Chemical Physics · Cross-listed from astro-ph.GA
Collisional excitation of cyclopentadiene by helium. A complete set of rate coefficients and astrophysical applications
Sándor Demes, François Lique, Marcelino Agúndez et al. (+1 more)
Complex organic molecules, including large cyclic species, are prevalent in interstellar space and play a key role in various astrochemical processes. Cyclopentadiene (c-C5H6) is a five-membered cyclic hydrocarbon recently detected in TMC-1 and some other interstellar molecular clouds. While accurate spectroscopic data were available, collisional rate coefficients for its rotational transitions were missing so far, introducing a potential limitation in the interpretation of the observations. This study aims to provide a comprehensive set of state-to-state thermal rate coefficients for the rotational excitation of c-C5H6 due to collisions with helium, crucial for non-local thermodynamic
equilibrium (non-LTE) radiative transfer modelling in astrophysical environments, and to examine how far the molecule is from thermalisation under the physical conditions of cold molecular clouds. The research employed accurate
quantum scattering calculations using the close-coupling (CC) and coupled states (CS) methods, based on a highly-correlated three-dimensional potential energy surface for the [c-C5H6 + He] collisional complex. Calculations were performed for a wide range of rotational states (from j = 0 to j \leq 25) and kinetic temperatures (from 10 to 50 K). We calculated a complete set of thermal rate coefficients for both ortho- and para-C5H6. Radiative transfer simulations demonstrated that most rotational levels of cyclopentadiene are fully thermalized under typical cold cloud conditions and exhibit minor non-LTE effects. Nevertheless, this study is the first to utilise accurate state-to-state rate coefficients for radiative transfer simulation of a large, five-membered cyclic species detected in space. This allows to draw some general conclusions and paves the way for future studies of complex astromolecules that will enable a more precise interpretation of upcoming detections.
Read the full abstract ▾
All authors Sándor Demes, François Lique, Marcelino Agúndez, José Cernicharo
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Thickness-Dependent Orbital-to-Spin Torque Signatures in Cr/Gd/Co Thin Films
Tiago de Oliveira Schneider, Michel Heidkamp, Luana Caron et al. (+5 more)
We studied orbital-torque generation in Cr(10nm)/Gd($t_{\mathrm{Gd}}$)/Co(3nm)/TaO$_x$ and the inverted stack Co(3nm)/Gd($t_{\mathrm{Gd}}$)/Cr(10nm) with $t_{\mathrm{Gd}}$ from 0 to $5\,\mathrm{nm}$ by combining electrical harmonic
Hall measurements with magnetometry. A detailed understanding of the magnetometric data is obtained by cross-sectional chemical composition mapping. The data show temperature-dependent
magnetic compensation points, while elemental analysis provides evidence of pronounced intermixing, in particular of Gd and Co layers. From the harmonic
Hall dataset we extract the damping-like (DL) and field-like (FL) torque efficiencies normalized to the applied electric field, $\xi_{\mathrm{DL}}^{E}$ and $\xi_{\mathrm{FL}}^{E}$, and interpret their dependence on the Gd interlayer thickness using two different descriptions: (i) a naive-layer model and (ii) an
alloy model that accounts for interfacial mixing. Notably, upon reversing the stack order, the FL contribution changes sign, whereas the DL contribution does not change sign within the harmonic
Hall measurements.
Read the full abstract ▾
All authors Tiago de Oliveira Schneider, Michel Heidkamp, Luana Caron, Inga Ennen, Matthias Opel, Alexey Arzumanov, Lambert Alff, Markus Meinert
Computational Physics · Cross-listed from cond-mat.str-el
Self-Healing Diffusion Monte Carlo applied to a simple fermionic model: A critical assessment of the method
Michel Caffarel, Manon Pinar and Anthony Scemama
We investigate the Self-Healing
Diffusion Monte Carlo (SHDMC) method using a one-dimensional model with periodic boundary conditions. An inversion
symmetry is introduced to mimic the antisymmetry property of fermionic wave functions, with the bosonic and fermionic sectors being modeled by the even and odd eigenstates, respectively. As in realistic fermionic systems, the nodal structure is only partially constrained by
symmetry, making this model a non-trivial testbed for nodal optimization
algorithms such as SHDMC. We show that the nodal
evolution under SHDMC iterations can be cast into a dynamical system exhibiting both attractive and repulsive fixed points. When applying SHDMC to this model in the absence of statistical noise, the fixed-node energy is found to increase during iterations and the node converges to an incorrect value. This occurs for any finite basis, even when the exact node is representable in it; the attractive fixed point approaches the exact node only as the basis becomes complete, while the convergence toward it becomes increasingly slow. We further show that this problem can be largely cured by modifying the nodal update criterion to give more importance to the nodal region. Our results suggest that, in the general case, an efficient nodal optimization may require both an improved nodal update criterion and a localized basis set allowing local distortions of the trial wave function, as is the case for this model.
