Showing 1–50 of 988 results for author: Kim, J

Preventing quart-NaI adhesion in Bridgman growth using ammonium iodide

Authors: Lam Tan Truc, N. T. Luan, Gul Rooh, O. Gileva, K. A. Shin, H. S. Lee, A. Iltis, C. R. Byeon, C. H. Lee, H. J. Kim

Abstract: Adhesion between NaI(Tl) single crystals and the walls of quartz ampoules remains a major limitation for Bridgman growth under sealed conditions, particularly for applications requiring ultra-radiopure scintillators for dark matter searches, where sealed handling is essential. In this study, ammonium iodide (NH4I) was used as an additive to generate HI in situ, thereby suppressing the NaOH-SiO2 re… ▽ More Adhesion between NaI(Tl) single crystals and the walls of quartz ampoules remains a major limitation for Bridgman growth under sealed conditions, particularly for applications requiring ultra-radiopure scintillators for dark matter searches, where sealed handling is essential. In this study, ammonium iodide (NH4I) was used as an additive to generate HI in situ, thereby suppressing the NaOH-SiO2 reaction that forms adhesive sodium silicate phases. Small-diameter crystals (8 mm) were first grown to determine the NH4I concentration required to eliminate adhesion. The optimized condition was then applied to the growth of a large NaI(Tl) crystal. A crack-free and bubble-free NaI(Tl) crystal with dimensions of 3 inches in diameter by 3 inches in length was successfully grown. The crystal exhibited a light output of 59,000 photons/MeV, which is higher than that of the commercial NaI(Tl) crystals used as references in this study. △ Less

Submitted 21 August, 2026; originally announced August 2026.

Comments: 27 pages, 14 Figures

Shift or curtail? How much data-center flexibility is worth depends on the host power grid

Authors: Saroj Khanal, Geon Roh, Boyu Yao, Abraham Silverman, Dennice Gayme, Charalambos Konstantinou, Jip Kim, Yury Dvorkin

Abstract: Data-center growth risks overbuilding power grid infrastructure and stranding capital. Flexible data-center operation can defer infrastructure investments, but its value depends on the flexibility mechanism and the host power grid characteristics. We classify data-center load as firm, flexible or interruptible, and embed them in capacity expansion applied to market-organized, fossil-heavy PJM and… ▽ More Data-center growth risks overbuilding power grid infrastructure and stranding capital. Flexible data-center operation can defer infrastructure investments, but its value depends on the flexibility mechanism and the host power grid characteristics. We classify data-center load as firm, flexible or interruptible, and embed them in capacity expansion applied to market-organized, fossil-heavy PJM and carbon-capped, centrally coordinated Korea. In PJM, the flexibility value is spatial: shifting workloads between zones reduces system cost by 6% in 2028 and 19% in 2038, avoiding 4.4 GW and 8.9 GW of gas and nuclear generation. In Korea, it is temporal: shifting load into midday solar hours makes 0.5 GW of additional solar worth building in 2028 and avoids 1.2 GW of gas and 0.3 GW of batteries in 2038. In both, realistic event-shape limits diminish the value of curtailment. The results show that flexibility procurement and its value are driven by grid characteristics and policy objectives. △ Less

Submitted 20 August, 2026; originally announced August 2026.

Comments: Submitted to Nature Energy

Physics-guided machine learning for sim-to-real calibration of NV diamond magnetometers

Authors: Jonathan Daniel, Martin Y. Kim, Jesse Hernandez, Emanuel Suarez, Sangwoo Lee, Jinhee Lee, Je-Hyung Kim

Abstract: Ensemble nitrogen-vacancy (NV) centers in diamond enable robust vector magnetometry in unshielded environments, yet deployment remains bottlenecked by complex calibration and a reliance on external data references. Conventional statistical machine learning requires an exorbitantly large volume of training data and suffers from severe simulation-to-reality mismatches. To address this, we introduce… ▽ More Ensemble nitrogen-vacancy (NV) centers in diamond enable robust vector magnetometry in unshielded environments, yet deployment remains bottlenecked by complex calibration and a reliance on external data references. Conventional statistical machine learning requires an exorbitantly large volume of training data and suffers from severe simulation-to-reality mismatches. To address this, we introduce a physics-guided hybrid machine learning framework that embeds the Zeeman splitting directly into the learning pipeline. Our physics-guided model significantly reduces the average tracking error demonstrating a 372-fold precision improvement over purely statistical baselines. Furthermore, our hybrid architecture pairs a sparse physical measurement with scalable synthetic data generation, seamlessly incorporating real-world hardware non-idealities. When deployed to decode uncalibrated, raw experimental ODMR data, our framework delivers exceptional predictive accuracy for the scalar magnetic field. This work paves the way toward self-calibrated sensors while establishing a machine learning training method applicable to other data-scarce physical systems △ Less

Submitted 19 August, 2026; originally announced August 2026.

Comments: 10 pages , 4 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.

Variable-Path-Length FTIR of E. coli in Aqueous Media

Authors: Jonathan Matsuura, Andrew Huang, Jaehyeon Kim, Ching-Ping Chang, Kai Zhang, Yingjie Zhang

Abstract: Transmission infrared spectroscopy has been widely used for chemical analysis of biological samples in aqueous environments. However, its scope of applications has been limited by the path length, which is either too large or fixed, posing challenges for analyzing highly absorbing or heterogeneous samples. In this work, a mid-infrared (mid-IR) optical fiber probe was used for Fourier transform inf… ▽ More Transmission infrared spectroscopy has been widely used for chemical analysis of biological samples in aqueous environments. However, its scope of applications has been limited by the path length, which is either too large or fixed, posing challenges for analyzing highly absorbing or heterogeneous samples. In this work, a mid-infrared (mid-IR) optical fiber probe was used for Fourier transform infrared (FTIR) micro-spectroscopy of aqueous Escherichia coli (E. coli) samples, providing continuous tuning of optical path length and sampling of near-surface and bulk regions. The mid-IR absorbance of the protein signal at 1548 cm-1 increased linearly with path length, consistent with the Beer-Lambert law. Path-length dependent spectra were used to calculate the spatially heterogeneous absorption coefficient of E. coli suspensions in aqueous media. The results demonstrate the ability of our fiber-based technique to resolve signals originating from different depths into the biological solution. △ Less

Submitted 14 August, 2026; originally announced August 2026.

Monoenergetic acceleration of charge-neutralized ion bunches to GeV-scale energies by the combination of a high-current electron beam and an ionization front

Authors: Jiyuan Chen, Jihoon Kim, Roopendra Singh Rajawat, Gennady Shvets

Abstract: Compact heavy ion accelerators have numerous applications, ranging from heavy ion fusion to carbon ion radiotherapy, and testing radiation-hardened electronics. The demand could be met by developing high-gradient traveling wave plasma accelerators of high-charge ($\simμ\mathrm{C}$) relativistic ion beams. We will discuss a novel ion acceleration regime -- Counter-propagating ionization Front Accel… ▽ More Compact heavy ion accelerators have numerous applications, ranging from heavy ion fusion to carbon ion radiotherapy, and testing radiation-hardened electronics. The demand could be met by developing high-gradient traveling wave plasma accelerators of high-charge ($\simμ\mathrm{C}$) relativistic ion beams. We will discuss a novel ion acceleration regime -- Counter-propagating ionization Front Acceleration (CFA) -- utilizing counter-propagating Ionization Front (IF) and high-current Relativistic Electron Beam (REB). Theoretical modeling and 3D PIC simulations demonstrate the possibility of using typical REBs produced by induction voltage adders propagating through a gas-filled tube undergoing laser ionization to achieve acceleration gradients in excess of $\sim 250 {\rm MeV/m}$ while accelerating micro-Coulombs of ions over meters distance. A unique energy conversion mechanism -- from the REB to electromagnetic fields to the ions is discussed, as well as the limits on the accelerated ions charge and the degree of its neutralization, acceleration gradient, and ion energy spread. △ Less

Submitted 12 August, 2026; originally announced August 2026.

Comments: 6 pages, 3 figures

Twist-Reconfigurable van der Waals Moiré Photonic Crystals

Authors: Hugo Quard, Jiyun Kim, Anastasiia Zalogina, Xuerong Hu, Evan Williams, Oscar J. Palma Chaundler, Owen R. Wolley, Alexander Tartakovskii, Haoning Tang, Igor Aharonovich

Abstract: Moiré photonics has emerged as a fascinating concept to design and in situ control of the optical bands. Moiré enabled light localisation arises from the relative twist between periodic layers, rather than from fixed, pre-fabricated cavity features. So far, however, the realisation of practical moiré photonic crystals in the visible range has been elusive, due to challenges in engineering nanoscal… ▽ More Moiré photonics has emerged as a fascinating concept to design and in situ control of the optical bands. Moiré enabled light localisation arises from the relative twist between periodic layers, rather than from fixed, pre-fabricated cavity features. So far, however, the realisation of practical moiré photonic crystals in the visible range has been elusive, due to challenges in engineering nanoscale structures and twisting them dynamically post fabrication. Here, we realise a mechanically reconfigurable moiré photonic crystal, comprising from two patterned van der Waals crystals (tungsten di sulphide, WS$_2$) slabs separated by an optically active hexagonal boron nitride (hBN) spacer. We reconfigured the same pair of WS$_2$ slabs from a twist angle of 3.8° to 8.4° and reconstructed their three-dimensional dispersion using momentum-resolved reflectivity spectroscopy. Further, by reducing the twist angle between the slabs, we observe a denser manifold of folded and hybridised resonances that coincides with a 30-fold enhancement of emission from embedded colour centres. Our results open exciting opportunities for in-situ dispersion engineering and programmable light matter interactions employing van der Waals nanostructures. △ Less

Submitted 12 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.

