Ball lightning on a quantum scale

Seen for the first time: 3d skyrmions in an ultra-cold gas.
Seen for the first time: 3D skyrmions in an ultra-cold gas.

Confirming a prediction made more than 40 years ago, scientists have succeeded in creating a three-dimensional magnetic phenomenon known as a Shankar skyrmion.

A Shankar skyrmion can be described as a collection of writhing knots comprising the spins – or “magnetic moments” – of atoms within a system. Researchers believe that such skyrmions serve as models for ball lightning, which is thought to comprise tangled streams of electrical currents.

Named after physicist Tony Skyrme, who proposed the mathematical structures in 1962, theoretical skyrmions have been used to model a range of phenomena from the interaction of subatomic particles within an atomic nucleus to the behaviour of neutron stars.

Magnetic skyrmions are described as the smallest possible perturbation to a uniform magnetic field – an area of reversed magnetism surrounded by whirling and twisting spins.

Until now, however, skyrmions have proved all but impossible to create in controlled conditions.

In a paper published in the journal Science Advances, researchers from Amherst College in the US and Aalto University in Finland report creating three-dimensional skyrmions inside an ultra-cold quantum gas.

To create the effect, the physicists cooled gas down to a temperature where it formed what is known as a Bose-Einstein condensate – a state in which all the constituent atoms exhibit the bare minimum of energy.

“The state does not behave like an ordinary gas anymore, but like a single giant atom,” explains co-author David Hall.

The team then polarised the spin of each constituent atom, such that they all pointed upward along an applied magnetic field. The gas was them subjected to electrical charges moving in opposite directions. This caused the field in the middle of the gas to vanish. The atoms positioned near this spot – point zero – suddenly started to rotate in a different direction, resulting in their spins combining into a knot.

“It is remarkable that we could create the synthetic electromagnetic knot, that is, quantum ball lightning, essentially with just two counter-circulating electric currents,” says co-author Mikko Möttönen.

“Thus, it may be possible that a natural ball lighting could arise in a normal lightning strike.”

The researchers now intend to scale their research up to see if the same technique can be used to produce real ball lightning. The research, they add, could lead to the creation of stable plasma balls that could be used in nuclear fusion reactors.

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