| Quantum computers use the superposition and entanglement principles of quantum mechanics to perform calculations and simulations,and the calculation speed for specific tasks can exceed all classical computers.Quantum computers can quickly solve certain problems that cannot currently be solved in polynomial time on classical computers,showing significant advantages in quantum simulation,quantum chemistry,factorization of large numbers,random database search,and solving linear equations.The schemes that can realize quantum computing include superconducting quantum computing,ion trap quantum computing,optical quantum computing,semiconductor quantum dot quantum computing,etc.Superconducting quantum computing is realized by fabricating superconducting quantum circuits based on Josephson junctions on chips.Since the processing technology of superconducting quantum chips is improved and developed on the basis of mature semiconductor technology,it is capable of integrating and expanding on a large scale,and can realize high-precision manipulation and high-fidelity readout of qubits,so it has great development potential.In the development process of superconducting quantum computing,realizing the large-scale and high-performance expansion of superconducting quantum chips is an extremely important research topic,which is related to whether superconducting quantum computers can be put into practical applications and realize universal fault-tolerant quantum computing.In recent years,superconducting quantum computing has achieved a series of breakthroughs in the realization of high-fidelity quantum gates,quantum simulation and quantum error correction.However,the qubit arrangement structure of previous superconducting quantum chips is mostly one-dimensional chain or quasitwo-dimensional ladder,and all qubit control lines and readout lines are led out to the edge of the chip to realize signal input and output.With the increase of the number of qubits,such a structure is difficult to expand,which will bring a series of problems such as wiring crowding and signal crosstalk.Moreover,the connectivity of the onedimensional chain structure is low,and the improvement of the connectivity of qubits can shorten the circuit depth required to implement quantum algorithms,enabling quantum algorithms to be implemented efficiently and with high fidelity.In addition,the realization of the surface code quantum error correction scheme also requires a twodimensional qubit array with nearest neighbor coupling.Therefore,realizing superconducting quantum chips with two-dimensional qubit arrangement is a key step to integrate the quantum chips.With the design of superconducting quantum chip and its packaging,as well as the fabrication process of quantum chip,this thesis solved the problems of wiring,suppressing crosstalk,suppressing cavity modes and grounding,and realized the twodimensional resonator-coupled quantum processor ’Zuchongzhi’ containing 64 qubits(the actual number of qubits available in the experiment was 62),which was the superconducting processor with the largest number of qubits published in the world at that time.From the design point of view,the author first designed a 12-qubit chip with a onedimensional chain structure,and realized a scalable two-dimensional structure from it.The two-dimensional quantum chip enabled the wiring in the center of it utilizing the innovative design of the pass-through holes,which shortened the wiring length and reduced the crosstalk between qubits.In addition,the multiplexing of the XY control line and the Z control line reduced the number of control lines,the high-fidelity readout of qubits was realized through the design of readout resonators and filters.The twodimensional scalable coupling structure was achieved by coupling each qubit and its adjacent qubits through a resonator.For quantum chip packaging,the cavity modes were effectively suppressed by a parallel conductive metal pillar structure,and highprecision control of the quantum chip was realized.From the fabrication point of view,the author developed a micro-nano fabrication process for large-area superconducting quantum chips with two-dimensional resonator coupled structure,and realized the stability,uniformity and precision of superconducting coplanar waveguide circuits and high-density air bridges in the large area of 32 mm×32 mm.Futhermore,the stability of the Josephson junction resistance of the twodimensional qubit array was improved,and the laser cutting technology for processing the pass-through holes of the quantum chip was developed.Through the parallel calibration and optimization of the performance of the ’Zuchongzhi’ two-dimensional resonator-coupled quantum chip,high-fidelity control and measurement were realized.The single-particle and two-particle programmable twodimensional quantum walks and Mach-Zehnder interferometers in superconducting system were demonstrated for the first time on this processor.Algorithms based on twodimensional quantum walks can achieve acceleration compared to classical algorithms in problems such as spatial search.Programmable two-dimensional quantum walks can deal with problems such as quantum transport,neural networks and graph theory,and are candidates for the universal quantum computing.The realization of twodimensional quantum processors and two-dimensional quantum walks in this thesis is an important progress in the field of superconducting quantum computing,which provides a solid basis for achieving the quantum advantage and quantum many-body simulations of complex systems.In the future,it could be applied to quantum search algorithms and even universal quantum computing. |
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