Measurement of the neutrality of matter using levitated microparticles

Optically levitated nano- and microparticles are highly sensitive force sensors, enabling a wide range of fundamental physics experiments, from exploring quantum behavior in macroscopic systems to testing gravity at short distances. They also provide a unique platform for investigating the neutrality of matter, specifically the equivalence of proton and electron charges or the presence of minicharges. Previous experiments have constrained the abundance of minicharged particles in matter to below 10^(-5) e^- [Moore et al.], with limitations arising from permanent dipole moments and noise floors. Here, we report a new experiment achieving a force sensitivity of 10^(-19) N/√Hz between 100 Hz and 1 kHz and operating in electric fields up to 1 MV/m. By combining permanent dipole cancellation [Priel et al.] with an advanced detection scheme [Mauer et al.], we demonstrate state-of-the-art sensitivity to minicharged particles and deviations from the neutrality of matter.