Polarization gradient cooling and trapping of charged and neutral microspheres

Laser cooling of macroscopic matters could pave the way for studying quantum-classic crossover and macroscopic quantum mechanics with potential application in quantum technologies. In this paper, we propose polarization gradient cooling and trapping of the microsphere in free space by exciting the degenerate whispering gallery modes using two counterpropagating optical fields with different polarizations. Cooling temperature is related to the internal temperature fluctuation and collision with residual air molecules as well as laser shot noise. Cooling and trapping of the microsphere are controlled by optical polarization of the optical waves. Orthogonal polarization cooling, compared with nonorthogonal polarization cooling, has higher cooling efficiency and is free from thermo-refractive and -elastic noises and thus has lower temperature. Simultaneous cooling and optical trapping of the microsphere could be achieved with the two nonorthogonally polarized optical fields. Our numerical simulation shows that a cooling temperature of less than 1 mK in a high vacuum environment could be achieved. Finally, influence of the electric affinity of a charged microsphere on optical forces has been investigated. The current scheme is for 1D cooling and trapping, but it could be extended to the 3D case.