Towards a search for non-Newtonian gravity with optically-levitated microspheres

The universal law of gravity has undergone stringent tests for more than a century, over length scales ranging from the atomic to the planetary. Of particular interest is the short distance regime, where modifications to Newtonian gravity may arise from axion-like particles and extra dimensions, while constraints on such explanations are mild. We have constructed a precision force sensor based on optically-levitated microspheres with a force sensitivity of ∼10^-17 N/√Hz, sufficient to increase the sensitivity of searches for non-Newtonian forces in the 1-100 μm range. Toward a measurement of the gravitational force and its possible modifications, we present results describing a novel trapping system and optics, and the characterization of the levitated microsphere test mass. Various control schemes inherent to the system, such as its 3D force sensitivity and electrically driven microsphere rotation, are also discussed, as they may reduce the effects of background forces.