Quadratic optomechanical cooling of a cavity-levitated nanosphere

Abstract

We report on cooling of the center-of-mass motion of a nanoparticle via a coupling between its motion and the optical field within a high finesse cavity. The resulting coupling is purely quadratic in displacement and gives rise to a van der Pol nonlinear damping. These dynamics are analogous to conventional parametric feedback where the cavity provides passive feedback without an additional measurement. We show experimentally that as feedback cooling, the resulting energy distribution is strongly nonthermal and can be controlled by the nonlinear damping induced by the cavity. Our work represents a demonstration of a cavity cooling dominated by this type of coupling across all optomechanical platforms.