Nanodiamonds in levitated optomechanics

Abstract

This thesis reports on research undertaken to explore the viability of using nanodiamonds containing nitrogen vacancy (NV) centres in optical dipole traps. The impact of illuminating single NV centres with 1550 nm, a common dipole trap wavelength, is investigated. A reduction of 7% in the fluorescence intensity is observed using 20-30 mW of illumination, whilst the NV centre’s optically detected magnetic resonance (ODMR) signal contrast and electron spin T2 time remain unaffected. These results are better than those of similar experiments with 1064 nm. A method for creating and characterising pure type IIa nanodiamonds containing NV centres is presented. Bulk chemical vapour deposition (CVD) diamonds are electron irradiated and annealed, before being ball milled into nanodiamonds. The bulk purity is determined by quantitative electron paramagnetic resonance. The nanodiamonds are characterised by Raman spectroscopy, electron microscopy and energy dispersive X-ray spectroscopy (EDX). Small quantities of contamination by the silicon nitride milling material could be found using EDX. A confocal microscope was constructed and single NV centres inside the nanodiamonds were found to be photostable and ODMR shows an average ODMR contrast of 9%. An optical dipole trap was constructed and CVD derived nanodiamonds were levitated. Measurements of the centre-of-mass motion show that unlike commercial type 1b nanodiamonds, they mostly remain at or close to thermal equilibrium in moderate vacuum where commercial material was previously reported to burn and/or graphitise, even when the optical intensity is raised above 700 GW/m². Nanodiamonds are observed to be suddenly ejected from the trap at ~1 mbar