Atmospheric and Oceanic Physics
Precipitation diffusion downscaling and application to out-of-distribution simulations with and without stratospheric aerosol injection
Cameron Dong, James W. Hurrell and Elizabeth A. Barnes
Stratospheric aerosol injection (SAI), a possible
climate engineering strategy where reflective particles are injected into the stratosphere, has been explored to mitigate global warming and its associated risks, such as the intensification of extreme precipitation events. However, current Earth system models (ESMs) often used to simulate SAI and other
climate change scenarios are too coarse to properly assess such risks. Traditional statistical downscaling methods, used to project higher resolution impacts, may be biased and unrealistic. To address this, we train a deep learning
diffusion downscaler to generate 0.25{\deg} contiguous United States (CONUS) daily precipitation using historical and future
climate simulations from the Mesoscale Atmosphere-Ocean Interaction in Seasonal-to-Decadal
Climate Prediction (MESACLIP) project, then apply the
diffusion downscaler to out-of-distribution CESM2 simulations with and without SAI. The
diffusion model generates realistic downscaled precipitation using either MESACLIP or CESM2 inputs. It also faithfully recreates the
climate change projections of extreme precipitation in MESACLIP.
Diffusion-downscaled projections of the future CESM2 SAI scenarios suggest that SAI could nearly cut in half the CONUS-average increase in yearly max precipitation, compared to the non-SAI scenario. However, there is considerable regional variation and internal variability, with SAI modeled to only slightly reduce increases in extreme precipitation frequency in the Mid Atlantic and the Pacific Northwest, but mitigating most intensification in other regions. Future application of
diffusion downscaling to a wider variety of SAI scenarios would provide valuable insight into how proposed SAI strategies may affect precipitation variability on fine spatial scales for regional impact assessments.
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Space Physics · Cross-listed from eess.SY
Reachability for Low-Thrust Trajectories via Maximum Initial Mass
Giacomo Acciarini, Dario Izzo and Zhong Zhang
Reachability analysis plays a central role in low-thrust spacecraft trajectory optimization by identifying which target states can be achieved under constraints on time, thrust, and propellant. Classical approaches construct reachable sets by solving many optimal control problems over grids of terminal states, requiring extensive forward simulations with fixed initial conditions. While effective, this approach is computationally expensive and becomes impractical for high-dimensional systems or strongly nonlinear dynamics, such as those encountered in cislunar environments or
solar sail missions. This work introduces a dual formulation of the reachability problem. Instead of computing reachable sets directly, we determine, for fixed transfer time and boundary conditions, the maximum allowable initial mass (or, for
solar sails, a scalar sail-strength parameter) that permits a successful transfer. A target is reachable if the spacecraft's initial mass does not exceed this threshold. This reformulation reduces reachability assessment to a scalar optimization problem for each target, producing a smooth scalar field that encodes equivalent feasibility information to classical reachable sets. We develop indirect maximum-initial-mass (MIM) formulations for both electric low-thrust and
solar-sail dynamics and show how they can serve as efficient reachability oracles. Building on this formulation, we construct data-driven surrogate models to approximate the MIM-based reachability indicator. We investigate fully connected neural networks and demonstrate that residual networks provide the best trade-off between accuracy, training stability, and model complexity. The resulting surrogates enable rapid reachability evaluation while preserving the numerical advantages of the dual formulation, offering a practical tool for preliminary mission design and feasibility assessment.
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Physics and Society
Unravelling Nature's Models for Transportation Network: Considering a Biomimicry Framework
Sofiane Madmar, Didier Josselin, Olivier Blight et al. (+3 more)
Researchers worldwide have drawn inspiration from nature to optimize network design and dynamics. Some of the wonders of the living world exhibit remarkable abilities in generating efficient and resilient spatial structures. By mimicking biological strategies, transportation infrastructures could be profoundly rethought. This paper aims to provide the basis for a biomimicry framework for addressing transportation networks. In light of examples from the literature, the relevance of such a framework for advancing research in nature-inspired networks is demonstrated, with the aim of achieving resilience and efficiency.
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All authors Sofiane Madmar, Didier Josselin, Olivier Blight, Vincent Labatut, Christophe Mazzia, Marc Ciligot-Travain
Chemical Physics
Nonlinear order separation in two-dimensional electronic spectroscopy quantifies properties of higher-excited states
Katja Mayershofer, Peter A. Rose, Julian Lüttig et al. (+4 more)
Two-dimensional (2D) spectroscopy combines high temporal and spectral resolution, allowing the observation of ultrafast energy transfer and the separation of homogeneous and inhomogeneous broadening. Typically, 2D spectroscopy is dominated by the lowest-order nonlinear signal for a given phase-matching configuration while signals of higher order are present but difficult to access separately. Recently, we introduced a technique to separate nonlinear orders in 2D spectroscopy by systematically varying the intensity of the pump pulses and appropriate post-processing. Here, we unravel the full potential of higher-order 2D spectroscopy by separating multiple nonlinear orders at different multi-
quantum positions. As an example, we investigate a squaraine dimer. Using a theoretical model, we find excellent qualitative and quantitative agreement throughout all nonlinear orders and multi-
quantum positions. Our simulations demonstrate the sensitivity and information content hidden in the higher-order spectra such as transition dipole moments and energy levels even of highly excited states. Our results pave the way for establishing higher-order spectroscopy as a unique extension of multidimensional spectroscopy, providing access to highly excited states and their properties encoded in successive orders of nonlinearity.
