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Physics Physics

physics Watch Physics

Monday 1 June

Optics

Polarization-Multiplexed Spatial Filtering in a Symmetric \ce{TiO2} Metasurface with an Anisotropic van der Waals Gap Fill

Shoumik Debnath and Sudipta Saha

Finite-difference time-domain simulations of a symmetric \ce{TiO2} nanobar-pair metasurface with a 60~nm $\alpha$-\ce{MoO3} gap fill give two Fano resonances that are selected by the input polarization angle, at 885.5~nm ($Q=50.5$) and 893.8~nm ($Q=44.8$). Both channels act as spatial high-pass filters and differ in their cutoff spatial frequency, 0.44 and 1.17~$\mu$m$^{-1}$, with the broader cutoff belonging to the lower-$Q$ resonance. The unit cell retains a mirror plane normal to the swept direction, so the momentum-space transfer function is even in $k_x$; over the accessible momentum range the broader channel follows $|H|\propto|k_x|$, which is the kernel used for edge enhancement. Both operations are applied to a USAF~1951 resolution chart in a simulated 4$f$ arrangement. The simulations use measured anisotropic optical constants for $\alpha$-\ce{MoO3} with the crystal axes assigned as they lie in an exfoliated flake. A control series with isotropic and uniaxial gap fillings indicates that the shape anisotropy of the bar pair sets the scale of the channel separation, that the anisotropy of the crystal acts mainly through its out-of-plane index contrast, and that the in-plane birefringence contributes a small part of it.
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Instrumentation and Detectors

Demonstrating CBM Capabilities by $\Lambda$ Baryon Reconstruction in Ni+Ni Collisions with the mCBM Experiment at SIS18 of GSI/FAIR

CBM Collaboration: A. Agarwal, Z. Ahammed, N. Ahmad et al. (+339 more)

The Compressed Baryonic Matter (CBM) experiment at the upcoming Facility for Antiproton and Ion Research (FAIR) is a high-rate fixed-target experiment designed to investigate nuclear matter at extreme baryon densities in relativistic nucleus-nucleus collisions. To enable high-statistics measurements of rare probes, CBM is designed to operate at event rates up to 10 MHz. This necessitates the development of fast and radiation-tolerant detectors, self-triggered front-end electronics, a free-streaming data acquisition architecture, and real-time event reconstruction capabilities. Prototype versions and pre-series productions of the CBM detector systems have been deployed in the mini-CBM demonstrator setup mCBM - an experimental precursor comprising sub-components of all major CBM systems, installed at the SIS18 facility of GSI/FAIR within the FAIR Phase-0 program. In 2024, Ni+Ni collisions at a kinetic beam energy of 1.93 AGeV and an average interaction rate of about 250 kHz were successfully recorded. This dataset enables a detailed evaluation of the operational performance of the detector systems as well as the complete CBM data chain, while the reconstruction of rare $\Lambda$ baryons serves as a natural benchmark. This paper presents the first results on $\Lambda$ signal reconstruction with the mCBM experiment, demonstrating the readiness of the detector technologies and the data chain for the upcoming full-scale CBM experiment.
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All authors CBM Collaboration: A. Agarwal, Z. Ahammed, N. Ahmad, L.J. Ahrens, M. Al-Turany, N. Alam, J. An, J. Andary, A. Andronic, H. Appelshäuser, B. Arnoldi-Meadows, B. Artur, M.D. Azmi, M. Balzer, A. Bandyopadhyay, V.A. Bâsceanu, J. Becker, A. Belousov, A. Bercuci, R. Berendes, D. Bertini, O. Bertini, M. Beyer, O. Bezshyyko, P.P. Bhaduri, A. Bhasin, M.S. Bhat, S.A. Bhat, T.A. Bhat, W.A. Bhat, B. Bhattacharjee, A. Bhattacharyya, N.K. Bhowmik, S. Biswas, T. Blank, N. Bluhme, C. Blume, D. Bonaventura, J. Brzychczyk, U. Bykova, M. Cãlin, J. Calvo-Lorenzo, A. Chakrabarti, P. Chaloupka, A. Chattopadhyay, So. Chattopadhyay, Su. Chattopadhyay, H. Cherif, S. Chernyshenko, I. Ciepał, E. Clerkin, L.M. Collazo Sánchez, M. Csanád, P. Dahm, A. Daribayeva, D. Das, R. Das, S. Das, J. de Cuveland, D.-A. Deară, H. Deppe, I. Deppner, A.A. Deshmukh, M. Deveaux, V. Dobishuk, A.K. Dubey, A. Dubla, M. Dürr, R. Dvořák, I. Elizarov, D. Emschermann, J. Eschke, L.J. Faber, C. Feier-Riesen, H. Feng, S.Q. Feng, F. Fidorra, C. Fischer, P. Fischer, H. Flemming, H. Floersheimer, J. Förtsch, P. Foka, U. Frankenfeld, V. Friese, I. Fröhlich, F. Frombach, J. Frühauf, T. Galatyuk, G. Gangopadhyay, P. Gasik, C. Ghosh, S.K. Ghosh, D. Gil, S. Gläßel, F.S. Goldenbaum, L. Golinka-Bezshyyko, S. Gorbunov, N. Greve, D. Grzonka, A. Gupta, S. Gupta, D. Gutiérrez Menéndez, B. Gutsche, D. Han, J. Han, X. He, N. Heine, H. Hesounová, J.M. Heuser, C. Höhne, O. Hofman, F. Hollfoth, Y. Huang, D. Hutter, M.J. Ijaz, O. Javakhishvili, Y. Jin, A. Jipa, I. Kadenko, P. Kähler, K.-H. Kampert, R.M. Kapell, R. Karabowicz, V.K.S. Kashyap, K. Kasiński, I. Keshelashvili, M.M. Khan, D. Kikoła, M. Kiš, I. Kisel, R. Kłeczek, C. Klein-Bösing, R. Kliemt, K. Koch, P. Koczoń, G. Korcyl, O. Kovalchuk, G. Kozlov, Y. Kozymka, D. Kresan, M. Kruszewski, O. Kshyvanskyi, B. Kubiak, A. Kugler, A. Kumar, A. Kumar, L. Kumar, V. Kyva, R. Lakos, R. Lalik, P. Lasko, J. Lehnert, Y. Leung, M. Li, S. Li, W. Li, Y. Li, Y. Liang, V. Lindenstruth, F.J. Linz, F. Liu, S. Löchner, P.-A. Loizeau, M. Lorenz, O. Lubynets, X. Luo, S. Mahajan, H. Mailaianthan, B. Mallick, S. Mandal, Y. Mao, A.M. Marin Garcia, J. Markert, F.A. Matejcek, T. Matulewicz, J. Messchendorp, A. Meyer-Ahrens, J. Michel, M.F. Mir, D. Miskowiec, A. Mithran, B. Mohanty, D. Moreira de Godoy Willems, W.F.J. Müller, C. Müntz, M. Nabroth, E. Nandy, S.R. Nayak, F. Nerling, S. Neuhaus, F. Nickels, D. Okropiridze, H. Olbring, A. Opíchal, P. Otfinowski, L. Pan, B. Parveen, H. Pauels, C. Pauly, P. Pawłowski, J. Peña Rodríguez, S. Peter, M. Petriş, D. Pfeifer, K. Piasecki, J. Pietraszko, R. Płaneta, V. Plujko, J. Pluta, N. Podgornov, T. Povar, K. Poźniak, S.K. Prasad, M. Pugach, V. Pugatch, P.R. Pujahari, A. Puntke, L. Radulescu, S. Raha, D.A. Ramírez Zaldivar, R. Rath, R. Ray, A. Redelbach, A. Reinefeld, O. Ristea, J. Ritman, D. Rodríguez Garces, A. Rodríguez Rodríguez, F. Roether, R. Romaniuk, A. Roy, S. Roy, E. Rubio, A. Rustamov, R. Sahoo, P.K. Sahu, S.K. Sahu, J. Saini, P. Salabura, S. Samal, S.S. Sambyal, K. Santos Marrero, K. Scharmann, C. Schiaua, F. Schintke, D. Schledt, C.J. Schmidt, H.R. Schmidt, L. Schramm, K. Schünemann, F.-J. Seck, T. Sefzick, I. Selyuzhenkov, P. Semeniuk, A. Senger, P. Senger, A.K. Sharma, A. Sharma, P.K. Sharma, S. Shi, M. Shiroya, V. Sidorenko, F. Simon, C. Simons, A.K. Singh, B.K. Singh, G. Singh, O. Singh, R. Singh, V. Singhal, A. Sk, D. Smith, B. Soból, Y. Söhngen, F.A. Sofi, D. Spicker, P. Staszel, T. Stockmanns, J. Stroth, C. Sturm, P. Subramani, G.S. Subramanya, O. Suddia, K. Sun, Y. Sun, Z. Sun, A. Szczurek, R. Szczygieł, E.D. Taka, J. Taylor, M. Teklishyn, S. Thakur, S.N. Thau, J. Thaufelder, A. Toia, M. Traxler, L. Trębacz, A. Twarowska, O. Tyagi, I.C. Udrea, F. Uhlig, K.L. Unger, I. Vassiliev, O. Vasylyev, R. Visinka, L. Wahmes, K. Wang, Y. Wang, F. Weiglhofer, J.P. Wessels, D. Wielanek, A. Wieloch, P. Wintz, M. Wojtkowski, G. Wolf, K. Wu, Q. Wu, A. Wyżykowski, H. Xu, N. Xu, J. Yang, R. Yang, M. Yao, Z. Yin, I. Yoo, I. Yurchanka, W. Zabołotny, H.P. Zbroszczyk, X. Zhang, X. Zhang, Y. Zhang, S. Zharko, S. Zheng, D. Zhou, W. Zhou, Y. Zhou, X. Zhu, M. Zieliński, G. Zischka, W. Zubrzycka, P. Zumbruch

