Exceeding the Parametric Drive Strength Threshold in Nonlinear Circuits

TL;DR

This paper investigates how strong parametric drives in nonlinear superconducting circuits cause ionization and chaos, limiting control fidelity and gate speed, with implications for quantum processor design.

Contribution

It demonstrates that drive-induced chaos and ionization occur in nonlinear circuits under strong driving, providing a Floquet spectrum framework for understanding these limitations.

Findings

Ionization occurs in nonlinear circuits under strong parametric drive.

Drive-induced chaos limits coherent control and gate speed.

Floquet spectrum characterizes the onset of chaos and ionization.

Abstract

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.