arXiv subjects

Byungjin Lee

Publications and source records attributed to Byungjin Lee.

4 recordsLinked to original sources

arXiv2026

Finite-temperature spin diffusion in the two-dimensional XY model

We present a combined theory-experiment study to quantify spin diffusion in the square lattice quantum spin-1/2 XY model at finite temperature. On the theory side, we leverage a recently developed dynamical high-temperature expansion method to faithfully capture the long spatiotemporal scales of the hydrodynamic regime. Experimental results are obtained from an optical lattice hard-core boson quantum simulator. The excellent agreement of spin diffusion constants marks a breakthrough in spin-transport beyond one dimension and for the quantitative validation of state-of-the-art quantum simulation platforms. We also provide theory predictions for future experiments on dynamic spin conductivity or anisotropy-induced integrability breaking.

cond-mat.quant-gas↗

arXiv2026

Universal Family-Vicsek scaling in quantum gases far from equilibrium

Fluctuations in the growing surfaces of classical systems can exhibit universal scaling behavior, known as Family-Vicsek (FV) scaling. Although this phenomenon was originally discovered in classical stochastic models, recent theoretical studies have demonstrated the presence of FV scaling in quantum many-body systems as well. Here, we observe the universal FV scaling in a one-dimensional Bose gas in an optical lattice. By monitoring the fluctuations of particle number in half of the system, which corresponds to the surface roughness, we extract all scaling exponents and demonstrate that the entire relaxation-from the growth of quantum fluctuations to their saturation-is captured by a single universal scaling function. Our results demonstrate that universal scaling laws of classical surface growth extend to quantum many-body systems, establishing a unified framework for nonequilibrium universality across classical and quantum systems.

cond-mat.quant-gas↗

arXiv2025

Stability of many-body localization in two dimensions

Disordered quantum many-body systems pose one of the central challenges in condensed matter physics and quantum information science, as their dynamics are generally intractable for classical computation. Many-body localization (MBL), hypothesized to evade thermalization indefinitely under strong disorder, exemplifies this difficulty. Here, we study the stability of MBL in two dimensions using ultracold atoms in optical lattices with variable system sizes up to $24\times 24$ sites, well beyond the classically simulable regime. Using the imbalance as a probe, we trace the long-time dynamics under two distinctive disorder potentials: quasiperiodic and random disorder. For random disorder, the MBL crossover point shifts to higher disorder strength with increasing system size, consistent with the avalanche scenario. In contrast, with quasiperiodic disorder, we observe no clear system size dependence, suggesting possible stability of MBL in two dimensions.

cond-mat.quant-gas↗

arXiv2025

Double-pass rotating z-cut quartz plate as a rapidly variable waveplate

We demonstrate a rapidly tunable waveplate based on a rotating z-cut quartz plate in a double-pass configuration. In contrast to previous single-pass implementations, where angular rotation of birefringent crystals causes significant beam path displacement, we show that the double-pass geometry effectively suppresses beam walk-off, reducing lateral shifts to below 10 $μ$m, which is stable enough to have a fiber coupling. We present a full theoretical description of the polarization changes using Jones matrix calculations and verify it through polarization-resolved measurements. Additionally, the retardation is stable across a broad spectral range without requiring wavelength-specific optimization. When combined with a polarizing beam splitter, the system functions as a high-speed optical power modulator, achieving a dynamic power conversion in 1~ms with its contrast about 1000:1. This compact and robust design is particularly suited for atomic, molecular, and optical (AMO) physics experiments requiring rapid and precise control of light intensity.

physics.optics↗