Single-Stage Sub-Doppler Cooling of Alkaline Earth Atoms

We report the first experimental study of sub-Doppler cooling in alkaline earth atoms ([Formula presented]) enabled by the presence of nuclear spin-originated magnetic degeneracy in the atomic ground state. Sub-Doppler cooling in a [Formula presented]-[Formula presented] configuration is achieved despite the presence of multiple, closely spaced excited states. This surprising result is confirmed by an expanded multilevel theory of the radiative cooling force. Detailed investigations of system performance have shed new insights into ([Formula presented]-[Formula presented]) cooling dynamics and will likely play an important role in the future development of neutral atom-based optical frequency standards.