Optics
Transverse Faraday Effect in Multimode Fibres
Mohammed R. Sharif and Mitchell A. Cox
The weak guidance approximation suppresses the longitudinal field component $E_z$, and with it an entire class of linear magneto-optic interactions. We derive and experimentally verify a transverse Faraday effect in step-index multimode fibres that couples $E_y$ into $E_z$. Using speckle decorrelation we isolate the linear Faraday signal from the quadratic Cotton-Mouton background, confirming four predictions: the effect vanishes without a strong index step, scales with launch angle, is completely polarisation-selective relative to the field, and tracks Verdet dispersion. Under 0.24 T we observe $\Delta\rho \approx 0.16$ for perpendicular input and a complete null for parallel input.
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Medical Physics · Cross-listed from cs.CV
You Cannot Recover What Was Never Measured: Quantifying the Information Ceiling of Ultra-Low-Field MRI Super-Resolution
Prathamesh Pradeep Khole, Shreya Handa, Utkarsh Gupta et al. (+1 more)
Generative super-resolution models can turn portable 64 mT MRI into images that look like 3T scans, and the field evaluates them with PSNR, SSIM, and pixelwise uncertainty, most often on pairs built by synthetically degrading high-field images. Prior work acknowledges that these models hallucinate and that the problem is ill posed, but to our knowledge no study measures how much information about the individual subject the real low-field scan actually contains. We measure it. Using paired 64 mT and 3T scans of the same subjects from three public
datasets, and a measurement protocol validated on tests whose correct answer is known in advance, we find that, judged over the whole
brain, real 64 mT scans carry structure specific to the individual only down to approximately 3 to 4 mm half-pitch in plane, and coarser still through plane. Standard synthetic degradations preserve subject information roughly 1 mm beyond this ceiling, so models trained and benchmarked on synthetic pairs are evaluated on information that real scanners never record. We then test trained
diffusion models and a publicly released external model on real paired acquisitions; 24 trained runs of five architectures (GAN,
diffusion, and
transformer families) give the coverage of the audit. On every subject where faithfulness can be measured, fine output detail is no more correlated with the subject's own 3T scan than with a stranger's, while sample-variance uncertainty does not distinguish fabricated structure from reconstruction difficulty. Because PSNR and SSIM score resemblance to a reference rather than whether detail belongs to the subject, a
benchmark scored by them cannot tell recovery from fabrication. Code for the measurement protocol will be released so that recoverability claims can be tested for newer models.
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All authors Prathamesh Pradeep Khole, Shreya Handa, Utkarsh Gupta, Razvan Marinescu
Fluid Dynamics
Radial flow of an Oldroyd-B fluid: theoretical and simulation results in the ultra-dilute limit
Ron Lottem and Evgeniy Boyko
Pressure-driven radial flows of viscoelastic fluids are common in various industrial applications, such as injection molding and extrusion. It is well known that viscoelastic rheology can significantly impact the hydrodynamic features of non-Newtonian flows. However, these hydrodynamic features remain not fully understood compared to those observed in Newtonian flows. We analyze the pressure-driven radial flow of an Oldroyd-B fluid between parallel plates and present a theoretical framework together with finite-element numerical simulations for determining the flow rate-pressure drop relation. Unlike previous theoretical studies restricted to the weakly viscoelastic limit of low Deborah ($De$) numbers, we apply lubrication theory and consider the ultra-dilute limit, which allows us to study viscoelastic radial flows at order-one Deborah numbers. Using the one-way coupling between the Newtonian velocity profile and elastic stresses, we derive closed-form expressions for the conformation tensor and pressure drop in the ultra-dilute limit. We show that the pressure drop monotonically increases with $De$, identify the physical mechanisms governing this increase, and delineate the range of validity of the ultra-dilute approximation. We further reveal that the low-$De$ asymptotic analysis of the pressure drop may fail to accurately capture finite-element simulation results, even at low Deborah numbers, owing to its inability to satisfy the inlet elastic stresses. In contrast, our theoretical predictions based on the ultra-dilute limit are in excellent agreement with the finite-element simulation results, enabling us to elucidate the pressure drop behavior for order-one Deborah numbers.
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Instrumentation and Detectors
Development and Performance Study of a Capillary Liquid Scintillator Neutron Detector
Guang Luo, Jian Yu, Dikai Li et al. (+9 more)
Capillary
liquid scintillator detectors are promising for high-resolution
neutron imaging, yet experimental data on their light spread mechanism and spatial performance remain limited. Here, we report a
neutron detector based on a hexagonal capillary array filled with EJ-309
liquid scintillator, with an inner diameter of about 50 um and a camera readout of 9 um pixels.
Laser experiments show that the FWHM of the full light spot decreases from 260 um to 90 um with a metal light absorber, confirming effective suppression of lateral light spread. Using an AmBe
neutron source, an effective field of view with a 5-sigma threshold was established from background frames. For single-capillary events, the pulse height spectrum follows a Landau distribution with a most probable value of 0.133 +/- 0.001 (stat.), and the intrinsic detection efficiency is 10.07% +/- 1.26% (stat.) +/- 1.43% (syst.), corresponding to about 13.55% when normalized to the active
liquid scintillator area. The point spread function core yields a radial FWHM of 12.8 um and a centroid positioning precision of approximately 5.5 um (1 sigma), while the intrinsic position resolution is limited by the capillary pitch to 54 um. Linearity is good for 1 to 2 capillaries, with deviation appearing for 2 to 3 capillaries due to additional capture of spread light. These results provide experimental basis and physical understanding for imaging applications of capillary
liquid scintillator
neutron detectors.
