| Summary: | Linear optical quantum computing (LOQC) benefits from photonic qubits with low decoherence, simple optical elements for qubit manipulation, and a developing integrated platform. The cost of the LOQC approach is the non-deterministic nature of many of the processes, including single-photon generation, which arises from parametric heralded sources and the lack of direct interaction between photons. Active multiplexing - repeating a generation process in time or space and rerouting to single modes using an optical switching network-has been proposed to overcome this challenge and could enable scalable quantum photonics. This thesis explores optical quantum computing, and quantum photonics in general, using active multiplexing and switching, starting from the single-photon source and extending to large-scale architectures. A theoretical framework for time and space multiplexed single photon sources is provided, and a proof-of-principle experimental implementation of a time and space multiplexed source using bulk and fiber components is demonstrated. Multiplexing heralded entangled states is explored theoretically, and a new technique to minimize active switching requirements in some scenarios- relative bin multiplexing- is introduced. Component level architectures for fully fault-tolerant LOQC using active switching are presented, as well as first estimates of their loss/ error thresholds and resource costs. An integrated silicon all-optical switch based on the Kerr effect is simulated and designed. Optical multiplexing using active switching is shown to be a promising approach to break through the current experimental limits in quantum photonics and enable larger experiments in the near future. With sufficient development, optical multiplexing is also a feasible alternative to quantum matter-based schemes for large-scale quantum photonics and computing.
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