Enhanced cooling and quantum control of divalent atoms for the next generation of optical lattice clocks

Abstract: Atomic clocks operating in the optical domain are now capable of measuring time at up to eighteen digits of precision, and fundamental limits offer significant potential for even higher performance. To reach this goal, the next-generation of optical lattice clocks will require more advanced control of lattice-trapped atomic samples. To this end, here we consider two novel laser cooling strategies that exploit the extensive atom-laser coherence possible with divalent atomic structure. The first is a pulsed cooling process that replaces two-photon Raman cooling techniques with single-photon velocity-selection using the narrowband clock transition. The second is an excited state Sisyphus cooling mechanism that offers efficient three-dimensional cooling in a lattice. We demonstrate sub-recoil, nK-regime cooling of ytterbium in both cases, which aid in loading very shallow lattices that are less susceptible to lattice-induced light shifts. We also implement coherent delocalization of ultracold ytterbium through controlled tunneling in a Wannier-Stark lattice, which helps reduce atomic interactions. Finally, we also discuss a parallel effort on development of portable ytterbium lattice clocks for applications beyond the lab.