Fluid Dynamics

A model for pulsation in high-speed double cone flow

Subhajit Das and Subrahmanyam Duvvuri

Periodic large-scale shock-wave unsteadiness over a canonical double cone, termed in literature as "pulsation," is experimentally studied at Mach 6. The general double cone geometry is defined by three non-dimensional geometric parameters: fore- and aft-cone angles ($\theta_1$ and $\theta_2$), and ratio of the conical slant lengths ($\mathit{\Lambda}$). While existing literature on pulsation offers detailed qualitative and phenomenological discussions, it is seen that analytical approaches to obtain insight into the unsteady flow phenomena are missing. The present effort is aimed at addressing this gap. Self-sustained flow pulsations for a particular double cone configuration with $\theta_1 = 0^\circ$ and $\theta_2 = 90^\circ$, commonly referred to as the spike-cylinder, is investigated in the $\mathit{\Lambda}$ parameter space. High-speed schlieren imaging and time-resolved pressure measurements are performed in the unsteady flow. The non-dimensional pulsation frequency (Strouhal number) is observed to increase monotonically with $\mathit{\Lambda}$. Schlieren and pressure data suggest that the unsteadiness is driven by a cyclic process involving the formation of high-pressure gas near the aft-cone and its subsequent expansion through the separation region formed over the fore-cone. Building on this understanding, a detailed analytical model for the flow is developed with no empirical parameters. The model successfully predicts the experimentally-measured Strouhal number, and provides an in-depth understanding of the mechanisms that drive flow pulsations.
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Optics

Gain and One-Way Propagation in Synthetically Moving non-Foster Gratings

Antonio Alex-Amor, Carlos Molero and Mario G. Silveirinha

In this paper, we analyze the electromagnetic properties of space-time grooved metal surfaces governed by uniform-velocity modulations. We begin by deriving the electromagnetic fields of a uniform-velocity-modulated parallel-plate waveguide (PPW) using Lorentz transformations, establishing it as the fundamental building block of a more complex space-time structures. We then analyze the dispersion and scattering characteristics of a space-time grooved surface and later extend the study to the interaction between two facing surfaces. Our findings show that these systems can indeed amplify electromagnetic waves and exhibit non-reciprocal as well as non-Foster behavior. Moreover, under specific conditions, they enable the formation of unidirectional propagation channels, effectively constraining light to be guided along a single direction. These results unveil new opportunities for the design of advanced electromagnetic and photonic devices.
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Plasma Physics

