Abstract
The positive maps of norm less than or equal to 1 form a convex set. It is natural to expect that the extreme points of this set have special properties. In Chap. 3 we study some of the main extremal maps, in particular Jordan homomorphisms and their applications to maps with strong extremal properties. In the last two sections we consider the relationship of the Stinespring theorem to extremal maps; first to the so-called non-extendible maps and then to a Radon-Nikodym theorem for completely positive maps together with the analogue of the GNS-representation for pure states.
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Størmer, E. (2013). Extremal Positive Maps. In: Positive Linear Maps of Operator Algebras. Springer Monographs in Mathematics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-34369-8_3
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