Optics
Giant backward Brillouin interaction in generic InP integrated photonics
Riley te Morsche, Lukas Puts, Weiming Yao et al. (+1 more)
We report the first measurement of backward stimulated Brillouin scattering (SBS) in generic InP waveguides, supporting enhanced Brillouin gain of $g_B/Q_m = 3.5 \pm 0.6~\text{W}^{-1} \text{m}^{-1}$ mediated by weakly-guided pressure waves in InGaAsP. This leads to SBS gain coefficients as high as $737 \pm 54~\text{W}^{-1} \text{m}^{-1}$, observed in a mature, foundry-accessible photonic integration platform.
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All authors Riley te Morsche, Lukas Puts, Weiming Yao, David Marpaung
Accelerator Physics
RF cavity design and beam loading effects in the rectilinear cooling channel for a muon collider
C. Barbagallo, A. Grudiev, D. Merenich et al. (+2 more)
High-gradient normal-conducting RF cavities are crucial components of the rectilinear cooling channel in a
muon collider, providing the accelerating field necessary to sustain the rapid six-dimensional ionization cooling essential to achieve high luminosity. To reach this goal, a
muon collider requires approximately $10^{12}$
muons per bunch. At such high beam intensities, beam loading induced by bunch-driven wakefields can significantly reduce the cavity accelerating gradient and compromise beam stability. This paper focuses on the conceptual RF design and beam-induced effect analysis of copper cavities with so-called beam windows developed to meet the beam dynamics requirements of the rectilinear
muon cooling channel. We first present the design and optimization of the cavities, evaluating their RF performance and power requirements. Thereafter, we analyze cavity wakefields and beam loading effects, proposing a new numerical method for their compensation, which takes the transverse distribution of the beam into account.
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All authors C. Barbagallo, A. Grudiev, D. Merenich, X. Lu, T. Luo
Optics · Cross-listed from cond-mat.mes-hall
Perfect absorption by metal-contacted two-dimensional systems with ultra-proximate reflectors
Kirill Kapralov, Vladislav Atlasov, Alina Khisameeva et al. (+2 more)
Electromagnetic absorbance by most two-dimensional electron systems is typically well below unity, which hinders both practical applications in photodetection and fundamental studies of their optical properties. Here, we show that a periodic structure comprised of narrow two-dimensional sections connected with wide perfectly conducting metal sections enables large absorbance. It reaches 50 % provided the filling factor by the two-dimensional system $f$ equals its dimensionless conductivity $\eta=\sigma Z_0/2$, where $Z_0$ is the free-space impedance. The absorbance is further raised to 100 % if the periodic structure is placed above a perfectly conducting electromagnetic reflector, and provided $f=2\eta$. Surprisingly, the optimal distance between two-dimensional system and reflector may fall well below the quarter of incident wavelength $\lambda_0/4$, which was assumed as conventional absorption enhancement condition in optics. For low filling factors $f\ll1$, large dielectric constants of the substrate, and grating periods comparable with $\lambda_0$, the optimal distance to reflector tends to zero. Above the critical values of the grating geometrical parameters, the absorbance maximum ceases to exist. The critical behavior manifests as a large-amplitude resonance in 'dirty' two-dimensional system with purely real conductivity, while enhancement of carrier momentum relaxation time lowers the resonant peak. Such resonance mimics the plasmonic one, but does not rely on high electron mobility.
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All authors Kirill Kapralov, Vladislav Atlasov, Alina Khisameeva, Viacheslav Muravev, Dmitry Svintsov
Optics
Fast Ptychographic Near-Field Computed Tomography
Sami Wirtensohn, Silja Flenner, Imke Greving et al. (+13 more)
Near-field X-ray ptychography enables quantitative three-dimensional imaging with nanometer-scale resolution, but its broader application is limited by long acquisition times - often necessitating cryogenic or
vacuum environments - and demanding sample preparation procedures. In this paper, we present a flexible near-field ptychography setup that operates under ambient conditions and features an adjustable geometry for different sample sizes and resolution requirements. By replacing stepwise angular acquisition with a fly-rotation sample motion, the scanning overhead is reduced by a factor of 11, drastically lowering the tomographic scan time. To address the bottleneck in sample preparation, we also introduce a sample milling machine that enables fast preparation of specimen pillars with diameters down to 20 um. By lowering both preparation effort and measurement time while maintaining high spatial resolution, the presented system overcomes key limitations of near-field ptychography and makes quantitative X-ray nanotomography substantially more accessible for biological research.
