Cooper Pair Transistor Embedded in a dc-Biased High-Q Microwave Cavity

A high-Q microwave cavity design based on the circuit quantum electrodynamics architecture has been developed to introduce a dc bias to the center conductor of the cavity without significantly degrading the Q at high frequencies [1]. Here we directly couple Cooper pair transistors (CPTs) to such a cavity. In the subgap region of the CPT, the dc bias generates a tunable oscillating current through the CPT via the ac Josephson effect. Evidence of such self-oscillations has been observed as current peaks in our dc measurements, which are in good agreement with calculated cavity modes, and indicate the strong coupling between the CPT and the cavity. Recent experimental results will be discussed.\\[4pt] [1] F. Chen, A. J. Sirois, R. W. Simmonds and A. J. Rimberg, Appl. Phys. Lett., 98, 132509 (2011).