A breakthrough can advance quantum computing

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Researchers at the University of Tsukuba have achieved micrometer spatial resolution for radiofrequency imaging of nitrogen vacancy centers in diamond by signal enhancing with quantum spin-locking. This work could lead to more precise characterization of materials, medical diagnostics and quantum computers. Credit: University of Tsukuba

Researchers at the University of Tsukuba are using radio frequency waves to image “locked” flaws in diamond with record resolution, which may lead to advances in materials characterization and quantum computing.

Scientists from the University of Tsukuba’s Division of Physics have used the quantum effect called “spin lock” to dramatically improve resolution when imaging nitrogen starvation defects in diamond by radiofrequency. This work could lead to faster and more accurate materials analysis, as well as a path to practical quantum computers.

Nitrogen vacancy (NV) centers have long been studied for their potential use in quantum computers. An NV center is a type of defect in the lattice of a diamond, in which two adjacent carbon atoms have been replaced by a nitrogen atom and a void. This leaves an unpaired electron, which can be detected using radio frequency waves, since its probability of emitting a photon depends on its spin state. However, the spatial resolution of radio wave detection using conventional radio frequency techniques has remained less than optimal.

Now researchers at the University of Tsukuba have pushed the resolution to its limit using a technique called “spin-locking”. The microwave pulses are used to put the spin of the electron into a top-down quantum superposition simultaneously. Then, a driving electromagnetic field causes the direction of the spin to precess, like a wobbling top. The end result is an electronic spin shielded from random noise but strongly coupled to the detection equipment. “The twist lock ensures a high precision and the sensitivity of electromagnetic field imaging,” says first author Professor Shintaro Nomura. Due to the high density of NV centers in the diamond samples used, the collective signal they produced could be easily picked up with this method. This allowed the detection of collections of NV centers at the micrometer scale. “The spatial resolution we achieved with RF imaging was much better than with existing similar methods,” Prof. Nomura continues, “and it was only limited by the resolution of the light microscope we used.”

The approach demonstrated in this project can be applied in a wide variety of application areas, for example, characterizations of polar molecules, polymers and proteins, as well as the characterization of materials. It could also be used in medical applications, for example, as a new way to perform magnetocardiography.

Reference: “Rotation-locked near-field radiofrequency imaging with a nitrogen-vacancy spin sensor” by Shintaro Nomura, Koki Kaida, Hideyuki Watanabe, and Satoshi Kashiwaya, July 9, 2021, Japanese Journal of Applied Physics.
DOI: 10.1063/5.0052161

The book is published in Journal of Applied Physics as “Spin-lock near-field radiofrequency imaging with a vacant nitrogen spin sensor” selected as featured article.

This work was supported in part by a Scientific Research Assistance Grant (nos. JP18H04283, 291 JP18H01243, JP18K18726, and JP21H01009) from the Japan Society for the Promotion of 292 Science.

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