Fabrication Engineering Of Superconducting Qubits And Related Devices

The principle of quantum computing determines that quantum computers can surpass classical computers on certain problems,such as the decomposition of large numbers.The realization of quantum computers is also of great significance for the study of quantum multi-body systems.In order to realize quantum computing,it is necessary to implement qubits,quantum logic gates,and quantum error correction.Among the physical systems that are expected to realize quantum computing,the superconducting quantum system based on Josephson junction has the good balance between long decoherence time,easily to manipulating and reading,and good scalability.It is one of the most promising systems to implement quantum computing.The implementation of superconducting qubits is based on a nonlinear LC resonant loop composed of capacitor and Josephson junction,which act as nonlinear inductance.On this basis,a series of qubit architectures have been developed.2D Transmon and Xmon achieve a good balance between qubit lifetime,scalability,ease of handling and ease of processing.At present,the main development goals of superconducting quantum computing are: increasing the number and performance of qubits,thereby realizing high fidelity gate operations,combined with quantum error correction,and finally realizing general quantum computers.In order to improve the number and performance of qubits and achieve high fidelity gate operation,high quality device fabrication techniques are essential.During my Ph.D.,I conducted a series of explorations on device fabrication processes,including: improving the coherence time of the qubits in the device by improving the process;Controlling the process to achieve the preparation of fully connected 20 Xmon qubits;Attempting to prepare samples with qubits and coplanar waveguide resonator that have tunable coupling strength;Attempts to prepare qubit with high anharmonicity;Preparation of Josephson parametric amplifiers.The following results were obtained: in order to reduce the influence of the process on the quality of the sample,the etching and lift-off combined process was proposed and used to deposit the alignment mark and the etching of the basic microwave transmission line with only one exposure;With these process,after several attempts,the qubit decoherence time of 70 microseconds or more was realized in samples,such as a liner 5 qubits;Combined with the Airbridge process,the qubit frequency,performance and coupling intensity uniformity were successfully satisfied the requiring of measurement,and the decoherence time of some qubits can also be up to 70 microsecond;Using the tunable inductance of the Josephson junction to form a tunable coupler,tunable coupling strength of 0 to 40 MHz between the qubit and the coplanar waveguide resonator is realized,and the lifetime of the qubit can still be up to nearly 20 microseconds;Tried to prepare a new architecture of qubit and achieved a high anharmonicity of 1.4GHz;Using a new preparation process,efficiently prepared multiple batches of wideband Josephson parametric amplifier that meet the need for simultaneously reading of multiple qubits.