1202.3673 (Erik Alfsen et al.)

Finding decompositions of a class of separable states    [PDF]

Erik Alfsen, Fred Shultz

By definition a separable state has the form \sum A_i \otimes B_i, where 0
\leq A_i, B_i for each i. In this paper we consider the class of states which
admit such a decomposition with B_1, ..., B_p having independent images. We
give a simple intrinsic characterization of this class of states, and starting
with a density matrix in this class, describe a procedure to find such a
decomposition with B_1, ..., B_p having independent images, and A_1, ..., A_p
being distinct with unit trace. Such a decomposition is unique, and we relate
this to the facial structure of the set of separable states.
A special subclass of such separable states are those for which the rank of
the matrix matches one marginal rank. Such states have arisen in previous
studies of separability (e.g., they are known to be a class for which the PPT
condition is equivalent to separability).
The states investigated also include a class that corresponds (under the
Choi-Jamio{\l}kowski isomorphism) to the quantum channels called
quantum-classical and classical-quantum by Holevo.

View original: http://arxiv.org/abs/1202.3673