Computational Physics
qNEP: A highly efficient neuroevolution potential with dynamic charges for large-scale atomistic simulations
Zheyong Fan, Benrui Tang, Esmée Berger et al. (+13 more)
Although electrostatics can be incorporated into machine-learned interatomic potentials, existing approaches are computationally very demanding, limiting large-scale, long-time simulations of electrostatics-driven phenomena such as dielectric response, infrared activity, and field-matter coupling. Here, we extend the neuroevolution potential (NEP), a highly efficient machine-learned interatomic potential, to a charge-aware framework (qNEP) by introducing explicit, environment-dependent partial charges. Each ionic partial charge is represented by a neural network as a function of the local descriptor vector, analogous to the NEP site-energy model. This formulation enables the direct prediction of the Born effective charge tensor for each ion and, consequently, the polarization. As a result, dielectric properties, infrared spectra, and coupling to external electric fields can be evaluated within a unified framework. We derive consistent expressions for the forces and virials that explicitly account for the position dependence of the partial charges. The qNEP method has been implemented in the free-and-open-source GPUMD package, with support for both Ewald summation and particle-particle particle-mesh treatments of electrostatics. We demonstrate the accuracy and efficiency of the qNEP approach through representative applications to water, Li7La3Zr2O12, BaTiO3, and a magnesium-water interface. These results show that qNEP enables accurate atomistic simulations with explicit long-range electrostatics, scalable to million-atom systems on nanosecond time scales using consumer-grade GPUs.
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All authors Zheyong Fan, Benrui Tang, Esmée Berger, Ethan Berger, Erik Fransson, Ke Xu, Zihan Yan, Zhoulin Liu, Zichen Song, Haikuan Dong, Shunda Chen, Lei Li, Ziliang Wang, Yizhou Zhu, Julia Wiktor, Paul Erhart
Optics
Quantized non-Abelian helicity of flat bands in 2D Floquet topological photonic insulators
Bo Leng and Vien Van
Flat-band states in topological systems provide a unique platform for investigating strongly correlated phenomena and many body physics. However, in 2D static tight-binding systems, perfectly flat bands can only exist in the topologically trivial phase, as characterized by a zero Chern number. Here we show that by introducing periodic driving into a 2D photonic Lieb
lattice composed of coupled microring resonators, the resulting Floquet topological
insulator can host perfectly flat bands with nontrivial
topology. In particular, by tracking the
evolution of the flat-band modes over each cycle, we show that the non-Abelian displacements of the flat-band modes are characterized by a nontrivial quantized helicity even though the quasi-energy bands have zero Chern number. The helical motion of the flat-band modes can be described by a braiding of the world lines of their trajectories, with a nontrivial winding number directly connected to the helicity. We also propose a scheme to experimentally measure the quantized non-Abelian helicity in a microring
lattice subject to a synthetic
magnetic field. These results suggest that Floquet topological photonic
insulators based on coupled microring resonators can provide a versatile platform for investigating non-Abelian topological physics and strongly correlated phenomena in photonic flat-band systems.
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Medical Physics
On the Application of Fractional Order Derivatives for Characterizing Brain White Matter Viscoelasticity
P. Pasupathy, J.G. Georgiadis and A.A Pelegri
Conventional viscoelastic characterization of
brain white matter (BWM), typically described using Prony series models, remains a largely empirical representation that is difficult to interpret physically. Growing evidence suggests that BWMviscoelasticity follows power-law behavior. Under the assumptions of linear viscoelasticity and causality, a power-law model in the frequency domain yields a fractional viscoelastic model in the time domain. A fractional viscoelastic constitutive model for the axon and extracellular
matrix (ECM) is implemented via a Fortran VUMAT subroutine. A biphasic periodic finite element (FE) model of hexagonally packed representative volume elements (RVEs) of axons embedded in an ECM is constructed in Abaqus under quasi-static loading. The inverse problem of extracting homogenized material properties is solved using an optimization workflow. The model predicts that the springpot coefficient, which determines the solid-fluid behavior and, the power-law exponent, which encodes information about the underlying tissue architecture, follows a bi-logistic function along the transverse normal and shear directions. The nonlinear variation of the parameters reveals two distinct stiffening stages: a lower rate at low axon volume fractions, followed by a higher rate as increased axonal content reinforces the RVE. To our knowledge, this study is the first to propose and implement a 3D fractional viscoelastic FE model of the corpus callosum of BWM in the time domain. The thread-safe implementation of the VUMAT achieves significantly faster performance than existing approaches. The results reveal nonlinear variation in material parameters, directional dependence of BWM mechanics, and the complex interplay among microstructural elements.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Frequency- and time-resolved second order quantum coherence function of IDTBT single-molecule fluorescence
Quanwei Li, Yuping Shi, Lam Lam et al. (+2 more)
The frequency- and time-resolved second order
quantum coherence function (g(2)({\tau})) of single-molecule fluorescence has recently been proposed as a powerful new
quantum light spectroscopy that can reveal intrinsic
quantum coherence in excitation energy transfer in molecular systems ranging from simple dimers to photosynthetic complexes. Yet, no experiments have been reported to date. Here, we have developed a single-molecule fluorescence g(2)({\tau})
quantum light spectroscopy (SMFg2-QLS) that can simultaneously measure the fluorescence intensity, lifetime, spectra, and g(2)({\tau}) with frequency resolution, for a single molecule in a controlled environment at both room temperature and cryogenic temperature. As a proof of principle, we have studied single molecules of IDTBT (indacenodithiophene-co-benzothiadiazole), a semiconducting donor-acceptor conjugated copolymer with a chain-like structure that shows a high carrier mobility and annihilation-limited long-range
exciton transport. We have observed different g(2)({\tau}=0) values with different bands or bandwidths of the single molecule IDTBT fluorescence. The general features are consistent with theoretical predictions and suggest non-trivial excited state
quantum dynamics, possibly showing
quantum coherence, although further analysis and confirmation will require additional theoretical calculations that take into account the complexity and inhomogeneity of individual IDTBT single molecular chains. Our results demonstrate the feasibility and promise of frequency- and time-resolved SMFg2-QLS to provide new insights into molecular
quantum dynamics and to reveal signatures of intrinsic
quantum coherence in photosynthetic light harvesting that are independent of the nature of the light excitation.
