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.

arXiv:1602.08049Physical Review ANov 18, 2016334 citations

Speakable and unspeakable after John Bell

Ian Colin Percival

`Philosophy' was speakable for John Bell but is not for many physicists. The border between philosophy and physics is here illustrated through Brownian motion and Bell experiments. `Measurement', however, was unspeakable for Bell. His insistence that the physics of quantum measurement should not be confined to the laboratory and that physics is concerned with the big world outside leads us to examples from zoology, meteorology and cosmology.

arXiv:quant-ph/0012021Dec 5, 20001 citation