QII-TAQS: All-Photonic Quantum Network

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Development of quantum computers and networks will require large-scale connections at the quantum level between many particles. These special connections between the particles, known as qubit entanglement, are essential for applications in quantum computing, communications, and sensing. Approaches that have been intensely studied to generate such entanglement utilize neutral atoms, ions, or superconducting circuits and rely on strong qubit-qubit interactions. Successful entanglement of these matter-based qubits is challenging due to deleterious interactions with the environment. Here an alternative approach is explored using a photonic-chip platform based on silicon nitride to realize highly entangled photon states. Such a platform has significant advantages over other photonic-chip materials such as silicon by offering record low losses in an integrated platform. Realization of an all-photonic platform for deterministic generation of photonic states will have broad impact across all quantum information technologies. For example, such a scheme would enable measurement-based universal computation, where computation occurs by performing single-qubit measurements on a highly-entangled resource state.This research project aims to create an integrated photonics platform that can generate highly-entangled states of light in near-deterministic fashion at high rates and with high fidelity. These highly-entangled states will serve as scalable photonic building blocks for generating cluster states for quantum computers and quantum networks. The platform will be based on a nonlinear multiplexing scheme in the frequency domain that allows overcoming the poor scaling with loss associated with spatial and temporal multiplexing. The rate of entangled photon generation will be dramatically increased by leveraging recent advances in massively parallel photonic on-chip devices that can (1) generate and convert photons within a well-defined spectral grid with high efficiency and (2) store light on-demand for timescales on the order of hundreds of nanoseconds with high efficiency, using massively parallel micron-size devices. It is projected that the generation rate of entangled Bell pairs can be increased over what is currently possible by at least two orders of magnitude, from 1 microsecond to 200 microseconds. Ultimately, the work aims to lead to a scalable platform for which the generation rate of entangled photons scales only polynomially (as opposed to exponentially) with the number of resources (detectors, resonators, etc.).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.