Materials Science
Sorption Molecular Dynamics of Point Defects in 2D Materials with a Machine Learning Potential
Nils-Ruben Skogemyr, Albin Sjöstedt, Isak Wernroth et al. (+6 more)
Defect engineering is a crucial tool for tuning and tailoring the properties of two-dimensional (2D) materials. A key challenge is identifying which defects are kinetically stable at room temperature and sufficiently promising to warrant further investigation. However, identifying stable defects with suitable properties using first-principles calculations, such as density functional theory (DFT) is computationally demanding, effectively limiting the scope of high-throughput studies. In this work, we investigate whether the machine learning interatomic potential MACE can reproduce sorption trends (adsorption vs. absorption) previously obtained from high-throughput DFT calculations and extend the analysis to elevated temperatures. A total of 17,624 defect structures from the ADAQ database are simulated using MACE-accelerated molecular dynamics (MD) at both 0 K and 300 K. The results show that MACE successfully reproduces the overall sorption trends observed in DFT calculations at 0 K at a fraction of the computational cost. Simulations performed at 300 K further indicate that the qualitative sorption trends remain largely the same when including finite-temperature effects. These findings demonstrate that MACE-driven MD can be used as an effective high-throughput prescreening tool for defect-related studies in 2D materials, specially related to sorption. While conventional first-principles methods, such as DFT, remain necessary for accurate and quantitative validation, the use of MLIPs enables MD simulations of finite-temperature defect behavior at a fraction of the computational cost of DFT-based MD.
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All authors Nils-Ruben Skogemyr, Albin Sjöstedt, Isak Wernroth, Isak Häggqvist, Isac Ljungwald, Hans-Ove Åkesson, Henricus R.A. ten Eikelder, Rickard Armiento, Joel Davidsson
Materials Science
Transverse magneto-gyrotropy driven by spin-induced ferroaxiality
Yoshihiro Okamura, Takumi Kagawa, Ayano Nakamura et al. (+5 more)
Photon chirality is inherently sensitive to structural handedness and magnetism, which break spatial inversion and time-reversal
symmetries, respectively. Ferroaxial order, by contrast, hosts two-dimensional chirality while preserving both
symmetries, thereby precluding its direct coupling to
photon chirality. Intertwining ferroaxiality with
magnetic order, however, may lift such constraints and enable unconventional coupling to
photon chirality. Nevertheless, the optical response arising from such intertwined order has yet to be demonstrated experimentally. Here, we demonstrate transverse magneto-gyrotropy arising from
spin-driven ferroaxiality in the Weyl magnet EuCd2Sb2. Whereas the conventional polar magneto-optical Kerr effect is governed by magnetization parallel to the light-propagation direction, we observe a gyrotropic response associated with magnetization transverse to the light-propagation direction. The optical rotation exhibits a characteristic 120-degree periodicity upon rotation of the in-plane
magnetic field, reflecting the threefold
symmetry of the emergent ferroaxial state and revealing the ferroaxial origin of the transverse gyrotropic response. This coupling to
photon chirality enables vectorial control of the gyrotropic response through the
magnetic field direction. Our findings establish an interaction between
photon chirality and transverse magnetization enabled by intertwined ferroaxial and
magnetic orders, demonstrating a novel form of multiferroicity with functional light-matter interaction.
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All authors Yoshihiro Okamura, Takumi Kagawa, Ayano Nakamura, Shinichi Nishihaya, Masaki Uchida, Susumu Minami, Ryotaro Arita, Youtarou Takahashi
Solar and Stellar Astrophysics
HD 152384: A 5 Myr old debris disk system showing a gaseous ring of refractory elements at the dust sublimation radius
Mario van den Ancker, Daniela Iglesias, Olja Panić et al. (+2 more)
Context: Circumstellar gas around young
stars provides key insights into
planet formation and disk
evolution. HD 152384, a young (5 Myr) A0 V
star in Sco-Cen, shows hybrid-disk traits: a modest infrared excess from small dust grains and atomic emission lines dominated by refractory elements, but its disk structure and origin remain unclear. Aims: We characterise the kinematics and excitation of the circumstellar gas around HD 152384 and constrain the physical properties of its emitting region. Methods: We use new high-resolution optical and near-infrared VLT/UVES and VLT/CRIRES spectra to re-examine the circumstellar environment of HD 152384, previously suggested to host a broad, gas-rich disk. Results: The observations reveal 74 narrow, double-peaked emission lines of Fe, Mg, Si, and Ca, with similar profiles and a 103 km/s peak separation. Keplerian modelling places the gas in a geometrically thin ring at 0.09-0.12 au, close to the dust sublimation radius (0.10-0.14 au for a sublimation temperature of about 1500 K). The Fe I emission is optically thick, whereas the optically thin Mg I lines imply 2.2 x 10^22 kg (3.6 x 10^-3 Earth masses) of magnesium gas in the ring. Conclusions: The dust and gas properties are consistent with a secondary origin involving collisions of rocky planetesimals. We propose that small collision-produced dust grains spiral inward and sublimate near the dust sublimation radius, accumulating atomic gas there. HD 152384 thus represents a young analogue of gas-bearing debris disks such as Beta Pictoris and gaseous debris disks around metal-polluted white dwarfs, offering a new window on the early violent processing of rocky planetesimals.
