Effect Of The Gradient Misfit Strain On Dielectic Constant Of BaTiO₃ Thin Films And The Realization Of Quantum Operation

Ferro-electric films have recently received considerable attention due to their application in the dynamic random access memory, optoelectronic devices, and novolatile memories. In this dissertation, the dielectric properties of epitaxial single-domain BaTiO 3(BT) thin film are studied by the extended Landau-Devonshire theory. The strain of the films is changed with the location be taken into account. Within the framework of Pertsev's thermodynamic theory, we studied the temperature dependences of the dielectric constant of BT thin films. We found the growth temperature and the difference of thermal expansion coefficients between the substrate and the film had significant influence on the dielectric constant and the maximum dielectric constant. The calculated results fit well with the experimental data.With the development of quantum computing and quantum information, it is more and more important to design a strong and effective quantum logic gate. At the same time, the study about quantum gates also greatly simplifies the physical implementation of quantum computers.Another part of this dissertation, we consider tripod artificial atom systems formed by SQUID's circuit, and show how to generate purely geometric phase. The geometric phases are controlled by three laser fields where pulse shapes, relative field strength, and phases can be controlled. Simultaneity, we present a scheme to implement three quantum gates based on these geometric phases, including a one-qubit phase gate, a Hadamard gate, and a two-qubit phase gate.