Two-level system (TLS) loss is typically limiting the coherence of superconducting quantum circuits. The loss induced by TLS defects is nonlinear, resulting in quality factors with a strong dependence on the circulating microwave power. We observe frequency mixing due to this nonlinearity by applying a two-tone drive to a coplanar waveguide resonator and measuring the intermodulation products using a multifrequency lock-in technique. This intermodulation spectroscopy method provides an efficient approach to characterizing TLS loss in superconducting circuits. Using harmonic balance reconstruction, we recover the nonlinear parameters of the device-TLS interaction, which are in good agreement with the standard tunnelling model for TLSs.
@article{arxiv.2402.10775,
title = {Intermodulation spectroscopy and the nonlinear response of two-level systems in superconducting coplanar waveguide resonators},
author = {Janka Biznárová and J. C. Rivera Hernández and Daniel Forchheimer and Jonas Bylander and David B. Haviland and Gustav Andersson},
journal= {arXiv preprint arXiv:2402.10775},
year = {2024}
}