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All authors Katja Mayershofer, Peter A. Rose, Julian Lüttig, Luisa Brenneis, Simon Büttner, Jacob J. Krich, Tobias Brixner
Optics
Development of EAP-based actuators for high-frequency adaptive optics system
A. Michel, D. Audigier, C. Richard et al. (+1 more)
The present work aims to enhance the electrostrictive strain of the P(VDF-TrFE-CFE) terpolymer for use in adaptive optics, specifically in deformable mirror actuation. In the context of the FlexSiMirror project, these systems seek to operate under alternating electric fields of up to 50 V/um and within the kilohertz (kHz) frequency range, thereby framing the ranges of characterization considered in this study. To achieve greater strains, the incorporation of a polymeric plasticizer up to 20 vol.% and its impact on the actuation strain performance was studied. Hence, the relevance of this approach lies both in the kHz characterization of the mechanical and dielectric properties of the materials and in the utilization of a polymeric plasticizer, instead of the commonly used phthalates suitable for lower frequency ranges. In the kHz range, polymeric plasticizer addition markedly reduces the elastic modulus while limiting molecular migration, leading to more than a threefold increase of the figure of merit associated with strain (FOMstrain) and yielding 1.50% strain output under 50 V/um, 3.6 times greater than that of the unmodified terpolymer. Therefore, these findings show that modified P(VDF-TrFE-CFE) exhibits enhanced electromechanical performance in the kHz range. This advancement opens new possibilities for developing next-generation actuators intended for adaptive optics applications.
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All authors A. Michel, D. Audigier, C. Richard, J.-F. Capsal
Space Physics
Conceptualizing and Defining the Circular Space Economy
Jonas Bahlmann, Michael Saidani, Enrico Stoll et al. (+1 more)
Space faces significant sustainability issues including orbital congestion and debris accumulation. The continued growth of space operations, accelerated by advancements such as reusable launch systems, further intensifies these pressures. Current mitigation strategies, such as deorbiting spacecraft or transferring them to graveyard orbits, remain inherently linear. This "take-make-waste" approach is environmentally unsustainable and economically inefficient. On Earth, similar challenges have driven the development of the circular economy (CE), which aims to eliminate waste and pollution, circulate resources at their highest value, and decouple economic growth from finite resource consumption. While these objectives have been extensively studied across terrestrial sectors, their application to the space domain remains largely unexplored. In particular, the concept of a circular space economy (CSE) remains constrained by narratives centered on reuse, recycling, and in-orbit servicing, lacking a structured definition, consistent terminology, and a clearly defined, comprehensive scope. This lack complicates the systematic integration of circularity into mission design, policy frameworks, and space system architectures. After a detailed analysis of established CE definitions and CSE definition proposals, this work conceptualizes the CSE and introduces a structured definition for the first time. It analyzes Earth-space distinctions, clarifies the relationship between space sustainability and the CSE, establishes the 10R Space Framework to narrow, slow, and close resource loops, and distinguishes three operational environments: (I) the CE in space, (II) the CE of the terrestrial (space) sector, and (III) the CE of celestial bodies beyond Earth. Ultimately, this work enables a shared understanding and aims to strengthen the concept's recognition in the space sustainability debate.
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All authors Jonas Bahlmann, Michael Saidani, Enrico Stoll, Andreas M. Hein
Optics
Enhanced magneto-optical intensity effect in a helicity-preserving all-dielectric metasurface at Mie resonances and the anapole state
P. V. Zorina, D. O. Ignatyeva, A. E. Bezmenova et al. (+4 more)
Nanophotonic structures provide an efficient route to enhancing magneto-optical effects by concentrating electromagnetic fields at subwavelength scales. In this work, we propose and experimentally demonstrate a helicity-preserving all-dielectric metasurface for enhancing magnetization-induced transmission modulation under circularly polarized excitation. The optical response of the structure is governed by the Mie resonances of silicon nanodisks and by a spectral feature associated with the anapole state. In the spectral regions of the Mie resonances, the metasurface exhibits a pronounced enhancement of the magneto-optical intensity response relative to a bare
magnetic film of the same thickness, with the normalized magneto-optical intensity effect increased by a factor of about 2-3. A strong response is also observed in the spectral region associated with the anapole state, manifested as a local transmission maximum. In this regime, the normalized magneto-optical intensity effect exceeds that of the bare
magnetic film by about 30%, while the metasurface transmission remains as high as around 80%. The enhanced response in this spectral region is preserved over a broad range of incidence angles. These results demonstrate that all-dielectric metasurfaces combining Mie resonances with the spectral feature associated with the anapole state provide an efficient platform for magneto-optical intensity modulation of circularly polarized light at high transmission.
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All authors P. V. Zorina, D. O. Ignatyeva, A. E. Bezmenova, A. N. Kalish, S. Xia, L. Bi, V. I. Belotelov
Optics
Real time monitoring of pressure-induced deformation of PDMS to evaluate pressure distribution in microfluidic channels
Kiran Acharya, Serge Monneret, Martin Brandenbourger et al. (+1 more)
Accurate pressure measurements in micrometric channels are essential for a wide range of microfluidic applications. Existing approaches rely on a variety of sensing mechanisms, but generally require the integration of additional probes or sensing elements during or after chip fabrication. Here, we introduce a pressure sensing approach based on quantitative phase imaging of the deformation of compliant microfluidic channels. We demonstrate real-time measurements of channel deformation over a large field of view with high sensitivity, without the need for embedded components or modifications of the microfluidic device.
