Entanglement Breaking Channels
  This paper has been removed and is superceded by a pair of papers on stochastic maps, or channels, which break entanglement (EBT). quant-ph/0302031 General Entanglement Breaking Channels by Michael Horodecki, Peter W. Shor and Mary Beth Ruskai includes the results originally in section 3, as well as a number of new results about the extreme points. (The remarks in previously in section 3 about "sign change condition" are incorrect and have been omitted from quant-ph/0302031.) The new paper contains a to the conjecture that all extreme points of EBT maps are CQ when d > 2. quant-ph/0302032 Qubit Entanglement Breaking Channels by Mary Beth Ruskai contains the results oroginally in section 2. The main result is that for qubits, EBT maps are precisely the convex hull of those known as classical-quantum channels. The complete positivity conditions in a canonical parameterization are reviewed and used to formulate EBT constraints. 
Mary Beth Ruskai