Differential phase shift-quantum key distribution

Quantum-key distribution has been studied as an ultimate method for secure communications, and now it is emerging as a technology that can be deployed in real fiber networks. Here, we present our QKD experiments based on the differential- phase-shift QKD protocol. A DPSQKD system has a simple configuration that is easy to implement with conventional optical communication components, and it is suitable for a high-clock rate system. Moreover, although the DPS-QKD system is implemented with an attenuated laser source, it is inherently secure against strong eavesdropping attacks called photon number-splitting attacks, which pose a serious threat to conventional QKD systems with attenuated laser sources. We also describe three types of single-photon detectors that are suitable for high-speed, long-distance QKD: an up-conversion detector, a superconducting single-photon detector, and a sinusoidally gated InGaAs avalanche photodiode. We present our recordsetting QKD experiments that employed those detectors.