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All authors Mario van den Ancker, Daniela Iglesias, Olja Panić, Monika Petr-Gotzens, Miguel Vioque
Solar and Stellar Astrophysics
Flares and flux ropes: an entangled story
Rony Keppens, Yang Guo and Wenzhi Ruan
Solar
flares serve as standard candles for all
magnetic-reconnection-based energy releases, and their consequences into the heliosphere can be modeled from first principles. This review presents the latest developments in modeling solar
flares and their associated flux rope expulsions with state-of-the-art multidimensional magnetohydrodynamic (MHD) descriptions. Observationally established ingredients beyond a single-fluid, thermal
plasma evolution have been incorporated to varying degrees, and we highlight self-consistent efforts realized in "standard
flare" setups.
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Quantum Gases
Dicke model of open-shell atoms with tensor polarizability
Ziheng Zhu and Yu Chen
We study the extended Dicke model obtained from the scalar–vector–tensor polarizability of open-shell atoms coupled to a shared cavity mode. For a single electric-dipole channel, rotational
symmetry fixes the tensor to vector ratio; we use $^{168}\mathrm{Er}$ with $J=6$ as a product-state example. A circular pump produces a chiral Raman vertex whose tensor-dependent
matrix elements select the occupied Zeeman sector. The resulting first-order transition occurs before the empty-cavity branch loses local stability, and the ordered state is read out through $\langle\hat J_z\rangle$. A linear pump instead produces an empty-cavity $\pm x$ cat and a continuous transition into an even-$m$ cat-like state with order parameter $\langle\hat J_z^2\rangle$. With cavity loss alone, the circular trajectory emits a
photon burst and approaches a Raman-dark Zeeman pole rather than a finite-field condensate. In the linear geometry, cavity-bright modes are damped toward the cat-like branch while a dark
spin mode remains undamped. These are phenomena of that model; the vector-only controls show that they depend on the channel-fixed tensor coupling.
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Quantum Physics
Advances in quantum optomechanical control based on cavity cold-atom systems
Baijun Li, Tianxiang Lu, Jie Wang et al. (+1 more)
Cavity optomechanics represents a frontier research direction in
quantum science and technology, centered on the control and exploration of interactions between electromagnetic fields and mechanical motion. Rooted in
quantum mechanics, this field realizes efficient coupling and precise manipulation of optical fields and mechanical vibrations through the structural design and precise regulation of optical microcavities and mechanical oscillators, thereby revealing and harnessing novel
quantum phenomena. In recent years, cavity optomechanics has evolved into an interdisciplinary frontier integrating
quantum optics, condensed matter physics, and
quantum precision measurement, exhibiting profound application in both fundamental physics research and
quantum information science. With advancements in technologies such as nanomanufacturing and
laser cooling, optomechanical interactions have been successfully demonstrated in various experimental systems. Among these platforms, cavity cold-atom systems stand out as one of the ideal platforms for implementing
quantum optomechanics. Featuring exceptional environmental isolation, long
quantum coherence times, and strong light-matter interaction, these systems provide a crucial testbed for exploring strong and even ultrastrong optomechanical coupling effects as well as rich nonlinear
quantum phenomena. This paper reviews the recent progress in optomechanical control and manipulation based on cavity cold-atom systems. We first outline the fundamental principles of standard cavity optomechanical systems. Then, we describe the experimental realization of linear and nonlinear optomechanical couplings in cold-atom systems. After that, we focus on the representative applications of this platform in high-precision
quantum sensing,
quantum memory, and the preparation of macroscopic nonclassical states. Finally, we give an outlook and challenges in this field.
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All authors Baijun Li, Tianxiang Lu, Jie Wang, Hui Jing
Optics
Bias-Modulated Electronically-Tunable Optoelectronic Chromatic Dispersion in Ge PN Photodiodes
Uttama Kumar Saint, Ziv Glasser, Egor Liokumovitch et al. (+3 more)
Optoelectronic Chromatic Dispersion (OED) is a source of significant wavelength-dependent current in photodiodes, offering a pathway to computational spectroscopy in a photodiode-only platform without the need for additional optical or mechanical components. Previous studies have activated OED through light modulation. Here, we present a theoretical and experimental investigation of bias-modulated OED in the C- and L-bands in a Ge PN photodiode, where the applied bias voltage is modulated sinusoidally, and the optical illumination is held constant. The spectral response is due to wavelength-dependent optical absorption together with bias-dependent competition between carrier drift, displacement current, and mobile-charge screening. With the RF phase-shift technique, the maximum measured OED sensitivity is +4.13 deg/nm in the L-band, significantly larger than that of light-modulated OED in Ge. The 15 mdeg phase-noise floor yields a spectral resolution of 3.6 pm. These results establish bm-OED as an electronically reconfigurable dispersive mechanism for applications in chip-scale computational spectrometers, photonic integrated
circuits (PICs), on-chip RF photonics, and wavelength-division multiplexing.
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All authors Uttama Kumar Saint, Ziv Glasser, Egor Liokumovitch, Endalamaw Ewnu Kassa, Asaf Albo, Shmuel Sternklar
Biological Physics
Full Three-dimensional Cell Geometry Matters for Epithelial Fluidization
Toshikaze Chiba, Jan Rozman and Matej Krajnc
Epithelial dynamics are often studied using two-dimensional models that omit
cell height. Here, we investigate how this third dimension influences tissue fluidization driven by
cell self-propulsion. We identify three effects absent from conventional 2D models. First,
cell height controls fluidization through a reentrant transition: squamous and columnar tissues are more resistant to fluidization than cuboidal ones. Second, neighbor exchanges through transient scutoid states substantially enhance
cell motility, compared to classic T1 transitions. Third, self-propelling
cells develop pronounced apicobasal shape asymmetry, with the experimentally less accessible basal surface providing a more accurate indicator of
cells' target shape index and motility.
