Blockade involving high-$n$, $n\sim300$, strontium Rydberg atoms

The blockade of high-$n$ strontium $n ^1F_3$ Rydberg states contained in a hot atomic beam is investigated both theoretically and experimentally. One difficulty in such experiments is that, once created, Rydberg atoms move out of the excitation volume reducing blockade effects. While the effects of such motion are apparent, the data provide strong evidence of blockade, consistent with theoretical predictions. Because of their relatively high angular momentum $(L=3)$, a pair of $n ^1F_3$ Rydberg atoms have many degenerate states whose degeneracy is removed by Rydberg-Rydberg interactions yielding a high density of states near the target energy. To evaluate the effect of blockade not only the energy shifts but also the modification of the oscillator strengths for excitation have to be taken into account. The $n$-scaling of the interactions and the importance of high-order multipoles will also be discussed.