Showing 1–50 of 582 results for author: Kim, K

Iterative Projection-Based Embedding Scheme Combined with Variational Quantum Eigensolver

Authors: Hongseok Choi, Kyungmin Kim, Young Min Rhee

Abstract: Quantum embedding methods offer a promising route to extend quantum chemical calculations to large multiscale systems by treating a chemically important subsystem at a high level of theory while describing its surrounding environment at an affordable level. The methods are also quite relevant for quantum computing approaches based on hardware with limited resources. Here, we present an iterative p… ▽ More Quantum embedding methods offer a promising route to extend quantum chemical calculations to large multiscale systems by treating a chemically important subsystem at a high level of theory while describing its surrounding environment at an affordable level. The methods are also quite relevant for quantum computing approaches based on hardware with limited resources. Here, we present an iterative projection-based embedding framework combined with VQE, in which the environment density is allowed to respond self-consistently to the refined electronic structure of the embedded subsystem described by VQE. Unlike conventional one-shot approaches where the environment remains frozen after the initial orbital optimization, the proposed iterative scheme alternates between the VQE-level treatment of the subsystem and a mean-field-level refinement of the environment until mutual self-consistency is achieved. The convergence behavior of the scheme is first examined using several small test systems. Its practical applicability is then demonstrated with a composite system with a CH2NH molecule sandwiched by two benzene rings, with the C=N dihedral angle rotating from 0 to 90 deg. The iterative procedure consistently converges within ~10 iteration steps across all tested geometries, yielding energies below the conventional one-shot embedding results. The converged results well reproduce the fully correlated reference energy employing the same active space, and the resulting potential energy surface with respect to the dihedral rotation is also in good agreement with the reference one. These results demonstrate that our iterative embedding framework is numerically robust and physically sound, yielding a self-consistent and reliable treatment of inter-subsystem correlation. We expect that its formulation will be particularly compatible with the emerging paradigm of quantum-classical hybrid computing. △ Less

Submitted 20 August, 2026; originally announced August 2026.

Comments: 28 pages, 5 figures

Development of a 10 mol% Rubidium-doped CsI Crystal for $^{87}$Rb Beta-Spectroscopy and Sterile Neutrino Searches

Authors: W. K. Kim, K. W. Kim, L. T. Truc, H. S. Lee, H. J. Kim, Y. D. Kim

Abstract: The third-forbidden non-unique beta-decay of $^{87}$Rb to $^{87}$Sr (Q$_β= 282.275(6)$ keV) has long served as an important benchmark for understanding forbidden beta-decay. To investigate this, we have developed a novel CsI scintillator with a 10 mol% Rb concentration using the Bridgman method. The incorporated $^{87}$Rb serves as an intrinsic radioactive source, enabling a source-in-detector con… ▽ More The third-forbidden non-unique beta-decay of $^{87}$Rb to $^{87}$Sr (Q$_β= 282.275(6)$ keV) has long served as an important benchmark for understanding forbidden beta-decay. To investigate this, we have developed a novel CsI scintillator with a 10 mol% Rb concentration using the Bridgman method. The incorporated $^{87}$Rb serves as an intrinsic radioactive source, enabling a source-in-detector configuration with high detection efficiency and minimal energy loss for low-energy electrons from beta-decay. We investigated both Rb doped and Tl co-doped CsI crystals and characterized their scintillation properties, including light yield, energy resolution, and non-linear response. We report distinct scintillation characteristics for the CsI:Rb and CsI:Tl,Rb crystals, with light yields of $1.38\pm0.01$ and $4.73\pm0.13$ PE/keV, respectively. Using the measured $^{87}$Rb beta-spectrum, we search for a keV-scale sterile neutrino admixture through the characteristic kink-like distortion induced by a heavy neutrino mass eigenstate. This study provides a basis for future sterile neutrino searches using rubidium doped CsI crystal. △ Less

Submitted 14 August, 2026; originally announced August 2026.

Emergence of moiré magnetic chaos in twisted bilayer CrI3

Authors: Gyuyoung Park, OukJae Lee, Kyoung-Min Kim

Abstract: The study of magnetic chaos has traditionally focused on macroscopic variables under external driving. Here we demonstrate a new type of magnetic chaos, termed moiré magnetic chaos, associated with mesoscopic magnetic domain variables in twisted bilayer CrI3 without external driving. The domains are stabilized by a characteristic interlayer exchange frustration, which supplies the multiple dynamic… ▽ More The study of magnetic chaos has traditionally focused on macroscopic variables under external driving. Here we demonstrate a new type of magnetic chaos, termed moiré magnetic chaos, associated with mesoscopic magnetic domain variables in twisted bilayer CrI3 without external driving. The domains are stabilized by a characteristic interlayer exchange frustration, which supplies the multiple dynamical degrees of freedom required for autonomous chaos. Through micromagnetic simulations, we show that relaxation toward moiré magnetic textures is extremely sensitive to minute local perturbations of the initial state, characterized by substantial finite-time Lyapunov exponents and a final-state sensitivity that persists over five decades of perturbation amplitude. Statistical analysis further reveals that the resulting domain configurations are stochastic and pairwise uncorrelated. Our results identify a form of microscopic, undriven chaos in twisted magnets that extends nonlinear magnetism beyond the conventional driven regime. △ Less

Submitted 13 August, 2026; originally announced August 2026.

Development and Initial Performance of an Upgraded NaI(Tl) Crystal Encapsulation for COSINE-100U

Authors: Doohyeok Lee, Jae Young Cho, Chang Hyon Ha, Eunju Jeon, Hongjoo Kim, Jinyoung Kim, Kyungwon Kim, SungHyun Kim, Sun Kee Kim, Won Kyung Kim, Yeongduk Kim, Young Ju Ko, Hyunseok Lee, Hyun Su Lee, In Soo Lee, Jaison Lee, Seo Hyun Lee, Seung Mok Lee, Reina H. Maruyama, Jong-Chul Park, Kangsoon Park, Kihong Park, Se Dong Park, Kyungmin Seo, Min Ki Son , et al. (1 additional authors not shown)

Abstract: The COSINE-100 experiment was designed to test the DAMA/LIBRA annual-modulation claim using low-background NaI(Tl) detectors. For the COSINE-100U upgrade, we developed a new crystal-encapsulation system to increase light-collection efficiency while preserving long-term detector stability, thereby improving sensitivity to low-mass dark matter. The upgraded design eliminates the quartz optical windo… ▽ More The COSINE-100 experiment was designed to test the DAMA/LIBRA annual-modulation claim using low-background NaI(Tl) detectors. For the COSINE-100U upgrade, we developed a new crystal-encapsulation system to increase light-collection efficiency while preserving long-term detector stability, thereby improving sensitivity to low-mass dark matter. The upgraded design eliminates the quartz optical windows used in COSINE-100 and directly couples the photomultiplier tubes (PMTs) to the crystal end faces through 2-mm-thick silicone optical pads, thereby reducing the number of optical interfaces. For the larger crystals, the crystal edges were beveled to guide scintillation light more efficiently onto 3-inch high-quantum-efficiency PMTs. The performance study uses 2462~h (102.6~days) of room-temperature COSINE-100U data and, for direct background comparisons, reference COSINE-100 data acquired near the end of operation. 698~h (29.1~days) of COSINE-100 data acquired near the end of operation in March 2023. All eight crystals showed higher light yields than in COSINE-100, with values ranging from 15.8 to 27.7~p.e./keV; six crystals exceeded 20~p.e./keV. The measured bulk-$α$ rates were lower than the COSINE-100 values and consistent with the expected time evolution of internal $^{210}$Pb, while the 1--2-MeV surface-$α$ rates were substantially reduced. The upgrade also restored two crystals that had previously been excluded from the COSINE-100 physics analysis because of poor optical performance. Independent validation tests demonstrated that the encapsulation remains mechanically robust and optically stable during long-term immersion in liquid scintillator at low temperature. This paper presents the encapsulation design, the room-temperature detector performance, and the reduction in surface-related backgrounds achieved at the Yemilab facility. △ Less

Submitted 12 August, 2026; originally announced August 2026.

Temperature-Dependent Performance of NaI(Tl) Crystal with Dual-Channel SiPM Readout for Low-Mass Dark Matter Searches

Authors: W. K. Kim, H. Y. Lee, K. W. Kim, H. S. Lee

Abstract: We report the first temperature-dependent characterization of a NaI(Tl) crystal readout by two silicon photomultipliers (SiPMs) directly coupled to opposite ends of the crystal for rare-event searches. A $6 \text{ mm} \times 6 \text{ mm} \times 13 \text{ mm}$ NaI(Tl) crystal was directly coupled to two SiPMs and characterized in a liquid nitrogen-cooled cryostat over a temperature range of 94$-$29… ▽ More We report the first temperature-dependent characterization of a NaI(Tl) crystal readout by two silicon photomultipliers (SiPMs) directly coupled to opposite ends of the crystal for rare-event searches. A $6 \text{ mm} \times 6 \text{ mm} \times 13 \text{ mm}$ NaI(Tl) crystal was directly coupled to two SiPMs and characterized in a liquid nitrogen-cooled cryostat over a temperature range of 94$-$293 K. The light yield, energy resolution, and scintillation decay time were measured using $γ$-ray peak from a $^{241}$Am source. After correcting for optical crosstalk contributions, the light yield increased, reaching $17.7 \pm 1.1$ photoelectrons/keV at 238 K, corresponding to a 34.5% enhancement relative to room temperature (293 K). Furthermore, dual-channel configuration effectively suppresses random thermal noise via coincidence triggers, which together with the observed increase in light yield, provides a critical pathway toward lowering the energy threshold for dark matter and coherent elastic neutrino$-$nucleus scattering searches. △ Less

Submitted 11 August, 2026; originally announced August 2026.

Surface passivation for narrowing optical linewidth of silicon T centers in nanophotonic devices

Authors: Fariba Islam, Chang-Min Lee, Kyu-Young Kim, Sorah Fischer, Purbita Purkayastha, Edo Waks

Abstract: Silicon T centers are promising spin-photon interfaces in solid-state platforms for telecom-compatible, scalable quantum information technologies. A major challenge for T centers in nanophotonics is spectral diffusion, where fluctuations in the local electric-field environment from surface and bulk charge states broaden the optical transition and reduce photon indistinguishability. Strategies that… ▽ More Silicon T centers are promising spin-photon interfaces in solid-state platforms for telecom-compatible, scalable quantum information technologies. A major challenge for T centers in nanophotonics is spectral diffusion, where fluctuations in the local electric-field environment from surface and bulk charge states broaden the optical transition and reduce photon indistinguishability. Strategies that directly suppress spectral diffusion are therefore critical for improving T-center-based quantum photonic devices. Here, we use atomic-layer-deposited Al2O3 to passivate the silicon surface and demonstrate a systematic narrowing of T center optical linewidths. Across our measurements, Al2O3 passivation reduces the T center emission linewidth by up to 57%. Complementary above-bandgap illumination and spectral hole burning measurements show that the remaining linewidth contains a significant spectral-diffusion component caused by adjacent charge traps, while placing an upper bound of approximately 75 MHz on the homogeneous linewidth. This work provides a CMOS-compatible path toward generating indistinguishable photons from silicon T centers for scalable quantum photonic applications. △ Less

Submitted 10 August, 2026; originally announced August 2026.

