Dynamics of a levitated microparticle in vacuum trapped by a perfect vortex beam: Three-dimensional motion around a complex optical potential

We trap a single silica microparticle in a complex three-dimensional optical potential with orbital angular momentum in vacuum. The potential is formed by the generation of a "perfect vortex" in vacuum which, upon propagation, evolves to a Bessel light field. The optical gradient and scattering forces interplay with the inertial and gravitational forces acting on the trapped particle to produce a rich variety of orbital motions with respect to the propagation axis. As a result, the particle undergoes a complex trajectory, part of which is rotational motion in the plane of the "perfect vortex." As the particle explores the whole three-dimensional volume and is not solely restricted to one anchor point, we are able to determine the three-dimensional optical potential in situ by tracking the particle. This represents the first demonstration of trapping a microparticle within a complex threedimensional optical potential in vacuum. This may open up new perspectives in levitated optomechanics with particle dynamics on complex trajectories.