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All authors Sami Wirtensohn, Silja Flenner, Imke Greving, Jens Brehling, Hilmar Burmester, Dominik John, Sara Baggio, Franziska Hinterdobler, Maximiliane Wojke, Kritika Singh, Benedikt J. Daurer, Johannes Hagemann, Frank Seiboth, Sara Savatovic, Fritz Vollrath, Julia Herzen
Fluid Dynamics
Autoregressive rollout error in latent-space reduced-order models of bluff-body wakes is accumulated phase drift
Suvam Samanta and Sachidananda Behera
Autoregressive reduced order models suffer from compounding long horizon rollout errors, typically treated as unstructured noise. We demonstrate that for bluff body wakes across Re=100 to 800, this rollout error is highly structured and reveals what these models actually learn. For a convolutional autoencoder LSTM model, 95 % to 98% of the error is pure phase error, peaking sharply at the
vortex shedding frequency. The network reproduces the attractor geometry almost exactly, matching limit cycle amplitudes within 0.15%, but traverses the cycle at slightly the wrong rate. This timing error, accumulating to just a few thousandths of a cycle over the entire rollout, drives the long horizon error even while one step validation errors appear virtually perfect. Because phase error drifts linearly, it can be corrected offline without retraining using just one parameter per latent coordinate, fitted on a short calibration window. The signal to noise ratio of this phase fit serves as a diagnostic that reliably predicts correction success (r=0.85 across 50 networks). While simple periodic baselines match this performance on stationary limit cycles, they fail by over an order of magnitude when applied to wakes driven by slowly varying inflows. Conversely, our phase correction requires only phase coherence, successfully removing roughly half of the rollout error during non stationary flow.
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Plasma Physics
Electron-Scale-Driven Turbulence by Negative-Density-Gradient in NSTX
C. Clauser, J. Candy, J. Parisi et al. (+7 more)
Gyrokinetic simulations of an NSTX spherical-tokamak
plasma reveal novel negative-density-gradient (NDG) drift waves at electron-gyroradius-scale that drive turbulent transport comparable to the experimental power flow. Linear simulations indicate that the dominant instability is a trapped-electron electron-scale tearing-parity mode driven mainly by negative electron density gradient, $a/L_{ne} \equiv - a/n_e \, (dn_e/dr) < 0$. Although thermal transport is mainly carried by transverse
magnetic, $\delta A_{\parallel}$, fluctuations, the growth rate is sensitive to compressional
magnetic fluctuations, $\delta B_{\parallel}$, differentiating these from standard microtearing modes (MTMs). Linear sensitivity analysis also reveals that the modes are most unstable at lower collisionality, consistent with the trapped-electron character. Electron-scale and multi-scale nonlinear simulations show that these modes can account for several megawatts of experimental power, with the latter suggesting that experimental gradients may lie at a bifurcation between distinct
turbulence regimes.
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All authors C. Clauser, J. Candy, J. Parisi, T. Rafiq, W. Guttenfelder, G. Avdeeva, E. Belli, J. Berkery, I. Sfiligoi, E. Schuster
Atomic Physics
Charge-state dynamics of barium ions in high-pressure xenon and its implications for Barium-Tagging in $0\nu\beta\beta$ searches
A. Peralta Conde
Barium tagging (BaTa) is one of the most promising techniques for achieving a nearly background-free search for neutrinoless double-beta decay ($0\nu\beta\beta$) in high-pressure xenon time detection chambers. However, the experimental implementation of BaTa depends critically on the chage-state dynamics of the daughter Ba$^{2+}$ ion produced in the
nuclear decay event. In this work, I review the possible recombination channels and evaluate their physical viability. The obtained results indicate that although binary recombination channels are strongly suppressed, three-body recombination assisted by neutral xenon atoms constitutes a physically plausible mechanism for the conversion of Ba$^{2+}$ into Ba$^+$ on timescales -milliseconds- comparable to the characteristic detection times in the NEXT experiment. These results suggest that the barium charge state should be regarded as a dynamical quantity with direct implications for the design and experimental implementation of BaTa techniques.
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Medical Physics · Cross-listed from cs.LG
Machine Learning-Based Inter-Crystal Scatter Recovery for Ultra-High Resolution PET Imaging
Alexandre Bernier, Roger Lecomte and Jean-Baptiste Michaud
Inter-
crystal scatter (ICS) events pose a significant challenge in ultrahigh- resolution positron emission
tomography (UHR-PET), especially as detector
crystals become smaller and their readouts increasingly segmented. Current approaches either reject these events, reducing sensitivity, or accept them with suboptimal positioning
algorithms, degrading image resolution. We present a feed forward neural network to optimize ICS event recovery by inferring the line-of-response belonging to the first Compton interaction. Our approach was validated using both Monte Carlo simulations and experimental data from the fully pixelated LabPET-IIbased preclinical and
brain UHR-PET scanners.Results demonstrate a 70% to 106% increase in sensitivity while preserving sub-millimeter spatial resolvability (down to 1.6 mm) compared to conventional methods. This ICS recovery approach is an effective solution that compensates for the lower detection efficiency of small, pixelated detectors in UHR-PET, enabling reduced scan times and lower radiation doses while largely preserving image quality.
