Communication complexity of channels in general probabilistic theories.

The communication complexity of a quantum channel is the minimal amount of classical communication required for classically simulating the process of preparation, transmission through the channel, and subsequent measurement of a quantum state. At present, only little is known about this quantity. In this Letter, we present a procedure for systematically evaluating the communication complexity of channels in any general probabilistic theory, in particular, quantum theory. The procedure is constructive and provides the most efficient classical protocols. We illustrate this procedure by evaluating the communication complexity of a quantum depolarizing channel with some finite sets of quantum states and measurements.