Michaël Simoen

Nondegenerate parametric oscillations in a tunable superconducting resonator

  1. Andreas Bengtsson,
  2. Philip Krantz,
  3. Michaël Simoen,
  4. Ida-Maria Svensson,
  5. Ben Schneider,
  6. Vitaly Shumeiko,
  7. Per Delsing,
  8. and Jonas Bylander
We investigate nondegenerate parametric oscillations in a multimode superconducting microwave resonator that is terminated by a SQUID. The parametric effect is achieved by modulating
magnetic flux through the SQUID at a frequency close to the sum of two resonator-mode frequencies. For modulation amplitudes exceeding an instability threshold, self-sustained oscillations are observed in both modes. The amplitudes of these oscillations show good quantitative agreement with a theoretical model. The oscillation phases are found to be correlated and exhibit strong fluctuations which broaden the oscillation spectral linewidths. These linewidths are significantly reduced by applying a weak on-resonance tone, which also suppresses the phase fluctuations. When the weak tone is detuned, we observe synchronization of the oscillation frequency with the frequency of the input. For the detuned input, we also observe an emergence of three idlers in the output. This observation is in agreement with theory indicating four-mode amplification and squeezing of a coherent input.
arxiv pdf

Single-shot Readout of a Superconducting Qubit using a Josephson Parametric Oscillator

  1. Philip Krantz,
  2. Andreas Bengtsson,
  3. Michaël Simoen,
  4. Simon Gustavsson,
  5. Vitaly Shumeiko,
  6. W. D. Oliver,
  7. C. M. Wilson,
  8. Per Delsing,
  9. and Jonas Bylander
We present a new read-out technique for a superconducting qubit dispersively coupled to a Josephson parametric oscillator. We perform degenerate parametric flux pumping of the Josephson
inductance with a pump amplitude surpassing the threshold for parametric instability. We map the qubit states onto two distinct states of classical parametric oscillations: one oscillating state, with on average 180 photons in the resonator, and one with zero oscillation amplitude. We demonstrate single-shot readout performance, with a total state discrimination of 81.5%. When accounting for qubit errors, this gives a corrected fidelity of 98.7%, obviating the need for a following quantum-limited amplifier. An error budget indicates that the readout fidelity is currently limited by spurious switching events between two bistable states of the resonator.
arxiv pdf