Anomalous Rydberg Line Broadening Observed

We have recently observed interaction-induced broadening of a Rydberg transition in rubidium trapped in a 3D optical lattice. Our observations cannot be attributed to the typical van der Waals interaction between Rydberg atoms in the same state, due to the magnitude and symmetry of the broadening and the insensitivity of the effect to the short-range spatial distribution of atoms. We identify a mechanism that closely matches the data in which the broadening is due to dipole-dipole interactions with a small number of atoms that undergo black-body transitions to nearby Rydberg states of opposite parity. These interactions are much larger and longer range than the van der Waals interactions (even one contaminant atom causes substantial broadening), and so the broadened regime is achieved very quickly under even far detuned excitation of a large ensemble of atoms. This result has significant implications for many proposals with coherently interacting many-body Rydberg systems. The result has been accepted for publication in Physical Review Letters. http://arxiv.org/abs/1510.08710