Digital Control of Superconducting Fluxonium Qubits

Two of the main challenges facing the development of superconducting quantum computers in the coming years will be (i) their limited coherence time and (ii) their scalability. This PhD aims to combine two state-of-the-art technologies to realise an architecture that mitigates both of these problems. The first problem of coherence time is addressed by utilising the fluxonium qubit (quantum bit). These qubits have been shown to provide much longer coherence times than the superconducting qubits that currently dominate the industry. The second issue, scalability, is a problem for superconducting qubits because, currently, each qubit requires significant experimental overhead to control, measure and readout the quantum information. This cannot be applied to the quantum computers that utilise thousands or millions of qubits. The problem of scalability is addressed by utilising digital single flux quantum (SFQ) control of superconducting qubits. This technology, being worked on by companies such as SEEQC, provides a promising path to control and measure qubits in the cryogenic environment in which superconducting qubits operate. This removes the significant overhead needed to use room temperature electronics to control cryogenic qubits. The project will involve the design and fabrication of a fluxonium qubit using readily available fabrication techniques. Upon successful fabrication, the aim is to couple this fluxonium qubit to an SFQ control chip provided by SEEQC to demonstrate the coherent control of a single fluxonium qubit. The successful combination of these technologies provides the building blocks for a high coherence and very scalable superconducting quantum computer.

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.