Sub-Recoil Cooling on the Meta-Stable Clock-State in Ytterbium

The ability to efficiently cool the atoms’ motion is essential to the accuracy of optical atomic

clocks. Here we present a novel 3D cooling method which leverages the mHz-linewidth clock

state in ¹⁷¹ Yb in a 1D optical lattice to achieve longitudinal cooling, T_z < 575 nK, and radial sub-recoil

temperatures T_rad < 165 nK ≈ 0.4 T_recoil. We present two potential dark state mechanisms leading to

sub-recoil temperatures. The ability to control the radial temperature distribution complements

our previous work with adiabatic rapid passage, allowing the preparation of atoms in arbitrary

lattice bands. Together these methods allow for improved control of the atomic distribution

in both the radial and longitudinal modes, a necessary step for characterization of the lattice

light shift at or below the 10^-19 decade including measurement of the M1/E2 contribution to the

lattice light shift.