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Fluid Dynamics
Transient Electrical Response Beyond Quasistatic Capacitance at Mechanically Excited Droplet–Dielectric Interfaces
Pramodt Srinivasula, Rameez Raja Khan, Diwakar Singh et al. (+1 more)
Dynamic electrowetting of conducting droplets under mechanical deformation is conventionally modeled as a quasi-static variable-capacitance system, in which the electrical response is assumed to be governed solely by the
evolution of the droplet–electrode contact area. Under the assumption of instantaneous charge equilibration, this framework successfully describes the cyclic steady-state electromechanical response of the system. However, its validity for transient interfacial electrical dynamics remains largely unexplored. Here, the transient electrowetting response of mercury droplets confined between a polymeric dielectric-coated electrode (PTFE or PVDF) and an opposing copper electrode is investigated under periodic mechanical excitation with multiple waveforms at 2 Hz. The measured contact area and corresponding capacitance evolve closely as predicted from instantaneous surface-energy minimization, confirming that the
liquid-interface mechanics remain quasi-static. In contrast, the measured transient current and instantaneous electrical power exhibit pronounced asymmetric excitation and relaxation phases that are independent of the excitation waveform, demonstrating that transient charge
evolution cannot be inferred from the instantaneous
geometric capacitance alone. This transient behavior is phenomenologically interpreted using constituent first-order interfacial dielectric charge-relaxation kinetics, indicating that the measured current arises from slow dielectric charging followed by dielectric relaxation over the timescale of the imposed periodic mechanical oscillations during discharging. These findings establish that transient electrowetting is governed by the coupled interplay of droplet electrohydrodynamics and dielectric interfacial polarization, requiring a constitutive description beyond quasi-static variable-capacitance models based solely on contact-line dynamics.
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All authors Pramodt Srinivasula, Rameez Raja Khan, Diwakar Singh, Gaurav Bhutani
Accelerator Physics
Autonomous discovery of accelerator commissioning algorithms
Thorsten Hellert
Simulated commissioning has become essential for de-risking modern light-source design and commissioning, but the procedures being simulated are still designed entirely by human experts. Their labor-intensive redevelopment after
lattice changes makes such studies hard to repeat and limits their use during early design iteration. This Letter demonstrates a closed research loop in which a
language-model
agent writes commissioning code, tests it in simulation, and improves the
algorithm from the results. Applied to RF beam capture in the ALS-U accumulator-ring model, the loop substantially improves a working expert procedure and can construct a working one from a minimal starting point, with more capable models succeeding from less initial code. Extending the same framework to multiple objectives produces 16 non-dominated
algorithms spanning physically distinct trade-offs between rapid beam capture and correction of seeded machine errors. This reframes commissioning studies from evaluating human-designed procedures toward a mode in which
agents participate directly in discovering accelerator
algorithms.
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Data Analysis and Statistics · Cross-listed from cs.HC
Thermodynamic Human-Computer Interaction
Uzafir Ahmad Rafaq, Muaz Hassan and Ali Muzaffar
Target acquisition is often modeled separately for desktop, mobile, and other interaction modalities. We present Thermodynamic HCI, a framework that splits interaction into thermal
equilibrium and non-
equilibrium regimes. The theory generalizes across interaction modalities by representing
agent-target interaction using kinetic and potential energies. We derive the movement time of Fitts' law and the speed-accuracy tradeoff observed in Schmidt's law from the principles of thermal physics. Furthermore, we develop
theorems that describe how target properties, such as the color of a button, affect user accuracy. The target acquisition model, derived from the theory, when evaluated on desktop and mobile website prefetching experiments, achieved an accuracy of 98% for both cursor and touchscreen based interaction. For every clicked link, it produced a fetch:click ratio of 1.37 for desktop and 1.75 for mobile.
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Optics
Non-monotonic dependence of OAM Schmidt spectrum on crystal thickness
Harshal Jain, Suman Karan, Radhika Prasad et al. (+1 more)
The orbital angular momentum (OAM) of
photons provides a high-dimensional resource for
quantum information protocols. The dimensionality of OAM-entangled states generated via spontaneous parametric down-conversion (SPDC) is quantified by the angular Schmidt spectrum. Here, we experimentally investigate the dependence of the angular Schmidt spectrum on the thickness of the nonlinear
crystal. Contrary to previous studies reporting a monotonic decrease in the Schmidt number with increasing
crystal thickness, we report the first experimental observation of a nonmonotonic behavior, as we demonstrate an increase in the Schmidt number beyond a certain
crystal thickness. We attribute this to the spatial walk-off effect in the anisotropic nonlinear
crystal and explain it using a theoretical model that is devoid of standard phase-matching approximations. These findings can have important implications for high-dimensional entangled state generation.
