Instrumentation and Detectors
A New Concept of Liquid Xenon Time Projection Chamber for Medical Imaging
B. Li, Y. Ma and K. Ni
Liquid xenon time projection chambers offer a homogeneous detection medium with excellent intrinsic energy resolution, fast scintillation, and true three-dimensional position sensitivity, making them an attractive alternative to
crystal-based detectors for positron emission
tomography (PET). In this work, we present a new single-phase
liquid xenon time projection chamber (TPC) concept optimized for medical imaging, employing combined scintillation and electroluminescence-based ionization readout to enable low-noise signal amplification and intrinsic depth-of-interaction measurement. We evaluate the system-level performance of this detector concept using Monte Carlo simulations based on OpenGATE and Geant4, with direct comparison to conventional LYSO-based PET systems. The study focuses on detection sensitivity, energy-based event selection efficiency, and reconstructed spatial resolution. While LYSO detectors provide higher absolute stopping efficiency due to their higher density,
liquid xenon detectors exhibit improved photopeak purity as a result of superior intrinsic energy resolution, leading to enhanced rejection of scattered events. Point-source reconstruction studies demonstrate that the intrinsic three-dimensional position sensitivity of the
liquid xenon TPC translates into a reconstructed spatial resolution of approximately 1~mm full width at half maximum (FWHM) at the system level, compared to approximately 4~mm for LYSO-based systems under comparable conditions. These results indicate that
liquid-xenon-based PET detectors can achieve competitive or superior imaging performance, particularly for applications requiring high spatial resolution, large axial acceptance, and scalable detector geometries.
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Plasma Physics
General-relativistic and non-ideal radiative cooling in neutron star magnetospheres
João Joaquim, Francisco Assunção, Pablo J. Bilbao et al. (+1 more)
Radiation reaction cooling plays an important role in describing the extreme
plasma conditions found in the magnetospheres of astrophysical compact objects. Strong electromagnetic fields, characteristic of these environments, can trigger the development of anisotropic ring-shaped
plasma distributions with inverted Landau populations in momentum space. In this work, we present the first systematic investigation of this mechanism in realistic astrophysical configurations, by accounting for how non-uniform electromagnetic field geometries and general-relativistic effects modify the phase-space dynamics of radiatively cooled
plasmas. We demonstrate analytically that drift velocities favour the formation of spiral-shaped momentum distributions that still display inverted Landau populations, and estimate the minimum and maximum
plasma injection distances required for inverted momentum distributions to be able to power the emission of coherent radiation through kinetic instabilities. From numerical simulations, we conclude that curved spacetime increases the gradient of the distribution function responsible for the development of kinetic instabilities, and prolongs the persistence of the inverted momentum structure relative to flat spacetime, confirming that realistic astrophysical conditions preserve and enhance the conditions necessary for synchrotron-powered emission of coherent radiation to occur.
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All authors João Joaquim, Francisco Assunção, Pablo J. Bilbao, Luis O. Silva
Atmospheric and Oceanic Physics
Do Climate Models Need Microphysical and Convective Parameterizations to Generate Accurate Precipitation Fields?
Raul Moreno and Dale Durran
Accurately representing surface precipitation is crucial for the operational use of weather and
climate models. Presently, global numerical weather prediction (NWP) models struggle to accurately generate precipitation due to their parametrization of unresolved deep convective clouds and, in regions of grid-resolved ascent, inadequate parameterizations of cloud microphysics. Here we bypass these parameterizations with a machine learning model that diagnoses precipitation from 13 ERA5 fields that are easily observed and assimilated, as opposed for example, to fields like rain or cloud
liquid water. We train a pair of models; ML_ERA5 using ERA5 precipitation as the target, and ML_IMERG using a satellite based precipitation product. ML_ERA5 closely reproduces the ERA5 precipitation at all intensities. When evaluated against the satellite
dataset, ML_IMERG closely matches observations, notably reproducing the diurnal cycle of the satellite product. ML_IMERG generally captures extremes better than ERA5 while also reducing ERA5's overproduction of light precipitation. When evaluated against a third ground-and-radar-based
dataset, ML_IMERG inherits the strengths of the satellite
dataset which is superior to ERA5 in the summer months.
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Space Physics
Solar Wind Reflected Ion Properties at Earth's Bow Shock: Dependence on Upstream Conditions and Shock Geometry
Runyi Liu, Terry Liu, Kun Zhang et al. (+2 more)
Solar wind ion reflection at collisionless shocks regulates foreshock
plasma dynamics, yet the quantitative dependence of reflected ion properties on upstream and shock-related parameters remains unclear, causing difficulties in predicting foreshock disturbances. We present a statistical study of
solar wind reflected ions near the Earth's bow shock using THEMIS observations from 59 well-defined shock crossings between 2016 and 2019. Reflected ion moments are derived after removal of the
solar wind core and compared with upstream and shock parameters. The reflection ratio decreases with increasing angle between interplanetary
magnetic field and shock normal, and increases with
magnetic compression ratio, indicating that shock geometry and
magnetic compression primarily regulate ion reflection. Reflected ion energies deviate from individual idealized reflection models: the adiabatic model overestimates total ion energy, whereas the specular model captures the perpendicular component. A combined adiabatic-specular representation improves the linear energy correspondence, and model-observation agreement increases under quasi-perpendicular shock conditions for all comparisons. Reflected ion temperature correlates with upstream
magnetic field strength and
solar wind temperature, and shows a substantially stronger dependence on
magnetic field fluctuation energy. Overall, reflected ion properties are primarily governed by upstream conditions and shock structure, with
magnetic field fluctuations contributing to ion thermalization, providing observational constraints on ion reflection and heating at Earth's bow shock.
