rodriguez et al. (+5 more)
The performance of convergent and divergent nozzles is critical in aerospace propulsion systems, where the efficient expansion of high-temperature, high-pressure gases directly impacts thrust generation. In this study, we investigate a series of nozzle geometries using numerical simulations in ANSYS Fluent, guided by classical compressible flow theory, initially developed by Ludwig Prandtl. The governing equations of conservation of mass, momentum, and energy are solved under steady-state conditions, with emphasis on shock formation, boundary-layer effects, and Mach number distributions across the nozzle throat and divergent section. Parametric analyses are conducted to evaluate the influence of nozzle contour, area ratio, and throat geometry on flow acceleration and thrust coefficient. The results demonstrate close agreement with theoretical predictions of isentropic compressible flow while also highlighting deviations due to viscous and three-dimensional effects. These findings provide design insights for optimizing nozzle performance across propulsion applications, from launch vehicles to high-speed air-breathing systems. We obtained absolute error differences of 2.05 percent, 6.03 percent, and 9.9 percent in the throat temperature measurements for the RL10B2, SSME-40k, and A-1 nozzles, respectively.
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All authors Noah L. Estrada, Marc A. Cantu, Arturo Rodriguez, Andrew R. Ybarra, Jeffrey H. Farris, Francisco O. Aguirre Ortega, Vineeth Vijaya Kumar, Vinod Kumar
Classical Physics
The vector potential of a steady azimuthal current density. Once again
Antonio O. Bouzas
We give an integral expression for the vector potential of a time-independent, steady azimuthal current density. Our derivation is substantially simpler and somewhat more general than others given in the literature. As an illustration, we recover the results for the vector potential of a circular current loop as an orthogonal expansion in spherical and cylindrical coordinates. Additionally, we obtain closed analytical expressions for the vector potential and the
magnetic induction of a circular current loop in terms of Legendre functions of the second kind, that are simpler than the results in terms of complete
elliptic integrals given in textbooks.
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Chemical Physics
Scalable Quantum Monte Carlo Method for Polariton Chemistry via Mixed Block Sparsity and Tensor Hypercontraction Method
Yu Zhang
We present a reduced-scaling auxiliary-field
quantum Monte Carlo (AFQMC) framework designed for large molecular systems and ensembles, with or without coupling to optical cavities. Our approach leverages the natural block sparsity of Cholesky decomposition (CD) of electron repulsion integrals in molecular ensembles and employs tensor hypercontraction (THC) to efficiently compress low-rank Cholesky blocks. By representing the Cholesky vectors in a mixed format, keeping high-rank blocks in block-sparse form and compressing low-rank blocks with THC, we reduce the scaling of exchange-energy evaluation from quartic to robust cubic in the number of molecular orbitals, while lowering
memory from cubic toward quadratic.
Benchmark analyses on one-, two-, and three-dimensional molecular ensembles (up to ~1,200 orbitals) show that: a) the number of nonzeros in Cholesky tensors grows linearly with system size across dimensions; b) the average numerical rank increases sublinearly and does not saturate at these sizes; and (c) rank heterogeneity-some blocks nearly full rank and many low rank, naturally motivating the proposed mixed block sparsity and THC scheme for efficient calculation of exchange energy. We demonstrate that the mixed scheme yields cubic CPU-time scaling with favorable prefactors and preserves AFQMC accuracy.
