Quantum discord and local demons

TL;DR

This paper explores different measures of quantum correlations, their relationships with thermodynamic engines, and introduces a simple test for zero discord, clarifying its connection to conditional entropy and local distinguishability.

Contribution

It introduces an easy method to test for zero quantum discord and clarifies its relation to conditional entropy and local distinguishability.

Findings

All three discord measures vanish simultaneously.

Zero discord can be tested simply and relates to Cerf-Adami conditional entropy.

Quantum discord does not correlate with local distinguishability.

Abstract

Quantum discord was proposed as a measure of the "quantumness" of correlations. There are at least three different discord-like quantities, two of which determine the difference between the efficiencies of a Szilard's engine under different sets of restrictions. The three discord measures vanish simulataneosly. We introduce an easy way to test for zero discord, relate it to the Cerf-Adami conditional entropy and show that there is no relation between the discord and the local disitnguishability.