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All authors Runyi Liu, Terry Liu, Kun Zhang, Vassilis Angelopoulos, Siqi Zhao
Optics
Raman scattering of phonon polaritons under nanoscale confinement: the role of structure and environment
George Zograf, Betul Kucukoz, Oleg Kotov et al. (+10 more)
Strong light-matter coupling gives rise to polaritons – quasiparticles that combine both photonic and material characteristics. Here, we show that polar nanocrystals exhibit structure- and environment-dependent Raman scattering, enabled by their hybrid
phonon polariton nature. Such dispersive behavior enables refractive index sensing in the mid-infrared range via visible-wavelength inelastic spectroscopy and draws parallels with molecular systems under vibrational strong coupling. Crucially, Raman scattering appears only under nanoscale confinement of
phonon polaritons. For optimal structures, this leads to self-hybridization between localized
phonon modes and surface
phonon polaritons hosted by the same nanoparticle.
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All authors George Zograf, Betul Kucukoz, Oleg Kotov, Naveen Shetty, Lunjie Zeng, Andrew B. Yankovich, Alok Ranjan, Avinas N. Shaji, Erik Lind, Tomasz J. Antosiewicz, Eva Olsson, Samuel Lara-Avila, Timur O. Shegai
Optics · Cross-listed from cs.CV
Polarization-Based Eye Tracking with Personalized Siamese Architectures
Beyza Kalkanli, Tom Bu, Mahsa Shakeri et al. (+4 more)
Head-mounted devices integrated with eye tracking promise a solution for natural human-computer interaction. However, they typically require per-user calibration for optimal performance due to inter-person variability. A differential personalization approach using Siamese architectures learns relative gaze displacements and reconstructs absolute gaze from a small set of calibration frames. In this paper, we
benchmark Siamese personalization on polarization-enabled eye tracking. For benchmarking, we use a 338-subject
dataset captured with a polarization-sensitive camera and 850 nm illumination. We achieve performance comparable to linear calibration with 10-fold fewer samples. Using polarization inputs for Siamese personalization reduces gaze error by up to 12% compared to near-infrared (NIR)-based inputs. Combining Siamese personalization with linear calibration yields further improvements of up to 13% over a linearly calibrated baseline. These results establish Siamese personalization as a practical approach enabling accurate eye tracking.
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All authors Beyza Kalkanli, Tom Bu, Mahsa Shakeri, Alexander Fix, Dave Stronks, Dmitri Model, Mantas Žurauskas
Optics
Self-Organized Optical Pathways in Optofluidic Photonic Crystals
Steven Motta
This paper reports FDTD simulations of optofluidic reconfiguration in two-dimensional silicon photonic
crystal waveguides, treating structural plasticity (the creation and destruction of optical pathways) via selective fluid infiltration. Using MPB eigenmode analysis, we decouple bandgap narrowing from defect-mode weakening, showing that defect weakening dominates (2.4 times faster transmission decay than bandgap narrowing at CS_2 indices). Infiltration
topology controls signal routing (L-bend selectivity S = 0.98), though modulation depth is weak (Delta varepsilon/ varepsilon_ textSi = 11 %). A phenomenological optothermal feedback model produces self-organized pathways that achieve 63 % of a hand-designed waveguide's bandgap transmission (7.6 times the heavily suppressed empty-
crystal baseline). Amplitude competition between counter-propagating sources produces strong, monotonic pathway steering (DeltaCOM_x from +0.03 to +4.92 ;a), while pulsed spike-timing-dependent plasticity yields a predictable null result: the timing-sensitive cross-term is suppressed by >10^2 when pulse delays exceed the temporal pulse width. The results provide
benchmarks and identify physical limits for bio-inspired reconfigurable optofluidic photonics.
