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.
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