The dielectric dipper: experimental comparisons of common dielectric substrates in isolation*

We have devised a method for characterizing bulk dielectric loss with a sensitivity on the order of 1e-8. The method probes the low-power behavior of dielectrics at cryogenic temperatures without the need for lithographic processes. So far, the method has identified bulk loss as a major source of decoherence of transmon qubits on EFG sapphire. With a bulk loss tangent of 6e-8, bulk loss in EFG sapphire places a limit on transmon lifetime of about 800 us. Using the same technique, we investigate other 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.