Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Physics

physics Watch Physics

Thursday 21 May

Fluid Dynamics

Perpendicular rod-airfoil aeroacoustics: experiments and modelling of interaction noise

Marios I. Spiropoulos, Filipe R. Amaral, Florent Margnat et al. (+2 more)

During the phase of landing, an important aircraft-noise source emanates from the interaction of the landing-gear wake with the deployed flap. In the present work we cast this problem in an academic framework, by studying a simplified configuration that consists of a cylinder placed upstream and perpendicularly to a symmetrical NACA-0012 airfoil. An experimental campaign is conducted, followed by modelling approaches to explore the flow phenomena associated with the acoustic field. Simultaneous acoustic and stereoscopic Time-Resolved Particle Image Velocimetry measurements are taken, to study the sound and flow-fields generated by the interaction of the cylinder-wake with the downstream airfoil, when the spans of the two objects are orthogonally aligned. The experimental data highlight the three-dimensional nature of the problem. The maximum sound pressure levels are obtained at frequencies close to $St \equiv f d/U = 0.38$ (cylinder's drag fluctuation frequency), where also the maximum linear coherence between the acoustic and cylinder-span-oriented fluctuation velocity is observed, demonstrating that the measured acoustic-field is an outcome of the three-dimensional cylinder-wake. Powell-Howe vortex-sound theory combined with an acoustically compact Green function for the NACA-0012 are employed for the aeroacoustic modelling. A linearised source-term based on the analysed experimental data is used as input to estimate the acoustic field and identify the acoustically important coherent structures of the flow-field. A reasonable agreement is obtained between the sound field estimations and the measurements. To further explore the mechanisms of sound generation, a semi-empirical source-model, informed by the experimental data, is proposed, based on Fourier modes in the cylinder's span direction.
Read the full abstract

All authors Marios I. Spiropoulos, Filipe R. Amaral, Florent Margnat, Vincent Valeau, Peter Jordan

Chemical Physics

pANO-F12: An atomic natural orbital-inspired route to more compact basis sets for F12 explicitly correlated methods

Vladimir Fishman and Jan M. L. Martin

Explicitly correlated methods such as MP2-F12 and CCSD(F12*) exhibit much faster basis set convergence (asymptotically $\propto L^{-7}$, with L the highest angular momentum) than orbital-only approaches. Yet it has been pointed out that cc-pVnZ-F12 basis sets themselves are substantially larger than the corresponding cc-pVnZ, and specifically that cc-pVDZ-F12 is the size of cc-pVTZ. One way to generate compact basis sets in an orbital-only context are Atomic Natural Orbital (ANO) basis sets [J. Almlöf and P. R. Taylor, JCP 86, 4070 (1987)]. However, obtaining the required first-order reduced density matrix while properly accounting for the F12 geminal is problematic. In this work, we show that an energy minimization-based contraction process under linear independence constraints yields `pseudo-ANO' (pANO) basis sets that are functionally equivalent in quality. Subsequently, we apply this recipe to obtain pANO-F12 basis sets from the same elements, then validate them for several thermochemical benchmarks and for the hypersensitive out-of-plane vibrations of benzene. We show that, unlike cc-pVnZ-F12, pANO-F12 exhibits the familiar shell structure seen in cc-pVnZ and ANO basis sets, and that pANO-F12 offers a route to more compact F12 basis sets more amenable to medium-sized systems, especially in conjunction with localized pair natural orbital approaches. Overall, the pANO approach is most beneficial for the smaller double-and triple-zeta basis sets, offering either superior performance to cc-pVnZ-F12 at same cost, or similar performance at lower cost.
Read the full abstract

Optics

Scattering correction for infrared spectra of biological cells using computational infrared microspectroscopy and deep learning

Sergio G. Rodrigo, Ilia L. Rasskazov, Luis Martin-Moreno et al. (+1 more)

IR microspectroscopy of single biological cells is challenged by strong light scattering, which produces baseline effects and peak distortions in the IR spectra and hinders the direct extraction of chemical information. Current methods for scattering correction typically rely on Mie theory and are accurate only under the assumption that the cell can be approximated by a sphere. Here, we present a framework for the scattering correction of IR absorbance spectra that is based on 3D ellipsoid models and provides efficient scattering correction for both suspended (spherical) and adhered (flattened) cells. Our approach combines deep learning approaches with computational IR microspectroscopy based on the finite-difference time-domain (FDTD) method. The FDTD method generates a synthetic library of realistic training spectra, while the deep learning model enables fast spectral inversion. We demonstrate scattering correction in silico using numerical cell phantoms of cervical cancer cells (HeLa) and show that the true absorption spectra can be inferred from IR absorbance spectra. We further show that the 3D cell dimensions can be recovered from the IR absorbance spectra, highlighting that the inherent light scattering could be exploited to realize the full analytical potential of IR spectroscopy. We anticipate that deep learning-based scattering corrections can be readily extended to increasingly complex sample geometries owing to the flexibility of the FDTD method to model arbitrary geometries.
Read the full abstract

All authors Sergio G. Rodrigo, Ilia L. Rasskazov, Luis Martin-Moreno, Martin Schnell

Instrumentation and Detectors

Energy Calibration and Performance of HPGe Detectors in the LEGEND-200 Experiment

The LEGEND Collaboration, H. Acharya, M. Agostini et al. (+259 more)

This paper describes the energy scale procedures and germanium detectors performance in the LEGEND-200 experiment, a critical component for the first unblinding in the search for neutrinoless double beta decay. We detail the digital signal processing pipeline, the methodologies for peak-shape modeling and energy calibration procedures utilizing weekly $^{228}$Th source calibration runs. The optimized energy reconstruction achieves a combined average resolution of $(2.47 \pm 0.08)$~keV at $Q_{\beta\beta} = 2039$~keV. The weekly variation of calibration peak positions are below 0.05~keV for energies up to 2614.5~keV, showing a high stability of the energy scale over time and across detectors. Furthermore, systematic corrections effectively address residual non-linearities and energy bias in the region of interest.
Read the full abstract

