The large transition dipole moments of Rydberg atoms make them much more sensitive to electric fields than less excited atoms. For example, the dc polarizabilities of low angular momentum Rydberg states scale like n7, where n is the principal quantum number. This high sensitivity can be employed for various means.
In this work, a microwave dressing field was used to induce resonant energy transfer in translationally cold Rydberg atoms. The 85Rb Rydberg atoms were obtained by laser excitation of cold atoms in a magneto-optical trap. When a 28.5 GHz dressing field was set at specific field strengths, the two-atom dipole-dipole process 43d5⁄2 + 43d5⁄2 → 45p3⁄2 + 41f was dramatically enhanced, due to the induced degeneracy of the initial and final states. The resulting spectrum had a series of resonant field amplitudes corresponding to different magnetic sublevels possible for the states involved.
This method for enhancing interactions is complementary to dc electric field induced resonant energy transfer, but benefits from the ability to shift energy levels in either direction by choice of frequency.