Quantum key distribution (QKD) systems have proven their theoretically unconditional security by quantum mechanics, but the scalability and cost barriers limit the rapid growth of the QKD system industry. The integration of QKD systems on chips has enabled their widespread adoption in secure quantum communication technologies, but the optimized platforms and designs are still being studied. Herein, we fabricated monolithic quantum photonic circuits for the BB84 QKD protocol using thin-film lithium niobate (TFLN), which enables flexible design in organizing both active and passive elements on one chip based on its superior material properties. The proposed circuit design for both transmitter and receiver parts are identical, which facilitates stable operation and mass production. Using our device, we demonstrated QKD over a field-deployed quantum channel, and its performance is comparable to state-of-the-art. This result proved the potential of TFLN for quantum communication technology.
This work was supported by the National Research Foundation of Korea (NRF) (Grant Nos. 2021M1A2A2043892 and 2022M3K4A1097119), the Institute for Information and Communications Technology Promotion (IITP) (Grant Nos. 2020-0-00947, 2020-0-00890, and RS-2023-00222863), the National Research Council of Science and Technology (NST) (Grant No. CAP21034-000), the Commercialization Promotion Agency for R&D Outcomes (COMPA) (Grant No. 2022SCPO_B_0210), the KREONET Advanced Research Program Grant from KISTI, and the KIST research program (Grant Nos. 2E33541 and 2E33571). We acknowledge Hyun-Joon Shin, a member of the Center for Bionics, Korea Institute of Science and Technology, for the provision of experimental equipment.
