  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.

Quantum Physics