Geophysics
Quantitative interpretation of Brookfield DV3TLV measurements: shear rate conversion, correction factors, and applicability limits
A. E. Vasiliev, A. S. Besov and D. O. Andreev
The flow behavior and hydrodynamic characteristics of fluids in rotational viscometry systems are investigated using the Brookfield DV3TLV viscometer, with emphasis on measurement reliability and applicability limits of different measuring geometries. The results are compared and validated using the high-precision MCR 302 rheometer manufactured by the Austrian company Anton Paar. Both Newtonian (water and glycerol) and non-Newtonian fluids (guar-based gels), exhibiting fundamentally different viscosity-shear rate behavior, were included in the study. Based on the comparison of measurements obtained with the Brookfield DV3TLV viscometer and the MCR 302 rheometer, empirical coefficients were determined that relate the spindle rotational speed to the shear rate, taking into account the geometry of the measuring systems. Analysis of the Reynolds number range showed that laminar flow conditions were maintained for all measurement systems, which justifies the application of quasi-static models that neglect possible flow
turbulence within them. Comparison with high-precision measurements performed on the MCR 302 rheometer showed that, with appropriate interpretation, the data obtained using the Brookfield instrument can be used to estimate the real viscosity of process fluids with an accuracy specific to each geometry and its operating conditions. The proposed methodology enables reliable characterization of flow properties in rotational systems and can be applied in engineering practice and laboratory analysis of complex fluids, especially at oil and food production facilities where high-end rheometers are unavailable or impractical to use. The study is formulated within the framework of experimental fluid mechanics and non-Newtonian flow characterization.
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Geophysics · Cross-listed from cs.LG
Boundary condition fidelity for bottom-hole pressure and CO2 plume prediction in geological carbon storage
Romal Ramadhan, Seyyed A. Hosseini and Larry W. Lake
Accurate prediction of bottom-hole pressure (BHP) and CO2 plume migration is essential for safe geological carbon storage, yet practical simulations often rely on truncated domains where artificial boundaries distort pressure
diffusion and CO2 saturation footprints. In this study, we evaluate how boundary-condition fidelity affects BHP and CO2 plume prediction by comparing ten reduced-domain boundary treatments against full-domain reference simulations in homogeneous and heterogeneous reservoirs. We test uniform pore-volume multipliers, transmissibility modifiers, corner-adjusted pore-volume corrections, layered corrections, and gradual modifiers using BHP RMSE, NRMSE, peak pressure deviation, and plume Intersection over Union (IoU) as performance metrics. Our results show that conserving corner pore volume is the most important requirement for truncated-domain modeling. We find that uniform treatments which neglect corner storage generate large pressure errors, with BHP RMSE of 362 to 382 psi in the homogeneous model and 250 to 304 psi in the heterogeneous model, and yield plume IoU values near 0.80 to 0.84, indicating roughly 16 to 20% of the combined plume area is misrepresented. Corner-adjusted scenarios substantially reduce pressure errors and raise plume IoU above 0.94, but we observe that transmissibility correction is not universally beneficial. In homogeneous reservoirs, uniform transmissibility adjustment improves pressure fidelity; in heterogeneous reservoirs, it can over-restrict flow across variable-permeability boundary faces, increasing BHP error and contracting the predicted plume. We find the gradual modifier with transmissibility correction provides the most consistent performance, achieving BHP NRMSE below 3.7% and plume IoU above 0.97 in both reservoir types.
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Physics and Society
Toward a Hybrid Digital Twin of Society: Quantifying Cognitive-Spatial Linkages Through Online-Offline Feedback Networks
Rafiazka Hilman and Julia Koltai
Digital platforms increasingly shape how people experience and navigate cities, linking virtual information seeking with physical mobility. Despite this interdependence, online and offline activities are often studied separately in urban mobility research. This paper introduces the Feedback Network, a computational framework that captures interactions between cognitive activity in digital environments and behavior in physical space. Using Google Search and Location History data from the same individuals, collected through a data donation framework in Budapest, Hungary, between 2018 and 2022, we examine how online search patterns and offline visitation behavior co-evolve. We combine semantic and spatial analytical approaches. Radius of gyration is adapted to measure variation in geographic mobility and semantic exploration, enabling comparison between physical movement and online cognitive dispersion. A Feedback Network models transitions between search-related and location-related activity clusters and is evaluated using Concentration
Entropy, which measures whether behavioral flows are concentrated around routine pathways or distributed across exploratory transitions. The results show that online exploration is more concentrated than offline mobility, suggesting narrower and more repetitive semantic interests, while physical movement remains relatively diverse. Persistent linkages between search and visitation activities related to retail and business services indicate stable cognitive-spatial behavioral loops. The COVID-19 pandemic disrupted spatial routines more strongly than cognitive exploration, widening the gap between digital engagement and realized movement. The findings demonstrate that urban mobility depends on the interaction between informational exposure and spatial encounter and provide a foundation for Hybrid Digital Twins of Society.