All authors The LEGEND Collaboration, H. Acharya, M. Agostini, A. Alexander, C. Alvarez-Garcia, V. Aures, F.T. Avignone III, M. Babicz, W. Bae, M. Balata, A.S. Barabash, P.S. Barbeau, C.J. Barton, L. Baudis, C. Bauer, S. Bellman, E. Bernieri, J.P. Ulloa Beteta, L. Bezrukov, K.H. Bhimani, V. Biancacci, A. Biondi, R. Biondi, E. Blalock, P. Bongratz, S.J. Borden, G. Borghi, F. Borra, B. Bos, A. Boston, G. Botogoske, R. Bouabid, R. Brugnera, T. Bürger, N. Burlac, M. Busch, S. Calgaro, N. Canci, L. Canonica, S. Capra, M. Carminati, R.M.D. Carney, L. Carroll, C. Cattadori, R. Cesarano, Y.-D. Chan, J.R. Chapman, A. Chernogorov, P.-J. Chiu, O. Chkvorets, C.D. Christofferson, A.I. Colon-Rivera, F. Confortini, D. D'Agostino, V. D'Andrea, G. De Gregorio, R. Deckert, J.A. Detwiler, N. Di Marco, F. Di Capua, C. Di Fraia, A. Di Giacinto, D. Di Leo, T. Dixon, K.-M. Dong, A. Drobizhev, G. Duran, Yu. Efremenko, S.R. Elliott, T. Elmikawy, C.H.J. Emmanuel, E. Engelhardt, E. Esch, L. Favilla, M. Febbraro, F. Ferella, R. Feriozzi, D.E. Fields, C. Fiorini, M. Fomina, N. Fuad, R. Gala, A. Galindo-Uribarri, A. Gangapshev, A. Garfagnini, S. Gazzana, A. Geraci, L. Gessler, C. Ghiano, A. Gieb, S. Giri, A. Gogosha, M. Gold, M.P. Green, G. Grünauer, J. Gruszko, I. Guinn, V.E. Guiseppe, Y. Gurov, K. Gusev, B. Hackett, F. Hagemann, M. Haranczyk, F. Henkes, R. Henning, J. Herrera, D. Hervas Aguilar, J. Hinton, R. Hodák, H.F.R. Hoffmann, M. Huber, M. Hult, A. Iorio, U.T. Islek, A. Jany, J. Jochum, D.S. Judson, M. Junker, J. Kaizer, V. Kazalov, M.F. Kidd, T. Kihm, K. Kilgus, A. Klimenko, K.T. Knöpfle, I. Kochanek, O. Kochetov, I. Kontul, V.N. Kornoukhov, A.B. Kowaleswska, P. Krause, H. Krishnamoorthy, V.V. Kuzminov, K. Lang, M. Laubenstein, N.N.P.N. Lay, A. Leder, B. Lehnert, A. Leonhardt, N. Levashko, A. Li, L.Y. Li, Y.-R. Lin, I. Lippi, A. Love, A. Lubashevskiy, B. Lubsandorzhiev, N. Lusardi, B. Majorovits, F. Mamedov, G.G. Marshall, E.L. Martin, R.D. Martin, R. Massarczyk, A. Mazumdar, G. McDowell, D.-M. Mei, M. Menzel, S. Mertens, E. Miller, I. Mirza, M. Misiaszek, M. Morella, B. Morgan, D. Muenstermann, C.J. Nave, M. Neuberger, N. O'Briant, F. Paissan, L. Papp, K. Pelczar, L. Pertoldi, W. Pettus, F. Piastra, M. Pichotta, P. Piseri, A.W.P. Poon, P.P. Povinec, A. Pullia, W.S. Quinn, D.C. Radford, Y.A. Ramachers, A.L. Reine, S. Riboldi, E. Richards, K. Rielage, C. Romo-Luque, B. Rossi, N. Rossi, S. Rozov, N. Rumyantseva, R. Saakyan, S. Sailer, G. Salamanna, F. Salamida, G. Saleh, E. Sanchez Garcia, C. Savarese, D.C. Schaper, J. Schlegel, S.J. Schleich, L. Schlüter, S. Schönert, O. Schulz, A.-K. Schütz, M. Schwarz, M. Schweizer, B. Schwingenheuer, C. Seibt, G. Senatore, A. Serafini, K. Shakhov, E. Shevchik, H. Shi, M. Shirchenko, Y. Shitov, N. Sierig, H. Simgen, F. Šimkovic, S. Simonaitis-Boyd, M. Singh, M. Skorokhvatov, M. Slavíčková, J.A. Solomon, G. Song, A.C. Sousa, A.R. Sreekala, L. Steinhart, I. Štekl, T. Sterr, M. Stommel, R. Stroili, S.A. Sullivan, R.R. Sumathi, K. Szczepaniec, L. Taffarello, D. Tagnani, V. Tretyak, M. Turqueti, E.E. van Nieuwenhuizen, L.J. Varriano, S. Vasilyev, V. Vatsa, C. Vignoli, C. Vogl, I. Wang, A. Warren, J.N. Warren, D. Waters, S.L. Watkins, C. Wiesinger, J.F. Wilkerson, M. Willers, M. Wojcik, D. Xu, E. Yakushev, T. Ye, C.-H. Yu, V. Yumatov, D. Zinatulina, K. Zuber, G. Zuzel

Optics

Hyperdoped silicon photodetectors enable room-temperature computational SWIR imaging at 1550 nm

Xiaolong Liu, Sören Schäfer, Jinyuan Chen et al. (+8 more)

