An international team of scientists has created a curious quasi-particle known as a skyrmion, 40 years after theory first predicted it. The discovery is reported in Science Advances.
The skyrmion was composed by constructing knots from the magnetic moment, or spin, of atoms in an extremely sparse and cold quantum gas. The resulting quasi-particle is similar to the rare phenomenon of ball lightning, which is believed to consist of tangled streams of electric currents within a plasma sphere.
"The quantum gas is cooled down to a very low temperature where it forms a Bose-Einstein condensate: all atoms in the gas end up in the state of minimum energy. The state does not behave like an ordinary gas anymore but like a single giant atom," Professor David Hall, leader of the experimental effort at Amherst College, said in a statement.
First, all the atoms were made to point upwards following a magnetic field. This was then varied so that a new magnetic field point appeared in the middle of the gas. When this happened, the atoms began to rotate towards the direction the magnetic field was pointing in. However, near the “zero” point at the center, the spins became tangled up in what was essentially a knot. Curiously, the knot could be loosened and moved but it couldn't be untied.
"It is remarkable that we could create the synthetic electromagnetic knot, that is, quantum ball lightning, essentially with just two counter-circulating electric currents," said Dr Mikko Möttönen, leader of the theoretical effort at Aalto University in Finland. "Thus, it may be possible that a natural ball lighting could arise in a normal lightning strike."
The phenomenon of ball lightning remains mostly unexplained, but maybe this new study could help us understand it. And this could also have some important technical applications. Skyrmions could come in handy for stabilizing plasma in nuclear fusion reactors.
"More research is needed to know whether or not it is also possible to create a real ball lightning with a method of this kind," Möttönen explained. "Further studies could lead to finding a solution to keep plasma together efficiently and enable more stable fusion reactors than we have now."
