Simultaneous ground-state cooling of two mechanical modes of a levitated nanoparticle

By using coherent scattering in an optical cavity, minimising decoherence sources like gas molecule collisions and the influence of phase noise, it was possible to reduce the average phonon occupation to below 1 and enter the quantum regime. By polarisation control, the influence of a dark mode is avoided, that otherwise hinders efficient, simultane-​ous cooling of several degrees of freedom. In combination with active feedback tech-​niques, 3D cooling of the centre of mass motion is in reach and paves the way towards full quantum control of large systems.