General method for extracting the quantum efficiency of dispersive qubit readout in circuit QED

  1. C. C. Bultink,
  2. B. Tarasinski,
  3. N. Haandbaek,
  4. S. Poletto,
  5. N. Haider,
  6. D. J. Michalak,
  7. A. Bruno,
  8. and L. DiCarlo
We present and demonstrate a general 3-step method for extracting the quantum efficiency of dispersive qubit readout in circuit QED. We use active depletion of post-measurement photons and optimal integration weight functions on two quadratures to maximize the signal-to-noise ratio of non-steady-state homodyne measurement. We derive analytically and demonstrate experimentally that the method robustly extracts the quantum efficiency for arbitrary readout conditions in the linear regime. We use the proven method to optimally bias a Josephon traveling-wave parametric amplifier and to quantify the different noise contributions in the readout amplification chain.
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