Dark states of single NV centers in diamond unraveled by single shot NMR

Understand

The nitrogen-vacancy (NV) center in diamond is supposed to be a building block for quantum computing and nanometer scale metrology at ambient conditions.

• Therefore, precise knowledge of its quantum states is crucial.
• Here, we experimentally show that under usual operating conditions the NV exists in an equilibrium of two charge states (70% in the expected negative (NV-) and 30% in the neutral one (NV0)).
• Projective quantum non-demolition measurement of the nitrogen nuclear spin enables the detection even of the additional, optically inactive state.