Silicon-based Integrated Single-Spin Quantum Information Technology

该项目的目标是在超薄绝缘体上硅（SOI）上实现世界上第一个基于硅的集成单自旋量子比特（qubit）系统。我们开发了一种精确控制的单电子转移技术，用于初始化真正的单电子自旋（single-spin）状态，用于单自旋操纵的微电子自旋共振（micro- esr），以及用于读出的“自旋到电荷”转换技术。这些具有挑战性的技术要求将通过协同结合南安普顿大学在尖端硅基纳米制造和单电子器件方面的专业知识，剑桥大学和日立剑桥实验室在固态量子比特和相关低温和射频测量方面的专业知识，以及NTT基础研究实验室在单电子/自旋控制技术方面的专业知识来满足。第一个基于硅的量子比特是由Kane提出的，使用硅中磷原子的核自旋（Si:P量子比特）。由于Si中核自旋的退相干时间很长，这一建议引起了人们的兴趣。然而，具有挑战性的自下而上的纳米技术，如STM光刻，需要控制相对于表面控制栅极嵌入硅中的P原子的数量和位置。与其使用类似原子的供体，还可以将电子限制在被称为量子点（QDs）的纳米结构中。在由砷化镓制成的量子点中，已经证明了对单电子自旋（单自旋）的精确控制程度。不幸的是，砷化镓是一个核自旋丰富的环境，导致电子自旋的相干性迅速丧失。最近，能够限制少量电子的量子点在具有低核自旋密度的硅基材料中也变得可行，因此为本研究计划提供了动力。最近出现的同位素纯Si材料（28Si 99.9%）通过进一步增加自旋退相干时间也有利于Si基体系。为了开发基于硅的集成单自旋量子比特系统，这是前所未有的，我们充分利用了我们项目团队中最先进的独特纳米技术。首先，采用单电子旋转门技术制备具有良好定义的初始单自旋态；其次，介绍了一种基于射频单电子晶体管（RF-SET）的高速电荷检测技术。第三，基于自旋-电荷转换方法实现了单自旋态的检测。我们提出了一种革命性的基于soi的集成单自旋量子比特技术平台，该平台将双单自旋旋转门器件（SSTDs）构建为两个平行的soi纳米线（SOINWs），其边缘由另一个短SOINW连接。SSTDs与其他三个关键组件共集成：(1)在SSTDs边缘附近形成的平面内单电子静电计，(2)使用金属波导形成的微esr器件，并放置在SOINW互连附近，以及(3)在单自旋量子比特上产生磁场梯度的纳米磁铁。通过将所有构建模块集成到纳米级足迹中，我们首次在Si上全面研究了单自旋量子比特的初始化，选择性操作和读出。

The aim of this project is to realize a world-first Si-based integrated single-spin quantum bit (qubit) system on ultrathin silicon-on-insulator (SOI). We develop a precisely-controlled single-electron transfer technique to initialize truly single-electron spin (single-spin) states, micro electron spin resonance (micro-ESR) for single-spin manipulation, and a 'spin-to-charge' conversion technique for readout. These challenging technical requirements will be met by synergistically combining the expertise of the University of Southampton on cutting-edge silicon-based nanofabrication and single-electron devices, the University of Cambridge and the Hitachi Cambridge Laboratory on solid-state qubits and the associated low-temperature & RF measurements, and the NTT Basic Research Laboratories on single-electron / spin control technology.The first Si-based qubit was proposed by Kane using nuclear spins of phosphorous donor atoms in Si (Si:P qubits). This proposal attracted much interest due to the very long decoherence time of nuclear spins in Si. However, challenging bottom-up nanotechnologies, e.g. STM lithography, are required to control the number and position of P atoms embedded in silicon relative to surface control gates. Rather than using donors, which are atomic-like species, it is also possible to confine electrons in nano-fabricated structures known as quantum dots (QDs). An exquisite degree of control over single-electron spins (single-spins) has been demonstrated in QDs made from gallium arsenide. Unfortunately gallium arsenide is a nuclear spin rich environment leading to a rapid loss of coherence from electron spins. Recently, QDs capable of confining few electrons have also become feasible in silicon based materials, which have a low nuclear spin density, therefore providing a motivation for this research proposal. The recent appearance of isotopically pure Si materials (28Si 99.9%) also works in favour of Si-based systems by further increasing spin decoherence time. In order to develop the Si-based integrated single-spin qubit system, which has never been achieved, we fully exploit the unique set of state-of-the-art nanotechnologies brought together in our project team. Firstly, single-electron turnstile technology is adopted in order to prepare the well-defined initial single-spin states. Secondly, a high-speed charge detection technique is introduced using the radio-frequency single-electron-transistor (RF-SET). Thirdly, the detection of a single-spin state is realized based on the spin-to-charge conversion method. We propose a revolutionary SOI-based technology platform for integrated single-spin qubits, which features double single-spin turnstile devices (SSTDs) built as two parallel SOI-nanowires (SOINWs) with their edges interconnected by another short SOINW. The SSTDs are co-integrated with three other key components: (1) an in-plane single-electron electrometer formed adjacent to the edge of one of the SSTDs, (2) a micro-ESR device formed by using a metallic waveguide and placed near the SOINW interconnect, and (3) a nanomagnet which generates a magnetic field gradient across the single-spin qubits. By integrating all the building-blocks in a nanoscale footprint, we fully investigate initialization, selective manipulation and readout of the single-spin qubits for the first time on Si.