The Superconducting Qubit And The Application Of STA Protocol In Quantum Simulation And Gates

The superconducting quantum computing is one of the main schemes to realize the quantum computer.I have been studying the related experimental technology and theoretical principles of the superconducting qubit since studying for my doctor's degree.Throughout the PhD stage,I mainly studied the experimental measurement and chip design of superconducting phase qubit and Xmon.The superconducting phase qubit and Xmon has the similar circuit structure,while Xmon has a longer coherence time.For now,the Xmon is widely used in superconducting qubit field.This thesis is focused on the theoretical principles and experimental control of Xmon.The main contents of this thesis include:(1)The introduction part introduces the history of the quantum computing development and some basic quantum mechanics knowledge.These basic knowledge includes qubit state,density matrix,quantum entanglement,single qubit quantum gate,two qubit gate and the decoherence.(2)In the chapter 2,we introduce the circuit model of the superconducting qubit.For the general LC resonance circuit,we quantize this circuit to get the uniform quantization level.By introducing the Josephson junction into the resonant circuit,we can get the non-uniform harmonic levels,and-the lowest two specific energy levels are encoded as qubit.(3)Subsequently,we introduced how to design a superconducting quantum chip with required parameters according to the relevant theories.The theoretical model and simulation methods of qubit design are explained.When designing related parameters,we also consider the follow-up tests and decoherence of qubit.(4)Taking our laboratory as an example,we introduce the measurement and control system of superconducting qubit.The whole measurement and control system is included the microwave generation and reading devices,the low temperature line system in the dilution refrigerator and the measurement and control software.The configuration method of low temperature line system is described in detail.And the commonly used microwave devices,including copper powder filter,RC filter,parameter amplifier,etc,are also described.(5)According to the chip design in chapter 4 and the existing control equipment,we designed a neighbor coupling 6-qubit chip.On such a 6-qubit chip,we introduce the calibration process of the basic parameters.These parameters include:the bare frequency of cavity,Q value,dispersive shift,qubit frequency,decoherence parameters and coupling parameters between two qubits.(6)In the superconducting phase qubit,the adiabatic trajectories obtained by 'shortcuts to adiabaticity'(STA)are used to simulate the topological phase transition of SSH model.At the same time,we consider the effect introduced by additional high energy level of superconducting phase qubit.Through the modification of DRAG auxiliary field,we achieve the adiabatic trajectory umder specific representation.This method can not only be applied to the simulation of one-dimensional SSH model,but also can be applied to the simulation of more complex system through simple generalization.(7)Furthermore,We use the STA protocol to realize high-fidelity quantum gates.In Xmon system,we theoretically design and experimentally implement a series of high-fidelity single qubit gates.Through precise microwave control,we control the evolution of qubit along a specific adi-abatic trajectory to get the desired quantum gate.By the interleaved randomized benchmarking measurement,we have obtained a single qubit quantum gate with fidelity of more than 99.8%.The innovation points of this thesis mainly include:· design the neighbor coupling 6-qubit chip,and the measured decoherence time is about 20us·utilize the STA protocol to simulate the topological transition· utilize the STA protocol to realize the high fidelity single qubit gates...