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Solar and Stellar Astrophysics
Tracking a solar energetic eruption and associated energetic particles from Sun to spacecraft
D. E. Morosan, M. Baumgartner-Steinleitner, K. Bhandari et al. (+17 more)
Context. Solar energetic particles (SEPs) in the heliosphere are produced by flaring processes on the Sun or shocks driven by coronal mass ejections (CMEs). Electrons, in particular, are regularly detected remotely as electromagnetic radiation (X-rays or
radio emission), which they generate through various processes, as well as in situ by spacecraft monitoring the Sun and the heliosphere. Aims. We aim to combine remote-sensing and in situ observations of an energetic solar eruption to link energetic processes in the solar corona to energetic particles observed in situ in the heliosphere. This will be done using the tools developed in the Horizon Europe SOLER project. Methods. Here, we investigate a solar energetic eruption at the Sun together with its associated signatures of accelerated electrons observed at
radio and X-ray wavelengths and combine these remote observations to in situ particles observed by spacecraft on 10 March 2024. These observations are combined with a magneto-hydrodynamic (MHD) model of the solar corona in order to make the remote to in situ connections. Results. We observe a high-energy SEP event at multiple spacecraft (>25 MeV
protons and 1 MeV electrons), despite the event being associated with a slow white-light CME. Remote observations of the Sun show that the event was associated with a fast large scale coronal wave (1400 km/s) and also multiple regions where electrons are accelerated around this large scale wave observed as type II
radio bursts. In addition, we observe a strong coronal dimming away from the main flaring region, providing evidence of field lines getting opened to interplanetary space, dislocated from the
flare site.
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All authors D. E. Morosan, M. Baumgartner-Steinleitner, K. Bhandari, N. Dresing, G. Farwa, J. A. J. Mitchell, C. Palmroos, A. Razquin, J. Zhang, C. Briand, K. Dissauer, A. Fedeli, J. Gieseler, E. K. J. Kilpua, S. Normo, J. Pomoell, D. J. Price, A. M. Veronig, A. Warmuth, R. Vainio
General Relativity and Quantum Cosmology
Testing Charged Black Holes Embedded in Anisotropic Matter and Surrounded by Plasma through Gravitational Lensing: Bounds from the Sloan Lens ACS Survey
Ritesh Pandey, Shubham Kala, Amare Abebe et al. (+2 more)
We investigate weak gravitational
lensing by a charged black hole surrounded by anisotropic matter, described by the two-component Kiselev metric, and immersed in a homogeneous
plasma. We first examine the black hole geometry and horizon structure and then derive the weak-deflection angle from the
Hamiltonian description of light propagation in
plasma, using an expansion with a fixed turning point that we verify against direct numerical integration. Using the gravitational lens equation, we obtain the Einstein-ring angle, the image positions, the total magnification and the fractional magnifications of the primary and secondary images. We then confront the model with the Einstein radii of two
galaxy-scale lenses of the Sloan Lens ACS Survey, J0008$-$0004 and J0029$-$0055. Because the Einstein angle cannot be smaller than the reduced deficit deflection, the observed radii give the mass-independent bounds $K<6.5\times10^{-6}$ and $K<4.2\times10^{-6}$, respectively. The charge correction to the Einstein radius is suppressed by $r_s/R_E\approx 5\times10^{-6}$ and is unobservable, while the
plasma parameter at the optical wavelengths of the SLACS imaging is of order $10^{-22}$ and cannot be constrained. Our results show that
galaxy-scale strong
lensing data place stringent limits on anisotropic matter surrounding the lens, whereas
plasma effects can be probed only at low
radio frequencies.
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All authors Ritesh Pandey, Shubham Kala, Amare Abebe, Hemwati Nandan, G. G. L. Nashed
Quantum Physics
Metric-Changing Quasi-Hermitian Quenches: Normalized Loschmidt Amplitude and Complex-Time Zeros
Xu-Yang Hou, Jia-Chen Tang and Hao Guo
In quasi-Hermitian mixed-state quenches, the initial and final
Hamiltonians generally possess different positive-definite metrics, so post-quench
evolution is not quasi-
unitary in the initial physical space. Choosing the preparation/measurement space as reference, we derive from first principles a normalized mixed-state Loschmidt amplitude using metric-compatible purifications. The resulting biorthogonal trace representation contains a normalization factor given by the norm of the evolved purification in the initial metric; this factor is essential for comparing states from different physical
Hilbert spaces and directly encodes the metric mismatch. We prove that this normalization function is strictly positive on the real-time axis, so real-time criticality arises solely from destructive interference in the dynamical overlap. In complex time, zeros of the normalization factor generate branch singularities distinct from Fisher zeros. For a general two-level system, we derive analytic expressions for the Fisher and normalization zeros and analyze exceptional-point scaling together with the temperature- and quasi-Hermiticity-dependent DQPT critical times in two solvable quench protocols. In contrast to metric-stationary quenches, where non-Hermitian effects may be absorbed into an equivalent Hermitian description, the metric mismatch here produces genuine non-Hermitian dynamics: a time-dependent normalization factor and complex-time branch structure that cannot be removed by any global similarity transformation.