Silicon's bandgap inherently restricts its photodetection to wavelengths below 1100 nm, necessitating the integration of costly III-V semiconductors for short-wave infrared applications. Hyperdoping silicon beyond the solid solubility limit offers a promising "silicon-native" alternative, yet achieving practical short-wave infrared applications at room temperature remains a formidable challenge. Here, we demonstrate a high-detectivity hyperdoped silicon photodetector enabling room-temperature computational short-wave infrared imaging beyond Si bandgap wavelength at {\lambda} = 1550 nm. By integrating an ultrafast laser heating process step to reduce the dark current while keeping high responsivity, we achieve a specific detectivity D^* exceeding 10^9 Jones for 1550 nm at room temperature working in a forward-biased, photoconductive mode. The improved detectivity, coupled with a 59.4 dB linear dynamic range and kHz-scale bandwidth, allows us to demonstrate a single-pixel imaging system that reconstructs 1550 nm scenes at 65x63 pixels without cryogenic cooling. Our devices simultaneously support visible-light imaging, offering a path toward monolithically integrated, multispectral Si-native optical sensors. These results establish ultrafast-laser hyperdoped silicon as a viable platform for low-cost, room-temperature, short-wave infrared photonics, bridging the gap between advanced materials science and practical computational imaging system.
Read the full abstract

All authors Xiaolong Liu, Sören Schäfer, Jinyuan Chen, Patrik Mc Kearney, Simon Paulus, Varsha Ashwin Vedaraj, Ville Vähänissi, Stefan Kontermann, Kenneth Crozier, James Bullock, Hele Savin

Chemical Physics · Cross-listed from quant-ph

Reduced Dynamical Maps in Finite Temperature Vibronic Coupling Models via Choi Matrices: Numerical Methods and Applications

Raffaele Borrelli and Hideaki Takahashi

We present a streamlined implementation of a computational framework for constructing and analyzing reduced dynamical maps for complex system–bath models at finite temperature. The methodology is based on three established ingredients of quantum dynamics: the Choi–Jamiołkowski isomorphism for the representation of quantum channels, thermofield (TFD) purification of thermal environments, and tensor-train (TT) propagation of the resulting enlarged pure state. The reduced map is obtained from a single unitary propagation in a thermofield-doubled Hilbert space and represented in matrix form through the Choi–Jamiołkowski isomorphism. The TFD evolution is implemented in the TT representation, enabling efficient propagation of high-dimensional purified thermal states. We illustrate the methodology for exciton transfer in the Fenna–Matthews–Olson complex with site-dependent structured spectral densities represented by discretized bosonic environments. The resulting maps are used to analyze decoherence, relaxation, and finite-memory effects, and to assess the crossover to an effectively time-local description. The proposed approach provides a route to compute reduced propagators and to post-process them into memory kernels, transfer tensors, and effective kinetic rate descriptions for complex molecular systems.
Read the full abstract

Optics · Cross-listed from cs.CV

Making the Discrete Continuous: Synthetic RAW Augmentations for Fine-Grained Evaluation of Person Detection Performance in Low Light

Valeria Pais, Malena Mendilaharzu, Daniele Faccio et al. (+3 more)

Real-world deployment of AI vision models is both fueled and limited by the data available for training and testing. Real datasets are sparse and uneven: long-tailed or unbalanced distributions hinder generalization, and the low number of samples in low density regions makes it hard to run evaluations. Synthetic data can fill these gaps, providing us with a way to sample the input space more continuously and improve data coverage for benchmarks. Focusing on the autonomous driving safety-critical case of pedestrian detection in the dark, we show how synthetic low-light samples can be used to better characterize the performance of a state-of-the-art object detection model as a function of the scene illumination. We use a synthetic RAW image augmentation technique to generate low-light samples that match the noise model of the camera sensor. Performance metrics on real and synthetic low-light data are similar, indicating that the AI model finds it hard to distinguish between them.
Read the full abstract

All authors Valeria Pais, Malena Mendilaharzu, Daniele Faccio, Luis Oala, Christoph Clausen, Bruno Sanguinetti

Atomic Physics

Inelastic collisions of fast charged particles with atoms. Relativistic plane-wave Born approximation

Francesc Salvat

A detailed formulation of the relativistic plane-wave Born approximation for inelastic collisions of charged particles with free atoms and positive ions is presented. The wave functions of the target atom or ion are calculated from a central-field independent-electron model with the Dirac-Hartree-Fock-Slater self-consistent potential, and the electromagnetic field is expressed in the Coulomb gauge. The double-differential cross section, depending on the energy loss and the recoil energy, is given as a sum of two terms which are products of purely kinematic factors and the generalized oscillator strengths (GOSs). Transitions induced by the instantaneous Coulomb interaction between the projectile and the active target electron are described by the longitudinal GOS. Transitions caused by the transverse interaction (exchange of virtual photons) are accounted for by a transverse GOS. We derive closed expressions for the longitudinal and transverse GOSs in terms of vector coupling coefficients and radial integrals. A set of Fortran programs have been written to compute the GOSs, the energy-loss differential cross section, and integrals of the latter. A complete numerical database of GOSs has been calculated for all the subshells of the ground-state configuration of neutral atoms of the elements with atomic numbers from 1 (hydrogen) to 99 (einsteinium). A systematic derivation of asymptotic formulas for the total cross section, the stopping cross section and the energy-straggling cross section is presented. The shell correction to the asymptotic formula for the stopping cross section of protons is obtained from the difference between computed numerical values and the predictions of that formula.
Read the full abstract

Chemical Physics

Dynamic electron correlation energy for multireference wavefunction methods from one- and two-electron reduced density matrices

