Anisotropy Spectroscopy Of Spin Qubits In Silicon Quantum Dots

In the last 10 years,the electronic spin quantum bit(qubit)in silicon quantum dots has become one of the main candidates for quantum computing.This new type of qubit has drawn a lot of academic and industrial attentions due to its ultralong decoherence time and its ability to integrate with classical semiconductor circuits.The research includes the readout,control,storage,the nearest-neighbor coupling and the long-range coupling of qubits.However,due to the existence of spin-orbit coupling in silicon quantum dots,this type of spin qubits will show an anisotropic behavior with respect to the magnetic field direction,which could affect the qubit properties severely.Therefore,it is of great significance and meaningful to investigate the anisotropy of spin qubits in silicon quantum dots.In this thesis,we focus mainly on this research direction and the main text contains:1.Brief introduction of the background of quantum computing and the motivation for the research on spin qubits in silicon quantum dots,the principle of electrically controlled semiconductor quantum dots,the definition and basic properties of spin qubits,and the spin-orbit coupling in silicon quantum dots and its effect on spin-qubit properties.2.Brief introduction of the micro/nano fabrication techniques,the low-temperature characterization techniques,and the data processing and analysis methods for the siliconquantum-dot-based-spin-qubit devices.3.Investigation of the charge state,the valley splitting,the orbital state,the electron temperature,the lever arm,the noise strength,the spin lifetime and other basic properties of silicon quantum dot devices.Along with these results,the basic characterization methods are also introduced,including the charge stability diagram,the magnetospectroscopy,the pulse spectroscopy,the noise spectrum,the real-time observation of electron tunneling and the single-shot readout of spin states.4.Investigation and discovery of the giant anisotropy of electronic-spin relaxation rates and spin-valley mixing in silicon quantum dots.By building a physical model of spin-valley mixing based on spin-orbit coupling,the experimental data is quantitively analyzed and explained.5.Investigation of the anisotropy of electric dipole spin resonance(EDSR)and synthetic spin-orbit coupling in silicon quantum dots.By analyzing and simulating the physical mechanism of EDSR,we explain the experimental data and give guidance for the future device design and experiments.The creative points in this thesis contains:1.The first discovery of the giant anisotropy of spin relaxation rates of electronic spin qubits in silicon quantum dots,the investigation of the effect of interface electrical field on this anisotropy,and the development of the physical model for spin-valley mixing.2.The first characterization of the anisotropy of EDSR for electronic spin qubits in silicon quantum dots and the discovery of a new method to optimize qubit control by controlling the magnetic field direction,which contribute to the study of synthetic spin-orbit fields.