Landau-Zener-Stuckelberg Interference In Superconducting Qubits

Quantum computation is a emerging subject with great application potential, and has draw much attention in recent years. Among which, superconducting quantum computation based on micromachining technology fabricated Josephson junction, act as a competitive candidate due to its flexibility and scalability, as well as outstand-ing controllability. This thesis introduce our research on Landau-Zener-Stuckelberg interference in superconducting quantum bits, with the following contents:In Chapter1, we start with the concept of quantum computation and basic in-formation of Josephson junction. Then we give an introduction to three major kind of superconducting quantum bits(qubit). In Chapter2, we perform the adiabatic-pulse model approximation on two-level system Hamiltonian of quantum bits, giving rise to Landau-Zener transition. After white noise background is added, we obtain rate for-mula of LZ transition between energy levels, which can be used to calculate population of qubit conveniently. In the end of Chapter2we illustrated the detail process of multi-photon Landau-Zener transition. In Chapter3, we studied the dynamics of TLS driven by strong external RF field, when the time between consecutive LZ transitions is less than decoherence time, Landau-Zener-Stiickelberg interference occurs. We begin with the double well potential of superconducting flux qubits, compare the amplitude of LZ transition and relaxation. We use rate equation method to calculate the stationary pop-ulation of qubits, which agrees well with experiment result. At last we show the change of interference fringes caused by different parameters, then introduce "negligible" anti-crossings and population inversion. In Chapter4we use Fourier transform to extract energy level information from interference patterns. We then discuss the confinement of rate equation method, as an alternative, we use Bloch equation to calculate a tripatite qubit system evolution under only1period of driving field. The good agreement of theory and experiment shows great potential of LZS interference in precise control of quantum bits.