  Quantum computation requires the precise control of the evolution of a
quantum system, typically through application of discrete quantum logic gates
on a set of qubits. Here, we use the cross-resonance interaction to implement a
gate between two superconducting transmon qubits with a direct static
dispersive coupling. We demonstrate a practical calibration procedure for the
optimization of the gate, combining continuous and repeated-gate Hamiltonian
tomography with step-wise reduction of dominant two-qubit coherent errors
through mapping to microwave control parameters. We show experimentally that
this procedure can enable a $\hat{ZX}_{-\pi/2}$ gate with a fidelity
$F=97.0(7)\%$, measured with interleaved randomized benchmarking. We show this
in a architecture with out-of-plane control and readout that is readily
extensible to larger scale quantum circuits.
