A negatively charged VSiON center for implementation as qubit
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摘要: γ相Si3N4是一种超硬氮基化合陶瓷材料, 在其尖晶石结构中硅原子分别占据四面体于八面体配位格点.基于第一性原理计算, 研究了这种材料之中一种氧空位复合体VSiON缺陷中心的不同价态下自旋极化的电子结构以及能量稳定性, 其中该缺陷中心由四面体配位的硅空位复合紧邻替位氧原子而成.发现负一价态的该缺陷中心VSiON-1在p型主体材料中是较为稳定的存在, 并满足净自旋S=1的基态三重态, 以及低激发能量的自旋守恒跃迁.通过平均场近似, 将其在绝对零度下的自旋相干寿命估计为0.4 s, 室温下可达毫秒量级.因此理论上表明了VSiON-1缺陷中心是可用作量子比特的相干操控的潜在候选者.Abstract: γ-Si3N4 is a nitrogen-based ultra-hard ceramic with Si atoms occupying both tetrahedral and octahedral sites in a spinel structure. Based on first-principles calculations, we investigate spin-polarized electronic structures and energetic stabilities of oxygenvacancy complex center (VSiON) consisting of a substituted oxygen atom and an adjacent tetrahedrally coordinated silicon vacancy in spinel silicon nitride (γ-Si3N4) with different charge states. We find that the negatively charged VSiON-1 center is stable in the p-type γ-Si3N4 and the defect center possesses an S=1 triplet ground state and a spin-conserved excited state with low excitation energy. By using a mean-field approximation, we estimate that the spin coherence time of VSiON is 0.4 s at T=0 K, which indicates that the VSiON-1 center is a promising candidate for spin coherent manipulation and qubit operation.
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Fig. 1 (a) The primitive cell of $\gamma $ -Si $_{3}$ N $_{4 }$ shows the spinel structure characterized with tetrahedrally coordinated and octahedrally coordinated Si atoms; (b) Optimized structure of the V $_{\rm Si}$ O $^{-1}_{\rm N}$ center in the $\gamma $ -Si $_{3}$ N $_{4}$
Dashed lines denote the dangling bond lengths
Fig. 3 Calculated density of states (DOS) for the V $_{\rm Si}$ O $^{q}_{\rm N}$ centers with different charge states in the $\gamma $ -Si $_{3}$ N $_{4}$ , (a) $q=+1$ , (b) $q=0$ , (c) $q=-1$ , and (d) $q=-2$ . The energies are relative to the calculated chemical potentials ( $E=0$ eV) denoted by thin vertical lines
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