Tunable low-loss couplers integrated with superconducting 3d-cavities*

Superconducting circuits are a leading platform for quantum information processing. On one hand, the most coherent qubits are stored in (3-dimensional) microwave cavities; on the other hand, planar circuits provide design flexibility and large-scale manufacturability. A particularly desirable element would permit tunable, on-demand coupling of a 3d-cavity to a planar circuit, without introducing unwanted dissipation to the cavity. This element could be used, for example, to implement a modular quantum network, where any pairwise interactions between cavities could be turned on and off by connecting to a planar network. To this end, we design and test superconducting switches that tune the cavity external coupling from zero up to 3 orders of magnitude larger than the intrinsic cavity dissipation, while also preserving a 2.8 million cavity quality factor. Furthermore, the switches can be flipped in 10 ns, and remain in a linear regime at the microwave power needed for readout of a transmon qubit.