Figure 4. Interpolation quality after applying the re-optimization scheme. Axes on the top plots correspond to the three Cartan coordinates of two-qubit gates. Reference pulses are generated by optimal control software for 14 reference points in parameter space. Pulses for any point in the chamber can be obtained by linear interpolation between reference pulses. Left: interpolated pulse infidelities at 819 test points (granularity 1/24) after initial optimization of reference points. Black lines connect reference points and define the simplicial mesh that is used for interpolation. Each colored point represents a unitary operation defined by its coordinates. The color of each point is the infidelity of the pulse that is obtained via interpolation. Mean infidelity is $1.3 \pm 1.2 \times 10^{-2}$. Right: results after repeatedly re-optimizing each reference point to be near the average of its neighbors. Mean infidelity is improved to $1.0 \pm 0.8 \times 10^{-4}$.