Real-field Hong–Ou–Mandel interference of indistinguishable coherent photons via long optical injection-locking over 50 km fiber Seoyeon Yang, Danbi Kim, Hansol Jeong, Han Seb Moon Optics Express, 2025 Measurement-device-independent quantum key distribution (MDI-QKD) has garnered significant attention for enabling security-loophole-free quantum communication. Successful MDI-QKD protocols rely on performing a two-photon Bell-state measurement at an intermediate node, where achieving a high-visibility Hong–Ou–Mandel (HOM) interference pattern between two independent coherent photons is crucial. In this study, we present an approach for developing indistinguishable coherent photon sources over 50 km of optical fiber under real-world conditions. We introduce the long optical injection-locking (long-OIL) technique, which enables frequency locking between two long-distance coherent photons separated by distances exceeding the coherence length of the master laser. Utilizing the long-OIL technique, we achieved time-resolved HOM interference with a visibility of 48(2)%, which is close to the theoretical limits of 50% for two independent continuous-wave coherent photons. Our results indicate that the long-OIL platform is a promising solution for MDI-QKD with repeaterless secret-key capacity.
Active offset-frequency control of optical frequency comb via sum-frequency mixing of passively mode-locked laser and continuous-wave laser Hansol Jeong, Deok Woo Kim, Hyunhak Kim, Myoungsik Cha, Han Seb Moon Scientific Reports, 2024 We propose a method for actively controlling the frequency of an optical frequency comb (OFC) using sum-frequency generation (SFG) with a nonlinear crystal. For the first time, OFC generation was experimentally demonstrated via sum-frequency mixing of a narrowband continuous wave (CW) laser and a passively mode-locked fiber laser. By adjusting the optical frequency of the CW laser, we successfully controlled the offset-frequency of the SFG-OFC, which was mapped from the OFC of the pulse pump laser. Furthermore, by comparing the spectral widths of the SFG-OFC modes generated from two CW lasers with different spectral widths, we confirmed that the spectral characteristics of the SFG-OFC modes depended on the spectral features of the CW laser.
Collective biphoton temporal waveform of photon-pair generated from Doppler-broadened atomic ensemble Heewoo Kim, Hansol Jeong, Han Seb Moon Quantum Science and Technology, 2024 Photonic quantum states generated from atomic ensembles will play important roles in future quantum networks and long-distance quantum communication because their advantages, such as universal identity and narrow spectral bandwidth, are essential for quantum nodes and quantum repeaters based on atomic ensembles. In this study, we report the collectively coherent superposition of biphoton wavefunction emitted from different velocity classes in a Doppler-broadened cascade-type atomic ensemble. We experimentally demonstrate that the three times difference of temporal width of both biphoton temporal waveforms varies dependent on the wavelengths of the signal and idler photons from both 6S1/2–6P3/2–6D5/2 and –8S1/2 transitions of 133Cs, corresponding to the idler and signal wavelengths of 852 nm–917 nm and 852 nm–795 nm, respectively. Our results help understand the characteristics of biphoton sources from a warm atomic ensemble and can be applied to long-distance quantum networks and practical quantum repeaters based on atom–photon interactions.
High-Performance Telecom-Wavelength Biphoton Source from a Hot Atomic Vapor Cell Hansol Jeong, Heewoo Kim, Han Seb Moon Advanced Quantum Technologies, 2024 Telecom‐band quantum light sources are critical to the development of long‐distance quantum communication technologies. A high‐performance telecom‐wavelength biphoton source from a hot 87Rb atomic vapor cell is reported. Time‐correlated biphotons are generated from the cascade‐type 5S1/2–5P3/2–4D5/2 transition of 87Rb via a spontaneous four‐wave mixing process. The maximum value of biphoton cross‐correlation to be 44(3) is achieved, under the condition of a high optical depth of 112(3), including two‐photon absorption, with a spectral width of approximately 300 MHz. The coincidence count rate of biphoton is estimated to be of the order of 38 000 cps mW−1. It is believed that the telecom‐wavelength biphoton source from an atomic vapor cell can be applied in long‐distance quantum networks and practical quantum repeaters based on atom–photon interactions.