Probing kinetic enhancement of fusion reactivity in turbulent hot spots

Yao Guo, Dong Wu and Jie Zhang

Traditionally, fusion reactivity in thermonuclear plasmas has been calculated by assuming a local Maxwellian ion distribution. However, recent theoretical work [Phys. Rev. Lett. 135, 155101 (2025)] suggests that turbulence in plasmas can generate non-Maxwellian tail distributions, thereby enhancing reactivity. In this paper, we investigate this effect through numerical simulations of a sinusoidal shear flow. By comparing steady-state distributions obtained with the Bhatnagar-Gross-Krook (BGK) and Fokker-Planck (FP) collision operators, respectively, we demonstrate that the BGK model overestimates the reactivity enhancement while the FP operator gives a much more modest enhancement that is nearly halved under typical ICF parameters. Particle-in-cell (PIC) simulations incorporating nuclear reactions are also conducted, which reveal that the combined effects of preferential ion heating during shear flow dissipation and tail enhancement can even amplify the reactivity enhancement to be larger than the steady-state prediction.
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Atomic Physics · Cross-listed from cond-mat.quant-gas

Two-body loss dynamics as a probe of dynamical bulk viscosity in ultracold atomic gases

Tingyu Zhang, Hiroyuki Tajima and Takeo Kato

We show that the equilibrium connected correlation of the two-body loss rate provides access to the dynamical bulk viscosity in weakly dissipative quantum gases. Starting from the Lindblad equation for weak inelastic losses, we derive the loss-current operator and, using a counting-field formulation of the loss statistics, the relation between the statistics of detected losses and the equilibrium loss-rate correlator. The connected correlation of the two-body loss rate is found to be proportional to the equilibrium contact correlation and hence to the bulk-viscosity spectrum. We show that the measured loss-counting covariance contains, besides the Poissonian self-correlation, a quantum-jump backaction term of the same order as the target correlator, which is fixed by the transient of the mean loss rate after the loss is switched on. The bulk-viscosity spectrum can therefore be reconstructed from the combination of the loss-counting covariance and the mean loss dynamics. Our result identifies weak two-body loss dynamics as a probe of dynamical bulk viscosity, whose measurement has remained elusive in experiments.
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Biological Physics · Cross-listed from cond-mat.soft

Stress relaxation in fiber networks via force-dependent stochastic severing

Prathamesh Kulkarni, Anatoly B. Kolomeisky and Fred C. MacKintosh

Fiber networks contribute to the mechanical stability of various biological systems, from cells to tissues. Such systems have been modeled by networks of springs or fibers that exhibit rigidity transitions as a function of either connectivity or applied strain. For a fiber network under constant applied strain, severing can reduce the connectivity and destabilize an initially rigid structure. Here, we investigate stress relaxation in spring and fiber networks in the presence of stochastic, force-dependent severing. A computational model to predict stress relaxation with mechanochemical feedback of stress on severing is developed. We also examine the effects of severing on the network topology and onset of rigidity transition. Using 2D triangular lattice-based computer simulations, we explore different limits of the feedback and demonstrate the shift in the onset of rigidity depending on the limit. The limit of tension-suppressed severing delays stress relaxation and shifts the transition into the bending-dominated regime to lower-than-expected connectivity. In contrast, tension-enhanced severing accelerates relaxation and shifts the transition to higher-than-expected connectivity. It is also found that the magnitude of this shift depends on the applied shear strain and the strength of the feedback. Our theoretical approach clarifies some microscopic aspects of these phenomena. Understanding the impact of such feedback mechanisms can provide valuable insights into designing systems by tuning the feedback to the desired response.
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Atomic Physics

Non-destructive cavity readout of molecules for precision measurements

Alejandro Salas-Estrada, Silviu-Marian Udrescu, Geoffrey Zheng et al. (+6 more)

We propose a non-destructive method to measure the population of molecules in a selected rotational-hyperfine state by coupling them to a high-finesse optical cavity. In contrast to traditional techniques, our approach enables fast (less than 1 ms) repeated measurements with reduced heating and losses, and with precision below the standard quantum limit. The method is particularly advantageous for radioactive molecules, systems of high interest for symmetry violation searches, for which production and sample size are limited, and repeated interrogation is essential for improved sensitivity.
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All authors Alejandro Salas-Estrada, Silviu-Marian Udrescu, Geoffrey Zheng, Qian Wang, Arian Jadbabaie, Vladan Vuletić, David DeMille, Ronald F. Garcia Ruiz, Edwin Pedrozo-Peñafiel

Optics

Near-UV Single-Pixel Imaging with All-Inorganic Lead-Free Perovskite

Jiyun Kim, Xinyang Yu, Zijian Feng et al. (+4 more)

Single-pixel imaging (SPI) is a powerful computational imaging technology that reconstructs spatial information from sequentially encoded optoelectrical signals without pixelated detector arrays. Solution-processible metal halide perovskites are promising photoactive candidates for SPI, but the toxicity of lead-based compositions remains a critical barrier to practical development. Here, we demonstrate one-step fabrication of low-dimensional, lead-free K$_2$CuBr$_3$ thin film as near-UV photoactive channels for single-pixel imaging. By systematic antisolvent engineering, compact and uniform K2CuBr3 films are obtained and integrated into planar photoconductors devices. The resulting photodetectors exhibit stale photoswitching under 405 nm illumination, low dark current on the order of $10^{-10}$ A, with fast response and recovery time 38.82 and 61.94 $\mu$s, respectively. Integrated into an SPI configuration, the K2CuBr3 photoconductor successfully reconstructs near-UV images, with the signal-to-noise ratio improving from 16.4 to 31.7 dB as the illumination irradiance increases. This work highlights solution-processed lead-free copper halides as promising photoactive materials for compact, non-toxic and cost-effective UV computational imaging systems.
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All authors Jiyun Kim, Xinyang Yu, Zijian Feng, Chun-Ho Lin, Dewei Chu, Igor Aharonovich, Chaohao Chen

