Plasma Physics
Free-Molecular Face-Flux Preprocessing for Reduced Neutral-Continuity Modeling in Hall Thrusters: Particle-Based Reference and Deterministic SN-DFEM Realization
Yingjie Chen, Xi Chen and Yinjian Zhao
Neutral gas transport directly affects the ionization source, propellant utilization, and low-frequency discharge oscillations in
Hall thrusters. High-fidelity particle-based neutral models or DSMC methods can describe rarefied gas transport, but they are computationally expensive; in contrast, reduced neutral-continuity models are cheaper but require a closure for the neutral velocity or face-normal flux. Under a low-pressure collisionless approximation, this work adopts a free-molecular preprocessing strategy to provide a reference density field and the mean-velocity or face-normal-flux closure used by the reduced neutral-continuity equation in a manner consistent with the underlying transport model.On this basis, a particle-based free-molecular faceflux preprocessor is used as a
stochastic reference, and an SN-DFEM deterministic free-molecular preprocessor is proposed to generate the corresponding reference density, velocity moments, and face-normal fluxes within a unified free-molecular transport framework. Results show that the SN-DFEM preprocessor preserves the main neutral-density and velocity structures and reduces the statistical error in face-flux closure by about three orders of magnitude in the baseline continuity-recovery test. A prescribed moderate ionization-loss case further demonstrates the extension of the framework to free-molecular preprocessing with volumetric neutral removal.
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Solar and Stellar Astrophysics
Magnetically Structured Oscillatory Power Along an Active-Region Transect in Near-UV Sunrise-III/SUSI Spectroscopy
Shahin Jafarzadeh, David B. Jess, Marco Stangalini et al. (+33 more)
We present a multi-line characterisation of how oscillatory power is organised across distinct
magnetic environments in an active region using seeing-free, stratospheric near-ultraviolet spectroscopy from the Sunrise-III UV Spectropolarimeter and Imager (SUSI). A two-hour time series of short raster scans in the line-rich 327-329 nm window samples along a single transect that contains the following regions: weak
magnetic-field surroundings, a plage, a sunspot, and a pore. From a set of 30 selected, relatively unblended absorption lines, we extract line-core Doppler-velocity time series and compute Morlet-wavelet refined global spectra from which we form band-integrated power maps for three frequency bands (2-4, 4-6, and 6-12 mHz). The stacked, line-resolved maps reveal a clear environment-dependent redistribution of power: 2-4 mHz power is strongest in the weak-field/plage segments but is commonly suppressed in the umbra and pore cores, while 4-6 mHz and 6-12 mHz power becomes relatively enhanced in the strongest-field regions, with line-dependent behaviour in the penumbra and plage. Across the line ensemble, this broad frequency structuring is coherent, but the detailed spatial distribution and relative band ranking are not identical from line to line - even among spectral lines with comparable effective formation depths - demonstrating clear line dependence. This novel result implies that single-line measurements may miss secondary components of the local wave spectrum because different lines weight co-existing perturbations and modes differently; therefore, the SUSI near-UV window provides a uniquely diagnostic-rich mapping of oscillations, offering leverage that is difficult to obtain with traditional one- or two-line approaches.
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All authors Shahin Jafarzadeh, David B. Jess, Marco Stangalini, Peter H. Keys, Samuel D. T. Grant, Timothy J. Duckenfield, Glen Chambers, Sami K. Solanki, H. N. Smitha, Andreas Lagg, Achim Gandorfer, Alex Feller, Francisco A. Iglesias, Tino L. Riethmüller, Bianca Grauf, Johannes Hoelken, Yukio Katsukawa, Pietro Bernasconi, Thomas Berkefeld, Alberto Álvarez-Herrero, Masahito Kubo, David Orozco Suárez, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Julian Blanco Rodríguez, Juan Sebastián Castellanos Durán, Edvarda Harnes, Ryohtaroh T. Ishikawa, Yusuke Kawabata, Takuma Matsumoto, Takayoshi Oba, Azaymi L. Siu-Tapia, Hanna Strecker, Dušan Vukadinović
Quantum Gases
Spin mixing induced dynamics of spinor solitons in $F=1$ Bose Einstein condensates
T. Panagos, A. Romero-Ros, G.C. Katsimiga et al. (+2 more)
We explore
soliton interactions in a homogeneous spinor $F=1$ Bose Einstein Condensate (BEC) in the presence of a
magnetic field, focusing on dark bright dark and bright dark bright configurations. We investigate how these interactions depend on the phase differences among bright
solitons and their influence during the dynamics. Our findings align with prior non spinor results, i.e., repulsion among in phase bright
solitons and attraction among out of phase pairs in self repulsive atomic BECs. The potential bright
soliton attraction, added to the short range repulsion of dark dark
soliton interactions, can lead to bound states. However, we find that these bound states break in the presence of spinor interactions due to the particle exchange dynamics between the hyperfine states of the components. Additonally, we develop an effective classical model to describe the
soliton dynamics, using a Lagrangian approach. The accuracy of the model is tested by comparing it against numerical simulations. Our results suggest that the proposed model captures the essential features of
soliton behavior in the presence of
spin interactions, and provides congruent
soliton trajectories and interspecies particle exchange dynamics in most of the cases.