Universality and Heterogeneity of Stylized Facts in Cryptocurrency and Equity Markets

Authors: Jaesung Kim, Changhee Cho, Jae Woo Lee

Abstract: This study investigates whether the macroscopic statistical maturity of cryptocurrencies implies dynamical equivalence with traditional equity markets. We analyze high-frequency data (2020--2025) using the Complexity--Entropy Causality Plane (CECP) and directed horizontal visibility graphs (directed HVG) to uncover complex temporal patterns and time-directed structures in the return series. While… ▽ More This study investigates whether the macroscopic statistical maturity of cryptocurrencies implies dynamical equivalence with traditional equity markets. We analyze high-frequency data (2020--2025) using the Complexity--Entropy Causality Plane (CECP) and directed horizontal visibility graphs (directed HVG) to uncover complex temporal patterns and time-directed structures in the return series. While conventional stylized facts show striking convergence across all assets, structural diagnostics reveal a compelling paradox: cryptocurrencies appear more locally random than the equity benchmark during ordinary periods, yet exhibit significantly stronger directional time-irreversibility around high-visibility return events. The absolute-return results show that large cryptocurrency fluctuations tend to begin abruptly and remain elevated afterward. Separate analyses of positive returns and negative-return magnitudes show that this pattern is shared across cryptocurrencies on the upside but varies across assets on the downside. We conclude that statistical maturity is only skin-deep; the underlying dynamical processes of mature cryptocurrencies remain fundamentally distinct from traditional benchmarks. △ Less

Submitted 11 August, 2026; originally announced August 2026.

Oxygen Reduction Reaction on Platinum Nanocatalysts Produces Long-Lived, Hysteretic Oxygenated Adsorbates

Authors: Jaehyeon Kim, Lalith Krishna Samanth Bonagiri, Fujia Zhao, Yingjie Zhang

Abstract: Aqueous electrocatalysis generates oxygenated intermediates at catalyst surfaces. While intermediate species on single-crystal catalysts have been observed, the nature and evolution of surface oxygenated species on industrially relevant nanoparticle (NP) catalysts remain largely unknown. Here, using in situ Raman spectroscopy, we tracked the formation and potential-dependent evolution of oxygenate… ▽ More Aqueous electrocatalysis generates oxygenated intermediates at catalyst surfaces. While intermediate species on single-crystal catalysts have been observed, the nature and evolution of surface oxygenated species on industrially relevant nanoparticle (NP) catalysts remain largely unknown. Here, using in situ Raman spectroscopy, we tracked the formation and potential-dependent evolution of oxygenated adsorbates in alkaline media on NP catalysts with an active platinum (Pt) surface. By comparing spectroscopic features in Ar- vs O2-saturated electrolytes, we determined three key intermediates produced by the oxygen reduction reaction (ORR): adsorbed OOH, OH, and O2. In contrast to the conventional wisdom that intermediates exist only during catalytic reactions, we found these oxygenated adsorbates to be highly long-lived and hysteretic, and to persist even after the termination of ORR. This adsorbate-retention effect exhibits a modest dependence on the surface oxidation state and the electrolyte cations (K+ vs Li+), and is likely facilitated by the heterogeneous nature of the catalyst surface. The results highlight the complexity of surface adsorption structures on realistic catalysts, which often extends beyond that captured by measurements or simulations on model single-crystal surfaces. △ Less

Submitted 8 August, 2026; originally announced August 2026.

Performance of an HRPPD in Tesla-scale magnetic fields

Authors: B. Azmoun, Y. Ilieva, Y. Jin, J. Kim, A. Kiselev, B. S. Page, M. Popecki, M. L. Purschke, A. Tamis, V. Teotia, C. P. Wong, C. Woody

Abstract: High-Rate Picosecond Photodetectors (HRPPDs) are state-of-the-art microchannel-plate (MCP) photodetectors that offer excellent timing and spatial resolution, together with high single-photon detection efficiency. They are currently being considered for the ePIC experiment at the future Electron Ion Collider (EIC) at Brookhaven National Laboratory. A key requirement for the application of this tech… ▽ More High-Rate Picosecond Photodetectors (HRPPDs) are state-of-the-art microchannel-plate (MCP) photodetectors that offer excellent timing and spatial resolution, together with high single-photon detection efficiency. They are currently being considered for the ePIC experiment at the future Electron Ion Collider (EIC) at Brookhaven National Laboratory. A key requirement for the application of this technology is reliable operation in a strong magnetic field up to 1.5 T, with magnetic flux lines at an inclination of $\le15^\circ$ to the normal of the MCP surface. Magnetic field-induced distortions of the collected charge in MCP-based detectors can be compensated by tuning the operating parameters; however, the objective of this study is to quantify this performance in the case of the EIC-HRPPD, a particular MCP stack-up specialized for operation within ePIC. This photosensor employs a high quantum efficiency photocathode, 10$~μ$m capillary pores, narrow transfer gaps, and a custom ceramic pixelated DC-coupled readout. This article explores the optimal operating parameters (mainly the voltages applied across the gaps and the MCPs) for single photon detection at various inclination angles in a uniform field up to 1.8 T. Ultimately, it was found that the gain and single photon detection efficiency of the HRRPD could be recovered over a range of polar inclination angles up to $\pm35^\circ$. △ Less

Submitted 7 August, 2026; originally announced August 2026.

Wave scattering around a submerged vertical permeable breakwater

Authors: Jeongin Kim, Yong Sung Park

Abstract: An analytical solution for a wave velocity field scattered by a submerged permeable vertical plate-type breakwater under the linear monochromatic wave is obtained and the applications of the solution are presented. The water has an infinite depth, and the flow is assumed to be incompressible, inviscid, and irrotational, which leads to the two-dimensional potential wave theory. The permeable breakw… ▽ More An analytical solution for a wave velocity field scattered by a submerged permeable vertical plate-type breakwater under the linear monochromatic wave is obtained and the applications of the solution are presented. The water has an infinite depth, and the flow is assumed to be incompressible, inviscid, and irrotational, which leads to the two-dimensional potential wave theory. The permeable breakwater vertically occupies a finite interval beneath the water surface and the water flows through the breakwater. The resulting nonlinear boundary condition is resolved by the perturbation method with a small parameter representing the permeability. The solution was expanded up to the first order so that the leading-order term can represent the wave scattered by the impermeable breakwater and the first-order term can give the correction to the solution considering the wave scattered by the permeable breakwater. Each order of the wave velocity potential is determined by a reduction method and this leads to the homogeneous Riemann-Hilbert problem for the leading-order problem and the nonhomogeneous Riemann-Hilbert problem for the first-order problem. \rev{The effects} of wavelength, breakwater length, and breakwater permeability conditions on the reflection and transmission coefficients are discussed in detail as an illustrative example of the application of the solution. \rev{An exact energy identity is also derived; it verifies the first-order solution and yields a closed-form boundary $\varepsilon_{\max}(kb)$ of the validity range of the expansion. △ Less

Submitted 13 August, 2026; v1 submitted 6 August, 2026; originally announced August 2026.

Comments: 23 pages, 8 figures. Under consideration for publication in Wave Motion

High Spectral Energy Density All-Fiber Nanosecond Pulsed 1.7 $μ$m Light Source for Photoacoustic Microscopy

Authors: Seongjin Bak, Sang Min Park, Yuon Song, Jeesu Kim, Tae Won Nam, Dong-Wook Han, Chang-Seok Kim, Soon-Woo Cho, Brett E. Bouma, Hwidon Lee

Abstract: We present a high spectral energy density all-fiber nanosecond pulsed 1.7 $μ$m light source specifically designed for photoacoustic microscopy (PAM). The system targets the first overtone absorption of C-H bonds near 1720 nm within the near-infrared-III (NIR-III) window, where lipids exhibit strong optical absorption and tissues benefit from reduced scattering and high permissible fluence. To achi… ▽ More We present a high spectral energy density all-fiber nanosecond pulsed 1.7 $μ$m light source specifically designed for photoacoustic microscopy (PAM). The system targets the first overtone absorption of C-H bonds near 1720 nm within the near-infrared-III (NIR-III) window, where lipids exhibit strong optical absorption and tissues benefit from reduced scattering and high permissible fluence. To achieve narrow linewidth, high pulse energy, and high pulse repetition rate (PRR), we developed a master oscillator fiber amplifier architecture based on stimulated Raman scattering. A 1589.80 nm Raman pump and a custom-built narrow-linewidth Raman seed laser were employed to generate spectrally pure 1719.44 nm pulses with an approximately 0.10 nm linewidth. The proposed light source delivers nanosecond pulses of approximately 5 ns with high pulse energy of at least 2.2 $μ$J and tunable PRRs up to 300 kHz, resulting in a spectral energy density of approximately 22 $μ$J/nm, which is significantly higher than that of conventional 1.7 $μ$m light sources. The performance of the NIR-PAM system was validated through resolution testing with a 1951 USAF target, demonstrating a spatial resolution of approximately 4.14 $μ$m and an axial resolution of approximately 85.5 $μ$m. Phantom imaging of CH$_2$-rich polymer films and ex vivo lipid-rich biological tissues confirmed the system's high spatial fidelity and strong contrast for lipid-specific structures. This compact, stable, and spectrally refined light source with high spectral energy density can offer an effective solution for high-resolution, label-free molecular imaging and represents a promising platform for clinical photoacoustic imaging applications involving lipid detection and metabolic disease diagnostics. △ Less

Submitted 5 August, 2026; originally announced August 2026.

Journal ref: Photoacoustics 44 (2025) 100744

Toward Compact Fiber In-line Nonlinear Devices via Highly Efficient Nanophotonic Cavity Interface

Authors: Mahsa Haddadi Moghaddam, Kirlie Iulius Figuera Michal, Sangwoo Lee, Sijin Sung, Jongwon Lee, Hyeong-Ryeol Park, Je-Hyung Kim

Abstract: Compact and efficient frequency conversion within optical fibers is highly desirable for nonlinear and quantum photonic technologies, yet it remains challenging due to weak nonlinear interactions and limited coupling efficiencies onto optical fibers. Here, we demonstrate resonantly enhanced second-harmonic generation (SHG) through the all-fiber integration of a gallium nitride (GaN) hole-type circ… ▽ More Compact and efficient frequency conversion within optical fibers is highly desirable for nonlinear and quantum photonic technologies, yet it remains challenging due to weak nonlinear interactions and limited coupling efficiencies onto optical fibers. Here, we demonstrate resonantly enhanced second-harmonic generation (SHG) through the all-fiber integration of a gallium nitride (GaN) hole-type circular Bragg grating (h-CBG) cavity, directly transferred onto a standard optical fiber. Together with the large second-order nonlinear susceptibility and wide optical transparency window of GaN, the fabricated h-CBG membrane cavity on GaN enables strong field confinement and vertically directional out-coupling of the generated SHG signal. As a result, we observe drastically enhanced SHG signals from the h-CBG device compared with the bulk GaN and the unpatterned freestanding GaN membrane. Using a deterministic pick-and-place transfer technique, we demonstrate robust and precise fiber integration of the GaN cavity device, enabling in-line SHG generation from a conventional fiber platform. This work establishes a compact and scalable approach for incorporating optical nonlinearity into fiber-based photonic systems. △ Less

Submitted 2 August, 2026; originally announced August 2026.

