Aquecimento por recuo na levitodinâmica não paraxial

Abstract

Levitodynamics is a subfield of optomechanics that studies the motion and manipulation of nano- and microparticles levitated by optical forces. It is a highly active research field, standing out especially as a tool used to investigate how mesoscopic mechanical systems behave when cooled to the quantum regime. In this work, we focus on a particularly popular experiment: a levitated dielectric nanoparticle (typically a silica sphere) trapped by an optical tweezer in ultra-high vacuum. One of the main obstacles to reaching the quantum ground state is the random momentum exchange between the photons of the trapping beam and the particle, an effect known in the literature as recoil heating. Given the relevance of this problem, there are many theoretical models in the literature for the optomechanical interaction between the laser and the particle. Several of them consider only the quantum nature of the particle’s COM, but model the electromagnetic fields classically. The advantages of a fully quantum model for this problem have been explored in recent publications, an approach we adopt in this work. Another widely used premise is the paraxial approximation to describe the trapping beam; however, given the tightly focused nature of the beams used in experiments, the need to go beyond this approximation has become clear. Therefore, we use the Richards- Wolf model for the optical trapping beam, built precisely to overcome the limitations of the paraxial model. Finally, we explore how focused vector Gaussian beams can be used to minimize recoil heating. We take as an example the focusing of a beam with radial polarization and show that the heating is, indeed, reduced in this case.