Quadratic optomechanical cooling of a cavity-levitated nanosphere

TL;DR

This paper demonstrates quadratic optomechanical cooling of a levitated nanosphere using a high finesse cavity, leading to nonthermal energy distributions and advancing the potential for generating nonclassical states.

Contribution

It introduces a purely quadratic coupling mechanism for cooling a levitated nanoparticle, enabling control over nonlinear damping and nonthermal energy distributions.

Findings

Quadratic coupling induces Van der Pol nonlinear damping.

Cooling results in strongly nonthermal energy distributions.

Experimental control of energy distribution via nonlinear damping.

Abstract

We report on cooling the center-of-mass motion of a nanoparticle due to a purely quadratic coupling between its motion and the optical field of a high finesse cavity. The resulting interaction gives rise to a Van der Pol nonlinear damping, which is analogous to conventional parametric feedback where the cavity provides passive feedback without measurement. We show experimentally that like feedback cooling the resulting energy distribution is strongly nonthermal and can be controlled by the nonlinear damping of the cavity. As quadratic coupling has a prominent role in proposed protocols to generate deeply nonclassical states, our work represents a first step for producing such states in a levitated system.