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All authors Quanwei Li, Yuping Shi, Lam Lam, K. Birgitta Whaley, Graham Fleming
Plasma Physics
Energy partition in collisionless counterstreaming plasmas
Alexis Marret and Frederico Fiuza
Fast, counter-streaming
plasma outflows drive
magnetic field amplification,
plasma heating, and particle acceleration in numerous astrophysical environments, from
supernova remnant shocks to active
galactic nuclei jets. Understanding how, in the absence of Coulomb collisions, energy is redistributed between the different
plasma species remains a fundamental open question. We use 3D fully-kinetic simulations to investigate energy partition in weakly magnetized counter-propagating
plasmas. Our results reveal a complex interplay between different processes, where at early times the Weibel instability drives a first stage of
magnetic field amplification and at late times the kinking of current filaments drives a second amplification stage via a dynamo-type mechanism. Electrons are heated primarily during the latter phase through
magnetic pumping. By the time the flows thermalize, we observe that the final temperature ratio $T_e/T_i$ and energy partition depend on the ion-to-electron mass ratio. For electron-
proton flows, the electron thermal energy only reaches up to a few percent of the initial ion kinetic energy.
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Fluid Dynamics
A theoretical model for oceanic submesoscales under next-order effects of strain and turbulence
Shirui Peng and Abigail Bodner
Submesoscale currents in the oceanic mixed layer, comprising fronts, eddies, and filaments, are characterized by $\textit{O}(1)$ Rossby numbers (Ro). These features, which constantly interact with background mesoscale flows and boundary layer
turbulence (BLT), are critical for mediating vertical exchange between the surface and the ocean interior. Despite growing insight into their generation and
evolution, the modification of initially balanced submesoscale dynamics by finite-Ro effects under the combined influence of mesoscale strain and BLT remains unresolved. In this study, we address this question through a perturbation analysis of two-dimensional, geostrophically adjusted oceanic fronts and filaments, adapting the analytical models of \citet{shakespeare_generalized_2013} and \citet{bodner_breakdown_2020}. This framework allows for a systematic exploration across a broad range of Rossby numbers Ro, Ekman numbers Ek, and strain parameters. The first-order solution under pure mesoscale strain exhibits clear frontogenesis and closely mirrors the full model dynamics during early inertial periods, despite the absence of an exponential collapse. Under BLT perturbation, the first-order solution confirms the distinct frontogenetic and frontolytic tendencies associated with eddy viscosity and diffusivity, respectively; however, no transition between these regimes is observed across the explored Ro and Ek parameter space for vertical mixing. When both strain and BLT perturbations are present, turbulent fluxes can strengthen, weaken, or even reverse strain-induced frontogenesis depending on the parameter regime. These results suggest that mixed-layer parameterizations must carefully account for the spatial variability of BLT within submesoscale currents to accurately capture frontal
evolution under mesoscale strain.
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Classical Physics
An alternative approach to several important systems in classical mechanics: energy factorization
Karlo Lelas and Dario Jukić
We show how several important classical problems, with positive definite potential energy, can be solved by starting from the factorization of the total mechanical energy using complex numbers. In particular, we derive in a new way exact analytical solutions for: simple harmonic oscillator, vertical projectile motion, motion under a repulsive inverse cube force, and damped harmonic oscillator (with linear damping). We also show how this approach easily yields an excellent approximation of the energy decay and a new approximate analytical solution in the case of a weakly damped harmonic oscillator. Our derivations are suitable for undergraduate physics teaching as an alternative to solving Newton's equations of motion. In addition, we comment on the limitations of our approach, but also on the insights it provides and opportunities for further research.
