Distillability via Protocols Respecting the Positivity of Partial Transpose
Tilo Eggeling, K. G. H. Vollbrecht, Reinhard F. Werner, Michael M. Wolf · Physical Review Letters · 2001
We show that all quantum states that do not have a positive partial transpose are distillable via channels, which preserve the positivity of the partial transpose. The question whether bound entangled states with non-positive partial transpose exist is therefore closely related to the connection between the set of separable superoperators and positive partial transpose-preserving maps.