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Physics Physics

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Tuesday 24 February

Plasma Physics · Cross-listed from astro-ph.SR

Rotation of a Solar Jet Driven by Plasma Flow along Helical Magnetic Fields in an Active Region

Solar jets, collimated plasma ejections driven by magnetic reconnection, play a vital role in energy transport and coronal heating. While rotational motions in jets are often attributed to magnetic field untwisting, alternative explanatory mechanisms remain possible. This study investigates a rotating jet in an active region observed on 2023 August 1 using multi-wavelength observations from Atmospheric Imaging Assembly (AIA), Chinese Ha Solar Explorer (CHASE), and Interface Region Imaging Spectrograph (IRIS), combined with a self-consistent time-dependent magnetofrictional (TMF) model and magnetohydrodynamic (MHD) simulation. Spectral diagnostics reveal coexisting red and blue shifts along the edges and central axis of the jet, indicating helical plasma motion within a twisted magnetic structure. Numerical simulations demonstrate that the jet's rotation arises from plasma propagating along helical open field lines, formed via reconnection between a pre-existing flux rope and overlying magnetic fields. Contrary to classical untwisting models, both linear and rotational velocities decrease with altitude during the jet propagation. These results highlight that the observed rotation results from plasma spiral motion along twisted fields rather than untwisting dynamics of the magnetic field itself, providing new insights into solar jet energetics and their connection to broader solar phenomena.
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All authors Lei Huang, Yang Guo, Zhen Li, Jinhan Guo, Mingde Ding

Optics

Range Emulator: A Compact Paraxial Optical System to Emulate Long-Distance Monochromatic Laser Propagation

Emulating long-distance light propagation on a laboratory scale is essential for the ground-based testing of intersatellite optical systems. To address this challenge, we propose and analyze a novel optical system called the Range Emulator (RE) to reproduce the spatial propagation effects of a long-distance beam within a compact apparatus. Our analysis identifies that three lenses are required as the minimum number of lenses to implement the RE. Through a numerical exploration, we quantify the fundamental trade-off between system compactness and manufacturing precision. This work provides a practical framework for designing compact optical testbeds for future multi-satellite laser link technologies.
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Optics

An Optomechanical Coin Flip: Wavelength-Modulated, Erbium-Powered Rotations in a Levitated System

Optical levitation of nano-scale systems offers a pathway to highly sensitive rotation measurements, which are critical for advancing gyroscopic technologies. While prior studies have primarily focused on controlling rotational degrees of freedom of optically levitated particles via modulation of optical power, polarization, and ambient pressure, here we demonstrate wavelength-controlled rotation of the "coin-flip" mode in optically levitated NaYF hexagonal prisms doped with erbium by modulating the wavelength of a secondary pump beam. By switching the pump light wavelength, we precisely modulate the particle's rotation rate in a binary fashion, encoding the ASCII message "hello" in its rotational frequency. Finally, we observe long-term bimodal periodic dynamics in the rotational motion of a levitated prism that are suggestive of a Dzhanibekov (or tennis-racket)-like effect.
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All authors George Winstone, Maddox Wroblewski, Lars Forberger, Zhiyuan Wang, Shelby Klomp, Scott Grudichak, Shafaq Gulzar Elahi, Yuqi Qian, Miriam M Florez, Zhaojie Feng, Peter J. Pauzauskie, Andrew A. Geraci

Optics

Enhancing FRET through DNA-controlled Emitters and ENZ Metamaterials

Simultaneous nanoscale spatial control and macroscopic electromagnetic enhancement are critical for maximizing resonance energy transfer. However, conventional systems with photonic platforms suffer from stochastic emitter distributions and steep field gradients. Here we demonstrate a unified architecture combining programmable DNA molecular beacons with an epsilon near zero (ENZ) multilayer metamaterial. Using DNA scaffolds, donor-acceptor pairs (Atto425/Cy3.5) are structurally locked into closed (2 nm) and extended (8.16 nm) conformations within the ENZ near field. Time-resolved photoluminescence reveals accelerated donor decay and an increase in extended state FRET efficiency from 56.7% on glass to 79.4% on ENZ, corresponding to a 5.8 fold transfer rate acceleration. Electromagnetic Green tensor modeling confirms that ENZ boundary conditions strongly amplify dipole coupling within first few nm of the interface exhibiting pronounced orientation selectivity. This hybrid platform provides a deterministic orientational and spatial control for sculpting molecular-scale light-matter interactions.
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All authors Akeshi Aththanayake, Andrew Lininger, Anh Pham, Radu Malureanu, Divita Mathur, Giuseppe Strangi

Optics

Dynamic Lattice Disorder and Collective Dipole Coupling Give Rise to Dicke Physics in Perovskite Quantum Dots