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Optics · Cross-listed from quant-ph
Complete transparency with three active-passive-coupled optical resonators
Xiao-Bo Yan, Liu Yang and Bing He
The phenomena of induced transparency, with the typical examples of electromagnetically induced transparency (EIT) in atomic media and those based on coupled optical resonators, have attracted tremendous interest since their discoveries. Owing to the limitations of the involved physical elements, however, near-100% transmissions were reported under highly demanding experimental conditions. With a structure of three linearly coupled optical resonators, an active one carrying optical gain and two passive ones simply with dissipation, we demonstrate that a transmitted light field can become completely transparent through the structure, which displays all properties similar to those of EIT. It is due to a destructive interference mechanism that totally eliminates the intracavity field in the dissipative resonator directly coupled to the transmitted field of any feasible power, when the coupling strength of two other resonators is tuned across a point determined by their associated gain and loss rates. This mechanism works for all possible coupling strengths of the dark resonator with the input field and its neighboring resonator, as well as for any available quality factor from its fabrication. The transparency window size and output field intensity can be freely adjusted by tuning two inter-cavity couplings of wide ranges, without modifying the built-in optical gain which can be just slightly stronger than the dissipation of the active resonator.
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Computational Physics
Tensorized Discontinuous Isogeometric Analysis Method for the 2-D Time-Independent Linearized Boltzmann Transport Equation
Patrick A. Myers, Joseph A. Bogdan, Majdi I. Radaideh et al. (+1 more)
We present the novel Tensorized Discontinuous Isogeometric Analysis (TDIGA) method applied to the discontinuous Galerkin (DG) time-independent 2-D linearized Boltzmann transport equation (LBTE) with higher-order scattering, discretized with discrete ordinates in angle, multigroup in energy, and isogeometric analysis (IGA) in space. We formulate operator assembly in the tensor train (TT) format, producing seven-dimensional operators for both fixed-source and $k$-
eigenvalue neutron transport problems solved using the restarted Generalized Minimum Residual Method (GMRES) and power iteration with an uncompressed solution vector. Our results on single-patch homogeneous and multi-patch heterogeneous problems, including a cruciform-shaped fuel array inspired by advanced reactor fuel designs, demonstrate the TT format's ability to compress interior operators from petabytes to megabytes, whereas the Compressed Sparse Row (CSR)
matrix format requires gigabytes of storage. However, highly coupled boundary operators present a significant challenge for TT. Despite the storage savings, TT formatted operators increase time-to-solution relative to CSR as an uncompressed solution vector forces operator-vector product scaling of $O(dr^2N^d\log(N))$ for TT while CSR scales at $O(\text{nnz})$. We mitigate this discrepancy by using mixed formats with interior operators in TT, while high-rank boundary operators remain in CSR format. We compare all results to Monte Carlo (MC) and analytic reference solutions. While CSR remains $<10\times$ faster than this mixed format, the TDIGA method enables high-fidelity transport for expensive high-order IGA meshes.
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All authors Patrick A. Myers, Joseph A. Bogdan, Majdi I. Radaideh, Brian C. Kiedrowski
Optics
On-Axis Optical Trapping with Vortex Beams: The Role of the Multipolar Decomposition
Iker Gómez-Viloria, Álvaro Nodar, Martín Molezuelas-Ferreras et al. (+5 more)
Optical trapping is a well_established, decades old technology with applications in several fields of research. The most common scenario deals with particles that tend to be centered on the brightest part of the optical trap. Consequently, the optical forces keep the particle away from the dark zones of the beam. However, this is not the case when a focused doughnut_shaped beam generates on_axis trapping. In this system, the particle is centered on the intensity minima of the
laser beam and the bright annular part lies on the periphery of the particle. Researchers have shown great interest in this phenomenon due to its advantage of reducing light interaction with trapped particles and the intriguing increase in the trapping strength. This work presents experimental and theoretical results that extend the analysis of on_axis trapping with light
vortex beams. Specifically, in our experiments, we trap micron_sized spherical silica (SiO2) particles in water and we measure, through the power spectrum density method, the trap stiffness constant ąppa} generated by
vortex beams with different topological charge orders. The optical forces are calculated from the exact solutions of the electromagnetic fields provided by the generalized Lorentz_Mie theory. We show a remarkable agreement between the theoretical prediction and the experimental measurements of ąppa}. Moreover, our numerical model gives us information about the electromagnetic fields inside the particle, offering valuable insights into the influence of the electromagnetic fields present in the
vortex beam trapping scenario.
