Reduction of Quantum Entropy by Reversible Extraction of Classical Information
We inquire under what conditions some of the information in a quantum signal source, namely a set of pure states ψa emitted with probabilities p a, can be extracted in classical form by a measurement leaving the quantum system with less entropy than it had before, but retaining the ability to regenerate the source state exactly from the classical measurement result and the after-measurement state of the quantum system. We show that this can be done if and only if the source states ψa fall into two or more mutually orthogonal subsets.
Bennett, Charles; Brassard, Gilles; Jozsa, Richard; Mayers, Dominic; Peres, Asher; Schumacher, Benjamin; and Wootters, William, "Reduction of Quantum Entropy by Reversible Extraction of Classical Information" (1994). Journal of Modern Optics 41(12): 2307-2314. Faculty Publications. Paper 263.
Journal of Modern Optics