Halide perovskite quantum dots exhibit cooperative optical phenomena that are absent in conventional semiconductor nanocrystals, including exciton superradiance, superabsorption, and biexciton superradiance within individual dots. Here we develop a microscopic theory that identifies the physical origin of these Dicke effects and establishes how they can be controlled by materials parameters. The central result is that cooperative emission emerges from a competition between collective coupling of optical transition dipoles and lattice-induced disorder, with the balance governed by the Raman-derived phonon spectral density and the excitonic oscillator strength. At elevated temperature, strong Fröhlich coupling and glassy lattice dynamics produce dynamic disorder that suppresses dipole synchronization and yields incoherent emission. Upon cooling, lattice fluctuations freeze and cooperative coherence emerges when the collective coupling exceeds residual static disorder, defining size- and composition-dependent crossover temperatures that we map as phase diagrams. Extending the framework to biexcitons, we show that a confined biexciton constitutes a single correlated charge distribution dressed by a shared lattice configuration, enabling pathway-indistinguishable decay and cooperative radiative enhancement. The theory quantitatively accounts for observed size, composition, and temperature trends in radiative-rate constant ratios and biexciton binding energies, while explaining why full Dicke saturation is not universal. More broadly, the results establish Raman spectral weight and oscillator strength as design parameters for engineering cooperative quantum-optical behavior in quantum materials.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Propagation of elastic waves in a flexomagnetic solid

Flexomagnetism is the coupling between magnetism and strain gradients and is a technologically relevant phenomenon. We present a theory of elastic wave propagation in a linear elastic flexomagnetic material with microstructure and strain gradient elastic interactions. The expressions of frequency, phase velocity, and group velocity of longitudinal and transverse waves are derived and are shown to depend on the flexomagnetic coefficient and microstructure. We also show that the effect of flexomagnetism and microstructure can lead to some interesting phenomena in wave propagation, which are not observed in classical linear elasticity theory of waves. Specifically, in contrast to classical linear elastic materials, where wave propagation is non-dispersive, flexomagnetic materials with microstructure can exhibit both normal and abnormal dispersion. It is also noteworthy that, in flexomagnetic materials with gradient elasticity, the phase velocities of transverse waves can exceed those of longitudinal waves, which is atypical in classical elasticity. Furthermore, waves can also attenuate for a certain range of wavenumbers that depend on the flexomagnetic coefficient and microstructural parameters. Finally, we explore the possibility of waves exhibiting zero group velocity modes, where waves are non-propagating but have strong local energy confinement, negative group velocity modes, where the wave packet moves in the opposite direction to that of wave propagation, and the phenomenon of wave freezing, where a propagating wave stops in space without diffusing or spreading.
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Plasma Physics · Cross-listed from astro-ph.HE

Introduction to Strong Alfvénic MHD Turbulence

Many astrophysical fluids are magnetized and turbulent. Such fluids can be often described by magnetohydrodynamics (MHD). In this review, we mainly consider MHD turbulence with a strong mean magnetic field whose energy density is greater than or equal to the local kinetic energy density. In these fluids, the MHD waves, especially Alfvén waves, play a dominant dynamical role. Alfvén waves travel along magnetic field lines and collisions of opposite-traveling Alfvén wave packets are essential for turbulence cascade. We focus on strong turbulence regime, where nonlinear interaction during the collision is sufficiently strong and thus one collision is enough to complete turbulence cascade. We will cover the following types of turbulence. First, we review strong Alfvénic MHD turbulence. If the mean magnetic field is very strong, wave packets move very fast and duration of collision is too short to complete turbulence cascade. Even in this case we will show that strong turbulence regime emerges on a small scale. Second, we will consider small-scale MHD turbulence, where interaction of small-scale variants of Alfvén waves (i.e., whistler waves) is important. Third, we review scaling relations in strong relativistic force-free MHD turbulence, where interaction of relativistic Alfvén waves is important. Finally, we briefly discuss scaling relations in compressible MHD turbulence, where interaction of Alfvén waves is still important.
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Plasma Physics · Cross-listed from astro-ph.SR

Evolution of Spatial Complexity in Flare Ribbon Substructure and Its Relationship to Magnetic Reconnection Dynamics

Recent three-dimensional flare models suggest that flare-ribbon substructure is linked to the fragmentation of the reconnecting current sheet in the corona. Flare-ribbon substructure can therefore potentially serve as a unique diagnostic tool for physical processes in the flare current sheet. In this paper, we describe a new method to quantify the evolution of ribbon substructure, which first extract the ribbon's leading bright front and the quantifies its morphology using the box-counting dimension and Correlation Dimension Mapping (CDM). We first test our method using synthetic observations. We then find that when the flare ribbon boundary has more multi-spatial-scale features (higher box-counting dimension), hard X-ray (HXR) emission and magnetic reconnection rates are the strongest. We also find that the flare-ribbon complexity characterized by CDM has moderate correlation with the IRIS Si IV 1402.77 Å non-thermal velocity (in the negative-polarity ribbon) and reconnection flux rates (in ribbons of both magnetic polarities). We conclude that the build-up of the spatial complexity of the ribbons at multiple spatial scales can serve as an observational proxy for current-sheet fragmentation in the corona.
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All authors Marcel F. Corchado Albelo, Maria D. Kazachenko, Ryan J. French, Vadim M. Uritsky, Emily Mason, Cole A. Tamburri, Rahul Yadav, Benjamin J. Lynch

