Local Blockade of Rydberg excitation in an ultracold gas

Robin Côté

Department of Physics, University of Connecticut, 2152 Hillside Road, Storrs, CT 06269-3046, USA

In recent years, numerous proposals to build quantum information processors have been suggested. Due to their very long coherence times and the well-developed techniques for cooling and trapping them, neutral atoms are particularly attractive for quantum computing. Implementation of quantum logic gates based on ultracold Rydberg atoms have been proposed(D. Jaksch et al.), Phys. Rev. Lett. 85, 2208 (2000)., and generalized to the possible use of collective states of mesoscopic ensembles via the dipole blockade mechanism(M.D. Lukin et al.), Phys. Rev. Lett. 87, 037901 (2001).. Here, we report an important advance towards this goal. We observe that the laser excitation of a macroscopic sample of ultracold atoms to high-lying Rydberg states can be dramatically suppressed by their strong long-range interactions. This leads to a local blockade effect, where the excitation of one atom prevents excitation of its neighbors. The blockade mechanism responsible for this suppression arises from van der Waals interactions. We will discuss a mean-field model that defines local blockade domains. The experimental observations agree well with the predictions of this model.