Cooling the motion of a levitated nanoparticle by quadratic coupling and coherent scattering*

We report on cooling the center-of-mass motion of a nanoparticle by coupling its motion a high finesse cavity [1]. Our experiment exploits a hybrid trapping potential obtained by overlapping an electrodynamic potential (Paul trap) and an optical standing wave. The coupling between the optical field and the motion of the nanoparticle along the cavity axis can be tuned to be purely quadratic in displacement. We experimentally demonstrate that the resulting energy distribution is strongly nonthermal and can be controlled by the nonlinear damping induced by the cavity. Quadratic coupling has a prominent role in proposed protocols to generate non-Gaussian quantum states. While still in the classical regime, our work represents the first experimental demonstration of cooling exploiting this type of interaction. We will also present our initial results on cooling of a tweezer levitated nanoparticle exploiting coherent scattering. This technique, initially developed in the context of cavity QED, has been instrumental in achieving ground state cooling in a levitated system. Among the many appealing aspects of this approach is the possibility to simultaneously cool many degrees of freedom (DoF) of the nanoparticle and for a nonspherical one this includes the librational DoF.