Phase-continuous comparison of three all-optical time scales over 20 days

Authors: Dahyeon Lee, Kyungtae Kim, Zoey Z. Hu, Ben Lewis, William Warfield, Kai Zhou, Alejandra L. Collopy, Jeffrey A. Sherman, Abijith S. Kowligy, Parth B. Patel, Jonathan D. Roslund, Arman Cingöz, Martin M. Boyd, Jun Ye

Abstract: Optical frequency standards have progressed rapidly over the past two decades, leading to the anticipated redefinition of the SI second by an optical frequency. However, time scales have not yet significantly improved despite this development because they are still fully reliant on rf flywheel oscillators, mostly hydrogen masers, which impose a performance limit related to incompletely sampled noi… ▽ More Optical frequency standards have progressed rapidly over the past two decades, leading to the anticipated redefinition of the SI second by an optical frequency. However, time scales have not yet significantly improved despite this development because they are still fully reliant on rf flywheel oscillators, mostly hydrogen masers, which impose a performance limit related to incompletely sampled noise known as the Dick effect. To best benefit from the exceptional stability and accuracy of optical frequency standards, time scales must employ optical flywheels with orders-of-magnitude better short-term (<$10^4$ s) stability than masers. Here, we introduce three optical flywheel oscillators (two cryogenic silicon cavities and one iodine optical clock) with superior short-term stability than hydrogen masers and long-term stability on par with masers. Steering each optical flywheel with a high-uptime Sr optical frequency standard generates three parallel all-optical time scales with continuous operation over >20 days. When compared with each other, these all-optical time scales achieve <$10^{-16}$ relative instability after just a few days of averaging. During typical steering gaps of ~6 hours, the accumulated time difference is ~20 ps, leading to the total time difference of <100 ps over the full measurement period. With the proliferation of long-distance optical fiber links and commercialization of optical flywheels and frequency standards, we anticipate all-optical time scales to be the future of timekeeping. △ Less

Submitted 1 August, 2026; originally announced August 2026.

Unconventional and Fragile Magnetic Exciton in a van der Waals Quantum Magnet

Authors: Kai-Xuan Zhang, Min Zhang, Minjae Kim, Yong-Hyun Kim, Junghyun Kim, Heejun Yang, Pyeongjae Park, Chaebin Kim, Mangesh Diware, Junik Hwang, Youjin Lee, Byeong-Gwan Cho, Hyeong-Do Kim, Tae-Yeong Koo, Chunhua Chen, Mingtao Li, Xujie Lü, Wenge Yang, Kee-Hoon Kim, Seung-Ho Baek, Hyeonsik Cheong, Sung-Keun Lee, Beom Hyun Kim, Christopher Lane, Jian-Xin Zhu , et al. (3 additional authors not shown)

Abstract: The recently discovered magnetic exciton in the van der Waals (vdW) antiferromagnet NiPS3 exemplifies these phenomena, exhibiting several distinctive characteristics. Despite extensive investigation, much of its physics remains unresolved, with key questions about why the NiPS3 magnetic exciton is so sharp and optically bright despite the nominally spin-forbidden transition, posing significant cha… ▽ More The recently discovered magnetic exciton in the van der Waals (vdW) antiferromagnet NiPS3 exemplifies these phenomena, exhibiting several distinctive characteristics. Despite extensive investigation, much of its physics remains unresolved, with key questions about why the NiPS3 magnetic exciton is so sharp and optically bright despite the nominally spin-forbidden transition, posing significant challenges to a proper understanding and practical manipulation of the exciton. An urgent question is to what extent it is due to chemical disorder, magnetic weakening, lattice modification, or intrinsic instability of the bright exciton itself: answers to which will put stringent constraints on possible theoretical models. Here we address these questions using hydrostatic pressure as a clean, continuous, reversible, and in-situ tuning parameter. We find that the sharp photoluminescence peak is drastically suppressed by as little as 0.4 GPa and completely quenched by 1.5 GPa, with demonstrating its reversibility. Crucially, this bright-to-dark conversion occurs without magnetic, crystallographic, or electronic reconstruction despite an increase in the Neel temperature, as established by Raman, X-ray absorption, nuclear magnetic resonance spectroscopy, and first-principles many-body calculations. Our results demonstrate that the optical brightness of the magnetic exciton is independent of chemical disorder, lattice expansion, and weakening of magnetic order, indicating that a higher-order correlated mechanism governs the bright exciton. We further propose experimentally constrained microscopic scenarios involving exciton pairing, crystal-field-controlled spin-orbit mixing, and symmetry breaking, providing a framework for future tests of entangled magnetic exciton in correlated quantum magnets. △ Less

Submitted 30 July, 2026; originally announced July 2026.

Comments: Our findings indicate that the sharp coherence of the entangled magnetic exciton benefits from its delicate quantum nature, and its optical brightness can be activated by exciton pairing or spin-orbit coupling, while its fragility under external control is achievable through a high-order perturbation rather than a first-order transition

Bright Telecom Spin-Photon Interface in Silicon Photonics

Authors: Carolina Crosta, Amirehsan Alizadehherfati, Purbita Purkayastha, Kyu-Young Kim, Jasvith Raj Basani, Chang-Min Lee, Fabio Pezzoli, Edo Waks

Abstract: Silicon is an attractive host for scalable quantum photonics, but the absence of bright telecom-band emitters with optically addressable spin states has limited its use for spin-photon interfaces. Here we demonstrate the Al1-center, an aluminum--carbon defect in silicon, as a bright waveguide-integrated single-photon emitter with a ground-state spin. Using isotopically purified silicon-on-insulato… ▽ More Silicon is an attractive host for scalable quantum photonics, but the absence of bright telecom-band emitters with optically addressable spin states has limited its use for spin-photon interfaces. Here we demonstrate the Al1-center, an aluminum--carbon defect in silicon, as a bright waveguide-integrated single-photon emitter with a ground-state spin. Using isotopically purified silicon-on-insulator nanophotonic devices, we isolate individual Al1-centers and observe high-purity single-photon emission with $g^{(2)}(0)=0.04$ without background subtraction. Time-resolved photoluminescence spectroscopy reveals a fast excited-state lifetime of 135 ns, nearly an order of magnitude shorter than the benchmark provided by the well-studied T-center. Resonant photoluminescence excitation measurements further resolve the zero-phonon transition and reveal a narrow homogeneous linewidth reaching 47 MHz, threefold narrower than the T-center under comparable temperature. Through magneto-optical spectroscopy, we resolve the spin-dependent transitions of the bound-exciton manifold and achieve spin-selective optical pumping, fulfilling the prerequisite for quantum state initialization and readout. These results establish the Al1-center as a bright telecom-band spin-photon interface in silicon photonics and introduce a promising platform for integrated quantum networks. △ Less

Submitted 27 July, 2026; v1 submitted 20 July, 2026; originally announced July 2026.

Mapping open quantum dynamics onto graphs

Authors: Kyuho Kim, Dayeong Lee, Seungkyun Park, Xianji Piao, Namkyoo Park, Sunkyu Yu

Abstract: Graph-theoretic frameworks have been widely employed in quantum physics to address the high-dimensional complexity of quantum systems. Although open quantum dynamics incorporates system-bath coupling via numerous interacting operators, it has been formulated algebraically with a partial set of jump operators or statistically universal reservoirs, leaving the underlying connectivity structure large… ▽ More Graph-theoretic frameworks have been widely employed in quantum physics to address the high-dimensional complexity of quantum systems. Although open quantum dynamics incorporates system-bath coupling via numerous interacting operators, it has been formulated algebraically with a partial set of jump operators or statistically universal reservoirs, leaving the underlying connectivity structure largely unexplored. Here, we propose a universal graph-theoretic framework for Markovian quantum dynamics. The framework maps open quantum dynamics onto two uniquely defined graphs, where the quantum master equation is rigorously interpreted as the average wave characteristic of operator-valued signals across the graphs. Applying this framework to the open quantum Rabi model, we demonstrate an open-system generalization of Fock-state lattices, characterize graph-topological signatures of dissipation, and classify the weak-to-ultrastrong coupling transition. Building on these representations, graph pruning reveals the backbone of open quantum dynamics, which enables superior graph neural-network learning. Our results bridge graph theory and open quantum dynamics, achieving efficient data-driven analysis of high-dimensional complexity. △ Less

Submitted 6 July, 2026; originally announced July 2026.

Verification and Performance Assessment of NuDEAL, a GPU-Accelerated Deterministic Transport Framework on Unstructured Meshes

Authors: Kyung Min Kim, Jaeuk Im, Han Gyu Lee, Yeon Sang Jung

Abstract: High-fidelity neutronic analyses of advanced reactors require deterministic transport solvers capable of handling complex unstructured geometries while maintaining computational efficiency. This work presents the development and verification of three GPU-accelerated deterministic solvers implemented within a unified framework, Neutronics using Deterministic Finite Element Algorithm (NuDEAL): the p… ▽ More High-fidelity neutronic analyses of advanced reactors require deterministic transport solvers capable of handling complex unstructured geometries while maintaining computational efficiency. This work presents the development and verification of three GPU-accelerated deterministic solvers implemented within a unified framework, Neutronics using Deterministic Finite Element Algorithm (NuDEAL): the planar Method of Characteristics coupled with the Hybrid Finite Element Method (MOC/HFEM), the Discontinuous Galerkin Method of Characteristics (DGMOC), and the Discontinuous Finite Element discrete ordinate method (DFEM-SN). These solvers provide complementary capabilities for consistently solving the multigroup transport equation and can be selectively employed to balance accuracy, computational cost, and memory requirements for a given problem. All methods emphasize efficient GPU execution by leveraging memory alignment, compressed-flux storage, and sequential azimuthal sweeps. The solvers are validated on the C5G7 benchmark and applied to advanced reactor problems, including the ABTR, Empire microreactor, and MSRE. DFEM-SN achieved the highest accuracy, with eigenvalue errors below 50 pcm, while MOC/HFEM and DGMOC provided superior efficiency, with single-GPU runtimes comparable to those of large CPU clusters. The results demonstrate that deterministic GPU solvers on unstructured meshes can deliver both accuracy and scalability, enabling practical whole-core simulations for heterogeneous advanced reactors. The unified NuDEAL framework establishes a foundation for future extensions toward transient and multiphysics analyses on large-scale GPU architectures. △ Less

Submitted 1 July, 2026; originally announced July 2026.

Comments: 39 pages, 14 tables, 15 figures. Author's original manuscript of an article published in Nuclear Science and Engineering. The final published version is available at https://doi.org/10.1080/00295639.2026.2652773

Symmetry classification of temporal reciprocity in time-varying electromagnetic media

Authors: Seulong Kim, Kihong Kim

Abstract: Time-varying electromagnetic media exhibit rich nonstationary wave phenomena, but the symmetry governing reversal of arbitrary temporal modulation sequences has remained unclear. We show that, in lossless, spatially homogeneous media with identical initial and final states, the scattering matrices of ordered and reversed sequences are related by inverse--conjugation, independent of the number of s… ▽ More Time-varying electromagnetic media exhibit rich nonstationary wave phenomena, but the symmetry governing reversal of arbitrary temporal modulation sequences has remained unclear. We show that, in lossless, spatially homogeneous media with identical initial and final states, the scattering matrices of ordered and reversed sequences are related by inverse--conjugation, independent of the number of stages. This yields a classification of temporal reciprocity in bi-isotropic media: isotropic and chiral media are channel-preserving, whereas Tellegen media are channel-exchanging despite Lorentz nonreciprocity. Deterministic time rewinding follows directly. Our results provide a framework for predicting and designing temporal scattering responses in photonic media. △ Less

Submitted 21 June, 2026; originally announced June 2026.

