Towards High-Fidelity Gates in the Soft Zero-Pi Qubit*

The soft zero-pi circuit [1, 2, 3] has shown experimental evidence of protection against relaxation and dephasing, making it a promising candidate for high-fidelity quantum processing. However, in the most recent realization, the small hybridization gap and weak drive coupling limited flux-noise insensitivity and gate speed. Here, we show recent advances in pushing the soft zero-pi further into its protected regime, especially through increasing the ratio of the charging energies for the two participating modes. Further, we discuss efforts to improve gate speed and characterize fidelity of the multi-level system through randomized benchmarking.

[1] A. Kitaev. arXiv:cond-mat/0609441 (2006).

[2] P. Brooks, A. Kitaev, J. Preskill. Phys. Rev. A 87, 052306 (2013).

[3] A. Gyenis, P. Mundada, A. Di Paolo et. al. PRX Quantum 2, 010339 (2021).