The laser excitation of Rydberg atoms in ultracold gases is often described assuming that the atomic motion is frozen during the excitation time. We show that this frozen gas approximation can break down for atoms that are held in optical lattices or microtraps. In particular, we show that the excitation dynamics is in general strongly affected by mechanical forces among the Rydberg atoms as well as the spread of the atomic wave packet in the confining potential. This causes decoherence in the excitation dynamics—resulting in a dissipative blockade effect—that renders the Rydberg excitation inefficient even in the antiblockade regime. For a strongly off-resonant laser excitation—usually considered in the context of Rydberg dressing—these motional effects compromise the applicability of the Born-Oppenheimer approximation. In particular, our results indicate that they can also lead to decoherence in the dressing regime.

• Received 15 March 2013

DOI:https://doi.org/10.1103/PhysRevLett.110.213005