Read the full abstract ▾
Fluid Dynamics
On the Non-Negativity of Longitudinal Velocity Autocorrelations in Homogeneous Isotropic Turbulence: Kinematic Constraints, Convexity, and Spectral Broadening
Pavan B. Govindaraju
A fundamental question in the statistical theory of homogeneous isotropic
turbulence is whether the longitudinal velocity autocorrelation $f(r)$ remains non-negative and if it can be shown from first principles such as kinematic realizability. While incompressibility forces the transverse correlation $g(r)$ to exhibit a negative loop ($\int_0^\infty r g(r)\,dr = 0$), the sign behavior of $f(r)$ is subtle. We show that positive-definiteness via Bochner's and Schoenberg's
theorems structurally fails to enforce pointwise positivity because the 3D spherical projection kernels are sign-changing. By mapping the problem to the one-dimensional spectrum $E_{11}(k_1)$ via the cosine transform and applying Pólya's criterion, convexity of $E_{11}(k_1)$ provides a rigorous sufficient condition for $f(r) \ge 0$. While pure Kolmogorov $-5/3$ scaling is strictly convex, physically realizable spectra with Batchelor ($k^4$) or Saffman ($k^2$) infrared scaling are necessarily concave near $k_1 = 0$. For mature broadband spectra such as the von Kármán–Pao model, high-precision quadrature confirms that the convex inertial bulk dominates, yielding strictly positive tails and demonstrating that apparent negative dips are discrete
Fourier artifacts. Also, we construct a smooth, divergence-free, finite-energy narrowband initial field that produces a genuine negative loop ($\min_r f(r) \approx -0.083$), serving as a counterexample to universal non-negativity. Spectral bandwidth is shown as the governing physical parameter, with nonlinear triad interactions rapidly broadening narrowband fields over an eddy turnover time, systematically suppressing negative excursions and preserving $f(r) \ge 0$ in mature
turbulence.
Read the full abstract ▾
Computational Physics
A Non-Isothermal Viscoplastic Constitutive Model for Clay Slip Surfaces
Saeed Tourchi, Ehsan Badakhshan, Milad Jabbarzadeh et al. (+2 more)
Clayey slip surfaces control the reactivation and long-term deformation of slow-moving landslides and may experience thermal fluctuations from
climate, seasonal ground-temperature changes, or subsurface heat sources. Experiments show that residual shear strength depends on temperature and shearing rate, yet most numerical approaches use temperature-independent strength parameters. We present a non-isothermal viscoplastic constitutive model for clayey slip surfaces implemented with zero-thickness interface elements. It includes temperature-dependent normal and tangential stiffness, progressive degradation of cohesion and friction angle, and rate-dependent viscoplastic slip governed by a non-associated flow rule. Coupling with hydraulic and thermal balance equations allows the interface response to evolve with stress state, temperature, aperture, and accumulated irreversible displacement. Validation against temperature-controlled drained ring-shear tests on bentonite and smectite-rich soils covers heating–cooling, cooling–heating, and combined thermal paths. The simulations reproduce thermal strengthening at slow shearing rates and thermal weakening or limited sensitivity at higher rates. Application to the Congress Street cut
benchmark shows that zero-thickness elements improve the representation of strain localization and progressive failure. Increasing temperature progressively degrades interface strength, increases displacement, joint aperture, and shear strain, and accelerates sliding. Temperature-dependent interface degradation can therefore reduce the apparent stability margin of clayey slopes and should be included in slope-stability assessments involving thermal fluctuations.
Read the full abstract ▾
All authors Saeed Tourchi, Ehsan Badakhshan, Milad Jabbarzadeh, Arash A. Lavasan, Jean Vaunat
Atomic Physics
Polarization measurements of the $2s$–$2p_{3/2}$ VUV transition in N$^{4+}$ excited by electron collisions
Nobuyuki Nakamura, Ryohko Ishikawa and Motoshi Goto
We present the linear polarization of the $2s$–$2p_{3/2}$ transition in Li-like N$^{4+}$ excited by electron collisions, measured at electron energies between 85 and 1000~eV. The measured polarizations are compared with theoretical values calculated using the Flexible Atomic Code (FAC). Although the overall trend that the degree of polarization decreases with increasing electron energy is reproduced, the theoretical values are systematically larger in magnitude than the experimental values. After examining possible experimental sources of depolarization, we suggest that the discrepancy likely originates from an overestimation in the theoretical model. Further theoretical and experimental investigations along the isoelectronic sequence are needed to resolve this discrepancy.
Read the full abstract ▾
Optics
Exceptional Points in Photonics: From Non-Hermitian Physics to Applications
Fan Zhang, Nikolay Solodovchenko, Dmitrii N. Maksimov et al. (+5 more)
Open photonic systems provide a versatile platform for non-Hermitian physics, enabling control over complex spectra, transport, and light-matter interactions. Exceptional points (EPs), at which
eigenvalues and eigenvectors coalesce and the governing operator becomes defective, play a central role because they combine branch-point spectral
topology, nonanalytic perturbative response, and controllable eigenstate conversion. This Review provides a unified framework for EP photonics by systematically distinguishing exceptional degeneracies according to the underlying operator, spectral variable, boundary conditions, and experimentally accessible observables. We discuss
Hamiltonian EPs, absorbing EPs associated with scattering zeros, real-frequency scattering-
matrix and Jones-
matrix EPs, Bloch and Floquet EPs, and Liouvillian EPs in open
quantum systems. We review their spectral
topology, static and dynamical encircling, higher-order exceptional structures, and coexistence with bound states in the continuum, together with applications in sensing, lasing, coherent absorption, directional scattering, polarization and wavefront control, nonlinear optics, optical storage, nonreciprocal photonics, and
quantum photonics. We also critically assess the current limitations, practical challenges, and future perspectives of EP-based photonic technologies, with particular
attention to robustness, noise, scalability, and experimentally measurable performance.