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Solar and Stellar Astrophysics
Stationary Resistive MHD Solutions Near an Isolated Three-Dimensional Magnetic Null
Kuljeet Singh Saddal, Dieter H. Nickeler, Rodrigo Meneses Pacheco et al. (+1 more)
Magnetic null points define the
magnetic field
topology in stellar coronae, planetary magnetospheres, and astrospheres, and are commonly associated with
magnetic reconnection. We investigate the local structure of stationary three-dimensional (3D) resistive, incompressible magnetohydrodynamic (MHD) flows in the vicinity of an isolated
magnetic null and an isolated velocity stagnation point, assuming that the two nulls are colocated. The governing MHD equations are solved self-consistently using a first-order local expansion of the
magnetic and velocity fields about the null. For any given
magnetic-null configuration, the equations admit a two-parameter family of stationary solutions, comprising multiple solution branches with distinct velocity
topologies. Along these families, the velocity-null polarity can change at bifurcation points where the flow becomes effectively 2.5D. A single
magnetic null can therefore support positive-radial, negative-radial, and spiral stagnation flows, with qualitatively different inflow, outflow, and rotational properties. The associated pressure and resistivity distributions are likewise determined self-consistently and vary across the solution family, demonstrating that they are coupled to the flow
topology rather than prescribed independently. The generic solutions do not require the velocity and
magnetic separatrices to coincide, allowing
plasma to cross the
magnetic fan separatrix and providing a local reconnective flow. These results demonstrate that, in the presence of nonuniform resistivity, the
magnetic topology alone does not uniquely determine the associated stationary flow, pressure, or resistivity structure around a 3D
magnetic null, revealing the nonlinear feedback between all macroscopic variables and resistivity. The constant-resistivity field-aligned and spiral field-crossing solutions identified previously are recovered as special cases.
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All authors Kuljeet Singh Saddal, Dieter H. Nickeler, Rodrigo Meneses Pacheco, Michaela Kraus
Quantum Physics
Multi-Instantons and Exact-WKB Stokes Jumps in Multi-Well Quantum Mechanics
Alireza Behtash and Syo Kamata
We study the relation between the exact-WKB Delabaere–Dillinger–Pham Stokes jumps and the multi-instanton expansion of a one-dimensional potential with $N$ equal-depth minima. For a single barrier this relation is the Bogomolny–Zinn-Justin cancellation between the instanton–anti-instanton ambiguity and the Borel ambiguity of perturbation theory, and we extend it to every consecutive barrier interval and to the integration contours themselves. In the dilute large-$T$ regime at fixed nonperturbative grade, we derive the quasi-zero mode integral over the instanton separations from the Euclidean path integral and reduce it to Gamma and Hankel periods. With the local Weber level function of each well and one normalization per well fixed by the local Weber connection
matrix, these periods reproduce the two lateral connected exact-WKB coefficients. The two lateral contours of each instanton–anti-instanton separation differ by exactly one Hankel cycle, and this linear Picard–Lefschetz relation reproduces the Stokes jump of the connected coefficient. A numerical solution of the Schrödinger equation for a symmetric triple well confirms the resulting two-barrier level splitting. At higher fixed grade, the map from ordered event sequences to normalized scalar coefficient products is not one-to-one. At leading dilute order the scalar weight of a closed event sequence depends only on the numbers of barrier crossings, $\mathcal I\bar{\mathcal I}$ pairs, and $\mathcal I\mathcal I$/$\bar{\mathcal I}\bar{\mathcal I}$ pairs. We construct two inequivalent grade-six triple-well event sequences with the same product of local Weber amplitudes, which embed in every potential with $N\ge3$ wells. Our results hold within the regular dilute, one-loop, local Weber approximation.
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Quantum Physics
Hyperentanglement in intermediate phase-space planes: benchmarking a photon-pair source for quantum key distribution
Murilo H. Magiotto, Millena B. Novaes, Wesley B. Cardoso et al. (+5 more)
We characterize a source of
photon pairs simultaneously entangled in polarization and in the transverse spatial degree of freedom, with the spatial measurements performed in intermediate planes of the fractional
Fourier transform. The source consists of two crossed type-I
crystals in a non-collinear geometry, such that the transverse variables carry information about the
crystal of origin. Detection in the
crystal plane reveals this information completely and destroys the polarization
entanglement, so that a scheme using the near and far fields as conjugate spatial bases cannot support a parallel polarization channel. In intermediate planes both spatial bases combine position and momentum, such that the which-
crystal information is partially erased, and the polarization
entanglement survives in all four combinations of spatial bases. Applying Bell and Einstein-Podolsky-Rosen criteria to the same
photon pairs certifies both degrees of freedom simultaneously. We evaluate
quantum bit error rates and asymptotic secret key rates in each degree of freedom, and find that the source delivers two simultaneously usable channels per
photon pair.
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All authors Murilo H. Magiotto, Millena B. Novaes, Wesley B. Cardoso, Ardiley T. Avelar, 1 Paulo H. Souto Ribeiro, Stephen P. Walborn, Guilherme L. Zanin, Rafael M. Gomes
Cosmology and Nongalactic Astrophysics
Testing Departures from the $\Lambda$CDM model in f(T) Gravity with DESI DR2
Jie Zheng, Mingzhi Wang and Ming Zhang
Recent analyses combining DESI baryon acoustic oscillation (BAO) measurements with other cosmological observations have reported indications of departures from the $\Lambda$CDM model within dynamical dark energy scenarios. We investigate whether such deviations are reproduced consistently in $f(T)$
gravity and whether they persist when different cosmological observations are combined. Using the DESI DR2 BAO measurements,
Cosmic Microwave Background (CMB), and Pantheon+ Type Ia
Supernovae (SNe Ia) sample, we constrain three representative $f(T)$ models: the power-law, exponential, and
hyperbolic-tangent models. We compare the constraints obtained from different combinations of data, distinguishing changes in marginalized parameter distributions from changes in the relative statistical performance of the models. For the power-law model, the mild deviation from the $\Lambda$CDM model obtained from BAO+CMB disappears after the SNe Ia data are included. In contrast, the exponential model retains a preference for a nonzero deformation parameter in the full analysis, while the allowed parameter space of the
hyperbolic-tangent model changes substantially after the CMB distance priors are included. Importantly, the parameter-level deviation found for the exponential model does not lead to a clear statistical preference over the $\Lambda$CDM model according to the information criteria, whereas the
hyperbolic-tangent model shows a poorer statistical performance for the combined data. Despite these differences in the model constraints, the inferred transition
redshift $z_T$ remains relatively stable among the three models and data combinations. Our results show that the departures from the $\Lambda$CDM model indicated by DESI analyses are not a generic feature of $f(T)$
gravity, but depend strongly on the specific modified
gravity parameterization and on the combination of cosmological observations.
