2-GHz clock quantum key distribution over 260 km of standard telecom fiber

摘要

We report a demonstration of quantum key distribution (QKD) over a standardtelecom fiber exceeding 50 dB in loss and 250 km in length. The differentialphase shift QKD protocol was chosen and implemented with 2 GHz system clockrate. By careful optimization of the 1-bit delayed Faraday-Michelsoninterferometer and the use of the super-conducting single photon detector(SSPD), we achieved a quantum bit error rate below 2% when the fiber length wasno more than 205 km, and of 3.45% for the 260 km length fiber with 52.9 dBloss. We also improved the quantum efficiency of SSPD to obtain high key ratefor 50 km length.