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.
© 2012 Optical Society of America
Original Manuscript: November 21, 2011
Revised Manuscript: February 2, 2012
Manuscript Accepted: February 2, 2012
Published: March 7, 2012
Shuang Wang, Wei Chen, Jun-Fu Guo, Zhen-Qiang Yin, Hong-Wei Li, Zheng Zhou, Guang-Can Guo, and Zheng-Fu Han, "2 GHz clock quantum key distribution over 260 km of standard telecom fiber," Opt. Lett. 37, 1008-1010 (2012)