First detection of “Barkhausen noise”

Iron screws and other so-called ferromagnetic materials are made up of atoms with electrons that act like tiny magnets. Normally, the directions of the magnets are aligned within one region of the material, but not from one region to the next. Think of the crowds of tourists in Times Square pointing at various billboards around them. However, when a magnetic field is applied, the magnets or spins in the different regions align and the material becomes fully magnetized. It’s like a bunch of tourists pointing at the same sign all at once.

However, the process of lining up the spins does not happen all at once. Rather, when a magnetic field is applied, different regions, so-called domains, influence other nearby regions, and the changes are spread throughout the material in chunks. Scientists often liken this effect to an avalanche. In an avalanche, one small chunk of snow starts falling, pushes other nearby chunks, and eventually the entire mountainside slides down in the same direction.

This avalanche effect was first demonstrated in magnets by physicist Heinrich Barkhausen in 1919. He showed that these jumps in magnetism could be heard by wrapping a coil around a magnetic material and attaching it to a speaker. as a crackling soundtoday known as Barkhausen noise.

now, report in diary Proceedings of the National Academy of SciencesResearchers at the California Institute of Technology have shown that Barkhausen noise can be generated not only by traditional or classical means, but also by quantum mechanical effects.

This is the first time that quantum Barkhausen noise has been experimentally detected. The research represents an advance in fundamental physics that could one day be applied to creating quantum sensors and other electronic devices.

“Barkhausen noise is a collection of small magnets that flip in groups,” says Christopher Simon, first author of the paper and a postdoctoral fellow in the laboratory of Thomas F. Rosenbaum, a professor of physics at Caltech. . and Presidential Chairs Sonia and William Davideau.

“We’re doing the same experiments with quantum materials that have been done many times before. We’re seeing that quantum effects can cause macroscopic changes.”

Typically, these magnetic reversals classically occur through thermal activation, where the particle must momentarily gain enough energy to jump an energy barrier. But new research shows that these inversions can also occur quantum mechanically through a process called . quantum tunneling.

Tunneling allows particles to jump to the other side of an energy barrier without actually passing through the barrier. If we could extend this effect to everyday objects like golf balls, it would be like a golf ball going straight through a hill instead of climbing up the hill to get to the other side.

“In the quantum world, the ball, or particle, is actually a wave, and part of it is already on the other side of the hill, so the ball doesn’t need to go over the hill,” Simon says.