Michał Hapka, Aleksandra Tucholska and Katarzyna Pernal

Efficiently recovering dynamic correlation in strongly correlated systems without incurring prohibitive computational costs remains a central challenge in quantum chemistry. In this Perspective, we review and benchmark methods capable of recovering dynamic correlation for multireference wave functions exclusively from low-order reduced density matrices and densities. These approaches require at most the two-electron reduced density matrix of the reference wave function and fall into two categories: density functional theory (DFT)-based methods and purely ab initio multireference adiabatic connection (AC) methods. The former include MC-srDFT, which recovers dynamic correlation through a short-range exchange-correlation functional depending on the charge and spin densities, as well as MC-PDFT and MC-srPDFT, which employ translated functionals that additionally depend on the on-top pair density. Within the post-CASSCF framework, we perform a direct, head-to-head benchmark of these approaches under identical computational settings (including active spaces and basis sets) against challenging multireference problems, including singlet-triplet gaps in organic biradicals, excitation energies, and spin-state splittings in iron complexes. Among the DFT-based methods, MC-srPDFT emerges as the most accurate, underscoring the benefit of incorporating the on-top pair density. However, all considered DFT-based methods fail to provide reliable spin-state energetics for transition-metal complexes. Conversely, linearized AC0 rivals or outperforms more computationally expensive second-order perturbation theory approaches across all benchmark sets. We discuss these findings in the context of alternative formulations and existing literature, highlighting critical limitations and identifying promising directions for the future development of scalable multireference methods.
Read the full abstract

Applied Physics

A Solid-state Sub-nm Pore for Single-mer Resolution Sequencing

Jianxin Yang, Dehua Hu, Wu Yuan et al. (+2 more)

Nanopore sequencing accuracy is inherently limited by the quality of data from individual molecular translocation events, requiring advances beyond traditional sequencing-by-synthesis methods. We introduce an oxidized pyramidal sub-nm pore (OPSP) integrated in a threeterminal sensing platform, where the sub-nm silicon pore functions as an electrode for detecting displacement currents across an oxide barrier, induced by counter-ion migration within the electric double layer. This platform achieves sub-1-nm-scale spatial resolution and a signal-tonoise ratio (SNR) up to 15 for biopolymer sequencing, enabling direct identification of individual bases in single-stranded DNA and single amino acids in peptides, with raw-read accuracies exceeding 98.5% and 95.5%, respectively, without consensus-based computational correction. The OPSP demonstrates high acid tolerance, reusability in varied chemical environments, and operational stability for over six months. This work establishes OPSP as a durable, high-accuracy platform for single-mer resolution sequencing, defining a reliable and robust paradigm for next-generation sequencing technologies.
Read the full abstract

All authors Jianxin Yang, Dehua Hu, Wu Yuan, Tianle Pan, Ho-Pui Ho

Chemical Physics

Benchmarking machine-learned interatomic potentials for molecular infrared spectroscopy

Nitik Bhatia, Ondrej Krejci and Patrick Rinke

Machine learning has transformed the field of atomistic simulations by enabling the development of interatomic potentials that are computationally efficient and highly accurate. These advances have opened the door to modeling molecular vibrations and predicting infrared spectra with near ab-initio accuracy at a fraction of the computational cost. Among these approaches, message-passing neural networks (MPNNs) have emerged as a particularly powerful class of models for representing complex atomic interactions. In this study, we benchmark five MPNN architectures, SchNet, FieldSchNet, SO3Net, PaiNN, and MACE, for predicting infrared spectra of small organic molecules. SchNet and FieldSchNet are invariant models, while SO3Net, PaiNN, and MACE are equivariant, explicitly accounting for rotational symmetries in molecular representations. We evaluate their performance in terms of computational efficiency, accuracy, and robustness. All models accurately predict properties, such as energies, forces, and dipole moments, required for infrared spectra calculations. They also capture harmonic frequencies and infrared spectra derived from molecular dynamics with high fidelity for molecules in the training set. However, SchNet and FieldSchNet show limited transferability to unseen systems, while SO3Net, PaiNN, and MACE generalize more effectively. In terms of computational efficiency, SchNet is the most efficient and FieldSchNet enables field-dependent response modeling but with higher cost. PaiNN achieves the best balance between accuracy and efficiency, MACE provides the highest spectral accuracy and transferability, and SO3Net performs between PaiNN and MACE.
Read the full abstract

Medical Physics · Cross-listed from cs.CV

Robustness of breast lesion segmentation under MRI undersampling improves with k-space-aware deep learning

Lukas T. Rotkopf, Marco Schlimbach, Julius C. Holzschuh et al. (+3 more)

Purpose: To assess whether breast lesion segmentation can be learned directly from acquired MRI k-space, and whether doing so improves robustness when data are accelerated or noisy. Materials and Methods: This retrospective study used public breast dynamic contrast-enhanced MRI (DCE-MRI) datasets with acquired and synthetic k-space, together with a within-dataset synthetic control. We compared four 3D U-Net variants: a hybrid k-space-to-image model, a native k-space model, and magnitude and complex image-space baselines. Models were evaluated under increasing undersampling and added complex Gaussian k-space noise. The primary outcome was patient-level Dice similarity coefficient under cross-validation, with the hybrid model prespecified as the main comparison against the magnitude image-space baseline. Results: At full sampling, the hybrid and image-space models performed similarly. As acceleration increased, the hybrid model retained substantially more segmentation accuracy and significantly outperformed the magnitude image-space baseline across moderate to high undersampling levels. The same pattern was observed when noise was added directly to k-space: the hybrid model degraded more slowly, whereas the image-space baseline failed under heavier noise. This advantage was reproduced in the within-dataset synthetic control. Feature analysis suggested that the k-space stage and image-space stage played complementary roles, with frequency-domain filtering concentrated before image-domain lesion localization. Conclusion: K-space-aware deep learning improves the robustness of breast lesion segmentation under MRI undersampling and k-space noise, while matching image-space methods at full sampling.
Read the full abstract

All authors Lukas T. Rotkopf, Marco Schlimbach, Julius C. Holzschuh, Heinz-Peter Schlemmer, Jens Kleesiek, Moritz Rempe

Fluid Dynamics

Lagrangian single-particle, multi-particle and topological analyses in turbulent Rayleigh-Bénard convection

Matti Ettel, Roshan J. Samuel, Michael Chertkov et al. (+1 more)

