Plasma Physics
Mechanism of Ionization Avalanche in Tokamak Microwave Gas Breakdown
Jinwoo Gwak, Yeongsun Lee, Jeongwon Lee et al. (+5 more)
Microwave breakdown driven by electron cyclotron (EC) waves provides a non-inductive route to
plasma initiation in reactor-scale tokamaks. We introduce a three-dimensional Monte Carlo simulation that, for the first time, self-consistently treats nonlinear wave-particle interactions, atomic collisions, and guiding-center transport. The Monte Carlo simulation unveils the key role of parallel Brownian motion in the ionization avalanche mechanism. The predicted breakdown boundary is validated against KSTAR experiments. This work concludes that microwave gas breakdown will be successful under ITER-relevant conditions at a D$_2$ prefill pressure near 2 mPa with 1 MW of injected EC power.
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All authors Jinwoo Gwak, Yeongsun Lee, Jeongwon Lee, Won Ik Jeong, Hyun-Tae Kim, Yong-Seok Hwang, Min-Gu Yoo, Yong-Su Na
Quantum Physics
Polariton Bell Node for Quantum Repeaters
Junhui Cao and Alexey Kavokin
We propose a Bell-measurement node for
quantum repeaters based on a planar
semiconductor microcavity operating in the strong-coupling regime. Cavity
photons hybridize with
quantum-well
excitons to form polaritons combining properties of
photons and matter quasiparticles. A control
photon loaded into one polariton mode changes the polarization response seen by a subsequently incident target
photon. This conditional rotation is governed by the interplay of self-induced Larmor precession triggered by
spin-dependent
exciton-
exciton interactions and the polarization beats caused by the splitting of transverse-electric and transverse-
magnetic cavity modes. We identify conditions of the experiment that enable implementation of a controlled-Z gate and allow to distinguish all four Bell states in the ideal limit. The one-sided scattering scheme provides a lower interaction threshold than a scalar Kerr reference under the same assumptions. At a selected operating point, the bandwidth-induced identification error scales as the fourth power of the pulse bandwidth in the narrow-band limit. An additional fixed input rotation reduces this error even further. We describe the
entanglement swapping between remote
memories and determine the minimum quality of the elementary links needed to obtain an entangled output.
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High Energy Physics (Theory)
Complex scalar field thick branes: stability of linear perturbation and evolution of scalar Kaluza-Klein modes coupled with gravity
Wang-Long Dong, Heng Guo, Qun Wei et al. (+1 more)
We investigate the stability and localization properties of Minkowski, de Sitter (dS), and anti-de Sitter (AdS) thick branes generated by a complex scalar field $\Phi$. The scalar self-interaction potential contains a temperature parameter $a$. As $a$ approaches its critical value, the imaginary part of $\Phi$ becomes double-kinked and the energy density splits into two peaks, indicating the formation of two sub-branes. The analysis of linear scalar, vector, and tensor perturbations shows no signs of instability in the scalar and vector sectors, while the factorization of the tensor perturbation equation excludes tachyonic tensor modes. The graviton zero mode is localized on the Minkowski and dS branes but is not normalizable on the AdS brane. We further study a real test scalar field $\Psi$ with a coupling function $F(R)$ between its kinetic term and the spacetime
curvature. The scalar zero mode can always be localized on the Minkowski and dS branes, with a continuous gapless spectrum of scalar Kaluza–Klein (KK) modes. Massive scalar resonances emerge near the critical value of $a$ for suitable values of $\beta$. Increasing $\beta$ produces more resonances and prolongs the lifetimes of the lower resonances, while their time
evolution exhibits the characteristic decay of metastable modes. For the AdS brane, the scalar zero mode is also localized, whereas the divergent effective potential at the boundaries traps the massive scalar KK modes as bound states, yielding a discrete mass spectrum.
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All authors Wang-Long Dong, Heng Guo, Qun Wei, Yong-Tao Lu
Quantum Physics
Ultimate Information Rate for Quantum Sensing under Multilevel Relaxation
Changhun Oh, Seok Hyung Lie and Youngrong Lim
We determine the ultimate information rate of a relaxing multilevel
quantum sensor under unrestricted adaptive control and construct an explicit strategy that attains it. We consider sensing a weak field that couples the ground state to several excited states that decay back to the ground state, a setting that reduces to amplitude-damping sensing for a single excited state. We show that the ultimate information rate is exactly the mean population lifetime of the bright state coupled to the ground state by the signal. Although the sensing dynamics generally involve several decay modes, an explicit rank-one protocol that monitors the ground–bright coherence using fresh meters and classical feedback attains this rate while keeping its finite-time information deficit bounded by a constant. For independently relaxing identical sensors, independent local monitoring attains the sum of their individual optimal rates, so intersensor
entanglement and joint
quantum error correction cannot increase the asymptotic rate. Consequently, the free population-decay curve provides an operational measure of the optimal sensing performance under arbitrary adaptive control.
