Quantum Discord for Investigating Quantum Correlations without Entanglement in Solids

TL;DR

This paper experimentally investigates quantum discord in separable thermal states, revealing sudden changes that relate to quantum criticality and highlighting quantum correlations beyond entanglement.

Contribution

It demonstrates the experimental observation of quantum discord dynamics in thermal states, linking quantum correlations to quantum critical phenomena at finite temperatures.

Findings

Quantum discord exhibits sudden changes near critical points.

Quantum correlations exist without entanglement in thermal states.

Quantum discord can indicate quantum criticality at non-zero temperature.

Abstract

Quantum systems unfold diversified correlations which have no classical counterparts. These quantum correlations have various different facets. Quantum entanglement, as the most well known measure of quantum correlations, plays essential roles in quantum information processing. However, it has recently been pointed out that quantum entanglement cannot describe all the nonclassicality in the correlations. Thus the study of quantum correlations in separable states attracts widely attentions. Herein, we experimentally investigate the quantum correlations of separable thermal states in terms of quantum discord. The sudden change of quantum discord is observed, which captures ambiguously the critical point associated with the behavior of Hamiltonian. Our results display the potential applications of quantum correlations in studying the fundamental properties of quantum system, such as quantum criticality of non-zero temperature.