Surface Electric-field Noise Detection And Spin Coherence And Temperature Sensing At High Temperature Based On NV Center In Diamond

Diamond NV centers have gotten a lot of attention recently because of their unique optical and spin properties,and they’ve been applied in a variety of applications,including quantum information processing,quantum sensing,and biological fluorescence labeling.The performance of related devices is directly related to the coherence time of the NV center.As a result,a systematic investigation of the spin coherence of NV centers is required.Furthermore,the shallow NV centers have a wide range of applications in the field of spin detection.The coherence time of shallow NV centers,on the other hand,is greatly influenced by the presence of surface noise.As a result,it is critical to investigate the noise from diamond surface,which will help not only to improve the coherence time of shallow NV centers,but also to better understand the ubiquitous noise in quantum systems.In view of this,we studied the above problems with the help of the home-made optical detected magnetic resonance(ODMR)system.The main contents are as follows1.Construction of ODMR platform and preparation of NV centerWe built an ODMR platform by combining microwave and magnetic field systems into a home-made laser confocal microscopy system to localize and coherently control the NV center.Simultaneously,we prepared NV center using various methods to meet the experimental requirements.We used the CVD method to prepare the NV center ensemble,which had a high concentration and a long coherence time.Ion implantation and high temperature annealing were used to create shallow NV center with good coherence.We prepared the single NV center array by combining electron beam lithography and ion implantation in order to obtain a single NV center with a long coherence time and easy positioning.2.Study on electric-field noise from diamond surfaceWe measured the electric-field noise on the diamond surface by using the NV double quantum relaxation method,and found that intensity of the noise satisfies the frequency relationship of 1/fα.At the same time,we also studied the change of electricfield noise on the surface with temperature We discovered that while the temperature was less than 420 K,the noise intensity grew steadily with increasing temperature,whereas at higher temperatures,the noise began to diminish and reached zero at 540 K.The Dutta-Horn model was introduced to explain the temperature dependence of the noise.According to the model,we obtained the relative energy density distribution of TLS(two-level system)on diamond surface.The density of states of TLS is basically constant between 0.33 eV and 0.47 eV,but as the activation energy increases,the density of states begins to decrease and eventually reaches zero at about 0.6 eV.Simultaneously,based on the experimental results,we hypothesized that TLS originated from the sp2 amorphous carbon layer on the diamond surface.We also investigated the effect of different organic covering layers on surface electric-field noise suppression.The findings show that solid PMMA suppresses noise better than liquid glycerol.We believe this is due to the fact that the surface electric-fleld noise is related to surface phonon,and the solid PMMA has an effect on the surface phonon.We anticipate that studying electric-field noise on the diamond surface will aid in improving the coherence of the shallow NV core and better understanding the 1/f noise that exists in many quantum systems.Furthermore,the double quantum relaxation method can be used to study polar or dielectric materials as an electric-fleld noise measurement technique.3.Study on the coherence of NV center at high temperature and temperature detectionWe studied the coherence time of diamond NV center ensemble at temperatures ranging from 300 K to 600 K,including T1,T2,T2*.We found that T2*basically did not change with temperature,while T1 and T2 rapidly decreased with the increase of temperature.The decrease of T1 was due to the enhanced interaction between NV center and phonons caused by high temperature,while the decrease of T2 was mainly due to the P1 center in diamond.In addition,we also verified the working performance of the NV thermometer based on the thermal-echo sequence at high temperature.The results showed that the NV based thermometer can work normally and has high sensitivity at 450 K(41 mK/(?)).We also estimate that it can maintain temperature sensitivity better than 100 mK/(?)in the temperature range of 300 K-600 K.These studies lay the foundation for the application of magnetic field and electric field sensing of NV center at high temperature.