Lattice-induced photon scattering in an optical lattice clock

TL;DR

This paper studies how lattice-induced photon scattering affects strontium optical lattice clocks, revealing decay processes that limit interrogation times but can be mitigated with shallow lattices.

Contribution

It provides the first experimental measurement and theoretical analysis of lattice-induced decay rates in strontium clocks, highlighting their impact on clock performance.

Findings

Lattice-induced decay rate measured at 556(15)×10^{-6} s^{-1} per photon recoil.

Natural lifetime of the excited state estimated at 330(140) seconds.

Lattice-induced decay can surpass spontaneous decay at typical lattice depths.

Abstract

We investigate scattering of lattice laser radiation in a strontium optical lattice clock and its implications for operating clocks at interrogation times up to several tens of seconds. Rayleigh scattering does not cause significant decoherence of the atomic superposition state near a magic wavelength. Among the Raman scattering processes, lattice-induced decay of the excited state $(5s5p)\,{}^{3}\mathrm{P}_{0}$ to the ground state $(5s^2)\,{}^{1}\mathrm{S}_{0}$ via the state $(5s5p)\,{}^{3}\mathrm{P}_{1}$ is particularly relevant, as it reduces the effective lifetime of the excited state and gives rise to quantum projection noise in spectroscopy. We observe this process in our experiment and find a decay rate of $556(15)\times 10^{-6}\,\mathrm{s}^{-1}$ per photon recoil energy $E_\mathrm{r}$ of effective lattice depth, which agrees well with the rate we predict from atomic data. We also derive a natural lifetime $\tau = 330(140)\,\mathrm{s}$ of the excited state ${}^{3}\mathrm{P}_{0}$ from our observations. Lattice-induced decay thus exceeds spontaneous decay at typical lattice depths used by present clocks. It eventually limits interrogation times in clocks restricted to high-intensity lattices, but can be largely avoided, e.g., by operating them with shallow lattice potentials.