Complete model for collective-effects-modified cascaded decay to extract single-atom 3D1 lifetimes

Develop a complete theoretical model for the cascaded decay process 5s4d ^3D1 → 5s5p ^3P1 → 5s^2 ^1S0 in strontium that incorporates collective radiation effects arising from dipole–dipole interactions (including superradiance and radiation trapping) and enables accurate extraction of single-particle ^3D1 lifetimes from fluorescence time traces when non-negligible ^3P0 population induces many-body modifications.

Background

The paper determines the strontium 5s4d ^3D1 lifetime to refine the dynamic blackbody radiation (BBR) shift ν_dyn, a dominant uncertainty in room-temperature Sr optical lattice clocks. During the measurement, the authors observe that at high densities in the ^3P0 state, spontaneous emission and dipole–dipole interactions (e.g., superradiance and radiation trapping) modify the simple cascaded double-exponential decay used to extract lifetimes.

They fit the lifetime’s density dependence and mitigate collective effects by reducing ^3P0 population and binning by atom number, but note deviations from linear models at high density and explicitly state they do not possess a complete theoretical model to extract single-particle lifetimes in the presence of these collective effects. A robust model is needed to accurately infer intrinsic lifetimes under realistic experimental conditions where many-body radiation effects occur.