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° 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.
© 2005 Optical Society of America
(270.0270) Quantum optics : Quantum optics
Xiao-Fan Mo, Bing Zhu, Zheng-Fu Han, You-Zhen Gui, and Guang-Can Guo, "Faraday-Michelson system for quantum cryptography," Opt. Lett. 30, 2632-2634 (2005)