Superconducting Resonators with Parasitic Electromagnetic Environments

Microwave losses in niobium superconducting resonators are investigated at milli-Kelvin temperatures and with low drive power. In addition to the well-known suppression of Q-factor that arises from coupling between the resonator and two-level defects in the dielectric substrate [1-4], we report strong dependence of the loaded Q-factor and resonance line-shape on the electromagnetic environment. Methods to suppress parasitic coupling between the resonator and its environment are demonstrated.\\[4pt] [1] Day, P.K. et al., Nature 425, 817-821 (2003).\\[0pt] [2] Wallraff, A. et. al., Nature 451, 162-167 (2004).\\[0pt] [3] Macha, P. et. al., Appl. Phys. Lett., 96, 062503 (2010).\\[0pt] [4] O'Connell, A.D. et. al., Appl. Phys. Lett., 92, 112903 (2008).