Quantum cloning and key distribution with continuous variables

Quantum information with continuous variables is a paradigm which has attracted a growing interest lately, as a consequence of the prospect for high-rate quantum communication systems that may result from the use of standard telecommunication components. After introducing the concept of quantum continuous variables in optics, we turn to the fundamental impossibility of cloning continuous-variable light states, a result which is at the heart of quantum key distribution. We then present state-of-the-art quantum key distribution systems relying on continuous variables, with a special emphasis on the experimental demonstration of protocols using coherent light states. Finally, we briefly review the recent security proofs of these cryptographic protocols.