Optical and electrical feedback cooling of a silica nanoparticle levitated in a Paul trap

Cooling the motion of nanoparticles levitated in magnetic, electrodynamic or optical traps to a low temperature state is an essential step in order to enable quantum experiments with these systems. Thanks to cavity and feedback cooling, the quantum regime has recently been achieved in optical-tweezer-based traps. In contrast to optical traps, Paul traps offer deeper and larger trapping potentials, which allow particles to be loaded under ultra-high-vacuum conditions. Paul traps are also compatible with low-intensity laser fields for particle detection, which reduces radiation pressure shot noise when compared to optical trapping. These key advantages establish the Paul trap as an attractive platform with which to perform quantum experiments with levitated particles in a highly isolated environment.
Here we will show how we apply a cold damping technique to cool all three motional modes of a silica nanoparticle levitated in a Paul trap down to temperatures of a few mK. As feedback actuators, we use either optical or electrical forces. For both feedback forces, we study the cooling efficiency as a function of feedback parameters, background pressure and the particle's position. Finally, we delineate the next steps necessary for reaching the quantum ground state with such a setup.