Probabilistic approach to quantum separation effect for Feynman-Kac semigroup

Quantum tunnelling phenomenon allows a particle in Schr"odinger mechanics tunnels through a barrier that it classically could not overcome. Even the infinite potentials do not always form impenetrable barriers. We discuss an answer to the following question: What is a critical magnitude of potential, which creates impenetrable barrier and for which the corresponding Schr"odinger evolution system separates? In addition we describe some quantitative estimates for the separating effect in terms of cut-off potentials.