Comments: 19 pages, 5 figures

Predictive Formulas for Scattering Mean Free Path for General Disordered Dielectric Media Beyond the Long-Wavelength Regime

Authors: Jaeuk Kim, Salvatore Torquato

Abstract: We derive predictive formulas for the scattering mean free path $\ell_s$ of statistically homogeneous two-phase dielectric media in dimensions $d=1,2,3$. Unlike Mie-based estimates limited to identical circular or spherical scatterers, the formulas apply to arbitrarily shaped and polydisperse particulate media as well as nonparticulate media, with microstructure entering through the spectral densi… ▽ More We derive predictive formulas for the scattering mean free path $\ell_s$ of statistically homogeneous two-phase dielectric media in dimensions $d=1,2,3$. Unlike Mie-based estimates limited to identical circular or spherical scatterers, the formulas apply to arbitrarily shaped and polydisperse particulate media as well as nonparticulate media, with microstructure entering through the spectral density. The formulas are based on the exact strong-contrast expansion for the effective dynamic dielectric constant. We apply them to five nonhyperuniform and hyperuniform models and validate selected cases using finite-difference time-domain simulations. For $k_1/s \lesssim 1$, where $k_1$ is the incident wavenumber and $s$ is the specific surface, the predictions agree well with simulations and are consistent with Mie theory where applicable, while improving accuracy for two-dimensional transverse-magnetic polarization. Mie estimates become more accurate for $k_1/s \gtrsim 1$. For hyperuniform media with $\widetildeχ_V(k)\sim k^α$ at small $k$, the theory predicts $\ell_s\sim k_1^{-(d+1+α)}$; stealthy hyperuniform media are transparent over a finite wavenumber interval. These results provide a microstructure-based route to predict and design wave transport in general disordered dielectric materials. △ Less

Submitted 2 August, 2026; originally announced August 2026.

Comments: 22 pages, 8+3 figures, one supplementary document and one supplementary data set

Journal ref: published: J. Kim and S. Torquato, Advanced Optical Materials, 14 e03370 (2026)

Quantifying the cost of network computations to unpack structure-function relationships in the brain

Authors: Suman S. Kulkarni, Jason Z. Kim, Panagiotis Fotiadis, Fabio Pasqualetti, Dani S. Bassett

Abstract: The brain supports computations through coordinated patterns of activity on an underlying network. These networks---from microscale navigational circuits in insects to macroscale brain areas in humans---are organized in structured ways that are thought to support their function. We seek a unifying quantitative framework to understand how network structure shapes the computations a network can read… ▽ More The brain supports computations through coordinated patterns of activity on an underlying network. These networks---from microscale navigational circuits in insects to macroscale brain areas in humans---are organized in structured ways that are thought to support their function. We seek a unifying quantitative framework to understand how network structure shapes the computations a network can readily support. To do so, we frame computation as a goal-directed transition of activity and quantify its cost on a given network using control theory. We then define the distribution of costs across all possible transitions as a $\textit{computational affordance landscape}$ that encodes which computations a network structure readily supports. We apply this framework to a circuit model for how insects maintain a sense of direction and show that updating orientation is the least costly computation, with predicted inputs consistent with known circuitry. In the human brain, we find that the affordance landscape varies systematically with the functional role of each network. Sensory networks display more heterogeneous landscapes (reflecting their role in specialized information processing), whereas association networks display more homogeneous landscapes (reflecting their role in generalized information processing). In recurrent neural networks trained on cognitive tasks, we show that learning progressively increases landscape heterogeneity, reshaping the distribution of affordable computations. Generally, we establish a quantitative framework for studying relationships between structure and computation in neural circuits, with future applications extending to other biological and physical networks. △ Less

Submitted 31 July, 2026; originally announced July 2026.

MWF-MIMOSA for efficient simultaneous relaxometry and myelin water fraction mapping

Authors: Yuting Chen, Yohan Jun, Hyeong-Geol Shin, Shizhuo Li, Shohei Fujita, Xingwang Yong, Jiye Kim, Jongho Lee, Gian Franco Piredda, Tom Hilbert, Aneri Bhatt, Susie Y. Huang, Huafeng Liu, Huihui Ye, Shahin Nasr, Borjan Gagoski, Kwok-Shing Chan, Berkin Bilgic

Abstract: Quantitative magnetic resonance imaging (qMRI) provides improved sensitivity and specificity to tissue composition and pathological alterations compared with conventional contrast-weighted imaging. Among various qMRI biomarkers, myelin water imaging is of particular interest because myelin plays a central role in brain function and its alteration is closely associated with many neurological diseas… ▽ More Quantitative magnetic resonance imaging (qMRI) provides improved sensitivity and specificity to tissue composition and pathological alterations compared with conventional contrast-weighted imaging. Among various qMRI biomarkers, myelin water imaging is of particular interest because myelin plays a central role in brain function and its alteration is closely associated with many neurological diseases. However, conventional myelin water fraction (MWF) mapping techniques are often limited by long scan times, low spatial resolution, reduced signal-to-noise ratio (SNR), and high specific absorption rate (SAR). Here, we propose MWF-MIMOSA for efficient simultaneous T1, T2, T2* mapping, magnetic susceptibility source separation, and MWF estimation. To achieve this, multi-contrast and multi-slice zero-shot self-supervised learning (MZS-SSL) was used to jointly reconstruct whole-brain complex-valued images. To improve computational efficiency of the parameter estimation step, a multilayer perceptron (MLP) was trained within the GACELLE GPU-accelerated parameter estimation framework to circumvent the computationally intensive Bloch simulation process, resulting in a >100-fold computational speed-up in MWF estimation. Numerical simulations were performed to evaluate the accuracy and precision of MWF-MIMOSA, and in-vivo results further demonstrated its robustness. Comparison with existing myelin water imaging methods showed that MWF-MIMOSA is highly correlated with established approaches, while providing complementary quantitative parameter maps at higher spatial resolution and with shorter scan times. Notably, simultaneous multi-parametric mapping was achieved in 5 min at 1 mm isotropic resolution, and in 10 min at 0.7 mm isotropic resolution. These results demonstrate the potential of MWF-MIMOSA for fast, high-resolution simultaneous relaxometry and myelin water imaging. △ Less

Submitted 30 July, 2026; originally announced July 2026.

Comments: 43 pages, 16 figures

MSC Class: 94A08; 92C55; 68T07

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

Geometry resolved atomic oxygen risk assessment for very low earth orbit spacecraft

Authors: Gun Hi Won, Hyun Jung Kim, SongYi Park, ChangWon Seo, Eunji Lee, SeongSik Yoon

Abstract: Atomic oxygen (AO) is a major durability concern for spacecraft in very low Earth orbit (VLEO), yet orbit-averaged fluence does not resolve exposure on individual surfaces and internal components. This study develops a geometry-resolved AO assessment by coupling NRLMSISE-00, HWM07, and SYSTEMA ATOMOX. One-year simulations were performed for a 350 km circular Sun-synchronous orbit at LTAN 06:00 and… ▽ More Atomic oxygen (AO) is a major durability concern for spacecraft in very low Earth orbit (VLEO), yet orbit-averaged fluence does not resolve exposure on individual surfaces and internal components. This study develops a geometry-resolved AO assessment by coupling NRLMSISE-00, HWM07, and SYSTEMA ATOMOX. One-year simulations were performed for a 350 km circular Sun-synchronous orbit at LTAN 06:00 and 12:00 using a baseline spacecraft, a wedge-modified body, and two synthetic aperture radar antenna sub-arrays. The LTAN 12:00 orbit produced 8-10% higher orbit-averaged AO flux than LTAN 06:00. For the baseline geometry, the ram-facing surface accumulated 6.9-7.5 x 10^21 atoms/cm^2, whereas side and zenith/nadir surfaces received only 3-5% of the ram fluence. Material-specific erosion yields changed the component-level risk ranking: the CFRP zenith panel was predicted to erode by 15.1-16.2 um/year despite receiving much lower fluence than the ram-facing multilayer insulation. The wedge generated approximately one order of magnitude spatial variation through local shielding. Housing openings also allowed AO to reach internal printed circuit boards, with maximum annual fluences of 9.5 x 10^16 and 4.0 x 10^19 atoms/cm^2 in the H- and V-polarized antenna models, respectively. HWM07 winds produced 10-20% side-panel asymmetry, which decreased below 1% when winds were disabled. Comparison with MISSE-8 reproduced the measured zenith-to-ram ratio of approximately 4% but underpredicted wake exposure, identifying a limitation of ballistic ray tracing. These results demonstrate that VLEO AO durability requires coupled consideration of orbit, atmospheric winds, geometry, and material response. △ Less

Submitted 28 July, 2026; originally announced July 2026.

Femtoscopy Measurement with S$π$RIT TPC in Radioactive BeamHeavy-ion Collisions

Authors: Y. J. Wang, C. K. Tam, Z. G. Xiao, W. G. Lynch, C. Y. Tsang, J. Barney, G. Jhang, J. Estee, M. B. Tsang, R. S. Wang, M. Kaneko, J. W. Lee, J. Park, Z. Chajęcki, G. Verde, T. Isobe, M. Kurata-Nishimura, T. Murakami, D. S. Ahn, L. Atar, T. Aumann, H. Baba, K. Boretzky, J. Brzychczyk, G. Cerizza , et al. (42 additional authors not shown)

Abstract: Femtoscopy is a powerful tool for exploring the dynamic emitting structure in heavy-ion collisions, while radioactive beam heavy-ion collisions enable the investigation of nuclear matter under extreme isospin conditions. Here, we successfully perform femtoscopy measurements using the S$π$RIT Time Projection Chamber (TPC). A dedicated correction scheme for track merging and splitting is proposed, w… ▽ More Femtoscopy is a powerful tool for exploring the dynamic emitting structure in heavy-ion collisions, while radioactive beam heavy-ion collisions enable the investigation of nuclear matter under extreme isospin conditions. Here, we successfully perform femtoscopy measurements using the S$π$RIT Time Projection Chamber (TPC). A dedicated correction scheme for track merging and splitting is proposed, which is well applicable to rectangular TPCs housed inside dipole magnets and effectively improves the reconstructed correlation functions at small relative momenta. Focusing on the proton-proton (p-p) correlation function in the 270 MeV/u $^{132}\text{Sn}+^{124}\text{Sn}$ system, we successfully apply the track merging and splitting correction; additionally, the TPC angular acceptance exhibits a negligible impact on the correlation function. A systematic uncertainty quantification framework is established. The experimental results of the p-p correlation function confirm the feasibility of the S$π$RIT TPC for femtoscopy measurements and provide technical support for high-precision femtoscopy studies using rectangular TPCs in radioactive beam heavy-ion collisions. △ Less

Submitted 15 July, 2026; originally announced July 2026.

