Deexcitation spectroscopy of strongly interacting Rydberg gases

We present experimental results on the controlled deexcitation of Rydberg states in a cold gas of Rb atoms. The effect of the van der Waals interactions between the Rydberg atoms is clearly seen in the deexcitation spectrum and dynamics. Our observations are confirmed by numerical simulations. In particular, for off-resonant (facilitated) excitation we find that the deexcitation spectrum reflects the spatial arrangement of the atoms in the quasi-one-dimensional geometry of our experiment. We discuss future applications of this technique and implications for detection and controlled dissipation schemes.