  The multi-level system $^{55}$Mn$^{2+}$ is used to generate two
pseudo-harmonic level systems, as representations of the same electronic
sextuplet at different nuclear spin projections. The systems are coupled using
a forbidden nuclear transition induced by the crystalline anisotropy. We
demonstrate Rabi oscillations between the two representations in conditions
similar to two coupled quasi-harmonic quantum oscillators. Rabi oscillations
are performed at a detuned pumping frequency which matches energy difference
between electro-nuclear states of different oscillators. We measure a coupling
stronger than the decoherence rate, to indicate the possibility fast
information exchange between the systems.