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Atomic Physics
Non-dipole effects in two-photon double ionization of the K-shell of a beryllium-like atomic ion
Alexey N. Hopersky, Alexey M. Nadolinsky, Rustam V. Koneev et al. (+1 more)
In the second order of the non-relativistic
quantum perturbation theory and outside the framework of the dipole approximation for the operator of the radiation transition between continuum-spectrum states, the analytical structures and absolute values of the generalized cross-sections of the two-
photon double ionization of the K-shell of beryllium-like ions of titanium (Ti18+), iron (Fe22+) and zinc (Zn26+) atoms were predicted. It has been established that taking into account non-dipole effects by several orders of magnitude (
giant non-dipole effect) reduces the generalized cross-sections calculated within the framework of the dipole approximation. It has also been established that at high (12.5 - 28 keV) energies of the absorbed
photons, the generalized cross-section of the two-
photon double ionization of the K-shell is several orders of magnitude greater than the generalized cross-section of the single ionization. At the same time, as was to be expected, the transition from a neon-like ion to a beryllium-like ion is accompanied by a significant increase in the role of non-dipole effects.
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All authors Alexey N. Hopersky, Alexey M. Nadolinsky, Rustam V. Koneev, Julia N. Kolesnikova
Instrumentation and Detectors · Cross-listed from cond-mat.mes-hall
Collection, characterization, and precision measurement of levitated charged nanoparticles
B. E. Kane, Joyce Coppock, Sunghyun Kim et al. (+1 more)
We describe apparatus and experimental procedures for high stability precision measurements of levitated nanoscale particles confined in an ion trap in high
vacuum. We discuss methods for particle generation and collection using electrospray emission, for rapid characterization by direct imaging of thermal motion, and for transfer of the particle from the trap where it is collected to a separate analysis trap in order to achieve better
vacuum and lower noise. In the analysis trap at high
vacuum (pressure $p\simeq10^{-8}$ Torr), we employ thermostatic control of the trapped particle oscillation amplitudes, allowing long-term, precision measurements of oscillation frequencies, from which the charge to mass ratio ($Q/M$) can be deduced. Under these conditions, we achieve $Q/M$ measurement precision approaching $10^{-5}$. This sensitivity will enable, for example, investigations of the surface chemistry of $\mu$m-scale levitated materials in ultra-high
vacuum environments.
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All authors B. E. Kane, Joyce Coppock, Sunghyun Kim, Sarah Westgate
Optics
Universal framework for the design of near-zero refractive index photonic crystals
Adrien Debacq and Michaël Lobet
Near-zero-index (NZI) media are of great interest for controlling light-matter interactions, but homogeneous NZI materials in the telecom band remain limited and often suffer from significant losses. Photonic
crystals provide an attractive alternative due to their tunability and use of low-loss constituent materials. This work presents a predictive framework for designing epsilon-near-zero (ENZ), mu-near-zero (MNZ), and epsilon-and-mu-near-zero (EMNZ) photonic
crystals. We demonstrate an equivalence between Dirac cones and EMNZ behavior, showing that a Dirac cone at the Gamma point is both necessary and sufficient to obtain an effective EMNZ response under normal incidence. This result implies that the presence of a Dirac cone fully determines the NZI response of a photonic
crystal, independent of the material composition. The prediction is based on mode
symmetry universality and effective medium theory. The approach enables switching between ENZ-MNZ and EMNZ regimes through
geometric tuning of the unit
cell. It is validated on triangular and rectangular
lattices. Overall, this work provides a predictive design strategy for NZI photonic
crystals, replacing trial-and-error optimization. It may also impact metamaterials in the telecom regime and applications in
quantum communication.
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Chemical Physics
Nonlinear Freezing of Vibrational Polariton Transport via Mesoscale Simulations
Xinwei Ji and Tao E. Li
Two-dimensional real-space imaging of vibrational polariton transport in planar Fabry–Pérot microcavities is numerically simulated via the mesoscale cavity molecular dynamics approach, which self-consistently propagates $\sim\!2\times10^4$ realistic molecular simulation
cells on a two-dimensional grid coupled to the same number of cavity modes. Beyond the well-known polariton ballistic-to-diffusive turnover in the linear response regime, these atomistic simulations reveal a nonlinear freezing mechanism of vibrational polariton transport, i.e., under strong pumping of the upper polariton, the initially ballistically propagating upper polariton completely freezes and localizes energy to molecules at specific locations. This mechanism originates from pump-induced breaking of the in-plane translation
symmetry: significant molecular excitations at the pulse hot spot broaden the polariton density of states, thus funneling population to the $k_{\parallel}\rightarrow 0$ band edge with vanishing group velocities. Overall, our work provides numerical insights for exploring novel mechanisms of vibrational polaritons.
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Chemical Physics
Direct imaging of enantiomer-specific orientation dynamics in unidirectionally rotating chiral molecules
Kenta Mizuse, Ilia Tutunnikov, Long Xu et al. (+7 more)
Selectively controlling the dynamics of molecular enantiomers underlies advances across chemistry, biology, and physics, yet direct imaging of enantiomer-specific motion has so far remained elusive. Here, we image ultrafast enantioselective orientation dynamics in isolated
chiral molecules. Unidirectional coherent rotation induced by a femtosecond
laser-pulse pair generates equal and opposite out-of-plane orientations of the two enantiomers. Applying this scheme to 2-methyloxirane, we follow the rotational wave packets by time-resolved Coulomb explosion imaging with two orthogonally arranged detectors. The measured angular distributions reveal that the unidirectional rotation is identical for both enantiomers, while the out-of-plane orientations are mirror images that persist through both early-time quasi-classical and
quantum dynamics regimes, in quantitative agreement with simulations. We demonstrate that full angular distributions provide richer dynamical information, with some qualitatively different distributions yielding similar orientation factors upon integration. Our approach opens a route to real-time observation and control of
chiral dynamics in the gas phase.
