Electro-optic Devices for Quantum Transduction

Quantum computers are a fundamentally new type of supercomputer which have the potential to make major impacts in drug discovery, material science, cryptography and machine learning. Connecting quantum computers together into a quantum network opens up even more applications, such as secure communication and enhanced sensing, and provides a path to scaling quantum computers to larger numbers of qubits. Superconducting qubits, with their relatively high gate fidelities and their scalable microfabrication, are a particularly promising hardware approach for quantum computing. However, these superconducting circuits operate at microwave frequencies, and connecting them into basic networks with microwave cables has so far been limited to distances of a few meters. To extend these connections to kilometer-scale distances we will need to leverage the low loss provided by optical fiber links. The key challenge is that this requires a new kind of transducer to bridge the gap between the microwave and optical domains.

This dissertation describes my work towards building this microwave-to-optical transducer, pushing electro-optic modulators towards the quantum limit by combining low-loss optical waveguides with superconducting circuits. This effort led us to explore three different nanophotonic platforms. The first, silicon-on-lithium-niobate, combines the straightforward waveguide fabrication available in silicon with the large electro-optic coecient of lithium niobate. The second, silicon-organic hybrid, leverages the exceptionally large electro-optic coecients available in electro-optic polymers. The third, lithium-niobate-on-sapphire, employs waveguides fabricated directly in lithium niobate to further increase performance. Here I describe results from each of these platforms, as well as some of the interesting problems we’ve had to address along the way, including challenging nanofabrication, cryogenic optical packaging, light-induced quasiparticles, and unintentional piezoelectricity.