The Hub’s flagship goal is to realise the Q20:20 engine: a hybrid light-matter quantum computer involving twenty nodes, optically interlinked, where each node is a small quantum processor of twenty qubits.

Realising this ambitious target requires rapid development in multiple hardware efforts: these include engineering the nodal processors themselves, each of which requires integrated laser and microwave subsystems, as well as the optical links formed from fibres, photonic switches, splitters and detectors.

Each processing node will be an ion trap, a device within which a small number of charged atoms – ions – are held suspended in a vacuum and manipulated by laser and microwave systems. Each trap will be segmented, meaning that it can shuttle ions back and forth like beads on an abacus, and will be capable of holding two different atomic species simultaneously – we will be using calcium and strontium. A single unit of quantum information, one qubit, is embodied within the internal hyperfine states of each ion, and control of the qubits is achieved optically via integrated lasers and through microwave manipulation.

Interlinking between the traps will be realised by single photon emissions, which are combined and measured by fibres, splitters, switches and detectors. The protocols for achieving information processing with this structure have been modelled in detail theoretically, and these models undergo continual evolution in tandem with the hardware development. The design achieves robustness versus hardware imperfections through a process called “entanglement purification” which involves upgrading the fidelity of the connective link by using it several times and filtering.

During the programme we will build a series of demonstrations that show the key steps in creating the Q20:20 engine. Initially we will connect two ion traps, then four using a switch. This will allow us to prove the concepts that we need to show work. Whilst we are doing this we will also be developing the miniature components that will allow us to shrink the system size to our target. We will use all of these components to build the final Q20:20 quantum computer demonstrator.