• DOI:10.1103/PhysRevLett.109.123602
• Corpus ID: 22163919

Weak qubit measurement with a nonlinear cavity: beyond perturbation theory.

@article{Laflamme2012WeakQM,
  title={Weak qubit measurement with a nonlinear cavity: beyond perturbation theory.},
  author={Catherine Laflamme and Aashish A Clerk},
  journal={Physical review letters},
  year={2012},
  volume={109 12},
  pages={
          123602
        }
}

• C. Laflamme, A. Clerk
• Published 21 June 2012
• Physics
• Physical review letters

We analyze the use of a driven nonlinear cavity to make a weak continuous measurement of a dispersively coupled qubit. We calculate the backaction dephasing rate and measurement rate beyond leading-order perturbation theory using a phase-space approach which accounts for cavity noise squeezing. Surprisingly, we find that increasing the coupling strength beyond the regime describable by leading-order perturbation theory (i.e., linear response) allows one to come significantly closer to the quantum limit on the measurement efficiency. We interpret this behavior in terms of the non-Gaussian photon number fluctuations of the nonlinear cavity. Our results are relevant to recent experiments using superconducting microwave circuits to study quantum measurement.