1303.4939 (Joachim Schäfer et al.)

Equivalence relations for the classical capacity of single-mode Gaussian
quantum channels    [PDF]

Joachim Schäfer, Evgueni Karpov, Raúl García-Patrón, Oleg V. Pilyavets, Nicolas J. Cerf

We prove the equivalence of an arbitrary single-mode Gaussian quantum channel and a newly defined fiducial channel preceded by a phase shift and followed by a Gaussian unitary operation. This equivalence implies that the classical capacity and Gaussian classical capacity of any single-mode Gaussian channel can be calculated based on this fiducial channel, which is furthermore simply realizable with a beam-splitter, two identical single-mode squeezers, and a two-mode squeezer. In a large domain of parameters, we also provide an analytical expression for the Gaussian classical capacity, exploiting its additivity, and prove that the classical capacity does not exceed it by more than 1/\ln2 bits.

View original: http://arxiv.org/abs/1303.4939