Research On A Superconducting Qubit Coupled To A Microscopic Two-level System

Being an emerging discipline, quantum computing, which can handle a fair amount of information far beyond the traditional computing, has gradually attracted people’s attention. Superconducting qubit is a promising physical system for quantum computing and there are three basic types: superconducting flux qubits, superconducting phase qubits, and superconducting charge qubits.In the experiments, we studied the flux-biased superconducting phase qubit coupled to a microscopic two-level system and measured the energy spectrum of the coupled system, in which an avoided energy-level crossing was clearly observed. We used Lorentzian function to fit the experimental data, and obtained the spectrum peaks and width. Then we used several methods, including Schrodinger equation, master equation and Lindblad equation, to simulate the energy spectrum theoretically. In addition, we has also measured the spectrum’s dependence on the microwave power and found that the spectrum lines gradually disappear with the decreasing of the power of the applied microwave. The spectrum line due to the two-photon transition disappeared earlier before those due to the single-photon transition. And we also did a theoretical simulation which agreed with the experimental result well.The rf-SQUID, with a double-well potential, is a nonlinear bistable system. We initialized the rf-SQUID in the left well potential. After adding a white noise to the flux bias line, we measured the probability of the rf-SQUID in the right potential well. A clear single resonance peak was observed when the intensity of the white noise increased. We made a qualitative research on the phenomenon of stochastic resonance.