Entanglement in C$^*$-algebras: tensor products of state spaces

Paper

Abstract

We analyze the Namioka-Phelps minimal and maximal tensor products of compact convex sets arising as state spaces of C

-algebras, and, relatedly, study entanglement in (infinite dimensional) C

-algebras. The minimal Namioka-Phelps tensor product of the state spaces of two C

-algebras is shown to correspond to the set of separable (= un-entangled) states on the tensor product of the C

-algebras. We show that these maximal and minimal tensor product of the state spaces agree precisely when one of the two C

-algebras is commutative. This confirms an old conjecture by Barker in the case where the compact convex sets are state spaces of C

-algebras. The Namioka-Phelps tensor product of the trace simplexes of two C

-algebras is shown always to be the trace simplex of the tensor product of the C

-algebras. This can be used, for example, to show that the trace simplex of (any) tensor product of two C

-algebras is the Poulsen simplex if and only if the trace simplex of each of the C

-algebras is the Poulsen simplex.