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Optics
Attosecond-level synchronisation of chip-integrated oscillators
Alexander E. Ulanov, Bastian Ruhnke, Theia El Sharkawy et al. (+4 more)
Synchronised
laser oscillators are essential for probing the fastest processes in chemistry, materials science, and biology down to atto-second timescales. Tight synchronisation is also crucial at scientific facilities such as free-electron
lasers or
radio-
telescopes, and increasingly relevant to communication and information technologies in multi-node networks. Current synchronisation approaches based on mode-locked
lasers achieve the required performance, but their complexity, cost, and size hinder deployment in multi-node networks. Here, we demonstrate attosecond-level synchronisation between chip-integrated microresonator
soliton oscillators operating at either 25 or 300 GHz pulse repetition rate. For synchronisation, each oscillator receives over fibre a pair of continuous-wave
lasers as a two-tone timing reference. The
lasers power the microcombs and Kerr-nonlinear synchronisation results in integrated relative timing jitter below 400 as (1 kHz to 1 MHz), without any active stabilisation. This approach enables scalable precision timing for large facilities, data centres, disaggregated computing,
navigation, and
quantum networks; ultimately, it may lead to chip-integrated attosecond photonics.
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All authors Alexander E. Ulanov, Bastian Ruhnke, Theia El Sharkawy, Thibault Wildi, Kemal Şafak, Franz Kärtner, Tobias Herr
Chemical Physics · Cross-listed from quant-ph
A Monte Carlo approach to bound Trotter error
Nick S. Blunt, Aleksei V. Ivanov and Andreas Juul Bay-Smidt
Trotter product formulas are a natural and powerful approach to perform
quantum simulation. However, the error analysis of product formulas is challenging, and their cost is often overestimated. It is established that Trotter error can be bounded in terms of spectral norms of nested commutators of the
Hamiltonian partitions [Childs et al., Phys. Rev. X 11, 011020], but evaluating these expressions is challenging, often achieved by repeated application of the triangle inequality, significantly loosening the bound. Here, we show that the spectral norm of an operator can be upper bounded by the spectral norm of an equivalent sign-problem-free operator, which can be calculated efficiently to large system sizes using projector Monte Carlo simulation. For a range of
Hamiltonians and considering second-order formulas, we demonstrate that this Monte Carlo-based bound is often extremely tight, and even exact in some instances. For the uniform electron gas we reduce the cost of performing Trotterization from the literature by an order of magnitude. For the Pariser-Parr-Pople model for linear acene molecules, which has $\mathcal{O}(N^2)$ long-range interaction terms, we show that it suffices to use $\mathcal{O}(N^{0.57})$ Trotter steps and
circuit depth $\mathcal{O}(N^{1.57})$ to implement
Hamiltonian simulation. We hope that this approach will lead to a better understanding of the potential accuracy of Trotterization in a range of important applications.
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Instrumentation and Detectors
Advancing Time-Resolved Spectroscopies with Custom Scanning Units and Event-Based Electron Detection
Yves Auad, Florian Castioni, Jassem Baaboura et al. (+9 more)
Direct electron detection is revolutionizing electron microscopy by offering lower noise, reduced point-spread function, and increased
quantum efficiency. Among these advancements, the Timepix3 hybrid-pixel direct electron detector stands out for its unique ability to output temporal information about individual hits within its pixel array. Its event-based architecture enables data-driven detection, where individual events are immediately read out from the chip. While recent studies have demonstrated the potential of event-based detectors in various applications in the context of continuous-gun scanning transmission electron microscopes (STEM), the use of such detectors with standard scanning units remains underdeveloped. In this work, we present a custom-designed, Timepix3-compatible scanning unit specifically developed to leverage the advantages of event-based detection. We explore its performance in enabling spatially and temporally resolved experiments, as well as its seamless interfacing with other time-resolved instruments, such as pulsed
lasers and electron beam blankers. Additionally, we examine the prospects for achieving enhanced temporal resolution in time-resolved experiments using continuous-gun electron microscopes, identifying key challenges and proposing solutions to improve performance. This combination of custom hardware with advanced detection technology promises to expand the capabilities of electron microscopy in both fundamental research and practical applications.
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All authors Yves Auad, Florian Castioni, Jassem Baaboura, Malo Bézard, Jean-Denis Blazit, Xiaoyan Li, Adrien Teutrie, Michael Walls, Odile Stéphan, Luiz H. G. Tizei, Francisco de La Peña, Mathieu Kociak