Comments: 35 pages, 6 figures

Journal ref: Optica 13(8), 1454 (2026)

Dynamically suppressed lattice rotations in SrTiO$_3$ as a basis for photo-induced ferroelectricity

Authors: Huaiyu Hugo Wang, Michael Fechner, Giovanni De Vecchi, Sylvia L. Griffitt, Gal Orenstein, Jade Stanton, Viktor Krapivin, Man T. Wong, Zhuquan Zhang, Mina Bionta, Vincent Esposito, Meredith Henstridge, Matthias C. Hoffmann, Patrick L. Kramer, Zach Porter, Ryan A. Duncan, Takahiro Sato, Soyeun K. Kim, Hasan Yavas, Samuel Teitelbaum, Keith Nelson, Ankit S. Disa, Michael F"orst, Mariano Trigo, Andrea Cavalleri

Abstract: Photo-induced ferroelectricity in the quantum paraelectric SrTiO$_3$ involves the dynamical interplay between a coherently driven Ti-O stretching vibration and multiple structural degrees of freedom, including antiferrodistortive rotations, strain, and the polar mode instability. In the high-temperature cubic phase, in the absence of average antiferrodistortion, time-resolved X-ray diffuse scatter… ▽ More Photo-induced ferroelectricity in the quantum paraelectric SrTiO$_3$ involves the dynamical interplay between a coherently driven Ti-O stretching vibration and multiple structural degrees of freedom, including antiferrodistortive rotations, strain, and the polar mode instability. In the high-temperature cubic phase, in the absence of average antiferrodistortion, time-resolved X-ray diffuse scattering has evidenced a correlation between a photo-induced reduction in antiferrodistortive fluctuations and the emergence of ferroelectric order. Here, we complement these measurements with time-resolved elastic X-ray diffraction in the low-temperature tetragonal phase, in which antiferrodistortive fluctuations are small but a finite average rotation has set in. In this phase, we observe a long-lived reduction of the equilibrium antiferrodistortive rotation angle. A unified theory of the nonlinear lattice dynamics based on first-principles calculations describes the dynamics in both high-temperature cubic and low-temperature tetragonal phases, providing a basis for light-induced ferroelectricity in SrTiO$_3$. △ Less

Submitted 15 June, 2026; originally announced June 2026.

Comments: Huaiyu Hugo Wang and Michael Fechner contributed equally to this work

Robust Control of ECH Deposition Profiles on DIII-D

Authors: A. Rothstein, H. J. Farre-Kaga, K. Yasoda, J. Lestz, N. Chen, S. K. Kim, A. Jalalvand, E. Kolemen

Abstract: Electron Cyclotron Heating (ECH) is a key actuator in DIII-D and future tokamaks that provides auxiliary heating, localized current drive for scenario development and MHD stability, and even impurity pump-out. Due to its control flexibility and applications, a gyrotron optimization algorithm was developed to multitask and fine-tune the deposition location and heating power of each gyrotron while p… ▽ More Electron Cyclotron Heating (ECH) is a key actuator in DIII-D and future tokamaks that provides auxiliary heating, localized current drive for scenario development and MHD stability, and even impurity pump-out. Due to its control flexibility and applications, a gyrotron optimization algorithm was developed to multitask and fine-tune the deposition location and heating power of each gyrotron while providing robustness to hardware failure. The ECH Optimization (ECHO) algorithm finds the optimal gyrotron mirror angle and power to achieve a target ECH radial deposition profile. This optimization is accomplished in real-time using a parallelized neural network surrogate of the TORBEAM code combined with a genetic optimizer. This has been deployed in a DIII-D experiment and has been validated with experimental ECE measurements and post-experiment offline ray tracing, showing the algorithm's reliability despite gyrotron failures and significant changes to plasma parameters. △ Less

Submitted 11 June, 2026; originally announced June 2026.

Comments: 20 pages, 9 figures

Polymer-Regulated Freezing of Water Droplets Revealed by Synchrotron X-ray Imaging and Raman Spectroscopy

Authors: Hyeonjun An, Bomi Kim, Jae Kwan Im, Min Woo Kim, Seob-Gu Kim, Jae-Hong Lim, Kitae Kim, Joonwoo Jeong

Abstract: Adding a polymer to a sessile water droplet not only lowers its freezing point but also suppresses the tip singularity that forms during its freezing on cold substrates. Here, we employ synchrotron X-ray and Raman imaging to elucidate the spatiotemporal mechanism underlying tip suppression in an aqueous polyvinyl alcohol (PVA) solution, a model polymer solution. As the polymer concentration increa… ▽ More Adding a polymer to a sessile water droplet not only lowers its freezing point but also suppresses the tip singularity that forms during its freezing on cold substrates. Here, we employ synchrotron X-ray and Raman imaging to elucidate the spatiotemporal mechanism underlying tip suppression in an aqueous polyvinyl alcohol (PVA) solution, a model polymer solution. As the polymer concentration increases, we observe slower propagation of the freezing front, reduced bubble entrapment, and a progressively more rounded apex across the volumes and molecular weights examined. X-ray tomography reveals that frozen PVA droplets retain low X-ray transmittance domains in their interiors and at the surface, and Raman spectral mapping confirms that these domains correspond to PVA-enriched regions, providing direct evidence of freeze-induced polymer segregation. These findings indicate that PVA is redistributed heterogeneously during water solidification rather than shifting bulk properties homogeneously, providing a spatially resolved framework for interpreting the observed tip blunting and the suppression of discrete bubble entrapment. Our work identifies freeze-induced polymer segregation as a pathway by which a dissolved polymer regulates both the external shape and the internal structure of a freezing droplet, and these findings shed light on potential applications in freezing-based processes such as freeze-casting and cryopreservation. △ Less

Submitted 31 May, 2026; originally announced June 2026.

Quantum Photonic Time Crystals: From Temporal Boundaries to Floquet Light-Matter Interactions

Authors: Younsung Kim, Kyungmin Lee, Kun Woo Kim, Bumki Min

Abstract: Photonic time crystals (PTCs) are temporally periodic media whose Floquet spectra can exhibit momentum gaps, parametric amplification, and effective non-Hermitian descriptions, making them an idealized setting for vacuum amplification and nonequilibrium light-matter dynamics. Their classical electrodynamics is now well developed; the quantum side is less so, and this focused review is an attempt t… ▽ More Photonic time crystals (PTCs) are temporally periodic media whose Floquet spectra can exhibit momentum gaps, parametric amplification, and effective non-Hermitian descriptions, making them an idealized setting for vacuum amplification and nonequilibrium light-matter dynamics. Their classical electrodynamics is now well developed; the quantum side is less so, and this focused review is an attempt to organize what exists. We trace that account from temporal boundaries to homogeneous Floquet media and light-matter dynamics. A single temporal boundary induces Bogoliubov mode mixing and photon-pair creation; in homogeneous bulk media, momentum conservation isolates counter-propagating $(k,-k)$ sectors and yields a two-mode $SU(1,1)$ squeezing structure. Temporal periodicity promotes this to a Floquet problem with band and momentum-gap regimes, compactly described in a fixed Nambu basis. We then relate PTCs to the dynamical Casimir effect and parametric amplification, which share the same pair-creation mechanism but organize it through discrete resonances rather than a momentum-resolved bulk spectrum. We close with light-matter settings: spontaneous-emission decay and modulation-assisted excitation, atom-PTC dynamics, LDOS-based observables and their limits, and finite, dispersive, and experimentally accessible platforms. △ Less

Submitted 4 June, 2026; v1 submitted 29 May, 2026; originally announced May 2026.

Comments: 25 pages, 9 figures

Binary Amplitude Modulation Suppresses Noise Up-Conversion in Coherent Diffractive Optical Networks

Authors: Hyuntae Lim, Kyoungsik Kim

Abstract: We establish a fundamental principle in coherent wave-optical computing: restricting the modulation manifold from continuous complex-valued to binary amplitude suppresses stochastic-noise up-conversion while preserving classification fidelity, yielding a counter-intuitive less-is-more robustness law. Seven-layer binary-amplitude-mask D2NN (BM-D2NN) achieve 90.9% (MNIST) and 81.9% (Fashion-MNIST) t… ▽ More We establish a fundamental principle in coherent wave-optical computing: restricting the modulation manifold from continuous complex-valued to binary amplitude suppresses stochastic-noise up-conversion while preserving classification fidelity, yielding a counter-intuitive less-is-more robustness law. Seven-layer binary-amplitude-mask D2NN (BM-D2NN) achieve 90.9% (MNIST) and 81.9% (Fashion-MNIST) test accuracy, within 2~4 pp of continuous-modulation D2NN (C-D2NN). Under pixel-wise Gaussian noise N(m,σ^2), spanning zero-mean (shot noise) to nonzero-mean (thermal/readout) regimes, BM-D2NN outperform C-D2NN by up to 32.8 pp (MNIST) and 18.5 pp (Fashion-MNIST). We analytically derive a noise-contribution metric C, governed by a transmission-bias factor K computable from clean data alone, that is consistently smaller for binary modulation than for continuous modulation (as verified for all test samples), guaranteeing the robustness ordering without noisy simulation. BM-D2NN additionally deliver a 6.79-fold higher imaging-plane intensity for clean data input. These results establish a quantitative physical principle connecting modulation-manifold geometry to noise robustness, applicable to any coherent optical processor in the z/λ >> 1 regime. △ Less

Submitted 29 May, 2026; originally announced May 2026.

Comments: 14 pages, 5 figures

Updates on Impedance Studies for the FCC-ee High Energy Booster

Authors: Keon Hee Kim, Adnan Ghribi, Santiago Martinez, Quentin Bruant, Antoine Chance, Barbara Dalena, Chiara Antuono, Dora Gibellieri, Carlo Zannini, Frank Zimmermann, Ahmad Mashal, Mauro Migliorati, Mikhail Zobov

Abstract: Following the Future Circular Collider (FCC) Feasibility Study completion, the impedance model for the FCC-ee High-Energy Booster (HEB) has been significantly expanded beyond the initial copper vacuum pipe resistive wall analysis. This paper presents a comprehensive impedance and wake budget incorporating RF cavities, bellows, and beam position monitors, evaluated through 3D electromagnetic simula… ▽ More Following the Future Circular Collider (FCC) Feasibility Study completion, the impedance model for the FCC-ee High-Energy Booster (HEB) has been significantly expanded beyond the initial copper vacuum pipe resistive wall analysis. This paper presents a comprehensive impedance and wake budget incorporating RF cavities, bellows, and beam position monitors, evaluated through 3D electromagnetic simulations and analytical methods. The updated model provides the basis for future beam dynamics studies, including transverse coupled bunch instability analyses and single bunch tracking simulations. The present work focuses on the construction and comparison of the main impedance and wake contributions, identifying the dominant sources and the components requiring further investigation. These results will be used to refine the HEB collective effects studies and to support future assessments of instability margins and mitigation requirements. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Comments: 17th International Particle Accelerator Conference (IPAC'26)

Universal zero-crosstalk photonic integration via slab-engineered mode hybridization

Authors: Kyungtae Kim, Yoseph Shin, Seungyong Lee, Inki Kim, Hyeyoon Jeon, Jibaek Song, Minseop Lee, Sanghyeon Kim, Hyounghan Kwon, Hojoong Jung, Sangsik Kim

Abstract: Photonic integrated circuits have emerged as a scalable platform for optical computing, communication, and quantum technologies, where high-fidelity optical processing is essential. However, as photonic systems scale in complexity, inter-channel crosstalk accumulates across cascaded components, fundamentally degrading signal fidelity, limiting system-level performance, and constraining integration… ▽ More Photonic integrated circuits have emerged as a scalable platform for optical computing, communication, and quantum technologies, where high-fidelity optical processing is essential. However, as photonic systems scale in complexity, inter-channel crosstalk accumulates across cascaded components, fundamentally degrading signal fidelity, limiting system-level performance, and constraining integration density. Existing crosstalk-suppression strategies rely on specialized nanostructures or platform-specific designs, hindering their adoption in standard foundry processes and across diverse material systems. Here we establish a universal and foundry-compatible route to eliminating crosstalk based on slab-engineered mode hybridization in standard rib waveguides. By tailoring the slab thickness, mode hybridization induces anisotropic modal perturbations that enable complete cancellation of coupling between adjacent waveguides. We experimentally demonstrate zero-crosstalk across diverse material platforms, including silicon-on-insulator, silicon nitride, thin-film lithium niobate, and germanium-on-insulator, spanning wavelengths from the visible to the mid-infrared. Our approach provides a manufacturable route toward scalable, high-fidelity, and high-density photonic integration, overcoming the long-standing trade-off between signal fidelity and integration density in large-scale photonic systems. △ Less

Submitted 27 May, 2026; originally announced May 2026.

