Likai Yang

Digital Predistortion for Flux Control of Tunable Superconducting Qubits

  1. Dharun Venkateswaran,
  2. Felice Francesco Tafuri,
  3. Yuanzheng Paul Tan,
  4. Bruno Aznar Martinez,
  5. Alisa Danilenko,
  6. Likai Yang,
  7. Arnaud Carignan-Dugas,
  8. Christoph Hufnagel,
  9. Rainer Dumke,
  10. Philip Krantz,
  11. and Eric T. Holland
Flux-tunable superconducting qubits rely on fast flux control pulses to implement two-qubit entangling quantum gates, a key building block for quantum algorithms. However, distortion
effects introduced by non-ideal control electronics, parasitic components, and the cryogenic quantum chip response can all degrade the gate fidelity. We present a digital predistortion (DPD) framework for characterizing and then compensating for these distortions using a combination of infinite impulse response (IIR) and finite impulse response (FIR) filters. Experiments on a flux-tunable quantum processing unit (QPU) demonstrate a successful correction of step-response distortions on the flux-control line, with a compensated control signal showing only sub-percent deviations from the ideal target linear behavior. The demonstrated method enables automated rapid calibration of flux control channels for superconducting QPUs.
arxiv pdf

Impact of Pump Phase-Noise on Josephson Traveling-Wave Parametric Amplifiers

  1. Daryoush Shiri,
  2. Likai Yang,
  3. Saesun Kim,
  4. Mohamed A. Hassan,
  5. Philip Krantz,
  6. and Eric T. Holland
Superconducting traveling-wave parametric amplifiers (TWPAs) are essential elements for enhancing the signal-to-noise ratio (SNR) and thus the read-out fidelity of superconducting qubits
because of their high gain and near quantum-limited noise. However, the impact of the pump source, e.g., phase noise on these amplifiers, has not yet been studied. In this work, we show that among the two amplification processes in JTWPAs, the three-wave mixing (3WM) process is more sensitive to the pump phase noise than the four-wave mixing (4WM) process. We show that the even-order nonlinearity of 4th order and above in three-wave mixing is responsible for more than 10 dB increase of phase noise at high frequency offsets within the phase noise mask as the power of the pump increases. A polynomial model of the amplifier and cyclo-stationary property of phase noise also corroborate with the simulations. The Harmonic Balance (HB) periodic noise analysis tool and Leeson phase noise model in Keysight Advanced Design System (ADS) simulator were used in this study.
arxiv pdf