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All authors Guang Luo, Jian Yu, Dikai Li, Yanmeng Dai, Meiling Chen, Jiaqiang Zou, Ke Yan, Shaoxuan Cui, Ge Jin, Zhao Xu, Chunhui Zhang, Leifeng Cao
Applied Physics
Study of LAGP coating on polyethylene separator for polysulfide suppression in thin Li-S batteries
Giovanni Ceccio and Jiri Vacik
The use of a thin solid electrolyte layer on polyethylene (PE) separators has been explored as a potential strategy to mitigate the polysulfide shuttle effect in lithium-sulfur (Li-S) batteries, a phenomenon responsible for significantly reducing their lifespan. While some solid electrolytes, such as LAGP , have demonstrated the ability to effectively suppress the shuttle effect, their brittle ceramic nature limits their application, particularly in flexible electronics. Coating PE separators with LAGP nanofilms offers a promising solution by combining the mechanical flexibility and thinness of
polymer separators with the electrochemical advantages of LAGP, due to its NASICON-like structure and high ionic conductivity. In this study, PE separators were coated with LAGP nanofilms using the ion sputtering technique and further modified with ferroic elements such as Ni and Co. The surface morphology of the coated separators was analyzed using scanning electron microscopy (SEM), and staircase voltammetry was employed to evaluate the electrochemical performance and modifications induced by the coatings. The results demonstrate that the use of PE separators with a thin LAGP layer significantly influences polysulfide
diffusion and suppresses the shuttle effect, thereby reducing unwanted processes in Li-S batteries.
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Optics
Multiplexed chiral and helical acoustic anomaly bulk states in an inverse-designed metamaterial
Xueyun Wen, Zhihao Lan, Zhongming Gu et al. (+2 more)
Valley and pseudospin are fundamental degrees of freedom (DOFs) in topological acoustics. However, they have so far been realized mostly in separate systems. Here, we achieve the multiplexing of valley and pseudospin DOFs in one acoustic system. An acoustic metamaterial simultaneously hosting single and double Dirac cones is inversely designed by the developed
topology optimization method. Thereafter, under a hard-boundary condition, valley-locked chiral states and pseudospin-locked helical states emerge within two separate frequency windows and can be selected by tuning the operating frequency. Furthermore, their applications for multifrequency acoustic energy enhancement are experimentally demonstrated. Our work provides a strategy to modulate acoustic waves carrying distinct topological DOFs within a single integrated platform, facilitating the development of multiplexed acoustic devices with robustness.
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All authors Xueyun Wen, Zhihao Lan, Zhongming Gu, Yafeng Chen, Jie Zhu
Computational Physics
Label-Permutation Symmetry and Stability in Oscillator Potts Machines
E.M. Hasantha Ekanayake and Nikhil Shukla
Oscillator Potts machines (OPMs) provide a physics-inspired, energy-minimization framework for solving combinatorial optimization problems described by the $q$-state Potts
Hamiltonian. Although OPMs may be viewed as multistate extensions of oscillator Ising machines (OIMs), here, we show that they exhibit dynamical properties absent in the binary case. Specifically, we derive a configuration-dependent local-stability condition for a recently proposed multiharmonic OPM formulation and show that configurations with the same Potts energy need not be dynamically equivalent. In particular, for $q\geq4$, permutations of the Potts labels can alter the Jacobian spectrum and, consequently, the regularization strength required to locally stabilize a given Potts configuration. Thus, different phase encodings of the same Potts solution can exhibit different local stability properties despite having identical Potts energies.
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Applied Physics
Integrated assessment of tritium releases from fission and fusion energy systems and their environmental implications
Liliana Arias, Jeffrey Wang, Ate Visser et al. (+4 more)
Tritium is a naturally occurring radioactive isotope of hydrogen; a low-energy beta emitter with its health significance through internal exposure. The anticipated deployment of fusion energy systems is expected to increase tritium production significantly. Here we present an integrated assessment of tritium generation, release pathways, and resulting environmental concentrations across existing and emerging nuclear technologies. We first compile a comprehensive database of tritium production and releases from monitoring reports and literature. Analysis of light-water-reactor operating data shows that tritium discharge levels and release pathways are governed mainly by plant-specific strategies rather than reactor power or design parameters. This pattern reflects industry operating practices and efforts, with releases remaining well below regulatory limits. Our synthesis further indicates that FLiBe-based (Li2BeF4) systems may increase tritium production and mobility through enhanced permeation of tritiated hydrogen, although mitigation strategies are available to further limit emissions. Environmental transport modeling suggests that, under appropriate siting conditions, resulting tritium concentrations remain below regulatory thresholds. Furthermore, comparative risk analysis indicates that the associated carcinogenic impacts are expected to be lower than those from fossil-fuel-based power generation. Together, these findings demonstrate the importance of a comprehensive monitoring framework for contextualizing and managing routine effluent releases across energy systems.