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Statistical Mechanics
Local Detailed Balance in the Lorenz Model: Replaces the Butterfly with Frenetic Bursting
Faezeh Khodabandehlou and Christian Maes
The Lorenz system is the canonical low-order model of convective instability, yet its dissipative and driving terms have never been checked against, nor constructed from, an explicit thermodynamic bookkeeping. We derive a modification that satisfies the local-detailed-balance condition for macroscopic relaxation toward nonequilibrium steady states, thereby identifying the thermodynamic force,
entropy-production rate and frenesy of the resulting flow. The resulting model produces a transition from a quiescent fixed point to a robust, large-amplitude relaxation oscillation, closely analogous to recharge-discharge oscillator paradigms used for the El Nino-Southern Oscillation. The system alternates between a long, nearly reversible recharge phase and a brief, violently frenetic discharge burst, during which essentially all of the cycle's activity and
entropy production is concentrated.
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Mathematical Physics
A Functorial Theory of Defects in Abelian Chern-Simons Theory
Daniel Galviz
Recent work has constructed Abelian Chern-Simons theories as categorical TQFTs, allowing us to naturally incorporate categorical defects and construct defect extensions of Abelian Chern-Simons TQFTs. We first identify the Turaev-Viro realizations of Abelian Chern-Simons theory in the center and doubled pointed modular cases, clarifying the distinction between single bulk realizations and canonical doubled ones. Then we obtain Turaev-Viro partition functions in terms of Reidemeister-torsion densities. Alternatively, the Alterfold construction supplies the associated topological boundaries, domain walls, and condensation sectors, establishing an explicit Alterfold/Chern-Simons dictionary. We show that the finite quadratic module is the invariant controlling the bulk theory, its topological
symmetries, orientation-reversal invariance, and defects. We further show that multicomponent Abelian BF theory arises as the extended TQFT of an off-diagonal Abelian Chern-Simons theory, placing it naturally within the same extended framework. Finally, we demonstrate that recently proposed Abelian Chern-Simons dualities do not define a genuine TQFT duality. These results provide a concrete model for defects in Abelian topological orders and suggest a route toward the non-Abelian case.
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High Energy Astrophysical Phenomena
Gamma-ray Quasi-periodic Oscillations in the Changing Look Blazar B2 1420+326 (OQ 334)
Sunanda, Shubham Kishore and Alok C. Gupta
In the
Fermi-LAT gamma-ray light curve from January 1 to August 25, 2026, of the changing look blazar B2 1420+326, we report here the detection of transient quasi-periodic oscillations (QPOs) of period ranging around 10-13 d. The source entered the
flare state around May 7, 2026, and lasted till around mid-August, 2026 during which it depicted strong QPO signatures. We utilized standard techniques, including weighted wavelet Z-transform analysis, generalized Lomb-Scargle periodogram, and phase dispersion minimization, to search for and confirm these findings. Prior to the
flare, the source displayed a mild damped oscillatory feature of similar periodicity with a damping timescale of around 20 d. Based on the period timescale and nature of the QPOs detected, we discuss possible physical mechanisms for the observed salient features.
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Geophysics
Predicting the Elastic Properties of a Cemented Granular Material during Chemical Damage (Debonding)
Alexandre Sac-Morane, Maria Olarte-Garzon, Philipp Braun et al. (+3 more)
While underground reservoirs emerge as essential elements to face global warming, these systems represent complex multi-physical and multiscale problems. The considered injection of fluids during hydrogen storage, carbon dioxide sequestration, or geothermal energy recovery involves a modification of the chemical
equilibrium of the fluid in the porous reservoir. Chemical reactions can induce microstructural changes of the rock
matrix, leading to a reduction of elastic properties of the material, and to potential settlement or stress redistribution. Consequently, it becomes pivotal to establish predictive behavior laws to describe the effect of chemical damage on elastic properties. Facing the difficulties to estimate experimentally the impact of chemical damage on mechanical properties, a Digital Rock Physics approach is proposed in this contribution. This numerical homogenization scheme is used to compare two distinct types of microstructure models: the first one consists in a Discrete Element Model, while the second one employs a continuous description. This continuous formulation is based on a Phase-Field description to predict the
evolution of the microstructure subjected to chemical alterations and on the Fast
Fourier Transform to estimate the macroscopic properties of the material. Finally, these frameworks establish different softening laws that can be used as constitutive ingredients for a cemented material during its weathering.