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All authors Kiran Acharya, Serge Monneret, Martin Brandenbourger, Thomas Chaigne
Physics Education
Democratising Optical Orbital Angular Momentum: a Set of Cost-Effective Tools
Natasha Bierrum, Lyuxuan Chen, Ananya Kudaloor et al. (+9 more)
Classical and
quantum optical communication has gained popularity and momentum in recent years, with growing investment and innovation in
quantum technologies. However, the main teaching method in the education of
quantum mechanics include mathematically intensive derivations or abstract analogies for the complex systems. We propose a "poor man's" spatial light modulator experiment that is an engaging and interactive learning aid for teaching
quantum mechanics and optical orbital angular momentum. Fork diffraction gratings were created on photographic slide film by outsourcing to an external company, and so the gratings were easy and cheap to produce. A simple setup with a fork diffraction grating and a
laser pointer successfully produces
vortex beams that possess orbital angular momentum, allowing for orbital angular momentum to be easily observed and investigated in a teaching environment. How the tools can be used effectively to enhance learning is discussed, either as a demonstration or as an investigative scientific learning environment activity.
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All authors Natasha Bierrum, Lyuxuan Chen, Ananya Kudaloor, Lok Kan Wan, Shupeng Yang, Yancen Hou, Xiwen Dong, Muskan Tuli, Richard Taylor, Petros Androvitsaneas, Carrie Weidner, Edmund Harbord
Instrumentation and Detectors
Application of LHC Gas Recuperation Systems for Methane Emission Control in Livestock Housing
Ilaria Vai, Francesco Alessandro Angiulli, Chiara Aimè et al. (+26 more)
The CH4rLiE (CH4 Livestock Emission) project investigates the technical feasibility of adapting gas recovery systems from high-energy physics to mitigate methane (CH4) emissions in livestock housing. This work presents a proof-of-principle based on the adaptation of CERN's gas recuperation systems for the capture of CH4 at low concentrations. A laboratory-scale prototype was developed to evaluate the performance of various adsorbent materials under realistic conditions, including multi-stage humidity removal and pressurized gas flows. Experimental results obtained with the prototype led to the selection of commercial Z5 zeolite as the primary adsorbent due to its high adsorption capacity and stable regeneration performance through
Vacuum Swing Adsorption cycles. The study demonstrates the feasibility of CH4 capture at concentrations down to 0.1%. Furthermore, it was observed that increasing the CH4 partial pressure enhances the adsorption capacity, with tests conducted up to approximately 5 bar. To bridge the gap between laboratory conditions and the representative 10-100 ppm levels found in dairy barn environments, a negative exponential extrapolation was applied to the experimental data. This allowed for the modeling of the adsorption behavior in the ultra-low concentration regime. These results validate the operational principle and provide the necessary parameters for the design of a full-scale system for field installation.
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All authors Ilaria Vai, Francesco Alessandro Angiulli, Chiara Aimè, Maria Cristina Arena, Davide Biagini, Amin Bouzaiene, Alessandro Braghieri, Matteo Brunoldi, Domenico Calabrò, Simone Calzaferri, Alessandro Caserio, Elio Dinuccio, Daniele Dondi, Linda Finco, Giulia Giannandrea, Samuel Guelfo Gigli, Gabriele Giunta, Roberto Guida, Nithish Kumar Kameswaran, Beatrice Mandelli, Paolo Montagna, Cristina Riccardi, Paola Salvini, Claudio Scagliotti, Alessandro Tamigio, Dhanalakshmi Vadivel, Filippo Vercellati, Riccardo Verna, Paolo Vitulo
Optics
Adjoint inverse design of microresonator frequency combs
Andrei Chuchalin and Alexey Tikan
Microresonator frequency combs are key components for integrating optical devices into photonic
circuits. They provide high stability, coherence, and low noise, even without external stabilization. Yet microcomb design remains largely heuristic: waveguide and resonator parameters are typically swept manually or semi-empirically, and the resulting spectra are evaluated only afterwards. This forward-design workflow is computationally costly, relies heavily on designer intuition, and does not generally identify optimal solutions. Here, we present an adjoint-based inverse-design framework for microresonator frequency combs that directly optimizes the comb spectrum with respect to pre-defined objectives. We demonstrate the power and flexibility of this approach by addressing three challenging problems: designing spectrally flat combs, synthesizing arbitrarily shaped comb spectra, and enforcing several performance metrics simultaneously through multi-objective optimization. Our results show that inverse design offers a systematic and efficient route to compact on-chip light sources with properties tailored to diverse applications.
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Biological Physics
Geometric Origin of Exact Mean-Field Reductions: Möbius Symmetry and the Lorentzian Ansatz
Hugues Berry and Leonardo Trujillo
Low-dimensional descriptions of large systems of coupled oscillators and spiking
neurons rely heavily on the Lorentzian Ansatz. We show that its privileged role is
geometric rather than heuristic: for the transport induced by Riccati dynamics, the Cauchy-Lorentz family indeed emerges as the unique connected two-dimensional family of continuous probability densities that is invariant under the induced projective transport. The key step of the demonstration is to reformulate the dynamics on the circle, where the problem reduces to the uniqueness of the rotation-invariant probability measure. Under stereographic projection, this yields the standard Cauchy law and, under the full projective action, the Lorentzian family. This result gives a unified
geometric foundation for the Ott-Antonsen [Chaos 18, 037113 (2008)] and Montbrió-Pazó-Roxin [Phys. Rev. X 5, 021028 (2015)] reductions, explains the failure of Gaussian closures, and identifies the structural condition underlying exact two-parameter reductions.
