Design And Application Of Superconducting Quantum Chip Based On Transmon

Since the discovery of charge qubits(the predecessor of transmon)in 1999,to the proposal of transmon in 2007,and then to the realization of quantum advantage based on transmon in 2019,the field of superconducting quantum computing can be said to have developed rapidly.The main work of this dissertation is to study the design and application of superconducting quantum chips based on transmon,and to provide a systematic introduction to superconducting quantum computing.First,the architecture of a superconducting quantum computer is divided into three levels:physical layer,drive layer and application layer.Then a deep study was conducted on the design of superconducting quantum chips at the physical level and some new design methods were proposed.Then an introduction was given to the calibration of superconducting quantum chips at the drive level and common experimental methods were summarized.Finally at the application level through three different experiments showed the application of superconducting quantum computing,including algorithm demonstration,quantum simulation and computational capability characterization.The design of superconducting quantum chips with large-scale scalable qubit numbers is the future direction of superconducting quantum computing as well as an important scientific challenge.Traditional planar processing technology is not sufficient to support two-dimensional layout design and it is difficult to expand the number of qubits.Therefore,the flip-chip technology is required to expand the design space.By placing the qubits and couplers on one chip and the readout cavity and control lines on another chip,a two-dimensional layout of qubits can be achieved.As the number of qubits grows on a large scale,wiring and packaging become complex issues and even bottlenecks.This paper proposes a sample box packaging design that takes into account the number of ports,spatial modes,and microwave crosstalk.A semi-automated wiring algorithm was developed to solve wiring problems that traditional manual wiring could not solve.Based on these methods,a superconducting quantum chip containing 66 qubits was successfully designed and named Zuchongzhi.These design methods can continue to be expanded and theoretically support hundreds to thousands of qubits.The circuit-cutting method is a way to solve large-scale quantum circuits using small-scale quantum devices and can scale up the problem size solvable by the noisy intermediate-scale quantum(NISQ)devices.By exploiting the symmetry of linearcluster states,the effectiveness of circuit-cutting can be estimated through simulating up to 33-qubit linear-cluster states,using at most 4 physical qubits for each subcircuit.Specifically,for the 12-qubit linear-cluster state,the experimental fidelity bound can reach as much as 0.734,which is about 19%higher than a direct implementation on the same 12-qubit superconducting processor.The results indicate that circuit-cutting represents a feasible approach of simulating quantum circuits using much fewer qubits.Floquet prethermal phase is a state in which periodically driven systems exhibit prethermalization behavior under certain conditions.Digital-analog quantum simulation method is utilized to construct experimental quantum circuits using superconducting qubits simulating spin model.For the first time,Floquet prethermal phase was observed in a superconducting quantum computing system.The experiment measured and compared the average spin magnetization,the Fourier spectrum of the average spin magnetization and the site-averaged square of the two-spin correlation function.It was found that U(1)interaction played a protective role,making Floquet prethermal phase significantly different from thermal states and having long lifetime and antienvironmental disturbance characteristics.This work reveals a promising prospect in discovering emergent quantum dynamical phases with digital-analog quantum simulators.Quantum advantage is a milestone event that marks the computational capability of quantum computers to surpass classical computers.Using the previously designed Zuchongzhi superconducting quantum chip,through random quantum circuit sampling,quantum advantage was successfully demonstrated,and is the second experiment in the world to achieve quantum advantage in superconducting quantum computing.The experimental results show that the 56-qubit 20-cycle random circuit sampling task completed by Zuchongzhi has a computational cost of the classical simulation that is 2-3 orders of magnitude higher than the previous work on 53-qubit Sycamore processor.It was also confirmed that the sampling task finished by Zuchongzhi in about 1.2 h is infeasible for classical computation in a reasonable amount of time.In addition,the qubit arrangement on Zuchongzhi is compatible with the surface code,a quantum errorcorrecting code,and can serve as a test platform for fault-tolerant quantum computing.