Microwave spectroscopy of radio-frequency-dressed 87Rb

We study the hyper ?ne spectrum of atoms of 87Rb dressed by a radio-frequency ?eld and present experimental results in three different situations: freely falling atoms, atoms trapped in an optical dipole trap, and atoms in an adiabatic radio-frequency dressed shell trap. In all cases, we observe several resonant sidebands spaced (in frequency) at intervals equal to the dressing frequency, corresponding to transitions enabled by the dressing ?eld. We theoretically explain the main features of the microwave spectrum using a semiclassical model in the low-?eld limit and the rotating-wave approximation for alkali-metal-like species, in general, and 87Rb atoms, in particular. As a proof of concept, we demonstrate how the spectral signal of a dressed atomic ensemble enables an accurate determination of the dressing con?guration and the probing microwave ?eld.