  The achievable rate of information transfer in optical communications is
determined by the physical properties of the communication channel, such as the
intrinsic channel noise. Bosonic phase-noise channels, a class of non-Gaussian
channels, have emerged as a relevant noise model in quantum information and
optical communication. However, while the fundamental limits for communication
over Gaussian channels have been extensively studied, the properties of
communication over Bosonic phase-noise channels are not well understood. Here
we propose and demonstrate experimentally the concept of optimized
communication strategies for communication over phase-noise channels to enhance
information transfer beyond what is possible with conventional methods of
modulation and detection. Two key ingredients are generalized constellations of
coherent states that interpolate between standard on-off keying and binary
phase shift keying formats, and non-Gaussian measurements based on photon
number resolving detection of the coherently displaced signal. For a given
power constraint and channel noise strength, these novel strategies rely on
joint optimization of the input alphabet and the measurement to provide
enhanced communication capability over a non-Gaussian channel characterized in
terms of the error rate as well as mutual information.
