No-Existence Of Generalize Diffusion

Abstract

We show that given two arbitrary states $\ket{\psi},\ket{\phi}$ it is impossible to compute the transformation: $ \ket{\psi}\ket{\phi} \mapsto \ket{\psi}\left( \mathbb{I} - 2 \ket{\psi}\bra{\psi} \right)\ket{\phi} $ The contradiction of the existence of such operator follows by showing that using it, two players can compute the disjoints of their sets in a single round and $O\left( \sqrt{n} \right)$ communication complexity, which shown by Braverman to be impossible \cite{Braverman}.