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

Abstract

We report on a search for non-Newtonian forces that couple to mass, with a characteristic scale of $\ensuremath{\sim}10\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$, 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 a force sensitivity of $\ensuremath{\lesssim}{10}^{\ensuremath{-}16}\text{ }\text{ }\mathrm{N}/\sqrt{\mathrm{Hz}}$. Separately searching for attractive and repulsive forces results in the constraint on a new Yukawa interaction of $|\ensuremath{\alpha}|\ensuremath{\gtrsim}{10}^{8}$ for $\ensuremath{\lambda}>10\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. This is the first test of the inverse-square law using an optically levitated test mass of dimensions comparable to $\ensuremath{\lambda}$, a complementary method subject to a different set of systematic effects compared to more established techniques.