Photodynamics of the nitrogen-vacancy colour centre in diamond

Abstract

The nitrogen-vacancy (N-V⁻) colour centre in diamond has potential applications in quantum information processing and single photon generation. It is currently the only known defect in a solid detected at a single site level that has a non-zero spin in the electronic ground state. For the proposed applications it is desirable to have a good understanding of the electronic structure and photodynamics of the centre, however this is currently not the case. Various models have been proposed to explain the fluorescence characteristics observed in single site experiments. The challenge has been to also account for the properties of the centre well-known from observations of the fluorescence from large ensembles of N-V⁻ in diamond. Firstly, that a non-Boltzmann population distribution between the. ground state spin levels is induced by optical excitation. Secondly, that the fluorescence intensity exhibits a strong dependence on the spin orientation. The models proposed to date either cannot account for these properties, or do so only by invoking optical processes that are arbitrary or, in some cases, not physical. In this thesis an alternative model is presented. The derivation of the model, from group theoretical considerations, does not form part of this thesis. This thesis is concerned primarily with a series of independent measurements to determine the transition rates which govern the photodynamics of the centre. When these transition rates are known, there will be no free parameters in the model and the N-V⁻ emission can be simulated for an arbitrary optical field by solving the classical rate equations. To conclude the first part of this thesis, a two-pulse optical excitation is considered and the results of experiment are compared to the predictions of the model. The latter part of t his thesis is concerned with optically detecting single N-V⁻ centres. A confocal microscope system, to enable single site detection, was developed as part of this work. The photon statistics from a single N-V⁻ centre is compared to the statistics predicted by the model. The implications for the modelling of individual N-V⁻ photon statistics are discussed.