Temperature Dependence of the Frequency and Noise of Superconducting   Coplanar Waveguide Resonators
  We present measurements of the temperature and power dependence of the resonance frequency and frequency noise of superconducting niobium thin-film coplanar waveguide resonators, carried out at temperatures well below the superconducting transition (T_{c}=9.2 K). The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level system (TLS) model for amorphous dielectrics. These results support the hypothesis that TLS are responsible for the noise in superconducting microresonators, and have important implications for resonator applications such as qubits and photon detectors. 
Shwetank Kumar (1), Jiansong Gao (1), Jonas Zmuidzinas (1 and 2),   Benjamin A. Mazin (2), Henry G. LeDuc (2), Peter K. Day ...