A note on the entangling properties of the C-SIGN and related quantum gates
Stephen Fenner · arXiv (Cornell University) · 2019
We show that any essential application of an $n$-qubit C-SIGN or related quantum gate $G$ leaves its qubits everywhere entangled, provided they were not everywhere entangled to begin with. By ``essential'' we mean roughly that $G$ is not equivalent to a similar gate of smaller arity (or to the identity) when applied to the same input state. By ``everywhere entangled'' we mean that the state is not separable with respect to any bipartition of the qubits.