Long-Range Exchange Coupling between Ge-Hole Spin Quantum Systems

Quantum processors promise to tackle problems deemed unsolvable by classical computers, advancing fields such as finance, climate change, chemistry and cryptography, amongst others. Current leading platforms for quantum computation include superconducting qubits, ion traps and spins in quantum dots. While there have been many experiments on single-qubit operation in such platforms, two-qubit entangling operations still remain elusive, which are a crucial requirement for realising a useful quantum computer. As such, of interest are systems which can easily manipulate and couple qubits to achieve multi-qubit connectivity, while leveraging state-of-the-art qubit control and read-out techniques.

This PhD project will therefore focus on the study of novel germanium-hole quantum-dot qubits, with the end goal of implementing and extending long-range coupling between spatially separated qubits. Hole spins in germanium are a particularly attractive platform due to fast manipulation speeds, low decoherence rates and ease of fabrication. The project will concern device design, modelling, measurement and characterisation, with considerations towards scaling this architecture. The majority of work will be carried out at the Hitachi Cambridge Laboratory (HCL), the industrial sponsor of this PhD. HCL are experts in gate-based qubit readout, with much work already performed on CMOS qubits. Devices will be fabricated by collaborators which are leaders in growing germanium structures. Due to the facilities and expertise in germanium qubits and long-range coupling techniques at the HCL, this project aims to advance qubit-to-qubit connectivity, paving the way towards scalable, universal quantum computation.

The first and most important impact of our Centre will be through the cross-disciplinary technical training it provides for its students. Through this training, they will have not only skills to control and exploit quantum physics in new ways, but also the background in device engineering and information science to bring these ideas to implementation and to seek out new applications. Our commercial and governmental partners tell us how important these skills are in the growing number of people they are hiring in the field of quantum technologies. In the longer term we expect our graduates to be prominent in the development of new technologies and their application to communication, information processing, and measurement science in leading university and government laboratories as well as in commercial research and development. In the shorter term we expect them to be carrying out doctoral research of the highest international quality.

Second, impact will also flow from the students' approach to enterprise and technology transfer. From the outset they will be encouraged to think about the value of intellectual property, the opportunity it provides, and the fundraising needed to support research and development. As students with this mindset come to play a prominent part in university and commercial laboratories, their common background will help to break down the traditional barriers between these sectors and deliver the promise of quantum technologies for the benefit of the UK and world economies. Concrete actions to accelerate this impact will include entrepreneurship training and an annual CDT industry day.

Third, through the participation it nucleates in the training programme and in students' research, the Centre will bring together a community of partners from industry and government laboratories. In the short term this will facilitate new collaborations and networks involving the partners and the students; in the long term it will help to ensure that the supply of highly skilled people from the CDT reaches the parts of industry that need them most.

Finally, the CDT will have a strong impact on the quantum technologies training landscape in the UK. The Centre will organise training events and workshops open to all doctoral researchers to attend. We will also collaborate with CDTs in the quantum technologies and related research areas to coordinate our efforts and maximise our joint impact. Working in consort, these CDTs will form a vibrant national training network benefitting the entire UK doctoral research community.