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

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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.