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Measurement-induced qubit state mixing in circuit QED from up-converted dephasing noise (1206.6946v2)
Published 29 Jun 2012 in cond-mat.mes-hall, cond-mat.supr-con, and quant-ph
Abstract: 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.
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