Mutual information of optical communication in phase conjugating Gaussian channels. (arXiv:1801.03811v1 [quant-ph])

In all practical communication channels, the code word consist of Gaussian
states and the measurement strategy is often a Gaussian detector such as
homodyning or heterodyning. In this paper we investigate the communication
performance using a phase conjugated alphabet and joint Gaussian detection in
an phase-insensitive amplifying channel. We find that a communication scheme
consisting of a phase conjugating alphabet of coherent states and a joint
detection strategy, significantly outperforms a standard coherent state
strategy based in individual detection. Moreover, we show that the performance
can be further enhanced by using entanglement and that the performance is
completely independent on the gain of the phase-insensitively amplifying

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