The Studies Of Near-field Radiant Of Microwave

The key challenge and opportunity in spintronics and experimental quantum information science is to identify and control solid system's qubit (quantum bit) in complex environment. Due to the unique characters of nitrogen-vacancy center in diamond, the diamond is one of the most promising host materials for carry out quantum computation.The thesis introduced the nitrogen-vacancy center in diamond, and explained its special characters. Due to its unique structure, we can realize the spin control in diamond quantum system using microwave signal at 2.87GHz. We used a microwave antenna which can transfer the energy from traveling wave to radiation wave. So, the thesis is studying in microwave radiation based on the experiment.The sample is too small, only mm order of magnitude and the electromagnetic in space is quickly decayed, which made us put the antenna to the sample very near. We studied three types of microwave antennae, and finally found out a copper wire as the near field antenna, which can not affect the optical system in the case of near to the sample, and in the same power, the copper wire has a higher current density, which has more bigger radiation at near-filed.In order to increase the radiation intensity of copper, we simulated the copper wires' radiation using HFSS software at different parameter, and measured the magnetic field intensity by near-filed probe. The results show that the length of the copper is related to the resonance frequency, and the magnetic field distribution along the axial is different with different length, but the difference between the maximum magnetic field intensity is not obvious. The experimental results told us that the magnetic field intensity along the radial is inversely proportional to the distance between the measurement point and the antenna that the distance between antenna and testing point have a great impact on radiant intensity.; in addition, we analyzed the materials of the sample's shelf, and the simulation results show that the metal shelf will change the resonance frequency and reduced the magnetic field intensity. The Plexiglas shelf has no effect on the magnetic field intensity. Based on the analyzed and measurement, we can optimize the near field radiation by these: (1) Using the antenna with 55mm length, and put the sample at 35mm location from the antenna's starting point; (2) change the aluminum shelf to the Plexiglas shelf; (3) design a device which can remove the antenna to the nitrogen-vacancy center. Using these ways, we can optimize the near field radiation at the sample, and increased the magnetic field. This work has laid a good foundation for achieve spin control to the nitrogen-vacancy center by microwave technology.