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All authors Harshal Jain, Suman Karan, Radhika Prasad, Anand K. Jha
Optics
Enhanced Scalability of Horseshoe-and-Spur Networks by Exploiting Hollow-Core Fiber
Mohammad M. Hosseini, Joao Pedro and Antonio Napoli
The convergence of metro and access networks into unified optical infrastructures requires cost-effective alternatives to conventional solid-core fiber (SCF). This paper examines using hollow-core fiber (HCF) with digital subcarrier multiplexing (DSCM) transceivers in horseshoe-and-spur filterless optical architectures. Leveraging HCF's ultra-low nonlinearity, we optimize amplifier placement to maximize power budgets under realistic constraints. Our results show that HCF shifts the main limitation from nonlinearity to amplifier output power, enabling up to a 20 dB spur power-budget gain over SCF. Considering balanced and unbalanced couplers, we find that increasing amplifier density boosts reach only up to a saturation point (about 11-13 units in a 5-transit-node network). A techno-economic break-even analysis of hybrid SCF-HCF deployments shows that targeted HCF use provides intermediate performance gains and can fully recover its fiber cost premium through amplifier reductions.
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Physics and Society
Coordinated incentives in AI-generated misinformation governance
Qin Li, Gui Zhang, Minyu Feng et al. (+2 more)
With the rapid
diffusion of AI-generated content, AI-driven misinformation is becoming increasingly pervasive and difficult to govern, undermining information credibility and social trust. This study models the strategic interdependence among a government regulator, an AI enterprise, and users through a three-party evolutionary game that incorporates heterogeneous rewards and punishments. From the resulting replicator equations, we characterize the evolutionary stability of competing governance and production strategies. The analysis indicates that neither unilateral regulation nor
market incentives alone can effectively curb misinformation. Instead, an evolutionarily stable regime of real-information production arises only when regulatory rewards and punishment intensity, enterprise reputation loss, and user adoption incentives collectively surpass critical thresholds. The findings highlight the need for coordinated and adaptive policy mixes that align regulatory instruments with enterprise behavior and user uptake while managing governance costs.
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All authors Qin Li, Gui Zhang, Minyu Feng, Matjaz Perc, Attila Szolnoki
Optics
Characterising Interleaver Length in a Turbulent Deployed Terrestrial Free-Space Optical Link
Kadir Gümüş, Vincent van Vliet, Menno van den Hout et al. (+3 more)
We investigate the correlation between interleaver length and
turbulence for a deployed terrestrial free-space optical link spanning 4.6 km. Using 24 hours of measurements, we show an indicative distribution of interleaver length for capacities up to 350 Gb/s/pol and outage probabilities down to $10^{-4}$.
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All authors Kadir Gümüş, Vincent van Vliet, Menno van den Hout, Thomas Bradley, Eduward Tangdiongga, Chigo Okonkwo
Applied Physics · Cross-listed from cond-mat.mes-hall
Magneto-optical signal from $\mathrm{Co_2Mn}$-based Heusler thin films in MOKE and BLS
Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher et al. (+3 more)
$\mathrm{Co_2Mn}$-based Heusler compounds offer a versatile, composition-tunable platform for magnonics and spintronics. Among them, the half-metallic $\mathrm{Co_2MnSi}$ is of particular interest for magnonics owing to its ultralow Gilbert damping, yet its weak magneto-optical response in the visible challenges optical probing such as Brillouin light scattering (BLS). We study the magneto-optical response of epitaxial $\mathrm{Co_2Mn}X$ films ($X = \{\mathrm{Al}_x\mathrm{Si}_{1-x}, \mathrm{Ga}_x\mathrm{Ge}_{1-x}, \mathrm{Sn}\}$) by magneto-optical Kerr effect (MOKE) spectroscopy and BLS. Angle-resolved MOKE resolves a significant, wavelength-dependent quadratic MOKE (QMOKE) only for $\mathrm{Co_2MnSi}$, whereas $\mathrm{Co_2MnAl}$, $\mathrm{Co_2MnGa}$ and $\mathrm{Co_2MnSn}$ respond dominantly linearly. Comparing BLS intensities of thermal
magnons at two wavelengths, $\mathrm{Co_2MnSi}$ gives the weakest signal at 532 nm yet among the strongest at 457 nm, tracking the spectral dependence of its Kerr angle. These results emphasise the relation between the two magneto-optical techniques, guiding the choice of probing wavelength for $\mathrm{Co_2Mn}$-based Heusler compounds.