Read the full abstract ▾
All authors Fan Zhang, Nikolay Solodovchenko, Dmitrii N. Maksimov, Xuchen Wang, Mingzhao Song, Filippo Capolino, C. T. Chan, Andrey Bogdanov
Optics
Low-threshold vortex lasing in three-dimensional cavities via flatband bound states in the continuum
Zi-Xin Zhou, Weimin Wang, Huijie Li et al. (+2 more)
Bound states in the continuum (BICs) offer a robust route toward high-Q resonators and topological structured-light generation. While optically pumped BIC
lasers have advanced significantly, realizing electrically pumped
vortex lasers remains challenging due to conflicting requirements for optical confinement and carrier injection. Here, we demonstrate an electrically pumped vector
vortex laser based on a photonic
crystal-guiding layer-distributed Bragg reflector (PC-GL-DBR)
heterostructure. The photonic
crystal slab precisely tailors the
symmetry and dispersion of BIC modes, including a flatband BIC state, while an intermediate guiding layer enables optical mode engineering without directly patterning the multiple-
quantum-well active region, preserving efficient carrier injection and strong optical confinement. Under optical pumping, the device achieves single-mode lasing with a Q of 9700, a threshold of 0.129 kW/cm$^2$, and a side-mode suppression ratio of 26 dB. Crucially, room-temperature electrically pumped
vortex lasing is achieved with a low turn-on voltage of 1.8 V, a threshold current density of 0.13 kA/cm$^2$, and a cavity Q of 8600, successfully preserving the characteristic vector-
vortex emission of the topological BIC state. These results establish a practical route toward electrically driven BIC
vortex lasers for integrated structured-light sources and topological photonics.
Read the full abstract ▾
All authors Zi-Xin Zhou, Weimin Wang, Huijie Li, Yan-qing Lu, Jun-Long Kou
Optics
Reaching the optical propagation limit in temporal analog computing
Zeki Hayran
A central goal of optical computing is to perform calculations on the timescale of light propagation. Yet many analog photonic solvers require feedback, storage or field build-up before the answer becomes available, introducing additional latency that limits real-time operation. Here we introduce the concept of two-time modulation for temporal analog computing, in which the material response is independently modulated along two temporal directions, allowing the computational operator to be constructed continuously as the waveform propagates. The solution can therefore form during optical transit, without an additional solution-formation timescale. This form of temporal control allows identical copies of a waveform separated only in time to reach entirely different target outputs within a single spatial channel, and enables nonlocal integral-equation solving in a single passage. The resulting framework brings compact, programmable, real-time analog computation within reach for ultrafast optical information processing.
Read the full abstract ▾
Optics
Direct laser-written optomechanical double membranes in an optical microcavity
Lukas Tenbrake, Daniel Stachanow, Florian Giefer et al. (+4 more)
Optomechanical membrane-in-the-middle systems that comprise several coupled compliant membranes offer enhanced optomechanical coupling and collective dynamics. Recent realizations were fundamentally restricted to two membranes and to limited structural optimization of the involved membranes due to their intricate fabrication and experimental integration. Here, we present a fiber-based Fabry-Perot microcavity incorporating monolithically integrated double-membrane resonators fabricated by 3D direct
laser writing. We realize controllable mechanical mode hybridization of membranes with coupling rates of up to $J_{\mathrm{mech}}/2\pi = 0.16$ MHz, exceeding the mechanical linewidths. We demonstrate enhanced collective optomechanical coupling of the membrane stack's breathing mode, reaching collective coupling strengths of up to $g_{\mathrm{col}}^{(-)}/2\pi \approx 0.1$ MHz. Our transfer-
matrix calculations predict further substantial enhancements with realistic reductions of membrane thickness and spacing, and a larger number of membranes. Our results establish direct
laser-written membrane arrays as a scalable platform for multimode cavity optomechanics, combining tunable mechanical interactions, enhanced collective optomechanical coupling, and scalability towards larger mechanically coupled resonator systems.
Read the full abstract ▾
All authors Lukas Tenbrake, Daniel Stachanow, Florian Giefer, Jana Blechmann, Wolfgang Alt, Sebastian Hofferberth, Hannes Pfeifer
Optics
High-Speed and High-Responsivity Asymmetric Waveguide Photodiode with Low Optical Back-Reflection
Zhijun Zhang, Xuejie Gao, Qiunan Li et al. (+1 more)
We numerically demonstrate an asymmetric corner-reflector uni-traveling-carrier waveguide photodiode (UTC-WGPD) that simultaneously suppresses optical back-reflection and breaks the bandwidth-responsivity trade-off. Off-center beam coupling introduces
geometric asymmetry to eliminate retroreflection while maintaining efficient light trapping. 3D optoelectronic simulations reveal that at 1550 nm, a 15-{\mu}m^2 device exhibits a 275-GHz 3-dB bandwidth, 0.68-A/W responsivity (54.5%
quantum efficiency), and -29-dB back-reflection, achieving a 150-GHz bandwidth-efficiency product. This design offers a scalable, low-reflection detection scheme for sub-terahertz transceivers and dense photonic integration.