Comments: 10 pages, 4 figures

Task-specific programming of chaos in neural circuits

Authors: Jungyoon Kim, Kyuho Kim, Kunwoo Park, Namkyoo Park, Sunkyu Yu

Abstract: Chaotic dynamics have emerged as a versatile resource for neuromorphic and probabilistic computing, enabling high-dimensional nonlinear processing and classical analogues of quantum randomness. Exploiting chaos for computation requires task-dependent control over complexity, as demonstrated in reservoir computing, random-number generation, and probabilistic inference. Existing approaches have focu… ▽ More Chaotic dynamics have emerged as a versatile resource for neuromorphic and probabilistic computing, enabling high-dimensional nonlinear processing and classical analogues of quantum randomness. Exploiting chaos for computation requires task-dependent control over complexity, as demonstrated in reservoir computing, random-number generation, and probabilistic inference. Existing approaches have focused on tuning element-level parameters, leaving the collective, many-body origin of chaos largely unexplored as a design freedom. Here, we demonstrate programmable chaotic dynamics for task-specific reservoir computing. Using a continuous-time neural-circuit model, we show that tuning network topology drives an ordered-to-chaotic transition, accompanied by transitions in correlation timescales, stability characteristics, and signal propagation. By jointly controlling element-level properties and network topology, we establish a unified chaos-latency phase diagram, revealing that small-world connectivity enables low-latency on-off switching of chaos via edge rewiring. Supported by distinct reservoir-computing benchmarks across various topological regimes, our results demonstrate that network topology serves as a reconfigurable parameter for task-specific computation and tunable randomness. △ Less

Submitted 19 May, 2026; originally announced May 2026.

Monolithic axial InGaAs quantum dot emitters in GaAs-based nanowires via Sb-mediated facet engineering

Authors: Hyowon W. Jeong, Aris Koulas-Simos, Imad Limame, Markus Döblinger, Sang Kyu Kim, Chirag C. Palekar, Jonathan J. Finley, Stephan Reitzenstein, Gregor Koblmüller

Abstract: GaAs-based nanowires hosting active quantum heterostructures provide a promising route toward monolithic integration of single-photon sources on silicon, a key requirement for scalable quantum photonics. However, ultrathin axial quantum-emitter formation is often hindered by facet-dependent growth dynamics and rotational twins, which induce lateral overgrowth and compromise interface abruptness. H… ▽ More GaAs-based nanowires hosting active quantum heterostructures provide a promising route toward monolithic integration of single-photon sources on silicon, a key requirement for scalable quantum photonics. However, ultrathin axial quantum-emitter formation is often hindered by facet-dependent growth dynamics and rotational twins, which induce lateral overgrowth and compromise interface abruptness. Here, we develop InGaAs-based quantum emitters by tailoring facet evolution via dilute Sb incorporation, which efficiently suppresses twins and promotes confined axial insertion at the growth-front facet. This approach significantly enhances the probability of obtaining abrupt, few-nanometer-thin quantum dots at the nanowire tip. Single-nanowire optical spectroscopy reveals intense, spatially localized emission from the active region with lifetimes as short as (0.51 $\pm$ 0.02) ns, and second-order photon-correlation measurements consistently exhibit pronounced antibunching with $g^{(2)}(0)<0.4$, confirming single-photon emission. These results establish a strong correlation between twin density and axial heterostructure formation, identifying defect control as a key factor in realizing monolithically integrated nanowire single-photon sources. △ Less

Submitted 16 June, 2026; v1 submitted 13 May, 2026; originally announced May 2026.

A Hardware-aware Hopfield Network with a Nonlinear Memristor Array for Robust Associative Memory with Superlinear Capacity

Authors: Younghyun Lee, Hakseung Rhee, Unhyeon Kang, Seungmin Oh, Kyungmin Lee, Hyun Jae Jang, Seongsik Park, YeonJoo Jeong, Inho Kim, Jong Keuk Park, Kyung Min Kim, Suyoun Lee

Abstract: Associative memory retrieves complete patterns from partial or corrupted inputs and constitutes a primitive form of generative inference. Classical Hopfield networks (CHN) provide a canonical framework for associative memory but suffer from limited memory capacity. Recently, modern Hopfield networks (MHN) were introduced to achieve higher capacity by using explicit pattern-wise storage and neurons… ▽ More Associative memory retrieves complete patterns from partial or corrupted inputs and constitutes a primitive form of generative inference. Classical Hopfield networks (CHN) provide a canonical framework for associative memory but suffer from limited memory capacity. Recently, modern Hopfield networks (MHN) were introduced to achieve higher capacity by using explicit pattern-wise storage and neurons with the softmax activation function, which makes the MHN vulnerable to noise and the hardware implementation complicated due to its network size varying with the number of stored patterns. Here, we introduce a hardware-aware Hopfield network (HHN), in which the intrinsic nonlinear current-voltage characteristics of a charge-trap memristor are leveraged to engineer the energy landscape of the HN, increasing the memory capacity. Using a 25 x 25 nonlinear memristor array, we demonstrate reliable reconstruction of corrupted patterns with memory capacity far exceeding the classical limit (K ~ 0.14N, where N is the number of neurons). The HHN preserves Hopfield-type energy-minimization dynamics and remains robust to synaptic conductance noise. Large-scale simulations on high-dimensional image data reveal an empirical memory capacity scaling of K ~ 0.3 x N^1.2 under a fixed synaptic budget. These results establish HHN as a scalable hardware-native architecture for low-power associative memory and generative inference. △ Less

Submitted 8 May, 2026; originally announced May 2026.

Gauge-Field-Mediated Symmetry Breaking of Matters Under Electromagnetic Fields and Its Impact on Spin Dynamics

Authors: Uiseok Jeong, Esmaeil Taghizadeh Sisakht, Angel Rubio, Carsten A. Ullrich, Kyoung-Whan Kim, Noejung Park

Abstract: When a condensed-matter system is subjected to external electromagnetic fields, the gauge-invariant formulation of physical operators must explicitly incorporate the gauge-field contribution. However, in the context of spin-orbit coupling (SOC), this gauge-field term is often regarded as negligible or merely additive compared to the canonical SOC, which is typically localized near atomic cores. He… ▽ More When a condensed-matter system is subjected to external electromagnetic fields, the gauge-invariant formulation of physical operators must explicitly incorporate the gauge-field contribution. However, in the context of spin-orbit coupling (SOC), this gauge-field term is often regarded as negligible or merely additive compared to the canonical SOC, which is typically localized near atomic cores. Here, we demonstrate that the symmetry breaking and consequent spin dynamics are governed by the gauge-field term, without which the spins remain symmetry-constrained. We perform real-time time-dependent density functional theory calculations to investigate spin-orbit dynamics, focusing on representative cases with mirror, glide, and screw-rotational symmetry. We demonstrate that when the gauge-field term in the time-dependent Hamiltonian perturbs the symmetry of the canonical term, a dynamical spin state gradually develops during the time evolution, beyond the symmetry-frozen states. We suggest that, for nonequilibrium spin-orbit dynamics, the gauge-invariant formulation of SOC is not only formally required but also quantitatively essential, even for a weak external field. △ Less

Submitted 17 May, 2026; v1 submitted 5 May, 2026; originally announced May 2026.

Comments: 14 pages, 9 figures, contains Supplementary Information, submitted to Nat. comm

Machine learning evaluation of structural descriptors for supercooled water

Authors: Kohei Yoshikawa, Kokoro Shikata, Kang Kim, Nobuyuki Matubayasi

Abstract: The anomalous behavior of liquid water is widely associated with a liquid-liquid phase transition between high- and low-density states in the supercooled regime. At the microscopic level, tetrahedral hydrogen-bond networks govern these properties, motivating structural descriptors that characterize local molecular environments. These structural descriptors quantify features such as tetrahedral ord… ▽ More The anomalous behavior of liquid water is widely associated with a liquid-liquid phase transition between high- and low-density states in the supercooled regime. At the microscopic level, tetrahedral hydrogen-bond networks govern these properties, motivating structural descriptors that characterize local molecular environments. These structural descriptors quantify features such as tetrahedral order, local density, and the separation between the first and second coordination shells; however, they have largely been proposed independently, with limited systematic comparison. Here we evaluate 16 previously proposed descriptors using a neural-network-based temperature classification framework, enabling an objective assessment of their ability to distinguish temperature-dependent structural changes in supercooled water. We further apply an explainable artificial intelligence method that identifies the structural features responsible for the model predictions. This approach reveals how different descriptors encode local structural information and establishes a data-driven framework for benchmarking structural descriptors in liquid water. △ Less

Submitted 9 July, 2026; v1 submitted 1 May, 2026; originally announced May 2026.

Comments: 15 pages, 5 figures, 1table for main text, 10 figures for supplementary information

Journal ref: Commun. Chem. 9, 217 (2026)

Effects of Tungsten Radiative Cooling on Impurity, Heat and Momentum Transport in DIII-D Plasmas

Authors: A. Tema Biwole, T. Odstrčil, X. Litaudon, S. Shi, D. Ernst, C. F. B. Zimmermann, J. Lestz, N. T. Howard, P. Rodriguez-Fernandez, F. Khabanov, F. Turco, C. Perks, P. Manas, D. Fajardo, S. K. Kim, L. Schmitz, H. Wang, W. Boyes, S. Ding, B. Victor, C. Christal, C. Lasnier, T. M. Wilks, G. McKee

Abstract: A first-of-its-kind experiment was conducted in the DIII-D tokamak under WEST similarity constraints on plasma shape and core parameters. This work presents a detailed transport study comparing a reference regime dominated by intrinsic carbon radiation and a high-radiation regime resulting from controlled tungsten (W) injection using the Laser Blow-Off system, with a core tungsten concentration… ▽ More A first-of-its-kind experiment was conducted in the DIII-D tokamak under WEST similarity constraints on plasma shape and core parameters. This work presents a detailed transport study comparing a reference regime dominated by intrinsic carbon radiation and a high-radiation regime resulting from controlled tungsten (W) injection using the Laser Blow-Off system, with a core tungsten concentration $n_{\mathrm{W}}/n_e \sim 3\times 10^{-4}$ and a radiated-power fraction $f_\mathrm{rad}>0.5$. The W-induced radiative cooling lowered the electron temperature, thereby decreasing $T_e/T_i$ and stabilizing trapped-electron-mode (TEM) turbulence. This transition in turbulence regime reduced momentum and ion thermal diffusivities, yielding ion temperature peaking and a factor-of-two increase in toroidal rotation. At the outer plasma region, enhanced $E\timesB$ shear and increased collisionality further suppressed ion-scale turbulence, causing a sharp drop in ion heat flux. Consequently, impurity transport, predominantly turbulent in the low-radiation regime, acquired a strong neoclassical inward W convection during radiative cooling, bootstrapping the cooling cycle. Despite $f_\mathrm{rad}>0.5$, radiative collapse was not observed, likely owing to collisional ion-to-electron energy exchange acting as an electron-energy reservoir, together with $1/1$ MHD activity modulating the radiated power through core impurity neoclassical $T_i$-screening. These results support preparation for a tungsten wall change in DIII-D by elucidating tungsten-induced turbulence stabilization. They also provide key insights for interpreting plasma performance in WEST and are relevant to future reactors expected to operate with radiating tungsten-walled plasmas. △ Less

Submitted 7 April, 2026; originally announced April 2026.

