Introduction of a DC Bias into a High-Q Superconducting Microwave Cavity
  We report a technique for applying a dc voltage or current bias to the center conductor of a high-quality factor superconducting microwave cavity without significantly disturbing selected cavity modes. This is accomplished by incorporating dc bias lines into the cavity at specific locations. The measured S-matrix parameters of the system are in good agreement with theoretical predictions and simulations. We find that at 4 K the quality factor of the cavity degrades by less than 1% under the application of a dc bias. 
Fei Chen, A. J. Sirois, R. W. Simmonds and A. J. Rimberg
cond-mat.supr-con