study of decoherence sources. However, only short coherence times have been demonstrated so far with this type of qubit. Here, we present a capacitively shunted flux qubit featuring improved relaxation times up to T1 = 25 μs and a frequency tunability range of ∼ 20 GHz at the flux-insensitive sweet spot. As a model application, we demonstrate detection of two-level tunneling defects in a frequency range spanning one octave.