Design And Fabrication Of Superconducting Quantum Bits And Mechanical Oscillators

Superconducting quantum bits(qubits)have become one of the most promising physical implementations for quantum computing because of their unique advantages such as flexible fabrication,easy integration and the tunability of circuit parameters.In recent years,great achievements have been obtained in superconducting quantum bits,including the energy relaxation time(T1)and the number of integrated qubits on a single chip.For example,Google and IBM have integrated qubits to several dozens,and the decoherence time reaches the order of 100 microseconds.However,the research of superconducting quantum bits in China started relatively late.In the study of superconducting quantum bits,sample fabrication is one of the most basic,important and difficult parts.Therefore,here I focus on the design and micro-fabrication technology of superconducting quantum bits.I have systematically explored the fabrication methods and process parameters.Moreover,many implementation architectures of quantum computing require qubits to be coupled with other systems.For example,coupling superconducting quantum bits with micro-nano mechanical oscillators is expected to realize information processing in the microwave,optical and phonon regimes.So while studying the fabrication of superconducting quantum bits,I also explore the fabrication of membrane mechanical oscillator based on vacuum gap capacitor(VGC)and doubly-clamped string mechanical oscillator.The main research results are listed in the following:1?Parameters of Transmon are analysed theoretically and optimized according to our measuring system.Furthermore,mechanical oscillators based on VGC and doubly-clamped string are designed,as well as the coupled system including the mechanical oscillator and Transmon.2?Samples including 3D Transmon,planar Transmon and mechanical oscillator based on VGC have been successfully fabricated.The methods of Josephson tunnel junction have been systematically studied.The process parameters in fabricating superconducting qubits and mechanical resonators on different substrates have been explored in detail and optimized.3?The basic parameters of the samples have been characterized.In the most potential and challenging qubit—planar Transmon,the energy relaxation time T1 is about 20 microseconds,which has already reached the domestic advanced level.This value has met the requirement of studying some basic quantum properties and lays a solid foundation for the following study of more complex quantum algorithms.In the VGC structure mechanical resonators,the sideband spectra caused by membrane vibration has been observed successfully.The response of the mechanical oscillator to the input microwave power and optical power has been systematically characterized,which sheds light on the research of the opto-electro-mechanical system consisting of superconducting qubits,mechanical oscillator,microwave and light.