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Disordered Systems and Neural Networks
Deep Learning of Phase Transitions for Bilinear-Biquadratic Spin-1 Chains from Correlation Aspects
Ming-Chiang Chung, Yu-Ting Kuo, Ian McCulloch et al. (+1 more)
We investigate the role of different correlation functions in reconstructing the phase diagram of the
spin-1 bilinear-biquadratic chain, parametrized by the angle $\theta$ between the bilinear and biquadratic couplings, using our previously developed label-free machine-learning pipeline \cite{Ming21, Ming23}, in which an autoencoder compresses iDMRG correlation
matrices into latent features and K-means clustering with silhouette analysis groups them into phases. Without any prior labels, the scheme reveals four natural phases, the Haldane, dimerized, critical trimerized, and ferromagnetic phases, and accurately locates the Takhtajan-Babujian ($\theta=-\pi/4$), $SU(3)$-symmetric Uimin-Lai-Sutherland ($\theta=\pi/4$), and Ferro-Dimer ($\theta=5\pi/4$) transition points; a shallow supervised refinement further sharpens the phase boundaries. We find that different correlation functions play fundamentally different roles in phase identification. The $SU(3)$-symmetric correlation alone selects a four-cluster partition that can be associated with the four phases, whereas the
spin-
spin and dimer-dimer correlations must be combined to recover the complete phase diagram. In contrast, the trimer-trimer correlation behaves as a marginal correlation: it is insufficient for phase identification by itself but improves the precision of the predicted phase boundaries when combined with the other correlations. Furthermore, the latent representations and silhouette values reveal signatures that we relate to the $\theta$ dependence of the correlations within each phase and, tentatively, to the underlying renormalization-group structure. These results demonstrate that machine learning can not only identify
quantum phases but also uncover the physical information encoded in different correlation functions.
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All authors Ming-Chiang Chung, Yu-Ting Kuo, Ian McCulloch, Yuan-Hong Tsai
Atmospheric and Oceanic Physics
PrecipCorrDiff: A Deep Learning Framework for Generating 0.0625$^\circ$ High-Resolution IMD Gridded Precipitation Data
Bipin Kumar, Rajib Chattopadhyay, Harsh P. Bachhav et al. (+7 more)
High-resolution precipitation
datasets are essential for weather forecasting, hydrological modeling, and
climate risk assessment, yet observation-based gridded products often lack the spatial detail required for regional applications. Here we present PrecipCorrDiff, a
diffusion-based downscaling framework built by modifying the original corrector
diffusion based archetecture that incorporates a customized loss function and a multi-scale residual generation strategy to improve the precipitation especially the representation of extremes. PrecipCorrDiff generates 0.0625{\deg} resolution India Meteorological Department (IMD) precipitation fields from 0.25{\deg} gridded data while preserving precipitation statistics and reconstructing fine-scale spatial variability. Validation against independent IMD station observations, comparing the proposed framework with the SRGAN-based model and the original CorrDiff model, indicates that the proposed framework substantially improves the representation of spatial precipitation patterns, rainfall intensity distributions, and extreme rainfall events, while eliminating the systematic negative bias present in the previously developed SRGAN-based model. Across four climatologically distinct homogeneous Indian monsoon regions, PrecipCorrDiff reproduces observed precipitation characteristics with near-zero spatial bias, demonstrating the potential of
diffusion-based downscaling for generating physically consistent, high-resolution precipitation
datasets for hydrological, meteorological, and
climate applications.
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All authors Bipin Kumar, Rajib Chattopadhyay, Harsh P. Bachhav, Jannu, Bhupendra Bahadur Singh, Ramesh Ragala, Ananda Kumar Das, Manish Modani, Thara Prabhakaran, Mrutyunjay Mohapatra
Mathematical Physics · Cross-listed from math.DS
An elementary proof of Brémont's theorem on the convergence of equilibrium measures at temperature zero
Oliver Jenkinson and Mark Pollicott
We give an elementary proof that if $f$ is a locally constant function on a topologically mixing subshift of finite type, then the
equilibrium measures for $tf$ converge as $t\to\infty$, a result due to Brémont. The proof shows that the limit measure assigns an algebraic number to every cylinder.
