Low loss hybrid Nb/Au superconducting resonators for quantum circuit applications

Abstract

Superconducting resonators play a crucial role in the development of quantum technologies such as quantum computing or high performance detectors. Yet, one of their main limitations regarding to noise and sensitivity is the interaction with two-level systems present in oxide layers in the device. Focused on mitigating this problem, we study a superconducting device combining a 100 nm niobium (Nb) circuit with a 10 nm gold (Au) capping layer. Our investigation covers a wide range of temperatures and driving powers, revealing that adding the Au layer reduces the density of two-level system defects while maintaining a very high quality factor. Moreover, an increase in the non-linearity response is also observed. Our findings suggest the potential of Nb/Au lumped element resonators as versatile and promising tools for advancing superconducting quantum technologies.