Theoretical Investigation Of Dipole Coupled NV Centers In Diamond

Negatively charged nitrogen-vacancy center (NV) in diamond shows bright and stable fluorescence. Its ground spin state has long coherent time in room temperature and can be manipulated by microwave precisely. These advantages make it not only an excellent luminescence defect used for quantum optics and for investigation of energy transfer in molecular, but also an excellent room temperature quantum system with lots of applications in quantum physics, quantum information, high sensitivity measurement and biological labeling.People are persuing faster and faster information processing speed with the infor-mation explosion. Traditional electron integrated chip has met serious physical limita-tions, such as quantum effect of electrons, the integrated techniques and effective heat dissipation. The Moore Law could not be continued. Based on the quantum physics, quantum information is the future information techniques. It has an unparallel prospects in the information acquisition, transfer and especially parallel processing. Various tech-niques for achieving quantum processor chip have been studied, and the solid system, especially the NV centers in diamond is one of the most competitive platform.At present, the single qubit operation of the quantum state of NV center is mainly based on microwave pulses. The wavelength of the microwave is the order of centime-ters, while the wavelength of the laser in microns. Qubits encoded on optical levels of NV centers can also realize single qubit operations and two qubit logic gates based on electric-dipole coupling. Qubit based on optical levels not only keeps the scalabil-ity of spin qubit, but also has good integrated feature. It is more suitable for quantum processor chip. However, as a crystal defects, the energy levels of NV center are rel-atively complex, and there are various dipoles and transition processes. The coupling dynamics have not been very clear. In order to have a good knowledge of the dynam-ics of electric-dipole coupled NV centers and use it better in application, we conducted theoretical studies as follows:1. First, we reviewed and described the energy level structure of a single NV center. The widely accepted group method was adopted to re-analyse the energy level structure. We reviewed the popular energy level model and carefully described its tunability by electric fields, strain and magnetic fields. Tuning the energy levels of different NV centers to be resonant is an indispensable technique in experiment. 2. The dynamics of the electric-dipole coupled NV centers were calculated in de-tail. NV center is a multi-level structure and the electric-dipole coupling can have differ-ent situations. We wrote the master equation of two coupling NV center using quantum electrodynamic method, and calculated the dynamics in detail, including situations of coupling by linear polarized dipoles, circularly polarized dipoles, linear polarization and circular polarization dipoles. These processes will be helpful in the investigation of energy transfer in quantum system, and in developing quantum devices based on the electric-dipole coupling. We also proposed several applications based on the electric dipole coupling, including vertical distance calibration in super-resolution imaging and nonlocal spin flipping control.3. We studied a scheme of enhancing the electric-dipole coupling by surface plas-mon polarization (SPP) on metal surface. NV centers in diamond can be produced by ion implantation in array and usually distribute several ten nanometers under surface. Metal film deposited on the surface can be used as a planar SPP waveguide to enhance their coupling. We reviewed the Green function method of calculating the coupling strength of the two dipoles, which could be used when the medium was inhomogeneous and with dispersion and absorption. Then we used it to calculate the lifetime and coupling strength of two NV centers near diamond interface and metal slab. Both the affection of the depth of NV centers and the thickness of metal slab were considered. This scheme makes NV centers effectively coupled in the distance of optical wavelength, and fa-cilitates the reading out the final quantum state of close NV centers without the aid of optical super-resolution.This thesis is arranged with the following contents. The first chapter introduces the research background and the current research of NV center, and states why we are interested in NV centers coupled by electric dipole; in the second chapter, we will anal-ysis and review the energy level structure of NV center based on group theory, and describes in detail the various methods of tuning the structure by external field; the third chapter shows the detailed calculation of coupling dynamics of NV centers by the master equation and possible applications based on the dynamics; the fourth chapter re-views the Green function method of calculating the coupling strength of the two dipoles and calculate the coupling of two NV centers affected by diamond interface; the fifth chapter shows detailed calculation of the coupling of two NV centers enhanced by the metal slab; the sixth chapter describes a minor application of coupled solid-state spins, which are used for entangled state preparation and magnetic field measurement; the last chapter summarizes the work here, discusses the unresolved problems and makes an outlook. Since NV center is a typical defect in solid, these theoretical studies are also useful for the investigation of coupling of other defects in solid. Researches on optical pro-cesses of NV centers can also be used for better controlling of its spin dynamics, and for combining the advantage of optical system and spin system. Therefore, optical process-es in NV centers and their electric-dipole coupling will have important applications in quantum information. In the future, we will consider the method of effectively coupling NV centers in environments with phonons, and consider developing quantum devices based on the enhanced dipole-coupling.