Strong coupling of two flux qubits to a colanar waveguide resonator

The field of circuit QED opens new possibilities in both quantum information processing and studies of fundamental quantum mechanics ''on a chip''. Central building blocks are qubit circuits, which interact with on-chip superconducting microwave resonators. Of particular importance is the strong-coupling regime, where the coupling strength exceeds all relevant decay rates in the system. Here, we present spectroscopic measurements on two superconducting flux qubits strongly coupled to a coplanar waveguide resonator.