Qubits in isotopically enriched 28Si

同位素富集的28 Si是自旋量子器件的一种非常有吸引力的材料体系。在磷掺杂的28 Si中使用浅施主的电子和核量子位提供极长的自旋弛豫和退相时间，因此是半导体量子信息技术的最有前途的候选者之一。28 Si：P中量子逻辑的主要挑战之一当然是电子和核自旋初始化，这已经由Yang等人通过选择性光泵浦磷施主跃迁实现。这些光跃迁的线宽是半导体中浅施主系综的最宽线宽之一，实验证明光自旋初始化程度相当高。然而，自旋极化的程度远低于理想的100%，这是最有可能与观察到的光谱烧成施主transition.The第一个目标，这个建议是深刻理解的非平凡的物理烧孔动力学。Thewalt的小组在连续波实验中观察到最小的烧孔线宽，这是一个因素的四个以上的计算从施主束缚trion复合时间。其原因尚不清楚，但可能归因于以下因素的组合：（a）与光激发自由电子和空穴的相互作用，（B）由于不可避免的、无意的p型背景掺杂而导致的内部电场波动，以及（c）电子-电子相互作用。我们将应用一种特殊的时间分辨泵浦-探测吸收装置来定量地确定不同的贡献，并使用这些信息（a）将光诱导自旋极化优化到远高于99%和（B）将能量分离的自旋子系综写入施主束缚电子系综。这个提议的第二个目标是宏观施主自旋系综的纠缠。我们将使用优化的自旋初始化，并将两个空间分离的宏观自旋系综写入高质量的28 Si样品中。 然后，我们用一个光脉冲纠缠这些自旋系综，并用类自旋噪声技术验证纠缠。施主束缚电子自旋系综与相应的核自旋系综的纠缠以前已经被证明，但空间分离的宏观施主电子自旋系综的纠缠迄今尚未在28 Si中建立，28 Si中的磷施主是量子比特的优秀候选者，但是单个光学缺陷是孤立的，明亮的，并且在电信波段中以相同的波长发射将另外实现可扩展的硅量子光子学的实现。最近的实验碳注入硅报告这样的单光子发射器，但强烈变化的波长。在高质量的28 Si中寻找具有相同波长的单光子发射器将是本提案的第三个任务。

Isotopically enriched 28Si is a fascinating material system for spin-based quantum devices. Electron and nuclear qubits using shallow donors in phosphorous doped 28Si offer extremely long spin relaxation and dephasing times and are thereby among the most promising candidates for a semiconductor quantum information technology. One of the major challenges of quantum logic in 28Si:P is of course the electron and nuclear spin initialization which has been achieved by Yang et al. by selective optical pumping of the phosphorous donor transitions. The linewidths of these optical transitions are among the narrowest linewidths of shallow donor ensembles in semiconductors and the experimentally demonstrated degree of optical spin initialization is rather high. However, the degree of spin polarization is well below the desirable 100 % so far which is most likely linked to the observation of spectral holes burned into the donor transitions.The first goal of this proposal is a profound understanding of the non-trivial physics of this hole burning dynamics. The group of Thewalt observed in continuous wave experiments minimal hole burning linewidths which are a factor of four larger than calculated from the donor bound trion recombination time. The cause is unknown but might be attributed to a combination of (a) interaction with optically excited free electrons and holes, (b) fluctuating internal electric fields due to unavoidable, unintentional, p-type background doping, and (c) electron-electron interaction. We will apply a special time-resolved pump-probe absorption setup to determine quantitatively the different contributions and use this information (a) to optimize the optically induced spin polarization to well above 99% and (b) to write energetically separated spin sub-ensembles into the donor bound electron ensemble. The second goal of this proposal is entanglement of macroscopic donor spin ensembles. We will use the optimized spin initialization and write two, spatially separated, macroscopic spin ensembles into a high quality 28Si sample. Afterwards, we entangle these spin ensembles by an optical pulse and verify the entanglement by a spin noise like technique. Entanglement of a donor-bound electron spin ensemble with the respective nuclear spin ensemble has been demonstrated before but entanglement of spatially separated macroscopic donor electron spin ensembles has not been established in 28Si so far, to the best of our knowledge.Phosphorous donors in 28Si are excellent candidates for qubits but single optical defects which are isolated and bright and emitting at identical wavelengths in the telecom bands would enable additionally the implementation of scalable silicon quantum photonics. Very recent experiments on carbon implanted Si report on such single photon emitter but with strongly varying wavelengths. The search for single photon emitters with identical wavelengths in high quality 28Si will be the third task of this proposal.