Extending spin coherence times of diamond qubits by high-temperature annealing

Spins of negatively charged nitrogen-vacancy (NV-) defects in diamond are among the most promising candidates for solid-state qubits. The fabrication of quantum devices containing these spin-carrying defects requires position-controlled introduction of NV- defects having excellent properties such as spectral stability, a long spin coherence time, and a stable negative charge state. Nitrogen ion implantation and annealing enable the positioning of NV- spin qubits with high precision, but to date, the coherence times of qubits produced this way are short, presumably because of the presence of residual radiation damage. In the present work, we demonstrate that a high-temperature annealing at 1000 degrees C allows 2 ms coherence times to be achieved at room temperature. These results were obtained for implantation-produced NV- defects in a high-purity, 99.99% C-12-enriched single crystal chemical vapor deposited diamond. We discuss these long coherence times in the context of the thermal behavior of residual defect spins.