Superconducting electric circuits are a strong contender for building a powerful new type of computer — a quantum computer. Such computers will operate in a fundamentally different way than conventional computers, storing and processing information encoded in quantum ‘superpositionsʼ (the information is in a sense in multiple states simultaneously) and ‘entangled’ states, in which the information in different quantum bits is correlated in a way that is impossible in conventional computers. It is anticipated that such computers will have a dramatic impact on the world once realised, but there is much still to do!

Superconducting circuits are a highly flexible ‘engineerableʼ platform to develop innovative approaches to quantum computing. We are working on many aspects, including recent development of a 3D coaxial circuit architecture [1] designed to simplify the task of scaling highly coherent circuits to the many qubits needed for useful computing. This architecture forms the basis of much of the current research in the group. Recently we have been working on implementing quantum logic gates [2], and developing ways to scale the platform up to support more qubits [3].

A particular area of physics that can be accessed using quantum electrical circuits is cavity quantum electrodynamics (QED). This is the study of light-matter interactions by confinement of single atoms and light inside a cavity. This enhances the interaction strength between the systems, and allows coherent exchange of quanta between them. The electrical circuit version of this concept is known as circuit QED. The flexibility of realising cavity QED in a circuit makes it a powerful platform for exploring the physics of light-matter interactions. We have recently worked on probing the physics of strongly coupled and strongly driven circuit QED [4,5].

[4] T Mavrogordatos et al., Phys. Rev. Lett. 118, 040402 (2017)

[5] P Brookes et al., arXiv:1907.123592 (2019)

Collaborators: Eran Ginossar (University of Surrey), Marzena Szymanska (UCL)

Superconducting circuit QED can be integrated with other quantum coherent degrees of freedom in solid state devices, to explore their quantum behaviour and their potential for use in quantum technologies such as computing or sensing. We have worked on developing prototypes of a variety of such ‘hybridʼ quantum circuits, including circuits incorporating surface acoustic waves [6], spin ensembles [7] and carbon nanotubes [8].

[6] R Manenti et al., Nature Communications 8, 975 (2017)

[7] M Mergenthaler et al., Phys. Rev. Lett. 119, 147701 (2017)

[8] M Mergenthaler et al., arXiv:1904.10132 (2019)

Collaborators: Anton Frisk-Kockum & Franco Nori (RIKEN, Japan),

Andrew Briggs & Edward Laird (Materials, Oxford)