REALISTIC PERFORMANCE OF THE MAXIMUM INFORMATION CHANNEL

For a fixed mean signal energy, the optimal narrow-band bosonic channe l is based on photodetection of a Bose-Einstein distribution of number states. A simple formula is obtained for the average error probabilit y per symbol of this channel when degraded by Gaussian noise and ineff icient detection. A general information bound is derived for narrow-ba nd channels degraded by Gaussian noise, which yields a lower bound for the average probability of error per bit. Results are applicable to a ll number-state channels in the limit of low noise and high efficiency .