A Gruss inequality for n-positive linear maps

Abstract

Let $\mathscr{A}$ be a unital $C^*$-algebra and let $\Phi: \mathscr{A} \to {\mathbb B}({\mathscr H})$ be a unital $n$-positive linear map between $C^*$-algebras for some $n \geq 3$. We show that $$\|\Phi(AB)-\Phi(A)\Phi(B)\| \leq \Delta(A,||\cdot||)\,\Delta(B,||\cdot||)$$ for all operators $A, B \in \mathscr{A}$, where $\Delta(C,\|\cdot\|)$ denotes the operator norm distance of $C$ from the scalar operators.