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All authors T. Panagos, A. Romero-Ros, G.C. Katsimiga, P. Schmelcher, P.G. Kevrekidis
High Energy Astrophysical Phenomena
Fortifying gravitational-wave population inference with normalizing flows
Christian Adamcewicz, Hugh McDougall, Paul D. Lasky et al. (+1 more)
As the LIGO-Virgo-KAGRA collaboration's (LVK's) gravitational-wave transient catalog grows, we are learning a wealth of information from the population properties of binary black hole mergers. Events in the catalog are represented with posterior samples describing the astrophysical parameters for each event. Population studies combine these samples to measure the distribution of astrophysical parameters such as black hole masses and
spins. However, the posterior-sample representation of each event is only approximate. We construct a mock population with masses drawn from an astrophysically-motivated distribution with sharp features. Using this, we demonstrate that when $\gtrsim 300$ events are combined, even with each event's posterior represented by $1 \times 10^4 {-} 2 \times 10^4$ samples, the numerical error can become large enough that the resulting population inference is unreliable. We consider two solutions. In the short term, we show that nested samples (already produced by LVK analyses) can be used to more accurately describe each event in population studies. But this will only grant a temporary reprieve until the nested-sample representation becomes inadequate. In the longer term, we propose to represent each event with a normalizing flow. In order to represent each event with sufficient accuracy, each normalizing flow can be used to generate an arbitrarily large number of new posterior samples with a significantly reduced computational cost relative to traditional sampling methods. When compared to nested sampling, our normalizing flows produce posterior draws with a median of $\approx 80\%$ fewer likelihood evaluations per sample, while also providing greater opportunity for parallelization. We believe refinement of normalizing flow architectures and training techniques in future works could further reduce this per-sample cost significantly.
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All authors Christian Adamcewicz, Hugh McDougall, Paul D. Lasky, Eric Thrane
Fluid Dynamics
Impact of alignments between fluctuating and mean density gradients on the scale-dependent energetics of stably stratified turbulence
Soumak Bhattacharjee, Stephen M. de Bruyn Kops and Andrew D. Bragg
Non-trivial
alignments between vorticity and the strain-rate tensor play an important role in the
evolution of velocity gradients and the energy cascade in isotropic
turbulence. Here we explore how
alignments between the fluctuating and mean density gradients impact the mechanisms governing the turbulent kinetic energy (TKE) and available potential energy (APE) across scales in stably stratified
turbulence. This is motivated by analytical results that demonstrate a connection between them, and is conducted using direct numerical simulations (DNS) of statistically stationary, stably stratified
turbulence for $Pr = 1, 7, 50$ in the strongly stratified regime. After demonstrating how the gradient field
alignments depend on scale and $Pr$, we show that the
alignments are intimately connected to the reversal of the buoyancy flux at small-scales, and that regions of strong
alignment and misalignment correspond to regions where the horizontal TKE inter-scale flux becomes weak. The same is also true of the APE flux, except that at larger scales, regions of strong
alignment are associated with an upscale APE flux. The TKE and APE dissipation rates, and the mixing coefficient also show a strong dependence on the
alignment, especially for $Pr=1$. Finally, we explore the connection between the local
alignment and stability of the flow, and we find a non-trivial relationship, with regions of strong
alignment surprisingly occurring most often in stable regions. This demonstrates that the dynamical significance of the
alignments on the flow energetics cannot be understood through a simple connection between the local
alignments and local stability of the flow.
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Quantum Physics
Efficient Simulation of Szegedy Quantum Walk Formulations and Algorithms
Sergio A. Ortega and Daniel K. Park
Quantum walks provide a versatile framework for
quantum algorithms across a wide range of applications. We develop efficient classical simulation methods for Szegedy
quantum walks that avoid explicit construction of the full
unitary evolution operator. Unlike previous approaches restricted to a particular walk formulation, our framework is built from fundamental update and reflection operators, enabling the simulation of a broader class of Szegedy walk formulations. We further extend these methods to phase-estimation-based
algorithms coupled to the walk, including implementations suitable for large sparse graphs. The resulting methods achieve optimal $O(N^2)$ complexity for dense graphs with $N$ nodes. For sparse graphs, the computational cost scales linearly with the number of edges, which is $O(N)$ in many cases. We implement the framework in the Python package SQWLib and illustrate its capabilities through simulations of representative
algorithms, including
quantum simulated annealing and
quantum search on graphs. These results provide a practical tool for studying Szegedy-walk-based
algorithms numerically beyond purely analytical treatments.
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Optics
Analysis of a compact interferometric imager
Laurent M. Mugnier, Vincent Michau, Hiyam Debary et al. (+1 more)
The advent of photonic integrated
circuits (PICs) will allow the replacement of the large aperture of an optical
telescope by a dense array of small apertures combined interferometically. The light coming from aperture pairs can be combined by a PIC in order to extract interferogram characteristics known as complex visibilities, from which the observed object can then be reconstructed. In such a compact interferometric imager, the optical components dedicated to image formation in a regular
telescope are no longer necessary. In particular, such a concept is relevant for space missions where weight and size are critical. In this communication, we study such an instrument concept, focusing on signal-to-noise considerations. We recall the design basis for the field and the spatial resolution, and we show that the spectral resolution must be no less than the field to resolution ratio. Then, we analyze the signal-to-noise ratio of this concept, assuming that each spatial frequency is recorded only once, and compare the signal-to-noise ratio with that of a monolithic
telescope. We perform the comparison in
Fourier space for an identical number of recorded
photons. We show that the noise propagation of the interferometric imager is identical to that of a monolithic
telescope that would have a flat Modulation Transfer Function with a level roughly given by the ratio of the small apertures' diameter to the maximum baseline. We conclude that the noise propagation in low and medium spatial frequencies is unfavorable for the interferometric imager.
