Entanglement, discord and the power of quantum computation

TL;DR

This paper demonstrates that creating entanglement is essential for bipartite quantum gates, highlighting the role of quantum discord as an indicator of the limitations of LOCC implementations even without entanglement.

Contribution

It reveals that shared entanglement is necessary for certain quantum gate executions and identifies quantum discord as a key indicator of LOCC failure.

Findings

Shared entanglement is required for bipartite gate execution.

Quantum discord signals the failure of LOCC implementations.

Entanglement creation is necessary even when no entanglement results from the gate.

Abstract

We show that the ability to create entanglement is necessary for execution of bipartite quantum gates even when they are applied to unentangled states and create no entanglement. Starting with a simple example we demonstrate that to execute such a gate bi-locally the local operations and classical communications (LOCC) should be supplemented by shared entanglement. Our results point to the changes in quantum discord, which is a measure of quantumness of correlations even in the absence of entanglement, as the indicator of failure of a LOCC implementation of the gates.