Setup microwave measurement system for circuit-Quantum electrodynamics experiment

• Main Authors: Hsu, Chi-Wen, 徐啟文
• Other Authors: Chen, Jeng-Chung
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/tv4rkv

碩士 === 國立清華大學 === 物理學系 === 106 === In recent years, quantum computers and quantum computing have become the important scientific and technological development directions and the development of Quantum bit (qubit) is the core of the quantum technology. The operation of qubits depends on the interaction between artificial atoms and photons, the quantum state needs to be operate in an ultra-low temperature environment (approximately 10 mK) and precision microwave manipulation techniques. The purpose of this dissertation is mounting the cryogenic measurement system for qubits experiment and the resonant cavity design. The experiment in the thesis uses a dilution refrigerator as a cryogenic system to lower the system temperature to 10 mK sample space through the multiple descending temperature layers. In the process, mount attenuator at the input to reduce heat conduction and noise. When the microwave signal is output from the 10 mK space, superconducting transmission line use first to avoid the noise interference, then the low temperature amplifier performs the first amplification to separate the signal from noise, and then the room temperature amplifier outside the fridge perform the secondary amplification. According to the general transition frequency of the artificial atom process, the operating frequency band of the measurement system is set at 4~12 GHz. The low temperature amplifier is a device most likely to affect the signal. Therefore, we use a 50 ohms resistor to measure the noise temperature from the low temperature amplifier, and estimate the noise. In order to enhance the coupling effect with photons, we put the artificial atoms in the resonant cavity. In this article, we focus on the measurement of two-dimensional coplanar waveguide (thanks to dr. J.W. Wang, a former laboratory member for the design and the simulation data) and design, simulate by HFSS and measurement of 3D cavity. The resonant frequency of the two-dimensional coplanar waveguide in the experiment is 8.24 GHz, and the sample is a semiconductor artificial atom, the experiment only measures the quality factor and resonant frequency of the cavity under T=10 mK. In order to cover the 4 to 12 GHz operating frequency band of the system, I designed 3D cavity with four resonance frequencies with copper and aluminum two different materials. At present, three groups of low temperature data have been measured, the photon loss rate of the 3D cavity in this paper compared with the literature that has achieved a strong coupling effect, we considered that there is an electromagnetic field environment that can make artificial atoms and photons strongly coupled.