Heikka Valja

Weird quantum particles simulated in droplet of ultracold gas

In physics, theorists are often way ahead of the curve in describing what weird quantum particles could and should exist. Now, physicists in the United States and Finland have teamed up to create an incarnation of a quasi-particle called a skyrmion, first proposed in 1962 by U.K. physicist and mathematician Tony Skyrme as a model of real protons and neutrons. A skyrmion isn’t a fundamental particle that “bops you over the head” like a quark or a muon, says physicist David Hall of Amherst College in Massachusetts. Instead, it’s a localized excitation in space, made in a field of spins. The result is a kind of self-reinforcing knot, a bit like a Mobius strip that can’t be torn apart except by extreme force. By precisely controlling electromagnetic coils surrounding a glass vacuum chamber filled with superfluid rubidium, the team created 3D skyrmions for the first time ever. Their shadowy photographs depict a droplet of 200,000 supercooled rubidium atoms, a few 10-billionths of a degree above absolute zero. What’s more, the atoms revealed the very spin profiles Skyrme predicted, held together by a looping magnetic field. Oddly, the discovery, reported in Science Advances, could yield insight into ball lightning, a rare and controversial electrical phenomenon that supposedly forms balls of electricity meters across that can float through walls and suddenly discharge like dynamite. One theory holds that ball lightning, like skyrmions, may be held together by electromagnetically knotted fields that are surprisingly stable.