Hyeonjae Kim

This project was conducted as part of Exploration Project in Physics 2 (PHYS0352), a senior undergraduate course-based research project.

This work explored quantum illumination by reconstructing error-probability bounds for Gaussian-state target detection. I studied quantum hypothesis testing and Gaussian-state discrimination, and applied them to classical illumination with coherent-state light and quantum illumination with a two-mode squeezed-vacuum state. The reconstructed results compared the target-detection error probabilities of the two cases, showing quantum advantage in the low-signal-photon-number regime and its degradation as the signal photon number increased.

This work presents the feasibility of integrating CsPbBr₃ perovskite quantum dots (QDs) with optical fibers for wired quantum communication. CsPbBr₃ perovskite QD samples were fabricated as single-photon sources by spin-coating colloidal solutions onto Si substrates under varying process conditions. QDs were characterized by micro-photoluminescence measurements at room and low temperatures (~4 K), and QD-fiber coupling was carried out using polydimethylsiloxane (PDMS) and an optical microscope. Furthermore, finite-difference time-domain (FDTD) simulations were employed to design a free-form intermediate structure to enhance quantum dot-fiber coupling efficiency. These results suggest the potential of perovskite QDs for fiber-based quantum communication, while future incorporation of single QDs into the designed structure may enable high-efficiency quantum dot–fiber coupling.

This work presents a quadrotor system integrating a hemisphere-shell passive wheel, designed and demonstrated for combined air and ground mobility. Structural robustness was assessed via Von Mises stress simulations to evaluate resistance to external forces such as obstacle-induced impacts, revealing enhanced durability of the hemisphere passive wheel with a linear spoke design. The fabricated quadrotor was experimentally evaluated for ground and aerial mobility. Ground tests confirmed stable obstacle traversal, while aerial tests examined obstacle crossing during forward flight through IMU-based pitch angle measurements. By enabling combined air and ground operation, the proposed system overcomes conventional quadrotor path constraints and shows strong potential for low-detectability missions and deployment in extreme environments, including both military and disaster-response scenarios.

This work presents a fabrication method for a flexible PEC cell with a bismuth vanadate (BiVO₄) photoanode using laser-induced crystallization. A sol–gel–derived precursor solution was deposited onto an ITO–PEN substrate and annealed on a hot plate to form a BiVO₄ precursor layer. Laser-induced crystallization was then used to convert the precursor into crystalline BiVO₄ on the flexible substrate. The deposition of BiVO₄ was confirmed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The fabricated flexible PEC cell demonstrated a water oxidation current density of 0.45 mA/cm² for hydrogen production.