Free expansion of a charged nanoparticle via electrostatic compensation

Coherent wavepacket expansion is a key component of recent proposals aiming to create non-classical states of a levitated dielectric nanoparticle. Free evolution, i.e., releasing the particle from its harmonic trapping potential and allowing its position variance to grow, is a simple but effective expansion scheme, but requires accurate force compensation to avoid significant mean displacements of the wavepacket during the free evolution. Here, using an optical trap-release-recapture sequence, we demonstrate an electrostatic compensation technique that enables free evolution without significant mean displacement in 3D, effectively compensating both gravity and stray electric fields. To achieve 100 mu s free evolution times with charged particles, we developed methods to map and correct for force cross-talk, as well as to control the environmental charge state. Combined with a low decoherence environment, our approach enables the preparation of largely delocalized states without the need for long freefall trajectories or a low-gravity environment.