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All authors Kenta Mizuse, Ilia Tutunnikov, Long Xu, Yuhei Oyagi, Naoya Sakamoto, Ryo Kondo, Allan Huang, Roman V. Krems, Ilya Sh. Averbukh, Yasuhiro Ohshima
Plasma Physics
Gyrokinetic Theory of Linear Gravitational Flute Interchanges with Flow Shear Stabilization
Zheng Yang Tan and Ian Abel
A collisionless electrostatic gyrokinetic theory is developed to describe how the presence of a differential velocity shear can help stabilize linear gravitational flute interchanges in slab geometry. This is made possible because the velocity shear acts to increase the perpendicular wavenumber of the unstable modes with time. Eventually, a threshold wavenumber is crossed where the effect of gyroaveraging, captured by the Bessel function in the gyrokinetic equation, results in a damping of the instability by nature of these Bessel functions being a decaying sinusoidal. However, transient amplification, responsible for subcritical
turbulence, can still occur. Numerical comparisons are made with a Magnetohydrodynamic model with gyroviscous corrections as well as the GX gyrokinetic code. It is demonstrated that an increasing shear acts not only to accelerate the stabilization effect but also to reduce the overall transient amplification.
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Plasma Physics
Sawtooth suppression by flux pumping on HBT-EP
Boting Li, J.P. Levesque, G.A. Navratil et al. (+1 more)
This study examines the mechanisms underlying sawtooth suppression in the High Beta Tokamak-Extended Pulse (HBT-EP) device. It is observed that strong-intensity sawtooth activities correlate with reduced-amplitude MHD edge modes which are identified as $m/n=3/1$ external kink modes (XK), while sawtooth suppression correlates with larger and saturated edge mode amplitudes. To further investigate these correlations, the
plasma-wall coupling was manipulated by adjusting the positions of the conducting walls in HBT-EP. It was found that strong sawtooth events occur when the normalized wall radius $b/a$ is within a critical value. This implies that the
plasma-wall distance must be sufficiently small to ensure effective stabilization of the edge mode. Even slight differences in major radius result in significantly different discharge styles, categorized as “sawtoothing discharges” and “sawtooth-suppressed discharges” respectively. Through a series of mode structure analyses, we confirm the coexistence and coupling of the $m/n=1/1$ helical core (HC), $m/n=2/1$ tearing mode (TM), and $m/n=3/1$ XK during sawtooth suppression, and that this coupling induces anomalous current broadening. Based on these findings, we conclude that sawtooth suppression in the HBT-EP tokamak is consistent with the process of
magnetic flux pumping.
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All authors Boting Li, J.P. Levesque, G.A. Navratil, M.E. Mauel
Optics
Analysis of Nonlinear Random Polarization in Dispersive Dielectrics
Nathan L. Gibson and Emmanuel E. Oguadimma
We present a study on the time-domain propagation of electromagnetic waves in dielectric materials modeled by a nonlinear Debye medium with random perturbations.
Polynomial Chaos Expansions are employed to transform the random nonlinear Debye polarization model into a deterministic framework. We extend the Yee discretization to the resulting coupled system, establish second order accuracy, and verify convergence numerically. We investigate the sensitivity of nonlinear properties to uncertainty, particularly when the amplitude of the input signal is large. Given the challenges in manufacturing where uncertainties can cause optimal parameters to vary and potentially disrupt nonlinear effects, our approach incorporates these uncertainties within the simulation. This can enable the model-based design identification of realizable materials that maintain their desired effects despite variations. The findings from this study contribute to a deeper understanding of wave propagation in complex media, with potential implications for applications in optical communications, material science, and electromagnetic wave control.
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Applied Physics · Cross-listed from cond-mat.supr-con
Elimination of Flux Trapping in Superconducting Circuits in Ambient Magnetic Fields
Rohan T. Kapur, Alex Wynn, Sergey K. Tolpygo et al. (+10 more)
Superconductor digital electronics and
quantum computing with superconducting
qubits are promising next-generation computing technologies. When cooled down or operated in the presence of a nonzero background
magnetic field $B_r$, superconducting thin films comprising the
circuits can trap
magnetic vortices that can degrade
circuit or
qubit performance. In this work, we report a practical solution for eliminating flux trapped during cooldown in ambient
magnetic fields, $B_r\leq 60$ $\upmu$T, based on controlled local thermal gradients and moats, etched holes in the superconducting films of the
circuit. Thermal gradients created by integrated on-chip resistive heaters move
vortices towards the moats, where they become trapped away from circuitry regions and pinning sites. Using
magnetic imaging and electrical
circuit readout, we demonstrate that this approach is capable of removing
magnetic flux trapped during field cooling and
magnetic flux nucleated by
circuit operation. If used in an environment with basic
magnetic shielding, this solution is capable of suppressing all
magnetic flux in a large-scale
circuit, overcoming one of the long-standing challenges preventing high-performance scalable computing using
superconductors.
