  In state-of-the-art quantum computing platforms, including superconducting
qubits and trapped ions, imperfections in the 2-qubit entangling gates are the
dominant contributions of error to system-wide performance. Recently, a novel
2-qubit parametric gate was proposed and demonstrated with superconducting
transmon qubits. This gate is activated through RF modulation of the transmon
frequency and can be operated at an amplitude where the performance is
first-order insensitive to flux-noise. In this work we experimentally validate
the existence of this AC sweet spot and demonstrate its dependence on white
noise power from room temperature electronics. With these factors in place, we
measure coherence-limited entangling-gate fidelities as high as 99.2 $\pm$
0.15%.
