title: Antiblockade in Rydberg excitation of an ultracold lattice gas.
abstract: It is shown that the two-step excitation scheme typically used to create an ultracold Rydberg gas can be described with an effective two-level rate equation, greatly reducing the complexity of the optical Bloch equations. This allows us to efficiently solve the many-body problem of interacting cold atoms with a Monte Carlo technique. Our results reproduce the observed excitation blockade effect. However, we demonstrate that an Autler-Townes double peak structure in the two-step excitation scheme, which occurs for moderate pulse lengths as used in the experiment, can give rise to an antiblockade effect. It is most pronounced for atoms arranged on a lattice. Since the effect is robust against a large number of lattice defects it should be experimentally realizable with an optical lattice created by CO2 lasers.
authors.affiliation: Max Planck Institute for the Physics of Complex Systems, Dresden, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Ates
authors.forename: T
authors.initials: T
authors.lastname: Pohl
authors.forename: T
authors.initials: T
authors.lastname: Pattard
authors.forename: J M
authors.initials: JM
authors.lastname: Rost