  Microwave pulse sequences are the basis of coherent manipulation of the
electronic spin ground state in nitrogen-vacancy (NV) centers. In this work we
demonstrate stimulated Raman transitions (SRT) and stimulated Raman adiabatic
passage (STIRAP), two ways to drive the dipole-forbidden transition between two
spin sublevels in the electronic triplet ground state of the NV center. This is
achieved by a multitone Raman microwave pulse which simultaneously drives two
detuned transitions via a virtual level for SRT or via two adiabatic and
partially overlapping resonant microwave pulses for STIRAP. We lay the
theoretical framework of SRT and STIRAP dynamics and verify experimentally the
theoretical predictions of population inversion by observing the
dipole-forbidden transition in the ground state of a single NV center. A
comparison of the two schemes showed a better robustness and success of the
spin swap for STIRAP as compared to SRT.