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All authors Alexandre Sac-Morane, Maria Olarte-Garzon, Philipp Braun, Jean-Michel Pereira, Manolis Veveakis, Hadrien Rattez
High Energy Physics (Phenomenology)
Anomalous Matter Potentials in Earth's Inner Core: A Phenomenological Probe of Dark Matter and Light Sterile Neutrinos
Bipin Singh Koranga and Vivek Kumar Nautiyal
Standard treatments of Earth matter effects in
neutrino oscillation experiments assume that the coherent forward scattering potential experienced by propagating
neutrinos is sourced entirely by the Standard Model electron density predicted by the Preliminary Reference Earth Model (PREM). We examine how an anomalous matter potential localized in Earth's inner core, motivated by gravitationally captured dark matter or resonant mixing of active
neutrinos with a light (eV-scale or lighter) sterile state, would distort the vu survival and vutove appearance probabilities relative to the Standard Model PREM expectation. Using a full three-
flavor matrix-exponentiation propagation code with a four-shell PREM density profile, we parametrize the new-physics contribution as a fractional enhancement ecore of the electron-sector potential confined to the inner core (r<1221 km) and compute oscillation probabilities for near-vertically upgoing atmospheric
neutrinos (L=8000to12742km). Trajectories that do not cross the inner core (L<=12500km) are essentially insensitive to ecore, reproducing the Standard Model expectation to better than 0.1%. In contrast, near-antipodal trajectories crossing the inner core (L>=12505km, corresponding to nadir angles within roughly half a degree of the vertical) show significant effects. The
muon-
neutrino survival probability is displaced by tens of percent for ecore=0.05to0.15 and by more than 100% at particular energies for the {\nu}{\mu} to {\nu}e appearance channel, with a pronounced neutrinoantineutrino asymmetry that mimics, but is physically distinct from, intrinsic CP violation. These results indicate that percent-level new-physics potentials confined to the inner core are within the discovery reach of high-statistics atmospheric
neutrino telescopes such as IceCube Upgrade, KM3NeT/ORCA, and next-generation megaton-scale detectors.
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Fluid Dynamics
Relative velocity between a particle and turbulence
Yutaro Motoori, Daiki Watanabe and Susumu Goto
The relative velocity between a particle and the surrounding fluid is a key quantity that determines the various phenomena of particle-laden
turbulence, such as particle clustering and
turbulence modulation due to particles. We theoretically derive the expression for the relative velocity of a particle laden in
turbulence by extending the argument of Balachandar (2009). This derivation provides a simplified form of the analytical model of Berk and Coletti (2024), and it makes the underlying physical assumptions explicit. Using direct numerical simulation data of
turbulence in a periodic cube and turbulent channel flow, we demonstrate the validity of the derived expression, and show that it also holds for non-spherical particles and droplets.
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Fluid Dynamics
Optimization of fluid mixing by reinforcement learning using limit cycles of a dynamical system
Masaki Shimizu, Daiki Watanabe, Takumi Aoyagi et al. (+1 more)
We propose a method to overcome the difficulties encountered when applying reinforcement learning to fluid mixing processes. The proposed method has two main features: (i) it does not require detailed measurements of the flow state, and (ii) by effectively exploiting a stable limit cycle of a two-dimensional dynamical system (the Li'enard system), it can stably perform optimization without imposing explicit constraints on the control parameters. As an illustrative example, we optimize a process in which a fluid contained in a cylindrical vessel is mixed by periodically rotating the vessel. The resulting optimal vessel motion is physically reasonable: it reverses its direction of rotation before a solid-body rotation state is established. Furthermore, even when the fluid viscosity increases with time during the mixing process, the method can continuously adapt the control parameters to the changing viscosity.
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All authors Masaki Shimizu, Daiki Watanabe, Takumi Aoyagi, Susumu Goto
High Energy Physics (Theory)
A Differential Form Description of Partial Entanglement Entropy: Testing a Killing Vector Construction in Covariant Phase Space
Chuanjia Zhu, Dong-Hui Du, Wen-Cong Gan et al. (+1 more)
The bit thread formulation provides a
geometric description of
holographic entanglement entropy, while partial
entanglement entropy (PEE) and PEE threads resolve this structure with respect to individual boundary points. Motivated by the fact that PEE thread flows can be superposed to reconstruct conventional bit thread flows, we introduce a differential form description of PEE thread flow. For an interval in the
vacuum AdS$_3$/CFT$_2$ setup, we show that the flux of the resulting form reproduces the known
entanglement contour, providing a consistency check of the proposed description. We then investigate whether the PEE form can be related, possibly up to an exact form improvement, to a current constructed from the covariant phase space (CPS) formalism. As a first test, we consider exact Killing vectors in Rindler-AdS$_3$. The Rindler parameter $a$ parametrizes a one-parameter family of backgrounds. At each value of $a$, the Killing vector of the corresponding background is substituted into the Iyer-Wald surface charge form, and the full $a$-dependence of the resulting form is retained. We define a finite candidate current by integrating this surface charge form over $a$. For the reflection-symmetric PEE flow sourced at the central boundary point $r_0=0$, we find that no choice of the Killing parameters reproduces both components of the known PEE flow after transforming to Poincaré-AdS$_3$. This result shows that the direct Killing vector CPS construction considered here is not sufficient to reproduce the central PEE flow. Possible extensions include an exact form improvement, a different CPS current, or a more general choice of generator.
