Quantum data processing and error correction
Benjamin W. Schumacher, Michael A. Nielsen · Physical Review A · 1996
This paper investigates properties of noisy quantum information channels. We define a quantity called coherent information, which measures the amount of quantum information conveyed in the noisy channel. This quantity can never be increased by quantum information processing, and it yields a simple necessary and sufficient condition for the existence of perfect quantum error correction. \textcopyright{} 1996 The American Physical Society.