Nonthermalizing dynamics of interacting Rydberg atoms

An isolated system of ultracold Rydberg atoms can come to equilibrium by exchanging energy through dipole-dipole interactions. In our experiment, a static electric field of a few V/cm shifts the energy levels of the atoms, so that the energy levels are nearly degenerate at zero field and fan out with increasing field to form a manifold. We excite atoms to energy levels near the center of the manifold, where the spacing is nearly harmonic. We allow them to interact for a few microseconds, by which time the popoulation of each energy level has reached a steady state. The population is then measured at various densities and compared to simulation results. We use the notion of dynamical typicality to predict the equillibrium configuration and show that the system fails to thermalize.