High performance imaging of $^{171}$Yb atom in shallow clock-magic tweezer by alternating dual-tone narrowline cooling

Authors: Yunheung Song, Kangheun Kim, Jeong Ho Han, Seungtaek Oh, Jongchul Mun

Abstract: We demonstrate imaging $^{171}$Yb single atoms in clock-magic tweezers of 759.4 nm wavelength, with above 99.9% fidelity and survival. We use alternating dual-tone narrowline imaging for more efficient three-dimensional cooling in tweezers, allowing several-millisecond imaging in 200 $μ$K trap depth, which is half of typical depth used for imaging in clock-magic tweezers. Accordingly, even without… ▽ More We demonstrate imaging $^{171}$Yb single atoms in clock-magic tweezers of 759.4 nm wavelength, with above 99.9% fidelity and survival. We use alternating dual-tone narrowline imaging for more efficient three-dimensional cooling in tweezers, allowing several-millisecond imaging in 200 $μ$K trap depth, which is half of typical depth used for imaging in clock-magic tweezers. Accordingly, even without repumping, imaging survival is still close to 99.9% with the high fidelity, which can enable high performance nondestructive qubit measurements based on metastable shelving. Moreover, our simulation predicts that more optimal configuration could further reduce the trap depth, as improving the imaging performance. This imaging capability in shallow traps opens high performance imaging for more general trap wavelength, and lays the foundation for large scale systems over 1,000 qubits, and highly repeatable tweezer clocks. △ Less

Submitted 26 May, 2026; v1 submitted 28 March, 2026; originally announced March 2026.

Comments: 10 pages, 7 figures

Deep learning of committor and explainable artificial intelligence analysis for identifying reaction coordinates

Authors: Toshifumi Mori, Kei-ichi Okazaki, Kang Kim, Nobuyuki Matubayasi

Abstract: In complex molecular systems, the reaction coordinate (RC) that characterizes transition pathways is essential to understand underlying molecular mechanisms. This review surveys a framework for identifying the RC by applying deep learning to the committor, which provides the most reliable measure of the progress along a transition path. The inputs to the neural network are collective variables (CV… ▽ More In complex molecular systems, the reaction coordinate (RC) that characterizes transition pathways is essential to understand underlying molecular mechanisms. This review surveys a framework for identifying the RC by applying deep learning to the committor, which provides the most reliable measure of the progress along a transition path. The inputs to the neural network are collective variables (CVs) expressed as functions of atomic coordinates of the system, and the corresponding RC is predicted as the output by training the network on the committor as the learning target. Because deep learning models typically operate in a black-box manner, it is difficult to determine which input variables govern the predictions. The incorporation of eXplainable Artificial Intelligence (XAI) techniques enables quantitative assessment of the contributions of individual input variables to the predictions. This approach allows the identification of CVs that play dominant roles and demonstrates that the committor distribution on the surface using important CVs is separated by well-defined boundaries. The framework provides an explainable deep learning strategy for assigning a molecular mechanism from the RC and is applicable to a wide range of complex molecular systems. △ Less

Submitted 15 July, 2026; v1 submitted 26 March, 2026; originally announced March 2026.

Comments: 17 pages, 12 figures, to appear in Chem. Phys. Rev

Journal ref: Chem. Phys. Rev. 7, 031303 (2026)

Ground Effects of the 2024 Mother's Day Superstorm: A Multi-source Observational Analysis

Authors: Yue Chen, Kyoung Ho Kim, Steven K. Morley, Jesse R. Woodroffe

Abstract: This report presents a brief review of the 2024 Mother's Day superstorm and its impacts on the near-Earth space environment and the ground-level effects, with emphasis on the latter. Drawing upon observations from multiple sources. we qualitatively illustrate how intense space weather disturbances can generate strong geoelectric fields and drive pronounced geomagnetically induced currents, as repo… ▽ More This report presents a brief review of the 2024 Mother's Day superstorm and its impacts on the near-Earth space environment and the ground-level effects, with emphasis on the latter. Drawing upon observations from multiple sources. we qualitatively illustrate how intense space weather disturbances can generate strong geoelectric fields and drive pronounced geomagnetically induced currents, as reported at numerous locations, particularly within the New Zealand power grids. △ Less

Submitted 16 March, 2026; originally announced March 2026.

Report number: LA-UR-26-21645

Cell strain-stiffening drives cell breakout from embedded spheroids

Authors: Shabeeb Ameen, Kyungeun Kim, Ligesh Theeyancheri, Minh Thanh, Mingming Wu, Alison E. Patteson, J. M. Schwarz, Tao Zhang

Abstract: Understanding how cells escape from embedded spheroids requires a mechanical framework linking stress generation within cells, across cells, and between cells and the surrounding extracellular matrix (ECM). We develop such a framework by coupling a 3D vertex model of a spheroid to a fibrous ECM network and deriving a 3D Cauchy stress tensor for deformable polyhedral cells, enabling direct cell-lev… ▽ More Understanding how cells escape from embedded spheroids requires a mechanical framework linking stress generation within cells, across cells, and between cells and the surrounding extracellular matrix (ECM). We develop such a framework by coupling a 3D vertex model of a spheroid to a fibrous ECM network and deriving a 3D Cauchy stress tensor for deformable polyhedral cells, enabling direct cell-level stress quantification in three dimensions. We analyze maximum shear stress in solid-like and fluid-like spheroids: solid-like spheroids exhibit broader stress distributions and radial stress gradients, while fluid-like spheroids show lower stresses with weak spatial organization. Cell shape anisotropy is not generically aligned with principal stress directions, indicating that morphology alone is an unreliable proxy for mechanical state. We further demonstrate strain stiffening at the single-cell level, where elongation produces nonlinear increases in maximum shear stress, allowing boundary cells in otherwise low-stress, fluid-like spheroids to transiently generate forces sufficient to remodel the matrix. To connect strain-induced stress amplification to invasion modes, we introduce an extended 3D vertex model with explicit, tunable cell-cell adhesion springs. In this minimal mechanical framework, single-cell breakout results from strain stiffening combined with reduced adhesion, whereas multi-cell streaming additionally requires anisotropic adhesion strengthened along the elongation axis and weakened orthogonally. Together, these results identify distinct mechanical pathways coupling cell strain, stress amplification, and adhesion organization to spheroid invasion. △ Less

Submitted 9 February, 2026; originally announced February 2026.

Energy Transport Velocity in Photonic Time Crystals

Authors: Kyungmin Lee, Younsung Kim, Kun Woo Kim, Bumki Min

Abstract: Steep or near-vertical Floquet dispersion in photonic time crystals (PTCs) is often read as fast, even apparently superluminal, transport. Here, we demonstrate that this anomaly arises from modulation-driven geometric drift, not energy flow. By deriving a Maxwell-flux Hellmann-Feynman relation, we prove that the cycle-averaged energy velocity remains strictly bounded. We further establish a univer… ▽ More Steep or near-vertical Floquet dispersion in photonic time crystals (PTCs) is often read as fast, even apparently superluminal, transport. Here, we demonstrate that this anomaly arises from modulation-driven geometric drift, not energy flow. By deriving a Maxwell-flux Hellmann-Feynman relation, we prove that the cycle-averaged energy velocity remains strictly bounded. We further establish a universal velocity-product law conserved throughout the passband, $ v_E v_g=\langle v_{\rm ph}^2\rangle_T $, fixing transport solely by the temporal average of the inverse permittivity. The divergent group velocity is then traced to a mismatch between electric and magnetic geometric phase connections, revealing apparent superluminality as a geometric effect of temporal modulation. △ Less

Submitted 6 August, 2026; v1 submitted 3 February, 2026; originally announced February 2026.

Observational Evidence for Wind-Driven Low-Pass Filtering of Infrasound at Short Range

Authors: Elizabeth A. Silber, Daniel C. Bowman, Sasha Egan, Lawrence Burkett, Michael Fleigle, Keehoon Kim, Tesla Newton, Loring P. Schaible, Richard Sonnenfeld, Nora Wynn, Jonathan Snively

Abstract: Infrasound from controlled explosions provide a unique opportunity to isolate atmospheric effects on propagation. We report observations from two campaigns in May and October 2024, each featuring 10-ton TNT-equivalent controlled surface chemical explosions recorded by a dense network of 31 single-sensor stations within 23 km. Despite identical sources, the observed wavefields were very different.… ▽ More Infrasound from controlled explosions provide a unique opportunity to isolate atmospheric effects on propagation. We report observations from two campaigns in May and October 2024, each featuring 10-ton TNT-equivalent controlled surface chemical explosions recorded by a dense network of 31 single-sensor stations within 23 km. Despite identical sources, the observed wavefields were very different. October signals followed a near-unimodal period-distance trend, whereas May signals exhibited a pronounced azimuthal bifurcation in both period and celerity. Downwind paths largely preserved the short-period baseline observed in October, while upwind paths showed systematically longer periods caused by wind-driven low-pass filtering. This study provides the first direct observational evidence that tropospheric winds can impose azimuth-dependent low-pass filtering at local ranges, without the influence of measured temperature inversions. Thus, the structure of the atmosphere can modify the spectral characteristics of low-frequency acoustic waves even at a distance of only a few kilometers. △ Less

Submitted 30 January, 2026; originally announced February 2026.

Comments: 25 pages, 4 figures, supplemental materials. Geophysical Research Letters (2026)

Report number: SAND2026-16694O

Laser interferometry as a robust neuromorphic platform for machine learning

Authors: Amanuel Anteneh, Kyungeun Kim, J. M. Schwarz, Israel Klich, Olivier Pfister

Abstract: We present a method for implementing an optical neural network using only linear optical resources, namely field displacement and interferometry applied to coherent states of light. The nonlinearity required for learning in a neural network is realized via an encoding of the input into phase shifts allowing for far more straightforward experimental implementation compared to previous proposals for… ▽ More We present a method for implementing an optical neural network using only linear optical resources, namely field displacement and interferometry applied to coherent states of light. The nonlinearity required for learning in a neural network is realized via an encoding of the input into phase shifts allowing for far more straightforward experimental implementation compared to previous proposals for, and demonstrations of, $\textit{in situ}$ inference. Beyond $\textit{in situ}$ inference, the method enables $\textit{in situ}$ training by utilizing established techniques like parameter shift methods or physical backpropagation to extract gradients directly from measurements of the linear optical circuit. We also investigate the effect of photon losses and find the model to be very resilient to these. △ Less

Submitted 5 March, 2026; v1 submitted 25 January, 2026; originally announced January 2026.

