Dr. Graeme Smith, IBM TJ Watson Research Center
Abstract
An accurate model of a physical communication device must include quantum effects, but typically this makes the theory intractable. As a result communication capacities are not known, even for transmission
between two users connected by an electromagnetic waveguide subject to gaussian noise. We present an exactly solvable model of noisy communications with a fully quantum electromagnetic field. This allows us to find explicit expressions for all point-to-point capacities. We also develop a theory of quantum networks by solving some rudimentary networks such as broadcasting and multiple access. When possible, we compare the predictions of our new model with those of the orthodox quantum gaussian model and in all cases we find capacities in agreement to within a few bits. Thus, in the limit of high signal to noise ratios our simple model captures the relevant physics of gaussian models while remaining amenable to detailed analysis.
Joint work with John Smolin.