Synthetic Dimension-Induced Conical Intersections in Rydberg Molecules.

We observe a series of conical intersections in the potential energy curves governing both the collision between a Rydberg atom and a ground-state atom and the structure of Rydberg molecules. By employing the electronic energy of the Rydberg atom as a synthetic dimension we circumvent the von Neumann-Wigner theorem. These conical intersections can occur when the Rydberg atom's quantum defect is similar in size to the electron-ground-state atom scattering phase shift divided by π, a condition satisfied in several commonly studied atomic species. The conical intersections have an observable consequence in the rate of ultracold l-changing collisions of the type Rb(nf)+Rb(5s)→Rb(nl>3)+Rb(5s). In the vicinity of a conical intersection, this rate is strongly suppressed, and the Rydberg atom becomes nearly transparent to the ground-state atom.