| The nitrogen-vacancy (NV) color center consists of a substitutional nitrogen im-purity adjacent to a missing carbon atom site in the diamond lattice. The electron spin of the NV center is a room temperature quantum bit which can be polarized and ma-nipulated by optical and magnetic resonance methods. Owing to its outstanding optical and spin properties at room temperature, the NV center in diamond has increasingly attracted attention in recent years, and various promising applications based on these properties have been exploited, such as quantum information processing, nanoscale highly sensitive physical quantities sensing, bio-imaging, quantum optics, etc.. The major aspects of our research work involves:a scanning confocal microscope system was built for getting the PL spectrum, NV center imaging and dectection, single photon source identification and other optical properties investigation. With the scanning con-focal microscope and magnetic resonance systems, various microwave pulse sequences were applied on the single NV center to manipulate and study its coherence properties that are of importance for the application as a quantum bit. For the NV center prepa-ration, we introduced a method of NV center generation in nanodiamonds based on annealing-oxidation process. Comparing with the traditional methods, this method has the advantages of high-efficiency, environment-friendly, high-quality, saving time and effort. Using thus prepared samples, we investigated a statistical correlation of T1and T2of the NV center to clarify the role of surface spins to the spin relaxation of nitrogen vacancy centers. As a result of the theoretical analysing and the experimental data fit-ting, the surface spin density was roughly estimated and some of the rules of relaxation of NV center to the surface spins was discussed.This thesis is composed of six chapters:1. First part of this thesis is the introduction. Firstly, different types of the dia-monds and the color centers in diamonds were introduced. The spin of the NV center is an outstanding candidate for the room temperature quantum bit which can be used for quantum computation. Further more, the NV center is a stable room temperature single photon source which can be used in the field of quantum information. Due to its dimension at the atomic-scale and properties sensitive to physical quantities, such as magnetic field, electric field and temperature, NV center has also found applications in the fields of nanoscale high sensitivity sensing and detecting.2. Second part of this thesis is about the basic properties and quantum manipu-lation of the NV center. The physical structure and related symmetry, PL spectrum, electronic structure and spin polarization mechanism of the NV center were firstly in-troduced. And then PL spectrum, imaging and single photon source identification of the single NV center were obtained by the scanning confocal microscope system. By mea-suring and analyzing the second order correlation function at different exciting power, the photophysics properties of a single NV center was demonstrated. To manipulate the quantum bit, microwave was applied to drive the spin states transition. CW-ODMR and Pulse-ODMR spectra of the single NV centers were firstly obtained. From these spectra, we can get information about electronic energy levels of the NV center and even its fine structures due to the interaction with the surrounding nuclear spins. After that, microwave pulse sequences were applied to manipulate and characterize the co-herence properties of the quantum bit, such as Rabi oscillation, Ramsey fringes, Hahn-echo, etc.. At last, taking CPMG sequence as an example, we introduced the dynamic decoupling methods to decouple the spin bath from a central NV center. The double electron-electron resonance (or electron-nuclear double resonance) for manipulating dark electron spins (or nuclear spins) was also shown. Based on these dynamic decou-pling and double resonance sequences, the principle and research progress of sensing dark spins using NV centers were given.3. In the third chapter, we give a brief introduction to the recent developments of NV center researches. Firstly, basic principle and research progress in nanoscale high sensitivity sensing of magnetic field, electric field, temperature, mechanical resonator motion and strain by using NV centers were summarized. Secondly, we listed some significant developments in the fields of quantum information processing using NV center. At last, other quantum systems which are similar to the NV center in solid states such as defects in SiC and rare earth doped YAG crystal emerged recently are introduced.4. In the fourth chapter, our work focuses on generation of NV centers in nanodia-monds by high temperature annealing. Different methods of NV center preparation for different types of diamonds were reviewed firstly. Owing to the importance of shallow NV centers in the research, the methods for generating this type of color centers were introduced in details. We have developed a method that the NV centers were created in nanodiamonds in a direct annealing process. Nanodiamonds used in the research are usually commercially available HPHT type, in which the N content is at the level of hundreds of ppm. However, only1%of the as-received nanodiamonds contain NV centers. The ratio of the nanodimonds that contained NV centers was highly improved after high temperature annealing. This result is attributed to that the inherent vacancies were activated to migrate in the diamond lattice and possiblely to meet the inherent N substitutions to form NV centers during annealing process. This suggested that we can utilize vacancies and N substitutions inherently existed in nanodiamonds to generate nitrogen-vacancy centers without using high energy particles irradiation. As a result of optimized temperature annealing, the ratio of the nanodiamonds that contain NV cen-ter increased more than ten times compared with that of untreated as-received samples. Further more, most of the NV centers in the nanodiamonds are single NV centers, which is very important for the practical applications. Comparing with the traditional meth-ods for NV center generation, the annealing method introduced here is high-efficiency, environment-friendly, saving time and effort. This method may also be of interest for NV center preparation in other types of diamonds. Using the NV centers prepared by this method, we also experimentally demonstrated energy transfer from a single NV cen-ter in nanodiamond to a graphene monolayer and developed one type of fiber-integrated diamond-based magnetometer.5. In the fifth chapter of this thesis, we demonstrated a statistical correlation in-vestigation for clarifying the role of surface spins to the spin relaxation of NV centers in nanodiamonds. Due to the existence of spins (mainly associated with surface dan-gling bonds) on the surface of diamonds, the relaxation time of the shallow NV center will, in general, decrease. For the same reason, the relaxation time of NV center in nanodiamonds is smaller than that of in bulk diamond with the same N content. With the development of the usage of the NV center as sensor for various quantities from inner diamond to the outside, the influence of the surface spins to the relaxation of NV centers and the mechanism behind have become research focuses recently. In our work, the Ti and T2of72single NV centers were measured, and their correlation is fitted to the numerical simulated results according to a spherical model. The surface spin den-sity was roughly estimated from the fitting results and the surface spin density of the nanodiamonds obtained here was much higher than that of CVD-bulk diamond as re-ported by other groups. This is reasonable due to the poor surface crystal quality of the nanodiamonds. We hope that this work can be helpful for the research of using NV center as nanoscale high sensitivity sensor.6. In the last chapter, a summarization and a prospect of our work were presented... |
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