Microfabricated Ion-Cavity nodes for Robust, Optically-Networked Quantum Computing (MICRON-QC)

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Quantum computing is poised to transform the way we tackle humanity's hardest computational problems, but despite recent progress in qubit control and error-correcting code design, no qubit platform has convincingly demonstrated a route to free scalability. Of all platforms, trapped ions retain the record for high-fidelity qubit operations, and enable highly-connected architectures, greatly reducing gate-count for large devices. However, scaling of qubit numbers on a single, monolithic processor is expected to hit a ceiling far below that required for useful fault-tolerant computation, and the ultimate route to scalability lies in distributing the quantum computer across a network of smaller processors.This project will construct and operate the first reconfigurable network of trapped ion processors linked by single photons emitted over fibre interconnects, ultimately consisting of 5 nodes. I will demonstrate all the elements required for efficient large-scale networked computation including: a flying qubit encoding and wavelength suitable for high-fidelity long-range transmission; a reconfigurable photonic network enabling any-to-any node connectivity and entanglement of multiple node-pairs in parallel; and sufficient qubit resource within each node to permit the assembly of arbitrary entangled graph states across the network. I will construct cavity-based network interfaces at each node capable of near-deterministic ion-photon entanglement at 1MHz attempt rates, allowing remote ion-ion entanglement creation at 100kHz rates, close to those of local gates. Through a combination of informed protocol design and advanced microsystem engineering, I will demonstrate that this can be achieved with nodes of remarkably simple and robust construction, enabling near-autonomous operation. While the 5-node network will enable many fascinating experiments, the principal objective of the project will be to prove that a network of hundreds or thousands of nodes is within reach.