The research group led by Arthur Christianen investigates the interplay between few- and many-body physics in quantum matter. The overarching goal is to understand how microscopic interactions give rise to collective phenomena. Of particular interest are systems where just a few interacting particles already exhibit remarkable behavior, and how this behavior changes when they become part of a larger quantum many-body system. The group studies how this physics manifests in platforms such as ultracold atomic and molecular gases as well as two-dimensional semiconductors, focusing on questions of direct experimental relevance. Its theoretical approach combines methods from scattering theory and quantum chemistry with variational techniques from quantum many-body physics.