Assessing the Influence of Broadband Instrumentation Noise on Parametrically Modulated Superconducting Qubits

  1. E. Schuyler Fried,
  2. Prasahnt Sivarajah,
  3. Nicolas Didier,
  4. Eyob A. Sete,
  5. Marcus P. da Silva,
  6. Blake R. Johnson,
  7. and Colm A. Ryan
With superconducting transmon qubits — a promising platform for quantum information processing — two-qubit gates can be performed using AC signals to modulate a tunable
transmon’s frequency via magnetic flux through its SQUID loop. However, frequency tunablity introduces an additional dephasing mechanism from magnetic fluctuations. In this work, we experimentally study the contribution of instrumentation noise to flux instability and the resulting error rate of parametrically activated two-qubit gates. Specifically, we measure the qubit coherence time under flux modulation while injecting broadband noise through the flux control channel. We model the noise’s effect using a dephasing rate model that matches well to the measured rates, and use it to prescribe a noise floor required to achieve a desired two-qubit gate infidelity. Finally, we demonstrate that low-pass filtering the AC signal used to drive two-qubit gates between the first and second harmonic frequencies can reduce qubit sensitivity to flux noise at the AC sweet spot (ACSS), confirming an earlier theoretical prediction. The framework we present to determine instrumentation noise floors required for high entangling two-qubit gate fidelity should be extensible to other quantum information processing systems.

Demonstration of a Parametrically-Activated Entangling Gate Protected from Flux Noise

  1. Sabrina S. Hong,
  2. Alexander T. Papageorge,
  3. Prasahnt Sivarajah,
  4. Genya Crossman,
  5. Nicolas Dider,
  6. Anthony M. Polloreno,
  7. Eyob A. Sete,
  8. Stefan W. Turkowski,
  9. Marcus P. da Silva,
  10. and Blake R. Johnson
In state-of-the-art quantum computing platforms, including superconducting qubits and trapped ions, imperfections in the 2-qubit entangling gates are the dominant contributions of error
to system-wide performance. Recently, a novel 2-qubit parametric gate was proposed and demonstrated with superconducting transmon qubits. This gate is activated through RF modulation of the transmon frequency and can be operated at an amplitude where the performance is first-order insensitive to flux-noise. In this work we experimentally validate the existence of this AC sweet spot and demonstrate its dependence on white noise power from room temperature electronics. With these factors in place, we measure coherence-limited entangling-gate fidelities as high as 99.2 ± 0.15%.