title: 2 GHz clock quantum key distribution over 260 km of standard telecom fiber.
abstract: We report a demonstration of quantum key distribution (QKD) over a standard telecom fiber exceeding 50 dB in loss and 250 km in length. The differential phase shift QKD protocol was chosen and implemented with a 2 GHz system clock rate. By careful optimization of the 1 bit delayed Faraday-Michelson interferometer and the use of the superconducting single photon detector (SSPD), we achieved a quantum bit error rate below 2% when the fiber length was no more than 205 km, and of 3.45% for a 260 km fiber with 52.9 dB loss. We also improved the quantum efficiency of SSPD to obtain a high key rate for 50 km length.
authors.affiliation: Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Wang
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Jun-Fu
authors.initials: JF
authors.lastname: Guo
authors.forename: Zhen-Qiang
authors.initials: ZQ
authors.lastname: Yin
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Li
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zhou
authors.forename: Guang-Can
authors.initials: GC
authors.lastname: Guo
authors.forename: Zheng-Fu
authors.initials: ZF
authors.lastname: Han