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Solar and Stellar Astrophysics
Nova shells in 3D: I. A catalog of integral field spectroscopic observations
Janis B. Rodríguez-González, Edgar Santamaría, Martin A. Guerrero et al. (+1 more)
Classical novae eject material during thermonuclear eruptions on accreting white dwarfs, forming expanding shells whose structures and kinematics provide insights into the eruption mechanism and binary interaction. However, their intrinsic three-dimensional (3D) structures remain poorly constrained. We present the first 3D catalog of nova shells based on integral field spectroscopy, enabling us to investigate their structures beyond projection effects. We compiled observations of 19 nova shells obtained with MUSE at the VLT, complemented by new MEGARA observations at the GTC and WEAVE observations at the WHT. We constructed 3D visualizations of selected emission lines to explore the diversity of shell morphologies and kinematics. The shells reveal a wide variety of structures, including ellipsoidal or spherical shells, rings, bipolar features, and clumpy or irregular components, many of which are not apparent in 2D projections. Approximately 60% of the sample exhibits predominantly ellipsoidal or spherical shapes, while about 30% shows ring-like or bipolar structures. Several objects display strong line-dependent morphological differences, with [O III] or [N II] tracing distinct kinematic components from those seen in H${\alpha}$. Compared with imaging studies, integral field spectroscopy reveals a larger fraction of bipolar or toroidal shells. The differences between emission lines highlight the diverse excitation mechanisms and physical conditions within the ejecta. Finally, comparing expansion velocities in the plane of the sky and along the line of sight suggests low intrinsic aspect ratios, consistent with estimates from projected shell shapes.
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All authors Janis B. Rodríguez-González, Edgar Santamaría, Martin A. Guerrero, Jesús A. Toalá
Statistical Mechanics
Absolute area under a scaled Brownian motion with resetting
Vicenç Méndez and Javier Cristín
We investigate the statistical properties and ergodic behavior of the absolute area below the trajectory of a particle subject to
stochastic resetting and moving according to a scaled Brownian motion with exponent $\beta$. We compare the contributions to the absolute area from the waiting times between resets and the backward recurrence time. Using the renewal formalism we derive the lower-order moments of the absolute area under both Poissonian and heavy-tailed power-law resetting waiting time distributions with exponent $\alpha$. For Poissonian resetting,
stochastic interruption suppresses fluctuations, driving the area to be ergodic, regardless of the value of $\beta$. In contrast, power-law resetting yields a rich spectrum of ergodic regimes. For $0 < \alpha < 1$, the system displays weak ergodicity breaking and the maximum contribution dominates the area accumulated during the waiting times. For $1+\beta < \alpha < 2$, we unveil an ergodic transition exclusive to the subdiffusive regime at $\alpha=1+\beta$, where ergodicity is restored. These results clarify the subtle interplay between anomalous
diffusion and power-law waiting times between resettings. Our results are tested by numerical simulations exhibiting an excellent agreement.
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Instrumentation and Detectors
Interactive event-driven 4D-STEM with Timepix4 and live analytical ptychography
Arno Annys, Hoelen L. Lalandec Robert and Jo Verbeeck
Four-dimensional scanning transmission electron microscopy provides access to rich diffraction information at every probe position, but the high data rates associated with pixelated detectors remain a major challenge for interactive operation. Event-driven detectors offer an efficient alternative by representing the measurement as a sparse stream of individual incidences, substantially reducing requirements related to data handling and enabling on-the-fly processing. Here, we develop a high-throughput, real-time, 4D-STEM workflow based on the Timepix4 detector and demonstrate its operation at microsecond dwell times and standard beam currents. A common clock shared by the scan unit and detector allows the probe position of each electron event to be determined directly from its time-of-arrival, eliminating the need for inter-stream synchronization and enabling fully concurrent and independent multi-stream processing. The resulting pipeline continuously processes the detector data during acquisition, with the reconstructed images directly available. We demonstrate live virtual annular detector imaging, Real-Time Integration Center of Mass and direct electron ptychography within the guided progressive reconstructive imaging framework. The workflow sustains the high event rates of Timepix4 while maintaining zero latency for live interactive operation, thus extending event-driven 4D-STEM towards beam currents and acquisition conditions beyond those previously demonstrated with Timepix3-based systems. These results demonstrate that the combination of high-bandwidth event-driven detection, hardware-level synchronization and parallel processing can transform 4D-STEM from an offline technique into an interactive imaging modality, in which dose-efficient phase contrast and diffraction-based signals can serve directly as immediate feedback during STEM experiments.
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Optics
Inferring Transition-Dipoles from Two-Dimensional Infrared Spectroscopy with Deep Learning
Hao-Yue Zhang, Rong-Hang Chen and Qing Ai
Two-dimensional infrared (2D IR) spectroscopy is a powerful nonlinear technique for probing vibrational couplings, anharmonicities, coherence, and molecular dynamics. Among the microscopic parameters encoded in 2D IR spectra, transition dipoles are fundamental quantities that characterize molecular structure and govern light-matter interactions. However, reconstructing these quantities from spectroscopic data remains a challenging inverse problem. Here, we introduce a physics-informed convolutional neural network (CNN), Spec2DipoleNet, trained on 2D IR spectra generated via the non-Hermitian
Hamiltonian (NHH) method. This multi-task CNN reconstructs the transition dipole
matrices under physically-motivated masking constraints. On the validation set, the model achieves a root-mean-square error (RMSE) of 0.085, an $R^2$ of 0.97, and a normalized cross-correlation of 0.98. It reliably recovers
matrix elements associated with allowed transitions, while larger deviations are observed for nominally forbidden transitions. Our results suggest that transition dipole operators can be quantitatively inferred from 2D IR spectra, highlighting the potential of physics-informed deep learning for extracting microscopic
quantum parameters from multidimensional spectroscopic data.
