| Achieving higher sensitivity of magnetic detection has always been a human pursuit.The emergence and development of quantum precision measurement techniques have led to an unprecedented increase in our ability to detect magnetic fields,Nitrogenvacancy(NV)in diamond has been applied to quantum information and quantum precision measurement in recent years due to its excellent optical properties and quantum coherence characteristics at room temperature.The magnetometry based on NV Center has made numerous breakthroughs in the research directions of condensed physics,biosensing,weak magnetic detection,etc.In the cryogenic environment,the transport phenomena of electrons in condensed systems and the magnetic process such as phase transitions and domain evolution of low-dimensional magnetic materials also need to be studied by novel detection method and NV has a wide working temperature range(1 to 1000 K)and a dynamic range from static magnetic fields(DC)to high-frequency magnetic fields(GHz),so the development of magnetometry based on NV Center for cryogenic environments is urgent.However,the cryogenic magnetometry and the commercial cryogenic equipment designed for NV Center are still under development.We have built several experiment systems for cryogenic Optically Detected Magnetic Resonance(ODMR)based on NV Center and developed related techniques under the cryogenic ODMR regime.Through measurement systems we have built,we also carried out experiments on the detection of high-frequency microwave signals by an ensemble of NV Center under weak light excitation conditions.My main research work during the Ph.D.period includes three major parts as follows.1.We have completed the development and validation of magnetic sensing cryogenic system based on NV Center,in which the measurement stick is compatible with both confocal microscopy and scanning confocal microscopy.We were able to carry out ODMR experiments in a cryogenic environment under a strong magnetic field;We also have built a cryogenic ODMR platform based on a commercial closed-cycle cryostat,which extended the working temperature range of ODMR experiments.2.We have carried out magnetic imaging of 2D magnetic materials chromium bromide under cryogenic conditions.Besides,the phase transition process of the twodimensional magnetic material was observed,and the phase transition temperature of the 11 nm thick material was given.The study of magnetic properties of twodimensional materials requires magnetic detection at nanoscale spatial resolution for few or even single-layer materials,while conventional magnetometry cannot detect weak magnetic signals at the microscopic scale.Based on the above experiment system,we employed the high magnetic sensitivity of NV Center to study magnetic phenomena in condensed systems.3.We have realized the measurement of high-frequency weak power microwave signal based on a continuous wave with a differential measurement method,which can effectively reduce the laser power while retaining a high sensitivity of the magnetic measurement.The magnetic measurement based on the ensemble of NV Center has a high demand for power of the laser,which limits the wide application of NV Center.In this thesis,we proposed a high-frequency weak power microwave measurement method,which amplifies the intensity of the weak microwave signal by introducing a reference microwave signal to reduce the demand for the laser power of NV Center,and has the advantages of arbitrary frequency resolution,simple and controllable detection sequence,etc.It is a further step towards achieving high-sensitivity magnetometry without laser excitation at cryogenic temperature,effectively reducing the laser power requirements for magnetometry based on NV Center. |
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