Exceeding the Parametric Drive Strength Threshold in Nonlinear Circuits

  1. Mingkang Xia,
  2. Cristóbal Lledó,
  3. Matthew Capocci,
  4. Jacob Repicky,
  5. Benjamin D'Anjou,
  6. Ian Mondragon-Shem,
  7. Ryan Kaufman,
  8. Jens Koch,
  9. Alexandre Blais,
  10. and Michael Hatridge
Superconducting quantum circuits rely on strong drives to implement fast gates, high-fidelity readout, and state stabilization. However, these drives can induce uncontrolled excitations,
so-called „ionization“, that compromise the fidelity of these operations. While now well-characterized in the context of qubit readout, it remains unclear how general this limitation is across the more general setting of parametric control. Here, we demonstrate that a nonlinear coupler, exemplified by a transmon, undergoes ionization under strong parametric driving, leading to a breakdown of coherent control and thereby limiting the accessible gate speeds. Through experiments and numerical simulations, we associate this behavior with the emergence of drive-induced chaotic dynamics, which we characterize quantitatively using the instantaneous Floquet spectrum. Our results reveal that the Floquet spectrum provides a unifying framework for understanding strong-drive limitations across a wide range of operations on superconducting quantum circuits. This insight establishes fundamental constraints on parametric control and offers design principles for mitigating drive-induced decoherence in next-generation quantum processors.

Computer-aided quantization and numerical analysis of superconducting circuits

  1. Sai Pavan Chitta,
  2. Tianpu Zhao,
  3. Ziwen Huang,
  4. Ian Mondragon-Shem,
  5. and Jens Koch
The development of new superconducting circuits and the improvement of existing ones rely on the accurate modeling of spectral properties which are key to achieving the needed advances
in qubit performance. Systematic circuit analysis at the lumped-element level, starting from a circuit network and culminating in a Hamiltonian appropriately describing the quantum properties of the circuit, is a well-established procedure, yet cumbersome to carry out manually for larger circuits. We present work utilizing symbolic computer algebra and numerical diagonalization routines versatile enough to tackle a variety of circuits. Results from this work are accessible through a newly released module of the scqubits package.