Observation of coherent many-body Rabi oscillations

Abstract

A two-level quantum system driven by an electromagnetic field can oscillate between its two states. The effects of these so-called Rabi oscillations are usually obscured in many-body systems by the variation in properties of the particles involved. Now, however, coherent many-body Rabi oscillations are observed in a vapour made up of several hundred cold rubidium atoms. A two-level quantum system coherently driven by a resonant electromagnetic field oscillates sinusoidally between the two levels at frequency Ω (refs 1, 2). In dilute gases, the inhomogeneous distributions of both the coupling strength to the field and the interactions between individual atoms reduce the visibility of these so-called Rabi oscillations and may even suppress them completely. However, in the limit where only a single excitation is present, a collective, many-body Rabi oscillation at a frequency arises that involves all N≫1 atoms, even in inhomogeneous systems3,4. When one of the two levels is a strongly interacting Rydberg level, many-body Rabi oscillations emerge as a consequence of a phenomenon known as Rydberg excitation blockade5. Here we report initial observations of coherent many-body Rabi oscillations between the ground level and a Rydberg level using several hundred cold rubidium atoms, with a 0.67(10) preparation efficiency of the singly-excited many-body state. The strongly pronounced oscillations indicate a nearly complete excitation blockade of the entire mesoscopic ensemble by a single excited atom.