Nonlinear optomechanically induced frequency locking and its application to room temperature mass sensing

We here propose a mass sensing mechanism based on nonlinear optomechanics. Driven by a laser field with a two-tone pump satisfying a specific frequency condition, a cavity optomechanical system can enter a special dynamical pattern correlating the mechanical oscillation and the sidebands of the oscillatory cavity field. Then, the associated mechanical oscillation frequency can be completely locked to the original mechanical frequency determined by the system fabrication. After adding a nano-particle, which has its mass δm to be measured, to the mechanical resonator as a detector, the cavity field sidebands will exhibit a detectable change, so that the tiny mass δm can be deduced from the measured sideband intensities. Most importantly, within a small range of δm, the modified amount of the sideband amplitude is linearly proportional to δm, thus providing a good method for the precise determination of the mass δm. Given a system with a membrane in the middle, one can apply an additional single-tone laser field to magnify the sidebands much further, achieving an ultra-high sensitivity δm/m ∼ 10^-11 (m is the mass of the membrane) even with a moderate mechanical quality factor of the system. The operation range of the sensors is very wide, covering 7 or 8 orders of magnitude. Moreover, a particular advantage of this type of mass sensor comes from the robustness of the realized dynamical pattern against thermal noise, and it enables such mass sensors to work well at room temperature.