Ultrafast Quantum Light Sources

Optoelectronic devices, which generate, manipulate and measure light, underpin modern communication and have enabled the internet to revolutionise the modern world. A new generation of quantum optoelectronic devices, which process light at the single photon level promise a further revolution in the way we communicate, measure and process data. Individual photons, the elementary particles of light, are the building blocks of this technology, but must first be generated by single photon sources. For practical applications the photons must be generated on-demand, at high repetition rates and must be indistinguishable, in other words identical in all degrees of freedom (for example energy and polarisation). Realising such on-demand indistinguishable photon sources is a massive scientific and engineering challenge and current solutions operate in highly controlled environments at temperatures close to absolute zero. The lack of such sources is currently a bottleneck to the development of these new quantum photonic technologies and a radical new approach is required.

The approach here is to utilise 2D materials, those with a thickness of just a few atoms, which host defects in their crystallographic structure. These defects, which consist of just one or two misplaced atoms, behave somewhat like isolated atoms, with discrete electronic energy levels that can be harnessed as single photon emitters, but with the advantage of being supported by a solid state host that can be integrated within optoelectronic devices. This project sets-out to understand these defect emitters and to integrate them in a new generation of high-performance photon sources. In particular, defects in hexagonal boron nitride (hBN) have recently emerged as robust quantum emitters with bright, stable fluorescence and nanosecond radiative lifetimes at room temperature. However, this potential is tempered by a lack of fundamental understanding of the emitter structure and how it interacts with its local environment. This fellowship will address this issue using spectroscopy to determine the microscopic structure of the defect/s responsible for the quantum emission and to study the dephasing processes arising from the interaction of the quantum system with its local environment, and which limit the indistinguishability of the emitted photons. Also, with a view to long-term manufacturing strategies, semiconductor nano fabrication technology will be developed to create these defects with pin point accuracy.

Furthermore, because the radiative lifetime of most quantum emitters is on the order of nanoseconds, this limits the photon emission rate to <1GHz and introduces timing jitter. In other words, there is uncertainty in the arrival time of the photons, which is a significant problem for applications, which require highly precise timing. To overcome these problems dielectric and plasmonic resonators will be coupled to create hybrid cavities, capable of significantly enhancing the radiative lifetime. This approach favours 2D materials because the emitter can be placed in close proximity to the plasmonic element, in the region of maximum enhancement, thereby enabling single photon rates of 10s or even 100s GHz, whilst vastly improving timing jitter and ultimately providing a route to the generation of indistinguishable photons.

Quantum Technologies are a key element of the UK's Industrial Strategy and are widely acknowledged to represent a multi-billion pound opportunity for the country. This fellowship directly addresses this strategic area, aiming to deliver quantum light sources, which are the key component required to drive quantum photonic technologies to unlock a broad range of applications in sensing, metrology, imaging and communication. The National strategy for Quantum Technologies recognises the importance of high performance photon sources, both for wealth creation and as a resource to enable companies to develop new quantum systems. The UK National Quantum Technologies Roadmap values the current market for quantum components at over £1bn per year, and predicts one market directly relevant for the technology at the heart of this fellowship, that of quantum secure ATM machines, to be worth up to £100m per year within 10-15 years.

This fellowship is well matched to the EPSRC's delivery plan, addressing the ambitions of Productive Nation (P1, P2, P4), Connected Nation (C1) and the Physics Grand Challenge of Quantum Physics for New Quantum Technologies. The work is directly relevant to the priority 'maintain' EPSRC research areas of Photonic Materials, Quantum devices, components and systems and Quantum optics and information. Furthermore, it will feed into the work of the EPSRC Quantum Hubs, for example the development of mobile Quantum Key Distribution and quantum metrology of the Quantum Communications Hub and QuantIC, respectively.

Quantum technologies are at a juncture where applications-focused research is vital and to realise this, a close partnership with Hitachi is central to this fellowship. My established collaboration with Hitachi will significantly expand the capacity of this fellowship. It will provide extra staff and laboratory capability, scientific and commercial expertise and a natural route for commercial exploitation. Direct access to one of the world's largest multinational companies will be of great benefit in identifying additional areas of commercial importance, in expanding market-awareness and in product development. To ensure the maximum benefit to the research and to build the strongest possible relationship, the Exeter-based research team will all spend a significant proportion of their time embedded within Hitachi, which will also give early career researchers first-hand experience of industrial research and development.

I see this fellowship as a fantastic opportunity to fulfil my personal ambition to work on fundamental research with a clear commercial application. I will use this opportunity to strengthen my existing links with industry, create new partnerships, and develop my entrepreneurial skills. It is paramount my growing research team and their individual careers also benefit from industry engagement, hence this fellowship budgets for their involvement in such activities. Indeed the development of highly skilled people is key to maximising the benefits of quantum technologies to the UK economy. Quantum engineers, such as my research team and I, must be equipped, not just with the necessary technical skills and knowledge, but also the creativity and commercial awareness to take advantage of the numerous opportunities that will arise in the quantum technology sector over the course of our careers. Through the mentorship structure in place for me at the University of Exeter, in addition to attendance at the MIT Entrepreneurship Development Program, and support from the University's Impact, Innovation and Business directorate, I will equip myself with the necessary skills and expertise to become an innovative research leader.