Optics

In-situ Silicon Doped hBN by High-Temperature Molecular Beam Epitaxy Enables Single Photon Emission

Jiyun Kim, Nika Teran, Juliette Plo et al. (+8 more)

Hexagonal boron nitride (hBN) has emerged as a leading host for optically active quantum defects. Yet introduction of specific impurity species other than carbon remains unexplored. Here, we demonstrate an in-situ silicon doping of hBN grown by high-temperature molecular beam epitaxy (HT-MBE). By systematically varying the growth temperature from 900 to 1390 {\deg}C under a constant silicon flux, we establish an optimal window for Si incorporation to host a diverse range of emitters from 430-750 nm at room temperature. By transferring silicon-doped hBN film on SiO$_2$ substrate, we verified that single photon emitter activity was sustained in the hBN, demonstrating compatibility with device integration. The plausible origins of the observed optical transitions were discussed, and several potential candidates were proposed. Our results demonstrate a step toward a comprehensive understanding of in-situ doping of hBN and its utilization for quantum photonic applications.
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All authors Jiyun Kim, Nika Teran, Juliette Plo, Jonathan Bradford, Guillaume Cassabois, Amy F. M. Collins, Tin S. Cheng, Christopher J. Mellor, Shery L. Y. Chang, Sergei V. Novikov, Igor Aharonovich

Space Physics · Cross-listed from astro-ph.SR

Large ephemeral regions and their tilt angles

Rambahadur Gupta, Anu Sreedevi, Bibhuti Kumar Jha et al. (+1 more)

The ephemeral regions (ERs), which are short-lived bipolar magnetic regions that emerge across the solar cycle but do not appear as sunspots, play a crucial role in the Sun's magnetic flux budget. However, their properties, particularly the tilt distribution, are poorly constrained by observations. In this study, we isolate ERs from the Automatic Tracking Algorithm for Bipolar Magnetic Regions (AutoTAB) catalog during Solar Cycles 24 and 25 by applying flux and footpoint-separation thresholds. Although AutoTAB was designed to track high-flux regions, it also records ephemeral regions with fluxes of 10^19 to 10^20 Mx, placing them at the upper end of the ER spectrum. The isolated ERs have an average lifetime of 1.2 days. Footpoint separation begins at supergranular scales (about 20 Mm), grows during the first half of the lifetime, and then saturates. ERs occur most frequently near solar minima, consistent with earlier studies and likely reflecting AutoTAB's greater sensitivity to weaker regions when strong BMRs are scarce. Tilt properties reveal a more complex picture. For lifetimes shorter than two days, ERs show a broad, noisy distribution with no systematic latitude dependence. Including longer-lived ERs produces a weak, though statistically insignificant, increasing trend with latitude, suggesting that short-lived ERs are shaped by turbulent convection, while stronger, longer-lived ERs may retain Coriolis-imparted tilts. Overall, these results support the view that ERs occupy the low-flux end of the BMR spectrum and contribute meaningfully to the solar dynamo.
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All authors Rambahadur Gupta, Anu Sreedevi, Bibhuti Kumar Jha, Bidya Binay Karak

Fluid Dynamics

Breaking-induced energy dissipation of surface gravity waves at varying scales and co-flowing wind stresses

Rui Cao, Enrique M. Padilla, Xu Chen et al. (+1 more)

Breaking-induced energy dissipation is studied for individual unsteady breaking waves using laboratory measurements of unidirectional surface gravity wave groups across a range of wave scales and wind stresses. A refined framework to estimate breaking-induced dissipation $\Delta E_{br}$ is proposed that accounts for background dissipation from non-breaking processes. Using this framework, we show that variations in wave scale primarily influence breaking energetics, such as fractional dissipation $\Delta E_{br}/E_0$ and dissipation rate $\epsilon_b$, by modifying the breaking onset threshold. Also, co-flowing wind systematically reduces both $\Delta E_{br}/E_0$ and $\epsilon_b$ relative to unforced conditions, as wind-forced waves break earlier with reduced crest forward-leaning. Exploiting the crest-front steepness at incipient breaking $\mathcal{S}_{\text{front}}(t_b)$ to characterise breaking onset and local crest geometry, we formulate a scaling for $\epsilon_b$ based on this local measure. This then yields $\Delta E_{br}/E_0 \propto \beta^{*}\,\mathcal{S}_b\,(\tau_b/T_b)$, where $\beta^{*}$ is crest forward leaning, $\mathcal{S}_b$ local steepness, and $\tau_b/T_b$ non-dimensional breaking duration. This scaling highlights the important roles of crest asymmetry and breaking duration in setting the breaking energy dissipation. Finally, we consider the breaking strength parameter $b$ by assessing existing steepness-based scaling laws, and relate $b$ to $\mathcal{S}_{\text{front}}(t_b)$, yielding an approximately linear dependence once the breaking-onset threshold is considered.
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All authors Rui Cao, Enrique M. Padilla, Xu Chen, Adrian H. Callaghan

Chemical Physics

Control of protein activity by photoinduced spin polarized charge reorganization

Shirsendu Ghosh, Koyel Banerjee-Ghosh, Dorit Levy et al. (+6 more)

Considerable electric fields are present within living cells, and the role of bioelectricity has been well established at the organismal level. Yet little is known about electric-field effects on protein function. Here we use phototriggered charge injection from a site-specifically attached ruthenium photosensitizer to directly demonstrate the effects of charge redistribution within a protein. We find that binding of an antibody to phosphoglycerate kinase (PGK) is increased two folds under illumination. Remarkably, illumination is found to suppress the enzymatic activity of PGK by a factor as large as three. These responses are sensitive to the photosensitizer position on the protein. Surprisingly, left (but not right) circularly polarized light elicits these responses, indicating that the electrons involved in the observed dynamics are spin polarized, due to spin filtration by protein chiral structures. Our results directly establish the contribution of electrical polarization as an allosteric signal within proteins. Future experiments with phototriggered charge injection will allow delineation of charge rearrangement pathways within proteins and will further depict their effects on protein function.
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All authors Shirsendu Ghosh, Koyel Banerjee-Ghosh, Dorit Levy, David Scheerer, Inbal Riven, Jieun Shin, Harry B. Gray, Ron Naaman, Gilad Haran

