Local, nonlocal quantumness and information theoretic measures

TL;DR

This paper explores quantum correlations beyond entanglement, highlighting how measures like quantum discord detect both local and nonlocal quantumness, demonstrated through a generalized Werner state.

Contribution

It introduces the concept of local quantumness alongside nonlocal quantumness and shows how quantum discord captures both types in mixed states.

Findings

Quantum discord detects local and nonlocal quantumness.

Local superposition contributes to quantum correlations.

Generalized Werner state illustrates interplay of quantumness types.

Abstract

It has been suggested that there may exist quantum correlations that go beyond entanglement. The existence of such correlations can be revealed by quantum discord, but not by the conventional measure of entanglement. We argue that a state displays quantumness that can be of local and nonlocal origin. The physical quantity such as the quantum discord probes not only the nonlocal quantumness but also the local quantumness, such as the "local superposition". This can be a reason why such measures are non-zero when there is no entanglement. We consider a generalized version of the Werner state to demonstrate the interplay of local quantumness, nonlocal quantumness, and classical mixedness of a state.