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All authors Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher, Sébastien Petit-Watelot, Stéphane Andrieu, Philipp Pirro
Applied Physics
Roadmap on UV-C photodetectors: materials, applications and industry perspectives
Fabien Massabuau, Drew Riley, Paul Meredith et al. (+44 more)
UV-C photodetectors are poised to play an increasingly important role in future photonic technologies, driven by the rapid emergence of UV-C light sources and new wide bandgap
semiconductors. These advances are enabling new levels of spectral selectivity, radiation hardness, sensitivity, and device integration, while opening opportunities across a broad range of applications. This roadmap provides a comprehensive overview of the current landscape of UV-C photodetection, spanning established and emerging material platforms (Ga2O3, AlGaN, BN, diamond, MgZnO, 2-dimensional materials, metal halide perovskites, micro-electromechanical systems), and their applications in metrology, astronomy, communications, environmental monitoring, fire detection, missile warning, gas sensing, and medical diagnostics. By identifying opportunities, bottlenecks, and future directions, this roadmap aims to support both newcomers and established researchers, with the aim of accelerating the translation of UV-C photodetectors into impactful technologies.
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All authors Fabien Massabuau, Drew Riley, Paul Meredith, Tilman Weiss, Damanpreet Kaur, Yuichi Oshima, Robert W. Martin, Eva Monroy, Le Chen, Hongwei Liang, Hong Yin, Keyun Gu, Meiyong Liao, Yaonan Hou, Fa Cao, Xiaosheng Fang, Ruiheng Li, Guoqiang Peng, Zhiwen Jin, Lijie Li, Nasim Zarrabi, Sebastian Wood, Jesper Skottfelt, Susan E. S. Spesyvtseva, Jonathan McKendry, Christopher G. Leburn, Daniel K. L. Oi, Ryan Pereira, Graeme Moore, Tom Lendrem, Christoph Wagner, David Maestre, Emilio Nogales, David J. Rogers, Eric Sandana, Michel Chamberlin, Ferechteh H. Teherani, Bianchi Méndez, Yana Suchikova, Marina Konuhova, Anatoli I. Popov, Luís F. da Silva, Eduard Llobet, Sangjin Yoon, Dohyung Kim, Sangwoo Hong, Seung Hwan Ko
Physics and Society · Cross-listed from cs.LG
Hyperbolic Graph Embedders for Link Prediction and Topology Reconstruction
Robert Jankowski, Maksim Kitsak and Dorota Celińska-Kopczyńska
Hyperbolic embeddings provide compact
geometric representations of complex networks in
hyperbolic spaces, but systematic comparisons of methods developed in machine learning, network science, and algorithmics remain rare. We
benchmark 13 unsupervised
hyperbolic graph embedders under a unified protocol for link prediction and
topology reconstruction on synthetic and empirical networks. The protocol captures both missing-link recovery and the preservation of local and global network structure. Maximum-likelihood and representation-learning-based approaches, including hybrid variants, achieve the strongest overall performance, although no method dominates across all tasks and structural regimes. Performance is more strongly associated with
embedding paradigm than with disciplinary origin. We identify the network regimes in which different paradigms succeed or fail and provide practical guidance for method selection in downstream applications.
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Biological Physics · Cross-listed from q-bio.MN
Simulating is not always understanding: When model complexity obscures biology
Lendert Gelens, Alejandro Fábregas-Tejeda, Grant Ramsey et al. (+2 more)
In
cell biology, computational models of biological systems range from minimal representations with a handful of parameters to whole-
cell simulations tracking thousands of molecular species across a complete
cell cycle. While these models span a continuum of detail, increasing complexity changes what they capture and are able to explain, what they can predict, and how they can fall short. A model contributes to understanding only when it makes novel predictions, reveals an unexpected coupling between processes, or fails in a way that identifies missing parameters. We contend that what is important for understanding is not the number of components or spatial dimensions a model contains, but the ratio of free parameters to the experimental constraints available to pin them down, and whether we can see why it produces the behaviors it does. Large-scale
agent-based models of cytoskeletal dynamics or tissue mechanics that are built on a small number of physically grounded rules can reveal rich self-organization behavior precisely because their parameter spaces are small enough to explore systematically. By contrast, when free parameters grow faster than the data available to constrain them, models become progressively harder to interpret – and even disprove –regardless of their biological scope. We argue that the field needs to reconsider the goal of complex models. We should move away from trying to include as many parameters as possible and instead aim for systematic comparisons with simpler representations, dynamical analysis, and explicit model hierarchies that trace how cellular behavior emerges from its parts.