Chemical Physics

Dynamic Breaking of Mirror Symmetry in Spin-Dependent Electron Transport through Chiral Media Causes Enantiomeric Excesses

Yossi Paltiel, Daniel Goldberg, Nir Yuran et al. (+9 more)

Two fundamental questions have puzzled scientists for more than 150 years. How did life become homochiral and why was this specific handedness selected. Recently, it has been shown that homochirality could have emerged through the enantioselective interactions of molecules with magnetic substrates due to the asymmetric crystallization of an RNA precursor on a magnetite substrate, abundant on early Earth. This phenomenon is based on the chirality-induced spin selectivity,CISS, effect. Despite its robustness, this model could not provide an answer to the second question: why one specific handedness, D for RNA, was selected. Here we demonstrate that spin-involving processes can have different outcomes in the two enantiomers of chiral molecules. In chiral molecules with unpaired electrons or while electrons are passing through them, the total angular momentum vector, J, is aligned along the easy axis, which is defined by the magnetic anisotropy induced by the spin-orbit coupling and asymmetry of the molecular field. The magnitude J is the same for both enantiomers, but the vectors may be aligned differently relative to the molecular frame in the two enantiomers. This difference can be quantified by, for example, by the angle between J and electric dipole moment of the molecule. We show by direct measurements, theory, and ab initio calculations that dynamic spin processes in chiral molecules could result in different efficiencies of spin-related phenomena, including the interaction of chiral molecules with magnetic surfaces. The findings may provide an explanation for the specific homochirality in nature.
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All authors Yossi Paltiel, Daniel Goldberg, Nir Yuran, Shira Yochelis, Jia Hao Soh, Christopher Seibe, Jurgen Gauss, Shmuel Zilberg, S. Furkan Ozturk, Jonas Fransson, Anna I. Krylov, Ron Naaman

Fluid Dynamics

Interaction between vapor bubbles during flow boiling heat transfer in microchannels

Odumuyiwa A. Odumosu, Mengqi Ye, Tianyou Wang et al. (+1 more)

Microchannel flow boiling is an efficient cooling solution for high-power-density miniaturized systems. Many studies on microchannel flow boiling focused on the dynamics of single vapor bubbles, while neglecting the interaction between bubbles, which is important in relevant applications. Here, numerical simulations are carried out to study the interaction between multiple vapor bubbles in microchannel flow boiling. The results show that for different numbers of bubbles in the microchannels with the same initial size and position of leading bubbles, the bubble size in a single-bubble microchannel is larger compared to the leading bubble of multiple-bubble cases because of heat absorption by the vaporization at the rear bubbles. As the initial volume ratio between the leading bubble and the rear bubble decreases, the leading bubble size in the downstream becomes smaller because of the reduced contact with the superheated thermal boundary layer. With increasing the Reynolds number, both the leading and the trailing bubbles increase slightly in size in the upstream of the heated region, because the bubbles at higher Reynolds number move faster and firstly get in contact with the superheated fluid. The increase in the bottom wall thickness increases the growth rate of the multiple bubble sizes with earlier bubble coalescence because of the higher upstream wall temperature by heat conduction in the solid wall.
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All authors Odumuyiwa A. Odumosu, Mengqi Ye, Tianyou Wang, Zhizhao Che

Chemical Physics

Control of Electrons Spin Eliminates Hydrogen Peroxide Formation During Water Splitting

Wilbert Mtangi, Francesco Tassinari, Kiran Vankayala et al. (+6 more)

The production of hydrogen through water splitting in a photoelectrochemical cell suffers from an overpotential that limits the efficiencies. In addition, hydrogen-peroxide formation is identified as a competing process affecting the oxidative stability of photoelectrodes. We impose spin-selectivity by coating the anode with chiral organic semiconductors from helically-aggregated dyes as sensitizers; Zn-porphyrins and triarylamines. Hydrogen peroxide formation is dramatically suppressed, while the overall current through the cell, correlating with the water splitting process, is enhanced. Evidence for a strong spin-selection in the chiral semiconductors is presented by magnetic conducting (mc-)AFM measurements, where chiral and achiral Zn-porphyrins are compared. These findings contribute to our understanding of the underlying mechanism of spin selectivity in multiple electron-transfer reactions and pave the way towards better chiral dye-sensitized photoelectrochemical cells.
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All authors Wilbert Mtangi, Francesco Tassinari, Kiran Vankayala, Andreas Vargas Jentzsch, Beatrice Adelizzi, Anja R.A. Palmans, Claudio Fontanesi, E.W. Meijer, Ron Naaman

Computational Physics · Cross-listed from math.NA

An alternating learning-based collocation method for solving inverse elliptic problems

Zhizhong Kong, Jerry Zhijian Yang and Cheng Yuan

We propose the Alternating Learning-Based Collocation (ALBC) method for solving inverse elliptic problems. Our approach employs sinusoidal shallow networks as adaptive basis generators. By alternately updating the state variable and the unknown parameter, we decompose the original nonconvex joint optimization problem into a sequence of tractable linear subproblems. This strategy effectively overcomes the fixed-basis limitations of classical collocation methods while avoiding the slow convergence typically encountered in deep learning approaches. Theoretically, we establish stability estimates and prove the convergence of the proposed algorithm. Numerical experiments on five benchmark problems demonstrate the efficacy of ALBC, which consistently outperforms the standard collocation method in accuracy. Furthermore, it achieves performance comparable to or better than that of physics-informed neural networks at a substantially lower computational cost. Finally, the method remains robust under noise levels of up to twenty percent.
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Optics

Manifold partitioning induced sequential optical reasoning and decision framework for photonic computing

Zhihao Li, Jing Pan, Wei Yan et al. (+4 more)

