  A flux qubit biased at its symmetry point shows a minimum in the energy
splitting (the gap), providing protection against flux noise. We have
fabricated a qubit whose gap can be tuned fast and have coupled this qubit
strongly to an LC oscillator. We show full spectroscopy of the qubit-resonator
system and generate vacuum Rabi oscillations. When the gap is made equal to the
oscillator frequency $\nu_{osc}$ we find the strongest qubit-resonator coupling
($g/h\sim0.1\nu_{\rm osc}$). Here being at resonance coincides with the optimal
coherence of the symmetry point. Significant further increase of the coupling
is possible.
