Qubit Entanglement Breaking Channels

Abstract

This paper continues the study of stochastic maps, or channels, which break entanglement. We give a detailed description of entanglement-breaking qubit channels, and show that such maps are precisely the convex hull of those known as classical-quantum channels. We also review the complete positivity conditions in a canonical parameterization and show how they lead to entanglement-breaking conditions.Comment: Contains main results from section 2 of quant-ph/0207100 Version 2 corrects minor typos. Final version to appear in Rev. Math. Phy