A cavity optomechanical system, consisting of an optical cavity with a macroscopic movable mirror, makes use of the high-Q optical mode to enhance the interaction between light and the mechanical oscillator. Such optomechanical interaction enables not only high-precision measurement of mass, force and displacement, but also precise manipulation of the mechanical motion, for example, cooling and amplification of the mechanical motion. When the mechanical oscillator is cooled to the quantum ground state, macroscopic quantum phenomenon can be explored in the oscillators containing more than 10^20 atoms or molecules.

Usually, the cavity optomechanical system is dominated by linear interaction, while the nonlinearity is extremely weak. Now, a report in Physical Review Letters describes the resonant enhancement of nonlinearity by orders of magnitude. In this work, the team led by Professor Yun-Feng Xiao and Professor Qihuang Gong at Peking University takes advantage of light-enhanced linear optomechanical coupling to create the normal mode splitting, and through frequency matching the nonlinear interaction becomes resonant, which greatly boosts the nonlinearity. They demonstrate parametric down-conversion for polariton pair generation, including photon-like polaritons, phonon-like polaritons and mixed photon-phonon polaritons. Such nonlinear interaction offers a promising way for harnessing the optomechanical nonlinearity to manipulate photons and phonons, and holds great potential for quantum information processing.

References: Yong-Chun Liu, Yun-Feng Xiao*, You-Ling Chen, Xiao-Chong Yu, and Qihuang Gong*, “Parametric Down-Conversion and Polariton Pair Generation in Optomechanical Systems,” Phys. Rev. Lett. 111, 083601 (2013)