Time-periodic Driving And Quantum Simulation With Superconducting Qubits

Quantum computing is based on the principles of quantum mechanics and quantum algorithm,which is expected to outperform universal classical computing in certain aspects.The physical systems for quantum computing are also an excellent platform for quantum simulation studies.Superconducting circuits are among the most promising candidates for quantum computing and quantum simulation due to their advantages of low dissipation,scalability,flexibility,and relatively long coherence time.This Ph.D.thesis work involved and utilized the superconducting circuits for the experimental studies of nonequilibrium dynamics in quantum many-body systems.The main results and achievements include:(1)Based on the principles of circuit quantum electrodynamics and considering the qubit structures and equivalent circuits in various forms,one-dimensional superconducting 10-qubit array devices were designed using Ledit software.The coupling capacitance and inductance as well as the resonant cavity characteristics in the circuits were carefully simulated using HFSS,Maxwell,and other electromagnetic simulation software.(2)Using the standard micro-nano fabrication techniques,the superconducting 10qubit devices and Josephson parametric amplifiers with A1 and Nb base layers were prepared.The aluminum film wet etching process was explored with good sample stability and reproducibility.Satisfactory performance of the devices was demonstrated.(3)A multiqubit measurement system,including the internal wirings in the refrigerator,attenuators and filters,various amplifiers,and room-temperature heterodyne mixing,was successfully built.A single-channel heterodyne demodulation scheme based on Hilbert transform was proposed and used in this work.(4)Based on the multiqubit measurement system,the superconducting 10-qubit device was fully characterized.The detailed optimizations of various pulse signals and measurement parameters were performed.High fidelities of single-and two-qubit gates,and entangled Bell states were achieved.(5)The periodic longitudinal-field driving was used to tune the effective coupling strength between qubits,demonstrating a fair Bessel-function-form dependence against the driving amplitude.In this way,quantum walk and dynamic behavior in the XY model describing the 10-qubit system with tunable coupling were investigated.Dynamic localization and edge state in the realized SSH model were observed.(6)The periodic driving was further used to change the sign of the effective Hamiltonian and realize the time reversal of quantum evolution.Taking advantage of this timereversal process,the Loschmidt echo experiment with a Bell initial state was performed and its special property arising from the superconducting multiqubit Hamiltonian was discussed.(7)Finally,the out-of-time-order correlators(OTOCs)with the Neel initial state were successfully measured.A light-cone-like operator propagation was clearly observed.The results were discussed and explained in terms of nonequilibrium processes in the near integrable quantum system.