Hyeonjae Kim

Publications

Journal articles and conference presentations are listed below; further details are available on Google Scholar and in my Curriculum Vitae. † Corresponding author.

Peer-Reviewed Journal Articles

  1. Magnetic Anomaly Detection of an Undersea Tunnel Using a Drone-Mounted All-Optical Pulsed Atomic Magnetometer
    IEEE Sensors Journal, accepted for publication. DOI: 10.1109/JSEN.2026.3729190
    Hyeonjae Kim, Sin Hyuk Yim†, Sangkyung Lee, Eun-Seok Bang, Sang Rae Yeo, Yun Jeong Kim, Taek Jeong, and Younghoon Lim
  2. Aging test of atomic vapor cell with Al2O3 wall coating on cubic glass
    Applied Optics 64, 7932-7937 (2025). DOI: 10.1364/AO.572036
    Hyeonjae Kim, Taek Jeong, Sang Hyuk Hong, Jeong Bin Nam, Sangkyung Lee, Younghoon Lim, and Sin Hyuk Yim†

Manuscripts

Conference Presentations

  1. Hyeonjae Kim, Sin Hyuk Yim†, Sangkyung Lee, Taek Jeong, and Younghoon Lim, “All-optical pulsed rubidium atomic magnetometer for magnetic anomaly mapping of subsurface transportation infrastructure,” Atomic and Molecular Physics Division Workshop, Aug. 2026, Muju, South Korea (Poster)
    Abstract

    Optically pumped magnetometers exploit the collective spin dynamics of alkali-vapor ensembles to achieve high sensitivity in compact sensor platforms, enabling applications in biomagnetic sensing, magnetic navigation, and magnetic surveys. In this study, we demonstrate an all-optical pulsed rubidium atomic magnetometer for magnetic anomaly mapping of subsurface transportation infrastructure. The optically pumped rubidium atomic magnetometer employs laser mode hopping in a single-beam configuration to perform sequential optical pumping and off-resonant probing for free induction decay readout. During the probing period, the total scalar magnetic field is determined from the Larmor frequency of the rubidium spin precession. The magnetometer was mounted on a drone platform and used for magnetic-field surveys over the Boryeong undersea tunnel at flight altitudes of 50, 100, and 150 m. The residual magnetic anomaly maps showed an elongated anomaly pattern near the mapped tunnel location. Line-profile analysis quantified the altitude dependence of the anomaly amplitude and spatial width. Magnetic anomaly measurements over an underground high-speed railway in Sejong are also presented as a second field demonstration.

  2. Hyeonjae Kim, Sangkyung Lee†, Younghoon Lim, Sang Hyuk Hong, Taek Jeong, and Sin Hyuk Yim, “Probing magnetic noise from portable sensor components using a zero-field optically pumped magnetometer,” APS Division of Atomic, Molecular, and Optical Physics Meeting, Jun. 2026, Providence, RI, USA (Poster)
    Abstract

    Zero-field optically pumped magnetometers (OPMs), including operation near the spin exchange relaxation-free regime, provide high magnetic-field sensitivity to detect small magnetic-field perturbations. As OPM systems are miniaturized, nearby components are placed closer to the atomic vapor cell, and even small stray magnetic fields and magnetic noise generated by individual components can degrade sensor performance. In this study, we realize a zero-field OPM system as a sensitive test platform for characterizing magnetic-field perturbations from components used in portable OPMs. Under active three-axis magnetic-field nulling inside a magnetic shield, individual optical components are positioned 3 cm above the rubidium vapor cell to evaluate their magnetic influence. For each component, magnetic noise is characterized using the amplitude spectral density of the OPM output, while the zero-field dispersion curve is used to evaluate the sensor response and the component-induced dc magnetic field along the y direction.

  3. Hyeonjae Kim, “Experimental systems for spectroscopy and zero-field OPM with atomic vapor cells,” KISTI-SNU Joint Workshop, May 2026, Daejeon, South Korea (Invited Talk)
    Abstract

    Quantum sensors based on atomic vapor cells are attractive because they offer high sensitivity in compact and relatively simple configurations. In this presentation, I introduce two experimental systems involving atomic vapor cells that I have developed. One is an automated absorption spectroscopy system with theoretical modeling for vapor cell characterization, and the other is a zero-field optically pumped magnetometer (OPM) system for magnetic-field and noise measurements. The absorption spectroscopy system is used to estimate the buffer-gas pressure in fabricated rubidium vapor cells and to assess their lifetime by monitoring rubidium number density during aging tests. The zero-field OPM system is used to characterize magnetic fields and magnetic noise generated by portable sensor components.

