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, successfully compensating both gravity and stray electric fields. To achieve 100 microsecond 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.