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All authors Rohan T. Kapur, Alex Wynn, Sergey K. Tolpygo, Neel Parmar, Anil Mankame, Adam A. Libson, Rabindra Das, Michele Kelley, Pauli Kehayias, Nathaniel J. O'Connor, Collin N. Muniz, Justin L. Mallek, Jennifer M. Schloss
Plasma Physics
Collective modes and screening in an electric-magnetic dual plasma
Hyeong-Chan Kim
We study the linear response of an effective relativistic two-fluid medium carrying separately conserved electric and
magnetic charge currents. The model is defined by the duality-symmetric Maxwell equations with electric and
magnetic sources, together with Lorentz-force dynamics for two fluids with independent inertia and possible Carter-type entrainment. The
magnetic component is treated as an effective charge-carrying constituent, so the analysis uses only the closed two-fluid equations. Around a homogeneous, neutral, and unmagnetized background, the transverse electromagnetic response contains two stable branches whose cutoffs are set by the electric and
magnetic plasma frequencies and are exchanged by electric–
magnetic duality. In the longitudinal sector, entrainment mixes the electric and
magnetic density oscillations, turns their crossing into an avoided crossing, and gives the stability condition $ \kappa^2<1 ,$ equivalent to positive definiteness of the two-fluid momentum
matrix. Resolving the
magnetic component into monopole and antimonopole species gives a neutral branch selected by
magnetic charge conjugation \(C_m\). In this branch the net
magnetic current vanishes, so the long-range monopole field is absent, while the total
magnetic density can still produce screened collective response. The resulting picture is that
magnetic charge can be statically hidden but dynamically visible. A robust observable signature is the density scaling $\omega_{\rm coll}^2\sim\omega_{pm}^2\propto n^0_{(m)},$ which may survive dissipative broadening even when sharp ideal-
plasma poles are not resolved. We briefly comment on possible dyonic interpretations of magnetically neutral composites, but the linear-response results do not rely on that interpretation.
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Optics
Accessing both electrochemical SEIRA and SERS with ultrasensitive metamaterials for enhanced molecular identification
Nicolas Spiesshofer, Tabitha Jones, Sarah May Sibug Torres et al. (+11 more)
Surface-enhanced IR absorption (SEIRA) and surface-enhanced Raman spectroscopy (SERS) are complementary techniques that allow for ultrasensitive chemical fingerprinting. Non-invasive optical sensing would be significantly improved by a robust implementation of a reusable substrate that combines these techniques. Here, we present an electrochemically-cleanable metamaterial that enables combined real-time SEIRA and SERS in flow. This metamaterial facilitates the study of surface-adsorbed species and
diffusion layers, elicits spectral shifts from changes in nanogap refractive index of 1400 nm/RIU, and delivers ultrasensitive analyte detection. Combining SERS and SEIRA clarifies molecular (electro)chemical transformations and tracks changes in selection rules and
symmetry breaking at the analyte-electrode interface. This development in enhanced
multimodal spectro-electrochemistry is suited for multiple domains, including understanding charge transport mechanisms and interfacial dynamics at electrodes, and is capable of real-time flow monitoring for a wide range of molecular processes.
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All authors Nicolas Spiesshofer, Tabitha Jones, Sarah May Sibug Torres, Zoltan Sztranyovszky, Caleb Todd, Shijie Zhu, Yeeun Roh, Rakesh Arul, Alexander Squires, Ivana Qianqi Lin, Angela Demtriadou, David O. Scanlon, Viv Lindo, Jeremy J. Baumberg
Applied Physics · Cross-listed from cond-mat.mtrl-sci
3D Imaging of Complex Skyrmion and Hopf Topologies in an Extended Sample
I. Binnie, H. Fang, B. Shearer et al. (+16 more)
Spin textures are key for emergent
magnetic phenomena such as topological protection and underpin novel spintronic device paradigms based on racetrack
memory, logic gates, and neuromorphic computing. Using a coherent diffractive imaging technique called vector ptycho-
tomography, in combination with
algorithms that are robust to noise, we image the 3D
magnetic texture of skyrmion and
Hopf topologies with no prior assumptions about the sample. This directly reveals experimentally for the first time an extended 3D skyrmion
lattice, including the domain wall shape, topological charge, helicity, and
Hopf index. Our findings demonstrate experimentally that dipole stabilized skyrmions in Fe/Gd multilayers exhibit barrel-shaped skyrmion tubes with a twisted helicity, transitioning from N$\'e$el-type winding at the surfaces to both clockwise and counterclockwise Bloch-type winding in the bulk, that can also be described as fractional hopfions. We image a
lattice of 24 skyrmions with topological charge 1, average depth-dependent domain wall width of 23 to 40 nm, depth-dependent twisted helicity from $\pm$155$\deg$ to $\pm$30$\deg$, and fractional
Hopf index of $\pm$0.3. Over 10 TB of data were analyzed to yield a fully-resolved 3D reconstruction over a >0.4 $\mu$m$^3$ volume, with high fidelity down to the Nyquist limit of 8 nm. This method fills a key gap in the current landscape of
magnetic imaging by enabling high-resolution, element-specific 3D reconstructions of full-field extended
spin textures - offering a new route for exploring the topological complexity of
magnetic materials in three dimensions.