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All authors Lendert Gelens, Alejandro Fábregas-Tejeda, Grant Ramsey, Sylvia Wenmackers, Bart Smeets
Atomic Physics
An ionic clock qubit inside a circular Rydberg atom
Fabian Thielemann, Aaron Götzelmann, Marius Thomas et al. (+4 more)
Neutral atoms trapped in optical tweezers and excited to Rydberg states, together with trapped ions, are among the most advanced platforms for
quantum simulation and
quantum computing. Current experiments often rely on additional atoms in neighboring traps to encode ancilla
qubits for local manipulation and readout. Here, we demonstrate a dual ion-Rydberg system comprising two
qubits encoded in two individually controlled electrons of the same alkaline-earth atom. The first, a microwave
qubit, is encoded in a pair of circular Rydberg states, while the second, an optical
qubit, is encoded on a narrow quadrupole transition of the Rydberg atom's ionic core. We demonstrate coherent control of the optical
qubit and achieve coherence times of several hundred microseconds under dynamical decoupling. Furthermore, we realize coherent coupling between the two electrons via electrostatic quadrupole interactions over the large separation between the Rydberg electron and the ionic core, and map out its angular tunability. Finally, we demonstrate a two-
qubit operation, reminiscent of a Mølmer-Sørensen gate, that evolves through an entangled state of the two
qubits driven by the quadrupole coupling. Our work opens a pathway to exploit a pair of individually controlled electronic
qubits with tunable coupling for
quantum simulation and
quantum metrology.
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All authors Fabian Thielemann, Aaron Götzelmann, Marius Thomas, Einius Pultinevicius, Armin Humić, Christian Hölzl, Florian Meinert
Optics
Real-Time Dynamic Crosstalk Tracking and Compensation via Photonic Blind Source Separation
Dongliang Wang, Yikun Nie, Dingqian Zhao et al. (+4 more)
Space-division multiplexing in few-mode fibers can substantially increase optical-link capacity, but its practical deployment is hindered by dynamically varying inter-modal crosstalk induced by environmental perturbations. Although silicon photonic reconfigurable mode processors have been widely demonstrated, continuous adaptation during high-speed intensity-modulation direct-detection (IM/DD) transmission remains challenging. Here, we experimentally demonstrate real-time tracking and compensation of dynamically varying inter-modal crosstalk using a hybrid photonic–electronic framework that combines an integrated silicon photonic processor with an FPGA-based control backend. The photonic processor performs signal separation in the optical domain, while the FPGA extracts signal statistics and implements a blind source separation (BSS)-based feedback
algorithm without requiring dedicated training sequences. A two-stage optimization strategy combines rapid crosstalk suppression with stable continuous tracking under dynamic channel variations. We demonstrate photonic blind source separation for signals up to 100 GBaud and FPGA-enabled continuous adaptation for two 64 GBaud data channels in a few-mode-fiber transmission system. The system maintains bit-error rates below $10^{-4}$ under dynamic crosstalk, with a per-update control latency of 4 ms. These results establish a practical route toward low-latency, hardware-efficient adaptive photonic front ends for dynamic high-speed IM/DD space-division-multiplexed links.
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All authors Dongliang Wang, Yikun Nie, Dingqian Zhao, Dan Yi, Gaolei Hu, Hon Ki Tsang, Chaoran Huang
Atomic Physics · Cross-listed from quant-ph
Single-qubit detection by collective phase imprinting
Kritsana Srakaew, Pascal Weckesser, Daniel Adler et al. (+4 more)
The amplification of
quantum information carried by a single
quantum excitation is a recurring challenge across diverse
quantum platforms. The coupling between a single
qubit and a mesoscopic ensemble of
spins, for example, can be leveraged to realize non-destructive detection of the
qubit state. However, realizing robust couplings between such systems is experimentally challenging and typically requires programmable
quantum gates or native long-range interactions. Here, we introduce a platform that couples a single
qubit, encoded in the ground-to-Rydberg transition of a control atom, to a Rydberg-dressed target ensemble of ground-state atoms trapped in an optical
lattice. We show that the state of the control
qubit can be coherently mapped onto the ensemble via a
qubit-controlled collective phase shift. By Rydberg-dressing the ensemble, the controlled phase shift per target atom becomes independent of the number of target atoms, making the protocol intrinsically insensitive to atom-number fluctuations and atom loss, which are the dominant experimental imperfections in our system. Exploiting the collective response of up to eight target
spins, we demonstrate the efficacy of the scheme by realizing non-destructive detection of a single Rydberg excitation with a state-assignment fidelity of $\mathcal{F} = 99.81^{+0.17}_{-1.47}\,\%$. Our approach demonstrates the key ingredients for high-fidelity transfer of
quantum information from a single
qubit to a mesoscopic ensemble, opening a route to non-destructive mid-
circuit readout of Rydberg states and to efficient interfaces between single
qubits and photonic modes.
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All authors Kritsana Srakaew, Pascal Weckesser, Daniel Adler, Suchita Agrawal, David Gröters, Immanuel Bloch, Johannes Zeiher
Physics and Society
How a shared state is described determines whether AI agents synchronize
Takahiro Ezaki, Naoto Imura and Katsuhiro Nishinari
Language-model
agents increasingly act in populations, where the outcome that matters is collective: whether they align, split or fail to coordinate. Each acts not on the world but on a text description of it, a choice usually fixed in software. Using synchronization, the canonical probe of how interaction rules produce collective order, we show that this choice can decide the outcome.