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All authors Liliana Arias, Jeffrey Wang, Ate Visser, Naofumi Akata, Hideki Kakiuchi, Shinji Ueda, Haruko M. Wainwright
Chemical Physics
Electronic excitation spectra and recovery of excited states with neural network wave functions
Xiaoyu Zhang, Weizhong Fu and Yixiao Chen
Accurate electronic spectra require both a flexible description of electron correlation and a tractable treatment of the many states contributing to the response. We combine neural network wave functions with the Lorentz integral transform to calculate electronic spectra directly in continuous coordinates, without truncation error from a fixed one-electron basis and with
polynomial computational cost per optimization step. Instead of constructing a prescribed set of excited states, the method solves an inhomogeneous Schrödinger equation at a chosen complex energy. This formulation gives access, in principle, to the entire spectrum coupled to a perturbation, including bound excitations and the ionization continuum, without explicitly determining all lower-lying eigenstates. A finite imaginary energy controls the resolution and keeps the response square integrable. Near an isolated bound excitation, the normalized response also recovers the corresponding eigenstate as the width tends to zero. A helium application illustrates the extraction of an excitation energy and oscillator strength. The formulation provides a route from neural descriptions of electronic correlation to spectra beyond a small
manifold of low-lying states.
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Optics
Co-design of Silicon Microring Modulator beyond 200 Gb/s per Lane: Device Physics, Operating Point, and Compact Models for Scale-Up and Scale-Out Optical I/O
Zhihong Huang, Yuan Yuan, Yiwei Peng et al. (+3 more)
Optical input/output (I/O) supports high-bandwidth communication between processors in artificial intelligence (AI) systems. Depletion-mode silicon microring modulators offer compact footprints, wavelength multiplexing and femtojoule-scale junction switching energy per bit. However, as lane rates increase to 200~Gb/s and beyond, a digital signal processor (DSP) performing equalization and forward-error correction can consume up to half of the optical module power. We analyze the junction and cavity physics of silicon microring modulators, relating modulation efficiency, capacitance, optical loss and coupling to bandwidth and drive requirements to guide device optimization above 200~Gb/s per lane.
Laser detuning and optimal operating points are examined by distinguishing maximum static slope, static and dynamic OMA, and gain–bandwidth product (GBW), including the influence of the junction RC response. The effects of optical self-heating, photocarriers and bias-network voltage droop on the resonance are discussed together with heater tuning and wavelength assignment in DWDM arrays. Cold-resonance design points are calculated from the required hot detuning, link-budget-derived optical power and assumed thermal parameters, with heater reserve and startup acquisition included as design constraints. A compact model of the coupled electrical, optical and thermal dynamics is used to evaluate PAM4 eye diagrams, and a Verilog-A implementation of the model core is provided for
circuit-level simulation.
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All authors Zhihong Huang, Yuan Yuan, Yiwei Peng, Samuel Palermo, Marco Fiorentino, Raymond G. Beausoleil
Fluid Dynamics
Leading-edge noise reduction by perforated and porous inserts: a compressible finite-chord prediction without fitted constants
Seongkyu Lee
Porous and perforated leading edges reduce
turbulence-interaction noise, but predictions of the reduction have relied on material impedances adjusted to the acoustic data. This paper removes that adjustment. The finite-chord scattering problem is solved in compressible subsonic flow for an arbitrary chordwise admittance, with the shed wake, the Kutta condition and permeability-dependent edge singularities, and closed to the far field with the finite span and the array aperture represented. The admittance of a perforated insert is derived from the Rayleigh conductivity of one aperture with three computed corrections: plate thickness, interaction between neighbouring apertures, and Howe's grazing-flow blockage evaluated at the aperture-averaged velocity of the boundary layer. A bulk porous insert is represented by its measured permeability and pore-fluid inertia. For three perforates at four flow conditions the prediction agrees with measurements to 2.5 dB rms over 84 comparisons, against 4.4 dB with the unscaled impedance used previously. Although the Mach number is 0.05, the chord is acoustically non-compact, and an incompressible solution rises where the measurement falls. Two of three bulk porous inserts are predicted to within 1.7 dB rms where interaction noise dominates. Narrow, equally spaced peaks measured on perforated plates are reproduced by none of the admittances tested; their spacing implies a source convecting at 0.62 of the free-stream speed, absent from a frozen-gust model. A parameter study shows that the perforate geometry acts almost entirely through one low-frequency admittance group, in which the hole radius cancels for holes buried in the laminar boundary layer.
