A single atom-like defect embedded in a crystal could act as an optical switch that operates at the level of individual particles of light. Today’s optical networks—the fibre-optic cables that carry internet traffic—rely on electronics to route signals, because light does not easily interact with itself. This project tackles that fundamental limitation: the weak nonlinearity of light means that all-optical switching requires high power and is too slow for practical use. The researcher will build a device that couples a single quantum dot or colour centre to a microscopic cavity, creating a spin-photon entangler that can induce strong correlations between individual photons. If successful, the technology would serve two purposes. For classical communications, it could enable low-power, high-speed all-optical routing and signal processing, reducing energy consumption in data centres and telecom infrastructure. For quantum technologies, the same component acts as a universal gate for quantum computation, opening a route to scalable quantum computers and a long-range “quantum internet” for secure information transfer. The work is primarily fundamental science, but the component it targets—a deterministic photon–photon gate—has been a missing piece in both fields for decades.
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Optical technologies are key to many communications, measurement and sensing tasks. In fact optical communication (in low loss fibres) underpins the global economy, supporting the near instantaneous transmission of terabits of information worldwide. However all-optical switching and computing have not developed dramatically despite optimism in the 1990's. This is primarily because of the problem of weak optical nonlinearity leading to high power requirements and low switching speeds. In this proposal I will develop a new optical switching technology based on the coupling of atom like defects in solid state hosts. The technology promises a high speed low power optical switch which could revolutionise all optical networks with routing and many other signal conditioning tasks performed in the all-optical domain. The more recent developments of quantum photonic technologies such as quantum secured key distribution and the vision of quantum computing are also limited by the lack of a non-linearity at the single photon level. The missing component is in fact a deterministic entangler capable of inducing strong correlations between separate photons or between separate solid state realisations of quantum bits. This project aims to develop such gates based on our earlier invention a spin photon entangler which uses a singly charged quantum dot or colour centre strongly coupled to a microcavity. It turns out this element is a universal gate for quantum computation and experimental realisation of this gate is a key target here. Once such a component is available it will pave the way to a long range 'quantum internet' and to the development of a scalable quantum computer technology allowing both circuit and measurement based quantum computing realisations to be envisaged. The end goal is to develop a technology that addresses both classical and quantum applications using single atom-like light emitters embedded in wavelength scale optical cavities (or waveguides) configured as either attojoule optical switches or high-fidelity efficient spin-photon entangling gates.
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