Designing optimum completely positive maps for quantum teleportation - art. no. 060301

We study a general teleportation scheme with an arbitrary state of the pair of particles (2 and 3) shared by Alice and Bob, and arbitrary measurements on the input particle 1 and one of the members (2) of the pair on Alice's side. We find an efficient iterative algorithm for identifying optimum oper ations on Bob's side. In particular, we find that simple unitary transforrn ations on his side are not always optimal even if particles 2 and 3 are per fectly entangled. We describe the most interesting protocols in the languag e of extremal completely positive maps.