http://arxiv.org/abs/1203.4323 2-GHz clock quantum key distribution over 260 km of standard telecom fiber Shuang Wang, Wei Chen, Jun-Fu Guo, Zhen-Qiang Yin, Hong-Wei Li, Zheng Zhou, Guang-Can Guo, Zheng-Fu Han (Submitted on 20 Mar 2012) 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 2 GHz system clock rate. By careful optimization of the 1-bit delayed Faraday-Michelson interferometer and the use of the super-conducting 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 the 260 km length fiber with 52.9 dB loss. We also improved the quantum efficiency of SSPD to obtain high key rate for 50 km length. Subjects: Quantum Physics (quant-ph) Journal reference: Optics Letters, 37, 1008-1010 (2012) DOI: 10.1364/OL.37.001008 Cite as: arXiv:1203.4323v1 [quant-ph]