  This paper has been removed and is superceded by a pair of papers on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.