Doppler-broadened four-wave mixing under double-resonance optical pumping in the 5S1/2-5P3/2-4D5/2 transition of warm 87Rb atoms Hansol Jeong, Heewoo Kim, Jinhyuk Bae, Jiho Park, Han Seb Moon Optics Express, 2021 We investigate stimulated four-wave mixing (FWM) in the 5S1/2–5P3/2–4D5/2 transition of warm 87Rb atoms. Here, the telecommunication wavelength (1529 nm) of the 5P3/2–4D5/2 transition is nearly twice that of the 5S1/2–5P3/2 transition (780 nm). The observed FWM signals of the 5P3/2–4D5/2 transition indicate that the FWM process is significantly influenced by the two-photon Doppler broadening due to the wavelength difference between both transitions and the double-resonance optical pumping (DROP) effect due to two-step excitation. We elucidate the suppression of the FWM process due to the DROP effect using a simple six-level atomic model.
RECENT SCHOLAR PUBLICATIONS
Real-field Hong–Ou–Mandel interference of indistinguishable coherent photons via long optical injection-locking over 50 km fiber S Yang, D Kim, H Jeong, HS Moon Optics Express 33 (13), 27800-27808 , 2025 2025
Biphoton Waveforms of Photon Pair from Velocity‐Selective Atoms in a Doppler‐Broadened Atomic Ensemble H Jeong, H Kim, D Kim, HS Moon Advanced Photonics Research 6 (6), 2400147 , 2025 2025
Highly Efficient Biphoton Generation from Thin Dense Atomic Ensemble H Kim, H Jeong, HS Moon Advanced Photonics Research 6 (4), 2400214 , 2025 2025 Citations: 2
Collective biphoton temporal waveform of photon-pair generated from Doppler-broadened atomic ensemble H Kim, H Jeong, HS Moon Quantum Science and Technology 9 (4), 045006 , 2024 2024 Citations: 5
Active offset-frequency control of optical frequency comb via sum-frequency mixing of passively mode-locked laser and continuous-wave laser H Jeong, DW Kim, H Kim, M Cha, HS Moon Scientific Reports 14 (1), 13485 , 2024 2024 Citations: 3
High‐Performance Telecom‐Wavelength Biphoton Source from a Hot Atomic Vapor Cell H Jeong, H Kim, HS Moon Advanced Quantum Technologies 7 (1), 2300108 , 2024 2024 Citations: 6
Doppler-broadened four-wave mixing under double-resonance optical pumping in the 5S 1/2 –5P 3/2 –4D 5/2 transition of warm 87 Rb atoms H Jeong, H Kim, J Bae, J Park, HS Moon Optics Express 29 (26), 42384-42393 , 2021 2021 Citations: 4
MOST CITED SCHOLAR PUBLICATIONS
High‐Performance Telecom‐Wavelength Biphoton Source from a Hot Atomic Vapor Cell H Jeong, H Kim, HS Moon Advanced Quantum Technologies 7 (1), 2300108 , 2024 2024 Citations: 6
Collective biphoton temporal waveform of photon-pair generated from Doppler-broadened atomic ensemble H Kim, H Jeong, HS Moon Quantum Science and Technology 9 (4), 045006 , 2024 2024 Citations: 5
Doppler-broadened four-wave mixing under double-resonance optical pumping in the 5S 1/2 –5P 3/2 –4D 5/2 transition of warm 87 Rb atoms H Jeong, H Kim, J Bae, J Park, HS Moon Optics Express 29 (26), 42384-42393 , 2021 2021 Citations: 4
Active offset-frequency control of optical frequency comb via sum-frequency mixing of passively mode-locked laser and continuous-wave laser H Jeong, DW Kim, H Kim, M Cha, HS Moon Scientific Reports 14 (1), 13485 , 2024 2024 Citations: 3
Highly Efficient Biphoton Generation from Thin Dense Atomic Ensemble H Kim, H Jeong, HS Moon Advanced Photonics Research 6 (4), 2400214 , 2025 2025 Citations: 2
Real-field Hong–Ou–Mandel interference of indistinguishable coherent photons via long optical injection-locking over 50 km fiber S Yang, D Kim, H Jeong, HS Moon Optics Express 33 (13), 27800-27808 , 2025 2025
Biphoton Waveforms of Photon Pair from Velocity‐Selective Atoms in a Doppler‐Broadened Atomic Ensemble H Jeong, H Kim, D Kim, HS Moon Advanced Photonics Research 6 (6), 2400147 , 2025 2025
