Strongly interacting quantum excitations of a cold atomic gas

Strong interactions of Rydberg atoms in a mesoscopic ensemble can be employed for fast preparation of desired many-particle states. In this work, Rydberg excitations are generated in an ultra-cold atomic Rb gas and are converted into light. As the principal quantum number n is increased beyond $\sim $ 70, no more than a single excitation is retrieved from a mesoscopic ensemble. These results hold promise for studies of dynamics and disorder in many-body systems with tunable interactions and for scalable quantum information networks.