Medical Physics

Radiation damage to normal mammalian tissue in vivo with laser-driven protons at ultra-high instantaneous dose rate

The differential sparing of normal tissues relative to tumor control observed at ultra-high dose rates, referred to as the FLASH effect, has recently gained considerable attention. The therapeutic advantages of FLASH radiotherapy are expected to be further amplified through the use of protons and ions, which enable precise dose deposition at tumor depth while minimizing irradiation of healthy tissues proximal and distal to the target. Nevertheless, the mechanism underlying this sparing effect remains poorly understood. Laser-driven proton accelerators are capable of delivering uniquely high instantaneous dose rates in ultrashort bunches. Here, we report the first in vivo investigation of normal tissue response to laser-driven proton irradiation, with exposures to 8 MeV protons, delivering total doses up to 50 Gy at 2 Gy per laser shot. Our findings reveal a reduction in tissue swelling following laser-driven proton treatment compared with X-ray irradiations at conventional dose rates. RNA sequencing identified differential gene expression associated with immune and epidermal programs following laser-driven proton irradiations at two different dose levels.
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All authors Lieselotte Obst-Huebl, Jamie L. Inman, Jared De Chant, Kei Nakamura, Sahel Hakimi, Morgan Cole, Hang Chang, Cameron G. R. Geddes, Anthony J. Gonsalves, Jian-Hua Mao, Carl B. Schroeder, Blake A. Simmons, Jeroen van Tilborg, Eric Esarey, Antoine M. Snijders

Chemical Physics

Continuous Local Symmetry: Connection to Reactivity and Recognition

Symmetry is one of the most beautiful yet mysterious concepts in science. In chemical systems, presence of local symmetries at specific fragments often serve as driving forces behind many physicochemical properties, including stability, spectroscopy, and reactivity. Moreover, degree of symmetry varies continuously with molecular dynamics and intermolecular interactions, making it a hidden but decisive factor. In this study, we propose a theoretical framework to quantify continuous degrees of symmetry and chirality localized within constrained regions of a molecular environment. Application of this method to reaction sites of dendralene molecules reveals strong correlations between local symmetry and molecular stability, parity-dependent behavior, and Diels–Alder reactivity. Additionally, representations of local chirality (chirotopicity) fields in porphyrins uncover unique signatures accounting for the chirality recognition power. Overall, these findings highlight the potential of local symmetries within a molecular framework on predicting chemical properties.
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Applied Physics

Toward a CMOS-integrated quantum diamond biosensor based on NV centers

We report progress toward a CMOS-integrated quantum diamond biosensing platform that combines nitrogen-vacancy (NV) centers in diamond with a custom 40 nm CMOS Single-Photon Avalanche Diode (SPAD) array. The system integrates on-chip active quenching and digital readout with external FPGA-based photon counting, compact microwave delivery, and practical optical excitation and collection schemes to support widefield optically detected magnetic resonance (ODMR). System-level design considerations spanning fluorescence collection efficiency, detector count-rate capability, and microwave homogeneity are analyzed with biological compatibility and scalability in mind. Using superparamagnetic iron oxide nanoparticle (SPION)-labeled HEK293T cells as a representative use case, simple dipole-field estimates indicate that sub-$\mu$T sensitivity is required to resolve ODMR shifts within typical ensemble linewidths. Based on the proposed architecture and efficiency analysis, a magnetic field sensitivity of approximately 90 nT/$\sqrt{\mathrm{Hz}}$ per pixel is estimated. These results outline a practical path from optics-heavy quantum diamond microscopes toward compact, CMOS-integrated NV-based biosensors for quantitative magnetic imaging in complex biological environments.
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All authors Ioannis Varveris, Gianni D. Aliberti, Felix J. Barzilaij, Zhi Jin, Samantha A. van Rijs, Qiangrui Dong, Daan Brinks, Salahuddin Nur, Ryoichi Ishihara

Accelerator Physics

Conceptual Design of Highly-Constrained Splitters for the FFA@CEBAF Energy Upgrade Study

The Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab is investigating a significant energy upgrade utilizing Fixed-Field Alternating-gradient (FFA) recirculating arcs. This upgrade requires the design of complex horizontal beam splitters to manage up to six concurrent beam passes. This paper presents the conceptual design of these splitters, which are subject to severe physical constraints imposed by the existing accelerator tunnel and multifaceted beam dynamics requirements for matching into the permanent-magnet FFA arcs. The design methodology, centered on multi-pass simulations in the Bmad toolkit, is detailed from the initial geometric layout through the advanced optics matching. Key results include a robust geometric arrangement that fits within the spatial boundaries and the development of multiple, flexible optics matching solutions. Furthermore, the design integrates a viable scheme for extracting high-energy beams for the experimental halls, a critical operational requirement. This work establishes a comprehensive and viable conceptual design, forming a baseline for future engineering and performance optimization studies.
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All authors Ryan Bodenstein, Jay Benesch, Alexander Coxe, Kirsten Deitrick, Brian Freeman, Randika Gamage, Reza Kazimi, Donish Khan, Katheryne Price, Ben Schaumloffel

Monday 23 February

Physics and Society

Photons = Tokens: The Physics of AI and the Economics of Knowledge

Debates about artificial intelligence capabilities and risks are often conducted without quantitative grounding. This paper applies the methodology of MacKay (2009) – who reframed energy policy as arithmetic – to the economy of AI computation. We define the token, the elementary unit of large language model input and output, as a physical quantity with measurable thermodynamic cost. Using Landauer's principle, Shannon's channel capacity, and current infrastructure data, we construct a supply-and-demand balance sheet for global token production. We then derive a finite question budget: the number of meaningful queries humanity can direct at AI systems under physical, information-theoretic, and economic constraints. We apply Coase's theory of the firm and the durable-goods monopoly problem to the AI value chain – from photon to atom to chip to power to token to question – to identify where economic value concentrates and where regulatory intervention is warranted. We argue that the expansion of the token budget does not resolve a deeper constraint: under structural uncertainty, the decisive variable is not how many questions can be answered but which questions are worth asking – a problem of agency and direction that computation alone cannot solve. We connect limits of measurement in the token economy to a structural parallel between Goodhart's law and the Heisenberg uncertainty principle, and to Arrow's impossibility result for efficient information pricing. The framework yields order-of-magnitude estimates that discipline policy discussion: at current efficiency, the projected 2028 US AI energy allocation of 326~TWh could support roughly $6.5 \times 10^{17}$ tokens per year, or 225,000 tokens per person per day – more than three orders of magnitude above estimated mid-2024 utilization.
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Physics and Society

The Potential for an Innovation Winter: Estimating Impact of Federal Research Reductions on Faculty Activity

The proposed reductions in federal research support proposed by the Trump Administration for 2026 would profoundly degrade the United States research universities, especially in the STEM fields and medicine (STEMM). A potentially devastating consequence would be on the funding distribution for individual faculty. Data and stochastic modeling demonstrate that the result would be large fractions of previously research active faculty having subcritical research support. Research expenditure data from Boston University suggests that the funding distribution has a heavy tail (a Pareto like distribution)where a relatively small number of faculty have responsibility for a large fraction of the funding and that another fraction have minimal external support. A log normal distribution fits the expenditure data, and a multiplicative stochastic model replicates the spending distributions for the STEMM faculty and, separately, the engineering faculty. Using data for the average expenditures by 146 R1 (very research intensive) engineering schools, the model predicts that the 40 percent funding reduction proposed by the Administration would increase from 26 to 47 percent the number of R1 universities with over half their faculty with less than 100,000 dollars of annual expenditures, if the reduction affects all equally. If the most research intensive universities win a disproportionate share, this percentage of universities jumps to almost 60. In such an environment, and in the face of other cost pressures, it would be difficult to maintain quality research and doctoral programs across many institutions, raising important questions about their optimal research strategy and organization if faced with this declining support. Ideas for navigating such a future are presented.
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Chemical Physics

Direct Variational Calculation of Two-Electron Reduced Density Matrices via Semidefinite Machine Learning

We introduce a data-driven framework for approximating the convex set of $N$-representable two-electron reduced density matrices (2-RDMs). Traditional approaches characterize this set through linear matrix inequalities that define its supporting hyperplanes. Here, we instead learn a vertex-based approximation to its boundary from molecular data and use this information to improve the set defined by low-order positivity constraints, without explicitly constructing higher-order conditions. The resulting semidefinite machine learning approach – combining an input convex neural network with semidefinite programming – drives a direct variational calculation of the 2-RDM with enhanced accuracy at computational cost comparable to two-positivity calculations. Applications to the potential energy curves of ${\rm C}_2^{2-}$, ${\rm N}_2$, and ${\rm O}_2^{2+}$ demonstrate these systematic improvements as well as close agreement with complete active space configuration interaction results. Overall, semidefinite machine learning interweaves data-driven boundary information with semidefinite positivity constraints to yield more accurate energies and 2-RDMs without explicit higher-order positivity conditions.
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Geophysics

