Superconducting qubit in waveguide cavity with coherence time approaching 0.1ms

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We report a superconducting artificial atom with an observed quantum coherence time of T2*=95us and energy relaxation time T1=70us.

• The system consists of a single Josephson junction transmon qubit embedded in an otherwise empty copper waveguide cavity whose lowest eigenmode is dispersively coupled to the qubit transition.
• We attribute the factor of four increase in the coherence quality factor relative to previous reports to device modifications aimed at reducing qubit dephasing from residual cavity photons.
• This simple device holds great promise as a robust and easily produced artificial quantum system whose intrinsic coherence properties are sufficient to allow tests of quantum error correction.