Structural approximations to positive maps and entanglement breaking   channels
  Structural approximations to positive, but not completely positive maps are approximate physical realizations of these non-physical maps. They find applications in the design of direct entanglement detection methods. We show that many of these approximations, in the relevant case of optimal positive maps, define an entanglement breaking channel and, consequently, can be implemented via a measurement and state-preparation protocol. We also show how our findings can be useful for the design of better and simpler direct entanglement detection methods. 
J. K. Korbicz, M. L. Almeida, J. Bae, M. Lewenstein, A. Acin