Quantum discord in nuclear magnetic resonance systems at room temperature

Abstract

We review the theoretical and the experimental aspects regarding the quantification and identification of quantum correlations in liquid-state nuclear magnetic resonance (NMR) systems at room temperature. We start by introducing a formal method to obtain the quantum discord and its classical counterpart in systems described by a deviation matrix. Next, we apply such a method to experimentally demonstrate that the peculiar dynamics, with a sudden change behaviour, of quantum discord under decoherence, theoretically predicted only for phase-noise channels, is also present even under the effect of a thermal environment. This result shows that such a phenomena are much stronger than we could think, at principle. Walking through a different path, we discuss an observable witness for the quantumness of correlations in two-qubit systems and present the first experimental implementation of such a quantity in a NMR setup. Such a witness could be very useful in situations were the knowledge of the nature of correlations (in contrast of how much correlations) presented in a given state is enough.