Researchers see Kelvin wave on quantum 'tornado' for first time

A spinning tornado of very cold liquid helium obeys the laws of quantum mechanics. Sometimes, two quantum tornadoes flex into curved lines, cross over and form an X, swap ends, and then retract—a process called reconnection. For the first time, researchers provide visual evidence that the reconnection of quantum vortexes launches Kelvin waves to quickly relax the system. Understanding turbulence in quantum fluids may offer clues to neutron stars, trapped atom systems and superconductors.

Draining the water from a bathtub causes a spinning tornado to appear. The downward flow of water into the drain causes the water to rotate, and as the rotation speeds up, a vortex forms that obeys the laws of classical mechanics. However, if the water is extremely cold liquid helium, the fluid will swirl around an invisible line to form a vortex that obeys the laws of quantum mechanics. Sometimes, two of these quantum tornadoes flex into curved lines, cross over one another to form a letter X shape, swap ends, and then violently retract from one another—a process called reconnection.

Computer simulations have suggested that after the vortexes snap away from each other, they develop ripples called "Kelvin waves" to quickly get rid of the energy caused by the connection and relax the system. However, the existence of these waves had never been experimentally proven.

Now, for the first time, researchers provide visual evidence confirming that the reconnection of quantum vortexes launches Kelvin waves. The study, which was conducted at the University of Maryland, will be published the week of March 24, 2014 in the online early edition of the journal Proceedings of the National Academy of Sciences.