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All authors I. Binnie, H. Fang, B. Shearer, A. Grafov, N. Jenkins, Y. Shao, C. O'Leary, Y. Liao, T. Feggeler, A. Oh, S. Yazdi, J. Zou, B. Wang, E-E. Cating, S. A. Montoya, D. Shapiro, J. Miao, H. C. Kapteyn, M. M. Murnane
Fluid Dynamics
Unpinning of trapped oil droplets via non-resonant acoustic streaming in capillary tubes
D. Tsiklauri
We establish self-consistent analytical model demonstrating that trapped non-wetting
liquid phases in narrow capillary channels can be successfully unpinned via non-resonant, second-order acoustic streaming coupled with background static drive gradients. Moving away from boundary-guided or resonant mechanisms, our approach exploits the bulk acoustic-wind force density generated by the steady-state momentum flux of attenuated first-order linear wave interactions. By expanding the hydrodynamic equations up to second order, we determine the critical assisted acoustic wave amplitude required to break capillary pinning thresholds and derive an explicit formulation for steady transport velocity under viscous wall constraints. Furthermore, incorporating both boundary-layer wall effects and bulk core thermo-viscous dissipation reveals a natural mathematical optimum condition where the spatial absorption coefficient matches half the inverse distance to the target droplet ($\alpha = 1/(2x_0)$). This condition is then numerically validated and cross-correlated against legacy industrial frequency baselines, providing a fundamental theoretical framework for minimizing transducer power requirements while maximizing localized mobilization velocities in geological pore networks. Finally, we demonstrate that this optimal operational frequency scales inversely with the transmission distance, providing an analytical framework to optimize downhole acoustic tools according to spatial damping constraints of the specific formation rather than relying on rigid hardware parameters.
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Fluid Dynamics · Cross-listed from cond-mat.soft
Weak-Flow Induced Dielectric Axes Rotation in Dipolar Suspensions
Pramodt Srinivasula
Conventional rheodielectric studies of dipolar suspensions primarily examine flow-induced variations in the principal permittivity components. In contrast, an asymptotic solution of the perturbed Fokker–Planck equation for orientable Brownian dipoles under weak flow predicts the emergence of off-diagonal permittivity components that are linear in the relative flow strength. For planar shear flow, these terms exceed the corresponding higher-order diagonal corrections, leading to a rotation of the principal dielectric axes. This previously unrecognized rheodielectric response suggests new possibilities for flow-controlled dielectric and electro-optical functionalities.
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Atmospheric and Oceanic Physics
Sparse Sensor Placement for Reducing Forecast Errors in Ensemble Kalman Filtering
Takumi Saito and Shunji Kotsuki
Designing efficient observation networks for reducing forecast errors is a fundamental challenge in numerical weather prediction. Data-driven sparse sensor placement (SSP) and ensemble-based data assimilation via the Ensemble Kalman Filter (EnKF) have each addressed this challenge independently, yet their mathematical connections have not been systematically formalized. This study presents a unified theoretical framework integrating SSP and EnKF through optimal experimental design, providing new theoretical and algorithmic results. While conventional SSP methods aim to reduce analysis errors, this study extends the SSP to target forecast error reduction by using a tangent linear model approximated by an ensemble forecast. We derive the Fisher information
matrices in the ensemble and model spaces for the EnKF, and clarify the mathematical interpretations of A-, D-, and E-optimality in terms of forecast error reduction. A-optimality in the model space minimizes the mean forecast error variance; D-optimality is ill-defined in the model space due to rank deficiency and is therefore formulated in the ensemble space, where it maximizes the Shannon information content of assimilated observations; and E-optimality in the model space minimizes the worst-case forecast error variance. We further propose a fast greedy
algorithm for selecting observation locations under A-optimality in the model space, avoiding
matrix inversion at each greedy step and substantially reducing computational cost. Numerical experiments using the Lorenz-96 model support these theoretical findings. Among the three optimality criteria, A-optimality in the model space most consistently reduces forecast spread and root-mean-square error, and yields stable incremental improvements consistent with post-assimilation observation impact diagnostics.
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Plasma Physics
Ion firehose and ion cyclotron instability with subtracted-Kappa distributions
Luiz F. Ziebell, Rudi Gaelzer and Danny Summers
In the present paper we discuss numerical solutions of the dispersion relation for electromagnetic waves propagating along the lines of an ambient
magnetic field, considering parameters representative of space
plasma environments, and considering the ion population described by a subtracted-Kappa distribution. We consider situations in which the ion thermal anisotropy is such that $T_{i\perp}<T_{i\parallel}$, and investigate the effect of some parameters associated to the subtracted-Kappa distribution on the ion firehose instability. We also consider situations in which $T_{i\perp}>T_{i\parallel}$, and investigate the effects of the same parameters on the ion-cyclotron instability. For both forms of instability, we also investigate the effect of the thermal anisotropy of the electron distribution, and the effect of the occurrence of a drift velocity in the electron distribution function. Among the results obtained, we show that the increase of the loss-cone feature in a bi-kappa distribution leads to a decrease of the growth rates of the firehose instability, and to an increase of the growth rates of the ion-cyclotron instability.
