  Controllable interaction between superconducting qubits is desirable for
large-scale quantum computation and simulation. Here, based on a theoretical
proposal by Yan et al. [Phys. Rev. Appl. 10, 054061 (2018)] we experimentally
demonstrate a simply-designed and flux-controlled tunable coupler with a
continuous tunability by adjusting the coupler frequency, which can completely
turn off adjacent superconducting qubit coupling. Utilizing the tunable
interaction between two qubits via the coupler, we implement a different type
of controlled-phase (CZ) gate with 'dynamically decoupled regime', which allows
the qubit-qubit coupling to be only 'on' at the usual operating point while
dynamically 'off' during the tuning process of one qubit frequency into and out
of the operating point. This scheme not only efficiently suppresses the leakage
out of the computational subspace, but also allows for the acquired two-qubit
phase being geometric at the operating point. We achieve an average CZ gate
fidelity of 98.3(0.6), which is dominantly limited by qubit decoherence. The
demonstrated tunable coupler provides a desirable tool to suppress adjacent
qubit coupling and is suitable for large scale quantum computation and
simulation.
