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.