Agents on a circle chose to advance, stay or move back after reading the others' relative positions, in 507,112 valid responses across matched populations, controlled inputs and three model families. In GPT, numerical summaries aligned every matched population at both positive couplings, whereas histograms aligned none; Claude showed the reverse at the stronger coupling. Re-describing identical states shifted action probabilities in all three families, even between histograms carrying the same information. No single directional coefficient explained the outcome: state descriptions are part of the interaction rule that turns individual responses into collective order.
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Chemical Physics · Cross-listed from cs.LG
How Molecular Generative Models Organize Molecular Identity
Raul Ortega-Ochoa, Tejs Vegge, Jens S. Bakander et al. (+3 more)
Generative models for matter are often evaluated as samplers over output representations, and their latent spaces are commonly used as proxies for navigating chemical space. Much less is known about how these models internally arrange discrete chemical identities within those representations. We study this arrangement by making molecular identity explicit and pulling it back through the generative process. Through these pullbacks we probe the regions that generate the same object, exposing the trained model's internal repertoire: a fixed partition that determines which objects (novel or not) the model can produce. Across three molecular generative architectures, we find that this repertoire is arranged into piecewise-constant regions separated by recurring coarse-to-fine boundaries. Its organization depends on the representation probed, the identity convention, decoder stochasticity, and the metric used to compare coordinates. During training, local chemical organization stabilizes while the number of distinct molecular identities represented within each neighborhood continues to change. Internal organization must therefore be characterized, rather than assumed, before a generative space can be treated as chemically navigable.
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All authors Raul Ortega-Ochoa, Tejs Vegge, Jens S. Bakander, Luis Mantilla Calderon, Alan Aspuru-Guzik, Tonio Buonassisi
General Physics
Information surfaces and overflow fields: a unitary evolution model based on the principle of information curvature scaling
Zheng Yahui
The black hole information paradox exposes a fundamental contradiction between
quantum unitarity and semiclassical
gravity. Although the
entanglement island paradigm is capable of reproducing the Page curve, the physical essence of
quantum extremal surfaces and the microscopic mechanism of information transfer have yet to be clarified. Taking
quantum information as a fundamental conserved quantity and adopting the principle of information
curvature scaling, this paper argues that no singularity exists inside a black hole. Instead, there exist information surfaces encoding
quantum information and attached overflow field structures. The model divides black hole evaporation into two stages: the unsaturated stage and the saturated stage. During the unsaturated stage, Hawking radiation dissipates the overflow field, resulting in a steady increase of
entanglement entropy. In the saturated stage, the overflow field is completely exhausted. The information surface then undergoes fragmentation and reconstruction, emitting high-energy particles carrying
quantum information and driving a gradual decline in
entanglement entropy. At the very final stage of black hole evaporation, all residual
quantum information and mass are released entirely through a
quantum outburst. This model establishes the physical correspondences between the event horizon and the
quantum extremal surface, as well as between the information surface and the
entanglement island, which can provide some phenomenological constraints for
quantum gravity theories.
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Optics
Unveiling charge dynamics on the generation of high extinction wide pulse generation on thin-film lithium tantalate
Ayed Al Sayem, Shiekh Zia Uddin, Ting-Chen Hu et al. (+6 more)
We experimentally demonstrate high-extinction optical pulse generation in thin-film lithium tantalate (TFLT), achieving a wide range of pulse widths with sharp rise and fall edges, without measurable distortion or long temporal tails. We further provide a direct one-to-one comparison with thin-film lithium niobate (TFLN) modulators under identical measurement conditions. Our results reveal that the distorted pulse response observed in TFLN originates from charge activation and transport, whereas the distortion-free response in TFLT is enabled by the substantially larger activation energy of defect-related charge carriers. This larger activation barrier suppresses leakage-current-induced charging dynamics, thereby enabling stable and distortion-free pulse generation. The successful generation of high-extinction, distortion-free optical pulses in TFLT can play a significant role in integrated
quantum photonic technologies, particularly for
qubit preparation, measurement, and fast feedback
circuits.
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All authors Ayed Al Sayem, Shiekh Zia Uddin, Ting-Chen Hu, Tam Huynh, Bongjun Choi, Alaric Tate, Mark Cappuzzo, Rose Kopf, Mark Earnshaw
Computational Physics
Adjoint shape optimization of oscillatory rarefied gas flows
Pengshuo Li and Lei Wu
A fast-converging and asymptotic-preserving adjoint shape optimization method is proposed for drag reduction of multiscale gas flows in vibrating micro-electro-mechanical systems. The convergence of the Boltzmann kinetic equation is accelerated by macroscopic synthetic equations, whose constitutive relations integrate continuum-limit terms and high-order kinetic corrections to faithfully characterize spatiotemporal rarefaction effects. As such, this method maintains near-continuum limit consistency while retaining high kinetic accuracy in rarefied flow regimes.
