Quantum entanglement and classical communication through a depolarising channel

Abstract

We analyse the role of entanglement for transmission of classical information through a memoryless depolarising channel. Using the isotropic character of this channel we prove analytically that the mutual information cannot be increased by encoding classical bits into entangled states of two qubits.

6 pages, 2 figures; contribution to special issue of JMO on the physics of quantum information; 2nd version: slight modifications and improved presentation