Collective Cascaded Decay Dynamics in Ensembles of Multilevel Atoms

Collective radiative decay in an ensemble of atoms is a prototypical problem of many-body physics. We study the cascaded 3D1-3PJ-1S0 decay of strontium atoms in an elongated cloud, where interatomic separations are comparable to the transition wavelengths. In this setting, photon-mediated dipole–dipole interactions give rise to cooperative phenomena: the 3D1-3P0/3P1 decay is collectively enhanced due to superradiance, whereas the 3P1-1S0 decay rate is reduced below the natural linewidth consistent with subradiant or radiation trapping. Using cluster mean-field and cumulant expansions, we model the many-body dynamics and investigate how the atomic populations depend on the initial excitation fraction and optical depth. Beyond the fundamental interest, our results are relevant for precision metrology, enabling more accurate evaluation of the leading blackbody-radiation shift in state-of-the-art optical lattice clocks [1].

[1] A. Aeppli, K. Kim, W. Warfield, M. S. Safronova, and J. Ye, “Clock with 8×10⁻¹⁹ Systematic Uncertainty,” Phys. Rev. Lett. 133, 023401 (2024).