Towards high-fidelity two-qubit gates on fluxonium qubits

Recently we demonstrated microwave two-qubit gate schemes [1, 2] using high levels of fluxoniums, where the gate fidelity is limited by the decoherence outside the computational space. To solve this problem, here we demonstrate the implementation of microwave two-qubit gates using only computational states. By applying a strong microwave drive between the two qubit frequencies, we can flip 00 to 11 in ~80 ns through the two-photon transition. On the other hand, we can induce a ZZ interaction (~5 MHz) by off-resonantly driving near the qubit frequencies. With these techniques, we can construct a bSWAP gate and a CZ gate and over 99.9% fidelities can be expected. These high-fidelity two-qubit gates on fluxoniums can benefit the development of Noisy Intermediate Scale Quantum (NISQ) processors and universal quantum computing.

[1] Physical Review X 11(2) (2021): 021026

[2] arXiv preprint arXiv:2103.04491 (2021)