A Neutral Diamond Defect
A negatively charged nitrogen-vacancy (NV–) center is a defect in a diamond crystal consisting of an absent carbon atom next to an implanted nitrogen atom. Its three possible spin states remain coherent for milliseconds, respond to laser light, and are exquisitely sensitive to the center’s environment. NV– centers are already being harnessed as quantum sensors. Until now, no other defect has come close to matching NV–, especially in its ability to work at room temperature. In 2009, a promising alternative defect dubbed WAR5 was discovered and later identified as the neutral oxygen-vacancy (OV0) center. Now Sounak Mukherjee of Princeton University and his collaborators have determined that the quantum coherence of OV0 is as robust as that of NV– [1].
Oxygen has one more electron than nitrogen, so OV0 has the same outer electron configuration as NV–. Consequently, OV0 is expected to share the advantageous properties of NV–. Mukherjee and his colleagues used electron spin resonance to measure two of those properties, the relaxation times T1 and T2, which quantify how long the center’s quantum coherence persists. The researchers found values that compare favorably with those of NV–. At room temperature, T1 was 1 millisecond for OV0 and 6.7 millisecond for NV–. At 4 K, the T1 of OV0 was 14.4 minutes, compared to an average of 3.3 minutes for NV–.
Electron spin resonance works in the microwave band, where the spin transitions of OV0 are readily isolated from those of other contaminating defects. However, the zero-phonon line (ZPL)—one of the most important properties of a vacancy center—lies in a thicket of optical lines and remains unknown. Once the ZPL is determined, OV0 could join NV– as a workhorse of quantum sensing.
–Charles Day
Charles Day is a Senior Editor for Physics Magazine.
References
- S. Mukherjee et al., “Defect in diamond with millisecond-scale spin relaxation time at room temperature,” Phys. Rev. B 114, 074105 (2026).