Near-Field Terahertz Nanoscopy of Coplanar Microwave Resonators

TL;DR

This study employs terahertz near-field microscopy to analyze local dielectric properties of superconducting aluminum resonators on silicon, aiming to identify material imperfections affecting quantum device performance.

Contribution

It introduces a novel application of THz SNOM with vector calibration to quantitatively evaluate dielectric properties and carrier concentrations in quantum device components.

Findings

Silicon in etched channels has higher carrier concentration than buffer oxide silicon.

Post-processing methods can reduce carrier concentrations.

Near-field THz techniques can identify potential loss channels in quantum devices.

Abstract

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 (SNOM) 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 calibration 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 applied to quantitatively evaluate and identify potential loss channels in quantum devices.