Experimental detection of non-classical correlations in mixed state quantum computation

TL;DR

This paper reports an experiment detecting non-classical correlations, specifically quantum discord, in a highly mixed state within a liquid state NMR quantum processor, demonstrating quantum correlations beyond entanglement.

Contribution

The experiment is the first to detect quantum discord in a mixed state during DQC1 quantum computation using NMR technology.

Findings

Quantum discord was successfully observed in the experiment.

Non-classical correlations exist even without entanglement.

The results support the role of quantum discord in quantum computational advantage.

Abstract

We report on an experiment to detect non-classical correlations in a highly mixed state. The correlations are characterized by the quantum discord and are observed using four qubits in a liquid state nuclear magnetic resonance quantum information processor. The state analyzed is the output of a DQC1 computation, whose input is a single quantum bit accompanied by n maximally mixed qubits. This model of computation outperforms the best known classical algorithms, and although it contains vanishing entanglement it is known to have quantum correlations characterized by the quantum discord. This experiment detects non-vanishing quantum discord, ensuring the existence of non-classical correlations as measured by the quantum discord.