Read the full abstract ▾
All authors Zhijun Zhang, Xuejie Gao, Qiunan Li, Xiaoyu Mi
Optics
Design and Physical Constraints of Synthetic-Frequency Photonic Switching Fabrics
Jorge Parra
Electro-optic frequency conversion and synthetic-frequency coupling are established functions in integrated photonic devices. Their role within a multiport switching fabric, however, depends on how simultaneous optical connections share spatial paths, frequency channels, and device controls. Here, we investigate how coherent coupling among frequency modes can be incorporated into photonic switching fabrics and identify the corresponding architectural and physical constraints. We show that synthetic-frequency coupling does not increase the number of simultaneous orthogonal frequency channels when all channels are freely accessible, but can establish connections that are otherwise blocked by fixed input frequencies, channel-continuity requirements, or unavailable output channels. Under the tested conditions, coupling over the first three frequency spacings in an $8\times8$ fabric with eight frequency channels per port achieves 96.1% of the blocking reduction obtained with unrestricted inter-mode coupling. We further show that a separate frequency-only conversion stage cannot replace missing spatial connectivity. A nominal reduction in spatial switching elements instead requires a joint element whose spatial state can be programmed independently for each frequency channel. Finally, we evaluate a thin-film lithium niobate resonator model using reported electro-optic coupling and
photon-decay scales within a multistage Mach-Zehnder interferometer switching fabric. These results clarify the architectural role of synthetic-frequency coupling and the device-level requirements for incorporating it into integrated photonic switching fabrics.
Read the full abstract ▾
Instrumentation and Detectors
Helium-Gas-Cooled Cryogenic Current Comparator Integrated with a Quantum Resistance Standard
Yuma Okazaki, Takehiko Oe and Nobu-Hisa Kaneko
We report a cryogen-free cryogenic current comparator (CCC) system for precision resistance measurements. A helium-gas chamber was developed and installed on the 4 K stage of a cryogen-free dilution refrigerator equipped with a pulse-tube cryocooler. The CCC probe was housed in this chamber and was cooled through helium gas serving as a heat exchange medium. The metrological performance of this helium-gas-cooled CCC was evaluated through precision resistance-ratio measurements and found to be comparable to that obtained under
liquid-helium cooling. A
quantum Hall resistance (QHR) device was also integrated into the same refrigerator, enabling QHR/100~$\Omega$ resistance-ratio measurements. The type-A uncertainty reached the 1~n$\Omega$/$\Omega$ level within an averaging time of 100~s, and the resulting resistance-ratio measurements agreed well with conventional
liquid-helium-based measurements at the level of a few n$\Omega$/$\Omega$. The system provides this level of measurement performance while consuming less than 1~L of helium gas per thermal cycle.
Read the full abstract ▾
Medical Physics
PyDoseRT Photon: Physics-Guided Pencil-Beam Dose Calculation with Neural Priors and Residual Correction for CT and MRI
Attila Simkó, Lukas Zimmermann, Hermann Fuchs et al. (+1 more)
We present a hybrid, physics-based analytical pencil-beam (PB) dose engine, augmented by two small frozen neural physics priors, followed by a 3-D convolutional residual-correction network (U-Net). We address the DoseRAD2026 (https://doserad2026.grand-challenge.org/)
photon dose-prediction task with PyDoseRT
Photon, a GPU PB engine implemented in PyTorch and corrected toward Monte Carlo (MC) accuracy in three learned stages of decreasing physical specificity. The engine reproduces the challenge's head-less MC source exactly where it can and models the patient with a beam-quality-indexed pencil kernel evaluated at the field's fluence-weighted radiological depth, and TERMA source scaling at the interaction site. Two tiny neural priors are trained through the frozen engine and then frozen themselves: a 39k-parameter 2-D fluence correction and a 48-parameter lateral heterogeneity correction mixing mass-conserving Gaussian redistribution operators. A compact 3-D U-Net (1.36M parameters) with a sequential refinement branch then predicts, per control point (CP) in the beam's-eye-view (BEV) frame, a bounded multiplicative gain and additive residual from seven channels. All learned stages are zero-initialized, so training starts from the analytical solution. For MRI, an nnU-Net regression model synthesizes a CT that enters the identical pipeline, with consecutively, the same trained corrector as the CT track. Design choices were driven by the challenge ranking, in which runtime carries double weight. The submitted method evaluated on our local CT and MR validation
dataset achieved CP MAE 0.0086 and 0.0098, IDD distance 0.0011 and 0.0013, plan MAE 0.0024 and 0.0047, gamma pass rate (1%/1mm) 99.12% and 96.95%, with runtimes of 46s and 49s, respectively.