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Optics
A Robust Hertz-Linewidth Quantum-Dot Coherent Swept Source with Adaptive Self-Linearization
Wei Chen, Anyao Zhu, Yueyang Zhang et al. (+9 more)
Frequency-modulated continuous-wave (FMCW) techniques underpin both coherent optical ranging and microwave radar, creating a common demand for highly coherent and highly linear frequency-chirped sources across the optical and microwave domains. Conventional
semiconductor lasers, however, are fundamentally constrained by trade-offs among linewidth, linear tunability, and operational robustness. Here, we present a robust self-linearized
quantum-dot (QD) coherent swept-source architecture through the co-design of source physics and system control. The chaos-free characteristics of QD
lasers enable stable low-quality-factor external-cavity locking, yielding a Lorentzian linewidth of 12.6 Hz. Unlike self-injection-locked
lasers, broadband external optical feedback allows the
laser to maintain high optical coherence and stable operation over a wide current-tuning range, thereby enabling robust turnkey operation together with a chirp bandwidth of 23.2 GHz. Furthermore, a statistically gated real-time iterative learning control (ILC) strategy reduces the chirp nonlinearity $(1-R^2)$ to as low as $8.96\times10^{-8}$, while maintaining excellent environmental stability under
laser-temperature variations. To demonstrate practicality, we demonstrate isolator-free coherent
LiDAR and photonic generation of frequency-agile, linearly chirped microwave waveforms, establishing a common FMCW source platform for optical ranging and radar waveform synthesis. To the best of our knowledge, we demonstrate for the first time a QD-based coherent swept source that simultaneously combines hertz-level linewidth and ultrahigh chirp linearity, which we envision as a unified source platform for FMCW signal generation and coherent sensing across the optical and microwave domains.
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All authors Wei Chen, Anyao Zhu, Yueyang Zhang, Cunyu Shi, Tao Shu, Taijie Li, Gaopeng Wang, Zhile Wu, Liang Tang, Ying Yu, Chenlei Li, Daoxin Dai
Optics
Single-Photon Nonlinearity from a Nanobeam with a Quantum Dot
Abhijit Biswas, Neelesh Kumar Vij, Allan S. Bracker et al. (+3 more)
An efficient single-
photon nonlinearity is a key resource for photonic
quantum technologies. Single-
photon nonlinearities have been demonstrated with
quantum dots (QDs) across a range of cavity and waveguide geometries. However, none of these realizations simultaneously provide high-efficiency direct fiber coupling and compatibility with scalable on-chip integration. The nanobeam cavity addresses these limitations through its in-plane geometry, which enables highly efficient, direct fiber coupling alongside scalable homogeneous and heterogeneous on-chip integration. Here, we report a single-
photon nonlinearity from a nanobeam cavity coupled to a single
quantum dot. The nanobeam interfaces directly with a single-mode fiber with an efficiency of 60%. Driven by resonant picosecond pulses, the platform achieves a single-
photon nonlinearity with a low threshold of 0.24 incident
photons per pulse. The system operates in the strong-coupling regime, exhibiting a coupling rate of g/2{\pi} = 29.1 GHz and a cooperativity of C = 3.98. These results establish the nanobeam cavity-QD system as a compact, chip-integrable, and fiber-compatible building block for scalable photonic
quantum technologies.
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All authors Abhijit Biswas, Neelesh Kumar Vij, Allan S. Bracker, Margaret Stevens, Joel Q. Grim, Edo Waks
Chemical Physics
Anomalous pressure-dependent viscosity of basaltic melts and its role in asthenosphere melt accumulation
Hongkun Zeng, Peiyu Zhang, Liang Yuan et al. (+3 more)
The asthenosphere's mechanical weakness enables plate tectonics, but its origin is debated. Partial melt has been proposed to cause this softening, yet recent studies suggest that the measured viscosity minimum in basaltic melts, an essential control on melt mobility, is an experimental artifact. Using
quantum mechanics-based, machine learning-accelerated molecular dynamics, we extend simulation timescales by more than a factor of 1000 and achieve percent-level precision. We show that basaltic melt exhibits a robust viscosity minimum (approximately 20% below 1-bar values) at approximately 3 GPa, driven by pressure-induced reorganization of aluminum coordination that facilitates shear relaxation while silicon-oxygen polyhedra remain structurally rigid. Our results reveal a depth-dependent rheological transition: melt mobility peaks below approximately 150 km, promoting efficient extraction, but declines sharply during ascent, causing melt to stagnate beneath the lithosphere. This mechanism provides a physical basis for the dual seismic signatures of a melt-depleted deep asthenosphere and a melt-enriched layer near the lithosphere-asthenosphere boundary.
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All authors Hongkun Zeng, Peiyu Zhang, Liang Yuan, Youjun Zhang, Xiang Wu, Junfeng Zhang
Atomic Physics
Attosecond circular-dichroism spectroscopy of hole ring currents
Guangru Bai, Zhihui Lyu, Jinlei Liu et al. (+2 more)
Ultrafast ionization of atoms by circularly polarized few-cycle
laser pulses generates a hole ring currents, offering a route for ultrafast manipulation of magnetism. Here we explore the subcycle formation of these currents whose circulation direction is determined by the driving-field helicity, whereas their magnitude is governed by the
quantum coherence of the residual ion. We show that the correlated ion-photoelectron dynamics can be probed with attosecond transient-absorption circular dichroism. Using the Wigner-Eckart
theorem, we derive a linear relation between state-resolved dichroic absorption and the orbital and
spin angular-momentum projections of the hole, thereby extending the Thole-Carra
magnetic CD sum rules from static X-ray spectroscopy to attosecond electron dynamics. The modulation depth of the dichroic signal provides a direct optical measure of the coherence injected by ionization, and its dependence on the pump-pulse duration reveals a competition between coherence build-up and ionization-induced dephasing. These findings demonstrate the potential of attosecond circular dichroism for probing ionic coherence and highlight the role of
quantum coherence in ultrafast angular momentum exchange between light and matter.
