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

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 (n) over bar (x) = (n) over bar (y) = 0.01, (n) over bar (z) = 8) even for a trap beam waist as small as w = 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. DOI: 10.1103/PhysRevLett.110.133001