First search for non-Newtonian interactions at micrometer scale with a levitated test mass

I will discuss a search for non-Newtonian forces that couple to mass, with a characteristic scale of 10 μm, using an optically levitated microsphere as a precision force sensor. A silica microsphere trapped in an upward-propagating, single-beam, optical tweezer is utilized to probe for interactions sourced from a nanofabricated attractor mass with a density modulation brought into close proximity to the microsphere and driven along the axis of periodic density in order to excite an oscillating response. We obtain force sensitivity of ≤10^-16 N/√Hz. Separately searching for attractive and repulsive forces results in the constraint on a new Yukawa interaction of |α| ≥ 10⁸ for λ > 10 μm. This is the first test of the inverse-square law using an optically levitated test mass of dimensions comparable to λ, a complementary method subject to a different set of system effects compared to more established techniques. Near-term improvements to the apparatus and experimental technique are expected to push the sensitivity into unexplored parameter space.