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All authors Chuanjia Zhu, Dong-Hui Du, Wen-Cong Gan, Fu-Wen Shu
Quantum Physics
A memory-information window in finite-duration quantum control
Doyeol Ahn
Environmental noise is a major source of decoherence and errors in
quantum systems. In a non-Markovian environment, the noise has a finite correlation time, and the system can retain information about its previous interactions with the environment. Here, we investigate how such environmental
memory can be observed through a finite-duration coherent
quantum operation. Coherent control dynamically reshapes the
stochastic coupling operator and thereby changes how two-time noise correlations affect the
quantum process. For Ornstein-Uhlenbeck noise, we show analytically that two different limits reduce the information on the correlation time. In the short-
memory limit, the leading dynamics depend on the integrated-noise combination {\sigma}/{\tau}c, where {\sigma} is the noise variance and {\tau}c is the correlation time, making these parameters locally degenerate. In the long-
memory limit, the
stochastic field becomes quasi-static during the operation, and sensitivity to the correlation time is suppressed. Exact
stochastic simulations for a driven single-
qubit X{\pi} rotation and a two-
qubit exchange gate show that independent correlation-time information becomes largest between these limits, when the environmental and control timescales are comparable. Noncommuting controls enhance this information, whereas commuting controls do not. Simulations at different gate durations tg further show that the information window approximately follows the dimensionless correlation ratio {\tau}c/tg. These results provide a timescale-matching principle for probing finite-correlation non-Markovian noise with coherent
quantum control.
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Quantum Physics
Denser Planar Color Codes
Noah Shutty
We consider the 4.8.8 color code in a brickwork layout on the square
lattice with nearest-neighbor gates. We identify periodic superdense
circuits with twelve CNOT layers that appear to preserve the full distance of these codes. Including ancillas, the family uses $q=(2d^2+5d-5)/2$ physical
qubits for distance $d$: asymptotically $2/3$ as many as the triangular 6.6.6 color code and $1/2$ as many as the rotated surface code at the same code distance.
Circuit-level simulations targeting superconducting architectures demonstrate favorable scaling of 4.8.8 color codes at plausible physical noise rates, including both for planar codes and their toroidal cousins under periodic boundary conditions.
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Optics
Topological Optical Frequency Combs
Rujiang Li and Wenfu Zhang
Optical frequency combs (OFCs) are revolutionary light sources characterized by discrete and equally spaced spectral lines, and they have found widespread applications in metrology, spectroscopy, and communications. In the early stages, OFCs were realized using mode-locked
lasers. With advancements in the fabrication of high-quality factor ($Q$) microresonators and the increasing demand for miniaturized and integrable photonic chips, microresonator-based OFCs, commonly referred to as microcombs, have been developed. Although early studies of microcombs primarily focused on single microresonators or a few resonators, a significant breakthrough occurred in 2021 when it was theoretically predicted that light propagating in the topological edge channel of an array of ring resonators could generate nested frequency combs known as topological OFCs. Since then, the field of topological OFCs has progressed rapidly, with experimental observations made in 2024. This Perspective will introduce the history of OFCs, placing particular emphasis on the emergence and development of topological OFCs, as well as exploring the research challenges and opportunities associated with them.
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Astrophysics of Galaxies
Fountain pattern of baryon cycle revealed in galaxy ecosystems
Chengyu Ma, Yangyao Chen, Enci Wang et al. (+11 more)
Baryons in
galaxy ecosystems are believed to undergo continuous cycles of inflow and
outflow, forming fountain-like patterns that encode key information about how
galaxies acquire matter from their environments and respond through feedback. The presence of such
baryon cycles has been inferred from pieces of observational evidence, but a concrete understanding remains elusive because individual
galaxy ecosystems are diverse and dynamic. Here we introduce a stacking method that combines baryonic fields across ensembles of individual
galaxy ecosystems to suppress irregularities and reveal the underlying pattern. Applied to a cosmological hydrodynamic simulation, this approach unveils strikingly regular patterns in gas properties across the full spatial extent of
galaxy ecosystems, in close agreement with those inferred from observations. This method is straightforward to implement, allowing the processes shaping the gas-cycling pattern to be fully understood within the structure-formation paradigm, and a solid framework to be constructed for linking simulated
galaxy ecosystems with observations.
