Coherence and Raman Sideband Cooling of a Single Atom in an Optical Tweezer

Abstract

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers (\bar n_x=\bar n_y=0.01, \bar n_z=8)) even for a trap beam waist as small as (\omega=900 nm). The small atomic wave packet with (\delta x=\delta y=24 nm) and (\delta z=270 nm) represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces.