The Hammerer group conducts research in theoretical quantum optics, with a particular focus on quantum metrology and precision measurement. We study physical systems that can be described and controlled at the level of individual quanta, and that can be employed in quantum technologies. Current research includes trapped ions for novel atomic clocks and quantum information processing, Bose–Einstein condensates for matter-wave interferometry, correlated quantum states of the electromagnetic field in resonators and waveguides, and quantum mechanical degrees of freedom of mesoscopic and macroscopic solid-state structures. Our work combines a broad range of analytical and numerical methods to describe the quantum dynamics of open systems and to analyze complex quantum correlations. The theoretical questions we address are closely linked to ongoing quantum optics experiments in national and international collaborations.