bibkey: schumachernielsen1996quantum authors: Benjamin Schumacher, M. A. Nielsen year: 1996 title: Quantum data processing and error correction doi: null url: https://arxiv.org/pdf/quant-ph/9604022v1 claim: “Coherent information is the output entropy minus the joint reference-output entropy for a supplied quantum process.” strata_touched: [] license: citation-only triage: anchor

Coherent information has a quantum carrier

The primary preprint, version 1, Section 4, p. 9, equation (3), defines coherent information as $S({\rho }_{Q^{\prime }})-S({\rho }_{R{Q}^{\prime }})$. Section 3, p. 8, specifies von Neumann entropy with logarithms base two. The reference purifies the supplied input and the channel acts on the input system.

The five-state comparison, Definition 22.3, consumes this definition only to distinguish its type from occupation covariance, a conditional table determinant and an observable mixed coefficient. No quantum process, non-diagonal phase or access to a quantum reference follows from a classical five-state law.