Quantum discord in nuclear magnetic resonance systems at room temperature

TL;DR

This paper reviews methods to quantify quantum correlations in room-temperature NMR systems, demonstrating the dynamics of quantum discord under decoherence and introducing an observable witness for quantumness of correlations.

Contribution

It introduces a formal method for obtaining quantum discord in NMR systems and experimentally demonstrates its dynamics under thermal environments, also presenting the first implementation of a quantumness witness.

Findings

Quantum discord exhibits sudden change behavior under thermal decoherence.

The introduced witness effectively detects quantumness of correlations in NMR.

Quantum discord dynamics are stronger than previously thought in thermal environments.

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.