Probabilistic purification of noisy coherent states

Abstract

(pp609-623) A basic feasible probabilistic purification of unknown noisy coherent states, outgoing from different state preparations with unknown mean number of thermal photons, is proposed. The scheme is based only on a linear-optical network with an avalanche photo-diode or heterodyne (homodyne) detection used to post-select a successful processing. The suggested probabilistic method can produce an output state with a lower noise than both quantum deterministic and classical probabilistic purification method. The purification applied in the state preparation can increase classical capacity of communication and security of quantum key distribution.