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Physics Education
Using Large Language Models in Physics Education
Jonah L. Donaldson, Aliya Nawaz, Konstantinos Doran et al. (+2 more)
The rapid advancement of Large
Language Models (LLMs) has introduced new possibilities and challenges in physics education, necessitating rigorous evaluation of their capabilities as both problem solvers and automated assessors. This paper presents the results of three complementary studies that evaluated frontier models released between mid-2024 and late-2025. Models were assessed on their ability to generate accurate, step-by-step solutions to university-level physics problems in Classical Mechanics, Electromagnetism, and
Quantum Mechanics, and subsequently on their reliability in grading student solutions against a formal mark scheme. The results indicate a clear trajectory toward
benchmark saturation in text-based
reasoning, with recent architectures (such as ChatGPT-5.1 and Gemini 3.0 Pro) achieving near-perfect scores. Furthermore, recent advances in native
multimodal integration have resolved previous limitations in spatial geometry and topological interpretation, enabling models to accurately process accompanying diagrams. As automated assessors, newer models demonstrated significant improvements in
alignment with human grading, heavily mitigating the systemic over-marking observed in earlier iterations. However, while models reliably evaluate fully correct handwritten work, assigning partial credit to flawed or incomplete
reasoning remains a persistent challenge. These findings suggest that as of late 2025, LLMs offer viable support for both independent student learning and instructional automation, provided their limitations in evaluating ambiguous
reasoning are actively managed.
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All authors Jonah L. Donaldson, Aliya Nawaz, Konstantinos Doran, Alysta Lim, Mario Campanelli
Applied Physics · Cross-listed from cond-mat.mes-hall
Graphene-based Photodetector with Engineered Hot Carrier Cooling Dynamics
Yishu Huang, Anand Nivedan, Florian Ludwig et al. (+9 more)
Graphene has emerged as a promising material for integration into silicon photonics, owing to its ultrafast and broadband photoresponse without the need for an external bias voltage. This photoresponse relies on the photo-thermoelectric effect created by hot carriers. A key factor underlying the performance of
graphene photodetectors is the cooling dynamics of these hot carriers. In this work, we engineer these dynamics in a WSe2-
graphene-WSe2 waveguide-integrated photodetector. In particular, by introducing proximity screening by a nearby graphite layer to this structure, we prolong the hot-carrier cooling time, leading to an enhanced photoresponse. We characterize the cooling dynamics under continuous-wave
laser excitation by employing a photomixing technique, revealing an increase in the cooling time by up to a factor of four. Direct photoresponse measurements show that the internal photoresponsivity improves by approximately 50%. Together, these results demonstrate the potential of proximity screening to enhance the performance of
graphene-based photodetectors on an integrated photonics platform.
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All authors Yishu Huang, Anand Nivedan, Florian Ludwig, Bohai Liu, Michiel Debaets, Steven Brems, Hai I. Wang, Alessandro Principi, Dries Van Thourhout, Christian Haffner, Aron W. Cummings, Klaas-Jan Tielrooij
Optics
C-band 160 Gbs-1 Zero-bias Graphene Photodetectors: Breaking the Responsivity-Bandwidth Trade-off by Heterostructure Engineering
Karuppasamy Pandian Soundarapandian, Alberto Montanaro, Ioannis Vangelidis et al. (+17 more)
Graphene photodetectors offer ultrafast response and broadband operation, but their responsivity is typically limited by rapid hot-carrier cooling, leading to a trade-off between sensitivity and speed. Here, we demonstrate that modifying the dielectric environment provides an effective route to control hot-carrier cooling and enhance device performance. By employing a WSe2 encapsulation architecture, we suppress out-of-plane energy dissipation, leading to an increased cooling length (~2.68 um) and a reduced heat-exchange coefficient. As a result, we obtain zero-bias
graphene photodetectors with responsivities up to ~0.12 A/W (potentially ~0.4 A/W) while maintaining ultrafast operation beyond the setup-limited 110 GHz bandwidth. The devices enable direct detection at data rates of 120 Gb s-1 (NRZ) and 160 Gb s-1 (PAM-4), with performance achieved using minimal digital signal processing. These results establish dielectric engineering as a key design axis for controlling hot-carrier dynamics, enabling energy-efficient, high-speed optical receivers for next-generation interconnects and AI-driven data systems.
