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Physics Physics

physics Watch Physics

Friday 10 October

Computational Physics · Cross-listed from quant-ph

A Decoy-like Protocol for Quantum Key Distribution: Enhancing the Performance with Imperfect Single Photon Sources

Chanaprom Cholsuk, Furkan Ağlarc{\i}, Daniel K. L. Oi et al. (+2 more)

Quantum key distribution (QKD) relies on single photon sources (SPSs), e.g. from solid-state systems, as flying qubits, where security strongly requires sub-Poissonian photon statistics with low second-order correlation values (\$g^{(2)}(0)\$). However, achieving such low \$g^{(2)}(0)\$ remains experimentally challenging. We therefore propose a decoy-like QKD protocol that relaxes this constraint while maintaining security. This enables the use of many SPSs with \$g^{(2)}(0) > \$0.1, routinely achieved in experiments but rarely considered viable for QKD. Monte Carlo simulations and our experiment from defects in hexagonal boron nitride show that, under linear loss, \$g^{(2)}(0)\$ remains constant, whereas photon-number-splitting (PNS) attacks introduce nonlinear effects that modify the measured \$g^{(2)}(0)\$ statistics. Exploiting this \$g^{(2)}(0)\$ variation as a diagnostic tool, our protocol detects PNS attacks analogously to decoy-state methods. Both single- and two-photon pulses consequently securely contribute to the secret key rate. Our protocol outperforms the Gottesman–Lo–Lutkenhaus–Preskill (GLLP) framework under high channel loss across various solid-state SPSs and is applicable to the satellite-based communication. Since \$g^{(2)}(0)\$ can be extracted from standard QKD experiments, no additional hardware is required. The relaxed \$g^{(2)}(0)\$ requirement simplifies the laser system for SPS generation. This establishes a practical route toward high-performance QKD without the need for ultra-pure SPSs.
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All authors Chanaprom Cholsuk, Furkan Ağlarc{\i}, Daniel K. L. Oi, Serkan Ateş, Tobias Vogl

Data Analysis and Statistics · Cross-listed from cond-mat.stat-mech

Deep Learning of the Biswas-Chatterjee-Sen Model

J. F. Silva Neto, D. S. M. Alencar, L. T. Brito et al. (+5 more)

We investigate the critical properties of kinetic continuous opinion dynamics using deep learning techniques. The system consists of $N$ continuous spin variables in the interval $[-1,1]$. Dense neural networks are trained on spin configuration data generated via kinetic Monte Carlo simulations, accurately identifying the critical point on both square and triangular lattices. Classical unsupervised learning with principal component analysis reproduces the magnetization and allows estimation of critical exponents. Additionally, variational autoencoders are implemented to study the phase transition through the loss function, which behaves as an order parameter. A correlation function between real and reconstructed data is defined and found to be universal at the critical point.
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All authors J. F. Silva Neto, D. S. M. Alencar, L. T. Brito, G. A. Alves, F. W. S. Lima, A. Macedo-Filho, R. S. Ferreira, T. F. A. Alves

Plasma Physics

Long Living Hot and Dense Plasma from Relativistic Laser-Nanowire Array Interaction

Ehsan Eftekhari-Zadeh, Mikhail Gyrdymov, Parysatis Tavana et al. (+13 more)

Long-living, hot and dense plasmas generated by ultra-intense laser beams are of critical importance for laser-driven nuclear physics, bright hard X-ray sources, and laboratory astrophysics. We report the experimental observation of plasmas with nanosecond-scale lifetimes, near-solid density, and keV-level temperatures, produced by irradiating periodic arrays of composite nanowires with ultra-high contrast, relativistically intense femtosecond laser pulses. Jet-like plasma structures extending up to 1~mm from the nanowire surface were observed, emitting K-shell radiation from He-like Ti$^{20+}$ ions. High-resolution X-ray spectra were analyzed using 3D Particle-in-Cell (PIC) simulations of the laser-plasma interaction combined with collisional–radiative modeling (FLYCHK). The results indicate that the jets consist of plasma with densities of $10^{20}$-$10^{22}$ cm$^{-3}$ and keV-scale temperatures, persisting for several nanoseconds. We attribute the formation of these jets to the generation of kiloTesla-scale global magnetic fields during the laser interaction, as predicted by PIC simulations. These fields may drive long-timescale current instabilities that sustain magnetic fields of several hundred tesla, sufficient to confine hot, dense plasma over nanosecond durations.
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All authors Ehsan Eftekhari-Zadeh, Mikhail Gyrdymov, Parysatis Tavana, Robert Loetzsch, Ingo Uschmann, Thomas Siefke, Thomas Käsebier, Uwe Zeitner, Adriana Szeghalmi, Alexander Pukhov, Dmitri Serebryakov, Evgeni Nerush, Igor Kostyukov, Olga Rosmej, Christian Spielmann, Daniil Kartashov

Physics and Society

(Anti)Gravitron: A Statistical Physics Perspective on Multidimensional Metrics of Polarizing Inequality

