Single Spin Qubit In Silicon Quantum Dots

In the recent decade,spin qubit based on silicon quantum dots has been regarded as one of the most promising systems for quantum computing.The advantages of silicon spin qubits include ultra-long coherent time,small footprint,potential scalability,and industrial manufacturability.The traditional qubit manipulation method based on the electron spin resonance uses the alternating magnetic field generated by the microwave antenna to flip the spin qubit,and the flip rate is relatively slow.In order to improve the qubit quality factor(ratio of coherence time to manipulation time),it is essential to increase the manipulation rate of qubits.However,due to the weak intrinsic spin-orbit coupling strength of electrons in silicon quantum dots,it is challenging to manipulate spin qubits based on spin-orbit coupling.Therefore,studying how to enhance the strength of spin-orbit coupling in silicon quantum dots is very important.In this dissertation,we integrate a micromagnetic near the silicon quantum dot to enhance the spin-orbit coupling.Based on this kind of silicon quantum dot,we investigate how to realize the manipulation of a single spin qubit in silicon quantum dot systemically:Describe a threshold-independent method for high-fidelity single-shot readout of spin qubits;Use the rapid adiabatic passage to identify the electron spin resonance frequency;Improve the strength of spin-orbit coupling by using the flopping mode electron dipole spin resonance,and increase the qubit quality factor by an order of magnitude.The dissertation includes the following parts:1.We briefly introduce the background and the basic properties of quantum computing,the principle of electrically controlled silicon quantum dots,and the definition and basic properties of a spin qubit,including single-qubit and two-qubit operations.2.The basic experiment methods:the structure of quantum dots,fabrication of quantum dots based on a nano-micro process in academic clean rooms,ultra-cold characterization of quantum dots,and software of the measurement systems.3.Investigation of the threshold-independent method for single-shot readout in silicon quantum dots.We introduce two basic characterization methods,i.e.,the charge stability diagram and real-time observation of electron tunneling,and the single-shot readout of spin qubits based on these two methods.Then,we introduce the corresponding data processing methods and analyze the readout process from the data.Finally,the threshold-independent method for single-shot readout is developed to realize a high-fidelity readout.4.Investigation of the single spin qubit in silicon quantum dots.We integrate a micromagnet to enhance the spin-orbit coupling strength and introduce the Rapid Adiabatic Passage to increase the bandwidth and signal-to-noise ratio of the electron spin resonance frequency.A chirped pulse is applied during the measurement.The Rabi oscillation is realized,and the spin dephasing time is characterized.5.Investigation of the "flopping-mode" single spin qubit in silicon quantum dots.We introduce the principle of "flopping-mode" electric dipole Spin resonance(EDSR).We realize the single spin qubit operation in a flopping-mode qubit in silicon quantum dots to enhance the spin-orbit coupling strength and observe an order magnitude improvement in Rabi frequency and quality factor at the symmetric point.The creative points in this dissertation mainly contain:1.The first proposition of threshold-independent single-shot readout method for spin qubits in silicon quantum dots.2.Improve the spin-orbit coupling strength of the silicon quantum dot by integrating a micromagnet structure.And implementation of the fabrication and coherent manipulation of a single spin qubit in silicon quantum dots.3.The first implementation of a flopping-mode single spin qubit in silicon quantum dots via single-shot readout.Further enhance the spin-orbit coupling strength of the silicon quantum dot.And improve the Rabi frequency and quality factor by one order of magnitude.