Read the full abstract ▾
All authors Attila Simkó, Lukas Zimmermann, Hermann Fuchs, Gerd Heilemann
Chemical Physics · Cross-listed from cond-mat.soft
Mass-conserving growth percolation in polymer gelation
Ameya Rege and Lorenz Ratke
Polymer gelation involves the emergence of a system-spanning network from growing
polymer-rich domains, yet conventional percolation models typically prescribe particle size independently of material consumption. We formulate gelation as a locally mass-conserving growth-percolation process in which Voronoi capture zones define finite material reservoirs for individual
nuclei. Local depletion determines the evolving supersaturation and limiting particle size, while particle contacts generate a dynamic network whose first spanning cluster defines the gel point. Three mechanisms, namely, interface-,
diffusion-, and
polymer-blob-controlled growth produce distinct gelation kinetics while sharing the same accessible final state. Spatial fluctuations in nucleation further generate a distribution of gelation times. The framework separates gelation from saturation and naturally captures post-gel aging as continued growth and topological maturation.
Read the full abstract ▾
Physics and Society
Behavioral calibration of mobile-phone GPS data for population-representative analyses
Nicolò Alessandro Girardini, Unchitta Kan, Eduardo López et al. (+3 more)
Mobile phone mobility data have transformed the study of human behavior, but demographic and behavioral biases can compromise their representativeness and distort population-level inference. Existing calibration approaches primarily address demographic and geographic representativeness, leaving behavioral discrepancies largely uncorrected. Here we introduce the Behavioral Population (BePop) framework, which jointly calibrates mobility data to representative demographic and behavioral distributions using census data and time-use surveys. BePop embeds mobility sequences into behavioral profiles and estimates person-level weights that align both population composition and daily activity patterns. Across three U.S. metropolitan areas, the framework consistently improves agreement between GPS-derived mobility and representative behavioral distributions, including time allocation, activity transitions, and mobility motifs. Calibration also substantially alters downstream mobility indicators, demonstrating that behavioral biases can propagate into commonly used mobility measures. Our results establish behavioral representativeness as a critical complement to demographic calibration and provide a general framework for population-representative mobility inference.
Read the full abstract ▾
All authors Nicolò Alessandro Girardini, Unchitta Kan, Eduardo López, Bruno Lepri, Lorenzo Lucchini, Simone Centellegher
Chemical Physics · Cross-listed from cs.DC
MakoXC: Rearchitecting DFT Exchange-Correlation with Matrix-Aligned and Knowledge-Organized Sparsity
Haozhi Han, Fusong Ju, Jing Bai et al. (+8 more)
Density Functional Theory (DFT) is indispensable for materials science and drug discovery, yet the exchange–correlation (XC) evaluation remains a major bottleneck due to its cubic scaling. Although linear-scaling methods exploit electronic nearsightedness to reduce asymptotic complexity, they produce irregular sparse workloads that hide implicit sparsity and prevent efficient use of modern AI accelerators. We present MakoXC, a modular
matrix-aligned XC evaluation engine that rearchitects nearsightedness-induced sparsity into regular, accelerator-friendly computations. MakoXC co-designs three key techniques: (1)
Matrix-Aligned
Cells reorganize nearsightedness-induced interactions into dense, accelerator-aligned data clusters; (2) Sparsity-Guided Activation translates deeper implicit sparsity into numerically correct structured execution for practical linear scaling; and (3) Kernel-Fused Pipeline consolidates fragmented workloads into a unified, compute-intensive execution path that fully unleashes accelerator throughput. Extensive evaluations show that MakoXC achieves average speedups of 67.8$\times$ speedup over standard XC evaluation and 4.7$\times$ over state-of-the-art linear-scaling methods. When integrated into a production-grade commercial DFT package, MakoXC scales XC evaluation to ubiquitin (1,231 atoms, def2-SVP) on 64 GPUs, enabling the end-to-end DFT calculation to complete in under five minutes. By restructuring XC evaluation into a unified, structured computation, MakoXC demonstrates how scientific workloads can achieve genuine low complexity while maximizing parallel efficiency on AI accelerators.
Read the full abstract ▾
All authors Haozhi Han, Fusong Ju, Jing Bai, Ruge Zhang, Xiang Zhao, Liang Yuan, Yunquan Zhang, Ting Cao, Liu Yunxin, Yifeng Chen, Kun Li
Medical Physics
PyDoseRT Proton: A GPU Pencil-Beam Engine with a Convolutional Residual-Correction Network for Fast Proton Dose Calculation
Lukas Zimmermann, Hermann Fuchs, Attila Simkó et al. (+1 more)
Architecture category. Hybrid method: a physics-based analytical pencil-beam (PB) dose engine followed by a 3-D convolutional residual-correction network (RepVGG-U-Net). We addressed the DoseRAD2026
proton dose-prediction task with PyDoseRT
Proton, a GPU-accelerated engine implemented in PyTorch and augmented by a learned residual toward Monte Carlo (MC) accuracy. A double-Gaussian PB kernel was calibrated to GATE/Geant4 integrated depth doses in water in two stages: a classical per-energy curve fit, then a gradient-based fit of the full 3-D dose through the PyTorch physics engine as it retains a differentiable execution path for gradient-based optimization of dose-dependent objectives. The engine computes each beamlet on a beam's-eye-view (BEV)
lattice with variance-preserving Gaussian splitting, an analytic
nuclear halo, and a
Fermi-Eyges heterogeneity term, then rotates the result into the patient frame. Additionally, a compact residual U-Net predicts an additive correction in BEV space. It is conditioned on voxelwise material-label
embeddings, a discrete energy
embedding and spot size. The same model was used for all anatomical sites (thoracic and abdominal). It was trained with a patient-space L1 objective emphasizing the scored high-dose region and multi-scale BEV deep supervision. The submitted CT configuration obtained preliminary-test beamlet MAE 0.0066, image-z IDD distance 0.0025, plan MAE 0.0049, 98.30% gamma pass rate (1%/1 mm), and DVH error 0.460.
