Expansion behavior and pair correlations in continuously excited Rydberg systems

Abstract

We study cumulative excitation of Rydberg atoms in blockaded and facilitated regimes. In order to observe the evolution of the system into a steady state, we employ excitation durations extending to longer than the kinetic time scale and the Rydberg-atom lifetime. Despite the presence of strong van der Waals repulsion, the most probable separation between atoms remains fixed due to the continual Rydberg excitation. This indicates that the time scale on which facilitated excitation replenishes the expanding Rydberg-atom cloud is faster than the van der Waals expansion time scale. The cloud expansion velocities are observed to be slower than the terminal velocity of Rydberg-atom pairs prepared at the facilitation radius and subject to binary van der Waals interaction. Atom statistics in the facilitated regime show bimodal Poissonian distributions, an observation we attribute to the statistical nature of the facilitation process. One peak is due to facilitation avalanches that produce many Rydberg atoms and the other reflects cases in which the facilitation does not gain traction.