We investigate inelastic microwave photon scattering by a transmon qubit embedded in a high-impedance circuit. The transmon undergoes a charge-localization (Schmid) transition upon the impedance reaching the critical value. Due to the unique transmon level structure, the fluorescence spectrum carries a signature of the transition point. At higher circuit impedance, quasielastic photon scattering may account for the main part of the inelastic scattering cross-section; we find its dependence on the qubit and circuit parameters.
@article{arxiv.2012.02233,
title = {Critical fluorescence of a transmon at the Schmid transition},
author = {M. Houzet and L. I. Glazman},
journal= {arXiv preprint arXiv:2012.02233},
year = {2021}
}