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Towards cooperatively enhanced resonant dipole forces in optical levitation, harnessing quantum emitters in diamonds
thesisposted on 2022-03-29, 03:10 authored by Reece P. Roberts
Optical trapping offers a non-contact, non-destructive tool for manipulating and handling particles, from micron sized particles down to individual atoms with light. One can distinguish two different applications for optical trapping. The first relying on the ability to trap small particles (from tens of nm to tens of µm); the second, related to the confinement and cooling of atoms or collections of atoms. Until now there has been no system that combines the forces due to both dielectric particle trapping and atom trapping as they are usually contained in completely separate parameter regimes, even though both of these trapping applications arise from the same force. The force is the result of the interaction of the polarisability of the trapped object with the electric field of the trapping laser, which depends directly on the dipole strength trapped object. In the case of classical trapping, the force acts on an induced dipole caused by the electric field on the object, whereas in the case of atom trapping, the induced dipole arises from the optical transitions present in the electronic structure. In this way, optically trapped nano-particles containing embedded optical defects brings about a new regime of trapping and cooling nano-particles. This new trapping regime will allow well established techniques from atom trapping to be applied to the more massive nano-particles. The result is an optical trap showing capabilities with improved trapping strengths and cooling mechanisms. The enhanced control will allow us to cool the centre of mass motion of nano-particles down to their quantum ground state, even in a room temperature environment, exciting for high precision sensing and macroscopic quantum experiments. In this thesis I focus primarily on identifying and observing the trapping forces on the optical defects inside of optically trapped nano-diamonds. I developed an experimental set-up and procedure to isolate, trap and reliably measure the trapping behaviour of nano-particles as a platform for investigating the atomic forces on optical defects in nano-diamonds. I continue with a detailed analysis of the photo-physics of the Nitrogen Vacancy centre which is the most interesting and studied optical defect in diamond. I explore the implications of the intense trapping laser field, required for optical trapping, on the feasibility of observing defect related forces on NV centres in nano-diamonds. Due to the limitations of the Nitrogen Vacancy defect I explore the properties of Silicon Vacancy centres in diamond, highlighting the properties that an ideal particle would posses, with a particular emphasis on generating collective effects. I investigate the effects of the high intensity, near infra-red trapping laser field and show the exciting possibilities of cooling the centre of mass motion and the internal temperature of the nano-particle simultaneously. Whilst I have not yet reached the goal of levitating a particle and observing the cooperatively enhanced resonant optical dipole forces on its internal embedded defects, I have undertaken a number of steps providing the ground work and foundations for ultimately observing and using these forces.