We present three-dimensional direct numerical simulations of turbulent Rayleigh-Bénard convection (RBC) in the Lagrangian frame of reference for Rayleigh numbers $10^5 \leq Ra \leq 10^{10}$ and a Prandtl number $Pr=0.7$ in a plane layer at an aspect ratio $L:L:H=4:4:1$ with a horizontal length $L$ and height $H$. We use particle accelerations, Lagrangian heat transfer, $Q$-$R$ invariant topology, Lagrangian particle pair dispersion, scale-dependent Lagrangian eddy viscosity, and principal component analysis (PCA) of dense particle clouds to characterise convective transport along material trajectories. By computing particle accelerations at the integration time step and controlling spectral element method signatures, we obtain robust acceleration statistics and recover Heisenberg-Yaglom behaviour. Lagrangian heat transfer is extremely intermittent: individual massless Lagrangian particles can carry convective heat fluxes up to $500$ times the global Eulerian mean, although higher-order heat flux moments decrease toward Gaussian values with increasing $Ra$. The analysis of velocity gradient invariants in the $Q$-$R$ plane along trajectories identifies a distinct topological footprint of dust-devil-like convective vortices in the quadrant of $Q>0$, $R<0$, associated with vortex stretching, plume detachment, and intense localised heat transfer. Global unconditioned pair dispersion exhibits neither extended Richardson nor Bolgiano-Obukhov scaling plateaus. Rather, scale-dependent eddy viscosity and conditioned PCA of dense particle clouds reveal that buoyancy- and shear-driven dispersion are temporally organised: rapid plume-driven ejection produces a short $t^5$-like episode, followed by sustained Richardson-like $t^3$-scaling. Thus, Lagrangian topology and cloud geometry provide mechanism-resolving diagnostics for active-scalar turbulence beyond RBC-specific global scaling laws.
Read the full abstract

All authors Matti Ettel, Roshan J. Samuel, Michael Chertkov, Jörg Schumacher

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

Two-dimensional alternating ferrimagnetism with strain-controlled half-metallic state and valley polarization

W. Z. Zhuo, Z. H. Guan, Z. L. Peng et al. (+4 more)

The discovery of altermagnetism offers new opportunities for exploring novel quantum states and developing spintronic devices for enabling momentum dependent spin splitting in compensated systems, while zero net magnetization limit its manipulability using conventional magnetic method. Here, we propose 2D alternating ferrimagnetism,a phase merging alternating momentum dependent spin splitting with a finite net magnetization. A tight binding model reveals that alternating ferrimagnetism originates from uncompensated magnetization in altermagnets, facilitating concurrent net magnetization and alternating spin splitting. First principles calculations and Monte Carlo simulations demonstrate stable alternating ferrimagnetism in strained and Cr substiting V2Te2O, which exhibit strain tunable net magnetization, reversable half metallicity and valley polarization, accompanied by long range magnetic order above room temperature. By combining altermagnetic and ferromagnetic properties, alternating ferrimagnetism expand the 2D magnetism landscape and offer pathways for energy efficient spintronic applications.
Read the full abstract

All authors W. Z. Zhuo, Z. H. Guan, Z. L. Peng, Y. N. Pan, J. Chen, Y. Yang, M. H. Qin

Atomic Physics

Shielded inner-shell transitions in atomic samarium for tests of fundamental physics

R. Aramyan, D. Budker, V. A. Dzuba et al. (+5 more)

Forbidden atomic transitions provide some of the most stringent low-energy tests of physics beyond the Standard Model, with sensitivity set by the interplay between the sought-for signals and systematics suppressed by symmetry. Here we identify the previously unobserved $4f^{6}6s^{2}\,{}^{5}$D$_{0}$ level of neutral samarium at $14\,564.90(2)\,\mathrm{cm}^{-1}$, opening the ${}^{7}$F$_{0}\rightarrow{}^{5}$D$_{0}$ inner-shell transition for precision spectroscopy. Candidate lines extracted from dual-comb absorption spectra were assigned using double-resonance population-depletion and sequential-excitation measurements. The observed pressure broadening, $0.12(2)\,\mathrm{MHz/torr}$, and pressure shift, $-0.145(4)\,\mathrm{MHz/torr}$, indicate an inner-shell $4f$-transition shielded from external perturbations. Many-body calculations predict a metastable lifetime in the range $120$-$200\,\mathrm{ms}$, corresponding to a quality factor of order $\mathcal{Q}\sim10^{14}$, large sensitivity coefficients for variation of the fine-structure constant, and a nuclear-spin-dependent parity-violation amplitude comparable to that of cesium. Crucially, the $J=0\rightarrow J=0$ selection rule suppresses by symmetry both the nuclear-spin-independent parity-violation channel and the M1 and E2 backgrounds that complicated previous heavy-atom experiments, yielding a uniquely clean window onto the nuclear anapole moment. The two stable spin-$7/2$ isotopes of samarium provide a remarkable opportunity to largely cancel atomic-structure uncertainties by measuring the ratio of parity-violation effects in the two isotopes. These results establish neutral samarium as a platform for inner-shell precision spectroscopy and tests of physics beyond the Standard Model.
Read the full abstract

All authors R. Aramyan, D. Budker, V. A. Dzuba, V. V. Flambaum, S. G. Porsev, M. S. Safronova, O. Tretiak, K. Zhang

Optics

Mid-infrared temporal ghost imaging via two-photon structured encoding

Ziyu He, Kun Huang, Huijie Ma et al. (+3 more)

Temporal ghost imaging (TGI) enables ultrafast signal reconstruction beyond electronic bandwidth limits. Extending this concept to the mid-infrared (MIR) regime through nonlinear frequency conversion offers new opportunities for high-fidelity temporal detection, but remains constrained by stringent phase-matching condition, limited spectral coverage, and intricate optical alignment. Here, we propose and demonstrate a broadband MIR TGI system based on non-degenerate two-photon absorption. A temporally encoded near-infrared pump transfers structured modulation onto a MIR signal directly at a silicon detector, which facilitates concurrent modulation and detection without external nonlinear crystals. The reconstructed temporal waveforms exceed the detector bandwidth by more than fortyfold, achieve a detection sensitivity of 0.05 pJ/pulse, allow compressed sensing with 80% fewer measurements, and support broadband operation across 2.5-3.8 $\mu$m. This compact, alignment-free, and room-temperature system establishes a practical route for fast and sensitive MIR time-domain analysis, holding great promise for applications in time-resolved molecular spectroscopy, high-precision infrared ranging, and high-speed free-space communication.
Read the full abstract