Rolando Gonzales Martinez

This paper introduces a novel framework for measuring multidimensional inequality based on a statistical physics reinterpretation of centrifugal and centripetal forces in rotating systems. Inspired by the mechanics of the Gravitron and extended via the conceptual AntiGravitron, this study proposes a new class of inequality metrics grounded in multivariate mixtures of Beta distributions. These composite metrics capture three key structural dimensions of polarizing inequality: the number and balance of population clusters (modal entropy), the internal uniformity of each cluster (concentration), and the separation between clusters in attribute space (geometric divergence). Monte Carlo simulations of the AntiGravitron show how bifurcation, stratification, and polarization jointly influence inequality measurements due to multidimensional attraction-repulsion forces. An empirical application of the AntiGravitron to US household income data reveals polarized inequality driven by intersecting centripetal and centrifugal socio-economic forces affecting Black and African American populations in the Philadelphia County. By bridging physical systems theory and social stratification analysis, this paper offers a rigorous, flexible, and interpretable metric that enhances the understanding of polarizing inequality in high-dimensional, structurally heterogeneous contexts. The AntiGravitron framework holds promise for small-area estimation of polarization-driven inequality in socio-economics and biomedicine domains such as epidemiology, where inequality arises from multi-axial exclusion and attractor dynamics.
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Optics

Skyrmionic polarization textures in structured dielectric planar media

Francesco Di Colandrea, Lorenzo Marrucci and Filippo Cardano

Skyrmionic patterns of optical fields have recently emerged across diverse photonic platforms. Here, we show that such textures also arise in the polarization eigenstates of light propagation through flat dielectric devices with an engineered, space-dependent optic-axis orientation. We focus on two-dimensional periodic structures, where propagation through multiple devices maps onto quantum dynamics on a synthetic optical lattice. Adopting the condensed-matter framework, a spatial period defines an effective Brillouin zone, and polarization eigenstates can be grouped in two bands, with the role of energy played by the opposite phase delay. When such eigenstates exhibit skyrmionic textures, the corresponding lattice model shows the topology of a Chern insulator. These structures result from the interaction between the optical field and the medium and do not reflect a topological structure of the medium itself. We validate these concepts in a system of three tunable liquid-crystal metasurfaces. Using quantum process tomography based on supervised machine learning, we reconstruct the polarization eigenmodes over one spatial period. We identify configurations of the devices' parameters that lead to topologically non-trivial bands, where we directly observe skyrmionic eigenpolarization textures. Along the analogy with condensed matter, we also extract local observables of lattice models, such as the Berry curvature and the quantum metric. We finally report a numerical simulation of an all-optical quantum Hall effect emerging when light propagates through a sequence of such devices, arranged so as to mimic the effect of an external force on the lattice.
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Atomic Physics

Magnetotactic bacterial populations studied with a Pound-Drever-Hall atomic magnetometer

María Hernández Ruiz, Christopher Kiehl, Vito Giovanni Lucivero et al. (+1 more)

We demonstrate an optically pumped magnetometer that monitors spin polarization using Pound Drever Hall (PDH) technique. The instrument exhibits a noise floor of 22.2 pT/sqrt(Hz) limited by optical photon shot noise, short-term instability of 30.8 pT/sqrt(Hz)/sqrt({\tau}) for averaging times {\tau} < 0.2 s , instability below 70 pT for 0.2 s < {\tau} < 20 s and a minimum instability of 47 pT at {\tau} = 6 s. We apply the OPM to investigate the ability of magnetotactic bacteria (Magnetospirillum gryphiswaldense, MSR-1) to orient in externally applied magnetic fields. Observing an opaque, concentrated suspension, we detect deviations from exponential relaxation dynamics on second time-scales, which give information about the dispersion of bacterial magnetic moment and rotational damping coefficient. These parameters are observed to evolve as the population further concentrates due to evaporation and settling. To our knowledge, this is the first time such magnetic inhomogeneities and long-term relaxation deviations have been directly observed. This study showcases both the sensitivity and stability of our OPM and its potential for probing biophysical processes.
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All authors María Hernández Ruiz, Christopher Kiehl, Vito Giovanni Lucivero, Morgan W. Mitchell

Physics and Society

PyPSA-DE: Open-source German energy system model reveals savings from integrated planning

Michael Lindner, Julian Geis, Toni Seibold et al. (+1 more)

Germany has set an ambitious target of reaching net zero greenhouse gas emissions by 2045. We explore how integrated cross-sectoral planning can reduce costs compared to existing national plans. Our new linear optimization model PyPSA-DE simulates the electricity and hydrogen transmission networks, as well as supply, demand, and storage in all sectors of the energy system in Germany and its neighboring countries with high spatial and temporal resolution. While our new model shows strong electricity transmission grid development, total expansion is one third lower than in the national grid development plan, lowering costs by 92 billion EUR$_{2020}$ to 191 billion EUR$_{2020}$ and average grid tariffs by 7.5 EUR$_{2020}$ / MWh. These savings are mainly due to integrated planning and operation, a market design with regional prices, and a system-optimal usage of offshore wind. PyPSA-DE is open-source and can readily be adapted to study related issues around the energy transition.
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All authors Michael Lindner, Julian Geis, Toni Seibold, Tom Brown

