基于碳化硅晶体色心的自旋单量子态构筑和测量的理论模拟

Diamond is quite promising for the application in the field of quantum information, because the so-called NV centers composing of a substitutional nitrogen atom and an adjacent vacancy defect in diamond are available for achieving the construction, manipulation, and measurement of single spin quantum state (SSQS). However, their manufacture is still embryonic and expensive, so the potential for expanding to large-scale quantum processor using diamond remain uncertain. Silicon carbide crystals possess similar tetrahedral atomic arrangement as that in diamond, but its manufacture has been well-established. In this project, we will investigate the plausibility of using the color centers in silicon carbide to achieve the construction, manipulation, and measurement of SSQS, aiming at the replacement of ‘expensive’ diamond by ‘cheaper” silicon carbide crystals in the field of quantum information. Density-functional theory and many-body perturbation theory on the basis of Bethe-Salpeter equation will be employed in the study of the following issues. (1) The roles of structural symmetry, the electronegativities of the atoms nearest to the vacancy defect, and the charge states of the color centers in silicon carbide crystals in tuning their electronic structures of ground states and excite states; (2) The potential energy surfaces in the structural evolution of the color centers at excite states and the intermediate states along the transition channels between excite state and the ground state. The color centers which are suitable for achieving the construction and measurement of SSQS will be predicted according to the results of these studies. Some fundamental data, such as the excitation energies and the emission spectrum will be presented to promote the progress of experimental works.

金刚石是量子信息领域的基础材料之一。利用其中的NV中心可以实现自旋单量子态的构筑、操作和测量。但是目前金刚石在材料生长和器件加工方面进展缓慢。碳化硅晶体具有与金刚石相似的原子结构，且生长和加工工艺相对成熟。本项目拟由碳化硅晶体中与空位相关的色心的基态电子结构和激发态特性的理论模拟出发，探索在碳化硅晶体中实现自旋单量子态的构筑、操作和测量的可能性，为最终利用“廉价”的碳化硅取代“昂贵”的金刚石提供理论基础。本项目将采用密度泛函理论和从Bethe-Salpeter方程出发的多体微扰理论研究碳化硅中(1) 色心的结构对称性、色心周围原子的电负性、以及色心的电荷态对其基态和激发态电子结构的调控规律；(2) 色心激发态结构演化的势能面以及激发态到基态跃迁通道中的中间态。在此基础上确定出适合自旋单量子态构筑和测量的色心结构，并为实验提供“激发能量”和“光谱特性”等关键的物理参量，推动实验研究的进展。

利用半导体中特殊缺陷（如色心）的电子态，可是实现固体量子比特操控。在这方面目前最为成功的材料是金刚石。本项目立足于在传统的半导体材料(如：碳化硅 等)中寻找可以用作固体量子比特操控的缺陷中心。主要的研究内容包括：(1)缺陷结构与电子态之间的关系；(2) 缺陷的形成规律；(3) 如何通过调控缺陷的电子态实现固体量子比特的构筑；(4) 缺陷电子态的演化规律，等。我们建立了用于计算半导体中电子自旋极化及磁相互作用的理论方法，纠正了传统计算方法中的误差；模拟了碳化硅晶体中不同色心的形成与退火规律；通过理论与实验相结合的方法揭示了碳化硅等半导体材料中缺陷电子自旋及光吸收特性的调控规律；从理论上预言了多个可以用于构筑固体量子自旋比特的半导体材料的缺陷结构；预言了一批包括碳化硅在内的具有特殊拓扑电子态的二维材料。为在碳化硅等半导体材料中实现固体量子自旋比特提供了理论和实验基础。在《Nano Letters》和《Advanced Materials》等学术期刊上发表 SCI 论文29篇，培养博士和硕士研究生各4名。