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Atomic Physics · Cross-listed from quant-ph
Quantum computer architecture with ions in tweezer arrays
Benjamin F. Schiffer, Christopher Monroe, Peter Zoller et al. (+1 more)
We propose a
quantum computer architecture based on ions confined in optical tweezer arrays, combining the long coherence times of trapped-ion
qubits with the reconfigurability and parallel operation enabled by tweezer platforms. Selected ions are transported to local interaction zones, where excitation to an auxiliary state with a displaced optical potential generates a controllable effective electric dipole. We develop and analyze entangling-gate mechanisms mediated by the Coulomb interaction between such effective dipoles, and show that they enable precise, temperature-robust closure of the center-of-mass and relative motional trajectories, leaving no residual
entanglement between the
qubits and the motion. We further outline a concrete implementation with barium ions based on state-selective polarizability, and study the suppression of cross-talk during parallel gate execution, with relevance to transversal gates in
quantum error correction. Our results thereby establish a realistic route toward scalable ion-tweezer
quantum processors.
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All authors Benjamin F. Schiffer, Christopher Monroe, Peter Zoller, J. Ignacio Cirac
Chemical Physics
Modular molecular toolkit for photochemical energy conversion in a self-assembling nanocontainer
David Kaftan, David Bina, Guy Michel Wolf et al. (+8 more)
Production of useful chemicals using photoelectrochemical biohybrid devices offers an environmentally friendly alternative to existing energetically demanding processes. These devices exploit light-driven charge separation, e.g. by a photosystem, and require efficient electron transfer to a tailored redox enzyme cascade. Here we demonstrate that electron transfer efficiency can be increased by confining the photosystem with the redox
protein inside a self-assembling, virus-based nanocontainer. The photosynthetic system from the phototrophic bacterium Cereibacter sphaeroides and cytochrome c were conjugated to a bacteriophage P22 scaffolding
protein and co-incorporated into the 50 nm diameter virus shell in vitro. The porous shell confined the macromolecular components for efficient electron transfer while allowing free exchange of small electron mediators. Sustainable and accelerated light-driven electron transfer between the encapsulated components was confirmed by optical spectroscopy. This self-assembly system presents a versatile platform for developing nanoreactors that combine photosystems with complex redox pathways.
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All authors David Kaftan, David Bina, Guy Michel Wolf, Martin Baroch, Jakub Kodel, Juraj Dian, Filip Dycka, J. Thomas Beatty, Heiko Lokstein, Jakub Psencik, Roman Tuma
Instrumentation and Detectors · Cross-listed from quant-ph
A hardware-safety-gated system for LLM-written native ARTIQ control code on a trapped-ion platform
Duanyang Wang, Lu Qi, Yuanheng Xie et al. (+2 more)
Large-
language-model (LLM)
agents can write and run experimental control code. This allows laboratory work to be conducted autonomously. However, this autonomy raises a safety problem that prior work has not addressed. Unchecked code can damage the apparatus, and there is no formal, per-operation boundary between human authorization/supervision, and
agent decisions. We present a control system that places an LLM
agent in the loop of a trapped-ion experiment while enforcing such a boundary. The
agent controls the existing Advanced Real-Time Infrastructure for
Quantum physics (ARTIQ) stack through tools provided by a Model Context Protocol (MCP) server. No tool call reaches the hardware unless it carries an authorization
token bound to its exact contents.
Tokens are issued in one of two ways: automatically, by running the
agent's proposed script in an isolated hardware simulation (dax.sim) and checking every operation against preset per-device bounds, or manually by a human operator for sensitive actions. Within this boundary the
agent develops its own experiments, rather than only calling pre-built routines. We deploy the system on a co-trapped $^{40}$Ca$^{+}$/$^{40}$CaOH$^{+}$
crystal, where the
agent autonomously builds a full calibration stack and, with targeted operator guidance, closes a cross-instrument
magnetic-field-stabilization loop. On a separate, independent $^{171}$Yb$^{+}$ platform, we confirm interface-level portability. We systematically test
token-authorization mechanism with
adversarial scripts that attempt to bypass it, mapping the precise boundary of its protection and prioritizing where to strengthen it next. Analyzing where the
agent still requires human guidance, we find that its limits lie in metacognitive control, namely recognizing when a problem must be re-framed, rather than in domain knowledge.
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All authors Duanyang Wang, Lu Qi, Yuanheng Xie, Norbert M. Linke, Kenneth R. Brown
Optics
Plasmonic coated scatterers for tunable coherent perfect absorption
Ali Ghorashi, Ali H. Alhulaymi and A. Douglas Stone
We derive, in closed-form, the surface conductivity required for coated subwavelength-scale spherical and cylindrical scatterers to perfectly absorb incident coherent light of fixed angular momentum. To address the challenge of synthesizing an incident wave of a fixed angular momentum, we analyze two geometries where this physics can be accessed from the far-field: a single coated sphere suspended above a good conducting surface, and an array of dipole-coupled coated cylindrical scatterers. We show that the required complex surface conductivities necessary for coherent perfect absorption over a large bandwidth in the terahertz may be easily achieved in moderately doped
graphene.
