  Unwanted $ZZ$ interaction is a quantum-mechanical crosstalk phenomenon which
correlates qubit dynamics and is ubiquitous in superconducting qubit systems.
It adversely affects the quality of quantum operations and can be detrimental
in scalable quantum information processing. Here we propose and experimentally
demonstrate a practically extensible approach for complete cancellation of
residual $ZZ$ interaction between fixed-frequency transmon qubits, which are
known for long coherence and simple control. We apply to the intermediate
coupler that connects the qubits a weak microwave drive at a properly chosen
frequency in order to noninvasively induce an ac Stark shift for $ZZ$
cancellation. We verify the cancellation performance by measuring vanishing
two-qubit entangling phases and $ZZ$ correlations. In addition, we implement a
randomized benchmarking experiment to extract the idling gate fidelity which
shows good agreement with the coherence limit, demonstrating the effectiveness
of $ZZ$ cancellation. Our method allows independent addressability of each
qubit-qubit connection, and is applicable to both nontunable and tunable
couplers, promising better compatibility with future large-scale quantum
processors.
