Charge transport through ultrasmall single and double Josephson junctions coupled to resonant modes of the electromagnetic environment

We have investigated charge transport in ultrasmall superconducting single and double Josephson junctions coupled to resonant modes of the electromagnetic environment. We observe pronounced current peaks in the transport characteristics of both types of devices and attribute them to the process involving simultaneous tunneling of Cooper pairs and photon emission into the resonant modes. The experimental data are well reproduced with the theoretical models.