Intrinsic-Stabilization Uni-Directional Quantum Key Distribution Between   Beijing and Tianjin
  Quantum key distribution provides unconditional security for communication. Unfortunately, current experiment schemes are not suitable for long-distance fiber transmission because of instability or backscattering. We present a uni-directional intrinsic-stabilization scheme that is based on Michelson-Faraday interferometers, in which reflectors are replaced with 90 degree Faraday mirrors. With the scheme, key exchange from Beijing to Tianjin over 125 kilometers with an average error rate is below 6% has been achieved and its limited distance exceeds 150 kilometers. Experimental result shows the system is insensitive to environment and can run over day and night without any break even in the noise workshop. 
Xiao-fan Mo, Bing Zhu, Zheng-fu Han, You-zhen Gui, Guang-can Guo