Date Added: Nov 2012
Information theory establishes the ultimate limits on performance for noisy communication systems. An accurate model of a physical communication device must include quantum effects, but typically including these 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. Here, the authors present an exactly solvable model of communications with a fully quantum electromagnetic field. This allows user to find explicit expressions for all the point-to-point capacities of a noisy quantum channel, with implications for quantum key distribution, and fiber optical communications. They also develop a theory of quantum communication networks by solving some rudimentary quantum networks for broadcasting and multiple accesses.