title: Faraday-Michelson system for quantum cryptography.
abstract: Quantum key distribution provides unconditional security for communication. Unfortunately, current experimental schemes are not suitable for long-distance fiber transmission because of phase drift or Rayleigh backscattering. In this Letter we present a unidirectional intrinsically stable scheme that is based on Michelson-Faraday interferometers, in which ordinary mirrors are replaced with 90 degree Faraday mirrors. With the scheme, a demonstration setup was built and excellent stability of interference fringe visibility was achieved over a fiber length of 175 km. Through a 125 km long commercial communication fiber cable between Beijing and Tianjin, the key exchange was performed with a quantum bit-error rate of less than 6%, which is to our knowledge the longest reported quantum key distribution experiment under field conditions.
authors.affiliation: Key Lab of Quantum Information, University of Science and Technology of China, Hefei Anhui 230026, China.
authors.forename: Xiao-Fan
authors.initials: XF
authors.lastname: Mo
authors.forename: Bing
authors.initials: B
authors.lastname: Zhu
authors.forename: Zheng-Fu
authors.initials: ZF
authors.lastname: Han
authors.forename: You-Zhen
authors.initials: YZ
authors.lastname: Gui
authors.forename: Guang-Can
authors.initials: GC
authors.lastname: Guo