Strongly coupled diamond spin qubits by molecular nitrogen implantation

Ionized nitrogen molecules (¹⁵N₂⁺) 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 ¹²C⁺ increased the yield of pairs, and a ¹³C-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 multiqubit systems and scalable NV^- quantum registers.