Chemical Physics

Understanding How Synthetic Impurities Affect Glyphosate Solubility and Crystal Growth Using Free Energy Calculations and Molecular Dynamics Simulations

Alejandro Castro, Ignacio Sanchez-Burgos, Nuria H. Espejo et al. (+3 more)

Glyphosate, the most widely used herbicide worldwide, crystallizes through complex intermolecular interactions that are strongly influenced by synthesis-derived impurities. Understanding this process at the molecular scale is critical for optimizing production, ensuring product quality, and assessing environmental impact. Here, we employ direct coexistence molecular dynamics simulations and free energy calculations to elucidate how glycine-a prevalent synthesis byproduct-modulates glyphosate solubility and crystal growth in aqueous solutions. Our simulations identify two major mechanisms by which glycine hinders crystallization. First, direct coexistence simulations show that glycine preferentially adsorbs at crystal surfaces, hindering glyphosate attachment and slowing growth. Second, free energy calculations demonstrate that glycine enhances glyphosate solubility, reducing the supersaturation driving force to incorporate into the crystal phase. Experimental measurements corroborate our predictions, confirming both enhanced solubility and reduced crystallization kinetics in glycine-bearing systems. These findings establish that glycine-typically considered an inert impurity-actively disrupts glyphosate crystallization by promoting its dissolution. More broadly, this integrated computational-experimental approach highlights the power of molecular simulations to disentangle impurity effects, interfacial phenomena, and solution thermodynamics in crystallization, providing molecular-level insights for optimizing industrial protocols and predicting agrochemical behavior under relevant environmental conditions.
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All authors Alejandro Castro, Ignacio Sanchez-Burgos, Nuria H. Espejo, Adiran Garaizar, Giovanni Maria Maggioni, Jorge R. Espinosa

Optics · Cross-listed from math.AP

Complex Gaussianity and spatio-frequential memory effect of random wave processes

Guillaume Bal and Anjali Nair

Wavefield speckle patterns are generated by interference of randomly scattered coherent light. In the weak-coupling regime of the Itô-Schrödinger paraxial model for long-distance wave propagation, we show the following multiscale character: a macroscopic envelope solves a deterministic diffusion equation while the local wavefield (the speckle) is described by a complex Gaussian process both in terms of spatial axial and lateral displacements as well as frequency and angular variations of the incident wavebeam. These results describe speckle patterns and corroborate chromato-spatial memory effects observed in laser light propagation through heterogeneous media.
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Atomic Physics

Acousto-optic lens for 3D shuttling of atoms in a neutral atom quantum computer

Zhichao Guo, Rik A.H. van Herk, Edgar J.D. Vredenbregt et al. (+1 more)

We present a novel acousto-optic lens (AOL) design for neutral atom quantum computing. This approach enhances atom rearrangement in optical tweezer arrays and addresses the speed limitations imposed by the cylindrical lensing effect of acousto-optic deflectors (AODs). By combining a double-pass AOD configuration for dynamic focal tuning with a standard pair of crossed AODs for transverse beam steering, our design enables the generation of arbitrary focal point trajectories. This configuration enables shuttling of atoms in 3D space, thereby helping to realise fully connected two-qubit gates and mid-circuit measurements. We detail the optical implementation, characterize its performance, and discuss its applications in scalable quantum computing architectures.
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All authors Zhichao Guo, Rik A.H. van Herk, Edgar J.D. Vredenbregt, Servaas J.J.M.F. Kokkelmans

Optics · Cross-listed from eess.SP

Optical Link Tomography: First Field Trial and 4D Extension

Takeo Sasai, Giacomo Borraccini, Yue-Kai Huang et al. (+11 more)

Optical link tomography (OLT) is a rapidly evolving field that allows the multi-span, end-to-end visualization of optical power along fiber links in multiple dimensions from network endpoints, solely by processing signals received at coherent receivers. This paper has two objectives: (1) to report the first field trial of OLT, using a commercial transponder under standard DWDM transmission, and (2) to extend its capability to visualize across 4D (distance, time, frequency, and polarization), allowing for locating and measuring multiple QoT degradation causes, including time-varying power anomalies, spectral anomalies, and excessive polarization dependent loss. We also address a critical aspect of OLT, i.e., its need for high fiber launch power, by improving power profile signal-to-noise ratio through averaging across all available dimensions. Consequently, multiple loss anomalies in a field-deployed link are observed even at launch power lower than the system-optimal level. The applications and use cases of OLT from network commissioning to provisioning and operation for current and near-term network scenarios are also discussed.
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All authors Takeo Sasai, Giacomo Borraccini, Yue-Kai Huang, Hideki Nishizawa, Zehao Wang, Tingjun Chen, Yoshiaki Sone, Minami Takahashi, Tatsuya Matsumura, Masanori Nakamura, Etsushi Yamazaki, Koichi Takasugi, Ting Wang, Yoshiaki Kisaka