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All authors Guangru Bai, Zhihui Lyu, Jinlei Liu, Jing Zhao, Zengxiu Zhao
Optics
Accurate recovery of the two linewidths hidden in laser beatnote statistics
Jingming Chen, Yuanchen Qi, Yuzheng Pang et al. (+12 more)
Photons from ultrastable
lasers can remain coherent over distances approaching the Earth-Sun separation, enabling optical clocks projected to lose less than one second over the age of the Universe. Yet characterizing these
photons poses an identifiability problem: a two-
laser heterodyne measurement produces a single beatnote linewidth that conflates contributions from both
lasers. For more than half a century, the standard solution has been the three-cornered-hat (TCH) method, which requires three independent ultrastable
lasers. Here we derive the mathematical form and elucidate the physical origin of asymmetric beatnote-linewidth distributions arising from finite
photon wave trains, a long-observed feature not captured by canonical Gaussian or Lorentzian statistics. This finding accurately recovers two linewidths hidden in
laser beatnote statistics without a third
laser. The framework consistently captures the observed coherence-length and coherence-time statistics of
photons, while comparison with TCH measurements confirms the quantitative validity of the extracted individual linewidths across five independent ultrastable-
laser datasets spanning nearly two orders of magnitude. Most notably, the method resolves the 7.8-mHz linewidth of a cryogenic silicon-cavity
laser beating with a broader
laser. This transformative function of beatnote-linewidth distributions, together with the resulting method, could fundamentally advance optical clocks and precision metrology.
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All authors Jingming Chen, Yuanchen Qi, Yuzheng Pang, Jie Miao, Congyu Wang, Yuan Yao, Zhi-Ang Chen, Run-Qi Lei, Zheyi Ge, Yanyi Jiang, Xibo Zhang, Xiaopeng Xie, Jianjun Wu, Duo Pan, Jingbiao Chen
Plasma Physics
Diffusion prior for KSTAR equilibrium reconstruction under sensor dropout
Hyungkeun Nam and Jaemin Seo
We study
equilibrium reconstruction for the Korea Superconducting Tokamak Advanced Research (KSTAR) device under
magnetic sensor dropout, with a
diffusion model as the prior.
Magnetic measurements leave most components of the toroidal current density $J_\phi$ undetermined, and sensor loss leaves more of them to the prior. The
diffusion model learns only $J_\phi$, conditioned on the coil currents, the
plasma current and the product of major radius and toroidal field, which do not depend on the dropout. The physics enters through a linear forward operator built from sensor response
matrices of the LIUQE code. Because the observations are linear, a variant of decoupled annealing posterior sampling fits them with a closed-form linear correction. On measured signals of 37 KSTAR shots, we switch off a random fraction (0.0 to 0.9, ten settings) of the 124
magnetic channels in use and compare with LIUQE under the same masks, taking the full-sensor LIUQE reconstruction as the label. Both methods fit the remaining channels to a similar level. The median relative distance of $J_\phi$ from the label stays at 3.22–4.07% for the
diffusion reconstruction in all settings, whereas that of LIUQE reaches 11.89% at dropout 0.9. At dropout 0.5–0.9, the
diffusion reconstruction is closer to the label on 27–37 of the 37 shots. At low dropout, LIUQE is closer on most shots. For the derived flux, the
diffusion reconstruction is closer on 21–36 shots at dropout 0.5–0.9, and its error at high dropout comes from the vessel current estimate, not from the prior.
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Accelerator Physics
Calculation of the temporal structure for a pulsed slow positron beam based on superconducting accelerator
H. Q. Zhang, P. Kuang, Y. H. Hu et al. (+4 more)
The development of superconducting accelerator (SCA) provides a novel approach to generating pulsed slow positron beams with high time resolution and high intensity. SCAs can produce electron beams with repetition frequencies on the order of MHz and pulse widths of less than 100 ps. A pulsed positron beam based on SCA can, to a certain extent, preserve the excellent temporal structure of the primary electron beam. However, thermalization,
diffusion, and surface re-emission of positrons in the moderator will inevitably lead to time broadening of positron pulses. In this paper, a calculation model coupling Geant4 Monte Carlo simulations with positron
diffusion theory is established to evaluate the effect of the positron moderation process on time broadening. After being moderated by a tungsten foil, the initial time broadening of the pulsed slow positron beam is approximately 320 ps. By combining the time broadening calculation of pulsed beam during its transport, it is expected that the pulsed slow positron beam generated by the SCA, can be directly applied to the measurement of positron annihilation lifetime.
