N. Haandbaek

Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor

  1. M. A. Rol,
  2. L. Ciorciaro,
  3. F. K. Malinowski,
  4. B. M. Tarasinski,
  5. R. E. Sagastizabal,
  6. C. C. Bultink,
  7. Y. Salathe,
  8. N. Haandbaek,
  9. J. Sedivy,
  10. and L. DiCarlo
We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in a quantum processor. We specifically use Cryoscope to measure the
step response of the dedicated flux control lines of two-junction transmon qubits in circuit QED processors with the temporal resolution of the room-temperature arbitrary waveform generator producing the control pulses. As a first application, we iteratively improve this step response using optimized real-time digital filters to counter the linear-dynamical distortion in the control line, as needed for high-fidelity, repeatable one- and two-qubit gates based on dynamical control of qubit frequency.
arxiv pdf

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.
arxiv pdf