Compact superconducting coplanar microwave beam splitters*

The recent evolution of circuit quantum electrodynamics with standing-wave microwave modes towards setups for propagating quantum microwaves has triggered the need for low-loss superconducting microwave beam splitters. Such a device should have ports obeying the coplanar geometry relevant for circuit QED and, at the same time, be compact for the sake of scalability. This combination presents a serious challenge. In this work, we present an experimental characterization of various compact superconducting coplanar microwave beam splitters. In addition, we briefly discuss efforts towards a tunable beam splitter.