  The most natural way to describe an information-carrying system containing a
specific noise is an additive white Gaussian-noise (AWGN) channel. In bosonic
quantum systems (especially the Gaussian case), although the classical
information capacity for a phase-insensitive and thermal-noise channel is
additive based on a proof of the minimum output entropy conjecture, several
open questions remain. By generalizing the Gaussian noise model from thermal
noise to general Gaussian noise, we rigorously revisit and calculate these
strong upper bounds on the information capacity for single-mode with general
Gaussian-noise channels. In this study, we use the quantum entropy power
inequality (QEPI) approach. This framework gives a new formula for finding
upper bounds on the information capacity of bosonic Gaussian channels.
