论文标题：Ab initio description of highly correlated states in defects for realizing quantum bits
期刊：npj Quantum Materials
数字识别码：10.1038 /s41535-018-0103-6
半导体缺陷主导的耦合局域电子自旋可实现量子比特，对彻底改变纳米级传感器和量子信息处理带来潜在应用。而对自旋态操纵和读出的光学手段的理解，急需对激发态的定量理论描述。近日，来自奥地利的Michel Bockstedte博士领衔国际团队，在基于多体微扰理论的第一性原理计算上取得突破：他们在金刚石的N缺陷和SiC中双空位中，实现室温点缺陷量子比特，为进一步量子应用提供潜在可能性(图1)。
图1：量子计算中的点缺陷。(a) 金刚石中的N缺陷；(b) SiC中的双空位，其中空位用小点表示。(c) N缺陷(NV)中心和(d) 双空位计算的自旋极化DFT Kohn-Sham能级示意图。
需要特别指出的是，该方法不依赖于任何经验参数。他们成功描绘了光学跃迁、自旋弛豫物理图像，并研究了自旋轨道和自旋声子耦合在其中的作用，与实验非常吻合 (图2)。此外，他们还计算了绝热近似下中心最低多重态的势能面(图3)。这种方法非常适用于具有上千个电子的大体系，因此可应用于模拟其他半导体的量子比特。
图2：动态关联对NV中心多重态的影响。
图3：(a) NV和(b) VCVSi在绝热近似下中心最低多重态的势能面。(c)(d) 对应光学激发和自旋弛豫途径。
摘要：Coupled localized electron spins hosted by defects in semiconductors implement quantum bits with the potential to revolutionize nanoscale sensors and quantum information processing. The present understanding of optical means of spin state manipulation and read-out calls for quantitative theoretical description of the active states, built-up from correlated electrons in a bath of extended electron states. Hitherto we propose a first-principles scheme based on many body perturbation theory and configuration interaction and address two room temperature point defect qubits, the nitrogen vacancy in diamond and the divacancy in silicon carbide. We provide a complete quantitative description of the electronic structure and analyze the crossings and local minima of the energy surface of triplet and singlet states. Our numerical results not only extend the knowledge of the spin-dependent optical cycle of these defects, but also demonstrate the potential of our method for quantitative theoretical studies of point defect qubits.
期刊介绍：
npj Quantum Materialsis an online-only, open access journal, publishing original research results and reviews on broad coverage of quantum materials, their fundamental properties, fabrication and applications.
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