| As an intrinsic property of the nucleus,the nuclear spin can interact with external magnetic field,surrounding electron spins and other nuclear spins.These interactions lead to various applications in magnetic resonance and quantum information process-ing.On one hand,nuclear spins are intrinsic probes for detailed structural information of molecules,and the developed nuclear magnetic resonance technology has been exten-sively explored in condensed matter physics and life science.On the other hand,nuclear spins possess long spin coherence time and are widely presented in various quantum systems,such as quantum dots and semiconductor defects system.These features make nuclear spins an excellent candidate for realizing quantum computing,quantum simu-lation and building quantum networks.However,the nuclear magnetic moment is three orders of magnitude smaller than that of the electron spin,which means nuclear spins are extremely difficult to polarize and control.Therefore,detection and coherent control of individual nuclear spins is still a challenging task.Utilizing the electron spin with a single nitrogen vacancy（NV）center in diamond to detect and control surrounding nuclear spins is a promising approach to address this challenge.This dissertation focuses on the multi-qubit quantum system composed of NV electron spin and adjacent nuclear spins,and is based on the following three exper-imental studies on room-temperature optically detected magnetic resonance platform:（1）The detection and coherent control of the nearby nuclear spins in NV center are the basis of multi-qubit quantum information processing.We demonstrate experimental techniques to detect nuclear spins and to measure their hyperfine parameters with cen-tral electron spin;we develop several schemes to realize high fidelity initialization and readout of nuclear spins;by using resonant radio-frequency microwave and hyperfine interaction,combined the dynamical decoupling techniques,we realize decoherence-protected two-qubit quantum gates.These experimental technologies are also applica-ble at low temperatures,providing basic technical support for quantum computing and quantum networks based on the NV multi-qubit system.（2）Based on the above techniques,we study the dynamical behavior in the quan-tum non-Markovian environment using the NV center three-qubit quantum system.We construct quantum non-Markovian dissipation channels through engineering the quan-tum states of two neighboring nuclear spins,and use the quantum Fisher information to study the evolution of spin coherent states and entangled states in the non-Markovian environment.We observe that the quantum Fisher information flows to and from the quantum non-Markovian environment.It experimentally tests the corresponding rela-tionship between the quantum Fisher information and quantum non-Markovianity.This work also demonstrates the high controllability of diamond NV center as a few-qubit quantum system,which is one of the ideal experimental platforms for open quantum system dynamics.（3）Optically detected magnetic resonance（ODMR）technology is the basic tech-nique for NV center-based quantum information science.We experimentally observe an non-magnetic splitting in ODMR spectrums of a single NV center.While after mea-suring the typical time scale of peak position jump,and systematically studying the dependence of jump rate on the laser power,it is speculated that this splitting originates from the jump behavior of laser induced NV center charge state.This work can provide an important reference for the subsequent detection of adjacent nuclear spins.Our results show that NV multi-qubit systems have great potentials in simulating open quantum systems,versifying fundamental problems of quantum physics and quan-tum memory.The experimental techniques of nuclear spin detection and coherent ma-nipulation developed in this dissertation can be generalized to other quantum systems,such as silicon vacancy（Si V）center in diamond,germanium vacancy（Ge V）center in diamond and silicon vacancy(VSi)center in silicon carbide. |