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Atmospheric and Oceanic Physics
Impact of Data-Driven Eddy Parameterization on Climate State in an Idealized Coupled CESM Model
Jia-Rui Shi, Pavel Perezhogin, Laure Zanna et al. (+1 more)
Mesoscale eddies remain poorly represented in most
climate models, motivating the use of parameterizations to account for their dynamical effects on the coupled system. In this study, we implement a data-driven eddy parameterization based on Zanna and Bolton (2020; ZB20) in an idealized, fully coupled CESM configuration and assess its influence on the mean
climate state. When applied within an eddy-permitting ocean model (MOM6) embedded in the coupled configuration, the ZB20 eddy momentum parameterization, which features upgradient (backscatter) momentum flux, energizes mesoscale eddies and strengthens poleward ocean heat transport. The response is particularly strong in the Southern Hemisphere, where the open circumpolar channel sustains vigorous eddy activity and is sensitive to the parameterization, further leading to a marked hemispheric asymmetry. The oceanic meridional overturning circulation also intensifies around 60{\deg}S. The resulting ocean adjustments produce a coherent dipolar temperature pattern, with cooling in mid-latitudes and warming at high latitudes, driven primarily by anomalous meridional heat transport rather than local surface fluxes, shown using a regional heat-budget analysis. The atmosphere, in turn, exhibits a compensating reduction in meridional heat transport and an equatorward shift of the mid-latitude jet, associated with the mid-latitude surface cooling and changes in the meridional temperature gradient. Together, these results highlight how a data-driven eddy momentum parameterization can affect large-scale circulation and the mean
climate state, providing a reference for understanding its impacts in more comprehensive
climate models.
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All authors Jia-Rui Shi, Pavel Perezhogin, Laure Zanna, Alistair Adcroft
Optics
Metasurface Engineering with Tantalum Pentoxide-Coated Microspheres: Tailoring Optical Resonances and Enhancing Local Density of States
Alexandra Fălamaş, Ana Maria M. Gherman, Renaud Vallée et al. (+1 more)
Hexagonally-packed polystyrene microsphere monolayers coated with tantalum pentoxide (Ta$_2$O$_5$) form scalable dielectric metasurfaces that support tunable photonic resonances and enhanced local density of optical states (LDOS). Here we combine fabrication, optical and fluorescence spectroscopy, and multiscale electromagnetic simulations to quantify how the thickness of the Ta$_2$O$_5$ shells control far-field resonances and Rhodamine 6G (Rh6G) emission. Experimentally, Ta$_2$O$_5$ shells of 10 - 70 nm deposited on microsphere
lattices generate resonances that shift red with the thickness of the shell and systematically enhance the Rh6G fluorescence relative to flat Ta$_2$O$_5$ films. The largest enhancement is obtained for 30 - 50 nm shells, when
lattice resonances overlap the Rh6G excitation and emission bands. Finite-cluster finite-difference time-domain simulations reproduce the measured transmittance and reflectance spectra, confirming the assumed geometry of the Ta$_2$O$_5$ shells covering the sphere
lattice. Periodic-
cell simulations of single electric dipoles yield wavelength-dependent Purcell factors $Fp(\lambda)$ and directional $\beta$-factors $\beta_{top}(\lambda)$, from which we construct emission-weighted figures of merit that link LDOS modulation to the experimentally accessible top-side fluorescence enhancement. As a complementary test of our emitter-environment model, we compare simulated and measured Purcell factors for PS/Ta$_2$O$_5$ microsphere
lattices. A physically motivated averaging that accounts for emitter position, orientation and ensemble spectral smoothing yields very good agreement across all shells. Overall, our results establish Ta$_2$O$_5$-coated microsphere
lattices as robust dielectric substrates for surface-enhanced fluorescence and clarify how shell thickness and emitter placement jointly control photonic resonances, LDOS and fluorescence response.
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All authors Alexandra Fălamaş, Ana Maria M. Gherman, Renaud Vallée, Cosmin Farcău
Optics
Ultrabroadband Passive Laser Noise Suppression to Quantum Noise Limit through on-chip Second Harmonic Generation
Geun Ho Ahn, Ziyu Wang, Devin J. Dean et al. (+5 more)
Laser intensity noise limits performance in
quantum sensing, metrology, and computing. Existing stabilization methods face a trade-off between bandwidth and complexity: electronic feedback loops are speed-limited, while optical resonators are constrained by narrow linewidths and locking requirements. Here, we demonstrate an all-optical "noise eater" that passively suppresses intensity fluctuations from DC to >10 gigahertz. By leveraging high-efficiency second-harmonic generation in nanophotonic lithium niobate waveguides, we operate at a pump-depletion stationary point where input fluctuations are decoupled from the output to first order. This passive and nonresonant nanophotonic device suppresses relative intensity noise by 25 to 60 dB over the full measurement bandwidth and stabilizes a noisy fiber amplifier output to the shot-noise limit. Our results establish a scalable, wide-bandwidth paradigm for
laser stabilization essential for high-throughput
quantum technologies and deployable photonic sensing systems.
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All authors Geun Ho Ahn, Ziyu Wang, Devin J. Dean, Hubert S. Stokowski, Taewon Park, Martin M. Fejer, Jonathan Simon, Amir H. Safavi-Naeini
Data Analysis and Statistics
Vision Transformers and Graph Neural Networks for Charged Particle Tracking in the ATLAS Muon Spectrometer
Jonathan Renusch
The identification and reconstruction of charged particles, such as
muons, is a main challenge for the physics program of the ATLAS experiment at the Large
Hadron Collider. This task will become increasingly difficult with the start of the High-Luminosity LHC era after 2030, when the number of
proton-
proton collisions per bunch crossing will increase from 60 to up to 200. This elevated interaction density will also increase the occupancy within the ATLAS
Muon Spectrometer, requiring more efficient and robust real-time data processing strategies within the experiment's trigger system, particularly the Event Filter. To address these algorithmic challenges, we present two machine-learning-based approaches. First, we target the problem of background-hit rejection in the
Muon Spectrometer using Graph Neural Networks integrated into the non-ML baseline reconstruction chain, demonstrating a 15 % improvement in reconstruction speed (from 255 ms to 217 ms). Second, we present a proof-of-concept for end-to-end
muon tracking using state-of-the-art
Vision Transformer architectures, achieving ultra-fast approximate
muon reconstruction in 2.3 ms on consumer-grade GPUs at 98 % tracking efficiency.
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Atomic Physics · Cross-listed from cond-mat.quant-gas
Francisco Machado, Sabrina Chern, Michael P. Zaletel et al. (+1 more)
Continuous control over
lattice geometry, when combined with long-range interactions, offers a powerful yet underexplored tool to generate highly frustrated
quantum spin systems. By considering long-range dipolar
antiferromagnetic interactions on a breathed Kagome
lattice, we demonstrate how these tools can be leveraged to stabilize a
chiral spin liquid. We support this prediction with large-scale density-
matrix renormalization group calculations and explore the surrounding phase diagram, identifying a route to adiabatic preparation via a locally varying
magnetic field. At the same time, we identify the relevant low-energy degrees of freedom in each unit
cell, providing a complementary
language to study the
chiral spin liquid. Finally, we carefully analyze its stability and signatures in finite-sized clusters, proposing direct, experimentally viable measurements of the
chiral edge mode in both Rydberg atom and ultracold polar molecule arrays.
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All authors Francisco Machado, Sabrina Chern, Michael P. Zaletel, Norman Y. Yao
Atomic Physics
Structured-Light Magnetometry in a Coherently Controlled Atomic Medium
Parkhi Bhardwaj and Shubhrangshu Dasgupta
A structured-light-based approach to magneto-optical rotation (MOR) magnetometry is proposed, in which magnetically induced polarization rotation is converted into a directly observable spatial displacement. A radially polarized Laguerre–Gaussian beam propagating through cold $^{87}\mathrm{Rb}$ atoms in the presence of a longitudinal
magnetic field experiences circular birefringence, which induces a relative phase shift between the $\sigma_+$ and $\sigma_-$ polarization components. This phase shift manifests itself as the angular rotation of a petal-shaped interference pattern, enabling the MOR angle to be determined directly from the spatial intensity distribution. Unlike conventional MOR detection techniques based on balanced polarimetry or Stokes-parameter reconstruction, the proposed method requires only a fixed-axis polarization projection and avoids computationally intensive polarization analysis. By translating polarization rotation into a
topology-dependent spatial observable, the scheme enables direct and spatially resolved
magnetic-field measurements. Furthermore, the use of electromagnetically induced transparency (EIT) allows low-loss operation while preserving high sensitivity. These characteristics make the proposed technique a promising platform for optical magnetometry and structured-light-based
quantum sensing.
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Plasma Physics
Challenges and opportunities for AI to help deliver fusion energy
Adriano Agnello, Helen Brooks, Cyd Cowley et al. (+5 more)
There is great potential for the application of AI tools in fusion research, and substantial worldwide benefit if fusion power is realised. However, using AI comes with its own challenges, many of which can be mitigated if responsible and robust methodologies are built into existing approaches. To do that requires close, long-term collaborations between fusion domain experts and AI developers and awareness of the fact that not all problems in fusion research are best tackled with AI tools. In April 2025, experts from academia, industry, UKAEA and STFC discussed how AI can be used to advance R&D in fusion energy at the first edition of The Economist FusionFest event. This Perspective is an expanded and updated summary of the round table discussion, providing more context and examples.
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All authors Adriano Agnello, Helen Brooks, Cyd Cowley, Iulia Georgescu, Alex Higginbottom, Richard Pearson, Tara Shears, Melanie Windridge
Physics and Society
SF2A Environmental Transition Commission: Chosen pieces from the survey 'French astronomy and astrophysics research activities in the face of the environmental crisis, from 2019 to 2024'
Faustine Cantalloube, Camille Noûs, A. Jolly et al. (+3 more)
In 2025, the French Society for Astronomy & Astrophysics (SF2A), gave the environmental transition commission the opportunity to share their considerations during a plenary session at the annual SF2A conference. This year, the presentation focused on some of the main results obtained from the survey entitled 'French astronomy and astrophysics research activities in the face of the environmental crisis, from 2019 to 2024'. The survey was initiated in 2019 by the group 'Environnement-Transition' (coordinated by P. Martin) at IRAP, whose results were presented during the SF2A annual conference 2019 in Nice. The survey was updated in 2024 by the CNRS INSU-AA prospective working group '
Climate and ecological challenge' (coordinated by S. Bontemp). The SF2A environmental transition commission took on the survey to the French institutes, sorted the answers and extracted the preliminary results. The full results will be published at the end of 2025 in the final CNRS INSU-AA 2024 prospective document. This publication presents a selection of pieces from the full survey, along with a few of the main discussions it triggers.
