Materials for superconducting qubits

The connection between microscopic material properties and qubit coherence are not well understood despite practical evidence that material imperfections present an obstacle to applications of superconducting qubits. In a new report now published on Communications Materials, Anjali Premkumar and a team of scientists in electrical engineering, nanomaterials, physics and angstrom engineering at Princeton University and in Ontario, Canada, combined measurements of transmon qubit relaxation (T1) times with spectroscopy, alongside microscopy of polycrystalline niobium (Nb) films used during qubit development. Based on films deposited via three different techniques, the team revealed correlations between transmon qubit relaxation times and intrinsic film properties, including grain size to enhance oxygen diffusion along grain boundaries, while also increasing the concentration of suboxides near the surface. The residual resistance ratio of the polycrystalline niobium films can be used as a figure of merit to understand qubit lifetimes, and the new approach charts a path for materials-driven improvements of superconducting qubit performance.