GreenPhase: A Green Learning Approach for Earthquake Phase Picking

Earthquake detection and seismic phase picking are fundamental yet challenging tasks in seismology due to low signal-to-noise ratios, waveform variability, and overlapping events. Recent deep-learning models achieve strong results but rely on large datasets and heavy backpropagation training, raising concerns over efficiency, interpretability, and sustainability. We propose GreenPhase, a multi-resolution, feed-forward, and mathematically interpretable model based on the Green Learning framework. GreenPhase comprises three resolution levels, each integrating unsupervised representation learning, supervised feature learning, and decision learning. Its feed-forward design eliminates backpropagation, enabling independent module optimization with stable training and clear interpretability. Predictions are refined from coarse to fine resolutions while computation is restricted to candidate regions. On the Stanford Earthquake Dataset (STEAD), GreenPhase achieves excellent performance with F1 scores of 1.0 for detection, 0.98 for P-wave picking, and 0.96 for S-wave picking. This is accomplished while reducing the computational cost (FLOPs) for inference by approximately 83% compared to state-of-the-art models. These results demonstrate that the proposed model provides an efficient, interpretable, and sustainable alternative for large-scale seismic monitoring.
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All authors Yixing Wu, Shiou-Ya Wang, Dingyi Nie, Sanket Kumbhar, Yun-Tung Hsieh, Yun-Cheng Wang, Po-Chyi Su, C.-C. Jay Kuo

Fluid Dynamics

Counterflow around a cylinder

The incompressible flow around a circular cylinder, positioned at the center of an unconfined planar counterflow, is studied by means of numerical solutions of the conservation equations and linear stability analysis. The flow is completely defined by the Reynolds number ($\Rey$) – based on the cylinder radius, the strain rate defining the counterflow, and the kinematic viscosity. For very low values of $\Rey$, the flow is steady, two-dimensional, and fully attached to the cylinder wall. Increasing $\Rey$ above $\Rey_s \approx 16.86$, the flow separates, giving rise to two symmetric, counter-rotating recirculation regions on each side of the cylinder. Further increasing $\Rey$ leads to a progressive enlargement of the recirculation regions and the appearance of multiple recirculation centers, akin to Moffatt eddies. However, the convective acceleration imposed by the counterflow limits their size. An oscillatory mode becomes linearly unstable for $\Rey_{c} \approx 4146$. This mode gives rise to a sinuous meandering of the wake flow, on each side of the cylinder, being analogous to the well-known von Kármán instability. The frequency of this mode is directly proportional to the strain rate defining the counterflow.
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All authors Matheus P. Severino, Leandro F. Souza, Elmer M. Gennaro, Daniel Rodríguez, Fernando F. Fachini

Instrumentation and Detectors

Surrogate neutron-capture studies with fission detection in inverse kinematics at the ESR storage ring

The NECTAR (Nuclear rEaCTions At storage Rings) experiment at the ESR heavy-ion storage ring at GSI/FAIR Darmstadt is dedicated to surrogate reaction studies of neutron-induced reactions on heavy nuclei in inverse kinematics. In this work, we report on the implementation and performance of a newly developed fission-fragment detection system integrated into the NECTAR experimental setup. The upgraded detector configuration enables, for the first time in a surrogate experiment, the simultaneous detection ofgamma-decay residues, multi-neutron-emission residues, and fission fragments. The full setup was used for the first time in an experiment where a stored beam of bare 238U92+ ions at 17.24 MeV/u interacted with a gas-jet deuterium target, populating excited 238U and 239U nuclei via the 238U(d,d') and 238U(d,p) reactions. We describe the geometry of the used fission fragment detectors, design constraints, and simulation-based efficiency determination. The target-like particle identification and beam-like residue spectra demonstrating the performance of the complete setup are also shown.
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All authors Bogusław Włoch, Camille Berthelot, Guy Leckenby, Beatriz Jurado, Jerome Pibernat, Manfred Grieser, Jan Glorius, Yuri A. Litvinov, Laurent Audouin, Bertram Blank, Lucas Bégué–Guillou, Alex Cobo Zarzuelo, Sophia Florence Dellmann, Marc Dupuis, Oliver Forstner, Alexis Francheteau, David Freire Fernández, Miki Fukutome, Mathias Gerbaux, Jérôme Giovinazzo, Alexandre Gumberidze, Andreas Heinz, Ana Henriques, Regina Hess, Indu Jangid, Anton Kalinin, Wolfram Korten, Sergey Litvinov, Bernd Lorentz, Antonio M. Moro, Nikolaos Petridis, Ulrich Popp, Gregory Potel, Diego Ramos, Mathieu Roche, Mohammad Shahab Sanjari, Michele Sguazzin, Ragandeep Singh Sidhu, Uwe Spillmann, Markus Steck, Thomas Stoehlker, Takayuki Yamaguchi

Atomic Physics · Cross-listed from cond-mat.quant-gas

Revealing Pseudo-Fermionization and Chiral Binding of One-Dimensional Anyons using Adiabatic State Preparation

