In this experiment, we couple a superconducting Transmon qubit to a high-impedance $645 Omega$ microwave resonator. Doing so leads to a large qubit-resonator coupling rate $g$, measured through a large vacuum Rabi splitting of $2gsimeq 910$ MHz. The coupling is a significant fraction of the qubit and resonator oscillation frequencies $omega$, placing our system close to the ultra-strong coupling regime ($bar{g}=g/omega=0.071$ on resonance). Combining this setup with a vacuum-gap Transmon architecture shows the potential of reaching deep into the ultra-strong coupling $bar{g} sim 0.45$ with Transmon qubits.
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