  We report on the observation of Rabi oscillations to a Rydberg state on a
timescale below one nanosecond in thermal rubidium vapor. We use a
bandwidth-limited pulsed excitation and observe up to 6 full Rabi cycles within
a pulse duration of ~ 4 ns. We find good agreement between the experiment and
numerical simulations based on a surprisingly simple model. This result shows
that fully coherent dynamics with Rydberg states can be achieved even in
thermal atomic vapor thus suggesting small vapor cells as a platform for room
temperature quantum devices. Furthermore the result implies that previous
coherent dynamics in single atom Rydberg gates can be accelerated by three
orders of magnitude.