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All authors Iker Gómez-Viloria, Álvaro Nodar, Martín Molezuelas-Ferreras, Jorge Olmos-Trigo, Ángel Cifuentes, Miriam Martínez, Miguel Varga, Gabriel Molina-Terriza
Applied Physics
Twisting Kelvin Cells for Enhanced Vibration Control
Lukas Kleine-Wächter, Anastasiia O. Krushysnka, Romain Rumpler et al. (+1 more)
This work investigates the propagation of elastic waves in periodic Kelvin-
cell chains, focusing on
symmetry-breaking
geometric modifications induced by twisting the
cell's faces. By imposing such twists, the original
lattice topology is preserved, while mirror
symmetries are strategically broken through modifying a single
geometric parameter, allowing wave characteristics to be adjusted without additional resonators or mass augmentation. The complex-valued Bloch-Floquet analysis reveals that twisting activates two distinct wave attenuation mechanisms: Bragg-type band gaps associated with periodicity-induced scattering, and polarization-dependent band gaps arising from longitudinal-torsional mode coupling and avoided crossings. To obtain qualitative and quantitative insight into these mechanisms, a simplified analytical model with coupled translational and rotational degrees of freedom is considered. The finite-element wave transmission calculations are experimentally validated on SLA-printed three-
cell specimens, for which wave attenuation reaches up to 20 dB within the predicted band-gap frequencies. Note that high prediction accuracy requires accounting for viscoelastic material behavior, underscoring the importance of material behavior on the wave propagation characteristics. Overall, the findings show that modest
geometric modifications to a classical Kelvin-
cell lattice can enhance wave-filtering behavior, offering a tractable design strategy for vibration control in lightweight architected
lattices.
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All authors Lukas Kleine-Wächter, Anastasiia O. Krushysnka, Romain Rumpler, Gerhard Müller
Chemical Physics · Cross-listed from quant-ph
Fault-tolerant quantum simulation of the Pauli-Breit Hamiltonian for ab initio hybrid quantum-classical molecular design with applications to photodynamic therapy
Emil Zak
Relativistic
spin effects drive subtle molecular phenomena ranging from intersystem crossing in photodynamic therapy to
spin-mediated catalysis and high-resolution spectroscopy. These effects are described by the Pauli-Breit
Hamiltonian, which extends the nonrelativistic electronic
Hamiltonian by including one- and two-electron
spin-orbit and
spin-
spin interactions. First-principles simulations of the full Pauli-Breit
Hamiltonian rapidly become intractable on classical computers due to the exponential growth of the
Hilbert space and the complexity of two-body
spin-dependent terms. We propose a fault-tolerant
quantum algorithm for computing molecular energy levels and properties governed by the Pauli-Breit
Hamiltonian. Our approach block-encodes the relativistic
Hamiltonian in a second-quantized, doubly factorized representation. By reformulating the
Hamiltonian in a
symmetry-adapted Majorana basis, we construct efficient linear-combination-of-
unitaries circuits that encode
spin-orbit interactions without effective or mean-field approximations. We introduce
spin-controlled Pauli-SWAP networks that decouple
spin and orbital control logic, enabling a unified treatment of relativistic
spin mixing with only modest overhead relative to
spin-free simulations. We analyze
quantum resources in terms of logical
qubits and T-gate complexity, showing that explicit
spin degrees of freedom do not worsen the asymptotic scaling. The prefactor is reduced by a factor of two compared to direct linear-combination-of-
unitaries approaches. Finally, we outline a hybrid
quantum-classical workflow for designing photodynamic therapy photosensitizers, artificial photosynthesis catalysts, and other systems where accurate relativistic
spin effects are essential.
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Physics and Society
Competition between private and expressed opinions in binary choice: the $\alpha$-EPO $q$-voter model
Barbara Kamińska, Barbara Nowak, Arkadiusz Lipiecki et al. (+1 more)
People often express opinions that differ from their privately held views, a phenomenon known in economy as preference falsification. Expressed-private opinion (EPO) models capture this by assigning each
agent two dynamical variables: a private (internal) and an expressed (external) opinion. Within the nonlinear $q$-voter model, two EPO variants have been studied so far: with and without self-anticonformity. In both formulations,
agents update private and expressed binary opinions, one after another and at the same rate, which has led to two update schemes studied previously: AT (act then think), in which an
agent first updates its expressed and then its private opinion, and TA (think then act), in which the order is reversed. To eliminate this ad hoc distinction and quantify the interplay between private and expressed opinions, we introduce the $\alpha$-EPO $q$-voter model with asynchronous updating – in each elementary step, an
agent updates its private opinion with probability $\alpha$ or its expressed opinion with complementary probability $1-\alpha$. We derive mean-field theory and, for the first time for EPO $q$-voter dynamics, a pair approximation, and validate them with Monte Carlo simulations on artificial and real organizational networks. Comparing the two model variants, we show that the collective outcome controlled by $\alpha$ strongly depends on self-anticonformity: with self-anticonformity the results are robust to $\alpha$, whereas without it $\alpha$ shifts the agreement-disagreement threshold and can change the type of phase transition. In the mean-field limit this change occurs only for $q=3$, but the pair approximation reveals an additional low-connectivity regime in which both $\alpha$ and the average degree $k$ control the emergence and width of hysteresis also for larger influence groups.
