硅量子点中能谷物理对自旋量子比特退相干的影响

The powerful parallel processing capability of a quantum computing promises its future application in the area of large scale data processing, the design of new material, and the national security and etc. To achieve the goal of quantum computing, one of the most important and challenging task is to protect the quantum coherence of a quantum computer. Spin qubit in semiconductor quantum dots, especially silicon quantum dots, is one of the most promising candidate to build a quantum computer because of its great quantum coherence, the scalability, and the compatibility with the existing semiconductor fabrication technique in the information industry. In this project, to address the new situations in experiments, such as the effect of valley physics and the consequence of the magnetic field gradient, we study the spin coherence in silicon quantum dot. We mainly focus on the study of the decoherence mechanisms, such as spin relaxation and spin dephasing, in silicon quantum dot, the interaction between spin qubit and valley states, and combined effect of spin-valley mixing and the magnetic field gradient. We will propose methods to predict and optimize the spin coherence in silicon quantum dot, which will eventually help realizing the semiconductor spin based quantum computing.

量子计算的强大并行计算能力将使量子计算在大规模数据处理、新材料设计、国防和军事等领域有巨大应用前景。为了实现量子计算，重要而又艰巨的任务就是保持量子比特系统的量子相干性。半导体量子点中，尤其是硅量子点中，电子自旋量子比特由于其优良的相干性和可扩展性是实现量子比特的有力候选方案之一。针对硅量子点自旋量子比特实验中存在的能谷自由度以及磁场梯度的新条件，本项目以硅量子点自旋量子比特为研究对象，以自旋量子比特的退相干的预测和优化为核心，以新条件下建模和等价模型为基础，系统研究能谷物理对自旋量子比特退相干的影响机理、磁场梯度与能谷自由度对自旋退相干的综合作用机理、以及自旋量子比特的退相干的预测和控制等关键科学问题，面向硅量子点自旋量子比特的退相干提出一套分析与预测控制方法，最终达到全面提升半导体量子计算水平的目的。

半导体自旋量子比特由于其优良的相干性和可扩展性是实现量子计算的有力候选方案之一。针对硅量子点自旋量子比特实验中存在的能谷自由度以及磁场梯度的新条件，本项目系统研究了硅量子点中自旋量子比特的退相干机制和规律。我们重点关注了磁场梯度与能谷自由度对自旋退相干的作用机理、以及自旋量子比特的退相干的预测和控制等关键科学问题，并完成了一系列研究工作。我们提出了自旋轨道相互作用的时间反演对称性对自旋比特的重要影响。通过调节外磁场方向可以有效抑制电噪声带来的自旋退相位，进而提升自旋比特操作的品质因子。我们还发现能谷物理对自旋弛豫和电偶极自旋共振均产生影响。通过调节自旋和能谷的杂化可以有效调节电偶极自旋共振强度，进而优化自旋比特量子门保真度。这些研究成果将为提升半导体量子计算水平提供了必要的理论基础。