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All authors Chengyu Ma, Yangyao Chen, Enci Wang, Houjun Mo, Huiyuan Wang, Tao Wang, Qirong Yuan, Min Du, Zhaozhou Li, Kai Wang, Cheqiu Lyu, Haoran Yu, Zeyu Chen, Xiaoxuan Chen
Quantum Physics
Passive Pauli Toggling of Polarization Qubits in Optical Fibers: Error Bounds and QKD Performance
Bongjune Kim and Jeongho Bang
Polarization
qubits offer a direct route to fiber-based
quantum communication, yet the fiber that carries them also scrambles their reference frame through uncontrolled birefringence. Active compensation commonly relies on monitoring and feedback, raising a natural question: can the link itself suppress coherent polarization drift before it reaches the receiver? We show that it can within a regime of sufficiently correlated
unitary drift. Our central idea is to embed a fixed cyclic sequence of Pauli rotations along the fiber, turning propagation distance into a spatial toggling frame. Rather than estimating and inverting the unknown transformation, the sequence repeatedly reverses its leading action. We establish exact refocusing for constant generators compatible with a two-segment echo, show that a four-frame Pauli
cell cancels the leading contribution of any traceless quasi-static generator, and bound the residual error for smoothly varying birefringence. We then connect these guarantees to operational BB84 quantities, including measured QBERs, the resulting secret fraction, and insertion loss. In simulations of a 50 km fiber with spatially correlated birefringence, a representative design reduces the mean QBER from 6.11% to 0.224% at a device spacing of 1.25 km. With an assumed per-device transmission of t = 0.997, this raises the asymptotic key rate per launched pulse by a factor of approximately 2.5. For this parameter set, the best design in the tested scan is not the densest one: error suppression and optical loss create a finite operating window. These results provide a loss-aware design principle for passive polarization stabilization and suggest a low-overhead complement to active tracking in polarization-encoded QKD networks.
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High Energy Physics (Theory)
Fabio Ori and Peng-Xiang Hao
Entanglement entropy in
holographic conformal field theories with boundaries of generic spacetime signature cannot be described entirely within the standard
holographic duality to a real bulk spacetime. We show, both in static and time-dependent setups, that an exact match with the conformal field theory predictions in two boundary dimensions entails an extension of the dual spacetime to complex coordinates. As a consequence, relevant bulk objects such as Ryu-Takayanagi surfaces and branes are in general complex, yet anchored on a real asymptotic boundary preserving the physical meaning of field-theoretical quantities. We also provide a third numerical check of the
holographic prediction with a two-dimensional system of free Gaussian
fermions exhibiting the same asymptotic regimes across different
entanglement phases.
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Quantum Physics
Weighted Berry curvature and global geometry of mixed quantum states
Dominik Kuczyński and Erik Sjöqvist
We examine the
geometric interpretation of the
quantum geometric tensor proposed in [Phys. Rev. B 110, 035404 (2024)] for mixed
quantum states, focusing on its imaginary part, which is proportional to a weighted sum of the Berry
curvatures of the eigenstates of the density operator. While the real part naturally decomposes into Fisher–Rao and weighted Fubini–Study contributions, we show that the imaginary part does not, in general, coincide with the
curvature of a connection on a globally defined U(1) line bundle whose holonomy yields a mixed-state
geometric phase. Using a two-level system as an explicit example, we demonstrate that its surface integral depends on the choice of surface bounded by the same closed path, with ambiguities that are not integer multiples of $2\pi$.
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Applied Physics
Multiplexing approaches to thermoradiative signatureless communications
Valerii Radchenkov, Peter J. Reece, Stephen P. Bremner et al. (+2 more)
Using mid-infrared emission from
semiconductor devices for covert communications remains a relatively unexplored and yet promising opportunity. The phenomenon of negative luminescence allows for a method of signatureless covert communications where the net infrared emission of an emitting optoelectronic device is balanced to be identical to the ambient thermal background. In this work we provide a practical demonstration of covert data transfer over a thermoradiative channel with data rates up to 100 kbps. In addition, we demonstrate several additional multiplexing techniques that make the proposed thermoradiative communications method more secure against interception by achieving zero instantaneous optical emission, while remaining detectable if a sufficiently spatially or spectrally discerning observation is utilised. Finally, we discuss various application scenarios in which the proposed methods can be used to achieve secure signatureless communications.
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All authors Valerii Radchenkov, Peter J. Reece, Stephen P. Bremner, Nicholas J. Ekins-Daukes, Michael P. Nielsen
Materials Science
Strain-Induced Relaxor Multiferroicity at Room Temperature in Hexaferrite BaFe12O19 Thin Films
Yilin Evan Li, Harikrishnan KP, Sankalpa Hazra et al. (+19 more)
Multiferroic materials that combine
magnetic and electric order at room temperature are rare. Here, we demonstrate strain-induced room-temperature polar order in the ferrimagnetic hexaferrite BaFe12O19. First-principles calculations reveal a strain-tunable energy landscape with multiple competing dipolar configurations and predict that compressive strain favors polar distortions. Using an isostructural Sr1.03Ga10.81Mg0.58Zr0.58O19 substrate, we grow coherently strained BaFe12O19 films with 1.1% in-plane biaxial compression. Second-harmonic generation measurements demonstrate inversion-
symmetry breaking and establish a strain-stabilized polar phase that persists to at least 1000 K. Multislice electron ptychography directly reveals enhanced off-centering of Fe3+ ions within the trigonal-bipyramidal sites of the strained films and spatially varying local polarization, demonstrating the formation of polar nanoregions. Path-integral Monte Carlo simulations further show that compressive strain suppresses
quantum fluctuations and stabilizes these local polar distortions. Together, these results establish strain-engineered BaFe12O19 as a room-temperature relaxor multiferroic, in which robust ferrimagnetism coexists with nanoscale polar order. Our work demonstrates a route for transforming an incipient ferroelectric ferrimagnetic into a polar
magnetic material through epitaxial strain.
