EPSRC-SFI: Developing a Quantum Bus for germanium hole based spin qubits on silicon

量子计算机有望成为未来几十年的主要技术进步之一。一些理论著作预测，有了这样的系统，就有可能运行预计将对许多行业产生重大影响的算法，例如：化学，制药，汽车和金融服务。麦肯锡公司最新的报告（2021年12月）证实了这一点，该报告还显示，全球对该研究领域的投资呈指数级增长，并预测到2035年市场价值将超过7000亿美元。实现量子计算机的主要限制之一是执行多个量子位操作的难度。在这个项目中，我们将解决这个基本问题。我们的主要目标将是探索和实现新型的介观效应来介导长距离量子比特操作。为了实现这一目标，我们将在PI发明的非常低的无序应变锗半导体材料上制造最先进的纳米级器件，并在标准硅衬底上外延生长。有几种用于实现量子比特的平台，量子比特是用于执行量子计算的量子信息处理的基本单元。广义上，它们可以基于离子阱、超导结、光子电路和半导体量子点，其中每一种都可以达到不同的时钟速度、门保真度和测量误差、串扰和连接性。虽然在所有平台上都有巨大的科学进步和概念验证，但在可扩展架构中产生高保真多量子位操作的主要挑战仍然存在。我们的目标是研究半导体量子点中自旋量子位的扩展范围交换相互作用，并基于这些发现，提出了一种允许量子错误消除和校正的2D量子位架构设计的概念验证演示。在CMOS兼容的2D网络中使用扩展范围耦合方案实现量子位操纵是一项重大的科学和技术突破，将为在微小的硅芯片上具有数十亿量子位的量子处理器的颠覆性可扩展架构奠定基础。我们的目标是通过开发基于交换相互作用的Ge量子总线来开发和实现长距离双量子比特耦合的替代方案。这种方法利用了与交换过程相关的高速，而不需要以直接接触的方式布置量子点，因此对于当前的半导体器件制造技术是有吸引力的。我们将介绍一个新的范例，自旋为基础的量子计算实验证明使用带正电的空穴的长程耦合。这里设想的架构利用了空穴的独特自旋特性，解决了自旋量子位面临的许多（如果不是全部的话）挑战，并提供了一个新的平台。重要的是，这个提议结合了学术界和工业界的努力。一方面，我们利用Myronov教授在应变锗材料研究和开发方面的一些重大进展，Smith教授在量子比特特性方面的实验专业知识以及Bose教授的理论支持。另一方面，器件将由廷德尔国家研究所制造。此外，该项目还将得到2个英国工业合作伙伴和8个国际学术研究团体的大力支持，这也将有助于量子比特设备的操作，表征和解释新的结果。这些能力使该联合体在国际上处于独特的地位，是进行拟议研究的理想场所。

Quantum computers promise to be one of the main technical advances of the forthcoming decades. Several theoretical works predict that with such a system it will be possible to operate algorithms which are expected to have a large impact on many industries such as: chemical, pharmaceutical, automotive, and financial services. This is confirmed in the latest McKinsey & Company report (Dec. 2021) where they also demonstrate a global exponential increase in investment in this research area and predict a market value of surpassing $700 billion by 2035. One of the main limitations for the realization of a quantum computer concerns the difficulty of performing multiple qubit operations. In this project we will address this fundamental issue. Our main objective will be to explore and implement new type of mesoscopic effects to mediate long distance qubit operations. To achieve this goal, we will fabricate state of the art nanoscale devices on very low disorder strained germanium semiconductor material, invented by the PI, and epitaxially grown on a standard silicon substrate. There are several proposed platforms for realising qubits, the basic units of quantum information processing used to perform quantum computation. Broadly they can be based on ion-traps, superconducting junctions, photonic circuits and semiconductor quantum dots, each of which can reach different clock speed, gate fidelity and measurement errors, crosstalk and connectivity. While there has been great scientific progress and proof-of-concept demonstrations on all platforms, the main challenge to produce high-fidelity multi-qubit operations in scalable architectures remains. We aim to research extended-range exchange interactions in spin-qubits in semiconductor quantum dots and based on the discoveries, propose a proof-of-concept demonstration of 2D qubit architecture design that allows for quantum error cancellation and correction. Achieving qubit manipulation with extended-range coupling schemes in a CMOS-compatible 2D network is a major scientific and technological breakthrough that will set the foundations for a disruptive scalable architecture towards a quantum processor with billions of qubits on a tiny silicon chip. We aim to develop and implement alternatives for implementing long distance two-qubit coupling by developing a Ge Quantum Bus based on exchange interactions. This approach makes use of the high speed associated with exchange processes, without the requirement to arrange quantum dots in direct contact and is therefore attractive for current semiconductor devices fabrication techniques. We will introduce a new paradigm for spin-based quantum computing by experimentally demonstrating long-range coupling using positively charged holes. The architectures envisioned here exploit the unique spin properties of holes and address many, if not all, of the challenges that spin qubits are facing, and provide a new platform too.Importantly, this proposal combines efforts from academy and industry. On one hand, we take advantages of some major advances on the strained germanium material research and development made by Prof. Myronov, the experimental expertise in qubits characterisation of Prof. Smith and the theorical support of Prof. Bose. On the other hand, devices will be fabricated by Tyndall National Institute. In addition, the project will be heavily supported by 2 UK industrial partners and 8 international academic research groups, which will also contribute towards qubit devices operation, characterization and interpretation of novel results. These capabilities uniquely position this consortium internationally as being ideally placed to perform the proposed research.