Comments: 9 pages, 10 figures

Technologies and novel components for broadband splitting and coupling in pairwise and nulling interferometry

Authors: Harry-Dean Kenchington Goldsmith, Nemanja Jovanovic, Anusha Pai Asnodkar, Sanny Ahmed, Elsa Huby, Sylvestre Lacour, Michael Fitzgerald, Yoo Jung Kim, Pierre Labeye, Nicolas Dunoyer, Michael Ireland, Stephen Madden

Abstract: Passive and active photonic components are central to the continued development of astronomical photonic integrated circuits (PICs), although achieving broadband achromatic performance remains a significant challenge. This work presents broadband evanescent tri-couplers, tapered directional couplers, and a chromatically controlled achromatic intensity modulator for astronomical interferometry in… ▽ More Passive and active photonic components are central to the continued development of astronomical photonic integrated circuits (PICs), although achieving broadband achromatic performance remains a significant challenge. This work presents broadband evanescent tri-couplers, tapered directional couplers, and a chromatically controlled achromatic intensity modulator for astronomical interferometry in the J- and H-bands. Silicon nitride and silicon oxide provide complementary low-loss platforms, while customised tapered components enable broadband operation across the 0.95-1.8 microns range. For the silicon nitride platform developed by STMicroelectronics, tapered tri-couplers and directional couplers were designed as replacements for conventional components in a pairwise beam combiner for the PLANETS project. Optimised tapered tri-couplers achieve less than 1% excess loss across the J-band, while tapered directional couplers provide broadband 40:60 splitting suitable for beam combination. For the silicon oxide platform from Enablence, a two-dimensional tapered tri-coupler was investigated for nulling interferometry. The device provides broadband starlight suppression while limiting exoplanet throughput loss to less than 2.2% across the H-band and simultaneously retaining broadband phase-sensing capability for fringe tracking. The chromatically controlled achromatic intensity modulator is introduced as a combination of a tapered directional coupler with a thermo-optic phase shifter, the device provides programmable broadband intensity control for applications including null-depth balancing in interferometric PICs. Future work will extend these concepts to lithographically fabricated chalcogenide glass platforms operating in the mid-infrared, enabling compact photonic beam combiners for future ground- and space-based nulling interferometers targeting Earth-like exoplanets. △ Less

Submitted 25 July, 2026; originally announced July 2026.

Comments: 21 pages, 23 figures, SPIE Astronomical Telescopes + Instrumentation 2026 Denmark

Self-stabilization of microcombs

Authors: Krishna Twayana, Fuchuan Lei, Junyong Choi, Jungwon Kim, Victor Torres-Company

Abstract: Optical frequency combs form phase-locked spectral lines arranged on an equidistant grid fully defined by two degrees of freedom, i.e., the repetition rate and frequency offset. Stabilizing these parameters to a common frequency reference results in a coherent frequency ruler, central for modern precision metrology. However, extending this level of stability to chip-scale microcombs remains an out… ▽ More Optical frequency combs form phase-locked spectral lines arranged on an equidistant grid fully defined by two degrees of freedom, i.e., the repetition rate and frequency offset. Stabilizing these parameters to a common frequency reference results in a coherent frequency ruler, central for modern precision metrology. However, extending this level of stability to chip-scale microcombs remains an outstanding challenge. Here, we demonstrate a self-stabilizing mechanism based on self-injection locking of a selected comb line via an external feedback loop. This process establishes a second anchor point in addition to the pump, thereby constraining the comb's frequency noise dynamics. We show that, with an appropriate choice between pump frequency noise and feedback strength, collective fluctuations of the repetition rate are strongly suppressed. The result is a microcomb exhibiting ultralow phase noise and dramatically reduced timing jitter. In a 100 GHz silicon nitride soliton microcomb, we achieve an unprecedented combination of high-conversion efficiency, sub-Hertz intrinsic linewidth across the entire C band, and an integrated timing jitter of 1 fs. This approach enables chip-scale microcombs with remarkable noise performance and fs-level pulse stability, surpassing conventional noise limits and opening new avenues for precision metrology at the chip scale. △ Less

Submitted 21 July, 2026; originally announced July 2026.

Biodegradable, Millimeter-Scale Light-Emitting Sensors for Distributed Environmental Monitoring-Functional Pixie Dust

Authors: Zhiming Hu, Danzhen Zhang, Janghun Ko, Haohui Zhang, Jiale Chen, Chanho Park, Jiatong Zhang, Qiuna Zhuang, Shiwei Xu, Xiaoran Yang, Dain Son, Taehoon Kim, Uikang Joo, Zhaojian Xu, Hyunsoo Kim, Richard Chai, Gwangmin Bae, Wooyoul Maeng, Qiong Wang, Sangmin Lim, Liangsong Zeng, Un-Seong Baik, Kaiqing Zhang, Liming Yuan, Yonggang Huang , et al. (2 additional authors not shown)

Abstract: Methods for large-area, precise monitoring across natural environments are of growing interest due to pressing needs for sustainable management of rapidly increasing anthropogenic activities. Established approaches involve sparse spatial sampling and/or sequential measurements, while emerging techniques exploit miniaturized electronics or passive optical methods. Various constraints in scalability… ▽ More Methods for large-area, precise monitoring across natural environments are of growing interest due to pressing needs for sustainable management of rapidly increasing anthropogenic activities. Established approaches involve sparse spatial sampling and/or sequential measurements, while emerging techniques exploit miniaturized electronics or passive optical methods. Various constraints in scalability, costs, robustness, operational range and other factors create a need for alternatives. Here, we introduce a concept that overcomes many of these limitations through the combined use of chemically induced light emission and chemically responsive optical filter elements in millimeter-scale systems that we refer to as functional pixie dust (fPD) sensors, designed specifically for monitoring natural water systems during nighttime to eliminate background optical interference and to enhance remote analysis. These floating devices act as Lagrangian tracers to follow surface flows and to simultaneously measure the concentrations of key chemical species along their trajectories. Optimized designs exploit environmentally compatible constituent materials that are also degradable through natural processes to benign end products, thereby eliminating the need for recovery. Spatially and spectrally resolved ratiometric measurement schemes ensure robust operation and ability to address practical requirements in range, operational lifetime, time response and sensitivity. Demonstrations include distributed measurements of pH, Hg2+, and NO2-, each of relevance to industrial discharge, toxic metal contamination, and nitrogen-rich runoff, adapted for static concentration gradients, flow-driven transport conditions, and outdoor aquatic settings. The results establish a framework for environmental sensing using degradable, self-powered microsystems capable of scalable deployment and remote readout. △ Less

Submitted 20 July, 2026; originally announced July 2026.

Operation and performance of ProtoDUNE Dual Phase liquid argon time projection chamber

Authors: DUNE Collaboration, S. Abbaslu, F. Abd Alrahman, A. Abed Abud, R. Acciarri, L. P. Accorsi, M. A. Acero, M. R. Adames, G. Adamov, M. Adamowski, K. Adhikari, C. Adriano, K. Agudelo-Jaramillo, F. Akbar, F. Alemanno, N. S. Alex, L. Aliaga Soplin, A. Alqaisi, M. Alrashed, A. Alton, R. Alvarez, T. Alves, A. Aman, H. Amar, R. Amarinei , et al. (1341 additional authors not shown)

Abstract: ProtoDUNE-DP was the largest ever built Liquid Argon Time Projection Chamber (LArTPC) operating in Dual-Phase (DP) mode, with a liquid target and charge read-out placed in the gas. It had an active volume of $6\times6\times6$\,m$^3$ corresponding to an active mass of 300\,t (total LAr mass of 720\,t), constructed at the CERN Neutrino Platform and took data from 2019 to 2020 with cosmic muons. In P… ▽ More ProtoDUNE-DP was the largest ever built Liquid Argon Time Projection Chamber (LArTPC) operating in Dual-Phase (DP) mode, with a liquid target and charge read-out placed in the gas. It had an active volume of $6\times6\times6$\,m$^3$ corresponding to an active mass of 300\,t (total LAr mass of 720\,t), constructed at the CERN Neutrino Platform and took data from 2019 to 2020 with cosmic muons. In ProtoDUNE-DP the electric drift field is oriented in the vertical direction, causing the electrons to drift vertically towards the anode at the top. The ionization charge is then extracted into the gaseous argon above the liquid surface, amplified by Townsend avalanches, and collected by the charge readout planes. The detector experienced significant technical problems affecting the long-term operation of the Charge Readout Planes, formed by the Large Electron Multipliers, but other critical segments demonstrated required performance including the delivery of -300 kV to the TPC cathode, verification of replaceable charge read-out electronics, and operation of the photon detection system. ProtoDUNE-DP experience resulted in improved designs of the Vertical Drift LArTPC. △ Less

Submitted 21 July, 2026; v1 submitted 17 July, 2026; originally announced July 2026.

