Fabrication And Control Of Superconducting Quantum Device

Quantum computing is currently one of the research fields that attract a lot of attention.So far,scientists have proposed various schemes to realize a universal quan-tum computer,including superconducting quantum circuits,quantum dots and trap ions.Among them,the scheme of superconducting quantum circuits has the most advantages and temporarily takes the lead in the research.The computing unit of a superconduct-ing quantum circuit,known as superconducting quantum bit or superconducting qubit,is an artificial atom based on nonlinear inductance of Josephson junction.It has advan-tages such as flexibility of parameters,easiness to scale up,convenience for reading and controlling,which make superconducting quantum circuits one of the most promising schemes.Fabrication of high quality sample and high precision measurement are two key directions in the research on superconducting quantum devices.The dissertation stud-ies high-precision fabrication technique,Josephson parametric amplifier,super-high-frequency arbitrary waveform generator(SHF-AWG)technology,and quantum state transfer via Landau-Zener effect in a three-qubit system.Quantum chip fabrication is an important process in the research of supercon-ducting quantum computing,which directly affects the decoherence performance of superconducting qubit.The fabrication of Josephson junction is a key step in the chip fabrication.We explored the method of optimizing exposure by simulating the process of electron beam exposure and the process of fabricating large-area Josephson junction.In the measurement of qubit,Josephson parametric amplifier(JPA)is an important sig-nal amplifier,which can amplify weak readout signals in the low temperature region.During the process,the introduced noise can reach as low as the quantum limit,which can greatly improve the signal-to-noise ratio of readout signals.This is very impor-tant for the high precision single-shot measurement.The dissertation presents the de-sign method and the detailed fabrication procedure of a broad band stepped impedance transform Josephson parametric amplifier(IMPA).In the sample measurement,it is very important to build a stable and low-noise measurement system.We studied the signal generation and demodulation process in the measurement,and summarized a set of signal processing program,including signal correction,digital filtering,etc.,and developed a Python module of waveform editing,wavedata.This is very helpful to improve the efficiency of the experiment.We explore a direct digital synthesis method using SHF-AWG to manipulate qubits and compare it with the traditional mixing method.Except the disadvantage in price,this new method is not inferior to the traditional mixing method in terms of deco-herence time and fidelity.The new method makes measurement circuit simpler and the control of qubits more accurate,which is very useful in scale-up qubit system.We also demonstrated the quantum state transfer via the multi-passage Landau-Zener-Stuckelberg(LZS)interference in a three-qubit system,which is a complete process in terms of dynamics.The three-qubit system include one tunable and two fixed frequency qubits,which the tunable qubit act as a quantum medium,similar to the traditional cou-pling resonator bus.This scheme can be extended to a system where multiple qubits are coupled to a frequency tunable qubit,and provides an useful tool for quantum gate.