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.
@article{arxiv.1910.01175,
title = {A note on the entangling properties of the C-SIGN and related quantum gates},
author = {Stephen A. Fenner},
journal= {arXiv preprint arXiv:1910.01175},
year = {2019}
}