Quantum Systems Theory Viewed from Kossakowski-Lindblad Lie Semigroups — and Vice Versa

The solutions to the celebrated Kossakowski-Lindblad equation extended by coherent controls yield Markovian quantum maps. More precisely, the set of all its solutions forms a semigroup of completely positive trace-preserving maps taking the specific form of a Lie semigroup. Non-trivial symmetries of these semigroups are shown to preclude accessibility in Markovian dissipative systems. This is the open-system analogue to closed systems, where triviality of (quadratic) symmetries of the Hamiltonian part suffices to decide that the system is fully controllable. The findings are placed into a unifying Lie frame of quantum systems and control theory alongside with illustrating examples.

On the extensions of infinite-dimensional representations of Lie semigroups

The necessary and sufficient conditions have been obtained for extendability of a Banach representation of a generating Lie semigroupSto a local representation of the Lie groupGgenerated bySwhen the tangent wedge ofSis a Lie semialgebra. The most convenient conditions we obtain correspond to the case of unitary representations. In this case, we give a criterion of global extendability ifGis exponential and solvable.