Quantum Control Study On Nitrogen Vacancy Center Spin In Diamond

In this dissertation,I mainly investigate how to control NV-center spin effectively and the geometric phase evolution during controlling.At first,I simply introduce the history of quantum information and the element of quantum computation--quantum bit and quantum logical gate.Then,I list some popular methods which are used to realize quantum computation nowadays.In the final,I lead to our object of study,NV center spin and present the background of quantum control of NV-center spin concisely.Generally,in S_z representation,the two level system can be written as a simple 2 × 2 matrix.It takes reverse-engineering approach,that is to say,what kind of pulse needed in order to realize target state.This method is especially appropriate in the context of quantum control,then derive its time evolution operator exactly which is the core of the problem.The constructed pulse is not only well localized,but also guarantee the high fidelity of logical gate.In this thesis,we solve the single NV-center spin in a special time-dependent magnetic field analytically.The most important thing is that we introduce the symmetric state (?) and antisymmetric state (?).In this way,the seemingly complex three-level system problem turns into a two-level system problem.Base on the exact method of solving two-level system,after unitary transform,we can derive the exact time-evolution operator for original three-level system.With this operator,we can realize state preparation and quantum logic gate operation in NV-center spin system.What's more,we also use Lindblad master equation to investigate how dissipation and fluctuation of magnetic field affects the system evolution.Due to our calculation,this method can also get a high fidelity in quantum logical gate operation.In addition,another useful method is used to solve this model.This method is more clear,and the introduced time-dependent parameter have larger freedom,so it is very easy to solve them.The physically realizable pulse can be derived with simple elementary function and the target logical gate operation can still be achieved in few nanoseconds.I also calculate the nonadiabatic geometric phase during evolution.According to our calculation,it is exactly the half of the solid angle formed by state vector on the Bloch sphere.