Maximal Coherence and the Resource Theory of Purity
Dagmar Bruss, University of Duesseldorf
The resource theory of quantum coherence studies the off-diagonal elements of a density matrix in a distinguished basis, whereas the resource theory of purity studies all deviations from the maximally mixed state. We establish a direct connection between the two resource theories, by identifying purity as the maximal coherence, which is achievable by unitary operations. The states that saturate this maximum identify a universal family of maximally coherent mixed states.