Excitation of Rydberg Atoms in a Bose-Einstein Condensate

The authors performed experiments on the coherent dynamics of Rydberg excitation in thermal clouds of ⁸⁷Rb for a wide range of atomic densities, single-atom Rabi-frequencies and excitation times in a specialized vacuum chamber. We further observed a clear signature of the phase transition to a Bose-Einstein condensate in the fraction of excited Rydberg atoms when cooling the thermal cloud below T_c. In our experiments the sample size is bigger than the so called blockade radius, which is defined as the interatomic distance where the interaction energy becomes equal to the power broadened linewidth of the excitation.