Fractional statistics give rise to quantum behaviors that differ fundamentally from those of bosons and fermions. While two-dimensional anyons play a major role in strongly correlated systems and topological quantum computing, the nature of their one-dimensional (1D) counterparts remains the subject of intense debate, with renewed interest fueled by recent experimental progress. Theoretically, 1D anyons are predicted to host exotic many-body phases and quantum phase transitions, yet experimental signatures have remained elusive. Using ultracold atoms in an optical lattice, we prepare two-body ground states of the 1D anyon-Hubbard model by combining Hamiltonian engineering via quasiperiodic drives and adiabatic state manipulation. We uncover the effects of statistical interactions that lead to pseudo-fermionization and to the formation of chiral bound states when particles remain close together. Our results establish a link between lattice and continuum realizations of anyon models, and mark important steps towards the precise control of 1D anyons in both equilibrium and out-of-equilibrium settings.
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All authors Brice Bakkali-Hassani, Joyce Kwan, Perrin Segura, Yanfei Li, Isaac Tesfaye, Gerard Valentí-Rojas, André Eckardt, Markus Greiner

Accelerator Physics

Driver-delay chicanes for a multistage plasma-based accelerator facility

The SPARTA project aims to design a medium-sized accelerator facility that facilitates new experiments in strong-field quantum electrodynamics using plasma-based accelerators. For this, we need several plasma stages and, therefore, several drivers. Drivers can be either an ultra-relativistic charged particle beam or a high-intensity laser beam. In case we use particle beams, we need a method of distributing these beams from a radio-frequency accelerator to the different plasma stages. A central part of this is a delay scheme that ensures temporal synchronization of the drivers. In this paper, we demonstrate how to achieve a 2 ns delay in $\sim$12 m, while keeping the first-order beam parameters periodic.
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All authors D. Kalvik, E. Adli, P. Drobniak, F. Peña, C.A. Lindstrøm

Optics

DC-to-GHz Modulation In Microring Modulators Using Ferroelectric Nematic Liquid Crystal-on-Silicon in a Foundry Photonic Process

Silicon-organic hybrid (SOH) platforms exhibit exceptional electro-optic (EO) properties, including high-speed operation, low energy consumption, and compact footprints. However, the absence of a scalable poling method for EO polymers, combined with the slow switching speeds characteristic of liquid crystals, has impeded the integration and compatibility of these materials with commercial silicon photonic foundries. On the other hand, the realization of very-large-scale photonic integrated circuits (PICs) in the native silicon photonics platform itself is impeded by the complexities associated with the wavelength and thermal stabilization for microring modulators (MRMs). This study establishes the foundation for a poling-free, CMOS-compatible SOH MRM platform by exploiting simultaneous AC phase shifts in ferroelectric nematic liquid crystals (FN-LCs). We present the first demonstration of an MRM coated with FN-LC, with both the RF signal and the DC bias applied to the same electrodes, taking advantage of the dual phase shift uniquely available in FN-LC. An EO bandwidth of f$_{-6dB}\approx$ 7.8 GHz is achieved \textendash~ the highest reported value for an SOH MRM to date. As a proof of concept, we demonstrate an approximately linear resonance shift across the full width at half maximum ($\approx$ 150 pm/V), with a static power efficiency of $\approx$ 4.5 nW/$\pi$ for an MRM occupying a total footprint of $\approx$ 0.084 mm$^2$ and exhibiting an on-chip optical insertion loss of $\approx$ 0.78 dB. Successful infiltration of FN-LC, selectively patterned on top of phase shifters, along with optical input/output channels established using free-form photonic wire bonds, is demonstrated in the proposed PIC.
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All authors Iman Taghavi, Alexander Tofini, Edward K. Leung, Cory Pecinovsky, Nicolas A.F. Jaeger, Lukas Chrostowski, Sudip Shekhar

Chemical Physics · Cross-listed from cond-mat.other

Transient Plastic Spin Labeling with Chlorine Dioxide

Plastic waste, being one of the most important problems for humankind, poses severe threats to ecosystems, wildlife, and human health. Tracing, quantifying, and identifying types of plastic waste is of crucial importance to understand its environmental pathways and develop targeted strategies for reduction, recycling, and remediation. To contribute to addressing this global issue, we investigated the spin-labeling capabilities of aqueous chlorine dioxide (ClO$_2$) radicals upon introduction into poly(ethylene terephthalate) and utilized electron spin resonance spectroscopy for detection. The technique is capable of identifying plastic species as the unpaired electron of the radical molecule is strongly sensitive to its local environment through its coupling parameters. Temperature-dependent measurements revealed that the molecules are immobilized at low temperatures and exhibit well-resolved anisotropic and hyperfine spectra that are quantitatively described by a model spin Hamiltonian. Even above the melting point of water, some degrees of freedom remain blocked as a result of the polymer matrix. Furthermore, employing a time-series measurement at room temperature enabled us to determine the diffusion coefficient of the molecule in the polymer.
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All authors Bence G. Márkus, Sándor Kollarics, Kristóf Kály-Kullai, Bernadett Juhász, Dávid Beke, László Forró, Zoltán Noszticzius, Ferenc Simon

