Extremal covariant quantum operations and POVM's
arXiv:quant-ph/0310024
Abstract
We consider the convex sets of QO's (quantum operations) and POVM's (positive operator valued measures) which are covariant under a general finite-dimensional unitary representation of a group. We derive necessary and sufficient conditions for extremality, and give general bounds for ranks of the extremal POVM's and QO's. Results are illustrated on the basis of simple examples.
18 pages, to appear on J. Math. Phys