Modeling the Effects of State-Mixing Interactions near Förster Resonance

State-mixing interactions can compromise the effectiveness of the Rydberg excitation blockade near Förster resonance.  Up to ∼ 50% of the detected Rydberg atoms can be found in dipole coupled product states within tens of ns of excitation.  We use state-selective field ionization spectroscopy to measure, on a shot-by-shot basis, the distribution of states populated during narrowband laser excitation of ultracold rubidium atoms.  Our method allows us to quantify both the number of additional excitations added by each mixing event, and the extent to which state-mixing “breaks” the blockade.  We use a Monte Carlo method to model the effect of experimental noise sources on our data.  We find good agreement with a three-body model for state-mixing, except near exact Förster resonance.