Real-world data are intrinsically embedded in highly entangled manifolds, making the extraction of separable representations a central challenge for artificial intelligent (AI) systems. While optical neural networks (ONNs) offer ultrafast and energy-efficient data processing, their capacity is constrained by limited physical depth. Here, we introduce a sequential optical reasoning and decision (SORD) framework, an architecture that performs time-sequenced hierarchical inference by decomposing global tasks into coarse-to-fine steps via geometry-guided data partitioning. At each step, SORD executes small reasoning via dynamic operator selection, effectively reducing the overall task complexity without scaling up physical architecture. Experimentally, SORD enables a single-layer diffractive ONN to achieve otherwise intractable 100-class optical fiber speckle classification with 94% accuracy and a system energy efficiency of 23.3 TOPS/W. This high-fidelity recognition is further examined in a human-machine interface, featuring real-time interactive all-optical sensing. Overall, our work establishes a scalable and hardware-efficient approach to expanding the effective expressivity of compact photonic AI systems, and may advance their deployment in applications requiring real-time sensing, inference, and control.
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All authors Zhihao Li, Jing Pan, Wei Yan, Yu Xie, Lingmei Ma, Xiaoyu Sun, Min Qiu

Computational Physics

Differentiable Particle-Mesh Ewald with Cartesian Tensor Message Passing for Learning Long-Range Electrostatics and Dipole Response

Zhiyue Guo, Junjie Wang, Haoting Zhang et al. (+4 more)

Machine learning interatomic potentials (MLIPs) can approach quantum accuracy for short-range chemistry, but most architectures remain local and fail to capture the long-range electrostatic and polarization interactions essential for ionic, polar, and interfacial systems. Recent Ewald-based MLIPs show that locally predicted electrostatic variables can recover important long-range physics, including multipolar response. However, many energy-based implementations still compute reciprocal-space terms by direct summation over k vectors, leaving a gap with production molecular dynamics, where particle-mesh Ewald (PME) with O(NlogN) scaling is standard. Here we introduce a fully differentiable PME framework for learned charges and learned atomic dipoles within an E(n)-equivariant Cartesian tensor message passing network. Charges are predicted from scalar local features, while dipoles are predicted from equivariant vector features and enter the same particle-mesh solver as an effective bound charge density. This dipolar density is constructed using analytic real-space gradients of Hockney-Eastwood spline assignment weights, enabling charge-dipole and dipole-dipole long-range forces to be trained end-to-end through FFT-space electrostatics without direct charge or dipole supervision. On a charged-dimer test case, the differentiable PME module reproduces explicit Ewald energies and forces to numerical precision when assignment-kernel deconvolution is enabled. On molten NaCl, the charge and dipole long-range channel gives the lowest force RMSE among the tested models, while all energy RMSE values remain in the sub-meV per atom regime. Timing tests show the expected crossover from explicit Ewald summation to particle-mesh scaling. These results establish differentiable dipole PME as a scalable route toward polarization-aware MLIPs for condensed-phase and interfacial systems.
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All authors Zhiyue Guo, Junjie Wang, Haoting Zhang, Zhixin Liang, Ziyang Yang, Yujian Pan, Jian Sun

Optics

Mid-Infrared Single-Photon Edge Enhanced Imaging based on Nonlinear Vortex Filtering

Yinqi Wang, Jianan Fang, Tingting Zheng et al. (+6 more)

Edge enhanced imaging via the spiral phase contrast enables to reveal the phase or amplitude gradients of a target, which has been proved useful in feature recognition, machine vision, and object identification. A long quest is to extend the operation wavelength into the mid-infrared (MIR) region, as highly demanded in various fields including infrared sensing, astronomic observation, and biomedical diagnosis. Here, we demonstrated ultra-sensitive MIR imaging at the single-photon level based on nonlinear frequency upconversion, where the spectrally converted replica of the MIR object image at 3070 nm was captured by a silicon electron multiplying charged coupled device. The imaging sensitivity was significantly improved by the coincidence pulsed pumping with a spectro-temporal optimization. Furthermore, the edge enhancement has been realized by imprinting the spiral phase pattern of the pump onto the upconverted field at the Fourier plane within the nonlinear crystal. Such a nonlinear spatial filter not only provided an effective way to implement the required high-fidelity vortex screening in the edge enhanced detection, but also rendered the MIR illumination into a visible image in an efficient and low-noise fashion. The presented system for MIR edge enhanced imaging might facilitate immediate applications in label-free histopathological diagnosis and non-destructive defect inspection.
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All authors Yinqi Wang, Jianan Fang, Tingting Zheng, Yan Liang, Qiang Hao, E Wu, Ming Yan, Kun Huang, Heping Zeng

Optics

High-precision passive stabilization of repetition rate for a mode-locked fiber laser based on optical pulse injection

Tingting Yu, Jianan Fang, Qiang Hao et al. (+4 more)

We have proposed and implemented a novel scheme to obtain high-precision repetition rate stabilization for a polarization-maintaining mode-locked fiber laser. The essential technique lies in the periodic injection of electronically modulated optical pulses into a nonlinear amplifying loop mirror within the laser resonator. Thanks to the nonlinear cross-phase modulation effect, the injected pulses referenced to an external clock serves as a stable and precise timing trigger for an effective intensity modulator. Consequently, synchronous mode-locking can be initiated to output ultrafast pulses with a passively stabilized repetition rate. The capture range of the locking system reaches to a record of 1 mm, which enables a long-term stable operation over 15 hours without the need of temperature stabilization and vibration isolation. Meanwhile, the achieved standard deviation is as low as 100 $\mu$Hz with a 1-s sample time, corresponding to a fluctuation instability of 5.0$\times10^{-12}$. Additionally, the repetition rate stabilization performance based on the passive synchronization has been systematically investigated by varying the average power, central wavelength and pulse duration of the optical injection.
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All authors Tingting Yu, Jianan Fang, Qiang Hao, Kangwen Yang, Ming Yan, Kun Huang, Heping Zeng

Plasma Physics · Cross-listed from nucl-th

A semi-classical study of muon-enhanced proton-boron-11 fusion

Hong-Yi Wang, Ming-Yu Chen, Hao-Le Ma et al. (+1 more)