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All authors Laurent M. Mugnier, Vincent Michau, Hiyam Debary, Frédéric Cassaing
Materials Science
Vapor-to-glass preparation of biaxially aligned organic semiconductors
Jianzhu Ju, Debaditya Chatterjee, Paul M. Voyles et al. (+2 more)
Physical vapor deposition (PVD) provides a route to prepare highly stable and anisotropic organic glasses that are utilized in multi-layer structures such as organic light-emitting devices. While previous work has demonstrated that anisotropic glasses with uniaxial
symmetry can be prepared by PVD, here, we prepare biaxially aligned glasses in which molecular orientation has a preferred in-plane direction. With the collective effect of the surface equilibration mechanism and template growth on an aligned substrate, macroscopic biaxial
alignment is achieved in depositions as much as 180 K below the clearing point $T_{LC-iso}$ (and 50 K below the glass transition temperature $T_g$ ) with single-component disk-like (phenanthroperylene ester) and rod-like (itraconazole) mesogens. The preparation of biaxially aligned organic
semiconductors adds a new dimension of structural control for vapor-deposited glasses and may enable polarized emission and in-plane control of charge mobility.
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All authors Jianzhu Ju, Debaditya Chatterjee, Paul M. Voyles, Harald Bock, Mark D. Ediger
High Energy Physics (Theory)
Real-time pseudo entropy and modular-Hamiltonian correlations
Tatsuhiro Misumi
Pseudo
entropy is a complex-valued generalization of
entanglement entropy defined from a reduced transition
matrix. We study the pseudo
entropy associated with a real-time transition
matrix between an initial pure state and its
unitary time
evolution. For a subsystem $A$, we show that the short-time behavior of real-time pseudo
entropy is governed by the correlation between the physical
Hamiltonian $H$ and the modular
Hamiltonian $K_A=-\log\rho_A$ of the initial reduced state, $ S_A(t,0)=S_A(0)-it \langle K_A(H-\langle H\rangle)\rangle + \mathcal{O}(t^2)$. For Hermitian dynamics, the initial imaginary response is controlled by the symmetrized covariance of $H$ and $K_A$ with an overall minus sign, while the initial real response is governed by their commutator. Thus the imaginary part of real-time pseudo
entropy is not merely a branch artifact: it is a time-oriented modular response generated by the correlation between microscopic time
evolution and subsystem coarse graining. We clarify the relation of this result to the known first law of pseudo
entropy, derive an all-order expression in a Schmidt-diagonal model, recover thermal pseudo
entropy as a special case, illustrate the covariance/commutator decomposition in a two-
qubit model, and confirm the covariance response in transverse-field Ising-chain quenches, including a finite-size study of a modular susceptibility near the Ising critical region. We discuss how this amplitude-level oriented response can be related to ordinary
entropy production, and also give a concrete $\mathcal{PT}$-symmetric toy-model illustration of the non-Hermitian extension.
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Chemical Physics
Fast and accurate simulation of Raman spectra of gold-organic systems
Auguste Tetenoire, Vijaya Raghavan Kannan, Mikaël Kepenekian et al. (+1 more)
Resolving the spectral Raman signature of molecules grafted on a metallic support is often a difficult task, in which
quantum chemistry methods allow for precious additional rationalization and signal attributions, especially to probe the formation of a bond with the support. In the specific case of gold-organic architectures based on a Au-C bond, only a limited amount of experimental and theoretical reference data are available in the literature, and Raman simulations based on
quantum mechanics quickly become unaffordable with the size of the system. In this work, we evaluate the precision of a cost-efficient DFTB method to simulate Raman spectra of gold-organic systems at different scales, from gold complexes to functionalized gold surfaces. After a validation of the method through a careful comparison of DFTB Raman spectra of organometallic gold(I) and (III) complexes to DFT and experimental reference data, we discuss the case of molecules grafted on gold aggregates. For these simulations, the choice of the model (cluster or periodic surface) appears to be critical, and significant differences arise (positions and intensities of the peaks) when considering a full metallic slab, as allowed by the low computational cost of the method.
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All authors Auguste Tetenoire, Vijaya Raghavan Kannan, Mikaël Kepenekian, Arnaud Fihey
Quantum Physics
Fourier analysis of quantum neural network with non-linear data embedding
Haiyue Kang, Martin Sevior and Muhammad Usman
Fourier analysis has become a crucial tool for understanding the expressivity of Variational
Quantum Circuit (VQC) models, as well as an important indicator of barren plateaus (BP). While existing literature has only studied angle-embedded VQCs in a noiseless environment, here we develop the
Fourier analysis of VQCs with non-linear data
embedding, with particular focus on amplitude
embedding, which provides a naturally compact encoding scheme. We first investigate a subtle difference in the domain of input features within amplitude
embedding that leads to a distinct expressivity of the zero-frequency
Fourier coefficient. By assuming that the ensemble of
unitaries generated from the parameter space forms at least a 2-design with respect to the
unitary group, we derive, via Weingarten calculus, that the mean of the
Fourier coefficients is concentrated at zero, and the variance scales at an exponentially decaying order with respect to the multi-dimensional frequency magnitude. When a noise channel with
unitary Kraus operators and probabilities $\{p_k\}$ is taken into account, the variance is further suppressed by a factor $\left(\sum_k p_k^2\right)^{Q}<1$, where $Q$ is the number of channel instances applied. Furthermore, we demonstrate and validate the analytical results through simulations, both noiseless and noisy, including a case where target functions are decomposed into non-integer frequencies, highlighting the practical utility of the approach. Our results establish a rigorous
Fourier framework for amplitude-encoded VQCs, offering both theoretical guarantees on expressivity, hence trainability scaling in the frequency domain, as well as practical simulations for deployment on noisy
quantum devices.