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All authors Karuppasamy Pandian Soundarapandian, Alberto Montanaro, Ioannis Vangelidis, Stefan M. Koepfli, Lorenzo Orsini, Matteo Ceccanti, Laurenz Kulmer, Misal Misal, Tom Reep, Sebastián Castilla, Kenji Watanabe, Takashi Taniguchi, Seth Ariel Tongay, Dries Van Thourhout, Juerg Leuthold, Klaas-Jan Tielrooij, Elefterios Lidorikis, Marco Romagnoli, Vito Sorianello, Frank H. L. Koppens
Optics · Cross-listed from quant-ph
Atom-Photon Bound States in Fractal Photonic Lattices: Localization Length and Anomalous Diffusion
Florian Bönsel, Flore K. Kunst and Federico Roccati
We study atom-
photon bound states seeded by two-level emitters coupled to self-similar photonic
lattices. By expressing the photonic Green's function through the heat kernel, we show that the far-field localization length obeys $\xi \sim \Delta^{-1/d_w}$, with the detuning $\Delta$ from the lower spectral edge and the walk dimension $d_w$ of the underlying fractal. This scaling is controlled by anomalous
diffusion and does not rely on translational invariance or a band-edge effective-mass approximation. Exact diagonalization on Sierpiński gaskets, pyramids, Vicsek graphs, and Sierpiński carpets confirms the far-field prediction once the bath
Hamiltonian is rendered
Laplacian-like by compensating the local inhomogeneity in the connectivities with on-site potentials. In the near field, the bound-state amplitude exhibits an additional algebraic variation. For nested finitely ramified fractals, the corresponding exponent agrees with the classical resistance/ first-passage scaling, whereas Sierpiński carpets display clear deviations from this simple law. Our results extend structured-bath waveguide QED to self-similar non-periodic geometries and connect bound-state profiles to transport exponents of the underlying fractal
lattice.
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Instrumentation and Detectors
Conceptual Design of PID Detectors for the EicC Spectrometer
Xin Li, Yuxiang Zhao, Yutie Liang et al. (+1 more)
The Electron-ion
collider in China (EicC) is a proposed future electron-ion
collider designed to achieve a high luminosity, with a center-of-mass energy ranging from 15 to 20 GeV. Excellent particle identification (PID) with extensive momentum coverage is essential for investigating exclusive and semi-inclusive processes, as well as enabling precise 3D imaging of the nucleon structure in the EicC experiment. To meet its PID requirement, the EicC Collaboration has proposed the conceptual design of various Cherenkov detectors, including the DIRC in the barrel region and the RICH in the endcap region. It also involving the TOF detector for PID in the low momentum region. The GEANT4 simulation, which integrate advanced optical transmission models and image reconstruction
algorithms, have been conducted to study and optimize the performance of these detectors.
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All authors Xin Li, Yuxiang Zhao, Yutie Liang, Xu Sun
Fluid Dynamics
From Optical Breakdown to Bubble Inception: A Coupled Plasma-Thermal Framework for Nanosecond Laser-Induced Cavitation in Water
Shuqi Zhou, Abdol Hadi Mokarizadeh and Ben Xu
Laser-induced cavitation under nanosecond optical breakdown is central to applications such as
laser-induced forward transfer (LIFT), microsurgery, and microfluidic actuation, yet the physical origin of the earliest cavity and its connection to subsequent bubble growth remain unresolved. Existing models typically describe bubble formation either as a
plasma-driven mechanical response or as a thermally driven nucleation process, without resolving how these mechanisms interact during inception. In this study, we developed a coupled
plasma-thermal framework that unifies free-electron dynamics,
plasma absorption, thermoelastic acoustic response, residual thermal energy retention, and post-inception bubble
evolution within a single description. The model shows that bubble inception is governed primarily by
plasma-induced thermoelastic acoustic relaxation, which generates transient tensile rarefaction pressures sufficient for cavitation on nanosecond timescales, while residual thermal energy sustains subsequent bubble growth. Because
plasma-mediated energy deposition is spatially anisotropic under moving breakdown conditions, the initial cavity is predicted to form as an elongated, asymmetric bubble rather than as a spherical
nucleus. This initial bubble shape reflects the spatial structure of the
plasma absorption region and provides the starting geometry for subsequent bubble dynamics. Comparison with time-resolved experiments demonstrates that the coupled framework captures both early-time cavity formation and long-time bubble expansion more accurately than
plasma-only or thermal-only models. These results show how breakdown-induced asymmetry controls the birth shape of the cavitation bubble and its early fluid-mechanical
evolution, providing a physics-based basis for modeling
laser-driven
liquid motion and material transport.
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Optics
Zhen Yang, Zeng-Quan Yan, Li Wang et al. (+3 more)
The extraction of information carried by light plays an increasingly important role in optical communication, imaging, and detection. However, the information can only be successfully extracted when the light pulse is comparably strong, leaving untouched scenarios where survived
photons are extremely sparse. Here, we propose and experimentally demonstrate a single-
photon Fourier transform scheme. By retrieving the implicit correlation shared in the sparse singlephoton stream globally, we are able to precisely classify each
photon and synchronously extract multiple ultra-weak signals with high fidelity against extreme environments. Our experiment results give a full picture of the scheme in terms of multi-terminal expandability, wide frequency adaptability, 125 dB loss tolerance, and -10.4 dB signal-to-noise ratio robustness. Even when the pulse repetition frequencies of all terminals are the same, we can still recognize the free-running clock drift and separate different messages. Our work can be a general scheme to extend the capability boundary for all the extremely low-light-flux scenarios, and makes many challenging tasks possible, such as in-orbit optical communication network with complex
topology,
navigation in extremely lossy and noisy environments, and wide-range single-
photon imaging with multi-source illumination.