Instrumentation and Detectors

LANTERN: Characterization technology for low threshold cryogenic detectors

The use of low-temperature detectors, such as cryogenic calorimeters, has pioneered the recent advancements in low-energy rare event searches. These detectors provide a low-noise environment essential for the direct detection of dark matter and neutrinos. Characterizing these detectors within the region of interest (ROI), typically spanning from O(10~eV) to O(1~keV), has proven to be a challenging task. Conventional radioactive sources produce signals above this range, leading to nonlinearities and saturation effects. Moreover, these detectors are usually deployed in low background environments, meaning that having a radioactive source during physics runs can spoil the measurement making the use of this type of solution unfeasible. As a solution to these issues, we introduce LANTERN, an optical calibration system designed for highly segmented cryogenic calorimeters. LANTERN utilizes the photostatistics resulting from the absorption of monochromatic UV-Vis photons emitted by LEDs to analyze the detector response curve, without needing prior knowledge of the total energy deposited. The system employs a fast-switching LED matrix that operates at excitation times faster than the typical response of cryogenic detectors and can currently characterize up to 64 calorimeters independently. In this work, the validation of the final electronics designed for the project is shown. The first test was carried out by calibrating one of the cryogenic detectors of the BULLKID-DM experiment and checking the energy-reconstruction error of the spectral features produced by the surrounding lead casing. An error of $\approx 2\%$ has been observed in the energy reconstruction. The second validation was carried out by cross-calibrating one of the CALDER thin detectors with a commercial LED driver, and compatible results between the two setups were achieved.
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History and Philosophy of Physics · Cross-listed from quant-ph

No change in Hilbert space fundamentalism

Hilbert space fundamentalism (HSF) states that everything about the physical world is encoded in the Hamiltonian operator and the state vector (as a unit vector, not a wavefunction, which requires additional specification of a configuration space, a position basis, or the position observables). That all structures needed to describe reality, including subsystems, space, fields, emerge from these. I show that HSF can't account for our observations that the physical world changes in time.
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Chemical Physics

Environment-Induced Exciton Renormalization in the Photosystem II Reaction Center

Protein electrostatics tune excitation energies in the Photosystem II reaction center (PSII-RC), yet a fully quantum-mechanical many-body description of how the surrounding protein environment renormalizes excitons has remained computationally inaccessible. The Bethe-Salpeter equation (BSE) within many-body perturbation theory accurately describes excitonic physics through an explicit electron-hole interaction, but is prohibitively expensive for systems containing thousands of valence electrons. Here, we show that for sufficiently large systems the BSE becomes simpler to solve when treated with modern stochastic sampling techniques, as atomistic interactions self-average. In this regime, the effective electron-hole interaction mediated by the environment is governed by collective $k$-dependent polarization. These insights enable an ab initio study of the PSII-RC in which all six chlorins forming the hexameric dye core are treated explicitly together with a roughly seven Angstrom local protein environment. We directly compare the low-lying optical excitations of the isolated chromophore hexamer (1276 valence electrons) and the protein-dye cluster (3238 valence electrons). For $Q_y$ excitations near 680 nm, inclusion of the protein environment induces polarization-dependent energy shifts, redistributes spectral weight, and alters exciton delocalization and pigment character. Lateral and transverse asymmetries in the low-lying excited states are captured at the BSE level of theory. These results establish that we now have the tools for many-body calculations of biological nanostructures.
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All authors Tucker Allen, Barry Y. Li, Nadine C. Bradbury, Daniel Neuhauser

Plasma Physics · Cross-listed from eess.SP

A general extractor for coherent patterns across time-frequency measurements

Scientific discovery increasingly depends on finding meaningful patterns within volumes of sensor data too large for manual inspection. Existing time-frequency event extractors are often engineered or trained on manually labeled examples for each instrument, which can be laborious and difficult to adapt to new environments. To address this, we introduce TokEye, a reference-free method that learns a general criterion for coherent structure from heterogeneous fusion measurements. A model developed under this method, without retraining, can extract signals from various other fields including marine bioacoustics and wideband radar. It recovers 82.5% of expert-annotated stellarator signals, detects 78% of dolphin whistles, and identifies radar events with 81.5% average precision across six benchmarks, while processing full experimental spectrograms in under one second on a GPU. This transfer across unrelated sensors and physical systems reveals common exploitable structure in time-frequency measurements and establishes a scalable foundation for automated scientific signal discovery.
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All authors Nathaniel Chen, Kouroche Bouchiat, Peter Steiner, Andrew Rothstein, David Smith, Max Austin, Mike van Zeeland, Marie Roch, Azarakhsh Jalalvand, Egemen Kolemen

