Application Of Landau-Zener Transition In Superconducting Qubits

Quantum computation and quantum communication is the study of the informa-tion processing tasks that can be accomplished using quantum mechanical systems. Superconducting qubit is one of the most possible realization of the physical quantum computers because of the stability in manipulation and scalability. The study of the ma-nipulation of the qubit states, and the quantum simulation with qubits, lie in the heart of the superconducting quantum computation. Landau-Zener transition (LZT) is a well-known quantum transition between energy levels at the avoid energy-level crossing. However, the application of Landau-Zener transition in the superconducting quantum computation has not been fully studied yet. In this thesis, the study of the qubit prop-erties and the application of Landau-Zener transition in quantum computation will be presented.In the basic characterization of the superconducting qubits, we demonstrated the experiments of spectroscopy measurement, determination of decoherence time, driven Rabi oscillation, coupling between the qubit and natural two-level-system (TLS), and so on. Based on the characterization, we systematically studied the properties of a single qubit and the manipulation of qubit states.In the area of quantum simulation, based on the prediction that there is a close correspondence between the Landau-Zener transition and Kibble-Zurek mechanism (KZM), we studied the KZM with the application of LZT in a superconducting qubit system. By studying the Landau-Zener transition in a 3D transmon qubit system, the adiabatic-impulse approximation, freeze-out time, and the scaling law of the topolog-ical defects in ID quantum Ising model are observed, confirming the correspondence between KZM and LZT. Furthermore, we studied the strong decoherence effect in LZT and KZM. The △ rescaled Hamiltonian is also used to study the decoherence effect, providing a useful tool in the realization of adjustable decoherence time in LZT.In a 3D transmon qubit system, we observed the Landau-Zener-Stiickelberg-Majorana (LZSM) interference with the application of chirped tone microwave. The avoid en-ergy level crossing is formed using the interaction of the dressed states generated by the microwave field and the qubit states. Besides, with the time step as 1 ns, we performed time-resolved state tomography measurements during the evolution of the interference, and observed the dynamical evolution of the state during the process of interference.The rapid adiabatic passage (RAP) is a reliable way in performing population trans-fer between different energy levels. With the application of modulated chirped fre-quency microwave, we have demonstrated chirp RAP as a useful tool in the field of state manipulation and initialization. Such technique provides us a robust state manip-ulation method which is insensitive to procedure time, resonant frequency and power range in comparison with a normal Rabi π pulse. In addition, to confirm the applica-tion of chirp RAP as a universal gate operation, we studied the fidelity of chirp RAP in acting as different universal gate operations. It is confirmed that with a set of parame-ters, the chirp RAP has the potential to act as applicable and effective quantum logical gates.