Towards single-photon switching via two-photon absorption in Rb vapour

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If we could induce a strong interaction between photons (mediated by atoms), this would allow the implementation of quantum logic operations at room temperature, opening the way to scalable (cryogenics-free) quantum computing. A strong candidate for engineering such interactions is the combination of optical waveguides and cavities with alkali vapours. We have the unique capability to explore this area at the CPPM in Bath. In this project, we will seek to experimentally test a proposal to switch the phase of a signal photon based on the presence of a control photon impinging on a cavity coupled to the two-photon absorption line in rubidium. This is a very ambitious goal, but there are a number of interesting tasks that will lead up to it. First, we will investigate switching in a fibre-based ring-cavity, which could have applications in photonic buffering and routing. In parallel we will develop a theoretical model for the two-photon interactions in a vapour-filled ring cavity. It will also be necessary to develop techniques to fabricate bubble resonators and fibre tapers, and a vacuum system enable us to load the resonator with rubidium. Each of these steps will provide opportunities to publish.