Quantum correlation beyond entanglement: Holographic discord and multipartite generalizations

TL;DR

This paper explores quantum correlations beyond entanglement, introducing holographic duals of quantum discord and multipartite measures, revealing new insights into quantum correlations in holographic and black hole systems.

Contribution

It constructs gravity duals for quantum discord and classical correlation, introduces reflected discord, and proposes multipartite correlation measures, expanding the understanding of quantum correlations in holography.

Findings

Discord exceeds entanglement in holographic systems and Haar random states.

Reflected discord remains effective outside the holographic regime.

Multipartite correlation measures are UV-finite and reduce to bipartite measures.

Abstract

While entanglement is a cornerstone of quantum theory and holography, quantum correlations arising from superposition, such as quantum discord, offer a broader perspective that has remained largely unexplored in holography. We construct gravity duals of quantum discord and classical correlation. In both holographic systems and Haar random states, discord exceeds entanglement, revealing an additional quantum correlation linked to the Markov gap and non-distillable entanglement, suggesting holographic states are intrinsically non-bipartite. In black hole setups, discord can increase despite decoherence and persists beyond the sudden death of distillable entanglement. Motivated by the holographic formula, we define reflected discord -- an optimization-free boundary quantity based on reflected entropy -- which remains effective even outside the holographic regime. We also propose several multipartite generalizations of correlation measures. It includes holography-inspired correlations based on multi-entropy, which are shown to be UV-finite and reduce to bipartite measures in the bipartite limit. These results provide new tools for quantifying quantum correlations beyond entanglement in strongly coupled many-body systems and offer a novel approach to multipartite correlation measures.