Accelerator Physics

A Living Review Pipeline for AI/ML Applications in Accelerator Physics

Adnan Ghribi

We present an open-source pipeline for generating a living review of artificial intelligence (AI) and machine learning (ML) applications in accelerator physics and technologies. Traditional review articles provide static snapshots that are quickly outdated by the rapid pace of research. The presented system automatically harvests publications from multiple bibliographic sources (arXiv, InspireHEP, HAL, OpenAlex, Crossref, and Springer), deduplicates entries, applies semantic filtering to ensure accelerator and ML relevance, and classifies papers into thematic categories. The resulting curated dataset was exported in JSON, HTML, PDF, and Bib\TeX formats, enabling continuous updates and integration with web frameworks. We describe the methodology, including semantic similarity filtering using sentence-transformer embeddings, threshold calibration, and expert-informed classification. The results demonstrate the robust filtering of $\sim$12000 raw papers/month into a focused corpus of $\sim$2% relevant works. The pipeline provides the basis for an evolving community-driven review of AI/ML in accelerator science.
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Biological Physics

Sub-Diffraction Chromatin Domains: Architecture, Regulation, and Functional Roles in Nuclear Organization

Vinayak Vinayak, Melike Lakadamyali and Vivek B Shenoy

Nanoscale chromatin domains, variously termed nucleosome clutches, nanodomains, or packing domains, have emerged as fundamental architectural units of the mammalian genome during interphase and mitosis. Unlike cohesin-dependent loops or TADs, these 50-200 nm structures persist in the absence of loop extrusion, pointing to a distinct organizing principle shaped by histone post-translational modifications and constrained by interactions with the nuclear lamina. Super-resolution microscopy and electron tomography now enable their direct visualization, revealing conserved features such as fractal packing, enrichment for linker histone H1, and radial stratification of active and repressive histone marks. Accumulating evidence indicates that these domains act as transcriptional hubs, dynamically remodel in response to developmental and environmental cues, and undergo pathological disruption in disease. Integrated experimental, theoretical, and computational insights suggest that chromatin-protein interactions, epigenetic read-write processes, and diffusion-driven dynamics together govern their formation, persistence, and nuclear positioning. Viewed in this light, nanoscale domains represent a privileged regulatory tier, complementary to compartments and loop-based structures, that bridges local chromatin states with global nuclear architecture. By situating them alongside lamin-associated (LADs) and nucleolus-associated domains (NADs), we propose a unified biophysical framework for chromatin organization across scales and outline key open questions for future exploration. Because their structural disruption is a recurring feature of aging, cancer, and degenerative diseases, understanding these domains may open new avenues for diagnostics and therapeutic intervention.
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Geophysics

Interactions between syn-rift magmatism and tectonic extension at intermediate rifted margins

Peng Yang, Marta Perez-Gussinye, Shaowen Liu et al. (+2 more)

Intermediate rifted margins exhibit neither seaward dipping reflectors nor exhumed mantle at the continent-ocean transition (COT). Instead, they transition into normal-thickness, magmatic Penrose-type oceanic crust, and thus diverge from the classic magma-rich and magma-poor end-member models. However, several intermediate margins, such as the South China Sea (SCS), display detachment faulting similar to magma-poor margins and magmatic underplating typical of magma-rich ones. How tectonics and magmatism interact in these intermediate environments is poorly understood. Here we use 2D numerical models to demonstrate that the elevated initial geotherm inherited from prior plate subduction in the SCS explains several key observations: an early phase of wide rifting, subsequent localization onto core complexes with substantial footwall magmatic intrusions, and eventual formation of normal igneous oceanic crust at break-up. Thermal weakening caused by syn-rift footwall magmatic intrusions facilitates lower crustal ductile flow, promoting the development of rolling-hinge type detachment faults and exhumation of core complexes. These structures are associated with accelerated tectonic subsidence, which is later moderated by detachment-related doming, as observed in the SCS. Normal-thickness oceanic crust occurs after break-up, even under ultra-slow extension rates used in our simulations, highlighting the importance of inheritance in determining margin architecture, the spatio-temporal distribution of syn-rift magmatism, and the nature of the COT. This behavior contrasts sharply with magma-poor margins, where a cooler lithosphere and similar ultra-slow extension produce no syn-rift magmatism, leading instead to crustal embrittlement, mantle serpentinization and exhumation at the COT.
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All authors Peng Yang, Marta Perez-Gussinye, Shaowen Liu, Javier Garcia-Pintado, Gudipati RaghuRam

Chemical Physics · Cross-listed from cond-mat.mtrl-sci

Magnetically Assisted Separation of Weakly Magnetic Metal Ions in Porous Media.Part 1: Experiments

Alwell Nwachukwu, Muhammad Garba, Jamel Ali et al. (+3 more)