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Quantum Physics
Streaming the partial-transpose moment hierarchy with order-independent quantum memory
Junxiang Huang, Xiaoyang Wang, Xiao Yuan et al. (+1 more)
Partial transposition reveals mixed-state
entanglement through the spectrum of $\rho_{AB}^{T_B}$, but this operator is not generally a physical state. Its power moments are accessible through collective permutations, whose coherent width grows with moment order. Here we introduce a streaming protocol that processes fresh copies sequentially while retaining one copy and a reusable ancilla. By realizing opposite cyclic permutations on the two subsystems, each measurement record yields unbiased
estimators of all moments $p_2,\ldots,p_K$ through successive outcome products. For an $n$-
qubit state, the protocol uses $2n+1$ active
qubits independent of $K$ and $O(K\log K/\epsilon_{\rm mom}^2)$ copies, matching $\Omega(K/\epsilon_{\rm mom}^2)$ lower bounds up to a logarithmic factor, including a PT-specific isospectral construction. Higher-order moments strengthen thermal-state
entanglement certification toward the exact PPT threshold. Simulations cover pure and mixed states, and a cloud
quantum processor implements a three-
qubit instance.
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All authors Junxiang Huang, Xiaoyang Wang, Xiao Yuan, Yukun Zhang
Instrumentation and Detectors · Cross-listed from cs.IT
Practical Low-Weight Codes for Energy-Efficient Bus Encoding
Lorenzo Valentini and Marco Chiani
We consider the transmission of data encoded into binary messages, with the goal of minimizing the Hamming distance, i.e., the number of bit-flips, between consecutive messages. This problem is relevant for enhancing the longevity of Non-Volatile
Memories and reducing transition-induced energy consumption in data buses. Known as Write-Efficient
Memory coding in the literature, this challenge has traditionally been addressed using optimal but complex schemes. In low-power computer systems the same topic is known as bus encoding. In this paper, we derive closed-form expressions to evaluate the average number of bit-flips for practical, sub-optimal encoding schemes, and propose two new schemes assisted by predefined random codebooks. We demonstrate that low-complexity solutions achieve performance very close to the optimal schemes, making them attractive for implementation in energy-sensitive and
memory-critical applications. For instance, by adding 8 extra bits to 64-bits data, sub-optimal schemes can achieve a bit-flip reduction (related to energy saving) of approximately 24.7%, compared to the 26.4% reduction offered by the significantly more complex optimal scheme.
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High Energy Astrophysical Phenomena
Licence to Bin: Accurate and Scalable Inference for Binary Neutron Stars in Next-Generation Gravitational-Wave Detectors
Nir Guttman, A. Makai Baker, Paul D. Lasky et al. (+1 more)
Next-generation gravitational-wave observatories will observe binary
neutron-
star mergers with much higher signal-to-noise ratios, over much longer durations and across broader frequency bands than current detectors. These long-duration signals present a major computational challenge for
Bayesian parameter estimation. Reduced-order quadrature is a promising approach for accelerating inference, but in this regime its standard construction encounters severe
memory and accuracy limitations. We present a practical reduced-order quadrature construction for long binary
neutron-
star signals with time-dependent detector response and full effects of the observatories' free-spectral range. Our approach combines improved adaptive frequency sampling, disk-backed streaming, and subbanded reduced-order quadrature construction, enabling efficient and accurate reduced-order models for signals that were previously intractable. We demonstrate for the first time reduced-order
Bayesian inference on an approximately 2 h binary
neutron-
star signal extending down to 5 Hz and with signal-to-noise ratio 2090. We show the resulting reduced-order quadrature remains sufficiently accurate for practical inference. The full analysis is carried out in about 48 h using 128 CPU cores. We also find that, when time-dependent detector-response effects are included, a single
Cosmic Explorer detector can localize such a signal to a 90% credible sky area of approximately $41~\mathrm{deg}^2$, with important implications for multimessenger astronomy and cosmology. These results demonstrate that reduced-order methods can make next-generation binary
neutron-
star inference computationally feasible.
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All authors Nir Guttman, A. Makai Baker, Paul D. Lasky, Eric Thrane
Strongly Correlated Electrons
Shinji Okada, Hiroto Suzuki, Nonoka Higa et al. (+3 more)
In a sawtooth
spin chain, competing nearest- and next-nearest-neighbor interactions suppress long-range order, yielding novel
quantum states such as a
spin-dimer singlet, 1/2 magnetization plateau, and
spin contraction. Here, we investigate the
magnetic properties of the orthorhombic
semiconductor ZnYb$_2$S$_4$, in which Yb$^{3+}$ ions with an effective
spin-1/2 form a sawtooth chain along the $b$-axis. The specific heat exhibits a sharp peak at ${T}_{\rm m}$ $=$ 1.4 K, at which the
magnetic entropy $S_{\rm m}$ reaches only 27% of $R$ln2. This reduced $S_{\rm m}$ at $T_{\rm m}$ indicates the
entropy release of the ground state doublet of Yb$^{3+}$ even for $T$ $>$ $T_{\rm m}$. The isothermal magnetization $M(B)$ at 0.28 K exhibits hysteresis for $\left|B\right| \leq 0.2$ T and increases monotonically for $B > 0.2$ T. The spontaneous magnetization is only 0.1 ${\it \mu}_{\rm B}$$/$Yb, an order of magnitude smaller than that expected for the ground state doublet of Yb$^{3+}$. Moreover, in powder
neutron diffraction measurements, no superlattice reflections due to
antiferromagnetic order are observed for $T$ $<$ $T_{\rm m}$. Therefore, in the ground state, the Yb moments are ferromagnetically aligned, but their amplitude is reduced by
magnetic frustration in the sawtooth Yb chain.
