Long-distance quantum key distribution over telecom fiber.

摘要

We present two long-distance quantum key distribution (QKD) systems over telecom fiber. The first one is the Sagnac QKD system implementing standard BB84 protocol. Novel polarization-insensitive phase modulators are used to simplify the conventional architecture. We are able to achieve a stable quantum bit error rate of 4-6.5% over 40km fiber loop over one hour without recalibration. The second one is the fiber-based QKD system using Gaussian-modulated coherent states. We have overcome the challenges imposed by the requirements for high detector sensitivity, long-term stability, and low signal crosstalk. Our GMCS QKD system is the first practical fiber-based one-way demonstration and is able to achieve a sifted secret key rate of 15.5 kbits/s over a transmission distance of 5km fiber.; Experimental QKD is still in its infancy. The results presented in this thesis represent a significant step forward towards the practical QKD over conventional fiber networks.