Maximally nonlocal subspaces

Abstract

A nonlocal subspace $\mathcal{H}_{NS}$ is a subspace within the Hilbert space $\mathcal{H}_n$ of a multi-particle system such that every state $\psi \in \mathcal{H}_{NS}$ violates a given Bell inequality $\mathcal{B}$. Subspace $\mathcal{H}_{NS}$ is maximally nonlocal if each such state $\psi$ violates $\mathcal{B}$ to its algebraic maximum. We propose ways by which states with a stabilizer structure of graph states can be used to construct maximally nonlocal subspaces, essentially as a degenerate eigenspace of Bell operators derived from the stabilizer generators. Two cryptographic applications-- to quantum information splitting and quantum subspace certification-- are discussed.