The universal law of gravitation has undergone stringent tests for many decades over a significant range of length scales, from atomic to planetary. Of particular interest is the short distance regime, where modifications to Newto- nian gravity may arise from axion-like particles or extra dimensions. We have constructed an ultra-sensitive force sensor based on optically-levitated micro- spheres with a force sensitivity of 10−16N/√Hz to investigate forces that couple to mass with a characteristic scale of ∼ 10μm. In this talk, I will present the first investigation of the inverse-square law using an optically levitated test mass, along with the technical development that preceded it.
Then I will present a recent precision measurement conducted with the same setup in which we demonstrate, for the first time, a technique capable of using data to model minute electromagnetic forces, hence eliminating the backgrounds limiting many measurements, including short-range forces. This process results in an unprecedented charge sensitivity of 3.3 × 10−5e for a macroscopic object. In addition to improving the sensitivity of experiments probing for new physics, this approach allows precision metrology of the dielectric properties of levitated microspheres. As a specific example, we apply the technique to test the obser- vation that the proton charge is equal in magnitude to that of the electron.