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All authors Barbara Kamińska, Barbara Nowak, Arkadiusz Lipiecki, Katarzyna Sznajd-Weron
Plasma Physics · Cross-listed from astro-ph.HE
Induced Scattering of Fast Radio Bursts in Magnetar Magnetospheres
Rei Nishiura, Shoma F. Kamijima and Kunihito Ioka
We investigate induced Compton/Brillouin scattering of electromagnetic waves in magnetized electron and positron pair
plasma by verifying kinetic theory with Particle-in-
Cell simulations. Applying this to fast
radio bursts (FRBs) in magnetar magnetospheres, we find that the scattering–although suppressed by the
magnetic field–inevitably enters the linear growth stage before the incident wave amplitude becomes comparable to the background
magnetic field during its outward propagation through the magnetosphere. The subsequent
evolution bifurcates: full scattering occurs when the density exceeds a critical value, whereas below it the scattering saturates and the FRB can escape without substantial induced-scattering attenuation. This nonlinear saturation eases the tension with observations of compact emission regions and may explain the observed diversity, including the presence or absence of FRBs associated with X-ray bursts.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
MAD-SURF: a machine learning interatomic potential for molecular adsorption on coinage metal surfaces
Manuel González Lastre, Joakim S. Jestilä, Rubén Pérez et al. (+1 more)
Predicting how organic molecules adsorb, assemble, and interact on metal surfaces is central to surface chemistry and molecular electronics, particularly in the context of interpreting high-resolution scanning probe microscopy. Yet, the application of first-principles simulations to interfaces is hampered by the computational cost for evaluating the electronic structure for the large number of atoms typically involved. We hereby present MAD-SURF, a machine learning interatomic potential specifically tailored for molecular adsorption on coinage metal surfaces. Trained on a broad
dataset spanning diverse molecules, adsorption motifs, surfaces, molecular dynamics trajectories and non-covalent aggregates, MAD-SURF achieves accuracy comparable to the underlying DFT reference while enabling simulations orders of magnitude faster than density functional theory. The model reliably reproduces energies, forces and adsorption geometries across the three coinage metal substrates. We demonstrate its capabilities on experimentally characterized systems, including organic monolayers, polycyclic aggregates, flexible biomolecules and the long-range herringbone reconstruction of gold. By merging accuracy, speed, and generalizability, MAD-SURF offers a practical framework for accelerating atomistic simulations and advancing data-driven workflows in surface science.
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All authors Manuel González Lastre, Joakim S. Jestilä, Rubén Pérez, Adam S. Foster
Fluid Dynamics
An Efficient Wavelet-based Physics Informed Residual Neural Networks for Flow Field Reconstruction with Extremely Sparse Data
Biswanath Barman and Rajendra K. Ray
This paper introduces wavelet-physics-informed residual neural networks (W-PIRNNs) to study complex fluid flow problems by reconstructing the flow field from highly sparse, supervised data. Our W-PIRNNs fundamentally integrate ResNet and employ the wavelet $W(t) = w_1 \sin(t) + w_2 \cos(t)$ as an activation function. Due to the vanishing and ballooning gradient problems associated with typical PINNs' deep networks, we implemented residual-based skip connections. Our W-PIRNNs, which integrate supervised data with physical principles, demonstrate efficacy even in scenarios of sparse or partial data, enabling the reconstruction of flow fields using merely $0.05\%$ velocity data for training. The wake flow around a circular cylinder served as the test case for our proposed technique, which depends exclusively on velocity data for training. This technique facilitates the precise reconstruction of velocity, pressure, streamlines, and vorticity, requiring fewer epochs and less processing time. Significantly, our proposed W-PIRNNs effectively resolve PDEs in both forward and inverse contexts. Burger's equation served as a test case for both the forward and inverse problem configurations. Our network calculates the
diffusion or viscosity coefficient ($\lambda_2$) with an absolute error of $0.065\%$ and the convection coefficient ($\lambda_1$) with an absolute error of $0.002\%$. Furthermore, the Schrödinger equation is examined in the forward setting to assess the framework's ability to handle periodic boundary conditions. To the best of our knowledge, W-PIRNNs represent the first method capable of flow reconstruction using highly sparse supervised data, as well as reconstructing streamline and vorticity, and they effectively address both forward and inverse problems with high accuracy.
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Medical Physics
Human Cardiac Measurements with Diamond Magnetometers
Muhib Omar, Magnus Benke, Shaowen Zhang et al. (+27 more)
We demonstrate direct, non-invasive and non-contact detection of human cardiac
magnetic signals using
quantum sensors based on nitrogen-vacancy (NV) centers in diamond. Three configurations were employed recording magnetocardiography (MCG) signals in various shielded and unshielded environments. The signals were averaged over a few hundreds up to several thousands of heart beats to detect the MCG traces. The compact room-temperature NV sensors exhibit sensitivities of 6-26 pT/Hz^(1/2) with active sensing volumes below 0.5 mm^3, defining the performance level of the demonstrated MCG measurements. While the present signals are obtained by averaging, this performance already indicates a clear path toward single-shot MCG sensing. To move beyond shielded environments toward practical clinical use, strong noise suppression is required. To this end, we implement NV-based gradiometry and achieve efficient common-mode noise rejection, enabled by the intrinsically small sensing volume of NV sensors. Together, these multi-platform results obtained across diverse
magnetic environments provide a solid foundation for translating
quantum sensors into human medical diagnostics such as MCG and magnetoencephalography (MEG).