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All authors Faustine Cantalloube, Camille Noûs, A. Jolly, Julien Milli, Jean-François Gonzalez, Françoise Laurent
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Electrostatic Photoluminescence Tuning in All-Solid-State Perovskite Transistors
Vladimir Bruevich, Dmitry Maslennikov, Beier Hu et al. (+2 more)
We demonstrate an all solid state
semiconductor device, based on epitaxial single crystalline metal halide perovskites, enabling reversible control of a perovskite photoluminescence with a gate voltage. Fundamentally distinct from electroluminescent diodes, such a photoluminescence field effect transistor uses the gate electric field to electrostatically modulate the interfacial density of mobile charges, thereby affecting the radiative and nonradiative recombination channels of photocarriers. Varying the gate voltage in such transistors efficiently changes the rate of nonradiative interfacial recombination and modulates the photoluminescence intensity by 65 to 98 percent (depending on temperature). At favorable gating, nearly complete elimination of non-radiative losses can be achieved. This functionality, coupled with the strong visible-range absorption and emission, possible due to the high absorption coefficient, as well as controllable thickness and macroscopically homogeneous morphology of epitaxial perovskite films, leads to high external photoluminescence
quantum efficiencies realized in large-area, thin-film devices. Such high-efficiency, scalable, electrostatically tunable optoelectronic switches broaden the potential applications of metal-halide perovskites in photonics and optoelectronics.
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All authors Vladimir Bruevich, Dmitry Maslennikov, Beier Hu, Artem A. Bakulin, Vitaly Podzorov
Optics · Cross-listed from quant-ph
Scalable Quantum Interference from Indistinguishable Quantum Dots
Sheena Shaji, Suraj Goel, Julian Wiercinski et al. (+7 more)
Quantum interference of indistinguishable
photons is the foundation of photonic
quantum technologies, yet scaling from a few to many identical
quantum light sources remains a major challenge. In solid-state platforms, spatial and spectral inhomogeneity and resource-intensive architectures impede scaling. As a result, interference between remote, independent
quantum emitters has been thus far limited to pairs. Here we introduce a wavefront-shaping approach that enables scalable interference from multiple indistinguishable
quantum dots on the same chip. Using programmable spatial light modulators, we independently excite, collect, and route emission from spatially distinct, yet spectrally degenerate dots. Scaling from two to five indistinguishable emitters, we verify interference through cooperative-emission phenomena and Hong-Ou-Mandel two-
photon interference, thereby establishing a route towards large-scale, programmable
quantum photonic architectures.
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All authors Sheena Shaji, Suraj Goel, Julian Wiercinski, Frederik Brooke Barnes, Moritz Cygorek, Antoine Borel, Natalia Herrera Valencia, Erik M. Gauger, Mehul Malik, Brian D. Gerardot
Plasma Physics · Cross-listed from astro-ph.HE
Double-Adiabatic Equations of State for Relativistic Plasmas
Agnieszka Wierzchucka, Pablo J. Bilbao, Alexander G. R. Thomas et al. (+2 more)
The adiabatic equation of state $P \propto n^{\Gamma}$ describes the pressure
evolution of highly collisional, isotropic
plasmas in terms of their density, providing a possible closure of the fluid moment hierarchy in the absence of heat fluxes and dissipation. An analogous closure exists for collisionless, magnetised
plasmas, whose pressure tensor is anisotropic with respect to the
magnetic field, and the closure is therefore double adiabatic, prescribing the
evolution of the parallel and perpendicular pressures in terms of the
magnetic-field strength and density. Here, we present a general first-principle formalism to derive adiabatic laws using the
symmetries of the system. With this theory we recover the adiabatic equation of state $P \propto n^{\Gamma}$ for isotropic
plasmas and the double-adiabatic equations of state for collisionless, magnetised
plasmas. We extend the latter to the relativistic regime, finding that their exact functional form depends on the pressure anisotropy and is not a simple power law. Our double-adiabatic equations of state describe simple geometries, like
magnetic mirrors or compressed homogeneous
plasmas, as well as complex high-energy astrophysical processes, such as the
evolution of plasmoid structures formed during
magnetic reconnection.
