Akio YOSHIZAWA^*, Ryosaku KAJI and Hidemi TSUCHIDA

National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba 305-8568, Japan

(Received April 2, 2003; Accepted June 16, 2003)

We demonstrate quantum key distribution based on Bennett's two-coherent-state protocol [Phys. Rev. Lett. 68 (1992) 3121]. The wavelength is set at 1550 nm for low-loss fiber transmission. A large reference pulse is used in order to enhance security of the protocol. The measured quantum bit-error rate is 2% for a fiber length of 10.5 km.

Key words: quantum key distribution, two-coherent-state protocol, large reference pulse, single-photon detector, optical fiber

^*E-mail address: yoshizawa-akio@aist.go.jp