Princeton finds surface molecules can protect diamond quantum sensors from noise

[Isaac70]

A team led by Princeton University has found something surprising about diamond quantum sensors. Molecules sitting on the diamond surface, usually thought of as contamination, can protect shallow nitrogen vacancy centres from noise rather than harm them. Quantum Zeitgeist covered the paper, which includes Nathalie de Leon, Zhiyang Yuan and Lila Rodgers, with co-authors from the University of Iowa and IBM's research centre

Nitrogen vacancy centres, or NV centres, are tiny defects in diamond that act as extremely sensitive magnetic sensors. The closer they are to the surface, the better they can sense things outside the diamond. The problem is that shallow NV centres lose their quantum coherence quickly, and surface contamination has long been blamed

The team tested this directly. They tracked the same individual NV centres in air and then in ultra high vacuum, after heating the diamond to 350°C to drive off the molecules on its surface. The coherence time dropped about fourfold in vacuum. That is the opposite of what the usual explanation would predict

Digging deeper, they found that electric noise dominated in air, while magnetic noise matched or exceeded it in vacuum. Their explanation is that the adsorbed molecules normally neutralise surface charges that would otherwise create low frequency noise. Fluctuating surface dipoles still produce some noise at intermediate frequencies

This is a lovely example of careful experiments overturning a common assumption. It could change how researchers prepare and protect diamond surfaces for sensing. Better shallow NV centres could improve applications from materials science to imaging single molecules

Were you surprised that cleaning the surface made things worse? And where do you see diamond quantum sensors making the biggest impact?

Surface 'dirt' Shields Quantum Sensors From Noisequantumzeitgeist.com

[Dolphin43]

De Leon's group has done excellent work on diamond surfaces for years. This feels like the payoff from all that patient characterisation. Careful surface science like this takes years of groundwork

[EddieKingston]

Fourfold drops in coherence after cleaning are a big effect. Plenty of groups have been working hard to get surfaces cleaner. They may need to rethink that strategy. Controlled coatings could be the answer instead

Ultra high vacuum is usually the gold standard for clean physics. Finding it hurts here is a lovely twist

[Southern Puma]

So the dirt was doing useful work all along. Science has a sense of humour sometimes. Every lab has a story like this somewhere