Investigation of Josephson interferometer potentials by ac excitations

The properties of the activation potential of a Josephson interferometer are investigated under the effect of external microwave signals. In particular, we measure the effects of the microwaves on an interferometer having a low inductance. Using as a probing tool thermal escape techniques we find that the plasma frequency excitations of this system when exposed to the radiation field are well described by a double-pendulum equation under the same ac biasing conditions. We discuss the results within the framework of the recent investigations on macroscopic quantum coherence.