Practical quantum cryptography

We report our recent results in development of the secure fiber-optics communication system based upon quantum key distribution (QKD). Emphasize is made on the limitation imposed by the state-of-the-art components crucial for the system performance. We discuss the problem of the interferometer design and highlight the possible security loopholes known. Together with single photon counting performance it places the main restriction on the distance range and the secure key rate of the QKD system based upon the weak coherent pulses. Finally we describe the result of the first test of the system using single photons produced by non-degenerate parametric down-conversion as a source.