  We have performed spectroscopy measurements on two coupled flux qubits. The
qubits are coupled inductively, which results in a $\sigma_1^z\sigma_2^z$
interaction. By applying microwave radiation, we observe resonances due to
transitions from the ground state to the first two excited states. From the
position of these resonances as a function of the magnetic field applied we
observe the coupling of the qubits. The coupling strength agrees well with
calculations of the mutual inductance.