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Applied Physics · Cross-listed from cond-mat.soft
Organic Semiconductor Alignment via Confinement in Vapor-Guided Droplets
Robert Malinowski, Alessandro Rossi, Lewis M. Cowen et al. (+8 more)
Organic
semiconductors are lightweight, solution-processable materials with strong potential for printed and flexible electronics, from deformable displays to wearable sensors. Despite significant advances in materials synthesis and manufacturing, controlling molecular and mesoscale
alignment during deposition remains a central challenge, as film morphology critically governs charge transport and device performance. Here, we demonstrate that flows developing within the intrinsically confined volume of microliter vapor-guided droplets can be harnessed to produce highly aligned organic
semiconductor films. As droplets move in response to an external vapor source, internal flows align organic semiconducting nanowires within the droplet prior to deposition, yielding films with pronounced directional order. Organic field-effect transistors fabricated with this approach exhibit approximately 40% enhancement in saturation current relative to
spin-coated controls. Beyond improved device performance, the contactless and compact nature of our method enables the deposition and
alignment of organic
semiconductors on curved and flexible surfaces. More broadly, vapor-guided droplets offer a scalable framework for the confinement-induced
alignment of functional soft materials, with potential for integration into existing additive manufacturing platforms for flexible electronics and beyond.
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All authors Robert Malinowski, Alessandro Rossi, Lewis M. Cowen, Peter A. Gilhooly-Finn, Michael A. Parkes, Ming-Hao Chang, Yu-Cheng Chiu, Ioannis Papakonstantinou, Matthew O. Blunt, Bob C. Schroeder, Giorgio Volpe
Computational Physics
Real Quantum Chemistry With Complex Orbitals
Hugo Åström and Susi Lehtola
We follow up our study of basis set truncation errors for atoms in
magnetic fields [Åström and Lehtola, J. Phys. Chem. A, 2023, 127, 10872]. Our previous study employed an approximate real-valued model. In this work, we implement a scheme to allow the use of complex basis functions and the true, complex
Hamiltonian with linear molecules in a parallel
magnetic field within the usual real-basis machinery of
quantum chemistry. Our method performs additional
unitary transformations before and after a conventional Fock build, thus allowing the reuse of existing software methods and
algorithms. We apply our approach to calculations on low-lying configurations of the atoms $Z \leq 18$ in static
magnetic fields up to 0.6 $B_0$. The calculations employ the uncontracted aug-cc-pVTZ and the benchmarking quality AHGBSP3-9 Gaussian-type orbital basis sets. We compare total energies obtained with real and complex orbitals using these basis sets to fully numerical ones at the complete basis set limit. We see that the states of the real-valued
Hamiltonian are superpositions of the true eigenstates that are correctly captured by the complex calculations. Our results show that the complex basis machinery is necessary for targeting states with the correct
symmetry for the studied range of
magnetic field strengths. The novel tool is key for future work where we aim to optimize basis sets for finite-field calculations.
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Physics and Society
On the Effects of Decentralized Moderation on Network Robustness and Information Diffusion in Mastodon
Beatriz Arregui-García, Lucio La Cava, Anees Baqir et al. (+3 more)
Decentralized online social networks such as Mastodon distribute moderation power across thousands of independently governed servers, raising fundamental questions about how local block decisions shape global structure and information flow. In this paper, we analyze Mastodon at the instance level by constructing a signed, directed, temporal network in which positive edges aggregate inter-instance follow relationships and negative edges encode daily block actions. Using one year of data, we show that despite continuous moderation activity and changing roles among instances, the network exhibits strong structural stability: signed dyadic motifs and degree distributions display highly persistent dynamics, and aggregated transition
matrices satisfy Markovian
equilibrium conditions over intermediate time scales. Building on the marked asymmetry between instances that predominantly issue bans and those that are mostly banned, we then study information
diffusion on the positive network via a hybrid contagion model that combines simple contagion within groups and complex contagion across groups. We find that information originating in the minority of moderating instances spreads more efficiently, both internally and toward the majority, while the opposite direction is fragile and sensitive to contagion parameters. Echo-chamber effects emerge even in a globally balanced signed network and become stronger under stricter contagion conditions. Together, these results show that decentralized moderation in Mastodon generates a stable macroscopic configuration that both structures and constrains information exchange, effectively isolating norm-violating domains without centralized control.
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All authors Beatriz Arregui-García, Lucio La Cava, Anees Baqir, Andrea Tagarelli, Riccardo Gallotti, Sandro Meloni
Biological Physics · Cross-listed from cond-mat.soft
Unraveling Internal Friction in a Coarse-Grained Protein Model
Carlos Monago, J. A. de la Torre, Rafael Delgado-Buscalioni et al. (+1 more)
Understanding the dynamic behavior of complex biomolecules requires simplified models that not only make computations feasible but also reveal fundamental mechanisms. Coarse-graining (CG) achieves this by grouping atoms into beads, whose
stochastic dynamics can be derived using the Mori-Zwanzig formalism, capturing both reversible and irreversible interactions. In
liquid, the dissipative bead-bead interactions have so far been restricted to hydrodynamic couplings. However, friction does not only arises from the solvent but notably, from the internal degrees of freedom missing in the CG beads. This leads to an additional ”internal friction” whose relevance is studied in this contribution. By comparing with all-atom molecular dynamics (MD), we neatly show that in order to accurately reproduce the dynamics of a globular
protein in water using a coarse-grained (CG) model, not only a precise determination of elastic couplings and the Stokesian self-friction of each bead is required. Critically, the inclusion of internal friction between beads is also necessary for a faithful representation of
protein dynamics. We propose to optimize the parameters of the CG model through a self-averaging method that integrates the CG dynamics with an
evolution equation for the CG parameters. This approach ensures that selected quantities, such as the radial distribution function and the time correlation of bead velocities, match the corresponding MD values.