We report experiments on the magnetophoresis of paramagnetic (MnCl2) and diamagnetic (ZnCl2) metal ions in porous media under the influence of a non-uniform magnetic field generated by a permanent magnet. Experiments were carried out in a range of initial ion concentrations (1-100 mM), porous media particle sizes (63 um and 500 um), and varying mixture ratios of metal ion concentrations. For single-ion magnetophoresis, paramagnetic MnCl2 migrated toward the magnet surface, with an enrichment of approximately 2-4 percent near regions of high magnetic field. Conversely, diamagnetic ZnCl2 moved away from regions of highest magnetic field gradients, with depletion levels of 0.5-1.8 percent relative to the initial concentration. Our results demonstrate that magnetophoresis is directly proportional to porous media particle size, increasing with larger particle sizes, a trend attributed to the reduced drag forces experienced by the ions in media with larger particles. Interestingly, in binary mixtures, both MnCl2 and ZnCl2 migrated toward regions of highest magnetic field, contrary to their individual behaviors. The magnetophoretic effect of MnCl2 was diminished with increasing concentrations of ZnCl2, indicating interactions between the two ions. These findings suggest that both metal ions undergo field-induced cluster formation, with cluster sizes in the micrometer range, in both single and binary ion systems. In binary mixtures, the two ions appear to interact, potentially forming mixed clusters containing both MnCl2 and ZnCl2.
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All authors Alwell Nwachukwu, Muhammad Garba, Jamel Ali, Theo Siegrist, Munir Humayun, Hadi Mohammadigoushki

Optics

Multiplexed back focal plane imaging with on-chip integrated microlens array

Magdalena Furman, Marcin Muszyński, Przemysław Oliwa et al. (+7 more)

On-chip optical architectures that enable angle-resolved spectroscopy are essential for advancing photonic platforms towards low-volume, scalable, and cryo-compatible devices. Here, we introduce spatially resolved momentum-space imaging using arrays of 3D-printed microlenses directly integrated onto semiconductor optical microcavities. Each microlens functions as an independent optical element with a high numerical aperture (approx. 0.95), enabling parallel back focal plane imaging across, in our implementation, 64 distinct locations. This approach eliminates the need for bulky microscope objectives while maintaining broad wavevector access, even under cryogenic conditions. We demonstrate its versatility across various cavity systems, including dielectric planar resonators, GaAs-based polariton microcavities, and CdTe platforms supporting nonequilibrium Bose-Einstein condensation of exciton-polaritons. The microlenses not only enhance collection efficiency but also enable tightly focused excitation, yielding an order of magnitude reduction in condensation thresholds compared with conventional setups. Our results establish 3D-printed microlens arrays as a compact, versatile, integrated platform for next-generation angle-resolved spectroscopy in nanophotonics and quantum materials.
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All authors Magdalena Furman, Marcin Muszyński, Przemysław Oliwa, Łukasz Zinkiewicz, Aleksander Bogucki, Jacek Szczytko, Piotr Wasylczyk, Wojciech Pacuski, Mateusz Król, Barbara Piętka

Physics and Society · Cross-listed from nlin.AO

Triadic percolation on multilayer networks

Hanlin Sun, Filippo Radicchi and Ginestra Bianconi

Triadic interactions are special types of higher-order interactions that occur when regulator nodes modulate the interactions between other two or more nodes. In presence of triadic interactions, a percolation process occurring on a single-layer network becomes a fully-fledged dynamical system, characterized by period-doubling and a route to chaos. Here, we generalize the model to multilayer networks and name it as the multilayer triadic percolation (MTP) model. We find a much richer dynamical behavior of the MTP model than its single-layer counterpart. MTP displays a Neimark-Sacker bifurcation, leading to oscillations of arbitrarily large period or pseudo-periodic oscillations. Moreover, MTP admits period-two oscillations without negative regulatory interactions, whereas single-layer systems only display discontinuous hybrid transitions. This comprehensive model offers new insights on the importance of regulatory interactions in real-world systems such as brain networks, climate, and ecological systems.
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Chemical Physics · Cross-listed from cond-mat.mtrl-sci

A Room-Temperature Ferrotoroidic Material Exhibiting Magnetic Semiconductor Properties with Superhigh Hole Mobility

Jianyuan Qi, Shijie Xiong, Beining Ma et al. (+1 more)

The design and fabrication of room-temperature ferrotoroidic materials and magnetic semiconductors are recognized worldwide as a great challenge, and of both theoretical and practical importance in the field of condensed matter physics and information storage. Reported herein are ferrotoroidic crystal powder and film formed by supramolecular self-assembly based on uranyl and cyclodextrin, with the Curie temperature above room temperature. Experimental measurements and calculations demonstrate spontaneous vortex-like alignment of magnetic moments and furthermore a macroscopic long-range arrangement in the crystal, which breaks simultaneously space-inversion and time-reversal symmetries, exhibiting strong superexchange, spin-orbit coupling as well as anomalous Hall effect (AHE). The electrical measurements show the film with a superhigh carrier mobility of 3200 cm2*V-1*s-1 and a Hall resistivity as high as 0.32 mV*A-1*cm at room temperature. This work is expected to pave greatly the applied research on new-generation magnetoresistive random access memory (MRAM), especially as flexible material.
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All authors Jianyuan Qi, Shijie Xiong, Beining Ma, Xinghai Shen

