Christian Roos‘ research is focused on creating, characterizing and using entanglement as a resource for quantum simulation and quantum metrology experiments. The main tools are trapped and laser-cooled ions as a well-controlled quantum system with long coherence times and tailored laser pulses that induce entangling interactions between the internal states of the trapped ions. One line of research focuses onto turning a system of a few tens of trapped ions into an interacting quantum many-body system for simulating quantum mangnetism. In this approach, each ion encodes a spin-1/2 particle that interacts with other particle via long-range interactions. Control of the quantum system at the single-particle level enables quantum measurements that provides insights into the quantum dynamics of this engineered quantum system. A second line of research focuses on using entanglement for the development of novel measurement approaches.