Measurement-induced qubit state mixing in circuit QED from up-converted   dephasing noise
  We observe measurement-induced qubit state mixing in a transmon qubit dispersively coupled to a planar readout cavity. Our results indicate that dephasing noise at the qubit-readout detuning frequency is up-converted by readout photons to cause spurious qubit state transitions, thus limiting the nondemolition character of the readout. Furthermore, we use the qubit transition rate as a tool to extract an equivalent flux noise spectral density at f ~ 1 GHz and find agreement with values extrapolated from a $1/f^\alpha$ fit to the measured flux noise spectral density below 1 Hz. 
D. H. Slichter, R. Vijay, S. J. Weber, S. Boutin, M. Boissonneault, J.   M. Gambetta, A. Blais, I. Siddiqi
cond-mat.mes-hall cond-mat.supr-con quant-ph