Chemical Physics

Control of chemical reactions in radiofrequency ion traps

Prerna Paliwal, Jutta Toscano and Stefan Willitsch

Over the past years, radiofrequency ion traps have become an attractive platform for studying chemical reactions as they enable a high degree of control over ion-molecule dynamics. In this review, we summarize techniques for the trapping and cooling of atomic and molecular ions in radiofrequency traps including Doppler and resolved-sideband laser cooling, sympathetic cooling, and cryogenic buffer-gas methods. We discuss strategies for controlling key reaction parameters: the preparation of specific internal quantum states by internal cooling, optical pumping, state-selective photoionization and quantum-logic spectroscopy; the manipulation of collision energies through micromotion control, dynamic trapping and combination with molecular beams; and the selection of molecular structure via isotopic substitution, conformational separation and isomer-specific ion generation. We illustrate applications of these approaches by discussing studies on quantum-state-dependent kinetics, quantum-resonance effects and structure-sensitive reactivity in ion-neutral collisions. We conclude by outlining future challenges, including full state-to-state reaction mapping, reaching the ultracold quantum regime free of micromotion, and the exploration of complex and chiral systems.
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Physics and Society

How liveable are London's 15-minute neighbourhoods? Exploring liveability profiles and active travel patterns in London

Philyoung Jeong, Ivann Schlosser, Alexei Poliakov et al. (+1 more)

Healthy and liveable neighbourhoods have increasingly been recognised as essential components of sustainable urban development. Yet, ambiguity surrounding their definition and constituent elements presents challenges in understanding and evaluating neighbourhood profiles, highlighting the need for a more detailed and systematic assessment. This research develops a composite Liveability Index for Greater London based on metrics related to the proximity, density, and diversity of POIs, along with population density, and investigates how neighbourhood liveability relates to active travel behaviour. The Index is based on the principles of the 15-minute city paradigm (Moreno et al. 2021) and developed in line with OECD guidelines for composite indicators (European Union and Joint Research Centre 2008). The Index revealed distinct spatial patterns of neighbourhood liveability, with high liveability neighbourhoods predominantly clustered in Inner London. Decomposing the Index provided further insights into the strengths and weaknesses of each neighbourhood. Footfall modelling using ordinary least squares (OLS) and geographically weighted regression (GWR) indicates a generally positive relationship between liveability and footfall, with spatial variation in the strength of this association. This research offers a new perspective on conceptualising and measuring liveability, demonstrating its role as an urban attractor that fosters social interaction and active engagement.
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All authors Philyoung Jeong, Ivann Schlosser, Alexei Poliakov, Elsa Arcaute

Optics

Spatio-Temporal Photonic Metalattice

Wallace Jaffray, Sven Stengel, Farhan Ali et al. (+9 more)

When coherent light interacts with an ordered lattice whose periodicity is comparable to its wavelength, constructive interference produces a diffraction pattern as in crystallography, where x-rays are employed to reveal atomic structures. By asking 'when' the diffractive object exist, rather than 'where', we implicitly introduce time as a design parameter, thus enabling the creation of spatio-temporal metalattices. In these structures, temporal modulation of optical properties complements the spatial patterning, unlocking advanced functionalities such as dynamic reconfigurability, nonreciprocal behavior, coherent amplification, and tailored spectral response. However, for these effects to be relevant an extreme temporal modulation of the refractive index is necessary. In this work, we realize a two-dimensional spatio-temporal metalattice by integrating a physically patterned spatial modulation with an orthogonal temporal lattice induced by interfering ultrafast pulses, using highly nonlinear, low-index transparent conducting films. While the optical pumps experience a uniform medium, the lattice emerges through a strongly enhanced and internally generated third harmonic signal. The transient lattice shows comparable diffraction efficiency to the physical structure and is also dynamically reconfigurable via a broad range of parameters, including pump pulse delay, incidence angle, and wavelength, offering exceptional versatility for ultra-fast transient lithography and photon manipulation in both momentum and frequency. This approach shifts device design from fixed fabrication constraints to radiation engineering, opening new pathways towards ultrafast reconfigurable photonics.
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All authors Wallace Jaffray, Sven Stengel, Farhan Ali, Mustafa Goksu Ozlu, Colton Bradley Fruhling, Maria Antonietta Vincenti, Domenico De Ceglia, Michael Scalora, Alexandra Boltasseva, Vladimir M. Shalaev, Andrea Di Falco, Marcello Ferrera

Optics

A quantum-coherent photon–emitter interface in the original telecom band

Marcus Albrechtsen, Severin Krüger, Juan Loredo et al. (+10 more)

Quantum dots stand out as the most advanced and versatile light-matter interface available today. Their ability to deliver high-quality, high-rate, and pure photons has set benchmarks that far surpass other emitters. Yet, a critical frontier has remained elusive: achieving these exceptional capabilities at telecom wavelengths, bridging the gap to fiber-optic infrastructure and scalable silicon photonics. Overcoming this challenge demands high quality quantum materials and devices which, despite extensive efforts, have not been realized yet. Here, we demonstrate waveguide-integrated quantum dots and realize a fully quantum-coherent photon-emitter interface operating in the original telecommunication band. The quality is assessed by recording transform-limited linewidths only 8 % broader than the inverse lifetime and bright 41.7 MHz emission rate under 80 MHz $\pi$-pulse excitation, unlocking the full potential of quantum dots for scalable quantum networks.
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All authors Marcus Albrechtsen, Severin Krüger, Juan Loredo, Lucio Stefan, Zhe Liu, Yu Meng, Lukas L. Niekamp, Bianca F. Seyschab, Nikolai Spitzer, Richard J. Warburton, Peter Lodahl, Arne Ludwig, Leonardo Midolo