Read the full abstract ▾
All authors Lukas Zimmermann, Hermann Fuchs, Attila Simkó, Gerd Heilemann
Optics · Cross-listed from quant-ph
Nonlocal wavefront shaping through complex media
Yanis Trouyet, Neelan Gounden, Pedro Ornelas et al. (+3 more)
Wavefront shaping is a key technique for mitigating scattering in complex media, enabling advanced imaging and optical communication. Yet existing approaches are inherently local, requiring active correction elements - such as spatial light modulators or deformable mirrors - to lie directly in the optical path of the scattered light, which limits their integration into compact imaging systems. Here, we experimentally demonstrate nonlocal wavefront shaping using spatially entangled
photon pairs. By applying a phase correction to a
photon that never interacts with the scattering medium, we compensate for the distortions experienced by its entangled partner and restore their initial spatial correlations. Our approach physically decouples the wavefront correction from the scattering medium, paving the way for imaging through complex media in compact and otherwise inaccessible systems.
Read the full abstract ▾
All authors Yanis Trouyet, Neelan Gounden, Pedro Ornelas, Patrick Cameron, Andrew Forbes, Hugo Defienne
Atomic Physics
Impact of light shift inhomogeneities on the contrast of light pulse atom interferometers
Maxime Pesche, Diego Lancheros Naranjo, Rayan Si-Ahmed et al. (+3 more)
We study the loss of the contrast in an atom interferometer when increasing the duration of Raman mirror pulses, and find the contrast decay rate to increase with the interferometer duration. We attribute this effect to the transverse spatial fluctuations of the intensity across the Raman beams, and to the dephasing induced by the associated light shifts inhomogeneities. Simulations based on the propagation of noisy synthetic Raman beams show that the contrast decay rate increases with the distance between the wavepackets at the mirror pulse, before reaching an asymptotic limit when intensity fluctuations between the two wavepackets become completely decorrelated. Finally, simulations based on the propagation of Raman beams having their measured intensity fluctuations predict contrast loss rates consistent with our measurements, confirming the detrimental role for the interferometer contrast played by intensity fluctuations across the interferometer
laser beams.
Read the full abstract ▾
All authors Maxime Pesche, Diego Lancheros Naranjo, Rayan Si-Ahmed, Gabriel Ducasse, Franck Pereira dos Santos, Sébastien Merlet
Optics
Topological charge switching in trapped polariton condensates
Jaewon Kim, Hyun Gyu Song, Daegwang Choi et al. (+1 more)
Topological charges in photonic systems provide a robust degree of freedom with direct applications in optical information processing. Bound states in the continuum (BICs) in photonic
crystal slabs inherently carry such quantized topological charges, yet they are topologically protected, making active reconfiguration fundamentally challenging. Here, we demonstrate topological charge switching in trapped BIC polariton condensates in a photonic
crystal, where spatial modulation of the photonic
crystals supports multiple confined states, each carrying a distinct charge. Trapped condensates within the Dirac bandgap are expelled into the leaky band via polariton blueshift, enabling single-mode selection by solely tuning the excitation power. This work offers a platform for optically controlling topological charges by harnessing polariton nonlinearity.
Read the full abstract ▾
All authors Jaewon Kim, Hyun Gyu Song, Daegwang Choi, Yong-Hoon Cho
Instrumentation and Detectors
Time performance of USTC-IME LGAD under synchrotron light source focused X-ray
Tianao Wang, De Zhang, Zheng Liang et al. (+9 more)
The time performance of Low Gain Avalanche Diodes (LGADs), designed by the University of Science and Technology of China (USTC) and fabricated by the Institute of Microelectronics of Chinese Academy of Sciences (IME), was characterized at the Shanghai Synchrotron Radiation Facility (SSRF). The experiment was conducted at the BL16B1 beamline, which delivers a focused X-ray beam with a diameter of 500 \textmu\text{m}, a repetition period of 2 ns, and a
photon energy of 10 keV. Using a fast oscilloscope, waveforms containing continuous signal pulses were recorded within a 50 ns time window. The LGAD under test successfully resolved the 2 ns period of the SSRF. To mitigate pile-up effects and extract pulse-by-pulse information from the acquired waveforms, a waveform-level global template fitting method was employed. The time resolution was then estimated using a combined profile likelihood approach, with a restricted maximum-likelihood (REML) correction accounting for the per-waveform degrees of freedom, yielding a value of 136.8 $\pm$ 0.15 (stat.) $\pm$ 11.9 (syst.) ps. The complete reconstruction and fitting chain was validated end-to-end using simulated waveforms in which the timing deviations of individual large pulses were drawn from Gaussian distributions with fixed standard deviations. The effect of random
photon absorption depth on the time resolution of LGADs was studied through dedicated simulations.
