  Nitrogen vacancy (NV) centers in diamond are promising elemental blocks for
quantum optics [1, 2], spin-based quantum information processing [3, 4], and
high-resolution sensing [5-13]. Yet, fully exploiting these capabilities of
single NV centers requires strategies to accurately manipulate them. Here, we
use optical tweezers as a tool to achieve deterministic trapping and 3D spatial
manipulation of individual nano-diamonds hosting a single NV spin. Remarkably,
we find the NV axis is nearly fixed inside the trap and can be controlled
in-situ, by adjusting the polarization of the trapping light. By combining this
unique spatial and angular control with coherent manipulation of the NV spin
and fluorescent lifetime measurements near an integrated photonic system, we
prove optically trapped NV center as a novel route for both 3D vectorial
magnetometry and sensing of the local density of optical states.
