Quantum Dots And Quantum Structures,

With the development of the science and technology, especially the discovery of the quantum algorithm and quantum error correction, the quantum information and quantum computer becomes the hot subject of the theory and the experiment. Contrary to the classic computer, the quantum computer has the mighty calculation capability and can finish some operations that the classic computer can't effectively do. The key problem to the realization of the quantum computer is how to construct the quantum bit and how to accomplish the quantum logical operations. Presently people try to carry out the actual quantum computer. Therefore scientists have proposed many patterns of quantum computers, including non-solid - state quantum computer and solid - state quantum computer. The active aspects include ion traps, nuclear magnetic resonance (NMR) technique, quantum electrodynamics cavities, Josephons Junctions, and semiconductors quantum dots. In this thesis, how to use the lens-shaped quantum dot as a quantum bit will be reported. Firstly the binding energies and the ground state energies of Hydrogen impurity in a lens-shaped quantum dot (GaAs/Inl-xGaxAs) under vertical magnetic field will be displayed. Then how to use the nuclear spin as the quantum bit will be given.The binding energies and the ground state energies of Hydrogen impurity in a lens-shaped quantum dot (GaAs/Inl-xGaxAs) under vertical magnetic field using effective mass approximation and variation method have been discussed. It turns out that: (1) Without the magnetic field for a spherical quantum dot, the ground state energy is the same, and has only relations with the distance of the impurity deviation. After applied the vertical magnetic field, the effects of the ground state energies on the deviation of in-plane or perpendicular to the plane are very small, while the effects on the deviation distance are great, the larger the distance, the more ground state energies will be. (2) For a lens-shaped quantum dot, due to the asymmetry of the bound potential of in-plane and perpendicular to the plane, the electric ground state energies are related not only with the deviation distance but also with the deviation direction. The effect of impurity on the electron wave function has calculated, it shows that for the perpendicular magnetic field and the strong boundpotential of the quantum dot the effect of impurity on the electron wave function can be neglected.By making use of the strong bound quantum dot model and neglecting the effects of impurity on electron wave function, this thesis is also reported how to use the spin of nuclear as the quantum bit. Here the hyperfine interaction between the electron and nucleus in the perpendicularly coupled quantum dots has been calculated, including its relation with the nucleus resonant frequency of single quantum dot. The changes of electron and nucleus exchange frequency along with external field in the coupled quantum dot, especially with magnetic field and the horizontal electric field has been given. It gives that one can control the hyperfine interaction between the electron and nucleus by changing the external field.