Fast Flux Entangling Gate for Fluxonium Circuits*

The superconducting fluxonium circuit with its strong anharmonicity and long coherence time is a promising candidate for qubit implementation in a quantum processor [1]. Experimentally realized two-qubit gates with fluxoniums are based on microwave irradiation leading to excitations of higher noncomputational levels [2, 3]. Alternatively, the full advantage of the long lifetime can be utilized by always staying in the computational subspace with possible two-qubit gate schemes based on the cross-resonance effect [4] or on driving a two-photon transition [5]. Here we analyze a highly accurate two-qubit gate with fluxoniums using fast flux pulses, which can be realized by temporarily detuning magnetic flux through the fluxonium loop away from the half flux quantum sweet spot [6]. We evaluate the effect of the flux noise and qubit relaxation on the gate fidelity and demonstrate that the gate error remains below 10^-4.

[1] A. Somoroff, et. al., arXiv:2103.08578 (2021).

[2] Q. Ficheux, Phys. Rev. X 11, 021026 (2021).

[3] H. Xiong, arXiv:2103.04491 (2021).

[4] J. M. Chow, et. al., Phys. Rev. Lett. 107, 080502 (2011).

[5] K. N. Nesterov, et. al., PRX Quantum 2, 020345 (2021).

[6] Y. Chen, et. al., arXiv:2110.00632 (2021).