Study of the Distillability of Werner States Using Entanglement   Witnesses and Robust Semidefinite Programs
  We use Robust Semidefinite Programs and Entanglement Witnesses to study the distillability of Werner states. We perform exact numerical calculations which show 2-undistillability in a region of the state space which was previously conjectured to be undistillable. We also introduce bases which yield interesting expressions for the {\em distillability witnesses} and for a tensor product of Werner states with arbitrary number of copies. 
Reinaldo O. Vianna and Andrew C. Doherty