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All authors Yilin Evan Li, Harikrishnan KP, Sankalpa Hazra, Zhiren He, Jayanti Higgins, ChanJu You, Mario Brützam, Jiaqiang Yan, Anna Park, Maya Ramesh, Wenwen Zhao, Jayda Shine, David G. Mandrus, Ramamoorthy Ramesh, Ankit S. Disa, Christo Guguschev, Guru Khalsa, Craig J. Fennie, Venkatraman Gopalan, Yu-Tsun Shao, David A. Muller, Darrell G. Schlom
Astrophysics of Galaxies
From Observation to Ground Truth: Reconstruction Losses of Galaxy Imaging Under Heteroscedastic Noise
Renhao Ye, Shiyin Shen and Quanfeng Xu
Deep learning is widely used to analyze
galaxy images, and the reconstruction loss determines which image features a model prioritizes during training. Mean squared error (MSE) and mean absolute error (MAE) correspond to homoscedastic Gaussian and Laplace likelihoods, respectively, whereas the inverse-variance-weighted $\chi^2$ loss accounts for the spatially varying uncertainties of heteroscedastic astronomical noise. Comparing how closely these objectives recover the underlying signal requires a ground truth (GT), which real observations cannot provide. We therefore generate noise-free
galaxy images with IllustrisTNG, SKIRT, and GalaxyGenius, convolve them with a point-spread function (PSF) to define the GT, and construct noisy simulated observations. We train otherwise identical variational autoencoders (VAEs) with the three reconstruction losses and evaluate their outputs against the GT. Over most of the evaluated signal-to-noise ratio (SNR) range, the $\chi^2$-trained model yields lower relative reconstruction errors than the MSE- and MAE-trained models, indicating that inverse-variance weighting improves
galaxy-image reconstruction under the heteroscedastic noise considered here.
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High Energy Astrophysical Phenomena
A Gamma-ray Emitting Head-Tail Radio Galaxy Swimming Through the Hot Medium of the Merging Cluster Abell 3627
Vaidehi S. Paliya, M. Böttcher, Swayamtrupta Panda et al. (+4 more)
Head-tail
radio sources are jetted active
galactic nuclei (AGN) moving through the dense intracluster medium of
galaxy clusters. They are extremely rare in the gamma-ray sky, likely because they are usually observed at large viewing angles. Therefore, every new gamma-ray detection of head-tail
radio galaxies allows us to probe the origin of the high-energy emission in this unique class of AGN. Here we report, for the first time, the association of ESO~0137-G007 (z=0.016), a head-tail
radio galaxy located at the outskirts of the merging cluster Abell 3627, with the gamma-ray source FL16Y~J1615.5$-$6034. The motion of the
galaxy through the dense cluster environment and subsequent ram pressure and/or intracluster medium
turbulence have led to the formation of a $>$500 kpc-long jet exhibiting a twisted, wiggly
radio morphology. Its optical spectrum, obtained with the 4.1 m SOAR
telescope, is devoid of emission lines, indicating that the underlying
accretion activity is radiatively inefficient. From the measured line-of-sight
stellar velocity dispersion, we estimate the mass of the central supermassive black hole to be $(3.36\pm1.32)\times10^9$ \Msun. We briefly discuss several radiative models to explain the observed broadband spectral energy distribution of ESO~0137$-$G007. We conclude that deeper multi-wavelength observations of this unique gamma-ray emitting head-tail
radio galaxy will enable us to better understand the interaction of the jet with the hot cluster environment, thus setting the stage for the research of this class of AGN with the upcoming Square Kilometer Array.