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All authors Muhib Omar, Magnus Benke, Shaowen Zhang, Jixing Zhang, Michael Kuebler, Pouya Sharbati, Ara Rahimpour, Arno Gueck, Maryna Kapitonova, Devyani Kadam, Carlos Rene Izquierdo Geiser, Jens Haller, Arno Trautmann, Katharina Jag-Lauber, Robert Roelver, Thanh-Duc Nguyen, Leonardo Gizzi, Michelle Schweizer, Mena Abdelsayed, Ingo Wickenbrock, Andrew M. Edmonds, Matthew Markham, Peter A. Koss, Oliver Schnell, Ulrich G. Hofmann, Tonio Ball, Juergen Beck, Dmitry Budker, Joerg Wrachtrup, Arne Wickenbrock
Optics
On-chip control of the coherence matrix of four-mode partially coherent light: rank, entropy, and modal Stokes parameters
Amin Hashemi, Abbas Shiri, Bahaa E. A. Saleh et al. (+2 more)
Partially coherent light offers salutary capabilities in optical information processing that cannot be matched by coherent light. To date, this `coherence advantage' has been confirmed in proof-of-principle optical communications protocols using bulk optics. Taking full advantage of such opportunities necessitates processing multimode partially coherent light in integrated photonics platforms that alone provide the requisite stability for cascaded operations on a large scale. Here we demonstrate on-chip manipulation of four-mode partially coherent light described by a $4\times4$ Hermitian coherence
matrix. Starting with generic maximally incoherent light, we utilize an on-chip hexagonal mesh of Mach-Zehnder interferometers to perform all the
unitary and non-
unitary tasks that are critical for realizing structured coherence: controlling the coherence rank (the number of non-zero
eigenvalues of the coherence
matrix); tuning the field
entropy; molding the structure of the coherence
matrix via $4\times4$
unitary transformations constructed out of sequences of $2\times2$
unitaries acting on pairs of modes; and tomographic reconstruction of the coherence
matrix by measuring the modal Stokes parameters associated with Kronecker-Pauli
matrices. These results confirm the scalability of utilizing $2\times2$ on-chip building blocks for the synthesis and reconstruction of high-dimensional coherence
matrices, and provide a decisive step towards large-scale on-chip manipulation of massively moded partially coherent light for applications in optical information processing.
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All authors Amin Hashemi, Abbas Shiri, Bahaa E. A. Saleh, Andrea Blanco-Redondo, Ayman F. Abouraddy
Instrumentation and Detectors
OptiGAN for Crystal Arrays: Physics-Informed Generative Modeling of Optical Photon Transport in PET Detector Arrays
Stephan Naunheim, Brandon Pardi, Guneet Mummaneni et al. (+2 more)
Monte Carlo simulations of optical
photon transport are computationally prohibitive for large-scale optical systems including detector arrays and PET systems, restricting their practical use to single-
crystal studies. This work presents an enhanced conditional generative
adversarial network capable of replacing optical simulations at the
crystal array level, extending our previous single-
crystal approach to a 3x3 BGO detector array. We introduce
Fourier feature encoding and a learnable latent mapping network as the modifications enabling stable training on the array geometry, together with a physics-informed loss term enforcing the unit-sphere state space $S^2$ of the generated propagation directions as a soft constraint. Training data requirements are reduced eight-fold by exploiting the array's
symmetry. Performance is benchmarked against GATE10/Geant4 ground truth, using the fluctuations between independent Monte Carlo runs. The enhanced optiGAN achieves similarity values within 3$\sigma$ agreement of the Monte Carlo baseline across all evaluation conditions. An ablation and attribution analysis shows that the physics-informed loss term reduces low-SSIM bin fractions by a factor of 3.6 on the outer
crystals, with a localized trade-off at the central
crystal, yielding a net 48% reduction over the full array. The model transitions from electron-emission training data to realistic gamma-
photon interactions, producing flood maps that reproduce experimental patterns including photopeak clusters and inter-
crystal scatter lines. This proof-of-concept demonstrates that a physics-informed generative model can simulate optical
photon transport in segmented scintillator arrays at a training and inference cost accessible on a single workstation GPU.