Comments: 103 pages, 66 figures

Report number: FERMILAB-PUB-26-0466-LBNF

Vortex-Beam Transient Absorption Microspectroscopy Resolves Ultrafast Free-Exciton and Polaron Diffusion in 2D Perovskites

Authors: Ju-Young Kim, Anirban Mondal, Gi Rim Han, Kwang Jin Lee, Jong Min Lim, Myeongsam Jen, Minhaeng Cho

Abstract: Two-dimensional (2D) Ruddlesden Popper perovskites are promising optoelectronic materials with strongly confined excitonic properties; however, probing their ultrafast carrier transport dynamics, particularly the initial nonequilibrium diffusion regime, remains challenging because conventional transient absorption microscopy requires complex spatial imaging and lacks sufficient temporal sensitivit… ▽ More Two-dimensional (2D) Ruddlesden Popper perovskites are promising optoelectronic materials with strongly confined excitonic properties; however, probing their ultrafast carrier transport dynamics, particularly the initial nonequilibrium diffusion regime, remains challenging because conventional transient absorption microscopy requires complex spatial imaging and lacks sufficient temporal sensitivity to resolve early time diffusion dynamics. Here, we demonstrate a vortex beam based transient absorption microspectroscopy platform (VTAM) enabling imaging free measurement of carrier transport by encoding spatial diffusion information into the mode dependent pump probe signal. By employing vortex probes with different topological charges, VTAM provides mode selective spatial sensitivity to excitonic dynamics with subpicosecond temporal resolution. Using VTAM, we resolved rapid free exciton (FE) diffusion followed by relaxation toward a slower steady state transport regime. A theoretically derived time dependent diffusion model separated transient and steady state transport contributions, yielding a transient diffusion enhancement (68.84 cm2 per s) and a steady state diffusion coefficient (1.85 cm2 per s), thus providing an initial diffusion coefficient (70.69 cm2 per s), and a cooling time of 0.35 ps. Measurements at the exciton-polaron (EP) resonance revealed strongly suppressed diffusion with nearly time independent signal ratios, indicating lattice-coupled EP transport. These parameters were extracted without spatial scanning or image reconstruction, establishing V-TAM as a powerful imaging free platform for investigating carrier transport in perovskites and other semiconductor systems. △ Less

Submitted 16 July, 2026; originally announced July 2026.

Automated Outlier-Robust Bayesian Profile Fitting for Magnetically Confined Plasmas with Modified Tanh Profiles and Good-and-Bad Gaussian Mixture Likelihoods

Authors: Jaewook Kim, Jekil Lee, Laurent Jung, Sang-hee Hahn, Sehyun Kwak

Abstract: We present an outlier-robust Bayesian approach for automated kinetic profile fitting in magnetically confined plasmas with the modified tanh (mtanh) parametrisation and demonstrate its implementation on KSTAR. The method addresses two systematic obstacles: anomalous diagnostic channels can bias least-squares fits, and multimodality of the mtanh cost surface can trap deterministic optimisers in sec… ▽ More We present an outlier-robust Bayesian approach for automated kinetic profile fitting in magnetically confined plasmas with the modified tanh (mtanh) parametrisation and demonstrate its implementation on KSTAR. The method addresses two systematic obstacles: anomalous diagnostic channels can bias least-squares fits, and multimodality of the mtanh cost surface can trap deterministic optimisers in secondary minima. The deployed workflow uses a good-and-bad Gaussian mixture likelihood based on the Box--Tiao formulation as the default outlier-robust likelihood for fitted diagnostic channels, with posterior outlier probabilities retained as channel-level quality indicators. The posterior is sampled with an affine-invariant ensemble MCMC sampler initialised near the result of deterministic maximum a posteriori (MAP)-seeking optimisation, reducing sensitivity to secondary minima on the multimodal mtanh surface. A batch automation layer retrieves diagnostic data from MDSplus and fits arbitrary time slices in parallel for the quantities \(n_e\), \(T_e\), \(T_i\), and \(v_T\) for which the relevant diagnostics are available. Results are written in formats suitable for MDSplus upload and downstream analysis. Representative KSTAR H-mode cases show that the mixture likelihood downweights contaminated measurements while preserving plausible pedestal profiles. The workflow provides a practical basis for future large-scale kinetic profile production for kinetic-EFIT, TRANSP, FASTRAN, and data-driven analysis workflows. △ Less

Submitted 13 July, 2026; originally announced July 2026.

Comments: 16 pages, 8 figures; submitted to Nuclear Fusion

A Quantum Computing Approach to Track Reconstruction in Strip-Type Detectors

Authors: Seungyeob Jwa, Hyunyong Kim, Jangho Kim, Minseok Oh

Abstract: This study investigates the use of quantum annealing for particle track reconstruction in strip-type gaseous detectors. In such detectors, ghost hits and multiple hit combinations can turn pattern recognition into a combinatorial optimization problem. We formulate two reconstruction subproblems as quadratic unconstrained binary optimization problems. The first subproblem selects detector hits asso… ▽ More This study investigates the use of quantum annealing for particle track reconstruction in strip-type gaseous detectors. In such detectors, ghost hits and multiple hit combinations can turn pattern recognition into a combinatorial optimization problem. We formulate two reconstruction subproblems as quadratic unconstrained binary optimization problems. The first subproblem selects detector hits associated with a single photon track inside a localized candidate region. The second subproblem selects cluster triplets from different detector layers so that multiple track candidates can be handled within a single quantum processing unit(QPU) submission. The proposed formulations are tested using simulated DAMSA detector events. For the single track hit selection task, the QPU based reconstruction gives position and angular resolutions close to those obtained with a Kalman based reconstruction. In the simultaneous association task, valid cluster triplets are first extracted from the QPU samples and then connected using an association rule based on graph connectivity to construct track candidates. The DAMSA event topology studied here has low pileup and is dominated by the two photon signal from axion-like particle(ALP) decay. In this setting, the results show that the QUBO formulations can reproduce local reconstruction decisions. This provides a practical basis for further studies of reconstruction methods that combine quantum and classical computing in more complex tracking environments. △ Less

Submitted 14 July, 2026; originally announced July 2026.

Interfacial chirality-induced magnetic-field-free switching with high energy efficiency in all-vdW heterostructures

Authors: Kai-Xuan Zhang, Suik Cheon, Seungbok Lee, Joonyoung Choi, Jihoon Keum, Hyuncheol Kim, Yeochan An, Woonghee Cho, Suhan Son, Jingyuan Cui, Pyeongjae Park, Younjung Jo, Jun Sung Kim, Hyun-Woo Lee, Je-Geun Park

Abstract: Chirality, a central concept across many scientific disciplines, continues to inspire the discovery of novel physical phenomena. In condensed matter physics, structural chirality - defined by the absence of mirror plane symmetries - has primarily been explored in bulk materials. However, new chiral phenomena can emerge uniquely at the interface, distinct from their bulk counterparts, when a chiral… ▽ More Chirality, a central concept across many scientific disciplines, continues to inspire the discovery of novel physical phenomena. In condensed matter physics, structural chirality - defined by the absence of mirror plane symmetries - has primarily been explored in bulk materials. However, new chiral phenomena can emerge uniquely at the interface, distinct from their bulk counterparts, when a chiral material forms a heterostructure. Here, we demonstrate that all van-der-Waals (vdW) heterostructure composed of the chiral Co1/3TaS2 and the achiral vdW ferromagnet Fe3GeTe2 exhibits two distinct and unconventional spin-orbit torques originating from the interfacial chirality. These torques enable magnetic-field-free switching of perpendicular magnetization with ultralow current density ~ 10^6 A/cm^2 and minimal power dissipation < 10^15 W/m^3. Moreover, by replacing Fe3GeTe2 with a similar vdW ferromagnet, Fe3GaTe2, but of higher Curie temperature, we achieved the magnetic-field-free switching at room temperature in the Fe3GaTe2/Co1/3TaS2 vdW heterostructure. Our findings establish interfacial chirality as a powerful new handle for spintronic control, opening a new pathway to explore chirality-induced phenomena beyond the bulk symmetry constraints - and paving the way toward highly efficient, low-power spintronic devices based on all-vdW heterostructures. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Comments: Accepted by Nature Communications; 30 pages; 4 main figures; 12 supporting figures

Journal ref: Nature Communications 17, 8620 (2026)

Refractive-index tomography of opaque tissue from its own backscattered light

Authors: Tran Dinh Hoang, Jaecheol Cho, Thi Van Anh Nguyen, Eunyoung Seong, Joowon Lim, Jin Hee Hong, Yongwoo Kwon, Jun Wan Kim, Juhee Yang, Seokchan Yoon, Sungsam Kang, Wonshik Choi

Abstract: The refractive index (RI) is an intrinsic, label-free marker of a living cell's dry mass and subcellular morphology, and hence of its physiological state. Its three-dimensional (3D) reconstruction has become a powerful way to study cells and tissues in their native state, spanning cell growth, drug response and disease diagnosis. Yet this capability rests on a fundamental constraint: the RI can be… ▽ More The refractive index (RI) is an intrinsic, label-free marker of a living cell's dry mass and subcellular morphology, and hence of its physiological state. Its three-dimensional (3D) reconstruction has become a powerful way to study cells and tissues in their native state, spanning cell growth, drug response and disease diagnosis. Yet this capability rests on a fundamental constraint: the RI can be recovered only from light transmitted through the specimen, which demands optical access to both sides. The cells that matter most -- those within thick tissues, intact organs and living animals -- are therefore out of reach. A tissue, however, can illuminate its own cells from behind: light backscattered by intrinsic tissue structures beneath a cell carries the same transmission information a microscope would collect from the far side. Here we develop a divide-and-conquer inverse-scattering framework that recovers this transmission from the backscattering and reconstructs a cell's 3D RI. We demonstrate label-free, quantitative imaging of cells within an engineered tissue, and a living mouse through its intact skull, where we further quantify the dry mass of individual osteocytes in vivo. By removing the need for two-sided access, this reflection-only approach extends RI tomography into living tissue, enabling non-destructive, longitudinal imaging of cells in their native environment. △ Less

Submitted 7 July, 2026; originally announced July 2026.

The performance of the TA$\times$4 surface detector array: 4.3 years of the first-half expansion

Authors: Telescope Array Collaboration, R. U. Abbasi, T. Abu-Zayyad, M. Allen, J. W. Belz, D. R. Bergman, F. Bradfield, I. Buckland, W. Campbell, B. G. Cheon, K. Endo, A. Fedynitch, T. Fujii, K. Fujisue, K. Fujita, M. Fukushima, G. Furlich, A. Gálvez Ureña, Z. Gerber, N. Globus, T. Hanaoka, W. Hanlon, N. Hayashida, H. He, K. Hibino , et al. (105 additional authors not shown)

Abstract: The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arriva… ▽ More The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arrival directions of cosmic-ray events with energy greater than 57 EeV. To improve the exposure for anisotropy studies of UHECRs, the TA$\times$4 upgrade was designed to expand the observational area by approximately 2,000 km$^2$ with 500 additional SDs. Half of the planned upgrade, consisting of 257 SDs, was completed, and the newly installed array began operation in 2019. In addition to the expanded SD array, two FD stations were constructed for the TA$\times$4 experiment. In this paper, we present a study of the performance of the expanded SD array, including the energy resolution, angular resolution, and effective aperture, over the first 4.3 years of data acquisition. While the effective aperture varied initially due to changing detector states, it has stabilized since June 2023 with more than 90\% operational SDs. Furthermore, a new inter-tower trigger system was implemented to connect six new communication towers to form two geographically separated arrays, increasing the effective aperture. The time variation of this effective aperture, the resulting total exposure of approximately 3,500 km$^2$~sr~yr, and a comparison with the original TA SD array are presented to demonstrate the performance of the expanded array. △ Less

Submitted 26 June, 2026; originally announced June 2026.

