# The no-cloning Theory There is no Unitary gate that when applied on an unknown qubit, outputs a clone of the qubit which is independent of it and leaving the original in tact. This means there is no $U$ s.t. $U(\ket\psi\ket 0)=\ket\psi\ket\psi$ where $\ket 0$ is a temporary qubit. ## Created 2026-07-19 18:03