Classical Petermann Factor as a Measure of Quantum Squeezing in Photonic Time Crystals

Authors: Younsung Kim, Kyungmin Lee, Changhun Oh, Young-Sik Ra, Kun Woo Kim, Bumki Min

Abstract: Photonic time crystals realize a continuum of momentum-resolved SU(1,1) parametric amplifiers. We show that a classical quantity, the Petermann factor of the effective Floquet Bogoliubov de Gennes (BdG) dynamical matrix, sets the scale of their quantum noise. In stable bands it fixes the Bogoliubov mixing and hence the mean bare-photon occupation of the Floquet vacuum, while in momentum gaps it se… ▽ More Photonic time crystals realize a continuum of momentum-resolved SU(1,1) parametric amplifiers. We show that a classical quantity, the Petermann factor of the effective Floquet Bogoliubov de Gennes (BdG) dynamical matrix, sets the scale of their quantum noise. In stable bands it fixes the Bogoliubov mixing and hence the mean bare-photon occupation of the Floquet vacuum, while in momentum gaps it sets the photon-number prefactor and enhances the squeezing dynamics, with the Floquet growth rate setting the time scale. This converts classical measurements of mode nonorthogonality into quantitative predictions for squeezing and photon generation, and offers a compact design parameter for engineering quantum resources in two-mode BdG platforms. △ Less

Submitted 27 July, 2026; v1 submitted 24 January, 2026; originally announced January 2026.

Validation of the COSINE-100U NaI(Tl) Encapsulation for Low-Temperature Operation in Liquid Scintillator

Authors: Kihong Park, Sungjin Cho, Luis Eduardo Franca, Chang Hyon Ha, Jinyoung Kim, Kyungwon Kim, SungHyun Kim, Won Kyung Kim, Young Ju Ko, Doohyeok Lee, Hyun Su Lee, In Soo Lee, Seo Hyun Lee, Se Dong Park, Gyun Ho Yu

Abstract: The COSINE-100U (upgrade) will enhance the sensitivity of the COSINE-100 dark matter search by operating the detector array immersed in liquid scintillator (LS) at $-30^oC$. To validate the detector design for these conditions, we constructed a module using the COSINE-100U encapsulation and performed a dedicated long-term stability study. The module was first monitored at room temperature for ~110… ▽ More The COSINE-100U (upgrade) will enhance the sensitivity of the COSINE-100 dark matter search by operating the detector array immersed in liquid scintillator (LS) at $-30^oC$. To validate the detector design for these conditions, we constructed a module using the COSINE-100U encapsulation and performed a dedicated long-term stability study. The module was first monitored at room temperature for ~110 days in air, followed by a one-week immersion in LAB-based LS to verify initial compatibility. Upon confirming stable optical performance, the temperature was lowered to $-33^oC$. During approximately 150 days of continuous operation at low temperature, we observed no degradation in performance. These results demonstrate the chemical and mechanical robustness of the encapsulation, confirming its suitability for the COSINE-100U physics run. △ Less

Submitted 24 March, 2026; v1 submitted 19 January, 2026; originally announced January 2026.

Comments: 11 pages, 5 figures

Journal ref: JINST 21 (2026) T03010

Comparison of plasma response models for RMP effects on the divertor and scrape-off layer in KSTAR

Authors: H. Frerichs, J. Van Blarcum, T. Cote, S. K. Kim, Y. Q. Liu, S. M. Yang

Abstract: Resonant magnetic perturbations (RMPs) are beneficial for control of edge localized modes (ELMs) in tokamaks. Nevertheless, a side effect is the appearance of a helical striations in the particle and heat loads onto divertor targets. The extent and field line connection of these striations is significantly altered by the plasma response to external perturbations. For an ELM suppressed H-mode plasm… ▽ More Resonant magnetic perturbations (RMPs) are beneficial for control of edge localized modes (ELMs) in tokamaks. Nevertheless, a side effect is the appearance of a helical striations in the particle and heat loads onto divertor targets. The extent and field line connection of these striations is significantly altered by the plasma response to external perturbations. For an ELM suppressed H-mode plasma at KSTAR, magnetic footprints are computed by FLARE based on plasma response from GPEC, MARS-F, M3D-C1 and JOREK with substantial differences in the resulting footprints (from 2 cm to 14 cm). This is reflected in EMC3-EIRENE simulations of the resulting heat loads: it is found that either the peak value or the extent of the striations appear to be overestimated compared to IRTV measurements. Reasonable agreement can only be achieved for the smallest footprint for lower input power and lower cross-field transport, or for higher upstream density and radiative power losses. △ Less

Submitted 14 January, 2026; originally announced January 2026.

Comments: 17 pages, 10 figures, 1 table

Journal ref: Nucl. Fusion 66 076005 (2026)

Two-Dimensional Twisted Ferromagnetic Domain Wall as a Spin-Wave Diffraction Grating

Authors: Ehsan Faridi, Se Kwon Kim, Giovanni Vignale

Abstract: We present a theoretical study of spin-wave scattering by a twisted domain wall (DW) in a two-dimensional ferromagnet with easy-axis anisotropy. While the twisted DW generates an effective gauge field for spin waves, leading to a deflection of their trajectories, our main focus is on a distinct effect that arises when a hard-axis anisotropy is present in addition to the easy-axis anisotropy. In th… ▽ More We present a theoretical study of spin-wave scattering by a twisted domain wall (DW) in a two-dimensional ferromagnet with easy-axis anisotropy. While the twisted DW generates an effective gauge field for spin waves, leading to a deflection of their trajectories, our main focus is on a distinct effect that arises when a hard-axis anisotropy is present in addition to the easy-axis anisotropy. In this case, the translational symmetry of the spin-wave Hamiltonian along the DW is broken, resulting in a periodic modulation of the Hamiltonian. This periodicity leads to the formation of multiple diffracted spin wave modes on both sides of the DW, engendering a DW-induced magnonic diffraction pattern. The interplay between the emergent gauge field and the anisotropy-induced periodicity reveals rich spin-wave dynamics and suggests potential applications for manipulating magnon flow in two-dimensional magnetic textures. △ Less

Submitted 13 January, 2026; originally announced January 2026.

Generation and characterization of coherent terahertz radiation from 100-TW laser-wakefield acceleration

Authors: Taegyu Pak, Dae Hee Wi, Sang Beom Kim, Jaewon Lim, Jae Hee Sung, Seong Ku Lee, Ki-Yong Kim

Abstract: We experimentally characterized terahertz (THz) radiation emitted from laser-wakefield acceleration (LWFA) driven at 100-TW laser power. Simultaneous measurements of the laser energy, electron-bunch charge, and THz energy reveal a quadratic dependence of the THz energy on both charge and laser energy. This behavior indicates coherent collective emission in the generation process and provides a use… ▽ More We experimentally characterized terahertz (THz) radiation emitted from laser-wakefield acceleration (LWFA) driven at 100-TW laser power. Simultaneous measurements of the laser energy, electron-bunch charge, and THz energy reveal a quadratic dependence of the THz energy on both charge and laser energy. This behavior indicates coherent collective emission in the generation process and provides a useful scaling law for THz output. Microbolometer-based beam profiling shows a relatively large THz beam divergence (~0.2 rad). Single-shot THz interferometry further shows that the emitted THz pulse is sub-picosecond in duration and broadband. Combining the beam-profile and interferometric measurements, the THz spectrum is expected to span approximately 1-20 THz. Together, these results support coherent acceleration radiation as the dominant mechanism for THz generation in 100-TW LWFA. △ Less

Submitted 31 December, 2025; originally announced January 2026.

Comments: 12 pages, 4 figures, 46 references

Atomic clock frequency ratios with fractional uncertainty $\leq 3.2 \times 10^{-18}$

Authors: Alexander Aeppli, Willa J. Arthur-Dworschack, Kyle Beloy, Caitlin M. Berry, Tobias Bothwell, Angela Folz, Tara M. Fortier, Tanner Grogan, Youssef S. Hassan, Zoey Z. Hu, David B. Hume, Benjamin D. Hunt, Kyungtae Kim, Amanda Koepke, Dahyeon Lee, David R. Leibrandt, Ben Lewis, Andrew D. Ludlow, Mason C. Marshall, Nicholas V. Nardelli, Harikesh Ranganath, Daniel A. Rodriguez Castillo, Jeffrey A. Sherman, Jacob L. Siegel, Suzanne Thornton , et al. (2 additional authors not shown)

Abstract: We report high-precision frequency ratio measurements between optical atomic clocks based on $^{27}$Al$^+$, $^{171}$Yb, and $^{87}$Sr. With total fractional uncertainties at or below $3.2 \times 10^{-18}$, these measurements meet an important milestone criterion for redefinition of the second in the International System of Units. Discrepancies in $^{87}$Sr ratios at approximately… ▽ More We report high-precision frequency ratio measurements between optical atomic clocks based on $^{27}$Al$^+$, $^{171}$Yb, and $^{87}$Sr. With total fractional uncertainties at or below $3.2 \times 10^{-18}$, these measurements meet an important milestone criterion for redefinition of the second in the International System of Units. Discrepancies in $^{87}$Sr ratios at approximately $1\times10^{-16}$ and the Al$^+$/Yb ratio at $1.6\times10^{-17}$ in fractional units compared to our previous measurements underscore the importance of repeated, high-precision comparisons by different laboratories. A key innovation in this work is the use of a common ultrastable reference delivered to all clocks via a 3.6 km phase-stabilized fiber link between two institutions. Derived from a cryogenic single-crystal silicon cavity, this reference improves comparison stability by a factor of 2 to 3 over previous systems, with an optical lattice clock ratio achieving a fractional instability of $1.3 \times 10^{-16}$ at 1 second. By enabling faster comparisons, this stability will improve sensitivity to non-white noise processes and other underlying limits of state-of-the-art optical frequency standards. △ Less

Submitted 16 July, 2026; v1 submitted 24 December, 2025; originally announced December 2025.