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All authors Agnieszka Wierzchucka, Pablo J. Bilbao, Alexander G. R. Thomas, Dmitri A. Uzdensky, Alexander A. Schekochihin
Physics and Society
Exploring carbon dioxide removal strategies to help decarbonise Europe using high-resolution modelling
Ricardo Fernandes, Alberto Alamia, Sina Kalweit et al. (+1 more)
The electrification of energy demand across sectors, powered by
solar and wind generation, is the best strategy for achieving carbon neutrality. Carbon dioxide removal (CDR) strategies are also expected to play a crucial role by providing net-negative emissions that can offset residual CO2 emissions, including those from cement manufacturing. While previous studies have assessed the role of CDRs in Europe's decarbonisation, most either focus solely on combinations of biogenic point-source capture and direct air capture (DAC) coupled with underground sequestration, or consider multiple CDR strategies at low spatial and temporal resolution, thereby limiting the representation of linkages amongst technologies. In this study, the sector-coupled European energy system model PyPSA-Eur is extended to include afforestation, perennialisation, biochar, and enhanced rock weathering (ERW) as additional CDR strategies. Using this model with a 3-hourly resolution and a network comprising 90 nodes, results show that a
climate-neutral energy system equipped with these CDR strategies is 9% less expensive. Afforestation, perennialisation, and ERW potentials are fully utilised across regions, whereas biochar is not selected due to limited solid biomass feedstock being allocated to other higher-value processes. Furthermore, when these CDR strategies are combined with underground sequestration and a continental CO2 transport network, DAC is no longer required to achieve
climate neutrality in Europe.
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All authors Ricardo Fernandes, Alberto Alamia, Sina Kalweit, Marta Victoria
Physics Education
A Low-Cost Teapot Effect Experiment for Introductory Physics
Yu-Chen Guo, Jin-Ming Wang and Ying-Xin Li
The teapot effect refers to the tendency of a poured
liquid to cling to the lip of a container and run down the outside. It is a familiar but physically rich example of flow separation. We present a low-cost experiment for introductory physics laboratories that uses 3D-printed cups, a simple flow regulator, and basic surface treatments to explore this phenomenon in a classroom setting. Students measure the run-off length along the outer wall as an accessible indicator of sticking versus separation and use it to compare the effects of flow velocity and surface wettability. Rather than attempting a full quantitative test of research-level models, the activity is designed to illustrate the inertial-capillary picture of the teapot effect in a form that is experimentally straightforward and pedagogically effective. The experiment connects a familiar everyday observation to fluid inertia, wetting, and interfacial forces in a form that is well suited to introductory instruction.
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Atmospheric and Oceanic Physics · Cross-listed from cs.LG
Anchored-Branched Steady-state WInd Flow Transformer (AB-SWIFT): a metamodel for 3D atmospheric flow in urban environments
Armand de Villeroché, Rem-Sophia Mouradi, Vincent Le Guen et al. (+5 more)
Air flow modeling at a local scale is essential for applications such as pollutant dispersion modeling or wind farm modeling. To circumvent costly Computational Fluid Dynamics (CFD) computations, deep learning surrogate models have recently emerged as promising alternatives. However, in the context of urban air flow, deep learning models struggle to adapt to the high variations of the urban geometry and to large mesh sizes. To tackle these challenges, we introduce Anchored Branched Steady-state WInd Flow
Transformer (AB-SWIFT), a
transformer-based model with an internal branched structure uniquely designed for atmospheric flow modeling. We train our model on a specially designed database of atmospheric simulations around randomised urban geometries and with a mixture of unstable, neutral, and stable atmospheric stratifications. Our model reaches the best accuracy on all predicted fields compared to state-of-the-art
transformers and graph-based models. Our code and data is available at https://github.com/cerea-daml/abswift.
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All authors Armand de Villeroché, Rem-Sophia Mouradi, Vincent Le Guen, Sibo Cheng, Marc Bocquet, Alban Farchi, Patrick Armand, Patrick Massin
Fluid Dynamics
Converting vertical heat supply into horizontal motion for microtechnological pumping and autonomous waste heat recovery
Jan-Niklas Schäfer, Tillmann Carl, Kristin Kühl et al. (+4 more)
The rapid advancement of high-performance computing infrastructure and its extended application produce an increasing amount of waste heat. This heat constitutes an unsustainable loss of energy as well as requires cooling solutions that transcend conventional thermal management. Here, we demonstrate a novel mechanism that converts vertical waste heat supply directly into horizontal fluid motion, enabling autonomous, self-powered pumping in microenvironments. Our approach is based on a concept that combines
geometric symmetry breaking with heterogeneous thermal conductivities to induce local thermocapillary Marangoni flows. We provide an implementation of the concept as well as an experimental and numerical proof-of-concept, showing good agreement between the respective flow fields. The approach is scalable and operates under realistic areal heating conditions. It enables versatile pumping designs for microtechnological applications, lab-on-a-chip architectures, passive thermal management and heat-driven microfluidic systems.