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All authors Carlos Monago, J. A. de la Torre, Rafael Delgado-Buscalioni, Pep Español
Data Analysis and Statistics · Cross-listed from cs.LG
Kolmogorov Arnold networks (KAN) for aerodynamic prediction: a comparison with MLPs and GNNs
Miguel Jaraiz, Fermin Gutierrez, Pablo Yeste et al. (+4 more)
Kolmogorov Arnold networks (KAN) have recently been introduced as a (deep) neural network architecture whose trainable parameters adapt the activation functions, instead of the coefficients of the affine transformations at the core of traditional architectures such as deep multilayer perceptrons (MLPs). This architecture builds on the Kolmogorov-Arnold
theorem, which endows it with universal approximation properties. While the advent of KANs has been received with excitement, there is a current debate about the possible KAN supremacy over deep multilayer perceptrons (MLPs) for classic fields such as symbolic regression, generic-purpose machine learning, natural
language processing or computer
vision. Here we assess the performance of KANs –and its nuanced comparison against MLPs and graph neural networks (GNNs)– in the realm of fluid dynamics surrogate modelling. To that aim, we consider the task of predicting the surface pressure distribution over subsonic and transonic airfoils, a canonical task in aerodynamics. Our results show that KAN models show good performance in predicting the whole pressure coefficients and is able to interpolate across Mach numbers and angles of attack, however its performance is comparable –marginally inferior– to a suitably trained MLP, where best performance is achieved by a GNN at the expense or requiring lengthier training. While the optimal KAN model have typically much lower complexity than MLP and GNN –hence resulting in faster training–, we find that KANs suffer from training instabilities, and their performance is highly dependent on a proper hyperparameter optimisation.
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All authors Miguel Jaraiz, Fermin Gutierrez, Pablo Yeste, Miguel Sánchez-Domínguez, Eusebio Valero, Gonzalo Rubio, Lucas Lacasa
Fluid Dynamics · Cross-listed from math.NA
An Arbitrary-Lagrangian-Eulerian solver for relativistic detonation waves
Sara Rinaldi, Olindo Zanotti and Michael Dumbser
In this paper we study the dynamics of relativistic detonation waves theoretically and numerically. The reaction is physically accounted for by an extra term in the definition of the total energy density and by an additional equation for the
evolution of the mass fraction of the reactant, while leaving formally unmodified the equations of mass and energy-momentum conservation. In this way, the Rankine-Hugoniot relations maintain the same formal structure of the inert version. For the numerical solution we use a finite volume ALE scheme with a second order TVD space-time reconstruction for the homogeneous part of the system, where the mesh velocity is chosen equal to the shock speed, and we combine it through operator splitting with a locally implicit
algorithm for the potentially stiff reaction source terms that arise in the equation of the reactant. We furthermore propose a particularly efficient
algorithm for the conversion from the conserved to the primitive variables, which for the relativistic Euler equations is known to be nontrivial. Following this approach, we can successfully solve the Zel'dovich-von Neumann-Doering profile of a relativistic detonation wave, up to Lorentz factors of the shock front $\gamma_s\sim 7$. Our analysis allowed us to highlight a new special relativistic effect, which has remained unnoticed so far. While in Newtonian detonations the Zel'dovich pressure jump decreases monotonically with the mass flux through the shock front, in the relativistic case it shows a minimum and then rises monotonically as a function of the mass flux. This may have interesting physical implications on the amount of energy that can be extracted from a relativistic detonation wave.
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Plasma Physics
A possible approach to overcome the saturation of the neutron yield in a Plasma Focus and to achieve breakeven
Andrea Di Vita
Saturation of the
neutron yield with increasing energy of the condenser bank in a
Plasma Focus led to the shutdown of PF research focussed on controlled
nuclear fusion in the past. We review available models of saturation and develop further the model of Lee S., Applied Phys. Lett. 95, 151503, 2009. This model relies on the well-known and generally accepted model of Lee S., J. Fusion Energy 2014, 33, 319 of
Plasma Focus discharges and describes saturation in terms of the dynamic resistance, i.e. the rate of change of PF inductance due to the motion of the
plasma sheath during rundown. A model of this sheath discussed in Di Vita A., J.
Plasma Physics, 1993, 50, 1 shows that its spontaneous filamentation rules the dynamic resistance, spoiling the power supply from the condenser bank to the
plasma at the values of condenser bank energy above 0.5 MJ values which are relevant to a fusion reactor. Together, these two models lead to the conclusion that suppression of such filamentation prevents saturation, multiplies the PF drive parameter by a factor 3 at least and allows breakeven in a 224 kV, 10 MJ
Plasma Focus working with DT. We can suppress filamentation by superimposing a radial
magnetic field to the interelectrode region of the
Plasma Focus where rundown occurs. A conservative estimate shows that a 1.4 T radial
magnetic field is enough to suppress many known filamentation instabilities. Suitably located magnets can generate this field. Their layout resembles the layout of the sources of radial
magnetic field in the cylindrical geometry of a
Hall thruster for space propulsion. For high temperature superconducting magnets, the required current density is too small to trigger quenching.
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