Realising scaleable systems for quantum photonics

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Systems level analysis will be crucial in realising scaleable quantum photonic systems. Having developed many imperfect lower level components, assessing trade-offs over a number of parameters will be required in order to implement useful systems. A useful case study of this is feedforward. Active feedforward of measurement outcomes is required in multiple areas of current integrated photonic quantum computing architectures. At the fundamental level feedforward is necessary to perform the adaptive measurements required to achieve universal computation. Non-deterministic single and pair photon sources, as well as probabilistic entangling gates mean multiplexing schemes will be required. These multiplexing schemes all require the feedforward of the measurement outcome of a heralding photon. Despite the importance of this sub-process, it has not yet been implemented on chip for quantum photonics. Recent developments in mid-infrared silicon photonics provide an opportunity for implementing feedforward, as silicon's high non-linear refractive index at this wavelength provides one route to the fast modulators required. This project will take a system engineering approach to implementing on chip feedforward in the mid-infrared and will look to develop and bring together a number existing and proposed subsystems. This will include integrated single photon detectors, guided and unguided on chip filtering and midinfrared modulators. A crucial problem will be to ensure the cryogenic compatibility of all subsystems and device packaging. The project will aim to implement a multiplexed source and a heralded entangling gate to perform one layer of entangled state fusion. Depending on progress, there may also be scope to explore graph states which are not available through post-selection.