Effect Of Diamond Surface Treatments On The Spin Coherence Of Shallow NV Centers

Nowadays,computer technology presents great progress with the development of hardware systems.The demand of high abilities of computing and data processing have been increased in recent years.However,classical computers have hit plateaus in the two abilities,so physicists and mathematicians are exploring "nonclassical" methods to solve the problems.Therefore,quantum information,a technology of processing information by using quantum mechanical systems,has been a popular issue.More precisely,quantum information is a new field of science and technology,combining a lot of subjects like quantum physics etc.With the development of quantum information science,the concept of quantum computer has also been proposed,which involves the quantum components,that is,hardware support,so solidstate quantum systems have become an important research direction.The diamond NV center is a very promising solid state quantum system.It is a composite structure composed of a substitutional nitrogen(N)atom in diamond and a carbon vacancy(V)in the nearest ortho position,which is a defect.It has many excellent features,such as fine biocompatibility,optical stability,long relaxation time and coherence time at room temperature,etc.,and is widely used in many fields,especially quantum precision measurement and quantum computing.Different from other solid state quantum systems requiring various experimental conditions such as low temperature etc.,the diamond NV center system can perform to manipulate various spin states,i.e.,quantum states at room temperature,and the long coherence time provides the possibilities for multiple quantum operations and longterm quantum operations.Therefore,the diamond NV center system has been researched by more and more researchers.This thesis introduces the investigation for solving the problems of making diamond NV center a solid state quantum device,including the following aspects:The first chapter:We first introduced the development and research background of solid state quantum systems,especially the diamond NV center system.Then we introduced the physical properties of the basic structure and spectral properties of the diamond NV center.Then we introduced the experimental platform made up of laser confocal system,microwave system and magnetic field system,which was designed according to the characteristics of the NV center.Finally,the content this thesis is outlined.The second chapter:We first analyzed the problems in using diamond NV centers for applications.Then,the methods of bulk diamond surface treatments by micronano processing technology and micronano processing platform instruments were introduced in detail,especially the surface etching technique and surface deposition technique.Finally,we summarized the characteristics and experience of our diamond surface treatment by using micronano processing technology.The third chapter:We introduced a method for preparing NV centers in diamonds.In nanodiamonds,we mainly introduced the characteristics of the NV center and how to extend its coherence time by high temperature annealing.In bulk diamond,we mainly introduced the method of ion implantation to prepare the NV center in highpurity electric grade diamond,and also included the NV center yield,methods to improve the coherence time of the implanted NV centers.Then we focused on how to use a surface mask and exposure technique and etching technique to prepare a shallow NV center array.Then we also studied the related properties of the implanted NV center:single photon,Rabi oscillation,Ramsey fringe,spin echo,coherence time and so on.And we gave methods to measure these related properties,such as using the basic microwave pulse sequence.The fourth chapter:We used plasma etching technique and surfacecoating liquid material technique to study the dependence of diamond NV center decoherence and depth,and the contribution of external spins and surface spins to decoherence.After continuous plasma etching,the deep NV center in the diamond approaches the diamond surface at nanometer scales.At the end of each etch,we applied a large amount of electron spin and nuclear spin on the diamond surface to further study the interaction between depthdependent decoherence and different kinds of spins.Our final research results showed that the surface spin effects could not be completely ignored when using the diamond NV center for external spin detection.The depth at which the applied spin contributes the most to the NV center decoherence is called the charateristic depth,which is about 6 nm from the diamond surface.This finding not only provides a basis depth for the NV center used for detecting external spin,but also provides an important reference for reducing the decoherence of the NV center.The fifth chapter:We first introduced the features and potential of the diamond NV center as an application device.A surface coating technique that could be used for device passivation and packaging is then proposed.This surface coating technique was a technique that used an ALD technique to deposit an oxide protective coating layer on the diamond surface to enhance the spin properties of shallow NV centers in diamond.This surface coating technique had many advantages.It not only controled the thickness of the oxide protective coating layer,but also did not damage the diamond surface and was reversible.For the improvement of the spin properties of shallow NV centers,it was obvious that when the thickness of the oxide protective layer was appropriate,the coherence times remained almost the same,and the relaxation times and the free induced evolution times were greatly improved.This surface coating technique was expected to provide technical support for passivation and packaging for solid state quantum system devices.The sixth chapter:We summarized our work and then presented the related work prospects.