A pot of water has just been stirred: the whirlpools and eddies gradually calm down, and the liquid becomes smooth. A similar process, but in the quantum world, occurs in superfluid helium or in a cloud of ultracold atoms. Only instead of water whirlpools, there are invisible vortex filaments — tiny quantum 'tornadoes' threading through the matter.
In the new experiment, physicists created a homogeneous three-dimensional cloud of rubidium atoms cooled to near absolute zero. Using special light waves, they magnified the image of the cloud, like a projector enlarging a slide, and took a snapshot of a thin layer. The image revealed traces of vortex lines pointing in different directions — a veritable tangle of microscopic hurricanes. By measuring how the total length of these lines decreased over time, the scientists compared the result with the prediction for 'ultraquantum' turbulence. This regime was described by British physicist William Vinen back in the 1950s.
The most unexpected result was that the behavior of a weakly interacting atomic gas closely resembled that of dense superfluid helium. Although the dilute cloud is easily compressible, its large-scale dynamics followed the laws of an incompressible fluid. The decay rate of the vortices did not depend on the strength of interactions between atoms, as if the quantum tangle unravels according to the same scenario, regardless of how sticky its filaments are to each other.
In a superfluid, a vortex cannot simply slow down and vanish: it must either reach the container boundary or collide with an 'antivortex' spinning in the opposite direction. That is why quantum turbulence decays quite differently from the ripples in a cup of tea.
In Peter Watts's novel Blindsight, alien beings use quantum vortices for information processing — almost like a neural network made of twisted filaments.