Complementarity of quantum discord and classically accessible information

TL;DR

This paper explores the relationship between quantum discord and accessible information, revealing how their interplay explains the emergence of objective classical reality from quantum correlations and the role of the environment.

Contribution

It introduces a fundamental complementarity between quantum discord and accessible information, providing a new understanding of how classical objectivity arises in quantum systems.

Findings

Accessible information is maximized for the pointer observable.

Quantum discord and accessible information exhibit an anti-symmetry property.

Objectivity emerges as quantum information becomes encoded in the environment, inaccessible locally.

Abstract

The sum of the Holevo quantity (that bounds the capacity of quantum channels to transmit classical information about an observable) and the quantum discord (a measure of the quantumness of correlations of that observable) yields an observable-independent total given by the quantum mutual information. This split naturally delineates information about quantum systems accessible to observers -- information that is redundantly transmitted by the environment -- while showing that it is maximized for the quasi-classical pointer observable. Other observables are accessible only via correlations with the pointer observable. Further, we prove an anti-symmetry property relating accessible information and discord. It shows that information becomes objective -- accessible to many observers -- only as quantum information is relegated to correlations with the global environment, and, therefore, locally inaccessible. The resulting complementarity explains why, in a quantum Universe, we perceive objective classical reality while flagrantly quantum superpositions are out of reach.