Fourier stability analysis performed in an infinite domain demonstrates that the present method yields a spectral radius below 0.5, indicating that the numerical deviation from the converged solution is halved per iteration. Numerical simulations are conducted on an oscillating cylinder and a comb-shaped resonator. The results verify the high accuracy of the derived adjoint sensitivities and the excellent drag reduction performance of the proposed method across various Knudsen and Strouhal numbers. Compared with conventional kinetic iteration methods, the present method produces convergent primal and adjoint solutions within dozens of iterations and features asymptotic preserving behavior, permitting spatial
cell sizes far larger than the molecular mean free path. This facilitates efficient design of vibrating micro-electro-mechanical systems.
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Optics · Cross-listed from eess.SP
Comparative Analysis of Spread-Spectrum Codes for Fibre-Optic Distributed Acoustic Sensing
Maria Freire-Hermelo and Elie Awwad
This paper presents a comprehensive performance comparison of several coded sequences for distributed acoustic sensing systems through numerical simulations. Correlation analysis reveals that perfect autocorrelation sequences provide accurate channel estimation. Phase noise sensitivity varies significantly with frequency diversity, with high-diversity sequences maintaining lower estimation errors for phase and intensity despite increased
laser linewidths. For a coded distributed acoustic sensing system with \qty{10}{\hertz}
laser linewidth, high-diversity sequences achieve $2.7\times10^{-3}$ rad phase error compared to $5.3\times10^{-3}$ rad for low-diversity codes for a \qty{1.5}{\kilo\meter} fibre length. The findings establish performance trade-offs between correlation quality, phase noise resilience, and practical implementation constraints for next-generation fibre-optic distributed acoustic sensing systems.
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Medical Physics
Lens-Aware Differentiable Beamforming for In Vivo Distributed Aberration Correction with Curvilinear Transducers
Benjamin N. Frey, Robin van Velzen, Hoda S. Hashemi et al. (+7 more)
We previously introduced ultrasound autofocusing, an iterative model-based aberration correction technique that estimates local sound speed and incorporates it into beamforming to correct image distortion from heterogeneous media. In this work, we extend ultrasound autofocusing to curvilinear arrays and introduce advancements to the underlying model. A differentiable bent-ray tracing approach accounts for refraction through the transducer lens, while a new adaptive-grid initialization accounts for changes in speckle position with sound speed. The method is validated in silico and in calibrated sound speed phantoms. Our distributed aberration-correction method is then applied to a first large-scale in vivo evaluation comprising 313 liver acquisitions from 76 high-BMI human subjects. In images containing anechoic regions, contrast and CNR improved by $1.38 \pm 1.60$ dB (+18.0%) and $0.09 \pm 0.14$ (+10.2%), respectively. Improvements were also observed in speckle brightness (+20.3%), coherence factor (+13.1%), lag-one coherence (+2.7%), common-midpoint correlation coefficient (+0.7%), and common-midpoint phase error (-9.1%; lower is better), with all metric improvements statistically significant. Target structure and visibility also improved significantly. These results demonstrate the potential of ultrasound autofocusing for clinically applicable distributed aberration correction.
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All authors Benjamin N. Frey, Robin van Velzen, Hoda S. Hashemi, Samuel Beuret, Martin Schneider, Alice C. Fan, Christian R. Hoerner, Aya Kamaya, Sergio J. Sanabria, Jeremy J. Dahl
Atomic Physics · Cross-listed from quant-ph
Entanglement-enhanced optical magnetometry beyond the standard quantum limit
Jun Jia, Túlio Brito Brasil, Maimouna Bocoum et al. (+6 more)
Optical atomic magnetometry is a powerful tool for continuous sensing applications, yet, in the absence of
quantum correlations, its sensitivity is limited by the standard
quantum limit (SQL) stemming from a trade-off between optical probe imprecision and
quantum measurement backaction. Beyond-SQL sensitivity requires
quantum correlations that modify these measurement noise sources. Here we demonstrate such sensitivity by using entangled state of the probe light and by engineering correlations between measurement imprecision and backaction. Having first explored SQL in a broad range of frequencies, we demonstrate overcoming the limit by combining variational readout with coupling the magnetometer to one mode of a bipartite entangled light state and conditioning the results on the other entangled mode. Tuning the detected light quadratures and combining the signals from the two measurement channels, we achieve sensitivity beyond the SQL in a broad range of acoustic frequencies which has so far remained inaccessible to
quantum-noise-limited optical magnetometry.
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All authors Jun Jia, Túlio Brito Brasil, Maimouna Bocoum, Andrea Grimaldi, Laurits Møberg, Mikhail Balabas, Jörg Helge Müller, Emil Zeuthen, Eugene Simon Polzik