High kinetic inductance thin films for compact readout of CMOS-compatible spin qubits

Lead Research Organisation: University College London
Department Name: London Centre for Nanotechnology


For quantum computers to fully demonstrate their advantage over classical approaches, the number of qubits available must significantly increase beyond that currently feasible using state of the art superconducting qubits. Spin qubits can be realised using silicon transistors fabricated in a way that is compatible with the CMOS processes used to manufacture chips found in modern technologies. Through the use of this mature silicon technology a qubit density of 1010 qubits/cm2 could be possible. However, the current readout circuitry reduces this value to 103 qubits/cm2 hindering the scalability that is the main benefit of a CMOS-compatible approach. To solve this issue, a high kinetic inductance (KI) material can be incorporated as the gate electrode to both confine electrons and act as the resonator for readout. This will reduce the size of the readout circuitry as a high inductance can be achieved in a smaller area due to the KI. To achieve this goal first involves investigating multiple high KI materials to determine their applicability. The material must demonstrate low loss and correspondingly high Q-factors for fabricated resonators as this determines the sensitivity to capacitance shifts used to readout the qubit state. Also of importance is their resilience to magnetic fields (_1T for singlet-triplet and _1.5T for other implementations) which are needed for manipulation of the spin qubits. Quantum dot devices that include the chosen high KI material as the gate electrode will then be designed, fabricated and tested. An understanding of these devices will allow the development of a nanowire with multiple gates to demonstrate the scalability of this approach with the fabrication of a 4-qubit unit cell.

Planned Impact

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.


10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S021582/1 01/10/2019 31/03/2028
2407155 Studentship EP/S021582/1 01/10/2020 30/09/2024 Thomas Swift