Ultra-Long-Range Rydberg Trimers with a Repulsive Two-Body Interaction

A Rydberg and a ground-state atom can form ultra-long-range diatomic molecules provided the interaction between the ground-state atom and the Rydberg electron is attractive [C. H. Greene , Phys. Rev. Lett. 85, 2458 (2000)]. A repulsive interaction does not support bound states. However, as we will show, adding a second ground-state atom, a long-range bound triatomic molecule becomes possible.