Microwave Spectroscopy of Low-l Singlet Strontium Rydberg States at Intermediate n

Microwave spectroscopy is used to measure the relative energy separations between strontium n ¹S₀, n ¹P₁, n ¹D₂, and n ¹F₃ Rydberg levels for 50 ? n ? 70 with uncertainties, limited by possible stray electric fields, of a few tens of kilohertz. The microwave results are referenced to earlier measurements of term values for the n ¹S₀ state to obtain term values, and hence quantum defects, for the higher-l states and develop a revised set of self-consistent Rydberg-Ritz parameters that can be used to predict level separations over a broad range of n with much greater precision than is possible using earlier published Rydberg-Ritz parameters. The determination of accurate transition frequencies is central to the planning of quantum simulation experiments that involve microwave-coupled Rydberg levels, such as in the creation of Rydberg synthetic dimensions.