Quantum discord for investigating quantum correlations without entanglement in solids

Abstract

Quantum systems exhibit diversified correlations which have no classical counterparts. It has been pointed out recently that quantum entanglement, the most well known measure of quantum correlations which plays essential roles in quantum information processing, cannot describe all the nonclassicality in the correlations. The quantum discord, which can describe quantum correlations in separable states, is subject to intensive theoretical studies. Herein, we experimentally investigate the quantum correlations of separable thermal states in solids. The sudden changes of the quantum discord are observed, which capture unambiguously the critical points associated with the behavior of the Hamiltonian. Our results display the potential applications of quantum correlations in studying the fundamental properties of quantum systems, such as quantum criticality of nonzero temperatures.