The Dielectric Dipper: Correlating bulk dielectric loss with underlying material properties

We have developed a differential probe of bulk dielectric loss with a sensitivity on the order of . The method uses a 3D cavity to probe the low-power behavior of dielectrics at cryogenic temperatures without the need for lithographic processing. Using this technique, we investigate various substrate materials and processes with the aim to better quantify dielectric loss, understand its origin, and determine how it can be mitigated in fabrication of superconducting quantum devices. In our investigation of float-zone silicon, we have observed a wide range of loss tangents spanning an order of magnitude, implying bulk coherence limits ranging from several milliseconds all the way down to hundreds of microseconds. These results indicate an intermittent barrier to our community's effort to reliably improve superconducting qubit lifetimes. Moving forward, this effort calls for a more robust system of supply-end quality control, targeting metrics relevant to cryogenic microwave behavior. To facilitate this, we investigate the relationship between these bulk loss tangents and various electrical, compositional and structural properties.