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All authors Zhen Yang, Zeng-Quan Yan, Li Wang, Xiao-Wei Wang, Ka-Di Zhu, Xian-Min Jin
Plasma Physics
A quasi-neutral electromagnetic hybrid model with drift-kinetic electrons and fully kinetic ions
Guo Meng, Nishant Narechania and Eric Sonnendrücker
In this work, we propose a hybrid model that combines drift-kinetic electrons with fully kinetic ions under the quasi-neutrality assumption, discretized using a
geometric particle-in-
cell framework on dual-grids. The model advances the perturbed electromagnetic fields $E$ and $B$ directly, rather than the scalar and vector potentials. The parallel electric field $E_\parallel$ is obtained from Ohm's law. The perpendicular electric field $E_\perp$ is computed from Ampère's law by extracting the $E_\perp$-dependent component of the drift-kinetic electron current. The quasi-neutrality constraint eliminates high-frequency light waves and Langmuir waves from the system. Temporal discretization is performed using low-storage Runge–Kutta schemes. In this quasi-neutral hybrid model, the right-hand polarized wave branch exhibits a whistler-like dispersion relation, which imposes a stringent timestep constraint. To address this, we develop a novel implicit-explicit splitting scheme for Faraday's law that significantly relaxes the timestep stability restriction. The model is validated in slab geometry by reproducing cold
plasma wave branches, ion Bernstein waves, compressional and shear Alfvén waves, and ion acoustic waves.
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Instrumentation and Detectors
Studies on photon-feedback and LaB$_6$ photocathode for the GasPM development
Simone Garnero, Kenji Inami, Kodai Matsuoka et al. (+2 more)
We present new developments, based on beam tests and
cosmic rays, on the gaseous photomultiplier (GasPM). The GasPM detects
photons by combining a photocathode with a resistive-plate-chamber avalanche. It achieves $\mathcal{O}$(10) ps time resolution with affordable scalability. The GasPM provides precise and efficient Cherenkov-based charged-particle identification too when combined with a radiator. Our target application in a future Belle II upgrade aims at suppressing beam-induced background
photons, which are typically detected off-collision time, that spoil the electromagnetic calorimeter performance. We reached 25 ps single-
photon time-resolution at 3.3x10$^6$ gain in 2022, using a picosecond-pulse
laser and a LaB$_6$ photocathode. However, electrons entering through a MgF$_2$ window upstream of a CsI photocathode showed a worsening to 70 ps in a 2023 test. Here we aim at addressing the chief causes of the observed degradation. We focus on ultraviolet-
photon emission from the de-excitation of the gas molecules, which generates a secondary "
photon-feedback" signal overlapping the primary one, and degrading time resolution. We conceive and operate an improved beam test that, along with multiple device-configuration changes, employes a new 10 GSPS frequency digitizer to separate the
photon-feedback signal from the genuine signal. We also use
cosmic-rays on a LaB$_6$ photocathode, which has higher than CsI's resistance to air and to ions drifting backwards onto the photocathode, to explore its
quantum efficiency.
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All authors Simone Garnero, Kenji Inami, Kodai Matsuoka, Ryogo Okubo, Koichi Ueda
Optics
Programmable high-harmonic emission in solids through photon pathways
Pieter J. van Essen, Aday Cárdenas, Rui E.F. Silva et al. (+2 more)
Ultrafast all-optical control of light emission is a central goal of extreme nonlinear optics, with implications for compact short-wavelength sources, petahertz optoelectronics, and label-free superresolution microscopy. High-harmonic generation in solids is a particularly attractive platform for this goal because it is highly sensitive to both the driving field and the material response, yet a generally applicable framework for controlling harmonic emission has remained elusive. Here, we demonstrate programmable control of high-harmonic emission in solids and show that it can be quantitatively described within a
photon-pathway framework. We find that harmonic emission can be suppressed or enhanced by tuning two experimentally accessible quantities: the effective nonlinear order and the intrinsic emission phase. Across a wide range of
semiconductors and dielectrics, this approach unifies parametric and non-parametric modulation, explains distinct delay-dependent spectral responses, and reproduces strong suppression, enhancement, and higher-order pathway revivals.
Semiconductor Bloch equation simulations support the model and provide a complementary time-domain picture in which the control field reshapes the interference of sub-cycle emission events. These results establish high-harmonic generation in solids as a programmable emission process and provide a general route towards ultrafast optical switching, compact coherent short-wavelength sources, and label-free attosecond super-resolution microscopy.
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All authors Pieter J. van Essen, Aday Cárdenas, Rui E.F. Silva, Álvaro Jiménez Galán, Peter M. Kraus
Optics
Vacuum-Triggered Instability in Paired Superradiance
Zhan Bai, Ningqiang Song, Min Chen et al. (+4 more)
Paired superradiance (PSR) is a macro-coherent two-
photon process capable of very large gain, making it promising for detecting ultra-weak signals induced by
neutrinos or dark matter. A major goal has been to increase the system volume $V$ and density $n$, since the signal intensity scales as $(nV)^2$. We recast finite PSR as a parametric amplifier driven by the electromagnetic
vacuum. The usual zero-field semiclassical initial condition is replaced by
vacuum inputs fixed by the
quantum two-point function. Combining this formulation with Maxwell–Bloch
evolution and finite-length stability analysis, we find that PSR produces an irreducible
vacuum background that can develop into macroscopic bursts once the gain-length product exceeds \(\Gamma L=\pi/2\) for a sufficient coherence time. These results, together with a closed-form formula for estimating the
vacuum-seeded
photon yield, establish a previously overlooked constraint for high-gain PSR, with direct implications for proposed
neutrino and dark-matter studies.
