Role of multilevel Rydberg interactions in electric-field-tuned Förster resonances

In this work, we investigate the dc electric-field dependence of two Forster resonant processes in ultracold ¨ 85Rb, 37D5/2 + 37D5/2 → 35L(L = O,Q) + 39P3/2, as a function of the atomic density. At low densities, the\ud39P3/2 yield as a function of electric field exhibits resonances. With increasing density, the linewidths increase\uduntil the peaks merge. Even under these extreme conditions, where the Forster resonance processes show little ¨\udelectric-field dependence, the 39P3/2 population depends quadratically on the total Rydberg atom population,\udsuggesting that a two-body interaction is the dominant process. In order to explain our results, we implement\uda theoretical model which takes into account the multilevel character of the interactions and Rydberg atom\udblockade process using only atom pair interactions. The comparison between the experimental data and the\udmodel is very good, suggesting that the Forster resonant processes are dominated by two-body interactions up to ¨\udatomic densities of 3.0 × 10^12 cm^−3