  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.
