Phys. Rev. Lett. 117, 173602 (2016)

Optomechanical interactions open up a new range of applications such as cooling nanoparticles and squeezing of light. However, processes reported so far are based on only a linear light–matter interaction, linear in both the position of the oscillator and the amplitude of the optical field. Now, Piergiacomo Zucconi Galli Fonseca and co-workers from University College London in the UK have developed a hybrid trap consisting of an optical cavity field overlapped by a Paul trap and observed for the first time cooling dynamics of levitated nanoparticles via nonlinear coupling. Silica nanospheres (radius 209 nm) were illuminated by a 1,064-nm laser in the hybrid trap. The mechanical frequency of the particle was shifted with respect to the cavity resonance by using two cascaded acousto-optic modulators. The system exhibited an unusual split-sideband structure; frequency-doubled sidebands were observed only in the first few milliseconds after the particle was trapped. The cooling rates were in the 1,000 s−1 range. The cooling rates were further enhanced by trapping the particle away from the Paul-trap centre where it was drawn away from the centre of the antinode of the optical potential.