Erbium implanted silicon for solid state quantum technologies

Silicon based information technology has revolutionized the modern world. As device features have decreased in size, integrated circuits (ICs) have become subject to quantum mechanical phenomena. Quantum technologies aim to exploit these quantum mechanical phenomena to perform tasks that are difficult or impossible with conventional technologies.

One of the main obstacles in developing quantum technologies is the rapid destruction of quantum superposition states caused by interference with the environment in a process called decoherence. Recently, extremely long coherence times (hours) have been demonstrated using small amounts of additives to silicon that have a "spare" electron (donor impurities). Although even longer times can be obtained for atoms in vacuum, an atom trapped permanently in a solid crystal such as silicon is much easier to handle. A major source of decoherence in solids is the nuclear spin of the atoms that make up the host crystals, as they often flop around uncontrollably. This has been eliminated by isotopically purifying the silicon (which normally contains a mix of isotopes, only a small number of which have nuclear spin). Even so, the donor impurities don't interact with telecoms wavelength light, and this is critical for many quantum technologies, quantum communication schemes in particular. There are currently no solid-state quantum technology platforms with long coherence times and optical fibre telecommunications compatibility. The optical transitions of the rare-earth atom erbium are, however, telecommunications compatible.

Rare-earth ions are also ideal systems for quantum technologies because the shielding of their electrons offers an atomic scale barrier to decoherence. When doped into relatively high nuclear spin metal oxide crystals, rare-earths show coherence times comparable to donor impurities in natural silicon, but are yet to be investigated in silicon themselves. Ion implantation is a well understood technology used in today's silicon IC manufacture and history has shown that commercial interest in new technologies favours those relying on established fabrication platforms and techniques. Given the expected improvement in coherence time from using erbium implanted isotopically pure silicon, it should be possible to develop a quantum technology platform that has a long coherence time, and is telecommunications and conventional IC tooling compatible.

Quantum computation schemes require the entanglement of quantum bits (qubits), this remains challenging in silicon based qubits but has been demonstrated in superconducting circuit qubits. As the latter has short coherence times and lacks optical addressability, I envisage a hybrid scheme where processing is performed with the superconducting resonators and erbium implanted silicon qubits are used as the quantum memory element and as a quantum transducer between telecommunications and microwave wavelength photons.

Through this project I will introduce a new quantum technology platform to the research community: erbium implanted silicon. This platform combines the telecommunication capability of erbium and integrated circuit capability of silicon, making it valuable for both quantum computing and quantum communication applications.

My proposed research aims to develop a QT platform that utilises standard IC fabrication techniques. The QT platform that I will use (erbium implanted silicon) is novel and as yet unexploited, there is also a good justification for it being higher performance than other similar platforms. In the short term this research has the potential to generate a lot of public interest. It is likely that the media will be very interested in my research findings because I will be using the same fabrication technology that is used in everyday electronics. It is this connection with everyday items that will help the public engage with my research, and editors of media outlets will be aware of this. This public interest will help me to promote my research and quantum technologies in general, which will help to justify research expenditure to the public. With my UK based industrial collaborator, Ionoptika Ltd, I will be working towards the development of a single-ion implantation tool. The ability to place individual atoms is fundamental to most related quantum technology schemes, and with ion implantation this individual placement can be scaled up massively. The successful development of this tool will not only be of benefit for work related to my project, but a range of other researchers aiming to exploit impurities in solids for quantum technology applications, including researchers working on donors in silicon and NV centres in diamond. There would also be tremendous spin-off benefits in conventional electronics where ordered dopant arrays would lead to massive improvements in performance.

The benefits of quantum technologies to the UK economy are potentially huge. The value of the intellectual property itself will be large, however, development and manufacture is likely to happen in the UK too, so the UK would benefit from both intellectual and manufacturing income.

The award of this grant will have a significant impact on my career by helping me establishing my own research group. It will allow me to set my own research agenda and develop as a research leader. This would put me on the path to getting further grant awards and to train additional PhD students and post-docs and build a world leading team.