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All authors H. Q. Zhang, P. Kuang, Y. H. Hu, F. Y. Liu, X. Z. Cao, B. Y. Wang, X. P. Li
Plasma Physics
Experimental demonstration of broadband-laser suppression of cross-beam energy transfer
Guoxiao Xu, Xiaoran Li, Ning Kang et al. (+22 more)
In direct-drive inertial confinement fusion (ICF), cross-beam energy transfer (CBET) redirects a significant fraction of the incident
laser energy out of the
plasma. We report the experimental demonstration that broadband
lasers reduce CBET-enhanced reflected-light return, performed at the low-coherence Kunwu
laser facility with two crossed beams of 0.6% bandwidth and up to 550J at $\sim$2.6$\times$10$^{14}$ W/cm$^{2}$. A coupled ray-tracing model shows that the strong CBET amplification of narrowband reflected light is much weaker under broadband illumination. In symmetric incidence condition of two orthogonal beams, the total fractional scattered energy decreases from 7.57% to 4.64%; in asymmetric incidence condition, which separates stimulated Brillouin scattering (SBS) from specular reflection, the SBS fraction decreases from 3.75% to 0.46% and the specular-reflection fraction decreases from approximately 2.2% to 1.3%. These results establish broadband
lasers as an effective, experimentally validated approach to reducing energy escape through CBET-enhanced reflection in direct-drive ICF.
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All authors Guoxiao Xu, Xiaoran Li, Ning Kang, Huiya Liu, Liang Hao, Zhiyuan Li, Guowei Yang, Honghai An, Xichen Zhou, Jian Wang, Lin Yi, Jun Xiong, Zhiyong Xie, Junjian Ye, Yuchun Tu, Zhiheng Fang, Guo Jia, Wei Wang, Lan Xia, Wei Feng, Lailin Ji, Xiaohui Zhao, Anle Lei, Lifeng Wang, Yanqi Gao
Computational Physics · Cross-listed from cs.LG
SCOPE: Observation-Conditioned Full-Target Prediction for Sparse PDE Inference
Ruichen Xu, Siyao Wang, Fang Wan et al. (+8 more)
Recovering complete physical fields from sparse observations is challenging because the measurements may not uniquely determine the underlying state.
Diffusion-based PDE solvers address this problem through iterative sampling whereas neural operators provide deterministic one-pass predictions. We propose SCOPE (Sparse-Context Observability-aware Predictive
Embeddings) to recover complete PDE fields from sparse observations by coupling full-field latent prediction with physical reconstruction. A shared decoder reconstructs fields from both predicted and complete-view representations so that representation learning is guided by both physical recovery and latent matching. We derive a quadratic risk decomposition at fixed teacher-decoder pairs showing why optimal latent prediction need not yield optimal field reconstruction. We also establish sufficient conditions for decoder improvements on complete inputs to transfer to recovery from partial observations. Experiments across five PDE settings show that SCOPE outperforms mask-aware neural operators on all ten forward and inverse tasks and achieves lower errors than those reported for
diffusion-based solvers including DiffusionPDE and FunDPS. Decoder-only adaptation further improves recovery without retraining the backbone while retaining deterministic single-pass inference.
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All authors Ruichen Xu, Siyao Wang, Fang Wan, Jiacheng Qiu, Wenhan Gao, Jiaxing Zhang, Linsey Pang, Ravid Shwartz-Ziv, Prakhar Mehrotra, Yann LeCun, Yuefan Deng
Computational Physics · Cross-listed from cs.LG
PDE-OBS: Controlled Evaluation Across Observation Patterns
Ruichen Xu, Siyao Wang, Fang Wan et al. (+7 more)
Physical-field reconstruction and forecasting depend on both measurement density and spatial layout, yet evaluation under a single observation pattern does not characterize performance when that pattern changes. We introduce PDE-OBS, an integrated benchmarking platform spanning numerical data generation, model training, and inference and evaluation under varying observation conditions. It combines 560,000 fields and trajectories from seven partial differential equation families with configurable observation operators and seven adapted baseline methods for stationary reconstruction and short-horizon forecasting. Separating observation construction from physical records allows users to specify parameterized patterns and deterministic mixtures for training and testing while preserving prediction targets and data splits. The evaluation protocol uses references trained for each test pattern to compare models on identical test observations and targets, alongside equal-count groups for spatial-layout comparisons. On a 14,000-record subset, we evaluate 441 trained models under nine test patterns, yielding 3,969 evaluations. Mean cross-pattern error exceeds mean matched-pattern error in all 49 PDE-method pairs, and this finding persists in a configuration-matched subset of 117 models. Denser test observations do not consistently reduce error for a fixed model. Mixed-pattern training on five completed pairs reduces large single-pattern transfer errors, although destination-trained references usually remain more accurate. Together, the
benchmark and findings support systematic evaluation of observation-pattern sensitivity and provide a reusable workflow for developing methods under changing measurement conditions. Code: https://github.com/ru1ch3n/PDE-OBS.
