We deal with the fundamental problems of quantum theory, i.e., the measurement theory and the so-called mesoscopic systems which lie on the border of the microscopic quantum and the macroscopic classical world. Our scientific objective is to extend the high-precision control achieved in the manipulation of individual atoms, trapped ions, photons and ultracold quantum gases to composite quantum systems, such as larger molecules or hybrid — optical and condensed matter based — systems, and to networks of elementary quantum objects. All of our research projects are related to specific physical systems, and are carried out in close collaboration with experimental groups.