Multilevel dynamical decoupling for a coupled superconducting two-qubit system

Recent advances have significantly enhanced the coherence times of superconducting qubits. However, high-fidelity storage of multiqubit quantum states in large-scale circuits is still limited by factors such as the flux noise and crosstalk. We propose an X-iSwap decoupling sequence combining single-qubit ${X}_{\ensuremath{\pi}}$ gates and two-qubit iSwap gates to effectively mitigate dephasing from the low-frequency flux noise and eliminate crosstalk between qubits. Numerical simulations of noisy random evolution show excellent agreement with the theoretical models. In quantum memory applications, our method substantially extends the decay time of two-qubit fidelity and eliminates fidelity oscillations caused by the ZZ crosstalk. Compared to the traditional decoupling methods based on single-qubit gates, the X-iSwap sequence exhibits superior robustness against small system errors, which holds promise for widespread application in two-qubit systems and large-scale quantum processors for tasks such as long-term quantum memory and entanglement protection.