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All authors Zhan Bai, Ningqiang Song, Min Chen, Xiangyan An, Baifei Shen, Liangliang Ji, Ruxin Li
Plasma Physics
The two-stream instability generation around Moon: Effect of Interplanetary Magnetic Field during Solar Wind - Lunar Plasma Interaction
Vipin K. Yadav, Abhinav Singh and Rajneesh Kumar
The relative motion of two interpenetrating streams of charged particles usually leads to the generation of two stream instability (TSI) and eventually result in the onset of non-linear
plasma processes such as the
turbulence or the
plasma waves. A natural example of such an event is the
solar wind interaction with the lunar electron
plasma where the interplanetary
magnetic field (IMF) is embedded within the
solar wind. The inclusion of IMF in the
solar wind lunar
plasma interaction modifies the dispersion relation of the TSI and an angular cyclotron frequency term appears in the denominator of the leading term and hence leads to the change in the parameters such as the instability growth rate as now it depends on the
solar wind electron velocity,
solar wind and the lunar electron
plasma density, and the IMF magnitude. It is observed that the growth rate increases fast with the increase in the
magnetic field initially but the increase slows down on further increasing the
magnetic field thereby smoothening the top. From the particle in
cell (PIC) simulations, it is observed that during the
solar wind IMF interaction with lunar
plasma, the non-energetic background electrons make a shield around the
solar wind electrons in the
vortices formed. It is further observed that those lunar electrons which are not participating either in the
vortices formation or in the shielding of
solar wind electrons, start moving in the direction of the incoming
solar wind. These observations indicate this interaction is capable in getting converted into a non-linear physical process in the lunar
plasma environment.
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Geophysics
Integrating b-Value and Background Seismicity Rate for Spatial Earthquake Forecasting in the Alborz Region, Northern Iran
Muhammed Hossein Mousavi, Hamzeh Mohammadigheymasi, Parva Sadeghi Alavijeh et al. (+1 more)
In this study, we evaluate the spatial
forecasting skill of the $b$-value and background seismicity rate $\mu$ across the Alborz region using a homogenized catalog of 23,961 earthquakes ($M \geq 1.5$) recorded by the Iranian Seismological Center between 2006 and 2024. Forecast performance for $M \geq 4.0$ and $M \geq 4.5$ is assessed using Molchan error diagrams, probability gain, probability difference, and the modified area skill score. The results show that $\mu$ provides a consistently strong spatial signal, with Molchan curves well below the random baseline and probability gains of 5–6 at low alarm rates, reflecting the persistent clustering of seismicity along major Alborz faults. The $b$-value exhibits limited skill at lower magnitudes but improves steadily with increasing magnitude; its skill score becomes positive above $M \approx 5.3$, indicating that $b$-value anomalies begin to capture meaningful stress concentrations only for larger events. Spatial patterns reveal low $b$ zones along active reverse and strike-slip structures and high $\mu$ zones following long-term seismicity clusters, underscoring their complementary physical roles. Retrospective testing confirms this complementarity: the combined $b$–$\mu$ forecast achieves detection rates of 0.81–0.83 at spatial alarm rates of 0.43 and 0.36 for $M \geq 4.0$ and $M \geq 4.5$, respectively, representing the most efficient forecast configuration among all tested models. These findings demonstrate that integrating stress-state and tectonic-loading indicators yields a more efficient and physically grounded framework for operational earthquake
forecasting in the Alborz region.
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All authors Muhammed Hossein Mousavi, Hamzeh Mohammadigheymasi, Parva Sadeghi Alavijeh, Marjan Tourani
Plasma Physics · Cross-listed from astro-ph.SR
Imaging spectroscopy reveals spike-like repeating radio burst pairs in the solar corona
Suli Ma, Eduard P. Kontar, Daniel L. Clarkson et al. (+2 more)
Solar radio bursts exhibit complex fine structures that reveal intricate coronal
plasma dynamics. Here, we report detection of spike-like repeating burst pairs, characterized by two short-lived (0.1-2 s), narrowband components separated by about 4 s at frequencies 30-50 MHz. Using high-resolution dynamic spectra and spectroscopic imaging, we analyzed 613 burst pairs, measuring their durations, bandwidths, drift rates, flux densities, and spatial characteristics. Imaging links sources to an active region, with earlier components spatially concentrated above the region while delayed components are displaced and exhibit reduced drift rates.
Radio-wave propagation simulations support the delayed bursts as turbulent echoes of harmonic emission in anisotropic coronal
plasma. The location of the burst sources high in the corona suggests ongoing
magnetic reconnection and electron acceleration well above typical
flare heights. Our findings offer new insights into coronal
turbulence effects while advancing diagnostics of coronal
plasma and the elusive nature of
solar radio echoes from ground-based transmitters.