Fluid Dynamics

Smart navigation of a gravity-driven glider with adjustable centre-of-mass

X. Jiang, J. Qiu, K. Gustavsson et al. (+2 more)

Artificial gliders are designed to disperse as they settle through a fluid, requiring precise navigation to reach target locations. We show that a compact glider settling in a viscous fluid can navigate by dynamically adjusting its centre-of-mass. Using fully resolved direct numerical simulations (DNS) and reinforcement learning, we find two optimal navigation strategies that allow the glider to reach its target location accurately. These strategies depend sensitively on how the glider interacts with the surrounding fluid. The nature of this interaction changes as the particle Reynolds number Re$_p$ changes. Our results explain how the optimal strategy depends on Re$_p$. At large Re$_p$, the glider learns to tumble rapidly by moving its centre-of-mass as its orientation changes. This generates a large horizontal inertial lift force, which allows the glider to travel far. At small Re$_p$, by contrast, high viscosity hinders tumbling. In this case, the glider learns to adjust its centre-of-mass so that it settles with a steady, inclined orientation that results in a horizontal viscous force. The horizontal range is much smaller than for large Re$_p$, because this viscous force is much smaller than the inertial lift force at large Re$_p$. *These authors contributed equally.
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All authors X. Jiang, J. Qiu, K. Gustavsson, B. Mehlig, L. Zhao

Accelerator Physics

Crab-waist interaction region design and integration for the Super Tau-Charm Facility

Linhao Zhang, Tao Liu, Ye Zou et al. (+10 more)

The Super Tau-Charm Facility (STCF) is a new-generation $e^+e^-$ collider proposed in China, designed to operate in the center-of-mass (CoM) energy range of 2-7 GeV. To achieve the design luminosity exceeding 5*10^34 cm^-2s^-1 at the optimal CoM energy of 4 GeV, a large crossing angle combined with the crab-waist correction scheme is adopted. However, this scheme introduces strong nonlinearities in the interaction region (IR) due to the extremely low vertical beta function of beta_y* <=1 mm, which significantly limits dynamic and momentum apertures of the collider ring. This paper presents a comprehensive modular optics design that addresses these challenges through several key features: 1) local chromaticity correction up to third order to enhance momentum bandwidth; 2) exact -I transformation between chromatic sextupole pairs for nonlinear cancellation; 3) minimization of the dispersion invariant along the IR to improve local momentum acceptance; 4) optimized beta functions at crab sextupole locations to reduce strength requirements and associated nonlinearities. Resonance driving terms analysis confirms effective suppression of geometric aberrations while preserving the intended crab-waist effects. When integrated into the collider ring, the design achieves a Touschek lifetime exceeding 300 s at beam energy of 2 GeV, meeting STCF requirements. The impact of fringe fields from superconducting quadrupoles is mitigated using octupole correctors, and detector solenoid effects are fully suppressed via local anti-solenoid compensation. Furthermore, the defined machine-detector interface layout ensures minimal synchrotron radiation background at the IP beryllium chamber, while ultra-high vacuum conditions are required to suppress beam-gas background. This IR design represents the current optimal solution for STCF and has been incorporated into the project's conceptual design report.
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All authors Linhao Zhang, Tao Liu, Ye Zou, Penghui Yang, Demin Zhou, Jiancong Bao, Ze Yu, Yuhan Jin, Yihao Mo, Sangya Li, Tianlong He, Qing Luo, Jingyu Tang

Optics

Alignment conditions of the human eye for few-photon vision experiments

T.H.A. van der Reep and W. Löffler

In experiments probing human vision at the few-photon level, precise alignment of the eye is necessary such that stimuli reach the most sensitive region of the retina. However, in literature there seems to be no consensus on the optimal eye alignment for such experiments. Typically, experiments are performed by presenting stimuli nasally or temporally, but the angle under which the few-photon pulses are presented varies between 7 deg and 23 deg. Here we combine a 3-dimensional eye model with retinal rod density measurements from literature in a ray tracing simulation to study the optimal eye alignment conditions and necessary alignment precision. We find that stimuli, directed at the eye's nodal point, may be best presented under an inferior angle of 12.6 deg with respect to the visual axis. Defining a target area on the retina with a radius of 0.5 mm around the optimum location, we find the horizontal and vertical angular precision should be better than 0.90 deg given a horizontal and vertical translational precision of $\pm$ 1 mm and a depth translational precision of $\pm$ 5 mm.
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Accelerator Physics

Implementation and Deployment of an Injection Tuning Tool Using Bayesian Optimization at the SuperKEKB Accelerator

