The Extension of Unital Completely Positive Semigroups on Operator Systems to Semigroups on -Algebras

The study of open quantum systems relies on the notion of unital completely positive semigroups on -algebras representing physical systems. The natural generalisation would be to consider the unital completely positive semigroups on operator systems. We show that any continuous unital completely positive semigroup on matricial system can be extended to a semigroup on a finite-dimensional -algebra, which is an injective envelope of the matricial system. In case the semigroup is invertible, this extension is unique.