arXiv subjects

Jaesung Lim

Publications and source records attributed to Jaesung Lim.

4 recordsLinked to original sources

arXiv2026

Robust Generation of Topological Biphoton Mode via Adiabatic Passage

Topological waveguide arrays support robust mode propagation in the presence of fabrication imperfections, providing a significant advantage for on-chip quantum information processing. However, this robustness does not fully extend to nonlinear biphoton generation. Structural disorder can enhance the excitation of non-topological biphoton modes during nonlinear interactions, which degrades the quantum properties of the generated state. To overcome this limitation, we propose an adiabatic passage that connects an isolated site to a topological defect array. By initiating the nonlinear process in a strongly isolated regime, nonlinear coupling to unwanted modes is effectively suppressed, thereby preserving the Schmidt number of the generated state. The subsequent adiabatic connection facilitates the high fidelity transfer of the generated biphoton into the topological biphoton mode. Our numerical simulations demonstrate that, unlike conventional topological structures, the adiabatic scheme maintains both high biphoton fidelity and a unit Schmidt number in the presence of waveguide gap disorder. Furthermore, we show that this robustness extends to path entangled NOON states, achieving a near-unity quantum interference visibility. Our approach provides a practical design strategy for disorder-tolerant integrated quantum photonic devices.

quant-ph↗

arXiv2026

Recon?figurable measurement scheme compatible with MDI-QKD and BB84 protocols using single-laser sideband generation

A quantum network can be operated efficiently by switching between measurement-device independent quantum key distribution (MDI-QKD) and BB84 according to the trust level of an intermediate node, since MDI-QKD is immune to all detector side-channel attacks while generally yielding a lower secret-key rate. Here, we present a proof-of-principle demonstration of a recon?figurable measurement scheme compatible with both protocols using a single laser. Two mutually independent weak coherent states (WCSs) are generated from a shared continuous-wave laser via electro-optic phase modulation and subsequent ?first-order sideband fi?ltering. Channel indistinguishability is verifi?ed using two complementary Hong-Ou-Mandel (HOM) measurements: time-resolved coincidence measurements and polarization mismatch scans, both yielding HOM visibilities close to the theoretical limit of 0.5 for WCSs. The measurement module performs a partial Bell-state measurement for MDI-QKD, while rotating a single half-wave plate to 22.5 degree reconfi?gures the same module into a dual-basis polarization analyzer for BB84. The quantum bit error rates measured in both confi?gurations agree well with theoretical expectations, verifying the operational feasibility of the reconfi?gurable receiver at the physical layer. By eliminating the need for active frequency locking while retaining independent sideband tunability, this approach provides a practical foundation for flexible and cost-effective quantum networks.

quant-ph↗

arXiv2025

Inverse Design of Chiral Structures for Giant Helical Dichroism

Investigating chiral light-matter interactions is essential for advancing applications in sensing, imaging, and pharmaceutical development. However, the chiroptical response in natural chiral molecules and subwavelength chiral structures is inherently weak, with the characterization tool limited to optical methods that utilize the light with spin angular momentum (SAM). To overcome this, orbital angular momentum (OAM) beams, characterized by helical wavefronts, have emerged as a compelling research focus. Helical dichroism (HD) describes the differential absorbance of OAM beams with opposite signs of topological charges. By using inverse design with adjoint methods for topology optimization, we design the chiral structure optimized to increase HD response under OAM beam incidence, demonstrating a giant HD response of ~107% with topological charges $|\pm\ell|$ = 3 at the wavelength of 800 nm. This study reveals distinct helicity-dependent interactions between the structure and OAM beams, highlighting the potential for custom-tuned chiroptical responses.

physics.optics↗

arXiv2024

Masked Language Modeling Becomes Conditional Density Estimation for Tabular Data Synthesis

In this paper, our goal is to generate synthetic data for heterogeneous (mixed-type) tabular datasets with high machine learning utility (MLu). Since the MLu performance depends on accurately approximating the conditional distributions, we focus on devising a synthetic data generation method based on conditional distribution estimation. We introduce MaCoDE by redefining the consecutive multi-class classification task of Masked Language Modeling (MLM) as histogram-based non-parametric conditional density estimation. Our approach enables the estimation of conditional densities across arbitrary combinations of target and conditional variables. We bridge the theoretical gap between distributional learning and MLM by demonstrating that minimizing the orderless multi-class classification loss leads to minimizing the total variation distance between conditional distributions. To validate our proposed model, we evaluate its performance in synthetic data generation across 10 real-world datasets, demonstrating its ability to adjust data privacy levels easily without re-training. Additionally, since masked input tokens in MLM are analogous to missing data, we further assess its effectiveness in handling training datasets with missing values, including multiple imputations of the missing entries.

cs.LG↗