Precision Spectroscopy and Density-Dependent Frequency Shifts in Ultracold Sr

Abstract

By varying the density of an ultracold ${}^{88}\mathrm{Sr}$ sample from ${10}^9$ to$>{10}^{12}{\mathrm{cm}}^{-3}$, we make the first definitive measurement of the density-related frequency shift and linewidth broadening of the ${}^{1}S_0\mathrm{\text{−}}{}^{3}P_1$ optical clock transition in an alkaline earth system. In addition, we report the most accurate measurement to date of the ${}^{88}\mathrm{Sr}$ ${}^{1}S_0\mathrm{\text{−}}{}^{3}P_1$ optical clock transition frequency. Including a detailed analysis of systematic errors, the frequency is $[434829121312334\pm 20(\mathrm{stat})\pm 33(\mathrm{syst})]\mathrm{Hz}$.