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All authors Stephan Naunheim, Brandon Pardi, Guneet Mummaneni, Carlotta Trigila, Emilie Roncali
Computational Physics · Cross-listed from quant-ph
Efficient Trotter-Suzuki Schemes for Long-time Quantum Dynamics
Marko Maležič and Johann Ostmeyer
Accurately simulating long-time dynamics of many-body systems is a challenge in both classical and
quantum computing due to the accumulation of Trotter errors. While low-order Trotter-Suzuki decompositions are straightforward to implement, their rapidly growing error limits access to long-time observables. We present a framework for constructing efficient high-order Trotter-Suzuki schemes by identifying their structure and directly optimizing their parameters over a high-dimensional space. This method enables the discovery of new schemes with significantly improved efficiency compared to traditional constructions, such as those by Suzuki and Yoshida. Based on the theoretical efficiency and practical performance, we recommend two novel highly efficient schemes at $4^{\textrm{th}}$ and $6^{\textrm{th}}$ order. We also demonstrate the effectiveness of these decompositions on the Heisenberg model and the
quantum harmonic oscillator, and find that for a fixed final time they perform better across the computational cost. Even when using large time steps, they surpass established low-order schemes like the Leapfrog. Finally, we investigate the in-practice performance of different Trotter schemes and find the decompositions with more uniform coefficients tend to feature improved error accumulation over long times. We have included this observation into our choice of recommended schemes.
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Optics
Coherent control of photon pairs via quantum interference between second- and third-order quantum nonlinear processes
Alessia Stefano, Samuel E. Fontaine, J.E. Sipe et al. (+1 more)
Genuine
quantum interference between independent nonlinear processes of different order provides a route to coherent control that cannot be reduced to a classical field interference. Here we present an all-optical analogue of coherent carrier injection by exploiting interference between second- and third-order
quantum nonlinear processes in an integrated photonic platform.
Photon pairs generated via spontaneous parametric down-conversion and spontaneous four-wave mixing coherently contribute to the same final two-
photon state, resulting in a phase-dependent modulation of both the generation rate and the spectral structure of the emitted biphoton state. We illustrate the features of such interference and how it can be used to shape biphoton wavefunctions and their
quantum correlations. These results identify interference between nonlinear processes of different order as a distinct form of coherent
quantum control within
quantum nonlinear optics.
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All authors Alessia Stefano, Samuel E. Fontaine, J.E. Sipe, Marco Liscidini
Accelerator Physics
Detection of high-frequency gravitational waves using SRF cavities
M. Wenskat, B. Giaccone, J. Branlard et al. (+21 more)
Today, apart from some isolated R&D efforts, there are no gravitational wave (GW) experiments, yet which explore a large part of the vast frequency range above the LIGO/Virgo band. It is planned to establish an experiment at Deutsches Elektronen-Synchrotron (DESY) and at the Superconducting
Quantum Materials and Systems (SQMS) Center at
Fermi National Accelerator Laboratory (Fermilab) to search for high-frequency GWs in the frequency range of 10 kHz to 100 MHz. The basic idea is to use superconducting radiofrequency (SRF) cavities to detect tiny harmonic deformations induced by GWs which change the boundary conditions of the oscillating electromagnetic field. This paper summarizes the challenging environmental boundary requirements, and the R&D to operate a cavity using a low level RF (LLRF) system which pushes beyond state-of-the-art accuracy and resolutions and a seismic noise mitigated cryostat at 1.8 K. The focus of this paper is the warm and cold commissioning of a prototype cavity, built 20 years ago during the MAGO collaboration, and its first measurement in our collaborative research project.
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All authors M. Wenskat, B. Giaccone, J. Branlard, V. Chouhan, C. Dokuyucu, L. Fischer, I. Gonin, A. Grassellino, W. Hillert, T. Khabiboulline, T. Krokotsch, F. Ludwig, G. Marconato, A. Melnychuk, G. Moortgat-Pick, A. Muhs, A. Netepenko, Y. Orlov, M. Paulsen, K. Peters, L. Pfeiffer, S. Posen, O. Pronitchev, H. Schlarb
Optics · Cross-listed from cond-mat.supr-con
Giant Resonant Enhancement of Photoinduced Dynamical Cooper Pairing, far above $T_c$
Sambuddha Chattopadhyay, Marios Michael, Andrea Cavalleri et al. (+1 more)
Pump-probe experiments performed on $\mathrm{K}_3\mathrm{C}_{60}$ have unveiled both optical and transport signatures of metastable light-induced superconductivity up to room temperature, far above $T_c$. Recent experiments have uncovered that excitation in the vicinity of $50 ~\textrm{meV}$ enables the observation of high temperature light-induced superconductivity at significantly lower fluences. Inspired by these experiments we develop a mechanism which can explain such a
giant resonant enhancement of light-induced superconductivity. Within a minimal non-linear Holstein model, we show that resonantly driving optical Raman modes leads to a time-dependent electron-
phonon coupling. Such a coupling then modulates the effective electron-electron attraction, with the strongest modulations occurring when the drive is resonant with the
phonon frequency. These dynamical modulations of the pairing interactions lead to Floquet-BCS instabilities at temperatures far exceeding
equilibrium $T_c$, as observed in experiments. We conclude by discussing the implications of our general analysis on the $\mathrm{K}_3\mathrm{C}_{60}$ experiments specifically and suggesting experimental signatures of our mechanism.
