Unification of quantum and classical correlations and quantumness measures

TL;DR

This paper provides a comprehensive framework for understanding and unifying quantum and classical correlations, including entanglement and discord, using relative entropy as a measure applicable to systems of arbitrary size.

Contribution

It introduces a unified approach to quantify all types of correlations in quantum states, including a new definition of dissonance, applicable to multipartite systems.

Findings

Unified measure of correlations using relative entropy

Introduction of dissonance as a component of quantum discord

Applicable to multipartite quantum systems of arbitrary dimensions

Abstract

We give a pedagogical introduction to quantum discord. We the discuss the problem of separation of total correlations in a given quantum state into entanglement, dissonance, and classical correlations using the concept of relative entropy as a distance measure of correlations. This allows us to put all correlations on an equal footing. Entanglement and dissonance, whose definition is introduced here, jointly belong to what is known as quantum discord. Our methods are completely applicable for multipartite systems of arbitrary dimensions. We finally show, using relative entropy, how different notions of quantum correlations are related to each other. This gives a single theory that incorporates all correlations, quantum, classical, etc.