  Particles with electric charge 10^(-12)e in bulk mass are not excluded by
present experiments. In the present letter we provide a feasible scheme to
measure the millicharged particles via the optical cavity coupled to a
levitated microsphere. The results show that the optical probe spectrum of the
micro-oscillator presents a distinct shift due to the existence of millicharged
particles. Owing to the very narrow linewidth(10^(-7) Hz) of the optical Kerr
effect, this shift will be more obvious, which makes the millicharges more easy
to be detectable. We propose a method to eliminate the polarization force
background via the homogeneously charged ring, which makes the scheme displays
strong advantages in precision than the current experiments. The technique
proposed here paves the way for new applications for probing dark matter and
nonzero charged neutrino in the condensed matter.
