On the Generators of Quantum Dynamical Semigroups with Invariant Subalgebras

The problem of characterizing GKLS-generators and CP-maps with an invariant von Neumann algebra [Formula: see text] appeared in different guises in the literature. We prove two unifying results, which hold even for weakly closed *-algebras: first, we show how to construct a normal form for [Formula: see text]-invariant GKLS-generators, if a normal form for [Formula: see text]-invariant CP-maps is known — rendering the two problems essentially equivalent. Second, we provide a normal form for [Formula: see text]-invariant CP-maps if [Formula: see text] is atomic (which includes the finite-dimensional case). As an application we reproduce several results from the literature as direct consequences of our characterizations and thereby point out connections between different fields.