Barkhausen noise is a term used to describe the crackling sound produced when a magnetic field is applied to a ferromagnetic material, such as iron screws. The noise is the result of the alignment of electron spins (or magnetic moments) within the material, which occurs in a piecemeal fashion through different regions, or domains, falling into line at different times. This process can be likened to an avalanche, where alignment spreads through the domains until all spins point in the same direction.
In the classical understanding of Barkhausen noise, the alignment of spins is driven by thermal activation, where particles must acquire enough energy to cross an energy barrier. However, the latest research demonstrates that these flips can also occur quantum mechanically via a process known as quantum tunnelling. In this process, particles can tunnel through energy barriers to reach the other side without physically crossing them, similar to a golf ball passing through a hill without climbing over it to reach the other side.
In a groundbreaking discovery, researchers from the California Institute of Technology (Caltech) and the University of British Columbia (UBC) have detected an effect known as quantum Barkhausen noise for the first time. This phenomenon, which arises from the cooperative quantum tunnelling of a vast number of magnetic spins, may be the largest macroscopic quantum phenomena yet observed in the laboratory.