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All authors Ruichen Xu, Siyao Wang, Fang Wan, Jiacheng Qiu, Wenhan Gao, Jiaxing Zhang, Linsey Pang, Ravid Shwartz-Ziv, Yann LeCun, Yuefan Deng
Computational Physics
TT-FDTD: Tensor Train Accelerated Three-Dimensional FDTD With Logarithmic Cost of Spatial Operators
Chris Nguyen and Vladimir Okhmatovski
Quantized tensor-train (QTT) compression is incorporated into a full-vector three-dimensional scattered-field finite-difference time-domain (FDTD) formulation on uniform Yee grids. All six electromagnetic-field components, material-dependent update coefficients, equivalent-current sources, and staggered finite-difference operators are represented in compatible QTT form. Gaussian regularization of voxelized material interfaces is used to reduce the coefficient ranks generated by abrupt dielectric and conductivity transitions. The formulation is evaluated for an anatomically heterogeneous human-head model and a homogeneous dielectric sphere on grids containing up to $512^3$ spatial
cells. The reported results show that interface smoothing substantially reduces material-coefficient ranks and that the TT–FDTD solution reproduces the full-grid transient fields with pointwise absolute errors on the order of $10^{-4}$ in the examined slices. Compared with conventional FDTD, the tensor representation greatly reduces storage at fine discretizations, although tensor contractions and recompression introduce additional per-step computational cost. These results demonstrate the feasibility and
memory–time tradeoff of QTT-accelerated three-dimensional FDTD for large structured-grid simulations.
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Physics and Society
Travel Mode- and Purpose-Specific Origin-Destination Matrices for England and Wales from Fused Travel Survey and Mobile Network Data
Bowen Zhang, Chen Zhong, Mingfei Ma et al. (+1 more)
Origin-destination (OD)
matrices sit behind much of quantitative transport planning, from model calibration and accessibility analysis to the appraisal of new services and development. The increasing emphasis on place-based solutions requires mobility data that can support decision-making not only at the strategic level, but also at finer spatial scales. This requires up-to-date OD evidence at small-area resolution, disaggregated by travel mode and purpose, which remains either inaccessible or unavailable. In this work, we present dense MSOA-to-MSOA OD
matrices for England and Wales, segmented by seven travel modes and representative time periods, with eight trip purposes for the weekday morning peak. The
matrices are built by calibrating aggregate mobile network data provided by BT against National Travel Survey (NTS), census and trip-rate evidence, preserving the observed spatial structure of movement while referencing its age, mode and purpose composition to the survey. The open-source data processing pipeline is released alongside the
matrices, so that the construction of the
dataset can be inspected in full and adapted to other years, regions or assumptions.
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All authors Bowen Zhang, Chen Zhong, Mingfei Ma, James Golding-Graham
Medical Physics
Quantifying the Impact of Upright Patient Positioning on Cardiac Substructures Using Deep Learning
Nicholas Summerfield, Yuhao Yan, Chase Ruff et al. (+4 more)
Upright patient positioners with diagnostic-quality vertical CT at treatment isocenter may improve image-guided radiation therapy (RT). However, cardiac substructure (CS) geometry in upright patients remains insufficiently characterized. This work evaluated if a supine-trained deep-learning (DL) CS segmentation model generalizes to upright CT images and quantified posture-dependent CS changes in thoracic patients, to assess potential CS-sparing benefits. 8 thoracic
proton therapy patients underwent paired supine/upright 4DCT imaging. 20 CS and lungs were manually labeled on both
datasets for positional comparisons. A previously developed supine-trained, DL pipeline generated the same CS, and performance was evaluated using Dice similarity coefficient (DSC) and 95% Hausdorff distance (HD95). Upright CTs were rigidly registered to corresponding supine CTs by aligning the thoracic vertebrae, and CS centroid shifts were measured in the registered coordinate frame and relative to the carina. Paired differences were assessed using Wilcoxon signed-rank tests (p<0.05). The DL model successfully predicted all 20 CS on both upright (DSC, 0.65(0.24); HD95, 7.6(5.6)mm) and supine (DSC, 0.72(0.19); HD95, 5.8(2.6)mm) images yet with lower (p<0.05) performance upright. Upright positioning significantly increased median lung volume by 20.6% (range, -8.9%-42.8%). After vertebral
alignment, most CS centroids shifted significantly inferior (median heart shift, 23mm; range, 18-37mm) and anterior (median heart shift, 5.0mm; range, 1.0-13.0mm) when upright. Relative to the carina, most CS shifted significantly inferior and closer anterior-posterior. A supine-trained DL model generalized to upright CT images for CS segmentation. Upright positioning produced increased lung volumes and significant inferior CS displacement, suggesting favorable geometry changes that may support cardiac-sparing workflows.
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All authors Nicholas Summerfield, Yuhao Yan, Chase Ruff, Mark Pankuch, Shae Gans, Niek Schreuder, Carri K Glide-Hurst
Optics
Acoustoelectrically enhanced acousto-optic modulation in an integrated silicon nitride and thin film lithium niobate platform
Matthew J. Storey, John H. Dallyn, Kiyan Hocek et al. (+5 more)
Acoustoelectric interactions in piezoelectric-
semiconductor heterostructures allow the propagation characteristics of microwave frequency
phonons in piezoelectric media to be controlled and radically enhanced, providing electrically controllable
phonon gain, large velocity tuning, isolation, and circulation, as well as extremely large electron-mediated phononic nonlinearities. Here, for the first time, we create such a piezoelectric-
semiconductor heterostructure with lithium-niobate-on-
insulator and InGaAs that also supports guided optical modes through the addition of a silicon nitride waveguide and modification of the acoustic materials to provide an optical lower cladding. We use this new architecture to demonstrate acoustoelectrically enhanced acousto-optic modulation, where 1 GHz
phonons are piezoelectrically generated and acoustoelectrically amplified on-chip by up to 60 dB before impinging on the optical waveguide, providing pure phase modulation with a $V_\pi L$ figure-of-merit of 0.077 V-cm while only consuming 3.77 mW of DC electrical power to provide the amplification. We then consider future applications enabled by these functionalities and describe a novel tunable optical delay and an optoelectronic oscillator (OEO) analog—an acoustoelectrically enhanced opto-acoustic oscillator (AE-OAO). We show that using Brillouin optomechanical transduction and acoustoelectrically lossless acoustic time delay, the AE-OAO could replace kilometers of optical fiber delay used in OEOs but on a single, centimeter-scale chip.
