Electromagnetic noise is a significant communications problem, forcing wireless carriers to invest heavily in technologies to solve this problem. Despite being a nuisance, it can tell many things by studying sound. By measuring the noise in a material, physicists can learn its composition and temperature, how electrons flow and interact, and how it spins to form magnets. It is generally difficult to measure how the sound changes in space or time.

Scientists from Princeton University and the University of Wisconsin-Madison have developed a method to measure noise in a material by studying correlations. They can use this information to learn the spatial structure and time-dependent nature of the sound. The method uses specially designed diamonds with nitrogen vacancy centers. This method, which tracks minute variations in magnetic fields, is a significant advance over previous methods that averaged numerous different measurements.

The highly controlled diamond structures are called nitrogen vacancy (NV) centers. These NV centers are modifications to a diamond’s carbon atom lattice when a carbon atom is swapped for a nitrogen atom, and there is an empty space or void next to it in the chemical structure. A diamond with NV centers is one of the few instruments that can record changes in magnetic fields at the scale and speed needed for critical studies in quantum technology and condensed matter physics.

Even though a single NV center made it possible to track magnetic fields with great precision, it wasn’t until scientists figured out how to use multiple NV centers that they could analyze the spatial organization of noise in a material.

Nathalie de Leon, an associate professor of electrical and computer engineering at Princeton University, said: “This opens the door to understanding the properties of materials with bizarre quantum behaviors that have so far only been theoretically analyzed.”

“It is a fundamentally new technique. It is clear from a theoretical perspective that it would be very powerful to do so. The audience that I think is most excited about this work are condensed matter theorists; now that there is a whole world of phenomena, perhaps they can be characterized differently.

Quantum spin fluid is one such phenomenon, where electrons are in constant motion, as opposed to the solid-state stability characteristic of a typical magnetic material when cooled to a specific temperature.

leon said, “The challenging thing about a quantum spin liquid is that by definition there is no static magnetic ordering, so you can’t just map a magnetic field” as you would with any other type of material. Until now there has been no way to measure these two-point magnetic field correlators directly, and instead people have tried to find complicated proxies for that measurement.

Scientists can determine how electrons and their spins flow through a material’s space and time by measuring magnetic fields at different locations simultaneously with diamond sensors. To create the new technique, the team exposed a diamond with NV centers to calibrated laser pulses and then observed two peaks in the number of photons emanating from a pair of NV centers, a readout of the electron spins in each center at the same time. moment.

Study co-author Shimon Kolkowitz, an associate professor of physics at the University of Wisconsin-Madison, said: “One of those two peaks is a signal that we apply, the other is a peak from the local area and there is no way to tell the difference. But when we look at the correlations, one is correlated from the signal we are applying, and the other is not. And we can measure that, which people couldn’t measure before.”

Magazine reference:

  1. Jared Rovny, Zhiyang Yuan, Mattias Fitzpatrick, et al. Nanoscale covariance magnetometry with diamond quantum sensors. Science. DOI: 10.1126/science.ade9858