Thin-Film Ferroelectrics for Low-Loss Quantum Microwave Devices

Superconducting quantum processors rely on low-loss microwave devices for qubit control, signal routing and quantum-limited readout. Established amplifier technologies based on Josephson junctions or kinetic inductance face trade-offs in dynamic range, pump power, scalability and magnetic-field compatibility. Thin-film ferroelectrics provide an alternative route because their electrically tunable permittivity and strong nonlinear response can be integrated directly into microwave circuits.

This PhD will investigate and suppress cryogenic microwave loss in thin-film ferroelectric devices, with primary focus on SrTiO3 and targeted comparison with other piezoelectric materials where scientifically useful. Superconducting resonators, coplanar waveguides and nonlinear microwave circuits will be used to separate dielectric, interface, conductor, domain-related and phononic contributions. The project will translate this understanding into low-loss device architectures and proof-of-concept quantum microwave components, including tunable resonators and parametric-amplifier building blocks. The outcome will be quantitative design rules connecting material stack, device geometry, processing and operating conditions to low-power microwave loss and nonlinear performance.