All authors Ziyu He, Kun Huang, Huijie Ma, Wen Zhang, Jianan Fang, Heping Zeng

Applied Physics

Simultaneously monitoring Ga adsorption and desorption kinetics on GaN(0001) using four in situ techniques

Huaide Zhang, Philipp John, Jingxuan Kang et al. (+3 more)

We present a systematic investigation of Ga adsorption and desorption kinetics on the wurtzite GaN(0001) surface using four in situ techniques operated simultaneously: reflection high-energy electron diffraction, laser reflectometry, line-of-sight quadrupole mass spectrometry, and optical pyrometry. Flux- and temperature-dependent experiments are performed for Ga coverages ranging from the submonolayer to the droplet regime. Despite their distinct transient responses, the signals from all four techniques and their trends with surface coverage are quantitatively reproduced by a unified kinetic model of Ga adsorption, diffusion, and desorption. An Arrhenius analysis of the Ga adlayer desorption yields an activation energy of (2.87 $\pm$ 0.04) eV.
Read the full abstract

All authors Huaide Zhang, Philipp John, Jingxuan Kang, Lutz Geelhaar, Yongjin Cho, Oliver Brandt

Fluid Dynamics

A unified gas-kinetic wave-particle method for multiscale binary-species gas mixtures

Junzhe Cao, Yufeng Wei, Wenpei Long et al. (+2 more)

This paper presents a unified gas-kinetic wave-particle (UGKWP) method for simulating multiscale binary-species gas mixtures. Benefiting from direct modeling in a discretized space, the UGKWP method enables the automatic decomposition of the gas distribution function into analytical hydrodynamic waves and discrete particles, which respectively describe its near-equilibrium and non-equilibrium parts. This approach offers significant advantages for simulating various multiscale physical phenomena, such as hypersonic flows, plasma transport, and radiation transport. In this study, we employ the model proposed by Groppi et al. [EPL, 96 (2011) 64002] to calculate the macroscopic velocity and temperature of the local target equilibrium distribution function, thereby recovering the correct viscosity and diffusion coefficients in the continuum flow regime. To address the heat conduction coefficient, the Shakhov model is incorporated to correct the Prandtl number. Diffusion effects are accounted for not only in the source term via an operator-splitting method, but also in the flux evolution through the characteristic integral solution, while strictly maintaining consistency between the wave and particle descriptions. Furthermore, the microscopic model for high-speed particles is improved by utilizing a physically corrected collision time to determine their free-transport time. Through a series of numerical tests spanning the continuum to rarefied regimes, the proposed UGKWP method is shown to accurately capture the differences in velocity and temperature between different species. Notably, for hypersonic flows, the predicted wall pressure, shear stress, and heat flux coefficients agree well with DSMC results.
Read the full abstract

All authors Junzhe Cao, Yufeng Wei, Wenpei Long, Chengwen Zhong, Kun Xu

Optics

Refractive index retrieval of 3D printed materials for photonic applications

Joseph Arnold Riley, Christian Johnson-Richards, Noel Healy et al. (+1 more)

The advent of additive manufacturing has opened opportunities to rapidly prototype devices and products ranging from automotive and aerospace applications to micro/nanoscale metastructures, as examples). Three-dimensional (3D) printing has become relevant for electromagnetic structures, integrated optics and photonics systems, however, the optical properties of commercially available 3D printed polymers at telecommunication wavelengths (wavelength 1550nm) is not always available. Provided the importance of 3D printing technologies, in this work, we evaluate both theoretically and experimentally the complex refractive index of four polymers including some recycled versions (namely Butenediol Vinyl Alcohol (BVOH), Polylactic Acid (PLA), Recycled Polyethylene Terephthalate (rPET), and recycled Polylactic Acid (rPLA)) as potential candidates for photonics applications. The 3D printed samples have thicknesses from ~100 to 400 nm (~64wavelengths to ~258wavelengths, respectively). The experimental reflectance and transmittance spectra are extracted and used to retrieve the complex refractive index of each printed material demonstrating extinction coefficients in the order of 10^-4 at wavelength=1550nm. The experimental results are validated using numerical simulations. Finally, as a proof-of-concept, a convex-planar lens and a Bragg mirror are designed and numerically evaluated, showing the potential of the proposed polymers for 3D printing photonic structures at telecommunication wavelengths.
Read the full abstract

All authors Joseph Arnold Riley, Christian Johnson-Richards, Noel Healy, Victor Pacheco-Peña

History and Philosophy of Physics

The Limitations of the Notion of `Observable' in Diffeomorphism-Invariant Models

Álvaro Mozota Frauca

The application of the notion of `observable' from gauge theory to diffeomorphism-invariant theories – most relevantly to general relativity – has led to numerous conceptual and technical issues when interpreting classical theories with this symmetry and building quantum versions of them. In this article I distinguish between two senses of gauge transformation: local and global, and I argue that the notion of observable appears more naturally in the local sense of gauge transformation. Then, I argue that diffeomorphism invariance can be understood as a gauge symmetry only from a global point of view, and hence, that the concept of observable applies only in a restricted manner. This has the consequence that some popular claims in the literature, such as the claim that the physical content of diffeomorphism-invariant models is encoded in correlations, are unfounded.
Read the full abstract

Optics

Single-pump hybrid nonlinearities in transparent conductors

Wallace Jaffray, Sven Stengel, Alexandra Boltasseva et al. (+7 more)

