| The superconducting quantum circuit based on superconducting quantum bits (qubits), is a kind of solid macroscopic quantum circuit. Its fabrication process is compatible with the semiconductor counterparts so it is easy to be integrated and scaled. Due to these advantages, superconducting quantum circuit is one of the most promising candidates as the physical implementations to quantum computer. In recent years, a substantial increase of the coherence time of superconducting qubits, which is above 100 microseconds, make it possible to demonstrate some quantum algorithm. Recently a demonstration of quantum error correction (QEC) with 9 superconducting qubits has been conducted by the Martinis group in UCSB. All of these remarkable achievements have greatly promoted the development of superconducting quantum computing based on the superconducting qubits. However the study of superconducting quantum computing in China is still in its infancy and there is a wide gap with foreign groups. In this thesis, following the international research hotspots, we focus on thetopic of 3D transmon as the start point to construct the measurement system which is suitable for the circuit quantum electrodynamics (Circuit QED) system. With the help of such measurement system, a study on 3D transmon has been conducted. The main research results include the following aspects:1). Construction of the measurement system which can conduct experimental study on the Circuit QED based superconducting qubits. The system has two parts:the cryogenic system and the one in room temperature. The cryogenic system is mainly based on an Oxford Triton 400 Cryogen free dilution refrigerator. Two microwave measurement circuits with different bandwidth have been made for different samples. The RF switches enable to measure up to 12 samples in a cooling cycle, greatly improving the efficiency. While the system in room temperature is a computer controlled measurement platform which controls the input microwave pulse pattern, the demodulation of output signal, data sampling and post-processing.2). Study of the basic quantum properties of 3D transmon and an improved version of 3D transmon, the tunable one. We designed and fabricated the 3D transmon, including the 3D cavity and sample. With the help of the system we have built, a detailed characterization of the 3D transmon, such as spectroscopy, Rabi oscillation, the energy relaxation time and phase coherence time, has been conducted. With the tunable 3D transmon, we have studied the spectrum of vacuum Rabi splitting and achieved a two-qubits coupled system with successful observation of avoided energy-level crossing and coherent oscillation.3). Realization of the Landau-Zener-Stuckelberg-Majorana (LZSM) interference in a chirped 3D transmon. By chirp method, driving the 3D transmon with chirped microwave fields, an effective avoided energy-level crossing has been made. A forth and back sweep process across the avoided energy-level crossing twice successfully shows the LZSM interference pattern. With such method, we can study the LZSM interference in a system with no intrinsic avoided energy-level crossing and preparing the system in arbitrary initial state, which provides a more effective way to study the LZSM interference.4). Demonstration of a tunable coplanar waveguide resonator (CPWR) with nanowires. By embedding the nanowires in the center of the half-wavelength CPWR, variations in the resonant peak due to light response have been observed. This demonstration may help to build an optically tunable superconducting microwave resonator. It is also a beneficial attempt to achieve coupling between photons and superconducting quantum circuits. |
