The dielectric dipper: a differential technique to measure dielectric loss tangents with high sensitivity

Dielectric loss is suspected to limit superconducting qubit lifetimes. This could be tested by a measurement capable of detecting bulk dielectric loss smaller than the bound inferred from recent experiments (i.e., loss tangent less than 10^-7). We have devised a method for characterizing bulk dielectric loss with a sensitivity on the order of 10^-8. The method is compatible with cryogenic temperatures and single-photon powers and does not require lithographic processes. This allows for rapid comparison of isolated substrates, processing techniques, and their statistical variations. Such comparisons will inform designs and practices to better minimize dielectric loss. We present experimental comparisons of common dielectric substrates measured using this method.