Undoing a Quantum Knot

Physical theories for many states of matter predict the existence of defects—vortices, knots, or monopoles—whose topology makes them exceptionally stable. This “topological protection” may explain persistent structures ranging from so-called skyrmions in magnetic materials to stringy textures of the cosmos. To better understand these defects, researchers create and study them in highly controllable systems like quantum condensates. Now, Tuomas Ollikainen of Aalto University, Finland, and coworkers have prepared a knot in a Bose-Einstein condensate (BEC) and then perturbed the condensate so as to “untie” the knot. Their work delivers the first time-resolved “movie” of a quantum knot’s decay.