Frozen Rydberg gases are currently of interest for two reasons. First, the atoms in such cold samples only move roughly 3% of the average interatomic spacing during the 1 microsecond time scale of experimental interest, so the interactions between them are almost static, as in a disordered solid. Second, a frozen Rydberg gas can spontaneously evolve into an ultracold plasma, and ultracold plasma can recombine to form Rydberg atoms.
In our lab, we have been studying these collective phenomena of cold Rydberg gases, especially by using millimeter waves. We have clearly demonstrated the many-body nature of the dipole-dipole interactions in such a system in recent resonant energy transfer experiments by adding an additional state to the system using a microwave transition. Moreover, our newly conducted experiments suggest the intimate connection between the dipole-dipole interactions and the formation of a plasma. The microwave spectroscopy shows that at high n states, the attractive dipole-dipole interaction provides the initial ionization mechanism responsible for producing the free ions necessary for trapping the electrons.

Contact: Steven Rolston