title: Quantum key distribution over 120 km using ultrahigh purity single-photon source and superconducting single-photon detectors.
abstract: Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 μm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks.
authors.affiliation: Devices &Materials Laboratory, Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Takemoto
authors.affiliation: Smart Energy Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nambu
authors.affiliation: Institute for Nano Quantum Information Electronics, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Miyazawa
authors.affiliation: National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Sakuma
authors.affiliation: Devices &Materials Laboratory, Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Smart Energy Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Yorozu
authors.affiliation: Institute for Nano Quantum Information Electronics, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.|Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan.
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Arakawa