Abstract

We give a short introduction in Quantum Key Distribution (QKD) and review the realised systems. The experimental approaches can be subdivided in phase or polarisation based schemes, entangled photon pairs or faint laser based schemes and optical fibre or free space schemes. We present in more detail two optical fibre phase coding setups realised by our group. First a faint laser scheme, commonly called "plug&play", since it is auto-aligned [1]. Secondly a setup based on energy-time entangled photons [2]. Comparing advantages and disadvantages of the two systems in the light of technical maturity and security, we find that the faint laser system has still the lead. Indeed, on the one hand, a first user-friendly prototype based on the plug&play system is available, on the other hand entangled photon QKD has not yet left the lab. Moreover, we argue that, despite multi-photon pulses, faint laser QKD is perfectly secure against attacks of "realistic" eavesdroppers. [3]. However, at the time, fibre based QKD in the 1550 nm telecom window is limited by the noise of the photon counters to about 50 km.

© 2001 EPS