Recent experiments and theory have further illuminated the concept of “quantum contextuality.” In this paper we take an inequality—the pentagram (or KCBS) inequality, which is violated by an unentangled spin-1 system—and given a relaxed assumption of noncontextuality show that a hidden-variable model may be constructed that replicates exactly the quantum bound. This is in contrast to the case of an entangled pair of spin-1/2 particles where a similar relaxation of the assumption of locality does not lead to a replication of the quantum bound. Some reasons are proposed for why this may be the case.

• Received 28 June 2013

DOI:https://doi.org/10.1103/PhysRevA.89.022108