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Exciton Science researchers have opened a pathway to enhanced sensitivity and greater efficiency across a range of emerging quantum technologies, by developing the first general theory to explain and predict nitrogen vacancy-plasmonic nanoparticle interactions in diamond.

The nitrogen-vacancy (NV) centre is a defect in diamond that’s highly versatile for quantum-based experimentation. It’s sensitive to magnetic and electric fields, strain, and temperature, and can also be used as a sensor with nanoscale resolution.

The NV centre can be used in a range of important applications, including brain imaging, minerals discovery, pharmaceuticals research and quantum computing. However, its effectiveness is limited by the optical brightness and collection efficiency of the defect.

Dr Harini Hapuarachchi of RMIT University said: “The NV centre in diamond provides a window into the nanoscopic world. Our goal is to make it brighter and increase the contrast.”

Experimentalists can use the electron oscillations (known as plasmons) in metal nanoparticles to tune the NV centre and achieve increases in brightness and efficiency.

Dr Francesco Campaioli, who worked with Harini at RMIT to develop the theory, emphasised the importance of isolating and amplifying the optimum frequency, with the nanoparticles acting as a mini resonator.

“It's almost like the resonating chamber of a guitar,” he said.

“It’s a way to make sure that there's one frequency, one vibration that resonates. And everything else is dissipated and doesn't matter.

“Imagine that the guitar neck with the strings is the NV center. If you pluck it, even if there's no resonating chamber, it still works. You can still hear the sound.

“But when you play in front of an audience, you want everybody to hear it, so you want to increase the intensity.

“If you put the right resonating chamber around it, in this case it's the metal nanoparticle, then you hear everything better and louder.”

Developing the first general theory to explain these useful interactions presented several challenges, including solving non-linear differential equations, but researchers will now be equipped with the information they need to explore this technology with more confidence.

“I think it will prompt a lot of new experiments and a lot of improvements on existing technological applications,” Professor Jared Cole of RMIT said.

“So you can really imagine taking an existing NV center platform, in any of those applications, and putting a plasmonic coating on it, and therefore improving the sensitivity.

“And I think what's really nice about the model Harini's developed is that we can predict that before you start the design process.”

The results of Harini, Francesco and Jared’s work has been published in the journal Nanophotonics, and are available here.