Direct Measurement of the $5s5p\,{}^1P_1 \to 5s4d\,{}^1D_2$ Decay Rate in Strontium

TL;DR

This paper presents the first direct experimental measurements of key decay rates and branching ratios in neutral strontium, providing crucial benchmarks for laser cooling and quantum information applications.

Contribution

It reports the first direct measurement of the decay rate and branching ratio in strontium, challenging existing theoretical values and aiding precise quantum control.

Findings

Branching ratio measured at 0.177(4), lower than theoretical 0.322.

Decay rate measured at 5.3(5)×10^3 s^{-1}, lower than recent theory.

Results serve as benchmarks for laser cooling and quantum experiments.

Abstract

We report the first direct experimental determination of the branching ratio of the $5s4d\,{}^1D_2 \to 5s5p\,{}^3P_2$ transition and the decay rate of the $5s5p\,{}^1P_1 \to 5s4d\,{}^1D_2$ transition in neutral strontium. For more than four decades, these quantities lacked an experimental determination independent of theoretical input. We measure the branching ratio to be $0.177(4)$, significantly lower than the widely cited theoretical value of $0.322$ [C. W. Bauschlicher Jr. {\it et al.}, J. Phys. B \textbf{18}, 1523 (1985)]. We also determine the decay rate to be $5.3(5)\times10^3\,\mathrm{s^{-1}}$, consistent with the value reported by Hunter [L. R. Hunter {\it et al.}, Phys. Rev. Lett. \textbf{56}, 823 (1986)] but substantially lower than the recent theoretical prediction of $9.25(40)\times10^3\,\mathrm{s^{-1}}$ [A. Cooper {\it et al.}, Phys. Rev. X \textbf{8}, 041055 (2018)]. These measurements provide an experimental benchmark for quantitative modeling of loss processes in laser cooling and single-atom fluorescence detection in optical tweezers with Sr.