M. Boissonneault

Quantum Heating of a nonlinear resonator probed by a superconducting qubit

  1. F. R. Ong,
  2. M. Boissonneault,
  3. F. Mallet,
  4. A. C. Doherty,
  5. A. Blais,
  6. D. Vion,
  7. D. Esteve,
  8. and P. Bertet
We measure the quantum fluctuations of a pumped nonlinear resonator, using a superconducting artificial atom as an in-situ probe. The qubit excitation spectrum gives access to the frequency
and temperature of the intracavity field fluctuations. These are found to be in agreement with theoretical predictions; in particular we experimentally observe the phenomenon of quantum heating.
arxiv pdf

Measurement-induced qubit state mixing in circuit QED from up-converted dephasing noise

  1. D. H. Slichter,
  2. R. Vijay,
  3. S. J. Weber,
  4. S. Boutin,
  5. M. Boissonneault,
  6. J. M. Gambetta,
  7. A. Blais,
  8. and I. Siddiqi
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.
arxiv pdf