Low-index transparent conducting oxides have attracted significant attention because ultrafast optical excitation in these materials can induce exceptionally large temporal index gradients. Due to this remarkable nonlinear optical behaviour, this material platform enables sub-picosecond, all-optical control of photon energy and momentum, with growing relevance for integrated photonics, quantum optics, and optical computation. Owing to their hybrid electronic structure, transparent conductors exhibit both intraband and interband nonlinearities, previously accessed using dual-colour excitation with near-infrared and ultraviolet pumps. Here, we show that both excitation regimes can be activated using a single, intense near-infrared pump. Above a threshold intensity, the pump drives hot-electron intraband dynamics while simultaneously generating higher harmonics that trigger interband excitation. The interplay of these two effects sharpens the temporal features of the recorded transmissivity which in turn substantially broadens the effective material bandwidth. Finally, by comparing linear and circular pumping conditions, we further demonstrate that the observed interband nonlinearities originate from harmonic generation rather than from direct multiphoton absorption. Our results provide key insights into the strong-field optical response in these time-varying photonic materials, opening new frontiers for the ultra-fast manipulation of photons in both classic and quantum regimes.
Read the full abstract

All authors Wallace Jaffray, Sven Stengel, Alexandra Boltasseva, Vladimir M. Shalaev, Carlo Rizza, Domenico de Ceglia, Maria Antonietta Vincenti, Michael Scalora, Matteo Clerici, Marcello Ferrera

Atmospheric and Oceanic Physics · Cross-listed from cs.LG

Decomposing Ensemble Spread in Lorenz '96 With Learned Stochastic Parameterizations

Birgit Kühbacher, Daan Crommelin and Niki Kilbertus

Weather and climate forecasts are inherently uncertain due to chaotic dynamics, imperfect initial conditions, and incomplete representation of the underlying physical processes. Operational ensemble forecasts aim to represent these uncertainties through forecast spread, yet many approaches yield underdispersive estimates, with spread that grows too slowly relative to forecast error. Using the two-scale Lorenz 1996 system as a widely used, controlled testbed, we design a systematic approach to disentangle intrinsic variability, initial-condition perturbations, and stochastic model uncertainty. We compare multiple ensemble configurations and parameterization strategies, including existing deterministic and autoregressive as well as novel Bayesian and flow-based approaches. Our results show that ensemble perturbations do not increase the system's long-term variance; rather, they regulate how rapidly trajectories decorrelate and explore the invariant measure. Stochastic parameterizations, particularly those with temporally persistent structure, enhance early spread growth and improve spread-error consistency. Overall, we bring clarity to how different sources of uncertainty interact in a chaotic system and provide guidance for the design and evaluation of stochastic parameterizations in weather and climate models.
Read the full abstract

Instrumentation and Detectors

Alpha Background in Multi-Grid Neutron Detectors

A. Backis, C.-C. Lai, J.R.M. Annand et al. (+4 more)

Alpha emission from actinide impurities in Al is a source of background counting rate in Multi-Grid type detectors of thermal neutrons. The alpha emission rates from samples of radio-purity Al and \mathrm{Al/B_{4}C} composite, used in grid construction, were measured on a large-area, low background spectrometer. Although the alpha emission rate from the composite was a factor \sim280 higher than radio-pure Al, \mathrm{25\:\mu m} Ni plating of the composite reduced the rate by a factor \sim1170. Background counting rates in two Multi-Grid prototypes were compared. They used identical configurations of \mathrm{B_{4}C}-coated, radio-pure Al normal blades for the grids, but the first employed radio-purity Al for the radial blades, while the second used Ni-plated \mathrm{Al/B_{4}C} on the radial blades. The background rate from the second prototype was around 20% of that from the first.
Read the full abstract

All authors A. Backis, C.-C. Lai, J.R.M. Annand, K.G. Fissum, G. Zuzel, M. Czubak, K. Livingston

Optics

OAM Light Demultiplexing from an Intensity Profile using Orthogonality Restoration of Pair Modes

Junsu Kim, Hyunchae Chun and SeungRyong Park

Orbital Angular Momentum (OAM) of light is a promising degree of freedom for next-generation communication. By exploiting the orthogonality of OAM modes, multi-channel division enables a linear increase in communication performance proportional to the number of available modes. However, the multiplexing and demultiplexing of each superposition state remain essential yet complex processes. Demultiplexing has been established through spatial-domain methods that require additional optical elements such as gratings and apertures, which can decrease communication efficiency and accuracy under various conditions. In this paper, we propose a demultiplexing method under a single intensity profile by orthogonality restoration of OAM pair states. This method can be applied directly to an OAM multichannel communication system without additional receiver-side optical structure. We present simulation results of our method under various conditions.
Read the full abstract

Fluid Dynamics

N-Component Free Energy Lattice Boltzmann Method with Reduction Consistency and Global Momentum Conservation

Michael Rennick, Xitong Zhang, Tim Niklas Bingert et al. (+2 more)

We present a free energy lattice Boltzmann model capable of simulating fluid systems with an arbitrary number of immiscible components in principle. Our method is strictly reduction consistent, ensuring that absent fluid components do not spontaneously nucleate. We introduce a novel discretization of the surface tension force that globally conserves momentum to machine precision, and we enforce reduction consistency through a flux correction that is independent of the mobility. The method is benchmarked with a range of static and dynamic problems, including: liquid lenses, Janus droplets, quaternary phase separation, and six-component layered Poiseuille flow, and we obtain excellent agreement with theoretical predictions throughout. Finally, we demonstrate the applicability of the proposed method through patterned liquid surfaces and microfluidic emulsion droplet generation.
Read the full abstract

All authors Michael Rennick, Xitong Zhang, Tim Niklas Bingert, Mathias J. Krause, Halim Kusumaatmaja

Fluid Dynamics · Cross-listed from math-ph

Global exponential stability for the three-dimensional Navier-Stokes equations on hyperbolic space

