Observation of Self-Induced Rabi Oscillations in Two-Level Atoms Excited Inside a Resonant Cavity: The Ringing Regime of Superradiance

A collection of N Rydberg atoms and a resonant millimeter-wave cavity are shown to exchange energy back and forth at a rate 2(d / ℏ)E₀sqrt[N], where d is the electric dipole matrix element of the atomic transition and E₀ the "field per photon" in the cavity. This experiment is a demonstration of self-induced Rabi oscillations in a two-level atom system coupled to a single electromagnetic field mode and can also be considered as a very simple illustration of "ringings" in superradiant emission.