Long-range interactions in cold Rydberg gases.
Atoms excited to high-lying quantum states, so-called Rydberg atoms, are highly polarizable and, therefore, can interact strongly with each other at large distances. These interactions make them attractive candidates for studies of strongly correlated systems and the implementation of quantum logic gates. One central ingredient for the Rydberg applications is the dipole blockade. In this mechanism, the excitation of an atom to a Rydberg state is inhibited if another, already excited, atom is less than the so-called blockade radius away. We have explored the dipole blockade for ultracold atoms and Bose-Einstein condensates.
A key signature of interactions between Rydberg atoms is the suppression of fluctuations in the number of excitations due to the dipole blockade. We have performed a systematic study of the sub-Poissonian statistics in the number of Rydberg excitations in a magneto-optical trap. Our experimental results are compared to a novel theoretical model based on Dicke states of Rydberg atoms including the dipole-dipole interactions.
We have realized experimentally Rydberg excitations in Bose-Einstein condensates of rubidium atoms loaded into quasi-one-dimensional traps and in optical lattices. Our results for condensates expanded to different sizes in the one-dimensional trap agree well with the intuitive picture of a chain of localized collective Rydberg excitations including nearest-neighbor blockade.