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All authors Vaidehi S. Paliya, M. Böttcher, Swayamtrupta Panda, Kiran Wani, D. J. Saikia, Mahadev Pandge, C. S. Stalin
Astrophysics of Galaxies
A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30
Scott C. Chapman, Kedar A. Phadke, Nikolaus Sulzenauer et al. (+20 more)
We present 11 newly identified ultra-red
galaxies selected with JWST/NIRCam in the core of the z=4.3 protocluster SPT2349-56. Although these sources are not yet spectroscopically confirmed, their extremely red colours (m200-m444 > 2.0 mag), strong spatial concentration, and number density - at least 2000 times that of comparable field populations - make a chance projected association unlikely. Their colours overlap those used to select the widely studied “little red dot” (LRD) population, although most of the sources are spatially resolved and are therefore better described as extended red dots (ERDs). The resolved morphologies disfavour continuum emission dominated by an unresolved active
nucleus and imply a substantial
stellar contribution. Deep ALMA observations put strong limits on obscured
star formation, and the ERD population mostly lies significantly below the
star-forming main sequence. One object, ERD1/Q1, is substantially brighter and more massive, lying far below the main sequence, making it a strong candidate for a massive quiescent
galaxy. These JWST-selected red
galaxies reveal a previously inaccessible population extending to lower luminosities and
stellar masses than the Dusty
Star Forming
Galaxy (DSFG) population which characterizes the dense protocluster core. SPT2349-56 may therefore capture an early phase of cluster assembly in which extreme starbursts coexist with
galaxies already transitioning toward the passive
galaxies characteristic of mature cluster cores.
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All authors Scott C. Chapman, Kedar A. Phadke, Nikolaus Sulzenauer, Dazhi Zhou, Hollis Akins, Manuel Aravena, James R. Burgoyne, Caitlin M. Casey, Erin Foley, Leah Fryer, Ryley Hill, Nicholas LeVar, Monica Natalia Isla Llave, Matt Malkan, Vismaya Pillai, William Rasakanya, Manuel Solimano, Justin S. Spilker, Aurelie Torti, Joaquin D. Vieira, Fabio Vito, David Vizgan, George Wang
Astrophysics of Galaxies
Patchy Reionization Delays Quenching in Isolated Ultra-faint Dwarf Galaxies
Juyoung Kim, Myoungwon Jeon, Yumi Choi et al. (+1 more)
The spatially inhomogeneous nature of
cosmic reionization is directly encoded in the quenching timescales of ultra-faint
dwarf galaxies (UFDs). While most cosmological simulations employ a spatially uniform UV background (UVB) for computational efficiency, such homogeneous treatment may oversimplify the physical impact of reionization on UFDs, whose
star formation histories (SFHs) are highly sensitive to local environments. Under these idealized, instantaneous UVB frameworks,
star formation in UFDs is typically truncated abruptly at the onset of reionization, creating a tension with the extended and diverse SFHs observed in Local Group UFDs. To address this discrepancy, we perform high-resolution cosmological zoom-in simulations to contrast two distinct reionization models: a conventional uniform UVB and an on-the-fly radiative transfer (RT)-based patchy reionization model. We find that RT-based reionization delays
star-formation quenching by ~440 Myr on average, a result consistent with recent observational constraints. However, this extended
star formation does not necessarily leave a discernible imprint on the
stellar metallicity distribution, indicating that the delay–while physically significant for gas dynamics–is still insufficient to drive substantial chemical enrichment. Our results emphasize the necessity of more realistic, patchy reionization modeling to explain the observed diversity of the Local Group population.
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All authors Juyoung Kim, Myoungwon Jeon, Yumi Choi, Sangmo Tony Sohn
Optics
Metasurface-integrated VCSEL designed for polarization control in optical Ising machines
Wenjie Chen, Zifeng Yuan, Hong-Lin Lin et al. (+4 more)
The orthogonal polarization states of vertical-cavity surface-emitting
lasers (VCSELs) can be used to describe candidate solutions to the Ising
Hamiltonian, which is useful for solving quadratic unconstrained binary optimization problems. However, the natural anisotropy of VCSELs tends to overly favor one polarization state, which impedes the system from working as desired. In this work, we have designed and fabricated a metasurface, which may lead to a VCSEL with reduced undesired anisotropy. By changing the
geometric size of nano-structures in the metasurface, the polarization state of the output light can be altered. Based on the injection-locking theory and
spin-flip model, we numerically show that VCSELs with lowered anisotropy are more easily affected by the injection locking needed in Ising systems. Additionally, we numerically study the
evolution of a 3-bit VCSEL-based Ising system and verify that the computational accuracy of the photonic Ising machine can be improved to more than twice that of its counterpart with higher anisotropy.
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All authors Wenjie Chen, Zifeng Yuan, Hong-Lin Lin, Luo Qi, Jiaru Chu, Aaron Danner, Yuhang Chen
High Energy Astrophysical Phenomena
Why most neutron star low-mass X-ray binaries accrete transiently: an evolutionary study of transient and persistent phases
Divyansh Tripathi, Sudip Bhattacharyya and Pulkit Ojha
A
neutron star (NS) low-mass X-ray binary (LMXB), in which an NS accretes matter from a low-mass donor
star, is an ideal source for probing some fundamental aspects of physics and astronomy, such as strong
gravity, superdense matter, and the
accretion-ejection processes. However, to reliably achieve these goals, one must adequately understand NS LMXBs, including why some accrete persistently and others transiently. Focused models, such as those based on a thermal-viscous instability in the
accretion disk, are considered to explain transient
accretion. However, broader perspectives, including which LMXB parameter values and phases cause transients and why there are more transients than persistents, remain poorly understood. Here, our computation of the long-term
evolution of NS LMXBs addresses these questions, providing insight into LMXB parameters and phases, naturally producing more transients than persistents, and being partially consistent with the known properties of observed sources. For example, we typically find a greater fraction of persistent phase at lower orbital periods from the LMXB
evolution computation, which is somewhat consistent with observations. However, a lack of full consistency calls for improving the aforementioned focused models, and our computations provide a new way to discriminate among these models.
