A First Principles Study Of Point Defect-Based Qubit Materials

Vacancies,anti-sites,interstitials,impurities are possible point defects in semiconductors and insulators.These point defects can play a determinant role in applications.They can be considered as artificial atoms embedded in semiconductors and insulators.Ideally,defect states generated by point defects in the band gap are isolated from the surrounding environment,i.e.being separated from the valence and conduction bands.Therefore,they exhibit quantum properties of isolated atoms without a requirement of sophisticated isolation techniques.Optically active point defects in wide-bandgap materials are a leading component of quantum information technology,since they are scalable and easy to be integrated into devices.They can be used as quantum processors,quantum repeaters,quantum simulators and quantum sensors and so on.Point defects are ubiquitous in semiconductor and insulator materials.Designing specific point defect configurations can produce electronic spin quantum states suitable for different quantum technologies.This thesis focuses on point defects in related insulators that are potential candidates of quantum bit.The first chapter introduces successful solid-state qubit candidates and the application of density functional theory in the screening and identification of solid-state qubits.The concept of qubits is briefly introduced.Then,studies based on density functional theory and experiments of some famous solid-state qubit candidates are introduced,especially the negatively charged NV center in diamond and the double vacancy defects in silicon carbide.The second chapter introduces the framework of first principles calculations based on density functional theory,including the basic principles of density functional theory,some exchange correlation functionals commonly used in calculation,and some commonly used simulation packages,such as VASP and Material studio.The third chapter briefly introduces methods of calculating the properties of solid-state quantum bits,such as ground state,excited state electronic structures and hyperfine coupling tensors.The fourth chapter mainly studies electronic and spintronic properties of transition metal Pt doped alkaline earth metal oxides(MgO and CaO)in the framework of density functional theory.Using VASP,we studied the spin-polarized defect energy levels,formation energies,their spin-conserved transition energies,hyperfine coupling tensors and magnetic coupling of the two spin-polarized defect centers for a certain point defect.We found that PtMg and Ptca both have a spin triplet ground state of S=1 and a spin-conserved excited state.By calculating the formation energies of these point defects in different charge states,they are found to be stable in n-type doped MgO or p-type doped CaO.Using constrained DFT,we obtained the optical properties of these point defects:absorption,emission and zero phonon energy(ZPL).By calculating the magnetic coupling of two spin polarization centers,we found that these defect centers can be operated as separate spin bit operations at room temperature.Finally,by calculating the hyperfine tensors,we provided theoretical support for future experiments.All results indicate that these systems can be potential candidates for solid-state qubits.