  We demonstrate the coherent excitation of a mesoscopic ensemble of about 100
ultracold atoms to Rydberg states by driving Rabi oscillations from the atomic
ground state. We employ a dedicated beam shaping and optical pumping scheme to
compensate for the small transition matrix element. We study the excitation in
a weakly interacting regime and in the regime of strong interactions. When
increasing the interaction strength by pair state resonances we observe an
increased excitation rate through coupling to high angular momentum states.
This effect is in contrast to the proposed and previously observed
interaction-induced suppression of excitation, the so-called dipole blockade.