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All authors Sambuddha Chattopadhyay, Marios Michael, Andrea Cavalleri, Eugene Demler
Physics and Society
Competitive Social Mobilization in Threshold Models of Collective Action
Bianca Y. S. Ishikawa and José F. Fontanari
Social mobilization often fails not for a lack of collective interest, but because of fierce competition between rival movements for the same limited pool of participants. We generalize the classic threshold model of collective behavior to analyze this competitive aggregation, exploring how populations with diverse participation thresholds navigate multiple, mutually exclusive causes. Focusing on the conditions necessary for a single consensus movement to encompass an entire population, our analysis reveals that the outcome of social competition depends critically on the stability of individual dispositions. In quenched environments where participation thresholds are fixed, increasing resistance initially allows a dominant movement to suppress its competitors; however, further resistance triggers a sudden collapse into total fragmentation as low-threshold instigators become too rare to sustain growth. Conversely, in annealed environments where opinions are fluid, higher resistance paradoxically drives a winner-takes-all consensus. In this fluid scenario, massive movements can only be avoided through a deliberate divide-and-conquer strategy. In both cases, the transitions between pulverized and massive movements are discontinuous. These findings demonstrate that the effectiveness of social control depends entirely on environmental stability: raising the cost of participation can either forge unity or shatter collective action into insignificance.
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Fluid Dynamics
Meltwater transport and mixing layer growth near the ice–ocean interface
Sofía Allende, Louis-Alexandre Couston, Simon Thalabard et al. (+1 more)
Ice melting into saline water plays a fundamental role in the dynamics near the ice-ocean interface in polar oceans. The physics of ice melting involves a non-trivial interplay between thermodynamics at the interface, hydrodynamic transport in the bulk and the properties of the ambient ocean. The key control parameters are the density ratio $R_\rho$ proportional to the ambient ocean salinity and the Lewis number $Le = \kappa_T/\kappa_S$, which compares the thermal and salt diffusivities. Increasing the salinity is known to slow down melting, with the melt rate transitioning from subdiffusive to diffusive as $R_\rho$ increases. Here, we ssess the role of
turbulence in this transition, using highly-resolved numerical simulations of the two-dimensional Boussinesq equations with a slowly melting upper boundary. We analyse the non-stationary growth of the temperature and meltwater mixing layers, varying the Lewis number and the density ratio. While meltwater is continuously entrained by convection inside the bulk, we identify a transition from convection to
diffusion close to the interface. This transition is reflected by the formation of an interfacial boundary layer that regulates the flux of meltwater pouring into the turbulent bulk for $R_\rho \gtrsim 10$. Using mixing-layer diagnostics based on meltwater-concentration thresholds, we observe that the turbulent layer grows super-diffusively $\propto t^{1.33}$, while the interfacial boundary layer expands diffusively $\propto t^{0.5}$ but with a non-universal prefactor. These results indicate that double-diffusive effects are here confined to the interface, and highlight potential limitations of diagnostics based on fixed concentration thresholds in oceanographic applications.
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All authors Sofía Allende, Louis-Alexandre Couston, Simon Thalabard, Benjamin Favier
Biological Physics
Non-Markovian non-equilibrium modeling of experimental cell-motion trajectories reveals dependence of propulsion-force correlations on solvent viscosity
Anton Klimek, Prince V. Baruah, Prerna Sharma et al. (+1 more)
Cell motility underlies many biological processes, including cancer metastasis, bacterial infection, and evolutionary adaptation. We introduce a non-
equilibrium single-
cell motility model inspired by the generalized Langevin equation, which accounts for hydrodynamic friction and correlated propulsion force. From
video microscopy of Chlamydomonas reinhardtii algae and Salmonella typhimurium bacteria we extract the propulsion-force dynamics on the single-
cell level, which we find to exhibit multi-exponential correlations, not captured by literature non-
equilibrium cell-motility models. Based on our data-driven model, we predict the effective
cell diffusivities beyond experimentally resolved timescales and demonstrate a diffusivity maximum at intermediate solvent viscosity for both
cell types. This means that
cells adapt their propulsion-force characteristics according to the solvent viscosity. In addition, our model predicts the power output of single
cells, which is on the order of aW for the salmonella and fW for the algae.
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All authors Anton Klimek, Prince V. Baruah, Prerna Sharma, Roland R. Netz
Data Analysis and Statistics
McSAS3: improved Monte Carlo small-angle scattering analysis software for dilute and dense scatterers
Brian Richard Pauw and Ingo Breßler
McSAS3 is the refactored successor to the original McSAS Monte Carlo small-angle scattering analysis software. It is intended to be integrated in automated data processing pipelines, but can also be used to process individual (batches of) scattering data. McSAS3 comes with a graphical user interface (McSAS3GUI), complete with guides, examples and
videos. McSAS3GUI will help to generate and test the three configuration files that McSAS3 needs for data read-in, Monte Carlo optimization and histogramming. The user interface can also be used to process individual files or batches, and can be augmented with machine-specific use templates. The Monte Carlo (MC) approach is able to fit most practical scattering patterns extremely well, resulting in form-free model parameter distributions. Theoretically, these can be distributions on any model parameter, but in practice the MC-optimized parameter is usually a (volume-weighted) size distribution, in absolute volume fraction for absolute-scaled data.
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