The Coupling Of NV Center And Energy Transfer Mechanism

The NV center in diamond has been studied by many research groups around the word recently. As a solid state quantum bit and single photon at room temperature, it has been widely applied in quantum memory, quantum information processing, quantum key distribution, fluorescence label in biology and high resolution imaging. Further-more, there are also some important applications in room-temperature nanoscale mag-netometry, bio-magnetometry, electrometry, sensitive nanoscale thermometry, electron spin and nuclear spin detection using NV center. Most of these applications and re-searches of the NV centers are based on the fluorescence detection of the NV center. Therefore, it is necessary to study the fluorescence mechanism of the NV centers.The fluorescence of the NV center is decided by the radiative rate and non-radiative rate. On the one hand, the NV centers can be coupled to optical structures, especially cavities and waveguides. These couplings can increase the radiative rate, enhance the fluorescence intensity and shorten the fluorescence lifetime. On the other hand, NV centers can transfer the energy nonradiatively to the nearby materials, leading to the increase of the non-radiative rate, the decrease of fluorescence intensity and the short-ening of fluorescence lifetime. However, this brings the application of NV center as the donors in resonance energy transfer microscopy.In view of the importance of the coupling of the NV center, we investigate the coupling of NV center to a tapered fiber. On the other hand, we demonstrate the energy transfer from a single NV center in a nanodiamond to a graphene monolayer. The main contents of my graduate thesis are summarized as below:1. Laser scanning confocal microscopy and the fabrication of NV centers in diamondWe built the laser scanning confocal microscope system to get the confocal scan-ning image of the NV center. A time-correlated single photon counting module was used for measuring second-order correlation function and fluorescence lifetime. Flu-orescence spectra were measured using the spectrometer of a laser confocal Raman microscope system. In order to increase the extinction ratio between the on and off in-tensities of the laser, we employ the double path configuration. A high extinction ratio is important in long experiments so that the electronic spin is not re-polarized to the ms=0state. In addition, we also study the fabrication of NV centers both in nanodiamond and in bulk diamond. The proportion of nanodiamonds containing NV centers increased dramatically after treatment; and single color centers were generated by nitrogen im-plantation in bulk diamond.2. Photoluminescence spectroscopy and spin spectroscopy of the NV centerThe physical structure, electronic structure and the fluorescence properties of the NV center were introduced. In addition, the photoluminescence (PL) spectroscopy and the second-order correlation function were measured. From the second-order correla-tion function measurement, the single photon source can be verified. Finally, we in-troduce the spin-Hamiltonian of the NV center. The continuous-wave ODMR spectra were measured, which provides a means to measure the energy levels of the NV spin system. Furthermore, we implemented pulsed microwave experiments, such as Rabi nutations, free induction decay, spin echo.3. Energy transfer from a single NV center in a nanodiamond to a graphene monolayerWe demonstrate the energy transfer from a single NV center in a nanodiamond to a graphene monolayer. We measured the fluorescence lifetime and intensity of single NV centers in nanodiamond on graphene substrate and quartz substrate, respectively. The results showed, for sample on a graphene monolayer, the lifetime and intensity of the single NV center in nanodiamonds were statistically smaller than that on bare quartz substrate. This result demonstrated the existence of the energy transfer from a single NV center in a nanodiamond to a graphene monolayer. Lastly, based on the theory of Swath and Sebastian, the energy transfer rate from NV center to graphene following a (distance)"4dependence was introduced. Energy transfer efficiency was calculated theoretically for the most probable nanodiamond size29nm in our work, which is consistent with the experimental value.4. Fiber-integrated diamond-based single photon source and magnetometerWe study the coupling of the NV center in nanodiamond to a tapered fiber. Com-paring the scanning images which were collected via tapered fiber and confocal micro-scope, the fluorescence counts from single NV centers through tapered fiber were signif-icantly higher than that from confocal microscope. The second-order correlation func-tion and optically detected electron spin resonance spectra of single NV centers were measured via tapered fiber. This makes the realization of fiber-integrated diamond-based single photon source and magnetometer possible. This fiber-integrated magne-tometer is promising for its high collection efficiency, high magnetometer sensitivity, convenient fabrication and compact optical design.