  Scalable quantum information processing requires the ability to tune
multi-qubit interactions. This makes the precise manipulation of quantum states
particularly difficult for multi-qubit interactions because tunability
unavoidably introduces sensitivity to fluctuations in the tuned parameters,
leading to erroneous multi-qubit gate operations. The performance of quantum
algorithms may be severely compromised by coherent multi-qubit errors. It is
therefore imperative to understand how these fluctuations affect multi-qubit
interactions and, more importantly, to mitigate their influence. In this study,
we demonstrate how to implement dynamical-decoupling techniques to suppress the
two-qubit analogue of the dephasing on a superconducting quantum device
featuring a compact tunable coupler, a trending technology that enables the
fast manipulation of qubit--qubit interactions. The pure-dephasing time shows
an up to ~14 times enhancement on average when using robust sequences. The
results are in good agreement with the noise generated from room-temperature
circuits. Our study further reveals the decohering processes associated with
tunable couplers and establishes a framework to develop gates and sequences
robust against two-qubit errors.
