Experimental proposal for achieving superadditive communication capacitieswith a binary quantum alphabet - art. no. 032309

We demonstrate superadditivity in the communication capacity of a binary al phabet consisting of two nonorthogonal quantum states. For this scheme, col lective decoding is performed two transmissions at a time. This improves up on the previous schemes of Sasaki et al. [Phys. Rev. A 58, 146 (1998)] wher e superadditivity was not achieved until a decoding of three or more transm issions at a time. This places superadditivity within the regime of a near- term laboratory demonstration. We propose an experimental test based upon a n alphabet of low photon-number coherent states where the signal decoding i s done with atomic state measurements on a single atom in a high-finesse op tical cavity.