Testing the Neutrality of Matter Using Optically Levitated Microspheres

The charge between the electron and proton is commonly considered to be the same in magnitude.

However, the potential unbalances between them could shed light on new physics. We report an

experiment system which traps and cools dielectric microspheres, which are levitated by high

intensity laser and isolated from the environment noise. Such a system offers us a highly sensitive

stage for measuring exceedingly weak forces. Combined with active feedback techniques, we

achieve a resonance peak around 500Hz for a microsphere with a diameter of 7.5?? trapped in a

focused laser beam at several mbar gas pressure in the vacuum chamber. These results provide us

with a solid foundation of future precision measurement and an exceeding charge sensitivity is

expected.