On the quantumness of correlations in nuclear magnetic resonance

TL;DR

This paper explores the quantum nature of correlations in NMR systems, demonstrating non-classical correlations beyond entanglement, and shows how these can simulate quantum dynamics using nuclear spins.

Contribution

It provides experimental evidence of quantum correlations like discord in NMR, beyond entanglement, and demonstrates their use in simulating quantum interferometric processes.

Findings

Quantum correlations in NMR can be non-classical without entanglement.

Separable states exhibit quantum discord, indicating quantumness.

NMR can simulate quantum interferometry using non-entangled correlations.

Abstract

Nuclear Magnetic Resonance (NMR) was successfully employed to test several protocols and ideas in Quantum Information Science. In most of these implementations the existence of entanglement was ruled out. This fact introduced concerns and questions about the quantum nature of such bench tests. In this article we address some issues related to the non-classical aspects of NMR systems. We discuss some experiments where the quantum aspects of this system are supported by quantum correlations of separable states. Such quantumness, beyond the entanglement-separability paradigm, is revealed via a departure between the quantum and the classical versions of information theory. In this scenario, the concept of quantum discord seems to play an important role. We also present an experimental implementation of an analogous of the single-photon Mach-Zehnder interferometer employing two nuclear spins to encode the interferometric paths. This experiment illustrate how non-classical correlations of separable states may be used to simulate quantum dynamics. The results obtained are completely equivalent to the optical scenario, where entanglement (between two field modes) may be present.