%0 Journal Article
%T Measurement-induced qubit state mixing in circuit QED from up-converted dephasing noise
%A D. H. Slichter
%A R. Vijay
%A S. J. Weber
%A S. Boutin
%A M. Boissonneault
%A J. M. Gambetta
%A A. Blais
%A I. Siddiqi
%J Physics
%D 2012
%I arXiv
%R 10.1103/PhysRevLett.109.153601
%X 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.
%U http://arxiv.org/abs/1206.6946v2