Long-range Rydberg-Rydberg interactions at very-high $n$

Excitation of very-high-$n$ strontium Rydberg atoms under blockade conditions in an atomic beam provides an opportunity to study strongly-coupled Rydberg-Rydberg systems under controlled conditions. ~In the present work, blockade is exploited to create a string of Rydberg atoms with approximately equal initial separations. ~Sudden application of an electric field ``step'' is then used to create Stark wave packets whose subsequent time evolution is monitored through ionization induced by a pulsed electric field. ~Measurements of the number of surviving Rydberg atoms reveal pronounced Stark quantum beats. Preliminary comparisons of the quantum beat behavior for single and multiple Rydberg atoms indicate that Rydberg-Rydberg interactions lead to dephasing and a reduction in the amplitude of the (collective) beats. ~The mechanisms responsible for this are being examined through further experimental studies and through theoretical analysis.