Dynamical Polarization And Measurement Of Nuclear Spin Based On Nitrogen-vacancy Center In Diamond

Quantum mechanics provides us a new way to understand nature and to significantly advance the development of science and technology.The world is currently witnessing the second quantum evolution with new technologies emerging rapidly.The booming of quantum information science and technology,which includes quantum communication,quantum computing and quantum sensing,is able to provide powerful tools for interdisciplinary fields.Over the past decade,nitrogen-vacancy center in diamond has become an appealing solid state spin system for quantum technology.Due to its excellent quantum properties,such as the long coherence time at room temperature,stable fluorescence,optical polarizing and high sensitivity to magnetic field,it becomes a promising candidate for the implementation of quantum sensor,quantum computer and quantum simulator.Based on the nitrogen-vacancy center in diamond,we investigate the polarization and the spin state readout of nuclear spin.The detection sensitivity of nuclear magnetic resonance(NMR)and the spatial resolutionof magnetic resonance imaging(MRI)are limited by the nuclear polarization.Dynamical nuclear polarization(DNP)is an efficient way to improve the nuclear polarization.However,the conventional DNP methods often require cryogenic temperature and large magnetic field.In this thesis,to overcome these constraints,we present a DNP method based on quantum control of nitrogen-vacancy center in diamond under continuous driving.Based on the Hartmann-Hahn resonance condition,our method can efficiently drive the ensemble nitrogen-vacancy centers via sweeping the frequency of the microwave field so that most of the nitrogen-vacancy centers can contribute to the DNP.We numerically simulate the dynamic process of ¹³C nuclear polarization.The result demonstrates that our method is able to efficiently reduce the influence of the inhomogeneous broadening of nitrogen-vacancy centers on dynamical nuclear polarization.In the second part,we investigate the readout of nuclear spin state.For a classical physical system,one can observe its state without destroying or disturbing its original state.However,once a quantum system is measured,its quantum sate usually will be changed.Furthermore,it is difficult to measure some“dark”quantum systems(e.g.nuclear spin system)directly.Quantum state tomography is an efficient way to reconstruct the quantum state from the measurement data.We adopt the idea of quantum sensing and propose a quantum state tomography scheme based on the local random control field using a single qubit sensor.We experimentally implement the method by using the nitrogen-vacancy center that couples to a ¹³C nuclear spin in diamond.This allows us to perform quantum state tomography of this two-qubit system by only applying a local random control field to the nitrogen-vacancy center.We characterize the fidelity of quantum state reconstruction,which shows high performance of our scheme.Therefore,the technique provides a new tool to readout the state of nuclear spin based on a quantum sensor.