Single Photon Source Fabrication And Spin Defect Study Based On Hexagonal Boron Nitride

Hexagonal boron nitride is a widely used insulator two-dimensional material with?6 eV band gap and the ability to host a plenty of defects like diamond.Since the first report about single photon emitters in atomic-thick hexagonal boron nitride flakes in 2016,the fluorescent defects in hexagonal boron nitride have attracted the attention of researchers due to its excellent optical properties and have been a rapid development.Similar to other solid color centers,the hexagonal boron nitride color centers can be widely used in quantum computation and quantum communication.Moreover,quantum devices based on hexagonal boron nitride color centers have many advantages in miniaturization and integration.During my postgraduate period,I mainly studied the preparation,characterization and application of single photon sources in hexagonal boron nitride,as well as the coherent manipulation of the spin color centers.The main research results described in this paper are:1.The preparation and characterization of a blister-induced single photon emitter in hexagonal boron nitride at room temperature and analysis of its physical mechanism.We report a blister-induced high-purity single photon emitter in hexagonal boron nitride under ambient conditions after the methods of ion implantation,high temperature annealing and transfer,which showing stable quantum-emitting performances,and no evidence of blinking and bleaching for one year.Remarkably,we observe the nontrivial successive activating and quenching dynamical process of the fluorescent defects at the single photon emitter region under low pressures for the first time,and the robust recoverability of the single photon emitter after turning back to the atmospheric pressure.The pressuretuned performance indicates the single photon emitter origins from the lattice defect isolated and activated by the strain induced from the blister,and sheds lights on the future high-performance quantum sources based on hexagonal boron nitride.2.Experimental realization a causal-modeled delayed-choice experiment with a deterministic single-photon emitter in hexagonal boron nitride.We experimentally realized a causal-modeled delayed-choice experiment using a single photon emitter in hexagonal boron nitride and performed it with a Mach-Zehnder interferometer under a path degree of freedom.To ensure the delayed-choice requirement in the measurement stage,we built a quantum random switch assisted by a quantum random number generator,which can select the measurement bases independently of preparation and provides a fast phase shift at the measurement stage on the path degree of freedom.In order to test the wave-particle objectivity,in our experiment,based on the two kinds of dimension-witness inequalities |Det(W2)| and IDW,we examined whether the statistics property of our results is compatible with any binary classical hidden-variable model.According to our experimental results,we can exclude any two-dimensional nonretrocausal classical models on account of the violation of the dimension-witness inequalities.In particular,results from the dimension-witness inequality |Det(W2)| are highly robust to technical imperfections under any nonzero detection efficiency,which can make the test be performed in a device-independent manner.Meanwhile,the outcomes obtained by IDW can also be applied to quantify the retrocausality.3.The realization of the coherent manipulation on the spin color centers of boron vacancies in hexagonal boron nitride.We have realized the Rabi oscillation of the boron vacancies spins in hexagonal boron nitride,based on which we also detect T1 and perform the spin-echo and Ramseyinterference experiments.We find T1 not affected by magnetic field;however,the results of Rabi oscillation,spin-echo and Ramsey oscillation are very different under the conditions of weak and relatively strong magnetic field.The results show the magnetic field could help elongate the spin coherence time by freezing the environmental spins.Moreover,our results suggest boron vacancy spin is highly correlated to the neighboring nuclear spins,which provides a potential tool to study the nuclear spins.4.Measuring the temperature dependence of energy level of boron vacancies in hexagonal boron nitride and analyzing the main factors of energy level shifts.We investigated the temperature dependence of the resonance spectrum of VB-defects in the range of 5-600 K.The energy level of VB-defects is found to decrease monotonicly with increasing temperature and can be described by Varshni empirical equation very well.We systematically study the differences among different hexagonal boron nitride nanopowders and speculate that the local strain in the hBN nanopowder and the distance of defects from the flake edges are the underlying causes of the difference in different samples.Considering the proportional relation between the energy level and reciprocal of lattice volume,the thermal expansion might be the dominant reason for energy-level shifts.We also demonstrate that the boron vacancies defects still exist stably at least at 600 K.Our results are helpful to gain insight into the spin properties of boron vacancies and for the realizations of miniaturized,integrated thermal sensor.