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All authors Suli Ma, Eduard P. Kontar, Daniel L. Clarkson, Huadong Chen, Yihua Yan
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Intrinsic Point Defects and Frenkel Pair Formation in Photovoltaic Absorber Zn$_3$P$_2$: Regulating $p$-type Conductivity through Growth and Annealing Conditions
Nico Kawashima and Silvana Botti
This study investigates the ground-state energetics and thermodynamics of intrinsic point defects in zinc phosphide Zn$_3$P$_2$ using ab initio density functional theory combined with an extensive potential energy landscape search. Our analysis reveals that the defect chemistry is dominated by zinc vacancies $V_\mathrm{Zn}$ and zinc interstitials Zn$_i$, with
equilibrium concentrations significantly surpassing those of other intrinsic species. Notably, we find that phosphorus interstitials P$_i$, previously suggested to be significant, possess high formation energies and likely exist only in negligible quantities. The characteristic $p$-type conductivity of undoped Zn$_3$P$_2$ is shown to be a direct consequence of zinc vacancies, which act as shallow acceptors and pull the
Fermi level toward the valence band. Furthermore, we identify a positive binding energy between $V_\mathrm{Zn}$ and Zn$_i$, leading to the formation of electrically benign Frenkel pairs that partially compensate the intrinsic p-type conductivity. Our results suggest that achieving $n$-type conductivity is fundamentally limited by these thermodynamic constraints. We conclude that hole densities can be optimized through phosphorus-rich growth conditions and high-temperature annealing, and suggest that future photovoltaic strategies should prioritize interface engineering over bulk $n$-type doping.
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Medical Physics
RadMaps: A Geospatial Framework for Simultaneously Modelling Capacity and Geographic Constraints on Radiotherapy Access
Laurence Wroe, Archie Brown, Sophia Martin et al. (+2 more)
Access to radiotherapy is constrained by two compounding factors: insufficient machine capacity to meet patient demand and geographic distance from treatment facilities. Existing analyses address these factors separately, in turn constraining the insights available to advocates, planners and policymakers. This paper presents RadMaps, an open-source geospatial framework that simultaneously models capacity and geographic constraints on radiotherapy access at any spatial scale. RadMaps operates on Uber's H3 hexagonal grid and integrates population density data with GLOBOCAN 2024 annual cancer incidence estimates and the IAEA DIRAC facility inventory. Radiotherapy demand is estimated using cancer site-specific radiotherapy utilisation rates, and geographic access is modelled via configurable decay functions (step, exponential, Gaussian, or power law) of distance or driving time. A capped three-step floating catchment area (3SFCA) method allocates demand to facilities subject to both capacity and geographic constraints, producing a localised access metric for every H3 hexagon. Globally, RadMaps estimates that installed capacity could meet 68.5% of radiotherapy demand, and 73.0% of demand is within geographic reach of a facility (2 h driving time with Gaussian decay, H3 Resolution-5), both comparable with published estimates. When both constraints apply, only 60.0% is met, leaving 3.7 million patients per year untreated. Countries are also grouped into one of four access profiles: strong access, capacity constrained, geography constrained, and doubly constrained. RadMaps provides a flexible, open-source framework for analysing, visualising and identifying radiotherapy access gaps at regional to global scales, with applications in advocacy, infrastructure planning, and policy prioritisation. Its modular framework is also extensible to other spatial access modelling applications.
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All authors Laurence Wroe, Archie Brown, Sophia Martin, Alika Ho, Steinar Stapnes
Physics and Society
Hyperedge approximation for stochastic processes on higher-order networks
Anzhi Sheng, Alex McAvoy, Ye Tian et al. (+3 more)
Graphs are a standard framework for describing dynamical processes shaped by pairwise interactions among
agents. But many systems involve interactions in groups of three or more
agents. Here, we develop a method of "$\ell$-hyperedge approximation", a framework to analyze
stochastic population processes on regular hypergraphs, in which each individual belongs to $k$ groups of size $\ell$. The framework accommodates both higher-order interactions that determine payoffs and higher-order processes for updating states in response to payoffs. Applied to evolutionary game dynamics, the framework generalizes the classical pairwise result on benefits and costs, $b/c>k$, that favors the spread of cooperation; and it provides critical benefit-to-cost ratios for nonlinear $\ell$-player public goods games that cannot be reduced to pairwise interactions. Applied to complex contagions, where inheritance of states occurs within hyperedges rather than along parent-offspring edges, the framework gives a closed-form result for the fixation probability, which shows how a complexity parameter governs the spread of rare types. Coupling the two processes produces a single
stochastic model of payoff-biased complex contagion in structured populations. These results extend pair approximation from graphs to hypergraphs, accommodating multi-way interactions and inheritance structures with no pairwise analog.
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All authors Anzhi Sheng, Alex McAvoy, Ye Tian, Silun Zhang, Angela Fontan, Joshua B. Plotkin
Optics
Enhancing broadband second harmonic generation in a thin film lithium niobate racetrack resonator with tunable-coupling
Olivia Hefti, Jean-Etienne Tremblay, Andrea Volpini et al. (+7 more)
Second harmonic generation in thin film periodically poled lithium niobate (PPLN) is constrained by an efficiency-bandwidth trade-off and fabrication-sensitive scaling. We demonstrate a racetrack resonator incorporating a short PPLN section and a tunable Mach-Zehnder interferometer coupler that enables in situ control of the coupling condition, compensating fabrication tolerances and stabilizing operation near critical coupling. The telecom pump is resonantly enhanced, while the near-infrared second harmonic is generated in single pass, eliminating dual-resonance requirements. The device achieves a 35 times efficiency enhancement over a non-resonant structure while maintaining a 7 nm bandwidth. This architecture provides a robust platform for broadband integrated frequency doubling.
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All authors Olivia Hefti, Jean-Etienne Tremblay, Andrea Volpini, Jannis Holzer, Alberto Della Torre, Homa Zarebidaki, Charles Caër, Hamed Sattari, Camille-Sophie Brès, Davide Grassani