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All authors Matthew J. Storey, John H. Dallyn, Kiyan Hocek, Michael Miller, Peter T. Rakich, Scott A. Diddams, Nils T. Otterstrom, Matt Eichenfield
Optics · Cross-listed from quant-ph
Transverse momentum as the counter-diabatic generator in bent waveguide couplers
Yu-kai Lee and Shuo-Yen Tseng
Bending the axis of a mode-
evolution coupler suppresses the nonadiabatic coupling between its supermodes, and bent couplers of this kind were recently shown to realize the counter-diabatic (CD) protocol. Here we identify the operator responsible. Rigid lateral displacement of a waveguide structure is generated by the transverse momentum $\hat p_x$, whose diagonal
matrix elements vanish in a real supermode basis and whose off-diagonal element is purely imaginary; in a two-mode system such an operator is proportional to $\sy$. The CD term of a two-waveguide coupler is itself proportional to $\sy$, while the detuning and the coupling, the two parameters set by the waveguide widths and spacing, lie in the $\sigma_z$–$\sigma_x$ plane and cannot produce it. The transverse momentum is therefore the CD generator of the bent coupler, by necessity rather than by design. Equating the term it supplies to the nonadiabatic coupling gives the axis slope in closed form as a ratio of two
matrix elements of the unperturbed supermodes at a single cross section, which a commutator identity recasts in coupled-mode variables as $\dot{\xo}=\dot\theta/(\gamma\dbeta^{2})$. The expression agrees with the numerical offset search to $0.3\%$ and requires no search. Beam propagation simulations confirm the design and compare it, for the first time, with the CD protocol realized by
unitary transformation in a straight coupler built from the same reference structure. The two devices reach $0.994$ and $1.000$ supermode fidelity where the untreated coupler reaches $0.886$, and agree in bandwidth and fabrication tolerance, while their internal trajectories differ by exactly the frame transformation that relates them.
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Physics and Society
Hybrid Work and the Restructuring of Urban Mobility in U.S. Cities
Baoqi Eileen Chen and Marta C. González
Entering the post-pandemic era, cities navigate a new normal shaped by hybrid work and space-time flexibility, but existing evidence is spatially scattered and temporally limited. Here we develop an analytical approach that examines this reorganization through three dimensions: remote work adoption via sector composition, daily travel behavior via trip-level metrics, and functional urban form via mobility-derived measures. To capture the interplay of urban dynamics, we synthesize three complementary spatial metrics. In particular, coupling overall trip centrality with work-trip concentration differentiates whether employment and daily activity organize around the same centers. Applied to population-scale data across 15 U.S. metropolitan areas spanning 2019-2024, our approach shows that daily car travel increased despite elevated remote work, a pattern consistent across cities with distinct spatial structures. Decomposition and regression identify trip frequency as the primary contributor to VKT growth, moderated by compact urban form and concentrated employment. The approach provides a replicable framework for comparative study of post-pandemic urban mobility.
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Data Analysis and Statistics
Attributing extreme-event probability to a source variable
Daniel F. T. Hagan
Information-flow theory quantifies directional coupling through the rate of change of a target's Shannon
entropy, a bulk functional insensitive to the tail of the distribution. We ask instead how a source variable contributes to the probability that the target exceeds a threshold. For source-additive drift the source's share of the marginal probability current is exact, and it separates into a mean-forcing part and a conditional-excess part that vanishes under independence. An identity links the two descriptions: the Liang information flow is the density-weighted mean of the derivative of the specific source current, whereas the exceedance current is its level at the threshold. This explains why
entropy-based coupling collapses in saturated regimes where the source contributes most to the extreme; the Rényi information flow, a higher-order expansion and a Fisher-normalised response fail for the same reason. The flux decomposition, although exact, does not attribute: its terms are gross transports that nearly cancel. The quantity that does attribute is an adjoint response built from the backward generator which, read as a relative change, is uniformly accurate across two decades of event probability. We map the operating envelope of the
estimator under omitted drivers, hidden slow
memory, state-dependent coupling and multiplicative noise. Under correct specification the attribution carries a reproducible shortfall of ten to twenty-five per cent; the misspecifications we test bias it upward by up to ninety per cent. Applied to the 2003 European and 2010 Russian heatwaves in reanalysis, the attributed contribution of soil moisture is strongly threshold dependent, rising from the per cent level at moderate thresholds to a factor of two at the rarest, so a contribution quoted without its threshold is underspecified.
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