Rydberg excitation of a Bose-Einstein condensate

We have performed two-photon excitation via the 6(2)P(3/2) state to the n = 50-80 S or D Rydberg state in Bose-Einstein condensates of rubidium atoms. The Rydberg excitation was performed in a quartz cell, where electric fields generated by plates external to the cell created electric charges on the cell walls. Avoiding accumulation of the charges and realizing good control over the applied electric field was achieved when the fields were applied for only a short time, typically a few microseconds. Rydberg excitations of the Bose-Einstein condensates loaded into quasi-one-dimensional traps and in optical lattices have been investigated. The results for condensates expanded to different sizes in the one-dimensional trap agree well with the intuitive picture of a chain of Rydberg excitations controlled by the dipole-dipole interaction. The optical lattice applied along the one-dimensional geometry produces localized, collective Rydberg excitations controlled by the nearest-neighbour blockade.