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All authors Shinji Okada, Hiroto Suzuki, Nonoka Higa, Yasuyuki Shimura, Takanori Taniguchi, Takahiro Onimaru
Statistical Mechanics
Stochastic Thermodynamics on Time-Evolving Curved Spaces
Rihito Nagase, Shoki Sugimoto, Asuka Takatsu et al. (+1 more)
We construct
stochastic thermodynamics of overdamped Langevin systems on nonrelaticvistic curved spaces with time-dependent metrics. The time dependence of the metric contributes to the energy balance by performing work on the kinetic energy, which is instantaneously dissipated as heat in the overdamped regime. This contribution makes our framework thermodynamically consistent so that
entropy production satisfies the second law of thermodynamics. As a special case, when the metric evolves according to backward
Ricci flow, the
entropy balance exhibits a structure similar to Perelman's
entropy functional. Our framework provides a way to quantify thermodynamic costs in dynamics on time-evolving spaces such as
diffusion on membranes.
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All authors Rihito Nagase, Shoki Sugimoto, Asuka Takatsu, Takahiro Sagawa
Solar and Stellar Astrophysics
Multi-line Wave Signatures in a Sunspot from Near-UV Sunrise III/SUSI Observations
Shahin Jafarzadeh, David B. Jess, Marco Stangalini et al. (+32 more)
Magnetohydrodynamic waves redistribute energy in
magnetic structures of the lower
solar atmosphere, yet constraints on how wave power and dominant frequencies are organised above sunspots remain limited because most studies use only a few well-separated diagnostics. Here we present multiline wave signatures in a sunspot from near-UV spectroscopy with the Sunrise-III UV Spectropolarimeter and Imager (SUSI). We analyse a two-hour time series of repeated raster scans of a sunspot near disc centre in the 327-329 nm spectral window (> 100 lines). From these, we select 44 lines that radiative-transfer calculations suggest sample effective formation heights within the umbral core from deep photosphere toward the low chromosphere. For each line, we extract line-core intensity and line-of-sight velocity time series using a dedicated multi-line fitting routine and compute Morlet-wavelet power spectra. The refined global wavelet spectra show that most lines (in both intensity and velocity) are genuinely multi-frequency, with a dominant peak and substantial statistically significant power up to 12 mHz. Unsupervised clustering of the normalised spectra groups lines into families with similar spectral shapes and reveals a progression of dominant frequencies from ~2 to ~10 mHz across the ensemble, for both intensity and velocity (not necessarily in the same lines). This behaviour is not reproduced by a simple formation-height ranking, suggesting that uncertainties in the formation-height estimates and line-dependent diagnostic response together shape the ordering. These Sunrise-III/SUSI observations open a new regime for near-UV multi-line wave studies and provide the first systematic characterisation of frequency-structured sunspot wave behaviour in this spectral region.
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All authors Shahin Jafarzadeh, David B. Jess, Marco Stangalini, Richard J. Morton, Tobias Felipe, Michele Berretti, Sami K. Solanki, H. N. Smitha, Andreas Lagg, Achim Gandorfer, Alex Feller, Francisco A. Iglesias, Tino L. Riethmüller, Bianca Grauf, Johannes Hoelken, Yukio Katsukawa, Pietro Bernasconi, Thomas Berkefeld, Alberto Álvarez-Herrero, Masahito Kubo, David Orozco Suárez, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Julian Blanco Rodríguez, Juan Sebastián Castellanos Durán, Edvarda Harnes, Ryohtaroh T. Ishikawa, Yusuke Kawabata, Takuma Matsumoto, Takayoshi Oba, Azaymi L. Siu-Tapia, Hanna Strecker, Dusan Vukadinović
Materials Science
The Structure-tuning Magnetism in the Co(NbxTa1-x)2O6 Series
Sirui Huang, Lun Jin, Yuchen Liu et al. (+2 more)
Low dimensional
quantum materials have been extensively studied within the physics community, among which Co2+ is one of the most popular
magnetic ions to be embedded into the structural motif. CoNb2O6 and CoTa2O6 both have adopted an effective
spin-1/2 state, with the former attracting enduring interest while the latter being rarely investigated. This difference can be attributed to their distinct
crystal structures, not only in
crystal systems, but more important, how the CoO6 octahedra are connected. We successfully merge these two compounds together and map out the doping limits. We find out Ta and Nb dopants modify the properties of the parent compounds in subtle but different ways and construct a
magnetic phase diagram of the Co(NbxTa1-x)2O6 (0 < x < 1) series. In addition, our results suggest that Ta-doping may pave a way to strengthen the lower-dimensional
quantum phenomena in CoNb2O6 before its
crystal structure starts to melt down.