Read the full abstract ▾
All authors Tianao Wang, De Zhang, Zheng Liang, Chaozhi Li, Jiaqi Luo, Yu Nie, Tianshuo Yue, Zebo Tang, Hao Liang, Tongpu Yu, Wanbing He, Yanwen Liu
Applied Physics · Cross-listed from nlin.CG
Optical free space extreme learning machine for the implementation of emergent complex systems
Elena Moreno, Fernando Soldevila and Daniel Torrent
Cellular automata conform a set of computational models which evolve with a reduced set of simple rules, yet still are able to show extremely complex emergent phenomena such as fractals and universal computation. Despite their apparent simplicity, they have shown great potential in simulating natural systems and solving challenging computational tasks such as classification and image generation. Instead of implementing cellular automata purely at the software level, it is desirable to design novel analog computing platforms that physically evolve following the automata's underlying rules, thereby reducing power requirements and latency. Here, we introduce an optical extreme learning machine for the simulation of a wide range of cellular automata. Our system operates in free space, and uses a spatial light modulator to encode the
evolution rules of the system, while coherent wave propagation performs the corresponding computations. Our results demonstrate a simple, fully-programmable, cost and power efficient, and easy to build and align platform for the implementation of a wide range of complex computational systems such as elementary cellular automata, Conway's Game of Life, and two-dimensional Turing machines.
Read the full abstract ▾
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Beyond Panchromatic Absorption: Deciphering the Excited-State Maze from Light Absorption to Photocatalysis in Dye-Sensitized MOFs
Manuela L. Kim, Mauricio E. Calvo, Katsuya Teshima et al. (+2 more)
Metal–organic frameworks (MOFs) are promising photocatalysts whose visible-light absorption can be extended through linker functionalization; however, a red-shifted absorption edge does not guarantee enhanced efficiency. Here, we establish a multi-spectroscopic framework to decipher the photophysical fate of photoexcited states in diazo-sensitized UiO-66 using 2D photoluminescence (PL/PLE) mapping and wavelength-resolved continuous-wave X-band photo-EPR. By correlating visible absorption with photo-EPR and PLE action spectra, we distinguish a productive red shift from a non-productive emissive red shift. In highly active UiO-66-Anisole (97% activity relative to \ch{TiO2}), photo-EPR tracks the new absorption band, confirming that excitation populates a charge-transfer pathway yielding persistent,
spin-separated states. Conversely, poorly active UiO-66-$\beta$-naphthol (4%) exhibits an extended visible absorption tracked by PLE but not photo-EPR. This reflects excitation trapping in a localized state caused by an ortho-$\mathrm{OH}$ group forming a rigid intramolecular hydrogen bond, which locks the keto-hydrazone tautomer and disrupts the conjugated azo bridge. A new optical overlap descriptor ($S_{\mathrm{Exc}}$) quantitatively captures this trade-off across the series. We demonstrate that photosensitizer design must suppress rigid tautomeric traps and target specific charge-transfer
manifolds ($\lambda \le 500$~nm) rather than merely maximizing apparent panchromatic absorption breadth.
Read the full abstract ▾
All authors Manuela L. Kim, Mauricio E. Calvo, Katsuya Teshima, Fabio La Mattina, Eugenio H. Otal
Atomic Physics · Cross-listed from quant-ph
Thermal screening and critical scaling of quantum energy teleportation in a harmonic chain
Taisanul Haque
We develop a finite-temperature Gaussian-state formulation of
quantum energy teleportation in the one-dimensional harmonic chain. For Gibbs states, the optimized measurement-feedback protocol reduces to thermal two-point functions. In the single-site protocol, the extracted energy is governed by a single correlator, which makes the thermodynamic and near-critical limits analytically tractable. At fixed finite temperature, the extracted energy is exponentially screened with distance and is controlled by a thermal correlation length for both critical and non-critical $\alpha$. In the zero-temperature critical limit taken after the thermodynamic limit, we derive the exact asymptotic law $E_{\mathrm{ext}}\sim d^{-4}$. Numerical results confirm both regimes and resolve the crossover responsible for the apparent drift of the effective decay exponent at intermediate distances. We also analyze squeezed Gaussian measurements and show that they modify the extraction prefactor: $p-$squeezing enhances the extracted energy, whereas $q-$squeezing suppresses it, without changing the large-distance scaling.
Read the full abstract ▾
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Fourier Neural Operators for Composition-Driven Crystal Structure Discovery
Zhijie Yu, Jingyu Li, Yang Huang et al. (+1 more)
Crystalline materials discovery is essential for energy, electronics, and catalysis, but the vast chemical and structural space makes exhaustive screening infeasible. Existing voxel-based methods are limited by the local receptive fields of three-dimensional convolutional neural networks and the posterior collapse of high-dimensional variational autoencoders. Here, we develop a
Fourier Neural Operator (FNO)-based
crystal-field solver that maps a prescribed chemical formula and
lattice parameters to periodic number-density and electron-density fields. By operating on global
Fourier modes, the solver captures long-range correlations in periodic
crystal fields beyond conventional local convolutions. Building on this solver, we construct a coupled generation-solving framework in which a conditional variational autoencoder generates diverse candidate
lattice parameters in a low-dimensional basis-coefficient space, followed by density-field prediction and atomic reconstruction through peak detection, position optimization, and weight optimization. The reconstructed structures are further screened using voxel-level filtering, machine-learning interatomic-potential relaxation, and first-principle calculations. The framework generates novel structures across 104 chemical formulas with competitive reconstruction accuracy, demonstrating high generative diversity and structural validity. By extending
Fourier neural operators to periodic
crystal fields and coupling them with composition-conditioned
lattice generation, our approach provides a scalable route to
crystal structure discovery from prescribed chemical compositions.