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Chemical Physics
High-Harmonic Generation Probes Quantum Nuclear Fluctuations in Liquid Water
George Trenins, Nicolas Tancogne-Dejean, Angana Mondal et al. (+5 more)
Nuclear
quantum effects are essential for an accurate description of the hydrogen-bonded structure of
liquid water, yet their spectroscopic signatures can be subtle and difficult to measure. Moreover, probing these effects in solution on femtosecond timescales (or below) is an open challenge that is pivotal for optical control of hydrogen bonds and ultrafast spectroscopy of
proton transfer. Here, we combine path-integral molecular dynamics with real-time time-dependent density-functional theory to explore high-harmonic generation (HHG) in
liquid water from first principles, rigorously accounting for
quantum nuclear delocalisation. Relative to classical-
nuclei simulations,
quantum sampling suppresses the harmonic yield around certain harmonics by up to an order of magnitude, inducing local structural minima. By analysing the ab initio simulations and reproducing the key effects with a simplified model
Hamiltonian, we trace the physical origins of the interference minima to the broadening of valence-band states induced by hydrogen-bond fluctuations, a mechanism expected to generalise to other hydrogen-bonded structures. Our work shows that nuclear
quantum effects are indispensable for capturing ultrafast electronic dynamics in
liquids, and demonstrates the power of
liquid HHG spectroscopy for attosecond probing of nuclear fluctuations.
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All authors George Trenins, Nicolas Tancogne-Dejean, Angana Mondal, Angel Rubio, Hans Jakob Wörner, Aaron Kelly, Ofer Neufeld, Mariana Rossi
Optics
Preservation of photon statistics upon selective molecular modulation in hollow-core fibers
Arturo Mena, Pau Arcos, María Sánchez-Hernández et al. (+7 more)
Preserving the underlying statistical properties of light during frequency transduction is essential for interfacing spectrally disparate
quantum systems. To do this successfully, the process needs to be highly efficient, broadband and noiseless. Despite significant progress in this field, satisfying all these conditions remains challenging. Recently, molecular modulation-based transduction in hollow-core fibers has emerged as a promising approach, where biphoton correlations were proven to be preserved during frequency up-conversion. However, beyond this previous demonstration of correlation-maintaining conversion, whether molecular modulation can preserve more general statistical properties of light remains experimentally unexplored. Here, we demonstrate the conservation of
photon-number statistics during selective frequency transduction by Raman molecular modulation in a hydrogen-filled hollow-core fiber. As a proof of concept, weak 585-nm signals are selectively converted to 773 nm in the near-infrared and to 471 nm in the blue spectral region with near-unity efficiencies. Phase matching between the generated coherence waves and the transitions of interest is achieved through the effective dispersion of the system, enabling independent selection of the frequency up- and down-conversion processes. The preservation of the
photon-number statistics of the shifted signals, along with the large frequency shifts, broad tunability and compatibility with
quantum-optical fields, provides a versatile fiber-based platform for
quantum frequency transduction. In particular, the demonstrated interfacing between visible and near-infrared wavelengths using low pump energies and low gas pressures offers a route towards connecting spectrally distinct
quantum systems, including
quantum emitters, sensors and atomic
quantum memories, within hybrid
quantum networks.
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All authors Arturo Mena, Pau Arcos, María Sánchez-Hernández, Benoit Debord, Frédéric Gérôme, Fetah Benabid, Nicolas Y. Joly, Oskar Arrizabalaga, Joseba Zubia, David Novoa
High Energy Physics (Theory)
The stability of non-Abelian $A_4$ vortices in $SO(3)$ gauge theory
Yoshihiko Abe, Tetsutaro Higaki, Kazuya Murakami et al. (+2 more)
We study the linear energetic stability of non-Abelian
vortices in an $SO(3)$ gauge-
Higgs theory with residual gauge group $A_4$. In our previous work, we identified two families of such
vortices associated with order-two and order-three elements of $A_4$, and found Bogomol'nyi–Prasad–Sommerfield-like behavior at special ratios of the
Higgs and gauge-
boson mass scales. Here, we investigate their stability against $SO(3)$ gauge and
Higgs perturbations by analyzing the second order variation of the
vortex tension using analytical and numerical methods. In particular, when all relevant mass scales are equal, we prove linear stability for all
vortices in the order-three family. By contrast, at the same mass point, we prove that a
vortex in the order-two family is unstable. Thus, although both
vortex families exhibit Bogomol'nyi–Prasad–Sommerfield-like behavior in their reduced equations at this mass point, their stability properties in the full $SO(3)$ theory are qualitatively different.
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All authors Yoshihiko Abe, Tetsutaro Higaki, Kazuya Murakami, Muneto Nitta, Ryo Yokokura
Quantum Physics
Testing graph isomorphism using simple quantum circuits
Samuel Beasley and Ashley Montanaro
The graph isomorphism problem asks whether two graphs are equivalent up to a permutation of their vertices. Its precise computational complexity remains unresolved, and it is still unknown whether a
polynomial-time
algorithm exists. We investigate whether simple graph-dependent Instantaneous
Quantum Polynomial-time (IQP) and
Quantum Approximate Optimisation
Algorithm (QAOA)
circuits can distinguish non-isomorphic graphs. We first show that suitable IQP and QAOA constructions allow the underlying graph to be reconstructed using a
polynomial number of samples. Building on previous work using the QAOA energy, we show that Hamming weight distributions can distinguish graph pairs at
circuit depths for which the numerically computed energy gap is zero. We then apply graph invariants to the
matrix of ZZ correlators on the output distribution. For the specific case of the graph spectrum, at QAOA depth $p=2$, this invariant numerically distinguishes all $10{,}486$ cospectral regular graph pairs tested on up to 18 vertices. For IQP
circuits, we introduce a finer invariant based on probability multiplicities within Hamming weight sectors, which distinguishes every non-isomorphic graph pair tested numerically. Finally, we derive exact graph-theoretic characterisations of the IQP output distribution at $\theta=\pi/2$ and $\theta=\pi/4$. These results show that simple graph-dependent
quantum circuits encode substantial structural information, while leaving open whether this information can be extracted efficiently for general graph isomorphism.
