Ultra-Sensitive Sensors from Impure Diamonds

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A Kyoto University research group has developed the longest spin coherence times at room temperature of an NV centre in diamond, using an artificially synthesised phosphorus-doped n-type diamond.

Furthermore, they succeeded in recording the highest magnetic field sensitivity of a single NV quantum sensor. Their findings were reported in Nature Communications.

An NV centre in diamond emerges when a carbon atom in the lattice is replaced by a nitrogen atom, and one of its adjacent atoms is removed. This generates a 'hole' in the lattice, known as a 'vacancy', hence the name N (nitrogen) V (Vacancy) centre. This vacancy attracts an electron and takes the property of a magnet.

Owing to its stability and sensitivity, NV centres in diamond are a major focus for researchers who hope to apply the technology to develop ultrasensitive quantum sensors, with applications even for devices in the life sciences.

The diamond samples used in NV-centric research have been mainly pure diamonds due to the conventional wisdom that impurities would hold electron spins that generate noise. However, the research team, collaborating with the National Institute of Advanced Industrial Science and Technology, found that phosphorus-doped n-type diamonds have remarkably long spin-coherence times.

After careful study, the team found that the diamonds have the longest inhomogeneous spin-dephasing time and spin decoherence time recorded in room-temperature solid-state systems and the highest magnetic field sensitivity.

Norikazu Mizuochi from Kyoto University's Institute for Chemical Research, who lead the study, explains that the team was surprised that adding impurities to the NV diamond was the key to improve its spin coherence.

"Phosphorus is one of the causes of magnetic noise due to its electron spin," explains Mizuochi. "We hope our new results will greatly contribute to the ever-expanding field of quantum technology."