Exploiting the Superconducting-to-Insulating Transition in Niobium Nitride Films for Circuit QED Applications

The thickness-driven superconducting-to-insulator transition (SIT) in niobium nitride (NbN) films offer new avenues for quantum information applications. One promising direction is exploiting weak links made by thinning a narrow patch of NbN, creating a one material junction (OMJ), which could be used for a variety of circuit elements such as parametric amplifiers, or single film transmons [1].

Such OMJ are advantageous for three reasons: First, the planar structure allows for lower parasitic capacitances. Second, these junctions are made from high-gap materials, making them suitable for high-temperature and high-frequency applications. Third, their monolithic construction holds potential for minimizing material interfacial loss.

To reliably control the thickness-tuned SIT of NbN we utilize atomic layer etching (ALE) of atomic layer deposited (ALD) films. We will present recent progress in both fabrication of high-quality factor resonators and tunable OMJs using ALE and conclude with a perspective on integrating these new elements into the circuit QED toolbox.

[1] C.G.L Bøttcher et al. A transmon qubit realized by exploiting the superconducting-insulator transition