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All authors Sirui Huang, Lun Jin, Yuchen Liu, Xiyu Chen, Leili Tan
General Relativity and Quantum Cosmology
Majorana Neutrinos in Sandwich Wave Spacetimes: Flavor Modulation and Helicity Transitions
Yorgo Senikoglu
We present the propagation of massive Majorana
neutrinos crossing an exact gravitational sandwich wave background. By employing a Takagi factorization to decouple the
matrix field equations, We show that the localized pulse breaks the kinematic
alignment of the mass eigenstates as they propagate through the wave zone, leaving a permanent residual phase shift across the transverse profile of the wavefront. The wave asymmetry couples directly to the Majorana
spin tensor, forcing a transition from left-handed to right-handed configurations. Behind the wave tail, the residual drift parameters act to polarize the state's chirality, introducing a strong anisotropy across the transverse momentum plane. These results show that a passing gravitational wave leaves a modification on both the
flavor and helicity of a
neutrino beam, as a sign of the gravitational
memory effect.
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General Relativity and Quantum Cosmology
Note on the local calculation of decoherence of quantum superposition in the static black holes
Ran Li, Zhong-Xiao Man and Jin Wang
We investigate the decoherence of a
quantum spatial superposition of a static particle in Schwarzschild and Reissner-Nordström black holes. By treating the particle as a localized classical source coupled to a
quantum scalar field, we reformulate the decoherence process in the Danielson-Satishchandran-Wald (DSW) gedankenexperiment through coherent state generation and derive the local expression for the decoherence functional in terms of the Wightman function. In the long-time limit, the decoherence rate is shown to be characterized by the low-frequency behavior of the Wightman function. We then employ the asymptotic matching method to calculate the analytical expressions of the Wightman functions in the Boulware, Unruh, and Hartle-Hawking
vacua. We show that the decoherence behavior depends on the
quantum state of the environmental field. While the Boulware
vacuum gives vanishing decoherence for a static superposition, the thermal effects associated with Hawking radiation in the Unruh and Hartle-Hawking
vacua can induce nonvanishing decoherence.
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Quantum Physics
Dynamically frozen long-distance entanglement via non-Hermitian PT-symmetric systems
Sejal Ahuja, Keshav Das Agarwal and Aditi Sen De
In distributed
quantum networks, interacting
spin systems can mediate the generation of highly entangled links between distant nodes. We investigate the role of effective parity-time (PT)-symmetric non-Hermitian
spin-1/2 bulks weakly coupled to two
quantum links, obtained due to the environmental interactions affecting both the bulk and the links. Focusing on effective non-Hermitian nearest-neighbor (NN) Su-Schrieffer-Heeger (SSH) models, we analyze how non-Hermiticity influences the dynamical formation of long-distance
entanglement (LDE). For a paradigmatic model consisting of a
quantum XX bulk subjected to imaginary staggered
magnetic fields, we analytically determine the exceptional points arising from the resulting bulk-mediated interactions between the links. Combining analytical and numerical methods, we demonstrate that an initially fully separable state can dynamically evolve into highly entangled link states near these exceptional points in the broken regime. Further, after optimizing over time and system parameters, near-unit time-averaged
entanglement between the links emerges under weak imaginary
magnetic fields and bulk-link couplings, which cannot be attained in the corresponding Hermitian systems. Moreover, the non-Hermitian dynamics exhibit a freezing of high
entanglement in the vicinity of exceptional points, a feature absent in Hermitian counterparts. We also identify regimes of long-range interaction strengths that yield a higher time-averaged
entanglement than the corresponding NN models. Furthermore, we establish that LDE persists in the stationary regime, highlighting the promise of engineered non-Hermitian dynamics for realizing robust and frozen entangled links in
quantum networks.
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Chaotic Dynamics
Universal Construction of Generalized Lyapunov Functions for Nonlinear Dynamical Systems Using Physics-Informed Neural Networks
Z. C. Tu
A scalar potential landscape provides an intuitive description of the stability, transitions, and global organization of dynamical systems. For non-gradient dynamics, however, constructing global Lyapunov-type functions for nonlinear flows with recurrent structures remains a formidable challenge. Here, we introduce the generalized Lyapunov function (GLF), a scalar potential that is monotonically non-increasing along deterministic trajectories, as a unifying framework for nonequilibrium potentials. Conventional Lyapunov functions, Freidlin–Wentzell quasi-potentials, and potentials arising from Ao-type decompositions naturally emerge as special cases within this framework. Furthermore, we develop a data-free physics-informed neural network (PINN) approach in which the Lyapunov inequality and a weak divergence-scale compatibility condition are directly embedded into the loss function. The framework is demonstrated on diverse systems, including linear dynamics, the
Hopf normal form, the van der Pol oscillator, a three-dimensional
Hopf-link flow, and symmetric and asymmetric competitive Lotka–Volterra systems. The learned landscapes agree closely with analytical results where available and, more generally, successfully reveal invariant sets as low- or constant-potential structures. In particular, the van der Pol oscillator,
Hopf-link flow, and asymmetric Lotka–Volterra system demonstrate that coherent GLFs can be constructed without relying on known closed-form expressions, establishing a versatile route to potential-landscape construction for complex nonlinear non-gradient systems.
