Quantum technology capital: Multi-species single-ion implantation

The exploitation of single atoms for Quantum Technologies (QT) is most advanced for single-atom and single-ion electromagnetic traps in vacuum. Dopants in solids provide a natural form of trapping, as the impurity is held in place by the electromagnetic fields of the host solid around it, but on a length scale orders of magnitude smaller. Some solids, such as silicon can be made with an astonishing purity of 1 part per 100,000,000,000. This is so pure that nano-scale devices can be expected to have zero unintentional impurities and, if the doping is carefully controlled, a device can be constructed with a single, solitary impurity atom opening up a wealth of possibilities for solid state QT. This brings new challenges in engineering the local environment, but they are ideal objects for robust, reproducable QT applications. Single dopants provide 'qubits' of quantum information for clocks, sensors and computation, and non- classical light sources for quantum key distribution systems, quantum repeaters, quantum lithography, multivalent logic and local sensing.

The first electronic observation of a single impurity in a semiconductor was made in a MOSFET device cooled to about 30K - the single, naturally occurring, unidentified bistable impurity close to the conduction channel produced random telegraph noise. Single electron transistor channels now allow specific nearby dopants to be identified by their effect on the electrical characteristics.

In some cases single impurities may be incorporated with nanometre precision using Scanning Tunnelling Microscope tips, but a much greater variety could, in principle, be achieved with ion implantation. Ion implantation is a microelectronic industry standard technique, and Surrey University houses the UK National Ion Beam Centre. Although implantation with a lateral accuracy of about 20 nm has been reported, it has only previously been possible with lithographically produced masks. This has already been used to create active devices that involve two phosphorus atoms in silicon close enough for their spins to exchange in a flip-flop interaction, but the functionality of this device was restricted by the limited accuracy of the implantation technique, and it has not been reproduced. A much more scalable, reproducible technology would be to use highly focused ion beams, but this requires a significant advancement in implantation tools.

This proposal is to install the world's first single ion implantation tool with 20nm lateral beam focus, with the ability to implant any species from gas or solid source. The tool will serve the UK need for an open access user facility for academia and industry in QTs.

Using this tool, we will enable implantation of single bismuth atoms in silicon, single nitrogen atoms in diamond, single erbium atoms in sapphire, and single manganese atoms in GaAs. Each of these exemplifies a different QT platform and covers applications from magnetometry to imaging, computation and single photon emission. We will characterize and image the single atom devices, either via collaboration with key partners (in the case of diamond NV) or in house (in the case of Bi in Si).

In the case of the Si:Bi (and other silicon shallow impurities) we will install a world leading near-field imaging system using terahertz frequency light. This will take advantage of Surrey's strategic partnership with the National Physical Laboratory (NPL).

Who will benefit from the capital investment?

The potential of quantum technologies (QTs) to impact across a breadth of sectors is recognised at the highest levels of the UK Government. This has lead to the formation of the UK National Quantum Technologies Programme and a National Strategy for Quantum Technologies established following substantial (£270M) financial investment being made available. The technologies that are expected to emerge from this investment include both short-term (e.g. compact UK-sourced atomic clocks) through to medium-term advanced in medical diagnostics, and longer-term quantum processors.

Advances in these areas, and others targeted by the National Strategy, will have an impact on everyone on the individual level (e.g. improved healthcare), on the commercial level (e.g. improved system performance and productivity), well as globally (e.g. enhanced communications and monitoring).

The capital investment proposed within will play a role in realising these impacts through providing globally-leading research programmes with the capability to study and develop the highly-advanced quantum systems required at the heart of QT devices. The route we propose to achieve this is via a highly-focused ion beam doping tool that performs single ion implantation. This solution has been chosen taking into consideration the requirement for future QTs to be commercial viable in terms of scale-up and fabrication. As a result of this industry will benefit from this investment, as the devices it enables will have a viable route to manufacture.

Even at the early stages of the technology development a number of industrial companies are supporting this work. These include those with leading basic research programmes in the area of quantum technologies: Hitachi Europe, Element Six (UK) and NTT (Japan) thus demonstrating industrial interest. Our proposal is also strongly supported by the UK National Physical Laboratory (NPL), members of the UK National Quantum Technologies Programme, and will benefit the Quantum Metrology Institute at NPL, and its wider user community.

Our proposed capital investment is directly aligned with the UK National Strategy (see Pathways to Impact). As part of those involve in defining this, the funding bodies and stakeholders that they represent will benefit from the capability we will provide and research it enables. The outcomes of this investment and the research it serves will provide direct support for future research programme prioritisation relating to these challenges. As users develop new material systems and technologies, other funders of research in different disciplinary areas will also benefit as the outcomes are translated into applications elsewhere (e.g. in bio/medical research for enhanced diagnostics).

The area of our proposed work represents a unique example where the interplay of electronic, optical, magnetic and quantum effects will be determined via the choice of dopant ion species and ability of the engineering to deliver it as intended. It therefore offers a wealth of training opportunities and is ideally suited for providing a series of learning resources in which these properties may be introduced to students and their interactions explained. This can be applied from a machine technology level (high-vacuum and vibration control) right through to fundamental quantum mechanical level (qubit creation and control). We will therefore design and make available learning resources, working with the QT training programmes in existence and to be created in parallel to this call.

The realisation of the materials, effects, and initial devices envisaged within the programme will be transformational on the field in the short term setting the agenda internationally. On a longer timescale as more sophisticated quantum devices are realised and move into production the impact on quality of life, manufacturing, and the economy will be dramatic.