3D Microwave Cavity for Qubit Measurement

We have investigated the loss mechanisms of the $\textrm{TE}_{101}$ mode (resonant frequency $\textrm{f}_0 = 8\textrm{ GHz}$) of a superconducting Al microwave cavity. The internal quality factor $Q_{int}$ of the cavity has been measured for a range of temperatures from 23 mK to 360 mK in a low photon number regime and from 360 mK to $\textrm{T}_c \sim$ 1.1 K in a high photon number regime, both with and without a sapphire chip in the cavity. With sapphire present, $Q_{int} \sim 10^6$ was strongly reduced by an applied magnetic field. Without sapphire, $Q_{int} \sim 4\times10^6$ was only weakly dependent on the applied field. The frequency stability of the cavity and the use of the cavity for qubit readout (following recent experiments by H. Paik \textit{et. al.}\footnote{arXiv:1105.4652v4}) will be discussed.