Comments: 5 pages main text with 4 figures; 1 page and 1 figure end matter; 9 pages and 7 figures supplemental material

Vertical NAND in a Ferroelectric-driven Paradigm Shift

Authors: Giuk Kim, Hyojun Choi, Prasanna Venkat Ravindran, Moonyoung Jung, Sanghyun Park, Kijoon Kim, Suhwan Lim, Kwangyou Seo, Kwangsoo Kim, Wanki Kim, Daewon Ha, Sukjoong Shin, Asif Khan, Sanghun Jeon, Kai Ni

Abstract: Over the past decades, the relentless scaling and mass production of flash memory have underpinned the data-centric era. Yet charge-trap-based 3D NAND flash is now constrained by intrinsic physical and architectural limits, including reliability degradation at the device level, high operating power at the array level, and vertical scaling saturation at the system level. These bottlenecks hinder fu… ▽ More Over the past decades, the relentless scaling and mass production of flash memory have underpinned the data-centric era. Yet charge-trap-based 3D NAND flash is now constrained by intrinsic physical and architectural limits, including reliability degradation at the device level, high operating power at the array level, and vertical scaling saturation at the system level. These bottlenecks hinder further advances in storage density and energy efficiency required by memory-centric computing. This Perspective outlines how coupling ferroelectric polarization with charge trapping can reconfigure the foundations of flash memory. In these hybrid architectures, polarization offers an energy-efficient pathway for charge modulation through enhanced Fowler-Nordheim tunneling, while trapped charges reinforce polarization-driven states to ensure stability. Such synergistic dynamics enable low-voltage operation and integration beyond one thousand layers without compromising process compatibility. We discuss the material, device, and architectural transitions required to realize this hybrid technology and chart future research directions to overcome the remaining scaling bottlenecks. Hybrid ferroelectric NAND extends conventional flash toward a scalable and energy-efficient platform, marking a paradigm shift for next-generation non-volatile memory. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Deep learning of committor for ion dissociation and interpretable analysis of solvent effects using atom-centered symmetry functions

Authors: Kenji Okada, Kazushi Okada, Kei-ichi Okazaki, Toshifumi Mori, Kang Kim, Nobuyuki Matubayasi

Abstract: The association and dissociation of ion pairs in water are fundamental to physical chemistry, yet their reaction coordinates are complex, involving not only interionic distance but also solvent-mediated hydration structures. These processes are often represented by free-energy landscapes constructed from collective variables (CVs), such as interionic distance and water bridging structures; however… ▽ More The association and dissociation of ion pairs in water are fundamental to physical chemistry, yet their reaction coordinates are complex, involving not only interionic distance but also solvent-mediated hydration structures. These processes are often represented by free-energy landscapes constructed from collective variables (CVs), such as interionic distance and water bridging structures; however, it remains uncertain whether such representations reliably capture the transition pathways between the two associated and dissociated states. In this study, we employ deep learning to identify reaction coordinates for NaCl ion pair association and dissociation in water, using the committor as a quantitative measure of progress along the transition pathway through the transition state. The solvent environment surrounding the ions is encoded through descriptors based on atom-centered symmetry functions (ACSFs), which serve as input variables for the neural network. In addition, an explainable artificial intelligence technique is applied to identify ACSFs that contribute to the reaction coordinate. A comparative analysis of their correlation with CVs representing water bridging structures, such as interionic water density and the number of water molecules coordinating both ions, further provides a molecular-level interpretation of the ion association-dissociation mechanism in water. △ Less

Submitted 7 February, 2026; v1 submitted 10 December, 2025; originally announced December 2025.

Comments: 10 pages, 6 figures, 2 tables for the main text, 1 page for supplementary material

Journal ref: J. Chem. Phys. 164, 094101 (2026)

Quantum Nanophotonic Interface for Tin-Vacancy Centers in Thin-Film Diamond

Authors: Hope Lee, Hannah C. Kleidermacher, Abigail J. M. Stein, Hyunseok Oh, Lillian B. Hughes Wyatt, Casey K. Kim, Luca Basso, Andrew M. Mounce, Yongqiang Wang, Shei S. Su, Michael Titze, Ania C. Bleszynski Jayich, Jelena Vučković

Abstract: The negatively charged tin-vacancy center in diamond (SnV$^-$) is an excellent solid state qubit with optically-addressable transitions and a long electron spin coherence time at elevated ($\sim1.7$ K). However, implementing scalable quantum nodes with high-fidelity optical readout of the electron spin state requires efficient photon emission and collection from the system. In this manuscript, we… ▽ More The negatively charged tin-vacancy center in diamond (SnV$^-$) is an excellent solid state qubit with optically-addressable transitions and a long electron spin coherence time at elevated ($\sim1.7$ K). However, implementing scalable quantum nodes with high-fidelity optical readout of the electron spin state requires efficient photon emission and collection from the system. In this manuscript, we report a quantum photonic interface for SnV$^-$ centers based on one-dimensional photonic crystal cavities fabricated in diamond thin films. Furthermore, we provide a rigorous description of the spontaneous emission dynamics of our system, taking into account individual contributions from both the C and D transitions of the emitter. This allows for determination of Purcell factors per transition and, by extension, the C/D branching ratio SnV$^{-}$ zero phonon line. We observe quality factors up to $\sim$6000 across this sample, and measure up to a 12-fold lifetime reduction, which translates into a Purcell factor of $F_C=26.2\pm1.5$ for a targeted C transition. By considering the cavity mode polarization alignment with the C and D transition dipole moments, we validate the C/D branching ratio to be $η_{\text{BR}}=0.75\pm0.01$, in line with previous theoretical and experimental findings. △ Less

Submitted 13 March, 2026; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: 18 total pages, 4 figures, 14 supplemental figures

Transmission Efficiency of the Recoil Mass Spectrometer EMMA at TRIUMF

Authors: B. Davids, N. E. Esker, J. Jaeyoung, Y. K. Kim, K. Pak, M. Williams

Abstract: The mean transmission efficiency of the EMMA recoil mass spectrometer at TRIUMF has been measured with 6 different angular apertures at 17 kinetic energy/charge deviations with respect to the central, reference trajectory. Measurements performed using a 148Gd alpha source installed at the target position of the spectrometer are compared to ion-optical calculations and Monte Carlo simulations. The… ▽ More The mean transmission efficiency of the EMMA recoil mass spectrometer at TRIUMF has been measured with 6 different angular apertures at 17 kinetic energy/charge deviations with respect to the central, reference trajectory. Measurements performed using a 148Gd alpha source installed at the target position of the spectrometer are compared to ion-optical calculations and Monte Carlo simulations. The transmission efficiency as a function of angle and kinetic energy/charge is described empirically using piecewise Gaussian functions whose parameters are fit to the data. △ Less

Submitted 14 January, 2026; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: 18 pages, 17 figures, revised version with fewer typographical errors accepted for publication in Nucl. Instrum. Meth. Phys. Res. A

Journal ref: Nuclear Instruments and Methods in Physics Research A 1085, 171295 (2026)

Coupled Aerodynamic-Electromagnetic Modeling for RCS Estimation of Million-Scale Chaff Clouds with Arbitrarily Curved 3D Geometries

Authors: Chung Hyun Lee, Bowoo Jang, Kyoungil Kwon, Kyung-Tae Kim, Dong-Yeop Na

Abstract: Accurate prediction of the radar cross section (RCS) of chaff clouds requires careful consideration of aerodynamic effects, as the orientation and spatial distribution of individual chaff elements evolve significantly after deployment. Building upon conventional six-degree-of-freedom (6-DoF) formulations for chaff aerodynamic analysis-which assumed straight or two-dimensionally bent geometries-we… ▽ More Accurate prediction of the radar cross section (RCS) of chaff clouds requires careful consideration of aerodynamic effects, as the orientation and spatial distribution of individual chaff elements evolve significantly after deployment. Building upon conventional six-degree-of-freedom (6-DoF) formulations for chaff aerodynamic analysis-which assumed straight or two-dimensionally bent geometries-we extend the framework to incorporate arbitrarily curved three-dimensional chaff geometries. This extension enables accurate modeling of both flattened and helical dynamics induced by aerodynamic moments acting along the roll, pitch, and yaw directions, thereby providing a more comprehensive and realistic description of chaff motion. We then finally develop a coupled aerodynamic-electromagnetic framework that integrates the extended aerodynamic model with our recently developed fast method-of-moments solver, which is optimized for efficiently estimating the RCS of million-scale chaff clouds. The proposed multiphysics coupled framework allows real-time, first-principles prediction of the monostatic and bistatic RCS of large-scale chaff clouds with arbitrary geometries, orientations, and lengths, accurately incorporating their time-varying aerodynamic evolution. Simulation results confirm that the monostatic RCS is strongly influenced by aerodynamic effects, with the coexistence of flattened and helical motions playing a critical role in determining the overall scattering response. The proposed framework thus provides a physically grounded and computationally efficient approach for predicting the RCS of large-scale chaff clouds. Furthermore, it can be directly extended to radar signal processing applications by utilizing multi-frequency complex-valued far-field responses, thereby enabling the reconstruction of Range-Doppler, Range-Angle, and Doppler-Angle maps. △ Less

Submitted 29 October, 2025; originally announced November 2025.

Comments: This manuscript was submitted to IEEE Transactions on Antennas and Propagation on October 29, 2025

ENDF/B-VIII.1: Updated Nuclear Reaction Data Library for Science and Applications

Authors: G. P. A. Nobre, R. Capote, M. T. Pigni, A. Trkov, C. M. Mattoon, D. Neudecker, D. A. Brown, M. B. Chadwick, A. C. Kahler, N. A. Kleedtke, M. Zerkle, A. I. Hawari, C. W. Chapman, N. C. Fleming, J. L. Wormald, K. Ramić, Y. Danon, N. A. Gibson, P. Brain, M. W. Paris, G. M. Hale, I. J. Thompson, D. P. Barry, I. Stetcu, W. Haeck , et al. (84 additional authors not shown)

Abstract: The ENDF/B-VIII.1 library is the newest recommended evaluated nuclear data file by the Cross Section Evaluation Working Group (CSEWG) for use in nuclear science and technology applications, and incorporates advances made in the six years since the release of ENDF/B-VIII.0. Among key advances made are that the $^{239}$Pu file was reevaluated by a joint international effort and that updated… ▽ More The ENDF/B-VIII.1 library is the newest recommended evaluated nuclear data file by the Cross Section Evaluation Working Group (CSEWG) for use in nuclear science and technology applications, and incorporates advances made in the six years since the release of ENDF/B-VIII.0. Among key advances made are that the $^{239}$Pu file was reevaluated by a joint international effort and that updated $^{16,18}$O, $^{19}$F, $^{28-30}$Si, $^{50-54}$Cr, $^{55}$Mn, $^{54,56,57}$Fe, $^{63,65}$Cu, $^{139}$La, $^{233,235,238}$U, and $^{240,241}$Pu neutron nuclear data from the IAEA coordinated INDEN collaboration were adopted. Over 60 neutron dosimetry cross sections were adopted from the IAEA's IRDFF-II library. In addition, the new library includes significant changes for $^3$He, $^6$Li,$^9$Be, $^{51}$V, $^{88}$Sr, $^{103}$Rh, $^{140,142}$Ce, Dy, $^{181}$Ta, Pt, $^{206-208}$Pb, and $^{234,236}$U neutron data, and new nuclear data for the photonuclear, charged-particle and atomic sublibraries. Numerous thermal neutron scattering kernels were reevaluated or provided for the very first time. On the covariance side, work was undertaken to introduce better uncertainty quantification standards and testing for nuclear data covariances. The significant effort to reevaluate important nuclides has reduced bias in the simulations of many integral experiments with particular progress noted for fluorine, copper, and stainless steel containing benchmarks. Data issues hindered the successful deployment of the previous ENDF/B-VIII.0 for commercial nuclear power applications in high burnup situations. These issues were addressed by improving the $^{238}$U and $^{239,240,241}$Pu evaluated data in the resonance region. The new library performance as a function of burnup is similar to the reference ENDF/B-VII.1 library. The ENDF/B-VIII.1 data are available in ENDF-6 and GNDS format at https://doi.org/10.11578/endf/2571019. △ Less

Submitted 28 April, 2026; v1 submitted 5 November, 2025; originally announced November 2025.

