Quantum measurement in living cells: Fluorescent diamond nanocrystals for biology

We have demonstrated optically detected magnetic resonance of individual fluorescent nanodiamond nitrogen-vacancy centres inside living human HeLa cells, and measured their spin levels and spin coherence times while tracking their location and orientation with nanoscale precision. Quantum coherence was measured through Rabi and spin-echo sequences over long (>10 h) periods, and orientation was tracked with 1° angular precision in 89 ms acquisition time. Individual centres were identified optically by their electron spin resonance spectrum, allowing simultaneous tracking of many otherwise identical flourescent particles. In addition, variation in the decoherence rates was linked to changes in the local environment inside the cells, representing a new non-destructive imaging modality for intracellular biology.