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Quantum Physics
Commutator Geometry and Information Preservation in the Quantum Switch
Xu Chen and Xue Ma
Two commuting channels yield the same composite channel in either fixed order, yet their
quantum switch can alter information preservation. We study how this effect depends on the input state, retaining the joint output of the control and target. Exact Kraus commutator identities determine overlap and squared fidelity gaps. Fixed order preserves product inputs at least as well as the switch in fidelity. The reverse inequality holds for pure states of two
qubits whose control Schmidt basis can be chosen to coincide with the order basis. A commutator
matrix determines the target basis that maximizes the squared fidelity gap at fixed
entanglement within this aligned family. For Pauli $X$ and $Y$ channels with equal error probabilities, the switch replaces a logical phase flip with an operator that stabilizes a joint code. At fixed noise, the switch preserves at least as much distinguishability and
quantum Fisher information as fixed order for every state family in this code. For the pure encoded family studied here, exact formulas connect the phase information gain to the squared fidelity gap and quantify the reduction in information about the noise probability. Optimizing the probes yields equal maximal
quantum Fisher information for noise estimation under both joint channels. These results connect commutator geometry and logical error structure to state preservation and the retention of encoded information.
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Materials Science
The Critical Role of Itinerant Contributions to Orbital Angular Momentum Relaxation and Dynamics
Andrew C. Grieder, Luis M. Canonico, Frederico Simões et al. (+2 more)
Orbital angular momentum (OAM) is a promising degree of freedom for low-dissipation transport and magnetization control, yet its relaxation mechanisms remain controversial, with atomcentered approximations (ACA) predicting much shorter OAM
diffusion lengths than experiments. We address this discrepancy using first-principles Lindbladian density-
matrix dynamics, capturing electron-
phonon scattering and itinerant OAM contributions, together with a first-principles parameterized tight-binding approach that separates the ACA and itinerant components. In MoS2,a strong-
spin-orbit-coupling (SOC) system, orbital relaxation is multi-timescale, with fast intervalley redistribution followed by slower decay coupled to the
spin. In weak-SOC silicene,
spin and orbital dynamics decouple; an electric field tunes
spin relaxation while leaving orbital lifetimes unchanged. In both materials, ACA orbital lifetimes are at least one order of magnitude shorter than itinerant ones, due to ultrafast precession driven by
crystal-field splitting, absent from the itinerant component. These results demonstrate that going beyond atom-centered models is essential for describing orbital relaxation and
diffusion.
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All authors Andrew C. Grieder, Luis M. Canonico, Frederico Simões, Aron W. Cummings, Yuan Ping
Soft Condensed Matter
Granular thermostat implementation within the soft-sphere Discrete Element Method (DEM) framework, considerations and limitations
Marco Previtali, Herbert Eric Huppert and Sergio Andres Galindo Torres
Dense granular flows are commonly investigated using the soft-sphere Discrete Element Method (DEM), whereas large-scale applications generally require continuum models. Granular temperature, defined as the variance of particle velocity fluctuations, is a relevant variable to collapse rheological scaling. However, experimental forcing approaches used to control temperature also affects other aspects of the granular state. An alternative is to use a thermostat
algorithm to control the fluctuation energy directly. Although thermostat
algorithms are well established in Molecular Dynamics (MD), their behaviour in dissipative DEM systems has received comparatively little
attention. We show that conventional Langevin and Nosé-Hoover thermostats exhibit complementary limitations: Langevin control requires strong coupling to offset collisional dissipation, thereby damping particle dynamics, whereas Nosé-Hoover does not independently disrupt the correlations and segregation generated by repeated inelastic collisions, leading to non-ergodic and numerically unstable states. To address these limitations, we introduce two pairwise hybrid formulations combining deterministic temperature regulation with
stochastic decorrelation. Both enforce the prescribed temperature, while variation of the
stochastic decorrelation timescale modifies velocity statistics and associated mesoscopic properties such as diffusivity. Finally, application to pressure-controlled simple shear shows that increasing granular temperature at fixed inertial number reduces the apparent friction, consistent with previously reported trends. The framework therefore provides controlled reference states for comparing differently forced granular systems and identifying the variables required for temperature-dependent constitutive models.
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