Comments: Article associated with the ENDF/B-VIII.1 release, updated with version accepted for publication in Nuclear Data Sheets

Journal ref: Nuclear Data Sheets Volume 210, May 2026, Pages 1-224

Electron-wave-stimulated mid-infrared emission from graphene-substrate quantum oscillators

Authors: Sunhwa Hong, Moo Jin Kwak, Yunseok Lee, Chan-Jin Kim, Sung Jin Hong, Ha Eun Lee, Yejun Lee, Koeun Kim, Juhyen Lee, Minkyung Lee, Youngdeog Koh, Joonhyun Lee, Miyoung Kim, Zee Hwan Kim, Myung Jin Park, Hoon Wee, Byung Hee Hong, Konstantin S. Novoselov

Abstract: Generating tunable, high-intensity mid-infrared (MIR) to terahertz (THz) radiation on-chip remains a formidable challenge due to the rigid spectral limits of conventional thermal emitters. While graphene has emerged as a promising platform for light-matter interaction, active control of its radiative properties has been largely confined to surface-limited phenomena mostly associated with plasmons.… ▽ More Generating tunable, high-intensity mid-infrared (MIR) to terahertz (THz) radiation on-chip remains a formidable challenge due to the rigid spectral limits of conventional thermal emitters. While graphene has emerged as a promising platform for light-matter interaction, active control of its radiative properties has been largely confined to surface-limited phenomena mostly associated with plasmons. Here, we introduce a new MIR radiation platform where multi-layer chemical vapor deposition (CVD) graphene is integrated with modular, vibrationally active dielectric substrates, ranging from organic thin films and inorganic matrices. A pivotal discovery is that the long-range de Broglie wavelength of drift carriers enables coherent coupling with vibrational transition dipoles deep within the substrate bulk. This transforms the substrate into a three-dimensional volume emission source, where complex spectra of characteristic molecular and lattice vibration energies are additively combined on demand. The exponential scaling of radiation intensity appears when the electrons' drift velocity in graphene exceeds the sound velocity of the substrates, consistent with quantum stimulated amplification associated with Cerenkov electron-phonon instability. Our work redefines the passive dielectric substrate as an active, programmable component driven by electron waves, paving the way for next-generation system-on-a-chip MIR-THz photonics, environmental and biomedical sensing, and highly efficient mode-specific electrothermal applications. △ Less

Submitted 3 June, 2026; v1 submitted 29 October, 2025; originally announced October 2025.

Comments: 12 pages,15 figures

Chip-scale modulation-free laser stabilization using vacuum-gap micro-Fabry-Pérot cavity

Authors: Mohamad Hossein Idjadi, Haotian Cheng, Farshid Ashtiani, Benjia Li, Kwangwoong Kim, Naijun Jin, Franklyn Quinlan, Peter T. Rakich

Abstract: Narrow-linewidth lasers are vital for a broad range of scientific and technological applications, including atomic clocks and precision sensing. Achieving high frequency stability is often as critical as ensuring scalability, portability, and cost-effectiveness in the development of low noise laser systems. Conventional electro-optic stabilization techniques, such as Pound-Drever-Hall locking to u… ▽ More Narrow-linewidth lasers are vital for a broad range of scientific and technological applications, including atomic clocks and precision sensing. Achieving high frequency stability is often as critical as ensuring scalability, portability, and cost-effectiveness in the development of low noise laser systems. Conventional electro-optic stabilization techniques, such as Pound-Drever-Hall locking to ultra-high-finesse resonators held in a vacuum chamber, provide excellent performance but remain challenging to scale. Here, we propose and experimentally demonstrate a cavity-coupled interferometric laser stabilization technique implemented on a silicon photonic chip and integrated with a compact, scalable micro-Fabry-Pérot cavity. The vacuum-gap optical cavity operates in air, achieving a quality factor of approximately $2.0\times 10^9$ and a fractional frequency instability of $1.45\times 10^{-12}$ at one-second averaging time. Integration of the proposed technique with the compact cavity yields more than 38-fold reduction in the laser's integrated linewidth and nearly three orders of magnitude suppression of frequency noise at 10 Hz offset frequency. The hybrid-integration of the proposed photonic chip with the micro-Fabry-Pérot cavity establishes a scalable and portable route toward chip-integrated ultra-stable lasers, paving the way for precision optical systems deployable beyond laboratory environments. △ Less

Submitted 24 October, 2025; originally announced October 2025.

Comments: 16 pages and 4 figures (main manuscript), 6 pages and 3 figures (supplementary document)

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Authors: Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert, Jiahao Chen, Rafael A. Choudhury, Kyudong Kim, Yu-Chun Wang, Ahmad E. Islam, Andrew J. Green, Shubhra S. Pasayat, Chirag Gupta

Abstract: In this work, we demonstrate a passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT on a sapphire substrate for W-band operation, featuring a 5.5 nm Al0.35Ga0.65N barrier under the gate and a 31 nm Al0.35Ga0.65N barrier in the gate access regions. The device achieves a drain current density of 1.8 A/mm, a peak transconductance of 750 mS/mm, and low gate leakage with a high on/off ratio of 10^7.… ▽ More In this work, we demonstrate a passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT on a sapphire substrate for W-band operation, featuring a 5.5 nm Al0.35Ga0.65N barrier under the gate and a 31 nm Al0.35Ga0.65N barrier in the gate access regions. The device achieves a drain current density of 1.8 A/mm, a peak transconductance of 750 mS/mm, and low gate leakage with a high on/off ratio of 10^7. Small-signal characterization reveals a current-gain cutoff frequency of 127 GHz and a maximum oscillation frequency of 203 GHz. Continuous-wave load-pull measurements at 94 GHz demonstrate an output power density of 2.8 W/mm with 26.8% power-added efficiency (PAE), both of which represent the highest values reported for Ga-polar GaN HEMTs on sapphire substrates and are comparable to state-of-the-art Ga-polar GaN HEMTs on SiC substrates. Considering the low cost of sapphire, the simplicity of the epitaxial design, and the reduced fabrication complexity relative to N-polar devices, this work highlights the potential of recessed-gate Ga-polar AlGaN/GaN HEMTs on sapphire as a promising candidate for next-generation millimeter-wave power applications. △ Less

Submitted 9 October, 2025; originally announced October 2025.

Frequency stability of $2.5\times10^{-17}$ in a Si cavity with AlGaAs crystalline mirrors

Authors: Dahyeon Lee, Zoey Z. Hu, Ben Lewis, Alexander Aeppli, Kyungtae Kim, Zhibin Yao, Thomas Legero, Daniele Nicolodi, Fritz Riehle, Uwe Sterr, Jun Ye

Abstract: Developments in ultrastable lasers have fueled remarkable advances in optical frequency metrology and quantum science. A key ingredient in further improving laser frequency stability is the use of low-noise mirror materials such as AlGaAs crystalline coatings. However, excess noise observed with these coatings limits the performance of cryogenic silicon cavities with AlGaAs mirrors to similar leve… ▽ More Developments in ultrastable lasers have fueled remarkable advances in optical frequency metrology and quantum science. A key ingredient in further improving laser frequency stability is the use of low-noise mirror materials such as AlGaAs crystalline coatings. However, excess noise observed with these coatings limits the performance of cryogenic silicon cavities with AlGaAs mirrors to similar levels achieved with conventional dielectric coatings. With a new pair of crystalline coated mirrors in a 6-cm-long cryogenic silicon cavity operated at 17 K, we demonstrate a clear advantage of crystalline coatings over dielectric coatings. The achieved fractional frequency stability of $2.5 \times 10^{-17}$ at 10 s is four times better than expected for dielectric mirrors and corresponds to more than tenfold reduction in the coating mechanical loss factor. We also combine two silicon cavities to demonstrate optical frequency averaging for enhanced stability. In addition, we present a long-term frequency drift record of four cryogenic silicon cavities measured over several years. These results open up realistic prospects for cavity-stabilized lasers with $10^{-18}$ fractional stability, as well as an all-optical timescale with continuously operating optical local oscillators. △ Less

Submitted 16 September, 2025; originally announced September 2025.

Benchmarking thermostat algorithms in molecular dynamics simulations of a binary Lennard-Jones glass-former model

Authors: Kumpei Shiraishi, Emi Minamitani, Kang Kim

Abstract: A systematic comparison was carried out to assess the influence of representative thermostat methods in constant-temperature molecular dynamics simulations. The thermostat schemes considered include the Nosé--Hoover thermostat and its chain generalisation, the Bussi velocity rescaling method, and several implementations of the Langevin dynamics. Using a binary Lennard-Jones liquid as a model glass… ▽ More A systematic comparison was carried out to assess the influence of representative thermostat methods in constant-temperature molecular dynamics simulations. The thermostat schemes considered include the Nosé--Hoover thermostat and its chain generalisation, the Bussi velocity rescaling method, and several implementations of the Langevin dynamics. Using a binary Lennard-Jones liquid as a model glass former, we investigated how the sampling of physical observables, such as particle velocities and potential energy, responds to changes in time step across these thermostats. While the Nosé--Hoover chain and Bussi thermostats provide reliable temperature control, a pronounced time-step dependence was observed in the potential energy. Amongst the Langevin methods, the Grønbech-Jensen--Farago scheme provided the most consistent sampling of both temperature and potential energy. Nonetheless, Langevin dynamics typically incurs approximately twice the computational cost due to the overhead of random number generation, and exhibits a systematic decrease in diffusion coefficients with increasing friction. This study presents a broad comparison of thermostat methods using a binary Lennard-Jones glass-former model, offering practical guidance for the choice of thermostats in classical molecular dynamics simulations. These findings provide useful insights for diverse applications, including glass transition, phase separation, and nucleation. △ Less

Submitted 16 September, 2025; originally announced September 2025.

Comments: 25 pages, 14 figures

Journal ref: J. Chem. Phys. 164, 164501 (2026)

Reconfigurable, non-volatile control of optical anisotropy in ReS2 via ferroelectric gating

Authors: Mahfujur Rahaman, Seunguk Song, Aaliyah C. Khan, Bongjun Choi, Aaron M. Schankler, Kwan-Ho Kim, Wonchan Lee, Jason Lynch, Hyeon Suk Shin, Andrew M. Rappe, Deep Jariwala

Abstract: Electrically tunable linear dichroism (LD) with non-volatile properties represents a critical yet elusive feature for next-generation integrated photonic elements in practical device architectures. Here, we demonstrate record-breaking, non-volatile control of optical anisotropy in two-dimensional ReS2 via ferroelectric gating with aluminum scandium nitride (AlScN). Our ferroelectric field-effect t… ▽ More Electrically tunable linear dichroism (LD) with non-volatile properties represents a critical yet elusive feature for next-generation integrated photonic elements in practical device architectures. Here, we demonstrate record-breaking, non-volatile control of optical anisotropy in two-dimensional ReS2 via ferroelectric gating with aluminum scandium nitride (AlScN). Our ferroelectric field-effect transistors achieve near-unity (~95%) LD tunability of differential reflectance at room temperature--the highest reported for any electrically controlled 2D optical system. Crucially, the programmed optical states exhibit exceptional retention exceeding 12,000 seconds without applied bias, enabling true non-volatile optical memory. Through combined experimental characterization and ab initio calculations, we reveal that ferroelectric polarization switching induces substantial asymmetric charge transfer to ReS2, selectively populating conduction band states and triggering structural distortions that dramatically enhance optical anisotropy in the "up" polarization state while leaving the "down" state unperturbed. This ferroelectric-semiconductor coupling provides a universal platform for voltage-programmable, energy-efficient photonic devices with dynamic polarization control, addressing critical needs in integrated photonics as well as programmable far-field optics and telecommunications infrastructure. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Comments: 5 main figures