  Ionized nitrogen molecules ($^{15}$N$_{2}^+$) are used as efficient point
sources for creating NV$^-$ pairs in diamond with nanoscale spatial separation
and up to 55 kHz magnetic coupling strength. Co-implantation of $^{12}$C$^+$
increased the yield of pairs, and a $^{13}$C-depleted diamond allowed 0.65 ms
coherence times to be obtained. Further coupling to a third dark spin provided
a strongly coupled three spin register. These results mark an important step
towards realization of multi-qubit systems and scalable NV$^-$ quantum
registers.