  4. Hyeonjae Kim, Younghoon Lim†, Sangkyung Lee†, Sang Hyuk Hong, Sin Hyuk Yim, Taek Jeong, and Jeong Bin Nam, “Towards the development of a SERF magnetometer,” Korean Physical Society Fall Meeting, Oct. 2025, Gwangju, South Korea (Poster)
    Abstract

    A spin exchange relaxation-free (SERF) magnetometer is one of the most sensitive atomic magnetometers, capable of achieving fT-level sensitivity. We demonstrate a rubidium magnetometer, operated in the SERF regime. To enter this regime, high alkali atom density and near-zero magnetic fields are required. These conditions were achieved by optimizing coil currents to null the residual magnetic field and scanning by the cell temperature. The SERF regime was experimentally verified through three observations. A sharp increase in spin relaxation time (T2) was observed in free induction decay (FID) signals as the temperature increased. The dispersion curve obtained from lock-in detection exhibited linewidth narrowing with increasing temperature and matched well with simulated results based on the Bloch equation. This setup will be used to characterize the magnetic noise of components employed in compact optically pumped magnetometer development.

  5. Hyeonjae Kim, Taek Jeong, Sangkyung Lee, and Sin Hyuk Yim†, “Lifetime extension of rubidium vapor cells by Al2O3 coating,” APS Division of Atomic, Molecular, and Optical Physics Meeting, Jun. 2025, Portland, OR, USA (Poster)
    Abstract

    Atomic vapor cells, where atoms undergo thermal motion, are actively studied in atomic magnetometers, NMR gyroscopes, quantum light generations, and time synchronizations due to their simplicity of the system. In particular, in the spin exchange relaxation-free (SERF) regime, a highly sensitive magnetometer, the atomic vapor system is heated to 150°C to maintain a high number of alkali atoms. However, in general, when an atomic vapor cell made of glass is exposed to high temperatures, alkali atoms permeate and adsorb onto glass surface, causing a decrease in their number. This loss eventually renders the atomic vapor cell unusable. To address this issue, we demonstrate that coating the inner surface of atomic vapor cells with Al2O3, which has high resistance to alkali atoms, reduces rubidium consumption and extends the cell lifetime. In this study, we compared the lifetimes of two atomic vapor cells: a cubic cell with an inner diameter of 5.5 mm fabricated using the tip-off method, and the other cell coated on its inner surface with Al2O3 using the electron beam deposition method. The lifetime of the atomic vapor cell is determined by the rubidium density inside the cell, and the amount of rubidium is monitored through absorption spectroscopy measurement of the rubidium D1 transition.

  6. Hyeonjae Kim, Taek Jeong, Sangkyung Lee, Jeong Bin Nam, Sang Hyuk Hong, and Sin Hyuk Yim†, “Linear absorption spectroscopy in rubidium vapor cells: Applications in buffer gas measurement and lifetime estimation,” Korean Physical Society Spring Meeting, Apr. 2025, Daejeon, South Korea (Poster)
    Abstract

    Quantum sensors using atomic vapor cells are widely investigated in the defense sector due to their compact size, lightweight and low power consumption. The selection of alkali atom, buffer gas, and cell shape and material is determined by the specific application. To ensure long-term high sensitivity in atom-based sensors, optimizing buffer gas pressure and continuously monitoring the alkali atom density inside the cell are essential. In this study, we present two applications of linear absorption spectroscopy in rubidium vapor cells: measuring buffer gas pressure and estimating the cell lifetime. In both cases, the absorption spectrum of the rubidium D1 line is measured and compared with profiles derived from theoretical calculations. The buffer gas pressure in enriched 87Rb cells with N2, used in atomic magnetometers, is determined by peak linewidth broadening and frequency shifts caused by collisions between 87Rb and N2. The lifetime of a natural rubidium cell is evaluated by periodically monitoring the rubidium number density inside the cell over time.

Related co-authored works from my research at ADD can be found here.