Slow Thermalization and the Role of Quantum Many-Body Scar States in Few-Body Dipole-Dipole Interactions*

We investigate the dynamics of energy exchange in ultracold Rydberg atoms undergoing two-, three-, and four-body dipole-dipole interactions through model and experiment. Based on recent computational results using a simplified model, we find that while the two-body case rapidly thermalizes, there exist regions in parameter space in which the three- and four-body interactions exhibit nonergodic behavior and either fail to thermalize or do so slowly. The results of our model suggest that high overlap of a pure initial state with quantum many-body scar states plays a significant role in impeding thermalization in the three- and four-body cases. Motivated by these results, we experimentally probe the energy exchange within a pseudo-one-dimensional lattice of Rydberg atoms in a MOT. We compare the fraction of atoms excited via Förester resonances for various initial states to further reveal the interplay between quantum many-body scars and nonergodic dynamics in experiment.