The Decoherence Theory And Its Application For Nitrogen-Vacancy Center In Diamond

Solid Spin-based quantum technology is one of the most important branches in physics, while the decoherence caused by the interaction between the solid spin and its environment is one of the key problems for quantum technology. The nitrogen vacan-cy center(NV color center) in diamond has a relatively long coherence time at ambient temperature, can be coherently controlled by Micro Wave and be optically read out, has recently become an ideal platform for quantum technology. The important advances include:sensing single nuclear spin, nanoscale magnetometry and implementation of quantum error correction and so on. However, the decoherence caused by hyperfine interaction between the surrounding nuclear spin bath is still the main obstacle for these technology. Although dynamical decoupling technology has acquired great success in decreasing the effect of decoherence induced by the nuclear spin bath, there are some disadvantages:it is not compatible with the coherent control process of the qubit, which may limits its application in some aspects. Except for the dynamical decoupling method, there are some other methods which can reduce the effect brought by decoherence:For example, one can prepare the nuclear spin bath state into a low noise state by dissipa-tive nuclear spin process induced by illuminated NV center. An example is increasing the polarization degree of the nuclear spin bath via dynamic polarization process. The advantage of this method is that it is not conflict with the coherent control of qubit and hence is an important direction for controlling the coherence of the NV center qubit.In this thesis, we mainly study two aspect:one is how to control the nuclear spin bath through the dissipative process of the nuclear spin induced by optically illuminated NV center, the other is how to optimize the data post processing in quantum metrology. For the first aspect, we study three problems, the first is the theoretical explanation of experiment phenomenon[1]:employing the the hyperfine interaction between the nu-clear spin and the N V center to suppress the Overhauser fluctuation of nuclear spin bath surrounding the NV center via dissipative method. Then we investigated theoretically how to optimize the suppressing effect. The second is proposing a method to polarize the nuclear spin bath near the ground state level anti-crossing point in NV center, the third is theoretical studying of the relaxation and depahsing process of the nuclear spin when NV center is optically illuminated. The result implies that enhancing the optical polarization degree of NV center is an effective method to suppress the nuclear spin dissipative process induced by illuminated NV center. For the second aspect, we study how to optimize the data post processing in the magnetometry based on the phase esti-mation algorithm and the real-time track ability of magnetic field for the magnetometry based on phase estimation algorithm.