Elimination of unwanted qubit interactions for parametric exchange two-qubit gates in a tunable coupling circuit

We experimentally demonstrate a simple-design tunable coupler, achieving a continuous tunability for eliminating unwanted qubit interactions. We implement two-qubit iSWAP gate by applying a fast-flux bias modulation pulse on the coupler to turn on parametric exchange interaction between computational qubits. Aiming to fully investigate error sources on the two-qubit gates, we perform quantum process tomography measurements and numerical simulations as varying static ZZ coupling strength. Our results reveal that the change in the two-qubit gate error is mainly attributed to unwanted high-frequency oscillation error terms, while the dynamic ZZ coupling parasitising in two-qubit gate operation may also contribute to the dependency of the gate fidelity. This approach, which has not yet been previously explored, provides a guiding principle to improve gate fidelity of parametric iSWAP gate by the elimination of unwanted qubit interactions. This controllable interaction, together with the parametric architecture by using modulation techniques, is desirable for crosstalk free multiqubit quantum circuits and quantum simulation applications.

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