Read the full abstract ▾
All authors Zhijie Yu, Jingyu Li, Yang Huang, Jingrun Chen
Optics
Direct Optimization of a 3D Finite-Source Reflector via Neural-Network Parameterization
Roel Hacking, Lisa Kusch, Martijn Anthonissen et al. (+1 more)
We present a direct optimization method for three-dimensional freeform reflectors that transform the light of a finite-étendue source into a prescribed far-field angular intensity distribution. The reflector profile is represented by a small neural network (a multilayer perceptron), which is trained end-to-end through a differentiable ray-tracing objective. We furthermore parameterize the emission directions in gnomonic coordinates, and show how we use this to ensure that every emitted ray intersects the reflector. At each iteration, the network is converted to a bicubic spline representation for ray-tracing efficiency, and intersections with this smooth surface are solved by a damped Newton solve, with gradients computed via the implicit function
theorem. The traced output distribution is compared with the desired target on a 'soft' histogram, under an $H^{-1}$-type spectral weighting that emphasizes long-range transport of flux to improve convergence. Optimization is performed using a BFGS method with self-scaled Broyden updates and a plateau-perturbation rule to prevent stalling. The method converges reliably within seconds on a single GPU for all examples tested.
Read the full abstract ▾
All authors Roel Hacking, Lisa Kusch, Martijn Anthonissen, Wilbert IJzerman
Data Analysis and Statistics · Cross-listed from cs.LG
iPINN for Broadband CARS Phase Retrieval: A Framework for Function Approximation and Inverse Modeling Problems in Nonlinear Spectroscopy
Ravi Teja Vulchi, Carl Messerschmidt, Mohammadsadegh Vafaeinezhad et al. (+4 more)
Phase
retrieval in broadband coherent anti-Stokes Raman spectroscopy (BCARS) is an ill-posed inverse problem. The Raman-like signal is encoded in the imaginary part of the resonant susceptibility, which mixes coherently with a non-resonant background (NRB) that varies across acquisitions. We introduce an inverse physics-informed neural network (iPINN) that predicts Lorentzian peak parameters from raw BCARS spectra and reconstructs the resonant susceptibility through a differentiable analytical forward model. A
transformer encoder assigns spectral features to 24 learnable peak slots, and a multi-view consistency loss enforces invariance across NRB pattern, NRB strength, and noise. Unlike direct spectral regression approaches, the method retains accuracy under varying acquisition conditions. On a public
benchmark, iPINN achieves the lowest error among the tested baselines (MAE 0.016 vs. next-best 0.046). On 28 zero-shot test spectra acquired across seven solvents and four focal positions, accuracy is depth-invariant in five of seven solvents. These results show that inverse parametric prediction with a differentiable physical decoder supports robust phase
retrieval across measurement conditions.
Read the full abstract ▾
All authors Ravi Teja Vulchi, Carl Messerschmidt, Mohammadsadegh Vafaeinezhad, Rajendhar Junjuri, Tobias Meyer-Zedler, Juergen Popp, Thomas Bocklitz
Computational Physics · Cross-listed from math.OC
Stochastic Optimization of Tree Tensor Networks
Marius Willner, Maximilian Scharf, André Uschmajew et al. (+2 more)
Tensor networks, originally developed for
quantum many-body physics, are promising models for machine learning. We derive
stochastic Riemannian optimizers for tree tensor networks (TTNs) on both their parameter and quotient
manifolds, including adaptive and learning-rate-free schemes suitable for minibatch training. Using a hybrid CNN-TTN architecture, we evaluate the methods on Fashion-MNIST, CIFAR10, and Imagenette. The proposed optimizers achieve predictive performance comparable to unconstrained optimization while enabling numerically stable downstream compression.
Read the full abstract ▾
All authors Marius Willner, Maximilian Scharf, André Uschmajew, Timo Felser, Marco Trenti
Optics
Spatio-temporal coherent molding and retrieval of pulsed signals in optical waveguides
Nika Durishvili, Ramaz Khomeriki, Vakhtang Jandieri et al. (+3 more)
Optical waveguides are key elements for high fidelity, long distance optical communications. Coupled waveguide arrays allow for higher information density, steerting the propagation direction, and for encoding information. However, due to the mixing of relative phases for short pulses containing multiple waveguide-mode frequencies, a process for retrieving an encoded input state once these signals undergo coherent propagation remains elusive. A concept is presented to extract with high fidelity the phase-encrypted input signal from spatio-temporal propagated states. As a realization, an array of coupled waveguides is suggested with the
retrieval mechanism being realized by local phase shifts that comply with the identified
retrieval concept. Three dimensional full-wave electromagnetic simulations for broadband optical signals in coupled dielectric waveguides confirm the validity of the scheme and the high fidelity of information
retrieval pointing to potential applications, for instance in ultrafast coherent coding and decoding of information imprinted on pulse sequences.
Read the full abstract ▾
All authors Nika Durishvili, Ramaz Khomeriki, Vakhtang Jandieri, Douglas H. Werner, Daniel Erni, Jamal Berakdar