  We present a quantum key distribution system with a 2.5 GHz repetition rate
using a three-state time-bin protocol combined with a one-decoy approach.
Taking advantage of superconducting single-photon detectors optimized for
quantum key distribution and ultra low-loss fiber, we can distribute secret
keys at a maximum distance of 421 km and obtain secret key rates of 6.5 bps
over 405 km.
