  Generating high-fidelity, tunable entanglement between qubits is crucial for
realizing gate-based quantum computation. In superconducting circuits, tunable
interactions are often implemented using flux-tunable qubits or coupling
elements, adding control complexity and noise sources. Here, we realize a
tunable $ZZ$ interaction between two transmon qubits with fixed frequencies and
fixed coupling, induced by driving both transmons off-resonantly. We show
tunable coupling over one order of magnitude larger than the static coupling,
and change the sign of the interaction, enabling cancellation of the idle
coupling. Further, this interaction is amenable to large quantum processors:
the drive frequency can be flexibly chosen to avoid spurious transitions, and
because both transmons are driven, it is resilient to microwave crosstalk. We
apply this interaction to implement a controlled phase (CZ) gate with a gate
fidelity of $99.43(1)\%$ as measured by cycle benchmarking, and we find the
fidelity is limited by incoherent errors.
