A Separability of mixed states: necessary and sufficient conditions
Michał Horodecki, Paweł Horodecki, Ryszard Horodecki · 1996
We provide necessary and sufficient conditions for the separability of mixed states. As a result we obtain a simple criterion of the separability for 2 x 2 and 2 x 3 systems. Here, the positivity of the partial transposition of a state is necessary and sufficient for its separability. However, this is not the case in general. Some examples of mixtures which demonstrate the utility of the criterion are considered.