Shinnosuke Kato and Gaku Mitsuka

As of July 2025, the SuperKEKB accelerator, which collides 7 GeV electrons with 4 GeV positrons to abundantly produce particles such as B mesons and tau leptons, holds the world record for the highest instantaneous luminosity. Continuous operation and upgrades are underway to achieve even higher luminosities. Maintaining a high instantaneous luminosity requires sustaining high beam currents in the storage rings, which in turn demands efficient beam injection from the injector. In particular, a high injection efficiency, defined as the ratio of the beam current successfully accumulated in the ring to the current delivered from the beam transport line, must be ensured. In the present study, we developed a tool to automate the injection tuning process using Bayesian optimization, a machine-learning-based technique, in order to improve the injection efficiency. During test operations conducted in November-December 2024, this tool successfully enhanced the injection efficiency by up to 32%.
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Optics · Cross-listed from cond-mat.mes-hall

Chern insulators and topological flat bands in cavity-embedded kagome systems

Hikaru Goto, Ryo Okugawa and Takami Tohyama

We investigate topological band structures of a kagome system coupled to a circularly polarized cavity mode, using a model based on a muffin-tin potential and quantum light-matter interaction. We show that Chern insulating phases emerge in the cavity-embedded kagome system due to the light-matter interaction that breaks time-reversal symmetry. We also find that a nearly flat band can be topologically nontrivial with a nonzero Chern number. By varying the light-matter interaction, we also reveal that topological phase transitions occur between different Chern insulating phases in the ultrastrong coupling regime. The phase transitions change the sign of the Chern number, switching the direction of the edge current. We demonstrate the existence of topological edge modes in the cavity-embedded kagome Chern insulators by constructing a low-energy effective tight-binding model.
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Plasma Physics

Statistics of Current and Vorticity Structures in Relativistic Turbulence

Zachary Davis, Luca Comisso, Colby Haggerty et al. (+1 more)

Coherent structures created through turbulent cascades play a key role in energy dissipation and particle acceleration. In this work, we investigate both current and vorticity sheets in 3D particle-in-cell simulations of decaying relativistic turbulence in pair plasma by training a self-organizing map to recognize these structures. We subsequently carry out an extensive statistical analysis to reveal their geometric and structural properties. This analysis is systematically applied across a range of magnetizations ($\sigma$) and fluctuating-to-mean magnetic field strengths ($\delta B_0/B_0$) to assess how these parameters influence the resulting structures. We find that the structures' geometric properties form power-law distributions in their probability density functions (PDFs), with the exception of the structure width, which generally exhibits an exponential distribution peaking around 2 electron skin depths. The measurements show weak dependence on $\sigma$ but a strong dependence on $\delta B_0/B_0$. Finally, we investigate the spatial relationship between current sheets and vorticity sheets. We find that most current sheets are directly associated with at least one vorticity sheet neighbor and are often situated between two vorticity sheets. These findings provide a detailed statistical framework for understanding the formation and organization of coherent structures in relativistic magnetized turbulence, allowing for their incorporation into updated theoretical models for structure-based energy dissipation and particle acceleration processes crucial for interpreting high-energy astrophysical observations.
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All authors Zachary Davis, Luca Comisso, Colby Haggerty, Joonas Nättilä

Physics and Society · Cross-listed from math.AP

Energy distance and evolution problems: a promising tool for kinetic equations

Gennaro Auricchio and Giuseppe Toscani

We study the rate of convergence to equilibrium of the solutions to Fokker-Planck type equations with linear drift by means of Cramér and Energy distances, which have been recently widely used in problems related to AI, in particular for tasks related to machine learning. In all cases in which the Fokker-Planck type equations can be treated through these distances, it is shown that the rate of decay is improved with respect to known results which are based on the decay of relative entropy.
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Accelerator Physics

Simultaneous Multi-Scale Homogeneous H-Phi Thin-Shell Model for Efficient Simulations of Stacked HTS Coils

Louis Denis, Benoît Vanderheyden and Christophe Geuzaine

The simulation of large-scale high-temperature superconducting (HTS) magnets is a computational challenge due to the multiple spatial scales involved, from the magnet to the detailed turn-to-turn geometry. To reduce the computational cost associated with finite-element (FE) simulations of insulated HTS coils, the simultaneous multi-scale homogeneous (SMSH) method can be considered. It combines a macroscopic-scale homogenized magnet model with multiple single-tape models and solves both scales monolithically. In this work, the SMSH method is reformulated using the $h$-$\phi$ thin-shell (TS) approximation, where analyzed tapes are collapsed into thin surfaces, simplifying mesh generation. Moreover, the magnetic field is expressed as the gradient of the magnetic scalar potential outside the analyzed tapes. The discretized field is then described with nodal functions, further reducing the size of the FE problem compared to standard $h$ formulations. The proposed $h$-$\phi$ SMSH-TS method is verified against state-of-the-art homogenization methods on a 2-D benchmark problem of stacks of HTS tapes. The results show good agreement in terms of AC losses, turn voltage and local current density, with a significant reduction in simulation time compared to reference models. All models are open-source.
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