New technique reveals changing forms of magnetic noise in space and time

New technique reveals changing forms of magnetic noise in space and time

Using specially designed diamonds with nitrogen vacancy centers, researchers at Princeton University and the University of Wisconsin-Madison have developed a technique to measure the noise in a material by studying correlations, and they can use this information to analyze the spatial structure and the Time variation to learn nature of the noise. In this image, a diamond with near-surface nitrogen vacancy centers is illuminated with green laser light from a microscope objective. Credit: David Kelly Crow

Electromagnetic noise poses a major problem for communications, prompting wireless service providers to invest heavily in technology to overcome it. But for a team of scientists exploring the atomic realm, measuring tiny fluctuations in noise could be the key to discovery.

“Noise is usually thought of as a nuisance, but physicists can learn many things by studying noise,” said Nathalie de Leon, associate professor of electrical and computer engineering at Princeton University. “By measuring the noise in a material, they can learn its composition, its temperature, how electrons flow and interact with each other, and how spins form magnets. It’s generally difficult to measure anything about how noise changes in space or time.”

Using specially designed diamonds, a team of researchers at Princeton and the University of Wisconsin-Madison have developed a technique to measure the noise in a material by examining correlations, and they can use this information to analyze the spatial structure and the time-varying nature of learning noise. This technique, which relies on tracking tiny fluctuations in magnetic fields, represents a significant improvement over previous methods that averaged many separate measurements.

De Leon is a leader in the manufacture and use of highly controlled diamond structures called nitrogen vacancy (NV) centers. These NV centers are modifications of a diamond lattice of carbon atoms in which a carbon has been replaced by a nitrogen atom and there is an empty space or void in the molecular structure. Diamonds with NV centers are one of the few tools that can measure changes in magnetic fields of the magnitude and speed required for critical experiments in quantum technology and condensed matter physics.

While a single NV center allowed scientists to take detailed readings of magnetic fields, it was only when de Leon’s team worked out a method to use multiple NV centers simultaneously that they were able to measure the spatial structure of noise in a material. This opens the door to understanding the properties of materials with bizarre quantum behavior that have so far only been analyzed theoretically, said de Leon, the senior author of a paper describing the technique and published online Dec. 22 in the journal Science.

“It’s a fundamentally new technique,” said de Leon. “From a theoretical point of view it is clear that it would be very powerful to do so. The audience I think will be most excited about this work are condensed matter theorists, now that there’s this whole world of phenomena that they might be able to characterize differently.”

One of these phenomena is a quantum spin liquid, a material that was first theorized nearly 50 years ago but has been difficult to characterize experimentally. In a quantum spin liquid, electrons are in constant motion, in contrast to the solid-state stability that characterizes a typical magnetic material when cooled to a certain temperature.

“The challenge with a quantum spin liquid is that, by definition, there is no static magnetic order, so you can’t just image a magnetic field,” like you would with any other type of material, de Leon said. “Until now, there was essentially no way to measure these two-point magnetic field correlators directly, and instead people were trying to come up with complicated proxies for that measurement.”

By simultaneously measuring magnetic fields at multiple points with diamond sensors, researchers can see how electrons and their spins move in a material over space and time. In developing the new method, the team applied calibrated laser pulses to a diamond containing NV centers and then detected two peaks in photon counts from a pair of NV centers – an indication of the electron spins in each center at the same time. Previous techniques would have taken an average of these measurements, discarding valuable information and making it impossible to distinguish the inherent noise of the diamond and its surroundings from the magnetic field signals produced by a material of interest.

“One of those two spikes is a signal that we apply, the other is a spike from the local environment, and there’s no way to tell the difference,” said study co-author Shimon Kolkowitz, associate professor of physics at the University of Wisconsin-Madison. “But if we look at the correlations, the one that correlates is from the signal we’re applying and the other isn’t. And we can measure what humans could not measure before.”

Kolkowitz and de Leon met when Ph.D. Students at Harvard University and have been in regular contact ever since. Their research collaborations emerged early in the COVID-19 pandemic, when lab research slowed, but long-distance collaborations became more appealing as most interactions happened over Zoom, de Leon said.

Jared Rovny, lead author of the study and a postdoctoral fellow in de Leon’s group, led both theoretical and experimental work on the new method. The contributions of Kolkowitz and his team were critical in designing the experiments and understanding the data, de Leon said. The paper’s co-authors also included Ahmed Abdalla and Laura Futamura, who conducted summer research with de Leon’s team in 2021 and 2022, respectively, as interns in the Quantum Undergraduate Research at IBM and Princeton (QURIP) program, which de Leon co-founded in 2019.

The article “Nanoscale Covariance Magnetometry with Diamond Quantum Sensors” was published online on December 22nd Science.

More information:
Jared Rovny et al., Nanoscale Covariance Magnetometry with Diamond Quantum Sensors, Science (2022). DOI: 10.1126/science.ade9858

Provided by Princeton University

Citation: New technique reveals changing forms of magnetic noise in space and time (2022 December 23) Retrieved December 24, 2022 from https://phys.org/news/2022-12-technique-reveals-magnetic-noise -space.html

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