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Optics · Cross-listed from cs.GR
HoloPathTracer: Fast and Accurate Wave Path Tracing for Holography
Wenbin Zhou, Xiangyu Meng, Jiankai Xing et al. (+3 more)
Holography offers unique advantages for delivering perceptual realism while preserving compact form factors in VR/AR. Its perceptual quality, however, hinges on encoding rich wavefronts of photorealistic scenes into interference patterns and then incoherently multiplexing the resulting wave fields for perception. Existing CGH paradigms decouple radiance estimation from wave propagation by pre-rendering radiance on discretized scene sectors. This separation between radiometric and wave-optical computation inherently limits the range of focus cues and visual effects that can be faithfully reproduced, including depth- and view-continuity, and physically based material behaviors such as glossy or mirror-like reflection and refraction. We present a physically accurate yet computationally efficient wave optics rendering framework leveraging path tracing to encode full 3D visual cues into phase holograms. Specifically, we employ a Monte Carlo method to solve both the rendering equation and the Rayleigh–Sommerfeld integral simultaneously. Our
algorithm is fully compatible with modern graphics techniques and can generate multiple time-multiplexed random holograms with minimal additional time cost via Path Reuse. By employing a fast approximation with an ambient radiance cache, we realize an order of magnitude convergence speed improvement. The resulting coherent wave fields that inherently encode comprehensive visual effects are converted into phase-only holograms under complex-amplitude supervision. Through extensive simulations and experimental validations on a spatial light modulator-based display prototype, we demonstrate faithful
holographic reconstructions of natural 3D cues and complex materials, including realistic defocus blur, view-dependent effects, as well as appearance highlights and reflections.
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All authors Wenbin Zhou, Xiangyu Meng, Jiankai Xing, Xin Liu, Suyeon Choi, Yifan Peng
Nuclear Theory
Teleportation in Proton Systems Revisited
H. Witała
We discuss the peculiarities of scattering in a three-
proton system induced by the presence of an entangled
proton-
proton Bell-like state in the initial configuration. We formulate the problem using the standard
spin formalism of
nuclear physics in order to follow in detail the reaction pathways leading to the teleportation of a
quantum-mechanical state within this system. By performing numerical simulations of the system and calculations based on a realistic nucleon-nucleon potential, we evaluate the relevant
spin observables and search for a simple, experimentally feasible signal that could provide clear evidence of
quantum teleportation. For the case in which
proton 2, belonging to the entangled
proton pair 23, interacts with hydrogen target 1, thereby triggering the teleportation process, we find clear evidence of teleportation through measurements of the final polarization of
proton 3', even for small values of the polarization of target
proton 1. The dominant component of this polarization is transferred almost entirely from target
proton 1 to
proton 3 in the angular region characterized by strong
entanglement. For an unpolarized target
proton 1,
quantum teleportation is no longer possible. The only unambiguous signature of the residual
quantum correlations would be provided by measurements of the
spin correlations within the strongly entangled final-state
proton pair 1'2'. Indirect evidence may also be obtained from measurements of the polarization of
proton 2' in the final state, although the corresponding effectis relatively weak.
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High Energy Physics (Phenomenology)
Thermal dileptons to probe the baryon-rich QCD matter in the forward region of LHC energy heavy-ion collisions
Motomi Oya, Nicholas J. Benoit, Chiho Nonaka et al. (+2 more)
We investigate thermal dilepton production from a
quark-
gluon plasma (QGP) with finite
baryon chemical potential ($\mu_{\text{B}}$) in central Pb-Pb collisions at $\sqrt{s_{\text{NN}}}=5.02~\text{TeV}$. Recent studies suggest that sizable
baryon densities can be achieved at forward rapidity even at LHC energies. We incorporate finite $\mu_{\text{B}}$ into a (3+1)-dimensional hydrodynamic framework and find that $\mu_{\text{B}}$ exceeds 500 MeV around $\eta_\text{s} = 6$ during the medium
evolution. Using this framework, we calculate thermal dilepton spectra over a wide rapidity range and evaluate the impact of finite $\mu_{\text{B}}$ on dilepton production. A suppression of 3-4% is observed in the forward-rapidity region $5.2 < y < 7.2$ due to the reduced
quark-antiquark abundance at finite
baryon density. We further examine the effective temperature extracted from dilepton mass spectra in the intermediate-mass region $1.2 < M_{\ell \ell} < 2.6~\text{GeV}$ . The effective temperature remains strongly correlated with the underlying hydrodynamic temperature and retains sensitivity to the early high-temperature stage of the QGP
evolution. These results demonstrate that forward-rapidity dileptons remain effective thermometers while providing sensitivity to finite
baryon density at the LHC.
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All authors Motomi Oya, Nicholas J. Benoit, Chiho Nonaka, Azumi Sakai, Yorito Yamaguchi
Quantum Physics
Collision models for open quantum systems coupled to finite environments
Gyaneswar Bhoi and Anil Shaji
We study a system
qubit repeatedly interacting with the same environmental
qubit, with a reservoir acting on the environment between collisions via a completely positive, trace-preserving map. We show that complete suppression of system–environment correlations uniquely requires a full environmental reset, recovering a semi group dynamics with a time-independent Gorini–Kossakowski–Sudarshan–Lindblad generator, whereas a partial reset yields a continuous transition between Markovian and non-Markovian regimes governed by a single dimensionless relaxation parameter. For a resonant excitation-exchange interaction, we obtain exact closed-form expressions for the Bloch-vector dynamics for both a generalized depolarizing channel and a generalized amplitude-damping channel acting as the reservoir-induced map. Using the Breuer–Laine–Piilo measure and a Choi-
matrix CP-divisibility witness, we identify three distinct dynamical regimes across the parameter space: CP-divisible Markovian dynamics, CP-indivisible but P-divisible dynamics, and non-P-divisible non-Markovian dynamics. The boundaries between these regimes, and the structural differences between uniform and anisotropic environmental relaxation, are characterized numerically.
