Characterization And Quantum Sensing Application Of Ensemble Nitrogen Vacancy Centers In Diamond

Quantum sensing is an important area in quantum information processing and quantum technology.Diamond quantum sensing has the advantages of high sensitivity and high spatial resolution,and can work under a wide range of magnetic fields,tem-peratures,and pressures.It provides advanced probing methods for condensed matter physics,earth science,life sciences,and so on.Nitrogen vacancy（NV）center in dia-mond is one of the most promising quantum probes.The sensitivities of NV based quan-tum sensing are determined by the density,spin and optical properties of NV centers,and using NV ensemble is the most direct and efficient way to enhance the sensitivity.Therefore,it is necessary to fabricate and character ensemble NV centers in diamond.Towards quantum sensing applications of ensemble NV centers in diamonds,this thesis first briefly introduces the physical structure,spin properties and optical proper-ties of NV centers in diamond,as well as the corresponding experimental methods.The main results of this thesis include:（1）Characterization of NV center density and spin coherence in single-crystal dia-monds synthesized by high-pressure and high-temperature methods.Currently,widely used quantum-grade diamonds are generally prepared by chemical vapor deposition（CVD）,but CVD method has disadvantages such as high stress and high hydrogen im-purity content.High-pressure and high-temperature（HPHT）synthesis schemes can ef-fectively avoid these disadvantages.We estimated the NV density in HPHT diamonds using the fluorescence intensity of NV centers and characterized their spin coherence properties,proving that the spin coherence properties of HPHT synthesized diamonds are sufficient for quantum computing and quantum sensing applications.These results provide a new technical path to improve the sensitivity of diamond quantum sensing.（2）Frequency multiplication soft magnetic film is measured using ensemble NV centers in nanodiamonds as in-situ quantum sensors.The frequency multiplication refers to the phenomenon that harmonic waves at9)1)₀is generated with an input of microwave at1)₀.The experimental results show that at zero magnetic field,spin waves in Ni Fe ferromagnetic films can achieve frequency multiplication in devices with both single-domain and multi-domain states.The applied magnetic field suppresses the fre-quency multiplication.Combining theoretical calculations and micromagnetic simula-tions,we propose that the non-uniform magnetization structure at the device edge leads to the excitation of nonlinear spin waves.Furthermore,we experimentally verified that the higher-order spin waves generated in this device can drive Rabi oscillations of NV electron spins,indicating that higher-order harmonic waves have good phase coherence and can be used for efficient quantum control.This research provides a new approach for preparing high-quality diamond quan-tum sensors and offers possibilities for quantum information and applications with non-linear spin waves effects.