Abstract
We address binary phase-shift-keyed communication channels based on Gaussian states and prove that squeezing improves state discrimination at fixed energy of the channel, also in the presence of phase diffusion. We then assess performances of homodyne detection against the ultimate quantum limits to discrimination, and show that homodyning achieves optimality in large noise regime. Finally, we consider noise in the preparation of the seed signal (before phase encoding) and show that also in this case squeezing may improve state discrimination in realistic conditions.
Highlights
Quantum hypothesis testing addresses the discrimination of nonorthogonal preparations of a quantum system
We have investigated the role of squeezing in phase-shift keying (PSK) quantum communication and shown that it represents a resource in the presence of phase diffusion and losses
We focused on binary encoding onto displaced squeezed states (DSSs) with coherent amplitudes having opposite phases
Summary
Quantum hypothesis testing addresses the discrimination of nonorthogonal preparations of a quantum system. The search for optimal receivers, i.e., detection schemes and strategies able to discriminate between the two coherent states reaching the corresponding Helstrom bound, has eventually led to the so-called Kennedy receiver [21] and Dolinar receiver [22] These are both based on the interference of the signals with a known reference, and on on-off photodetectors, able to check the presence or absence of light. Coherent-state encoding and homodyne detection have been used to establish ground-satellite links [11], whereas squeezed states have been suggested to improve quantum key distribution [26] Motivated by these results, here we consider a binary communication channel in which the seed |ψ0 is a squeezed vacuum |r = S(r)|0 where S(r) =. We analyze the effect of losses, resulting in a reduced purity of the seed state
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