Centre for Quantum Computation and Communication Technology, School of Electrical Engineering and Telecommunications, UNSW Australia, Sydney, New South Wales 2052, Australia.
School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, 223-8522, Japan.
Nat Nanotechnol. 2014 Dec;9(12):986-91. doi: 10.1038/nnano.2014.211. Epub 2014 Oct 12.
The spin of an electron or a nucleus in a semiconductor naturally implements the unit of quantum information--the qubit. In addition, because semiconductors are currently used in the electronics industry, developing qubits in semiconductors would be a promising route to realize scalable quantum information devices. The solid-state environment, however, may provide deleterious interactions between the qubit and the nuclear spins of surrounding atoms, or charge and spin fluctuations arising from defects in oxides and interfaces. For materials such as silicon, enrichment of the spin-zero (28)Si isotope drastically reduces spin-bath decoherence. Experiments on bulk spin ensembles in (28)Si crystals have indeed demonstrated extraordinary coherence times. However, it remained unclear whether these would persist at the single-spin level, in gated nanostructures near amorphous interfaces. Here, we present the coherent operation of individual (31)P electron and nuclear spin qubits in a top-gated nanostructure, fabricated on an isotopically engineered (28)Si substrate. The (31)P nuclear spin sets the new benchmark coherence time (>30 s with Carr-Purcell-Meiboom-Gill (CPMG) sequence) of any single qubit in the solid state and reaches >99.99% control fidelity. The electron spin CPMG coherence time exceeds 0.5 s, and detailed noise spectroscopy indicates that--contrary to widespread belief--it is not limited by the proximity to an interface. Instead, decoherence is probably dominated by thermal and magnetic noise external to the device, and is thus amenable to further improvement.
电子或半导体核的自旋自然实现了量子信息的单位——qubit。此外，由于半导体目前被用于电子工业，因此在半导体中开发 qubit 将是实现可扩展量子信息器件的有前途的途径。然而，固态环境可能会在 qubit 和周围原子的核自旋之间提供有害的相互作用，或者由于氧化物和界面中的缺陷而产生电荷和自旋涨落。对于硅等材料，自旋零（28）Si 同位素的富集大大降低了自旋浴弛豫。在（28）Si 晶体中的体自旋集合体上进行的实验确实证明了非凡的相干时间。然而，仍不清楚这些是否会在单自旋水平上，在非晶界面附近的门控纳米结构中持续存在。在这里，我们展示了在顶部门控纳米结构中单个（31）P 电子和核自旋 qubit 的相干操作，该结构是在同位素工程（28）Si 衬底上制造的。（31）P 核自旋设定了任何固态单量子比特的新基准相干时间（>30s，具有 Carr-Purcell-Meiboom-Gill（CPMG）序列），并达到>99.99%的控制保真度。电子自旋 CPMG 相干时间超过 0.5s，详细的噪声光谱表明——与普遍的看法相反——它不受接近界面的限制。相反，退相干可能主要由器件外部的热和磁噪声主导，因此可以进一步改进。
