Exploring parametric gate rate limits in transmons and other couplers (Part 2)

Fast and high-fidelity gates are an essential requirement in quantum information experiments. Parametric couplers based on non-linear circuits driven at specific frequencies allow us to implement these interactions with high on-off ratios. In our work, we focus on exchange/iSWAP gates based on low frequency drives, below the lowest mode of the qubits or coupler. Although these parametric gate speeds uniformly increase with drive strength at low powers, several effects limit the rate as one increases the drive power. The hardest to mitigate is a broadband threshold on drive strength beyond which the coupler undergoes uncontrolled excitation into highly excited states. In the case of transmon couplers, strong hybridization involving many Floquet modes of the driven system has been used to explain this observation [1]. In this talk, we will present our work on matching the measured performance of transmons and

predicting the drive threshold for a wide range of possible coupler parameters. We compare amongst several different heuristics for drive strength threshold based on average excitation number of Floquet modes at different drive strengths. We show that the ideal transmon coupler design depends on the number of drive photons used in the parametric process. Finally, we discuss our work to apply this framework to more complex circuits with the aim of finding optimal parametric coupler designs that allow the fastest and higher-fidelity gates.

[1] M.Xia, et al. arXiv:2506.03456v1 (2025)