We experimentally investigated the optical responses of a superconducting niobium resonator. It was found that, with increasing radiation power, the resonance frequency increases monotonically below around 500 mK, decreases monotonically above around 1 K and exhibits a nonmonotonic behavior at around 700 mK. These observations show that one can operate the irradiated resonator in three temperature regimes, depending on whether two-level system (TLS) effects or kinetic inductance effects dominate. Furthermore, we found that the optical responses at ultra-low temperatures can be qualitatively regarded as a photon-induced thermalization effect of TLSs, which could be utilized to achieve thermal sensitive photon detections.
@article{arxiv.1310.1504,
title = {Photon-induced thermal effects in superconducting coplanar waveguide resonators},
author = {Yiwen Wang and Pinjia Zhou and Lianfu Wei and Haijie Li and Beihong Zhang and Miao Zhang and Qiang Wei and Yurong Fang and Chunhai Cao},
journal= {arXiv preprint arXiv:1310.1504},
year = {2013}
}