A recent theoretical study has suggested that muons can enhance proton-boron-11 (p-$^{11}$B) reaction cross-section by several orders of magnitude in the low-energy regime. In this work, we investigate this reaction process using a semi-classical treatment, that is, a muon and a proton first form a muonic hydrogen atom p$\mu$, which subsequently collides with a $^{11}$B nucleus. During the collision, the p$\mu$ atom approaches the $^{11}$B nucleus and is then repelled by the Coulomb repulsive potential. At the distance of closest approach between the proton and the $^{11}$B nuclei in this classical scattering process – namely, the classical turning point – quantum tunneling through the Coulomb barrier can occur, allowing the proton to penetrate into the range of the nuclear force of the $^{11}$B and trigger the fusion reaction. We determine the turning point statistically by using the classical trajectory Monte Carlo method, where the initial phase-space distributions of the proton and muon are sampled from the ground-state microcanonical distribution. Our results show that, compared with the bare-nucleus case, the reaction cross-section is enhanced by several orders of magnitude in the low-energy region. A comparison with the static charge-shielding treatment reveals certain differences; however, both approaches demonstrate that the catalytic effect of the muon can significantly enhance the low-energy p-$^{11}$B reaction cross-section.
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All authors Hong-Yi Wang, Ming-Yu Chen, Hao-Le Ma, Zhu-Fang Cui

Optics

Single-Photon Infrared Imaging with a Silicon Camera Based on Long-Wavelength-Pumping Two-Photon Absorption

Jianan Fang, Yinqi Wang, E Wu et al. (+3 more)

We experimentally demonstrated an ultra-sensitive imaging system for telecom photons based on the non-degenerate two-photon absorption in a silicon-based electron multiplying charge-coupled device (EMCCD). The proposed long-wavelength-pumping scheme with mid-infrared pulsed excitation could not only effectively increase the two-photon absorption coefficient, but also significantly suppress the background noise caused by the harmonic absorption of the strong pumping field. In comparison to the photoelectric response via the degenerate two-photon absorption, the implemented configuration could offer over 30-folded enhancement of the photon-counting rate in the infrared imaging. The resulting detection sensitivity up to 1 photon/pixel/pulse was unprecedentedly approached, thus facilitating the single-photon operation. The elimination of the stringent phase matching as typically required in the optical parametric conversion has led to a high spatial resolution of 13 $\mu$m. Moreover, the on-chip nonlinearity of the optical imager would enable a broadband spectral window and an enlarged field of view. In combination with the 5-ps temporal resolution due to the coincident optical gating, the presented imaging system would find various promising applications, such as low-light fluorescence lifetime microscopy and photon counting time-of-flight 3D imaging.
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All authors Jianan Fang, Yinqi Wang, E Wu, Ming Yan, Kun Huang, Heping Zeng

Chemical Physics

Variational free complement method with Gaussian-expanded complement functions: convergence with fixed Gaussian expansion length

Cong Wang

For the free complement theory with Gaussian-expanded complement functions, the energy convergence of $n_\mathrm{G} = \mathrm{constant} < \infty, n\rightarrow\infty$ is discussed, where $n_\mathrm{G}$ is the number of the Gaussian functions in the STO-$n$G expansion.

Atomic Physics · Cross-listed from gr-qc

Gravitational-wave astronomy with a space-based optical clock network

Dhruva Ganapathy, Divya Singh, Sammith Singamsetty et al. (+1 more)

Since the first detection of a merging binary black hole system a decade ago, gravitational-wave astronomy has emerged as a powerful tool for astrophysics. Future space-based observatories, such as the Laser Interferometer Space Antenna (LISA), will unlock the millihertz (mHz) band, which remains entirely inaccessible to ground-based detectors due to terrestrial noise. In parallel, proposed atom-based gravitational-wave detectors, specifically those based on space-based optical clocks and atom interferometers, offer capabilities that are unique and complementary to traditional optical interferometers. Their highly tunable character enables sensitive measurements across a broad frequency band extending from the mHz up to and possibly even above the Hz regime. In this work, we investigate the use of one-way Doppler tracking in space-based atomic clock networks operating in concert with detectors like LISA. We analyze the dominant noise sources and develop dedicated measurement protocols, which operate in a targeted mode, using an externally supplied signal model to track the response coherently as the source chirps. Performing preliminary parameter estimation on simulated signals, we demonstrate how these detectors could be used to extract critical astrophysical information about binary gravitational-wave sources. We further show that the same instrument retains sensitivity in a search mode, where no prior on the source is assumed.
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All authors Dhruva Ganapathy, Divya Singh, Sammith Singamsetty, Shimon Kolkowitz

Instrumentation and Detectors

He-CF4-CH4 ternary mixtures as target gas for the CYGNO directional dark matter experiment

F.D. Amaro, R. Antonietti, E. Baracchini et al. (+41 more)

The CYGNO collaboration is advancing a high-resolution optical Time Projection Chamber (TPC) for directional dark matter searches and solar neutrino spectroscopy at LNGS. The detector uses a He-40%CF4 gas mixture at atmospheric pressure and a triple-GEM cascade for ionization signal amplification. Scintillation light from GEM electron avalanches is read out using sCMOS cameras, enabling high sensitivity to interactions in the few keV range, alongside precise ionization event tracking and particle identification. This study investigates the effects of adding 3-10% methane to the He-40%CF4 mixture. Methane improves the electrical stability of the TPC, allowing for higher GEM voltages before discharge onset, which compensates for its scintillation quenching and leads to enhanced overall scintillation yield. Compared to prior studies performed with isobutane, methane demonstrates a lower quenching effect on visible and UV photons while maintaining good energy resolution. Importantly, the inclusion of methane lowers the dark matter detection threshold by providing a lighter target and extending track lengths of light nuclear recoils, thus enhancing directional discrimination. These results establish methane as a promising additive for optimizing CYGNO's performance in detecting low-mass dark matter candidates.
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All authors F.D. Amaro, R. Antonietti, E. Baracchini, L. Benussi, C. Capoccia, M. Caponero, L.G.M de Carvalho, G. Cavoto, I.A. Costa, A. Croce, M. D'Astolfo, G. D'Imperio, G. Dho, E. Di Marco, J.M.F. dos Santos, D. Fiorina, F. Iacoangeli, Z. Islam, H. P. Lima Jr, G. Maccarrone, R.D.P. Mano, D. J. G. Marques, L.G.M. de Carvalho, G. Mazzitelli, P. Meloni, A. Messina, C.M.B. Monteiro, R.A. Nobrega, I.F. Pains, E. Paoletti, F. Petrucci, S. Piacentini, D. Pierluigi, D. Pinci, F.Renga, R.J. da C. Roque, A. Russo, G.Saviano, P.A.O.C. Silva, R.C. Sousa, N.J.C. Spooner, R. Tesauro, S. Tomassini, D. Tozzi

