How to quantify coherence: Distinguishing speakable and unspeakable notions
Iman Marvian, Robert W. Spekkens · Physical Review A · 2016
A general framework for studying quantum coherence as a resource is presented, where coherence is classified as ``speakable'' or ``unspeakable'' based on whether or not the identity of the subspaces that appear in the coherent superposition is significant.