Radiation effects on coplanar waveguide microwave resonators

We used superconducting microwave resonators to study the effect of radiation on devices used for quantum information. Niobium (Nb) and titanium nitride (TiN) coplanar waveguides (CPWs) were exposed to gamma radiation from a closed Cesium-137 (Cs137) source. We measured a change in internal quality factor and a change in resonance frequency when exposed to a gamma radiation source of about 3 microcuries. A shift of about 2000-4000 hertz was observed in the resonance frequency nitrogen passivated Nb samples. In the TiN samples, the shift was larger by two factors of 10. Shifts of 100,000 to 300,000 Hz were recorded. By better understanding the effects of radiation on quantum materials, mitigation methods can be further developed to increase the stability of quantum systems. It is important to understand the relationship between radiation on internal quality factor (Qi), since internal quality factor is a measure of how effective the resonator is at storing quantum states for computation. A decline in Qi factor was observed in most samples of NbN, and larger declines in TiN samples. The degradation in NbN Qi is more pronounced at lower power levels with the greatest shifts appearing in the TiN samples at low power. While Nb is still an important material for quantum information, even small amounts of radiation can make it less effective.