Near-field terahertz nanoscopy of coplanar microwave resonators
X. Guo, X. He, Z. Degnan, B. C. Donose, K. Bertling, A. Federov, A. D. Rakic and P. Jacobson
Appl. Phys. Lett. 119, 091101 (2021)
Superconducting quantum circuits are one of the leading quantum computing platforms. To advance superconducting quantum computing
to a point of practical importance, it is critical to identify and address material imperfections that lead to decoherence. Here, we use terahertz
scanning near-field optical microscopy to probe the local dielectric properties and carrier concentrations of wet-etched aluminum resonators
on silicon, one of the most characteristic components of the superconducting quantum processors. Using a recently developed vector calibra-
tion technique, we extract the THz permittivity from spectroscopy in proximity to the microwave feedline. Fitting the extracted permittivity
to the Drude model, we find that silicon in the etched channel has a carrier concentration greater than buffer oxide etched silicon and we
explore post-processing methods to reduce the carrier concentrations. Our results show that near-field THz investigations can be used to
quantitatively evaluate and identify inhomogeneities in quantum devices.