Probabilistic amplification and cloning of phase-covariant coherent states

A fundamental characteristic of quantum mechanics is that amplification of a quantum state is an operation that is inevitably linked to the addition of noise [1]. As a direct consequence, it is in general impossible to generate perfect copies of an unknown quantum state. This is known as the famous no-cloning theorem [2].

However, it was shown recently, that noiseless amplification is possible by releasing the constraint of determinism [3–6], hence allowing the amplifier to generate an output only occasionally. In this probabilistic regime the output states are heralded based on some measurements that indicate successful amplification.