The core of our theoretical research lies at the interface of atomic physics, quantum optics and many-body physics. The rapidly expanding capabilities of modern quantum science to control (artificial) atoms, molecules and ions with light or other external fields makes it nowadays possible to build complex quantum systems from single quanta to mesoscopic or macroscopic scales. Such synthetic quantum systems continue to provide a unique stage for exploring new emergent phenomena and addressing pivotal questions, e.g., in statistical or condensed matter physics. In our group we seek to further the theoretical understanding of these fascinating systems and explore new avenues for their control and design. Uncovering the basic mechanisms behind such exotic light-matter interactions can provide a conceptual foundation for future quantum technology and enable fundamental studies of non-equilibrium phenomena with controllable interactions between particles, photons or both combined.