Measuring Loss Tangents of Substrates for Superconducting Qubits with Part per Billion Precision*

This talk will present a comparative study on the dielectric loss tangent of various substrates measured with an ultra-high quality factor niobium SRF cavity at the low electric fields and mK temperatures relevant for superconducting quantum computing architectures. We study the loss tangent evolution of c-plane sapphire with atmospheric annealing and correlate the resulting RF performance with materials analysis including time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS).