  In this article, we present an experimental study of a Josephson junction
-based high-impedance resonator. By taking the resonator to the limit of
consisting effectively only of one junction, results in strong non-linear
effects already for the second photon while maintaining a high impedance of the
resonance mode. Our experiment yields thus resonators with the strong
interactions both between individual resonator photons and from the resonator
photons to other electric quantum systems. We also present an energy diagram
technique which enables to measure, identify and analyse different multi-photon
optics processes along their energy conservation lines.
