Effect of Forster resonances on the excitation statistics of many-body Rydberg systems

We provide evidence for the dipole blockade of Rydberg excitation by examining the distributions of the number of Rydberg excitations created in ensembles of interacting Rydberg atoms. We show that, over a range of densities, the Rydberg excitation number distributions become significantly narrower when an applied electric field is used to tune the Rb-85 interaction channel 45D(5/2)+45D(5/2)-> 43F+47P(3/2) into Forster resonance. Substantially sub-Poissonian distributions that agree with published theory were achieved using very dense atom samples tuned into Forster resonance.