From quantum cloning to quantum key distribution with continuous variables: a review (Invited)

Quantum information processing with continuous variables is a paradigm that has attracted a growing interest over the past years, partly as a consequence of the prospects for high-rate quantum communication systems based on standard optical telecommunication components. In this overview article, we introduce the concept of quantum continuous variables in optics and then turn to the fundamental impossibility of cloning continuous-variable light states, a result that lies at the heart of quantum key distribution. Then we present state-of-the-art quantum key distribution systems relying on continuous variables, focusing mainly on the protocols using Gaussian-modulated coherent light states and emphasizing the current experimental demonstration of these systems. Finally, we briefly review recent security proofs of these cryptographic protocols. (c) 2007 Optical Society of America.