Entangling gate
= Entangling gate
A <unitary gate> on two <quantum systems> is entangling if it maps at least one <pure state> that is a <product state> to an <entangled state>. The <controlled-NOT gate> qualifies because it maps $|+\rangle|0\rangle$ to a <Bell state>. A gate that merely exchanges the two systems need not be a <local unitary operation>, but cannot create <quantum entanglement> from a <product state>.