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Astrophysics of Galaxies
Identifying Warped Galaxies in Pan-STARRS and Euclid using Deep Convolutional Neural Network
Saranya Suguna and Arunima Banerjee
Warped
galactic discs are common, yet their detection remains challenging, as the outskirts of
galaxies are typically faint. Advances in deep imaging surveys improve the detectability of such features, while machine learning enables efficient analysis of large
datasets. Using the Pan-STARRS EGIPS catalogue, we develop a deep learning framework by fine-tuning the Zoobot convNext-nano model on 1000 edge-on
galaxy FITS images to distinguish warped and non-warped edge-on
galaxies with 83% accuracy. The trained model is then applied to a larger sample, identifying 2088 warped and 1398 non-warped
galaxies with a high prediction probability threshold ($\geq 0.85$). Additionally, we use the model to predict on 3226 edge-on
galaxies from the Euclid Q1 survey, demonstrating the model's ability to generalise across
datasets with differing resolutions. To analyse the model predictions, we employ LayerCAM to identify the regions of
galaxy images that contribute to the classification. We find that warped
galaxies differ primarily in their structural properties, exhibiting lower axis ratios and higher asymmetry. Warped
galaxies were found to be bluer, with younger
stellar populations and enhanced
star formation. These results highlight the effectiveness of deep learning methods in identifying subtle morphological features, such as warps, and demonstrate their potential for studying structural properties of
galaxies in current and upcoming large imaging surveys.
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High Energy Physics (Theory)
Yu Hao, Yunfeng Jiang, Bi-Quan Yang et al. (+1 more)
We investigate the
quantum entanglement of Bethe states across a family of integrable
spin chains, including the XXX$_{\frac{1}{2}}$ model, its higher-
spin generalizations (XXX$_s$), and the non-compact $SL(2,\mathbb{R})$ chain. For on-shell eigenstates, we perform a comprehensive scan of the bipartite
entanglement entropy across the entire spectrum of finite chains with periodic boundary conditions, and identify the Bethe solutions that minimize and maximize the
entanglement. These extremal solutions follow systematic,
spin-dependent patterns in the Bethe
quantum numbers. In the XXX$_{\frac{1}{2}}$
spin chain, for the
antiferromagnetic chain, the state with minimal
entropy always coincides with the lowest-energy state (the ground state) within a given fixed-
magnon sector. For the higher-
spin XXX$_s$ model, however, the lowest-
entropy state is not always identical to the ground state, and can even be the state of highest energy. By contrast, the Bethe roots that maximize
entropy exhibit considerably more intricate structure. Our analysis further reveals how special Bethe root configurations, such as singular and strange solutions, affect
entanglement, and it uncovers characteristic
entanglement features in the non-compact $SL(2,\mathbb{R})$ chain that are absent from compact
spin chains. For off-shell Bethe states, we develop an optimization
algorithm that extremizes the
entanglement entropy over rapidity distributions, enabling us to explore the maximum
entanglement achievable by a Bethe state without imposing the Bethe ansatz equations.
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All authors Yu Hao, Yunfeng Jiang, Bi-Quan Yang, De-liang Zhong
Fluid Dynamics
Optimal heat transport at the edge of energy stability
Zijing Ding, Baole Wen and Hui Li
High heat transfer in Rayleigh–Bénard convection is commonly associated with vigorous turbulent motion, but
turbulence intensity alone does not explain how a limiting transport state is selected. We propose that such limiting states are organized by marginal energy stability. Starting from the exact perturbation-energy balance, we determine, for a prescribed mean temperature profile, the smallest neutral Rayleigh number over the balance parameter and all admissible disturbances. The corresponding marginal modes are then coupled to the exact mean-temperature equation, producing a self-consistent profile and heat flux. At large $Ra$, the selected branch gives $Nu\simeq0.0245Ra^{1/2}$ and develops conductive inner layers, logarithmic-like intermediate regions and a weakly stably stratified core. An equivalent background-field formulation yields the same governing equations and establishes uniqueness of the selected mean profile. Three-dimensional simulations at $10^6\le Ra\le10^8$ show that distributed thermal forcing based on this profile suppresses convective motion while retaining a large wall heat flux.
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Quantum Gases
Fermi gas of polar molecules in the Pauli-blocked regime
Junyu Lin, Annette N. Carroll, Phillip Martin et al. (+6 more)
Quantum gases of polar molecules have recently emerged as a powerful platform for exploring exotic many-body dynamics and correlated
quantum behavior. To achieve the full potential of this platform, the production of deeply degenerate
quantum gases of molecules in arbitrary confinement geometries is necessary. Here, we successfully evaporate fermionic KRb molecules in both 3D and quasi-2D geometries to well below their
Fermi temperatures utilizing dipolar collisions. As we evaporate deeper into degeneracy in both geometries, we enter the Pauli-blocked regime with polar molecules, which we independently confirm by measuring the Pauli suppression of elastic collisions. Moreover, the Pauli suppression of collisions contributes to the limitation of our final molecular temperature to about 25% of the
Fermi temperature in both geometries, particularly limiting quasi-2D evaporation where the Pauli blockade drastically reduces an otherwise large elastic to inelastic scattering ratio. This work demonstrates the production of degenerate
Fermi gases of polar molecules both in a 3D harmonic trap and in mono- and bi-layer 2D configurations. Further, our work explores the fundamental limits on evaporation of molecular
Fermi gases set by the Pauli-exclusion principle, which could be overcome in the future by introducing distinguishable scattering partners.
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All authors Junyu Lin, Annette N. Carroll, Phillip Martin, Calder Miller, Reuben R. W. Wang, Kevin B. Xu, John L. Bohn, Tim de Jongh, Jun Ye