Measurement And Control Of Superconducting Quantum Qubits And Multistable States Quantum Simulation

With the development of computer science,people have increasingly high performance requirements for computers.Although traditional computers have been widely used in various fields,their computing power still limits them in solving certain problems.These difficulties have led to the development of quantum computing,which has begun to attract people’s attention as a new type of computing machine.Unlike traditional computers,quantum computers are based on quantum physical principles and are composed of quantum bits(qubits).Quantum computers have certain capabilities that traditional computers do not have,such as qubits can be in quantum superposition states and quantum entanglement states,etc,which can be used to solve large-scale and complex problems that traditional computers cannot handle.There are many approaches towards general quantum computing,including nuclear magnetic resonance quantum computing,ion trap quantum computing,superconducting quantum computing,and optical quantum computing.Among them,superconductor-based superconducting quantum computing has made some important progress since the 1990 s.This progress has marked the continuous development and progress of superconducting quantum computing,and also demonstrated its important position in the field of quantum computing.This thesis mainly introduces my research on superconducting quantum computing during my master’s degree and related achievements.The first section of the thesis introduces the necessity and advantages of quantum computing and reviews the important advances in the field of superconductor-based superconducting quantum computing in the past three decades.The second section introduces the hardware platform of superconducting quantum computing,including the principles of chip preparation and dilution refrigerators.The third section introduces the principles of driving and reading out superconducting qubits,including the introduction of a rotating operation as a driving force and the derivation of the J-C model for qubit excitation and readout.The IQ mixer technology is introduced in this section as an important experimental technique.The IQ mixer converts the input frequency into a higher-frequency signal,which can then be demodulated into the qubit state by measuring the resonant frequency of the readout cavity.This chapter also introduces the IQ mixer’s conversion and demodulation processes,as well as the source of error and calibration methods.The fourth section takes a typical multi-qubit chip,Transmon/Xmon,as an example,and describes how to characterize it experimentally.In addition,due to the distortion and crosstalk of the control signal,we need to calibrate the measurement signal to ensure more accurate control and measurement.Furthermore,various types of single-level defects in superconducting quantum chips can have harmful effects on qubit dephasing performance,so this section also describes a simple characterization method for two-level-system defects.In section 5,I introduced my main research work during my master’s degree,which was to study long-range correlation in dissipative bit chains and multi-stable states.I prepared high-fidelity multiple remote Bell states,and theoretically and experimentally implemented a method that can control the decoherence performance of bits with pure pulses.This method can be applied to the study of fast bit reset or multi-bit nonHermitian systems.I used a method of transverse modulation to change the coupling strength,performed quantum walks on Bell states,and observed the localization of entangled states in the process of propagation.Finally,we observed multiple stable states with different Bell states and Bell states in different phases on a nine-bit chain.In conclusion,my research work during my master’s degree is summarized,and I also provide a prospect for the development of the field.