Optically-trapped and cooled nanoparticles as scanning surface force sensors at sub-micron distances

Optically levitated nanospheres in vacuum serve as a powerful probe for precision force sensing due to their excellent decoupling from the environment. We describe a method for 3-D scanning force sensing of a conducting surface with a levitated nanosphere. 3-D control of a nanosphere near a conductive surface could enable attonewton-level scanning force microscopy, precision tests of non-Newtonian gravity at micron distances, measurement of Casimir forces as well as further study of patch potentials that contribute to the background. We trap a ~170 nm diameter silica nanosphere with an optical tweezer trap, and transfer it into an optical lattice by retroreflecting the tweezer beam with a gold-coated silicon surface. The nanosphere can be trapped axially at discrete positions from a quarter of the laser's wavelength to tens of microns away from the conducting surface, while a piezo-driven mirror allows us to scan tens of microns in the remaining two dimensions parallel to the surface. Lastly, we demonstrate attonewton-level force sensing independent of the nanosphere's position relative to the conducting surface. Additionally, we also discuss methods we are developing to sympathetically cool the motion of our nanoparticles using laser cooled atoms. Such ultra-cold nanoparticles may serve as a matter wave based sensor of short-range surface forces