Hyperpolarizability effects in a Sr optical lattice clock

Abstract

We report the observation of the higher order frequency shift due to the trapping field in a \(^{87}\)Sr optical lattice clock. We show that at the magic wavelength of the lattice, where the first order term cancels, the higher order shift will not constitute a limitation to the fractional accuracy of the clock at a level of \(10^{-18}\). This result is achieved by operating the clock at very high trapping intensity up to \(400 \)kW/cm\(^2\) and by a specific study of the effect of the two two-photon transitions near the magic wavelength.