Rotational Optomechanics

Abstract

Levitated optomechanics opens the door for many quantum experiments and sensing applications with the advantage of minimising the dissipation to the environment. It provides a unique research platform to control and cool the motion of micro/nano-size objects to the quantum regime, pushing the mass limit of exploring macroscopic quantum phenomena. Apart from the centre-of-mass motion of levitated nanoparticles, control and cooling of rotational degrees of freedom are of significant research interest, which explores another avenue for studying fundamental physics and developing quantum technologies.

This thesis focuses on ro-translational optomechanics with optically levitated nanoparticles in vacuum. A 1550 nm counter-propagation standing-wave optical trap experimental platform has been established for studying levitated optomechanics in high vacuum. Direct loading, optical trapping and corresponding detection techniques for high-efficiency measuring ro-translational degrees of freedom of levitated nanoparticles have been built. A clean, vacuum-compatible method based on laser-induced acoustic desorption (LIAD) is developed for directly loading nanoparticles into the optical trap, enabling us to load tailored silicon nanorods from the substrate with very high efficiency. The translational and rotational dynamics of levitated nanoparticles in vacuum have been systematically studied. Besides driving the levitated silicon nanorotor by circularly polarised light, it has been driven to full rotations at tens of MHz in several millibars in the transverse plane by transferring transverse orbit angular momentum, achieving five orders of magnitude higher applied torque compared to other reported nanorotors with the same optical power. Furthermore, the ro-translational motion of levitated nanoparticles can be cooled by implementing feedback cooling schemes, such as parametric feedback for centre-of-mass and polarization feedback for librational motion. These paves way for next-step tests of rotational macroscopic quantum superposition experiments, such as orientational quantum revivals.

Date of Award	1 Dec 2022
Original language	English
Awarding Institution	King's College London
Supervisor	James Millen (Supervisor) & Anatoly Zayats (Supervisor)