Quantum noise in a nano mechanical Duffing resonator
  We determine the small signal gain and noise response of an amplifier based on the nonlinear response of a quantum nanomechanical resonator. The resonator is biased in the nonlinear regime by a strong harmonic bias force and we determine the response to a small additional driving signal detuned with respect to the bias force. 
E. Babourina-Brooks, A. Doherty, G. J. Milburn