Mediating high-fidelity interactions between superconducting microwave cavities, part II.*

The coherence and large Hilbert spaces of three-dimensional superconducting microwave cavities make them an attractive platform for building quantum memories. Such memories may be coupled together by the fourth-order nonlinearity of a transmon, allowing for bilinear (beam-splitter, single-mode, and two-mode squeezing) interactions. These in turn may form the building blocks for cavity-cavity gates. We examine how these bilinear interactions can be improved by designing custom nonlinear coupling elements. These ‘converters’ can be engineered to suppress spurious fourth-order processes, such as self and cross-Kerr effects, and improve the desired bilinear coupling. In this talk, we discuss preliminary measurements on pairs of three-dimensional microwave cavities coupled by such a custom conversion element.