Exploring the effect of growth and surface quality of niobium thin-films for superconducting devices

We explore the potential improvement of coherence in niobium-based superconducting devices with a focus on two aspects. The first aspect is the role of the niobium and substrate surfaces. We use an approach for sample packaging where devices can be quickly isolated in vacuum after metal oxide removal, using a special purpose sealable microwave cavity. The second aspect is the role of film growth, with both sputtering and electron cyclotron resonance growth being considered.

In this talk we will present the design of several types of test structures, including lumped and distributed resonators and transmon qubits, used to probe various contributions to loss, including surface and interface loss and quasiparticle losses. We will present our preliminary results on the fabrication and characterization of these devices.