Theoretical Study Of Superconducting Quantum Devices And Quantum Information Processing

Quantum computation is an interdiscipline of Quantum Mechanics and computer science. Recently quantum information processing has attracted much attention due to the potential advantages provided by quantum-mechanical principles such as entanglement and coherence. With the robust macroscopic quantum behavior and scalability, superconducting qubits are widely regarded as excellent candidates due to inherent scalability using well-established microfabrication techniques.This dissertation comes in 8 parts. In chapter 1 and chapter 2, a brief review about the development and basic content of quantum computation are given, as well as coherent control of superconducting Josephson devices. In chapter 3, we present the development and status of the superconducting Quantum Computation in detail. In chapter 4, special attention is paid to the spectrum and transition matrix element of the flux qubit containing 4 Josephson junctions, as well as the charge qubit based on asymmetric SQUID.In chapter 5, we propose an experimentally feasible scheme to couple the charge qubit and the flux qubit. As an application of our scheme, an iSWAP gate operation is constituted to transfer desirable quantum state from the charge qubit to the flux qubit. CNOT gate and specific two-qubit gate working at the optimal points of the two kinds of qubits are also discussed. In chapter 6, we engineer a macroscopic superconducting circuit to deterministically exhibit quantum correlations of two qubits with a macro-scopical distance and further make maximal entanglement long-lived. A macroscopic EPR pairs, with components in opposite regimes, can be also generated.In chapter 7, we have studied a variable-frequency-control approach in charge-qubit circuits. The charge qubits are chosen to work at their optimal points. Moreover, the effects of the microwave field on the supercurrent of the two qubits are discussed. It is found that the supercurrent of the qubits significantly depends on the statistics of the microwave field states.In chapter 8, we discuss the decoherence mechanism by introducing the classical Langevin equation and Bloch equation of Laser theory. Finally, we derivate the Quantum Master equation in detail.