Zhi-Wei Wang and Samuel L. Braunstein

We prove that the three-dimensional incompressible Navier-Stokes equations with the deformation Laplacian on hyperbolic 3-space $\HH^3$ admit a unique global mild solution for sufficiently small initial data in $L^3(\HH^3)$, and that this solution decays exponentially to zero. The exponential decay rate is $\mu\lambda_\Def^{(3)}$, where $\mu$ is the kinematic viscosity and $\lambda_\Def^{(3)} = 26/9$ is the effective spectral gap of the deformation Laplacian in $L^3$. On flat $\R^3$, the corresponding Kato-type result gives only algebraic decay. The exponential stability is a macroscopic consequence of the spectral gap provided by negative curvature. We also show that the $L^2$ norm is supercritical on $\HH^3$ (as on $\R^3$), with the obstruction arising from the local ultraviolet scaling of the heat kernel, which is insensitive to global geometry. The boundary between what curvature can and cannot improve is located exactly: the Fujita-Kato integral has a scaling exponent $1/2 - 3/(2p)$ that depends only on the integrability of the initial data, not on the geometry of the manifold. For $p \geq 3$ (the Kato critical space), the integral is bounded and the spectral gap contributes exponential time decay. For $p < 3$, the integral diverges at $t = 0$ (and strictly diverges for all $t>0$ when $p \le 3/2$) regardless of the curvature.
Read the full abstract

Optics

A Residual-Subspace Constraint Framework for Fourier Ptychographic Microscopy

Sui-peng Wang, Si-yi Xie, Chang-tao Cai et al. (+2 more)

The reconstruction fidelity of computational optical imaging is fundamentally constrained by the model-reality gap, i.e., the inevitable discrepancy between idealized forward models and the physical imaging process. Conventional paradigms attempt to bridge this gap through exhaustive system calibration or explicit parameter estimation, which are often computationally intensive and prone to severe non-convex stagnation. This paper introduces a Residual-Subspace Constraint Framework (RSCF) to achieve robust Fourier ptychographic microscopy. Instead of treating residuals as unstructured errors, RSCF leverages subspace decomposition to decouple low-rank, systematic mismatches from stochastic noise, thereby isolating stable information manifolds that remain invariant to forward-model inaccuracies. By embedding this subspace constraint into the iterative engine, the framework selectively suppresses error-amplifying components, enabling high-fidelity phase and amplitude recovery without explicit hardware calibration. Numerical simulations and experimental validations demonstrate that RSCF yields superior convergence acceleration and artifact suppression under severe optical aberrations and LED misalignment. This information-centric paradigm provides a versatile, model-agnostic strategy to enhance robustness across diverse computational imaging modalities.
Read the full abstract

All authors Sui-peng Wang, Si-yi Xie, Chang-tao Cai, Zhun Wei, Rui Chen

Optics · Cross-listed from cond-mat.mes-hall

Quasinormal mode quantization of bound and propagating photons in complex lightguiding nanostructures for integrated devices

Robert Meiners Fuchs and Marten Richter

Open optical or plasmonic resonators are placed on and connected through surfaces or via waveguides, forming complex lightguiding nanostructures, e.g. for integrated photonic quantum devices. We derive general boundary conditions for quasinormal modes that account for the structure's specific geometry. We then present a general quantization scheme for multiple, interacting quasinormal-mode cavities coupled to quantum emitters and to a non-bosonic bath of propagating photons on waveguides or a surface. We derive a system-bath Hamiltonian with rigorously defined coupling elements that can be computed using Maxwell solvers, including light-matter coupling between the electromagnetic field and quantum emitters. We define system-bath correlation functions for an effective, bath-mediated, and time-delayed interaction between the quasinormal modes and quantum emitters, which is a main ingredient commonly used to simulate open quantum system dynamics.
Read the full abstract

Optics

Electron modulation and ultrafast near-field imaging with vectorial laser fields

J. Kuttruff, L. Möhrle, L. Ciorciaro et al. (+2 more)

Controlled interaction of laser light with electron beams is fundamental for ultrafast electron microscopy and electron-based quantum optics, yet their direct coupling is forbidden in free space. Here we use longitudinally polarized light at a thin membrane and show that the emerging focal fields can modulate the electron beam in a direct, coherent and linear way, without the need for nanostructured materials or slanted interaction geometries. Also, we use vectorial polarizations to excite and probe three-dimensional nanophotonic near-fields in metallic mesocrystals by coherent electron energy gain and loss. We find that longitudinal electric fields excite axial near-fields in a direct way while longitudinal magnetic fields excite oscillating ring currents via azimuthal electric fields. These possibilities enable tilt-free, collinear generation of attosecond electron pulses or free-electron qubits and provide novel imaging modes in ultrafast electron microscopy and metamaterial tomography.
Read the full abstract

All authors J. Kuttruff, L. Möhrle, L. Ciorciaro, L. Schmidt-Mende, P. Baum

Biological Physics

Conditional Enhancement of Radical Pair Dynamics via Chiral State Preparation

Tristen Gwynn, Betony Adams and Francesco Petruccione

Chiral-induced spin selectivity (CISS) has been shown to enhance magnetic sensitivity in radical pair mechanism (RPM) models under specific Hamiltonian conditions, yet whether these enhancements persist across a broader parameter space remains untested. We incorporate the CISS effect as a spin-dependent initial state and recombination operator and systematically evaluate the spin dynamics of a model radical pair across a comprehensive parameter sweep of the RPM Hamiltonian. We characterise the orientational response through symmetric and antisymmetric decomposition of the yield distribution under field reversal, providing a direct quantitative signature of CISS-induced symmetry breaking. Our analysis demonstrates that CISS does not function as a generic amplifier of magnetic sensitivity. Claimed enhancements are conditional on the relative alignment of the internal hyperfine and dipolar interaction axes, arising specifically under conditions of non-collinear internal interactions. Extension to a two-nucleus model confirms that these enhancements are sensitive to nuclear spin. CISS-induced effects observed in the single-nucleus model are substantially suppressed when a second collinear nucleus is introduced, with the exception of the hyperfine axis rotation sweep where non-collinear tensor misalignment drives a robust antisymmetric response. These findings indicate that the conditions for CISS-enhanced magnetoreception are more stringent than previously demonstrated, requiring highly ordered and rigid molecular geometries to sustain the effect.
Read the full abstract