Spectroscopy of three strongly coupled flux qubits

We have carried out spectroscopic measurements of a system of three strongly coupled four-junction flux qubits. The samples studied cover a wide range of parameters with the coupling energy between neighboring qubits varying between $0.75\mathrm{GHz}$ and $6.05\mathrm{GHz}$. The observed complicated spectra agree well with eight-level theory. The experiments are relevant for the realization of a tunable coupling between qubits.