Nonlinearity enhancement in optomechnical system
  The nonlinearity is an important feature in the field of optomechanics. Employing atomic coherence, we put forward a scheme to enhance the nonlinearity of the cavity optomechanical system. The effective Hamiltonian is derived, which shows that the nonlinear strength can be enhanced by increasing the number of atoms at certain range of parameters. We also numerically study the nonlinearity enhancement beyond the effective Hamiltonian. Furthermore, we investigate the potential usage of the nonlinearity in performing quantum nondemolition (QND) measurement of the bosonic modes. Our results show that the present system exhibits synchronization, and the nonlinear effects provide us an effective method in performing QND. 
Ling Zhou, Jiong Cheng, Yan Han, Weiping zhang
quant-ph