Understanding mechanisms of RF loss in dielectric substrates in mK temperature range

Recent improvements in fabrication of superconducting qubits led to significant reduction of losses associated with amorphous surface oxides naturally forming on unprotected interfaces after exposure to ambient atmosphere. Further advancements in qubit coherence call for understanding of the mechanisms of decoherence and reduction of losses related to dielectric substrates these quantum devices are fabricated on. We use a tunable superconducting resonator that allows to characterize losses in various dielectric substrates as a function of frequency and power.

We demonstrate and discuss the experimental testbed that allows us to characterize various dielectric materials in sub-1K temperatures and wide frequency range from 4 - 7 GHz. Our measurements of the loss tangent as a function of frequency, temperature, and probing power help to identify the dominant loss mechanisms and select optimal materials and fabrication procedures for the next generation of QC devices.