Spectroscopic Observation of Resonant Electric Dipole-Dipole Interactions between Cold Rydberg Atoms

Abstract

Resonant electric dipole-dipole interactions between cold Rydberg atoms were observed using microwave spectroscopy. Laser-cooled ${}^{85}\mathrm{R}\mathrm{b}$ atoms in a magneto-optical trap were optically excited to $45d_{5/2}$ Rydberg states using a pulsed laser. A microwave pulse transferred a fraction of these Rydberg atoms to the $46p_{3/2}$ state. A second microwave pulse then drove atoms in the $45d_{5/2}$ state to the $46d_{5/2}$ state, and was used as a probe of interatomic interactions. The spectral width of this two-photon probe transition was found to depend on the presence of the $46p_{3/2}$ atoms, and is due to the resonant electric dipole-dipole interaction between $45d_{5/2}$ and $46p_{3/2}$ Rydberg atoms.