History and Philosophy of Physics

Relativity from the Perspectives of Observers

Tao Wang and Yu Shi

This paper reviews the role of observers in the development of relativity theory, from special relativity to general relativity, emphasizing that observer-dependent descriptions are as fundamental as the covariance of physical laws. This paper reviews the role of observers in the development of relativity theory, from special relativity to general relativity, emphasizing that observer-dependent descriptions are as fundamental as the covariance of physical laws. After the introduction of a geometric framework for observers using timelike worldlines, Frenet-Serret formulas, projection operators, and the Frobenius condition for hypersurface-orthogonal families, the paper revisits key problems in early relativistic mechanics, such as the transformation of velocity and acceleration, the variational principle for particle motion, and the Ehrenfest paradox concerning rigid rotation. It shows that while early physicists often conflated coordinate systems with reference frames, their results remain valid because the underlying geometric objects are observer-independent. The historical analysis, from Einstein's 1905 work to the development of general relativity and later advances such as Hawking radiation, demonstrates that clarifying the concept of observers not only resolved paradoxes but also paved the way toward a field-theoretic formulation of gravity. The paper concludes that observer dependence, far from being a nuisance, is an essential ingredient for understanding spacetime physics.
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Sunday 31 May

Geophysics

Korzhinskii-Net: Physics-Informed Neural Network for Sub-Surface Mineral Prospectivity Modelling

Boris Kriuk

Mineral prospectivity modelling (MPM) underpins exploration economics, yet most operational pipelines reduce to data-driven classifiers trained on shallow surface proxies. Such models are blind to the subsurface physics that actually localises ore: heat advection, fluid flow, and lithology-dependent precipitation. We present Korzhinskii-Net, a 2-D radial physics-informed neural network (PINN) that couples Darcy flow, advective-diffusive heat transport, and a softplus-saturated reaction rate into a single differentiable forward model, weakly supervised by surface and remote-sensing proxies. The network is named after Dmitri S. Korzhinskii (1899-1985), whose theory of infiltration metasomatism provides the physical scaffold. We evaluate Korzhinskii-Net on six ore provinces spanning three commodity classes - Udokan (sandstone-hosted Cu), Sukhoi Log, Olimpiada, and Berezovskoye (orogenic Au), Vorontsovskoye (Carlin-type Au), and Dalnegorsk (skarn polymetallic) - under a fair, leakage-controlled 5-fold cross-validation protocol with hard ring-shaped negatives and baseline proxy features disabled. Korzhinskii-Net attains a mean PR-AUC of 0.708 versus 0.235 for the strongest classical baseline (support vector machine), and a mean fractional rank of 0.036 versus 0.475. The improvement is consistent across all six provinces and three commodity systems, suggesting that physics-informed differentiable simulators, even when constrained only by global open-data proxies, can recover localisation patterns that pure feature-based learners systematically miss. We release the full pipeline and evaluation harness as open source.
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Atmospheric and Oceanic Physics

On an Airborne Proton Accelerator for Enhancing Cloud Formation or Inducing their Precipitation

Orfeu Bertolami

We argue that an airborne proton accelerator is an interesting tool for weather control. Following the findings of the CLOUD experiment at CERN, one expects that a beam of protons, likewise cosmic rays and other aerosols, can enhance the formation of low-altitude clouds, allow for tailor made cooling of overheated areas and induce the precipitation of high-altitude clouds that trap solar radiation reflected from the ground. The proton accelerator can also be used to mitigate droughts, regularise precipitation and avoid that it takes place through large and harmful storms.
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General Physics

Quantitative Nonequilibrium Pathway from Fundamental Physics to the Emergence and Persistence of Exoplanetary Biospheres

Slava G. Turyshev

We present a physics-based framework that runs from fundamental interactions and constants to biospheres, using a sequence of quantitative nonequilibrium thresholds ("gates"). Each gate is an inequality in measurable variables-free-energy flux, reaction-transport rates, replication fidelity, coding capacity, ecological closure, and climate feedback gains. Crucially, the gate vector is anchored in fundamental physics: dimensionless constants, nuclear resonance placements (e.g., the $^{12}$C Hoyle state), statistical mechanics (Landauer's bound $k_BT \ln 2$) fix the energetic, kinetic, information-theoretic margins that propagate through the gates. This anchoring lets us propagate sensitivities of the constants into biosphere-level metrics (net primary productivity (NPP), cycle-closure ratios, and climate feedback gain), yielding an end-to-end map from constants to biospheres. The framework is predictive: it yields testable inequalities, margin rankings, and population-level correlations between stellar and planetary boundary conditions and biosphere feasibility. It does not claim point predictions of life prevalence; rather, it specifies which gate margins are observable-bounded versus prior-dominated under explicitly stated chemistry/solvent families and forward models. Darwinian dynamics (heritable variation under selection) appears mid-pipeline; the end of the pipeline is a planet-scale biosphere capable of sustaining positive NPP, closing elemental cycles over geologic time. Questions of prevalence are secondary; our primary objective is to establish a constructive physics->chemistry->biology->genetics->ecosystems pipeline with testable margins and observables. As a result, we recast abiogenesis and biosphere persistence as a gate vector of falsifiable inequalities and map their margins to exoplanet observables, turning the problem into a phase diagram with explicit, testable slack.
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