Multi-Qubit Quantum Random Walk And Scalable Quantum Qubit Control

Quantum computing is expected to solve the problems that traditional computers are difficult to solve.Quantum computing has great application prospects in the fields of cryptography,big data analysis,machine learning,and material analysis.There are many physical systems can be used for implementing quantum computing,such as su-perconducting qubits,ion traps,neutral atoms,optics,quantum dots,and cavity quantum electrodynamics.As one of the most promising platforms for realizing quantum computing in recent years,superconducting qubit has been used to demonstrate many significant experi-ments.Such as quantum error correction,quantum simulation,and quantum annealing.Based on the current error rate in quantum gates,a general error correction quantum computer requires about one million superconducting qubits,and a medium-sized quan-tum computer is expected to be realized requires hundreds of qubits.However,as the number of qubits increases,the control of qubits faces some challenges.First,the room temperature control system produces a lot of energy.Second,many RF/DC control lines,parametric amplifiers,HEMTs,and isolators are required at low temperatures in the dilution refrigerator.At present,the cooling power and internal space of the re-frigerator will be far from meeting the needs of the future superconducting quantum computing processors.This thesis studies the multi-qubit system and the scalable DC control of superconducting quantum qubits,which will be intended to solve the key problem of the superconducting quantum qubit,Promoting the development of general quantum computing.There are many algorithms to implement general quantum computing,such as surface-code,quantum random walks,etc.The first part of the thesis demonstrated quantum random walk in a processor with 12 qubits,which is a phased and exploratory work and will promote general quantum computing.This thesis will elaborate on this work in the design,fabrication,and measurements.The second part of this thesis studied the Rf-Squid based DC source,attempting to achieve in-situ low-temperature superconducting qubit DC control.The purposes of this research work are mainly in two aspects.First,trying to improve the stability of DC control of current qubits.Secondly,it paves the way for exploring RSFQ-based scalable qubit controls.This thesis will introduce the design,fabrication,measurement,and the next generation design of the DC source.The quantum random walks experiments performed in this thesis are the first suc-cessful demonstrations of quantum random walks in the superconducting qubit system.It is an significant exploration and phased work which will promote general quantum computing.The Rf-Squid based DC source successfully biased the x-mon qubit with high stability.