Comments: 24 pages, 9 figures, submitted to Nuclear Inst. and Methods in Physics Research, A

Unlocking Cryogenic Energy Storage by Constructing Dipole Glass with Unit-cell-level Polar Disorder

Authors: Yangyang Si, Denan Li, Yijie Li, Changsheng Chen, Jingxuan Li, Chao Zhou, Hao Xiong, Tianfu Zhang, Wenjin Liao, Zhongqi Ren, Huaicheng Yuan, Dong Li, Jing-Kai Qin, Cheng-Yan Xu, Ye Zhu, Yunlong Tang, Sujit Das, Jieun Kim, Junling Wang, Hao Pan, Fei Li, Zhen Chen, Shi Liu, Zuhuang Chen

Abstract: Cryogenic energy storage is vital for frontier technologies including deep-space exploration and quantum computing, yet conventional electrochemical energy systems fail below ~230 K due to frozen ion migration. While relaxor-based dielectric capacitors provide high efficiency at room temperature, the intrinsic freezing/growth of polar nanodomains at extended cryogenic regime limits their applicati… ▽ More Cryogenic energy storage is vital for frontier technologies including deep-space exploration and quantum computing, yet conventional electrochemical energy systems fail below ~230 K due to frozen ion migration. While relaxor-based dielectric capacitors provide high efficiency at room temperature, the intrinsic freezing/growth of polar nanodomains at extended cryogenic regime limits their applications with deteriorated hysteresis losses. Here, we realize superior cryogenic energy-storage performance by designing unit-cell-level disordered dipole-glass state in Pb0.6Sr0.4ZrO3 thin films with composition near antiferroelectric-paraelectric phase boundary. The antiferroelectric-derived dipole-glass introduces enhanced unit-cell-level complexity of dipole interaction that suppresses long-range ferroelectric order. This enables ultralow-hysteresis operation (efficiency > 88%) down to 4 K, delivering record-high energy density (211 J/cm^3) at 9 MV/cm, stability over 10^8 charge/discharge cycles and microsecond-scale charge/discharge capability. This work establishes a dipole-glass paradigm for cryogenic dielectric capacitors, opening a new avenue to highly-efficient energy-storage systems with broad applications in frontier nanoelectronics. △ Less

Submitted 26 June, 2026; originally announced June 2026.

Comments: 23 pages, 4 figures

Experimentally-determined performance limits for joint imaging and wavefront sensing with a photonic lantern

Authors: Aditya R. Sengupta, Vincent Chambouleyron, Rebecca Jensen-Clem, Emiel Por, Benjamin L. Gerard, Jordan Diaz, Zoe Weber-Porter, Yoo Jung Kim, Steph Sallum, Matthew DeMartino, Daren Dillon, Kevin Bundy, Anna K. Gagnebin, Philip Hinz, Caleb Dobias, Tara Crowe, Stephen S. Eikenberry, Rodrigo Amezcua-Correa, Stephanos Yerolatsitis

Abstract: The photonic lantern (PL) is a focal-plane wavefront sensor (WFS) that can be used for second-stage control of extreme adaptive optics (AO) systems. While the number of sensed modes and the dynamic range with respect to each mode have been relatively well characterized, little attention has been paid to the PL's sensitivity, i.e. how measurement noise impacts the accuracy of PL wavefront reconstru… ▽ More The photonic lantern (PL) is a focal-plane wavefront sensor (WFS) that can be used for second-stage control of extreme adaptive optics (AO) systems. While the number of sensed modes and the dynamic range with respect to each mode have been relatively well characterized, little attention has been paid to the PL's sensitivity, i.e. how measurement noise impacts the accuracy of PL wavefront reconstruction. We compute the PL's sensitivity to photon noise as a function of spatial frequency, and compare it to existing WFSs, using simulations as well as experiments on the muirSEAL testbed. We further assess these metrics in the case where only a subset of PL ports are available for wavefront sensing. In this configuration, the remaining ports are used to spatially and spectrally reconstruct the observed scene using algorithms such as SPADE. Using more ports for wavefront sensing enables greater aberration sensitivity but leaves less spatial information for image reconstruction. This allows us to trade off between fewer samples with smaller aberrations and more samples with larger aberrations. This work sets the stage for AO system design incorporating the PL as a joint WFS and imager. △ Less

Submitted 25 June, 2026; originally announced June 2026.

Comments: submitted to SPIE Astronomical Telescopes and Instrumentation 2026, paper number 14150-167

Effects of spatial environmental noise on evolution of cooperation

Authors: Janguk Kim, Seung-Woo Son, Hye Jin Park

Abstract: We investigate the effects of environmental noise on cooperation in a spatial evolutionary game model with variable population size. Building on a one-dimensional lattice model in which vacancies promote cooperation through spatial selection, we add random noise to the environmental quality parameter and consider two distinct types: annealed noise, where the environmental quality fluctu ates indep… ▽ More We investigate the effects of environmental noise on cooperation in a spatial evolutionary game model with variable population size. Building on a one-dimensional lattice model in which vacancies promote cooperation through spatial selection, we add random noise to the environmental quality parameter and consider two distinct types: annealed noise, where the environmental quality fluctu ates independently at each site and each time step, and quenched noise, where each site is assigned a permanently fixed random value. For annealed noise, we develop a mean-field theory by replacing the noise-dependent death probabilities with their distribution averages, and find that increasing the noise intensity shifts both the cooperator-defector phase boundary and the absorbing boundary upward in the parameter space, simultaneously expanding the cooperative regime and the extinc tion region. These predictions are confirmed by numerical simulations. In contrast, quenched noise leaves the phase boundary nearly unchanged across all noise levels, exerting only a weak effect on cooperator frequency. Together, these results demonstrate that temporal fluctuations, rather than static spatial heterogeneity, are the primary driver of noise-induced shifts in the cooperative phase structure. △ Less

Submitted 17 June, 2026; originally announced June 2026.

Journal ref: J. Korean Phys. Soc. (2026)

Activated Migration of Localized Ligand-Field Excitons in Atomically Thin CrCl3

Authors: Hyesun Kim, Renlong Liu, Sangho Yoon, Hyunjong Lim, Takashi Taniguchi, Kenji Watanabe, Jonghwan Kim, Changgu Lee, Sunmin Ryu

Abstract: Two-dimensional crystals with densely packed atoms exhibit a range of emerging properties, particularly a wide variety of excitonic behaviors. Thickness-variable layered chromium trihalides with finite surface recombination sites provide an ideal system for understanding how excitons confined in octahedral ligand fields migrate on nanometer length scales, a regime that defies conventional transpor… ▽ More Two-dimensional crystals with densely packed atoms exhibit a range of emerging properties, particularly a wide variety of excitonic behaviors. Thickness-variable layered chromium trihalides with finite surface recombination sites provide an ideal system for understanding how excitons confined in octahedral ligand fields migrate on nanometer length scales, a regime that defies conventional transport probes. In this work, we demonstrate that Cr3+-derived photoluminescence in CrCl3 is spectrally thickness-independent, but its relaxation dynamics are strongly sensitive to thickness and temperature, thereby indicating significant activated migration. A diffusion-coupled surface recombination model reveals an effective out-of-plane diffusivity of 4.5 x 10-6 cm2/s for the ligand-field excitons and a diffusion activation energy of 130 meV. The latter is comparable to the reorganization energy independently estimated from optical Stokes shifts, suggesting that exciton transport is coupled to local lattice relaxation. Furthermore, we show that the relaxation dynamics can be systematically tuned by either enhancing or suppressing surface recombination through controlled surface reactions or encapsulation. This work not only reveals the nanoscopic transport of localized ligand-field excitons but also establishes a spectroscopic transport probe applicable to various 2D materials. △ Less

Submitted 15 June, 2026; originally announced June 2026.

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

Authors: Jiyun Kim, Xinyang Yu, Zijian Feng, Chun-Ho Lin, Dewei Chu, Igor Aharonovich, Chaohao Chen

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

Submitted 1 June, 2026; originally announced June 2026.

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

Authors: Jiyun Kim, Nika Teran, Juliette Plo, Jonathan Bradford, Guillaume Cassabois, Amy F. M. Collins, Tin S. Cheng, Christopher J. Mellor, Shery L. Y. Chang, Sergei V. Novikov, Igor Aharonovich

Abstract: Hexagonal boron nitride (hBN) has emerged as a leading host for optically active quantum defects. Yet introduction of specific impurity species other than carbon remains unexplored. Here, we demonstrate an in-situ silicon doping of hBN grown by high-temperature molecular beam epitaxy (HT-MBE). By systematically varying the growth temperature from 900 to 1390 °C under a constant silicon flux, we es… ▽ More Hexagonal boron nitride (hBN) has emerged as a leading host for optically active quantum defects. Yet introduction of specific impurity species other than carbon remains unexplored. Here, we demonstrate an in-situ silicon doping of hBN grown by high-temperature molecular beam epitaxy (HT-MBE). By systematically varying the growth temperature from 900 to 1390 °C under a constant silicon flux, we establish an optimal window for Si incorporation to host a diverse range of emitters from 430-750 nm at room temperature. By transferring silicon-doped hBN film on SiO$_2$ substrate, we verified that single photon emitter activity was sustained in the hBN, demonstrating compatibility with device integration. The plausible origins of the observed optical transitions were discussed, and several potential candidates were proposed. Our results demonstrate a step toward a comprehensive understanding of in-situ doping of hBN and its utilization for quantum photonic applications. △ Less

Submitted 1 June, 2026; originally announced June 2026.

