Controlling the spontaneous emission of a superconducting transmon qubit
  We present a detailed characterization of coherence in seven transmon qubits in a circuit QED architecture. We find that spontaneous emission rates are strongly influenced by far off-resonant modes of the cavity and can be understood within a semiclassical circuit model. A careful analysis of the spontaneous qubit decay into a microwave transmission-line cavity can accurately predict the qubit lifetimes over two orders of magnitude in time and more than an octave in frequency. Coherence times $T_1$ and $T_2^*$ of more than a microsecond are reproducibly demonstrated. 
A. A. Houck, J. A. Schreier, B. R. Johnson, J. M. Chow, Jens Koch, J.   M. Gambetta, D. I. Schuster, L. Frunzio, M. H. Devor...