Finite-temperature quantum discordant criticality

TL;DR

This paper demonstrates that entropic quantum discord can reveal critical behavior at finite-temperature phase transitions, unlike entanglement, in integrable bosonic field theories.

Contribution

It shows that quantum discord, a broader quantum correlation measure than entanglement, can signal criticality at finite temperatures in quantum many-body systems.

Findings

Quantum discord decays algebraically with distance at criticality.

Entanglement negativity vanishes beyond nearest neighbors.

Discord connects smoothly to entanglement as temperature approaches zero.

Abstract

In quantum statistical mechanics, finite-temperature phase transitions are typically governed by classical field theories. In this context, the role of quantum correlations is unclear: recent contributions have shown how entanglement is typically very short-ranged, and thus uninformative about long-ranged critical correlations. In this work, we show the existence of finite-temperature phase transitions where a broader form of quantum correlation than entanglement, the entropic quantum discord, can display genuine signatures of critical behavior. We consider integrable bosonic field theories in both two- and three-dimensional lattices, and show how the two-mode Gaussian discord decays algebraically with the distance even in cases where the entanglement negativity vanishes beyond nearest-neighbor separations. Systematically approaching the zero-temperature limit allows us to connect discord to entanglement, drawing a generic picture of quantum correlations and critical behavior that naturally describes the transition between entangled and discordant quantum matter.