Energy spectra and cascade in the spin turbulence of a driven spinor Bose-Einstein condensate

Authors: Junghoon Lee, Jongmin Kim, Donggyu Lee, Yong-il Shin

Abstract: We investigate the spin-interaction energy spectrum of spin turbulence in a driven spinor Bose-Einstein condensate. Continuous spin driving of a spin-1 condensate produces a nonequilibrium steady state with spatially fluctuating magnetization. We observe a power-law scaling consistent with the $-7/3$ exponent predicted for spin-wave turbulence, which persists across our full range of drive strengt… ▽ More We investigate the spin-interaction energy spectrum of spin turbulence in a driven spinor Bose-Einstein condensate. Continuous spin driving of a spin-1 condensate produces a nonequilibrium steady state with spatially fluctuating magnetization. We observe a power-law scaling consistent with the $-7/3$ exponent predicted for spin-wave turbulence, which persists across our full range of drive strengths despite substantial changes in the spectral anisotropy. After switching off the drive, we track the free-decay evolution and find evidence consistent with a direct cascade of spin-interaction energy toward higher wavenumbers. These results establish an energy-spectral hallmark of spin turbulence and enable quantitative studies of cascade dynamics in spinor superfluids. △ Less

Submitted 30 May, 2026; originally announced June 2026.

Comments: 11 pages, 6 figures

Tailoring Defects in Photonic Time Crystals for Coherent Energy Control

Authors: Dayeong Lee, Jongheon Yeo, Gitae Lee, Jungmin Kim, Namkyoo Park, Sunkyu Yu

Abstract: Recent advances in time-varying photonics have revealed new degrees of freedom for manipulating optical states, arising from the distinctive nature of the temporal axis: causality and open-system dynamics. A representative example is photonic time crystals (PTCs) characterized by discrete time-translational symmetry, which exhibit space-analogous yet distinct phenomena, such as momentum gaps and a… ▽ More Recent advances in time-varying photonics have revealed new degrees of freedom for manipulating optical states, arising from the distinctive nature of the temporal axis: causality and open-system dynamics. A representative example is photonic time crystals (PTCs) characterized by discrete time-translational symmetry, which exhibit space-analogous yet distinct phenomena, such as momentum gaps and amplifying-decaying Floquet-mode pairs. Although PTCs enable optical-energy amplification beyond conventional gain media, their application as programmable energy-functional devices remains challenging. Here, we propose a design framework for tailoring optical energy via defective PTCs. By optimizing defect permittivity and duration using analytic gradients of time transfer matrices, we realize prescribed coherent energy amplification and suppression. We show that a single defect enables continuous energy tailoring, while revealing an intrinsic asymmetry between amplification and suppression due to the inherently amplifying nature of the momentum gap. Extending the framework to coupled defects expands the design space and markedly improves suppression, establishing temporal-defect engineering as a route to programmable coherent energy control. △ Less

Submitted 28 May, 2026; originally announced May 2026.

Magneto-Optical Detection of Anisotropic Spin Currents in Altermagnetic RuO2

Authors: Joongwon Lee, Jeonglyul Kim, Sreejith Nair, Seung Gyo Jeong, Changi Kim, Jae-Pil So, Bohm-Jung Yang, Bharat Jalan, Hyobin Yoo, Farhan Rana, Taekoo Oh, Hong-Gyu Park

Abstract: Altermagnets are a recently identified class of collinear antiferromagnets that host large spin-split electronic bands, offering a promising platform for efficient spin-current generation. Among proposed candidates, the metallic oxide RuO2 is predicted to exhibit strong altermagnetic spin splitting; however, whether it sustains robust magnetic order beyond the ultrathin thickness limit remains unr… ▽ More Altermagnets are a recently identified class of collinear antiferromagnets that host large spin-split electronic bands, offering a promising platform for efficient spin-current generation. Among proposed candidates, the metallic oxide RuO2 is predicted to exhibit strong altermagnetic spin splitting; however, whether it sustains robust magnetic order beyond the ultrathin thickness limit remains unresolved. Here, we employ optical probes to investigate charge-to-spin conversion in a 12-nm-thick (101)-oriented RuO2 film grown on sapphire. Polarization-resolved second-harmonic generation reveals nonlinear optical responses consistent with the surface symmetry and Néel order of RuO2. Under an applied current, both second-harmonic generation and polar magneto-optical Kerr effect measurements detect a pronounced, directionally anisotropic spin polarization, exhibiting enhanced signals for current along [010] and strongly suppressed responses for current along [-101], in agreement with the symmetry of the altermagnetic spin-splitter effect. Non-magnetic or Rashba-type mechanisms cannot explain this symmetry-selective response. Scanning transmission electron microscopy further reveals that substantial strain persists even in relatively thick films, providing a possible explanation for the observed behavior. Therefore, these results establish RuO2 as an efficient spin source and demonstrate the potential of altermagnets for field-free spintronic devices. △ Less

Submitted 26 May, 2026; originally announced May 2026.

Experimental and theoretical studies of hyperfine structures in $^{21}$Na

Authors: Junho Won, Jeongsu Ha, Deuk Soon Ahn, Sunghoon Ahn, Vivek Chavan, Anastasiia Chekhovska, Gyoungmo Gu, Kevin Insik Hahn, Seongjin Heo, Jangyong Huh, Dahee Kim, Do Gyun Kim, Dong Geon Kim, Jung Bog Kim, Sunji Kim, Yeong Seok Kim, Yung Hee Kim, Zeren Korkulu, Donghyeon Kwak, Jens Lassen, Jin Ho Lee, Jung Woo Lee, Chaeyeong Lim, Joochun Park, Ben Ohayon , et al. (16 additional authors not shown)

Abstract: We measured the hyperfine structure constants, $A(3s^2S_{1/2})$ and $A(3p^2P_{1/2})$, of the neutron-deficient isotope $^{21}\text{Na}$ using CLaSsy, a setup dedicated to collinear laser spectroscopy at RAON. The hyperfine structure constants of $^{21}\text{Na}$ were measured to be $103.6(10)_{\mathrm{stat}}(9)_{\mathrm{syst}}$ MHz for $A(3p^2P_{1/2})$ and… ▽ More We measured the hyperfine structure constants, $A(3s^2S_{1/2})$ and $A(3p^2P_{1/2})$, of the neutron-deficient isotope $^{21}\text{Na}$ using CLaSsy, a setup dedicated to collinear laser spectroscopy at RAON. The hyperfine structure constants of $^{21}\text{Na}$ were measured to be $103.6(10)_{\mathrm{stat}}(9)_{\mathrm{syst}}$ MHz for $A(3p^2P_{1/2})$ and $954.9(11)_{\mathrm{stat}}(25)_{\mathrm{syst}}$ MHz for $A(3s^2S_{1/2})$. A systematic comparison with the state-of-the-art ab-initio relativistic coupled cluster calculations shows the role of higher-order correlation effects such as triple excitations in $^{21}$Na. Furthermore, the measurement demonstrates a capability of the CLaSsy setup to conduct collinear laser spectroscopy experiments with a radioactive beam. △ Less

Submitted 26 May, 2026; originally announced May 2026.

Atomic-referenced Hz-linewidth lasers via fiber interferometric stabilization

Authors: Changmin Ahn, Hansol Jeong, Seoyeon Yang, Junyong Choi, Igju Jeon, Hanseb Moon, Jungwon Kim

Abstract: Narrow-linewidth lasers with absolute frequency anchoring are essential for precision metrology, coherent sensing, and emerging quantum technologies beyond laboratory environments. Optical cavities and interferometers provide exceptional short-term spectral purity but lack intrinsic absolute frequency references. Atomic transitions, in contrast, provide stable frequency anchors but offer limited d… ▽ More Narrow-linewidth lasers with absolute frequency anchoring are essential for precision metrology, coherent sensing, and emerging quantum technologies beyond laboratory environments. Optical cavities and interferometers provide exceptional short-term spectral purity but lack intrinsic absolute frequency references. Atomic transitions, in contrast, provide stable frequency anchors but offer limited discrimination sensitivity. Recent hybrid approaches have demonstrated the combination of compact optical resonators with atomic references, yet achieving the Hz-level regime remains challenging. Here, we present a hybrid architecture that enables simultaneous realization of Hz-level linewidth and atomic-referenced frequency stability. An external-cavity diode laser is first stabilized to a fiber interferometer to achieve Hz-level spectral purity, while the interferometer is subsequently anchored to an 87Rb D2 transition via modulation transfer spectroscopy to suppress long-term drift and define the laser frequency relative to the atomic transition. This dual-stabilization scheme realizes a compact atomic-referenced laser with a 3.4-Hz linewidth (1-rad integrated-phase method), a minimum fractional frequency stability of 3.4x10-14 at 0.56 s, and 9x10-13 at 100 s. This architecture establishes a practical and scalable route toward compact and field-deployable atomic-referenced narrow-linewidth lasers for precision metrology and quantum technologies. △ Less

Submitted 25 May, 2026; originally announced May 2026.

Comments: 24 pages, 4 figures

Development of a system for testing full-size CMS LGAD sensors

Authors: Kyungmin Lee, Hoyong Jeong, Junho Kim, Seokhyeon Lee, Jaebak Kim, Jae Hyeok Yoo

Abstract: Low-Gain Avalanche Diode (LGAD) sensors, offering timing resolutions of the order of tens of picoseconds, are being widely adopted in particle physics experiments and related applications. As these applications scale to large numbers of sensors with varying pixel geometries, conventional manual characterization techniques become inadequate for large-scale quality control. We present a modular prob… ▽ More Low-Gain Avalanche Diode (LGAD) sensors, offering timing resolutions of the order of tens of picoseconds, are being widely adopted in particle physics experiments and related applications. As these applications scale to large numbers of sensors with varying pixel geometries, conventional manual characterization techniques become inadequate for large-scale quality control. We present a modular probe card system for automated electrical characterization of pixelated LGAD sensors, consisting of a probe card, a switching board, precision measurement instruments, and control software. The system supports flexible pixel selection and measurement. Its performance is demonstrated through current-voltage (I-V) and capacitance-voltage (C-V) measurements of a $16 \times 16$ LGAD array. A rapid row-wise I-V scan of the full array is completed in approximately 20 minutes, while a pixel-by-pixel I-V scan from 0 to 300 V with a 1 V step requires about 340 minutes. The switching matrix introduces less than 1 nA of leakage current even in a conservative worst-case configuration, remaining small compared with the leakage current of a normal LGAD pixel. The modular architecture and automation capability make the system a practical and scalable solution for large-scale LGAD sensor quality control and distributed testing environments. △ Less

Submitted 26 May, 2026; v1 submitted 22 May, 2026; originally announced May 2026.

