Quantum sensors based on the spins of atomic-scale defects can detect tiny magnetic fields, but the best-performing defects live deep inside bulk crystals, which limits how close they can get to the samples they measure. Defects in atomically thin materials could solve this problem—if only they did not lose their quantum properties so quickly.
In this issue, Becker and colleagues report that defects in a layered antiferromagnet retain their coherence for more than a millisecond at room temperature. The trick, they show, is that the host's magnetic order quietens the fluctuating environment that normally scrambles a spin's quantum state.
The result raises the prospect of sensors only a few atoms thick that can be placed directly on top of a chip or a biological sample. Challenges remain, including improving the brightness of the defects and controlling where they form, but the path ahead now looks clearer.
