Coherent-state discrimination via non-heralded probabilistic amplification

A scheme for the detection of low-intensity optical coherent signals was studied which uses a probabilistic amplifier operated in the non-heralded version, as the underlying non-linear operation to improve the detection efficiency. This approach allows us to improve the statistics by keeping track of all possible outcomes of the amplification stage (including failures). When compared with an optimized Kennedy receiver, the resulting discrimination success probability we obtain presents a gain up to ~1.85% and it approaches the Helstrom bound appreciably faster than the Dolinar receiver, when employed in an adaptive strategy. We also notice that the advantages obtained can be ultimately associated with the fact that, in the high gain limit, the non-heralded version of the probabilistic amplifier induces a partial dephasing which preserves quantum coherence among low energy eigenvectors while removing it elsewhere. A proposal to realize such transformation based on an optical cavity implementation is presented.