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All authors Jan-Niklas Schäfer, Tillmann Carl, Kristin Kühl, Sonja Kiehren-Ehses, Jan Aurich, Georg von Freymann, Clarissa Schönecker
Computational Physics · Cross-listed from cond-mat.mtrl-sci
General-Purpose Machine-Learned Potential for CrCoNi Alloys Enabling Large-Scale Atomistic Simulations with First-Principles Accuracy
Yong-Chao Wu, Tero Mäkinen, Mikko Alava et al. (+1 more)
CrCoNi medium-
entropy alloys exhibit exceptional mechanical properties arising from pronounced chemical complexity, including short-range order (SRO), and low stacking fault energy, posing challenges for large-scale atomistic simulations. While most models focus on equimolar compositions, deviations from equimolarity provide an effective route to tuning properties, requiring transferable interatomic potentials that capture composition-dependent behavior. Here we develop a general-purpose machine-learned interatomic potential for the CrCoNi system within the neuroevolution potential (NEP) framework, achieving near first-principles accuracy with high computational efficiency. Trained on a comprehensive
dataset spanning pure elements, binary and ternary
alloys across a wide compositional range, diverse
crystal structures and thermodynamic conditions, and based on
spin-polarized ab initio data, the model accurately reproduces equations of state,
phonons, elastic constants, dislocation dissociation, surface and defect energies, melting temperatures and strain-induced phase transformations. It further captures SRO and its effect on stacking fault energies across both equimolar and non-equimolar compositions, in agreement with first-principles and experiments. In contrast to existing potentials, typically limited to equimolar
alloys and less accurate for pure elements, the present model delivers consistent accuracy across the full compositional space while retaining superior efficiency. These results enable reliable atomistic simulations of composition-dependent behaviour and provide a framework for the design of non-equimolar CrCoNi
alloys.
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All authors Yong-Chao Wu, Tero Mäkinen, Mikko Alava, Amin Esfandiarpour
Optics · Cross-listed from quant-ph
Robust continuous-variable multipartite entanglement in circular arrays of nonlinear waveguides
Sugar Singh Meena, David Barral, Ankan Das Roy et al. (+2 more)
Encoding continuous-variable
quantum information in the optical domain has recently enabled the generation of large entangled states, yet robust implementation remains a challenge. Here, we present a straightforward protocol for generating multipartite
entanglement based on spontaneous parametric down-conversion in a circular array of quadratic nonlinear waveguides. We provide a rigorous theoretical framework, including comprehensive derivations of the propagation equations and the identification of regimes where analytical solutions are possible. Crucially, our approach identifies the pump and detection configurations required to sustain and measure multipartite full inseparability across arbitrary propagation distances and for any number of waveguides $N=4 n$. This regime, elusive to standard numerical methods, represents a key requirement for scalable
quantum protocols. Our scheme is inherently robust as it relies on phase-matched propagation eigenmodes, making it resilient against variations in sample length, coupling, and nonlinearity.
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All authors Sugar Singh Meena, David Barral, Ankan Das Roy, Sunita Meena, Amit Rai
Optics · Cross-listed from cond-mat.mes-hall
Puiseux series about exceptional singularities dictated by symmetry-allowed Hessenberg forms of perturbation matrices
Ipsita Mandal
We develop a systematic framework for determining the nature of exceptional points of $n^{\rm th}$ order (EP$_n$s) in non-Hermitian (NH) systems, represented by complex square
matrices. By expressing
symmetry-preserving perturbations ($\propto \epsilon$) in the Jordan-normal basis of the defective
matrix at an EP$_n$, we show that the upper-$\ell$ Hessenberg structure of the perturbation
matrix directly dictates the leading-order
eigenvalue- and eigenvector-splitting to be $\propto \epsilon^{1/\ell}$, when expanded in a Puiseux series. Applying this to three-band NH models invariant under parity (P), charge-conjugation (C), or parity-time-reversal (PT), we find that EP$_3$s in P- and C-symmetric systems are restricted to at most $\sim \epsilon^{1/2}$ branch points, while PT-symmetric systems generically support EP$_3$s with the strongest possible singularities (viz. $\sim \epsilon^{1/3}$). We illustrate these results with concrete three-dimensional models in which exceptional curves and surfaces emerge. We further show that fine-tuned perturbations can suppress the leading-order branch point to a less-singular splitting, which have implications for designing direction-dependent EP-based sensors. The appendix extends the analysis to four-band P- and C-symmetric models, establishing the existence of EP$_4$s with $\sim \epsilon^{1/4}$ and $\sim \epsilon^{1/2}$ singularities, respectively.