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High Energy Physics (Experiment)
MoEDAL-MAPP: the first dedicated search experiment at the LHC
John R. Ellis, Nick E. Mavromatos, Vasiliki A. Mitsou et al. (+1 more)
This special issue brings together a collection of original research articles and review papers addressing topics directly related to the MoEDAL-MAPP experiment at the Large
Hadron Collider (LHC). The experiment is designed to search for (meta-)stable, anomalously ionising particles predicted by theoretical extensions of the Standard Model. Several contributions explore the theoretical and phenomenological aspects of models of particular relevance to the experiment, including scenarios involving
magnetic monopoles, highly electrically charged particles, and millicharged particles. Other contributions focus on experimental developments, highlighting novel detection techniques and technological advances aimed at identifying these unconventional signatures and probing new phenomena beyond the Standard Model.
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All authors John R. Ellis, Nick E. Mavromatos, Vasiliki A. Mitsou, James L. Pinfold
Astrophysics of Galaxies
Galactic Morpholography: Linking present-day galaxy compactness to assembly history and relic formation in the COLIBRE simulations
Maximilian Zemsch, Claudia D.P. Lagos, Chiara Spiniello et al. (+11 more)
Compactness is widely used to identify candidate relic
galaxies, the largely untouched survivors of the first compact massive
galaxies. Yet relicness is an evolutionary rather than structural property. Using the COLIBRE cosmological hydrodynamical simulations, we test whether present-day structure traces
galaxy formation and assembly histories. Six complementary tracers (stellar age,
metallicity, [Mg/Fe], sSFR, velocity dispersion and ex-situ mass fraction) vary coherently across the stellar mass-size plane and independently identify a characteristic compactness scale of $\log_{10}(\Sigma_{1.5,\mathrm{crit}}/(\mathrm{M}_\odot\mathrm{kpc}^{-1.5}))=9.75\pm0.10$. We term this mapping between present-day structure and assembly history morpholography. Combining this threshold with the Degree of Relicness ($\mathrm{DoR}>0.6$), which quantifies early and rapid
star formation, we distinguish compact from ancient
galaxies and identify 267 relic candidates at their intersection. Ancient
galaxies span nearly the full ex-situ-fraction range, from predominantly in-situ formation to substantial merger-driven growth. Relic candidates are concentrated at stellar masses of $\approx 10^{10}$-$10^{11}$ solar masses, host black holes that lie $\approx 0.25$-$2.5$ dex above the median black-hole-stellar-mass relation, and are predominantly satellites (76%), preferentially in cluster environments. Only $\approx 3$% show evidence of strong tidal stripping, suggesting that environment primarily preserves rather than creates relic-like systems. Approximately one third (87/267) are direct descendants of the $z=2$ massive quiescent
galaxies identified in COLIBRE. Present-day structure thus retains a statistical fossil record of assembly history, supporting morpholography as a link between nearby
galaxies and the early Universe.
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All authors Maximilian Zemsch, Claudia D.P. Lagos, Chiara Spiniello, Michele Cappellari, Ángel Chandro-Gómez, Katy L. Proctor, Evgenii Chaikin, Johanna Hartke, Filip Huško, Sylvia Ploeckinger, Alexander J. Richings, Mahsa Sanati, Joop Schaye, James W. Trayford
Mesoscale and Nanoscale Physics
Observation of correlations beyond the single-particle picture in fermionic counting statistics
Johann Zöllner, Hendrik Mannel, Daniel Oppers et al. (+3 more)
The analysis of charge fluctuations in a mesoscopic device can shed light on the fundamental question of whether or not a single-particle picture of electron transport is appropriate, even in the presence of Coulomb interaction. It has been shown on general grounds that mapping the interacting system onto a fermionic single-particle description is subject to strict constraints on the charge-transfer statistics. These constraints can be formulated in terms of a sign rule for the factorial cumulants of the full counting statistics. We report here on the experimental observation of a sign-rule violation in a most elementary model system, i.e. a single-level
quantum dot, and provide theoretical modeling that can quantitatively reproduce the experimental data. This reveals the presence of correlations introduced by electron-electron interaction.
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All authors Johann Zöllner, Hendrik Mannel, Daniel Oppers, Martin Geller, Axel Lorke, Jürgen König
Quantum Physics
Joint-measurement advantage and finite-time transitions in accelerated detector registers
Zhiming Huang
The Unruh response thermalizes accelerated detectors, but the
entanglement remaining in a register does not by itself specify what distributed measurements can recover. We study this distinction for a four-
qubit cluster state whose two assisting nodes independently undergo generalized amplitude damping, while the target nodes remain isolated and the environments are inaccessible. We derive the exact joint-assisted concurrence and the exact one-way value for arbitrary local measurements. The joint optimum equals the bipartition negativity, and computational-basis measurements attain the one-way optimum. A polar-decomposition argument, together with compactness, establishes a necessary and sufficient condition for separable measurements to attain the joint optimum and proves a strict gap whenever this condition fails. For assisting detectors at equal Unruh temperature with relaxation-rate ratio $r>1$, joint advantage exists precisely when the thermal excitation factor satisfies $q<1/r$. At finite positive temperature it ends at a unique finite time, while the remaining
entanglement is nonzero. For $r=2$, both the transition time and remaining resource have closed expressions. These results identify when joint assistance is necessary within the independent weak-coupling thermalization model.
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