EXPERIMENTAL SYSTEM FOR QUANTUM CRYPTOGRAPHY BASED ON 2 NONORTHOGONALPHOTON POLARIZATION STATES

Quantum cryptography allows the establishing of a highly confidential sequence of random bits between two parties who share no secret inform ation in advance. Its security is guaranteed by the basic laws of quan tum mechanics rather than mathematical difficulty. An experimental sys tem based on a novel protocol for quantum cryptography using only two nonorthogonal photon polarization states is implemented. The photon so urces are two semiconductor laser diodes operated at 680 nm, their lig ht pulses which are heavily attenuated to far below one photon per pul se are employed to encode the key. Gated single photon detection techn ique is used to minimize the dark count effect of the photon multiplie r tube. Key establishing rate of 40 b/s and error rate of 2.1% are obt ained. Compared with other systems, our system has the simplest experi mental setup.