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Plasma Physics
On the double-adiabatic equations in the relativistic regime
Francisco Ley, Aaron Tran and Ellen G. Zweibel
We revisit the double adiabatic
evolution equations and extend them to the relativistic and ultrarelativistic regimes. We analytically solve the relativistic, time-dependent drift kinetic equation for a homogeneous, magnetized, collisionless
plasma and obtain a solution explicitly dependent on the
magnetic field and density variations. In the case of an initial relativistic Maxwellian distribution, a natural extension to an anisotropic Maxwell-Jüttner is obtained. We calculate the moments of this time-dependent solution and obtain analytical expressions for the
evolution of the perpendicular and parallel pressures in the ultrarelativistic case. We numerically solve the moment equations in the relativistic case and obtain general expressions for the double-adiabatic equations in this regime. We confirm our results using fully kinetic particle-in-
cell simulations of shearing and compressing boxes. Our findings can be readily applied to relativistic species including
cosmic-rays and electron-positron pairs, present in astrophysical
plasmas like
pulsar wind nebulae, astrophysical jets, black hole
accretion flows, and Van Allen radiation belts.
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Plasma Physics
Radiation safety considerations for ultrafast lasers beyond laser machining
Simon Bohlen, Julian Holland and Rudolf Weber
The interaction of ultrafast
lasers with
plasmas has been studied for many years, primarily with respect to fundamental emission mechanisms. Only in recent years has ionizing radiation emerged as a safety concern in ultrafast
laser-based material processing, where high pulse energies, repetition rates, and average powers, combined with continuous material supply, can lead to sustained X-ray emission. These processing-specific findings have informed German radiation protection legislation, which mandates notification or approval for
laser systems exceeding irradiances of $1 \times 10^{13}~W/cm^2$. However, this threshold does not distinguish between material processing and other ultrafast
laser applications. In this work, we show that the conditions required for X-ray generation are highly specific and are typically only met during material processing. We assess the applicability of existing radiation studies to non-processing environments and present experimental results demonstrating negligible or no dose production under representative laboratory conditions, such as ultrafast
laser interactions with underdense gas or stationary solid targets. We conclude that current legislation generalizes a processing-specific hazard to all ultrafast
laser applications and does not adequately reflect the relevant physical conditions.
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Atomic Physics
A high-flux atomic strontium oven with light-driven flux modulation
Kenneth M. Hughes, Jesse S. Schelfhout, Charu Mishra et al. (+3 more)
A high-flux source of strontium atoms is required for cold atom
quantum technology applications. We present a re-entrant oven design that avoids the need for any
vacuum feed-throughs and has an inherent temperature gradient to guard against clogging of the nozzle. The nozzle is fabricated by micro-machining of fused silica using selective
laser etching; this specialised technique is capable of making many thousands of fine microchannels and is suitable for batch production. Operating with only electrical heating, using <20W of electrical power, a total flux of $8(1)\times 10^{14}$ atoms/s is achieved at an oven temperature of 475{\deg}C, of which we estimate $1.8(2)\times 10^{13}$ atoms/s could be captured. A heated in-
vacuum sapphire window grants optical access directly opposite the oven, and can be cleared of metallization without breaking
vacuum. We used this optical access to modulate the flux of the atomic beam by direct illumination of the nozzle and the strontium metal with high-power
laser light. Heating by
laser light increased the useful flux by a factor of up to 16(3) on a timescale of 40s, and a factor of 2.5(5) on a timescale of 1s. This flux modulation serves to increase the operating lifetime of the oven. We report experimental measurements of the performance of the oven in long-term operation over many months.
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All authors Kenneth M. Hughes, Jesse S. Schelfhout, Charu Mishra, Timothy Leese, Elliot Bentine, Christopher J. Foot
Physics and Society · Cross-listed from quant-ph
Stochastic Multipath Routing for High-Throughput Entanglement Distribution in Quantum Repeater Networks
Ankit Mishra and Kang Hao Cheong
Quantum repeater networks distribute
entanglement over lossy links while many users share a limited pool of entangled pairs. Most existing routing schemes either always use a single best path or rely on global optimizations that are hard to run in real time. Here we propose and analyze a simple alternative: a
stochastic multipath rule in which each
entanglement request is sent at random along one of several edge-disjoint repeater paths, with a single parameter that controls the bias between shorter and longer routes. Using a distance-dependent lossy network model with finite per-link capacities and probabilistic
entanglement swapping, we develop an analytic description of the resulting end-to-end
entanglement rate as a function of this bias and validate it with large-scale numerical simulations. We find that an intermediate bias consistently outperforms both deterministic extremes across distances, traffic patterns, attenuation, swapping noise, and congestion, bringing the rate close to simple capacity upper bounds and making link usage more even across networks. These results identify
stochastic multipath routing as a lightweight classical control strategy for boosting performance and scalability in near-term
quantum repeater networks.
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Physics and Society
Migration of Voters in Florida, 2017-2022
Fangzhou Xie
Florida has experienced significant population increase in recent years, driven in part by domestic migration from other states. This study analyzes the migration patterns of voters in Florida between 2017 and 2022 using voter registration data. By examining demographic characteristics such as race/ethnicity, gender, age, and party affiliation, I identify trends in voter migration and their implications for Florida's political landscape. The findings reveal that minorities, younger individuals, Republicans, and those possibly with non-conforming gender are more likely to migrate into Florida. These insights contribute to understanding the dynamics of Florida's migration patterns and the effect of migration on recent elections.
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