We investigate open- and closed-loop quantum optimal control in nitrogen-vacancy (NV) centre systems, using gate set tomography (GST) for pulse characterisation and calibration. Open-loop optimisation with GRAPE revealed a strong dependence of gate fidelity on pulse duration and the need for phase correction in echo-based gates.

Despite promising simulations of advanced pulse designs, experimental performance was consistently higher for a standard weak $\pi$ pulse, highlighting model limitations. Closed-loop optimisation with dCRAB improved performance but exhibited sensitivity to environmental drift, confirming magnet-induced variations.

GST identified dominant coherent error channels, notably ZZ, attributed to AC Stark-induced phase shifts. A novel gate design suppressed ZZ errors but introduced greater stochastic noise.

These results demonstrate the importance of integrating model-driven and data-driven approaches with advanced tomography protocols to achieve robust, high-fidelity quantum control in noisy intermediate-scale quantum (NISQ) devices.