  We address a problem of generating a robust entangling gate between
electronic and nuclear spins in the system of a single nitrogen-vacany centre
coupled to a nearest Carbon-13 atom in diamond against certain types of
systematic errors such as pulse-length and off-resonance errors. We analyse the
robustness of various control schemes: sequential pulses, composite pulses and
numerically-optimised pulses. We find that numerically-optimised pulses,
produced by the gradient ascent pulse engineering algorithm (GRAPE), are more
robust than the composite pulses and the sequential pulses. The optimised
pulses can also be implemented in a faster time than the composite pulses.
