Clock-Line-Mediated Sisyphus Cooling

We demonstrate subrecoil Sisyphus cooling using the long-lived ³P₀ clock state in alkaline-earth-like ytterbium. A 1388-nm optical standing wave nearly resonant with the ³P₀→³D₁ transition creates a spatially periodic light shift of the ³P₀ clock state. Following excitation on the ultranarrow clock transition, we observe Sisyphus cooling in this potential, as the light shift is correlated with excitation to ³D₁ and subsequent spontaneous decay to the ¹S₀ ground state. We observe that cooling enhances the loading efficiency of atoms into a 759-nm magic-wavelength one-dimensional (1D) optical lattice, as compared to standard Doppler cooling on the ¹S₀→³P₁ transition. Sisyphus cooling yields temperatures below 200 nK in the weakly confined, transverse dimensions of the 1D optical lattice. These lower temperatures improve optical lattice clocks by facilitating the use of shallow lattices with reduced light shifts while retaining large atom numbers to reduce the quantum projection noise. This Sisyphus cooling can be pulsed or continuous and is applicable to a range of quantum metrology applications.