Title: Absence of Collective Decay in a Cold Rydberg Gas

Tao Zhou, B.G. Richards, and R.R. Jones

University of Virginia, Charlottesville, VA 22904, USA

Abstract:

We have studied the decay of Rydberg excitations in a cold Rb gas. A 10 ns, pulsed dye-amplified diode laser excites Rb atoms at 70 microK in a MOT to ns or np Rydberg states with principal quantum numbers 25 < n < 41. Time-delayed state-selective field ionization (SSFI) is used to directly monitor the population in the initial and neighboring Rydberg levels. The measured time-dependence of the Rydberg population is well described by numerical simulations which consider only spontaneous emission and population transfer by black-body radiation. No evidence for collective decay is found at atom densities up to 3 x 10^9 1/cm^3. This result is in contrast to a previous study in which superradiant decay was theoretically predicted and experimentally inferred for atom density and laser focal volume conditions very similar to those considered here. Suppression of collective emission is likely due to variations in transition energies within the atom sample, dominated by inhomogeneities in dipole-dipole exchange interactions for initial s-states, or by a combination of dipole-dipole and electric field inhomogeneities for initial p-states.

Status: Published Physical Review A 93, 033407 (2016).