Optomechanical Backaction in the Bistable Regime

With a variety of realisations, optomechanics utilizes its light matter interaction to test fundamental physics. By coupling the phonons of a mechanical resonator to the photons in a high quality cavity, control of increasingly macroscopic objects has become feasible. In such systems, state manipulation of the mechanical mode is achieved by driving the cavity. To be able to achieve high drive powers the system is typically designed such that it remains in a linear response regime when driven. A nonlinear response and especially bistability in a driven cavity is often considered detrimentally to cooling and state preparation in optomechanical systems and is avoided in experiments. Here we show, that with an intrinsic nonlinear cavity backaction cooling of a mechanical resonator is feasible operating deeply within the nonlinear regime of the cavity. With our theory taking the nonlinearity into account, precise predictions on backaction cooling can be achieved even with a cavity beyond the bifurcation point, where the cavity photon number spectrum starts to deviate from a typical Lorentzian shape.光力学（optomechanics）凭借多样的实现方案，借助光与物质的相互作用来检验基础物理规律。通过将机械谐振器的声子与高品质腔中的光子耦合，对日益宏观的物体实现操控已成为可能。在这类系统中，机械模式的态操控可通过驱动光学腔完成。为达成高驱动功率，这类系统通常被设计为在驱动过程中始终处于线性响应区间。驱动腔中的非线性响应，尤其是双稳态效应，常被认为会损害光力学系统的冷却与态制备效果，因此实验中通常会规避此类情况。本文证明，借助本征非线性腔，即便在腔的深度非线性区间内运行，仍可实现机械谐振器的反作用冷却。我们的理论将非线性效应纳入考量范畴，即便当腔光子数谱开始偏离典型洛伦兹（Lorentzian）线型的分岔点之外，仍可对反作用冷却实现精准预测。