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