Comments: 18 pages, 11 figures

OAM Light Demultiplexing from an Intensity Profile using Orthogonality Restoration of Pair Modes

Authors: Junsu Kim, Hyunchae Chun, SeungRyong Park

Abstract: Orbital Angular Momentum (OAM) of light is a promising degree of freedom for next-generation communication. By exploiting the orthogonality of OAM modes, multi-channel division enables a linear increase in communication performance proportional to the number of available modes. However, the multiplexing and demultiplexing of each superposition state remain essential yet complex processes. Demultip… ▽ More Orbital Angular Momentum (OAM) of light is a promising degree of freedom for next-generation communication. By exploiting the orthogonality of OAM modes, multi-channel division enables a linear increase in communication performance proportional to the number of available modes. However, the multiplexing and demultiplexing of each superposition state remain essential yet complex processes. Demultiplexing has been established through spatial-domain methods that require additional optical elements such as gratings and apertures, which can decrease communication efficiency and accuracy under various conditions. In this paper, we propose a demultiplexing method under a single intensity profile by orthogonality restoration of OAM pair states. This method can be applied directly to an OAM multichannel communication system without additional receiver-side optical structure. We present simulation results of our method under various conditions. △ Less

Submitted 10 July, 2026; v1 submitted 21 May, 2026; originally announced May 2026.

Comments: 12 pages, 5 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.

Polarization-sensitive tunable extraordinary terahertz transmission based on a hybrid metal-vanadium dioxide metasurface

Authors: S. Hadi Badri, Sanam Saeidnahaei, Jong Su Kim

Abstract: A thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO2) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops while the loops are connected with strips of VO2. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of the VO2. For y-polarized incident f… ▽ More A thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO2) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops while the loops are connected with strips of VO2. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of the VO2. For y-polarized incident field, the resonance transmission peak redshifts from 0.88 to 0.81 THz upon insulator-to-metallic phase transition of VO2. For x-polarized incident field, the transmission resonance at 0.81 THz is observed in the insulator phase. However, in the metallic phase of VO2, the electromagnetic field is effectively reflected in the 0.5-1.1 THz range with a transmission level lower than 0.14. The proposed metasurface can be utilized as a terahertz modulator, reconfigurable filter, or switch. △ Less

Submitted 11 May, 2026; originally announced May 2026.

Journal ref: Applied Optics 61.20 (2022): 5972-5979

Teaching Molecular Dynamics to a Non-Autoregressive Ionic Transport Predictor

Authors: Jiyeon Kim, Byungju Lee, Won-Yong Shin

Abstract: Unlike most static material properties widely studied in the machine learning literature, ionic transport properties are inherently dynamic, making their fast and accurate prediction from static atomic structures challenging. The current standard approach, molecular dynamics (MD) simulations, suffers from prohibitively high computational cost. Recent autoregressive learning-based MD acceleration m… ▽ More Unlike most static material properties widely studied in the machine learning literature, ionic transport properties are inherently dynamic, making their fast and accurate prediction from static atomic structures challenging. The current standard approach, molecular dynamics (MD) simulations, suffers from prohibitively high computational cost. Recent autoregressive learning-based MD acceleration methods requiring sequential inference remain slow and prone to error accumulation; in contrast, existing non-autoregressive material property prediction models are less accurate because they fail to exploit dynamics. Moreover, existing methods typically benefit from datasets either with or without atomic trajectories, but not both. To overcome these limitations, we propose a non-autoregressive learning framework based on auxiliary modality learning, which treats atomic trajectories as an auxiliary modality during training but does not require them at inference. This enables the predictor to learn dynamics without sequential inference while benefiting from both types of datasets. As a result, our framework achieves over 200 times speedup compared to autoregressive models on the dataset with atomic trajectories while substantially reducing prediction error relative to non-autoregressive benchmarks across both types of datasets. Our code is available at https://github.com/jykim-git/MD. △ Less

Submitted 10 May, 2026; originally announced May 2026.

Comments: International Conference on Machine Learning (ICML 2026) (to appear) (Please cite our conference version.)

Semi-Supervised Neural Super-Resolution for Mesh-Based Simulations

Authors: Jiyeon Kim, Youngjoon Hong, Won-Yong Shin

Abstract: Mesh-based simulations provide high-fidelity solutions to partial differential equations (PDEs), but achieving such accuracy typically requires fine meshes, leading to substantial computational overhead. Super-resolution techniques aim to mitigate this cost by reconstructing high-resolution (HR), high-fidelity solutions from low-cost, low-resolution (LR) counterparts. However, training neural netw… ▽ More Mesh-based simulations provide high-fidelity solutions to partial differential equations (PDEs), but achieving such accuracy typically requires fine meshes, leading to substantial computational overhead. Super-resolution techniques aim to mitigate this cost by reconstructing high-resolution (HR), high-fidelity solutions from low-cost, low-resolution (LR) counterparts. However, training neural networks for super-resolution often demands large amounts of expensive HR supervision data. To address this challenge, we propose SuperMeshNet, an HR data-efficient super-resolution framework for mesh-based simulations aided by message passing neural networks (MPNNs). At its core, SuperMeshNet introduces complementary learning, a semi-supervised approach that effectively leverages both 1) a small amount of paired LR-HR data and 2) abundant unpaired LR data via two jointly trained, complementary MPNN-based models. Additionally, our model is enriched by inductive biases, which are empirically shown to further improve super-resolution performance. Extensive experiments demonstrate that SuperMeshNet requires 90% less HR data to achieve even lower root mean square error (RMSE) than that of the fully supervised benchmark without the inductive biases. The source code and datasets are available at https://github.com/jykim-git/SuperMeshNet.git. △ Less

Submitted 9 May, 2026; originally announced May 2026.

Comments: International Conference on Machine Learning (ICML 2026) (to appear) (Please cite our conference version.)

A micromechanical frequency reference with parts-per-trillion holdover stability

Authors: Jie Yan, Jintark Kim, Rakibul Islam, Jiawei Yang, Karim Elmeligy, Alkim Bozkurt, Thomas W. Kenny, Pavan K. Hanumolu, Gaurav Bahl

Abstract: Microelectromechanical (MEMS) resonators are widely used in timekeeping applications, and recent advances in fabrication, materials, and encapsulation technology have advanced their potential as high stability frequency references. However, for holdover applications that require the highest levels of long-term frequency stability, compact vapor atomic clocks remain dominant. In this work, we demon… ▽ More Microelectromechanical (MEMS) resonators are widely used in timekeeping applications, and recent advances in fabrication, materials, and encapsulation technology have advanced their potential as high stability frequency references. However, for holdover applications that require the highest levels of long-term frequency stability, compact vapor atomic clocks remain dominant. In this work, we demonstrate a 268 MHz MEMS clock that achieves record fractional frequency stability of ~8 parts-per-trillion at an averaging time of 8 hours, competitive with chip-scale atomic clocks. We achieved this using a single-crystal silicon electrostatic resonator that has no currently known intrinsic drift mechanism and is protected from the environment with a wafer-level encapsulation. We specifically identify gain variations in the sustaining electronics as the dominant limitation in conventional phase-locked oscillator architectures -- originating from temperature sensitivity and drifts in the electronic components -- and overcome this by implementing a frequency-locked loop architecture based on dual-frequency resonance tracking (DFRT). This novel approach removes the specific gain of the supporting electronics as a frequency determining variable in the oscillator. When combined with dual-mode tracking and ratiometric temperature stabilization of the resonator, this approach enables a dramatic enhancement to long-term frequency stability and establishes gain-insensitive DFRT locking as a general paradigm for high-stability MEMS clocks. △ Less

Submitted 27 April, 2026; originally announced May 2026.

High-Q Fano resonance in all-dielectric metasurfaces for molecular fingerprint detection

Authors: S. Hadi Badri, M. M. Gilarlue, Sanam Saeidnahaei, Jong Su Kim

Abstract: We present and numerically investigate a high-quality factor (high-Q) meta-atom with Fano resonance. Numerical simulations indicate that the designed meta-atom has a single sharp Fano resonance in the 1350-1750 1/cm range. Moreover, the frequency of the single resonance can be tuned in this frequency range by scaling the meta-atom. We exploit these properties to design a pixelated metasurface for… ▽ More We present and numerically investigate a high-quality factor (high-Q) meta-atom with Fano resonance. Numerical simulations indicate that the designed meta-atom has a single sharp Fano resonance in the 1350-1750 1/cm range. Moreover, the frequency of the single resonance can be tuned in this frequency range by scaling the meta-atom. We exploit these properties to design a pixelated metasurface for spectrometer-less molecular fingerprint retrieval. The proposed meta-atom with an average quality factor of 2000 makes it possible to decrease the scaling step of metapixels without introducing any resonance overlap between the metapixels leading to higher precision in label-free and non-destructive identification of the molecular fingerprints. △ Less

Submitted 8 May, 2026; originally announced May 2026.

Journal ref: Journal of the Optical Society of America B 39.2 (2022): 563-569

Narrowband-to-broadband switchable and polarization-insensitive terahertz metasurface absorber enabled by phase-change material

Authors: S. Hadi Badri, M. M. Gilarlue, Sanam SaeidNahaei, Jong Su Kim

Abstract: A terahertz absorber with controllable and switchable bandwidth and insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO2) and verify its performance by the finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a reso… ▽ More A terahertz absorber with controllable and switchable bandwidth and insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO2) and verify its performance by the finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a resonator separated from a gold ground-plane by a polyimide spacer. Switching from narrowband to broadband absorber is achieved via connecting VO2 patches to the gold first-order cross fractal converting the resonator to a third-order cross fractal. In the insulator phase of VO2, the main narrowband absorption occurs at the frequency of 6.05 THz with a 0.99 absorption and a full-width half-maximum (FWHM) of 0.35 THz. Upon insulator-to-metal transition of VO2, the metasurface achieves a broadband absorption with the FWHM of 6.17 THz. The simulations indicate that by controlling the partial phase-transition of VO2, we can tune the bandwidth and absorption level of the absorber. Moreover, the designed absorber is insensitive to polarization due to symmetry and works well for a very wide range of incident angles. In the metallic state of VO2, the absorber has an absorption exceeding 0.5 in the 3.57-8.45 THz frequency range with incident angles up to 65°. △ Less

Submitted 7 May, 2026; originally announced May 2026.

Journal ref: Journal of Optics 24.2 (2022): 025101