Research On Microwave Quantum Optics In Superconducting Qubits

A superconducting qubit is an artificial atom based on Josephson junctions.It's one of the most promising physical systems for quantum computing.Quantum computing based on superconducting qubits has developed rapidly over the decades.The number of qubits is more than 50,and the coherence time has reached the order of milliseconds.Quantum gates,amplification and readout of quantum signals have been extensively explored.Quantum error correction,quantum supremacy,quantum simulation,and quantum algorithms based on superconducting qubits have obtained great achievements.Superconducting qubits,as artificially designed solid-state quantum systems,also provide good platforms for investigating microwave quantum optics.Many physical phenomena in quantum optics and atomic physics have been confirmed in the superconducting qubits.Starting from the research background of superconducting qubits,this thesis introduces the basic theory of qubits and quantum gates implemented in the quantum information processing,details the most widely used circuit quantum electrodynamics system in superconducting qubits,and focuses on quantum mechanics in the transmonresonator coupling system.Based on the theory,the researches on planar transmon and 3D transmon have been carried out,and the following research results have been obtained:1.The measuring system for the superconducting qubit at low-temperature and room temperature has been established.Based on this system,experimental techniques related to superconducting qubits have been studied,including the quantum states readout through bright state readout and dispersion readout,single-shot readout,arbitrary quantum gates in a single qubit,quantum state tomography,and randomized benchmarking.The basic properties of superconducting qubit,such as spectrum,Rabi oscillation and coherence time have been characterized.Besides,general use of a Josephson parametric amplifier has been summarized.2.The regular Autler-Townes(AT)effect and the dynamical modulated AutlerTownes effect have been studied both theoretically and experimentally.In the regular Autler-Townes effect experiment,single-photon process and two-photon process have been used to detect superconducting qubits coupled to a driving field.Based on the regular Autler-Townes effect,the driving field is modulated with random telegraph noise.In this situation,the motional average has been observed.It has been found that the motional average is related to the average jumping rate of the random telegraph noise.In addition,using the bichromatic field as the driving field,the experimental data shows more dressed states.Theoretical models for the regular Autler-Townes effect and two dynamical modulated Autler-Townes effects are constructed.The numerical calculations are in good agreement with the experimental results.3.The absorption spectra of superconducting qubits driven by bichromatic microwave fields have been studied.The bichromatically driven absorption spectra from single-photon process to up to eleven-photon processes have been demonstrated experimentally.A graph theory method based on Floquet theory has been used to model the interaction between qubits and microwave fields.The direct product graph and Cartesian product graph in the model represent the transversal and longitudinal couplings between the qubit and the microwave field,respectively.Our experimental and theoretical results have shown that the single-photon process driven by bichromatic fields is mainly produced by the transversal coupling,while the two-photon and three-photon processes are mainly produced by the longitudinal coupling.