Hybrid Quantum Circuits with van der Waals Superconductors

Superconducting microwave circuits are exceptionally sensitive probes of small changes in the electromagnetic response, and are especially useful for exploring the properties of novel superconductors. At the same time, van der Waals superconductors provide a rapidly expanding platform for unconventional superconductivity: they can be isolated as thin crystalline flakes, assembled into heterostructures and integrated with other materials. By combining these systems, hybrid circuits can investigate superconductors in regimes that are difficult to access using conventional transport measurements.

Our group has recently developed low-loss microwave resonators incorporating micron-scale van der Waals superconductors without requiring a galvanic contact [1]. The resonator geometry can be adapted to each material and measurement task, for example, by placing the flake at a current antinode to maximize its inductive participation in the mode. In this PhD project, you will design and fabricate such hybrid devices and study their response at millikelvin temperatures. Microwave measurements will be used to probe the superfluid response, dissipation mechanisms, and nonlinear electrodynamics of unconventional superconductors. The project combines expertise in microwave circuits, nanofabrication, van der Waals assembly, cryogenic microwave measurements, and theoretical modeling.

Hybrid superconducting circuits are not only excellent probes of quantum matter, but can be building blocks of new devices for quantum technology. One possible direction is the flowermon, a proposed protected qubit based on a twisted cuprate Josephson junction [2]. Near a twist angle of 45 degrees, the symmetry of a sign-changing nodal superconducting order parameter may suppress ordinary single-Cooper-pair tunneling and produce an unusual nonlinear circuit element. Hybrid-resonator measurements can test this physics and provide a route toward future material-based quantum devices. The project lies at the interface of condensed-matter physics and quantum information, with opportunities ranging from fundamental spectroscopy to the development of new superconducting circuits.