Neutrality of matter search with levitated microspheres

 It is commonly accepted that the charge of the electron is equal in magnitude to the charge of the proton. This observation has been tested with great precision over the last century and has supporting arguments from the theory side. However, the measurement of this equality is a sensitive tool to probe new physics as it is breaking down in few suggested extensions of the standard model. We report on a neutrality of matter test conducted with optically levitated microspheres. In this test, the electrostatic response of a micron size sphere with an equal number of protons and electrons is measured with very high sensitivity. This technique is complementary to other methods used to test matter neutrality in the past. The current sensitivity is not due to fundamental physical limitations and ongoing improvements of the system targeting better background mitigation and modeling, together with improved force sensitivity, are expected to further extend the parameter space covered by the technique.