Date of Degree
PhD (Doctor of Philosophy)
Michael E. Flatté
In the most recent two decades, the development of impurity controls with ultra-high precision in semiconductors motivates people to put more and more attentions on the solotronic devices, whose properties depend on one or a few dopants. One of the most promising applications of solotronic device is the qubit in quantum computing. In the procedure of exploring qubit candidates, the most straightforward challenges we need face include that the qubit must be highly isolated and can be initialized/manipulated efficiently with high fidelities. It has been proved that qubits based on single defects have excellent performances as quits. For instance, the NV center in diamond forms a ground spin triplet which can be manipulated at room temperature with electromagnetic fields. This work focuses on searching for new single defects as qubit candidates with density functional theory.
Lanthanides element possesses excellent optical characteristics and extremely long nuclear coherence time. Therefore, combining it into the diamond platform can be possible design for integrated quantum information processing devices in the future. To investigate the stability of lanthanides dopants in the diamond matrix, the formation energies of charge states of complexes are calculated. The broadening of Eu(III) peak in the photoluminescence spectrum can be verified according to the existence of more than stable configuration and steady 4f electron occupation.
In the case of transition-metal dopant in the silicon carbide, it is found that both silicon and carbon substituted nickels in 3C-SiC shows a magnetic-antimagnetic transition under applied strains. The virtual hopping rate of electrons strongly depends on the distance between the spin pair residing in the nickel and dangling bonds. Therefore, the Heisenberg exchange coupling between them can be adjusted subtly by controlling the external strain. According to the the spin Hamiltonian of the defect, the spin state can be manipulated universally with strain and electromagnetic fields. In contrast, the nickel dopant in 4H-SiC exhibits a very stable magnetic property. Other than that, the electronic structure of Cr in 4H-SiC implies that optical manipulations of spin states might be realized in the excited state.
Density functional theory, Diamond, Electronic structure, Qubit, Silicon carbide, Single dopant
Copyright 2016 Wenhao Hu