Computational Physics · Cross-listed from quant-ph

Entanglement Barriers from Computational Complexity: Matrix-Product-State Approach to Satisfiability

We approach the 3-SAT satisfiability problem with the quantum-inspired method of imaginary time propagation (ITP) applied to matrix product states (MPS) on a classical computer. This ansatz is fundamentally limited by a quantum entanglement barrier that emerges in imaginary time, reflecting the exponential hardness expected for this NP-complete problem. Strikingly, we argue based on careful analysis of the structure imprinted onto the MPS by the 3-SAT instances that this barrier arises from classical computational complexity. To reveal this connection, we elucidate with stochastic models the specific relationship between the classical hardness of the $\sharp$P $\supseteq$ NP-complete counting problem $\sharp$3-SAT and the entanglement properties of the quantum state. Our findings illuminate the limitations of this quantum-inspired approach and demonstrate how purely classical computational complexity can manifest in quantum entanglement. Furthermore, we present estimates of the non-stabilizerness required by the protocol, finding a similar resource barrier. Specifically, the necessary amount of non-Clifford operations scales superlinearly in system size, thus implying extensive resource requirements of ITP on different architectures such as Clifford circuits or gate-based quantum computers.
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Atomic Physics · Cross-listed from hep-ph

Earth Matter Enhanced Axion Dark Matter Search

Laboratory searches for ultralight axion dark matter (DM) have traditionally assumed the terrestrial density of axions is equal to the average density of DM in the solar system. However, quadratic couplings to matter introduce a non-trivial field profile near the Earth. In this work, we present the first dedicated experimental implementation of this environment-aware axion DM wind search framework. Leveraging the extreme sensitivity of a K–Rb–$^{21}$Ne comagnetometer to pseudo-magnetic fields induced by axion DM, we analyzed our data in the context of the massively enhanced local gradient of axions due to interactions with matter, though no signal candidates were found. Consequently, we have set the most stringent limits on axion-neutron derivative interactions for masses $m_a \in [0.041, ~28.9]~\rm feV$, improving from previous experiments that ignore terrestrial matter effects by as much as three orders of magnitude for certain masses. Our work highlights the necessity of accounting for environmental modifications in precision frontier experiments and demonstrates how geophysical variations can be harnessed to act as a natural amplifier for DM possibly enabling future detection in parts of the parameter space that were previously beyond reach.
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All authors Xiaofei Huang, Xiaolin Ma, Zitong Xu, Itay M. Bloch, Kai Wei

Accelerator Physics

Operational Accelerator Tuning via Model-Coupled Optics and Bayesian Steering

We present an on-line tuning strategy for the ISAC post-accelerator that pre-sets machine optics with a digital twin and then performs Bayesian optimization for steering under online operation with beam. The model computes end-to-end tunes in seconds and interfaces with the control system under device bounds, slew-rate limits, and loss interlocks. We report three experimental case studies demonstrating that decoupling optics from steering yields faster and more reliable convergence than a fully Bayesian optics-plus-steering baseline under identical conditions. Across these cases, iterations to high transmission tunes are reduced by a factor of 4-6, with final average transmissions in the mid- to high-90% range. By factorizing optics from steering, the dimensionality of the parameter space is reduced, convergence becomes more predictable, and operational safeguards are easier to enforce.
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All authors O. Hassan, O. Shelbaya, P. M. Jung, O. Kester, T. Planche, W. Fedorko

Chemical Physics · Cross-listed from cs.LG

Coupled Cluster con MōLe: Molecular Orbital Learning for Neural Wavefunctions

Density functional theory (DFT) is the most widely used method for calculating molecular properties; however, its accuracy is often insufficient for quantitative predictions. Coupled-cluster (CC) theory is the most successful method for achieving accuracy beyond DFT and for predicting properties that closely align with experiment. It is known as the ”gold standard” of quantum chemistry. Unfortunately, the high computational cost of CC limits its widespread applicability. In this work, we present the Molecular Orbital Learning (MōLe) architecture, an equivariant machine learning model that directly predicts CC's core mathematical objects, the excitation amplitudes, from the mean-field Hartree-Fock molecular orbitals as inputs. We test various aspects of our model and demonstrate its remarkable data efficiency and out-of-distribution generalization to larger molecules and off-equilibrium geometries, despite being trained only on small equilibrium geometries. Finally, we also examine its ability to reduce the number of cycles required to converge CC calculations. MōLe can set the foundations for high-accuracy wavefunction-based ML architectures to accelerate molecular design and complement force-field approaches.
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All authors Luca Thiede, Abdulrahman Aldossary, Andreas Burger, Jorge Arturo Campos-Gonzalez-Angulo, Ning Wang, Alexander Zook, Melisa Alkan, Kouhei Nakaji, Taylor Lee Patti, Jérôme Florian Gonthier, Mohammad Ghazi Vakili, Alán Aspuru-Guzik