Physicists probing the nature of quantum matter have become tied up in knots – but don’t worry, that’s a good thing. The find could lead to new theories about the particles that make up our universe, and perhaps help develop quantum computers.

Researchers have previously made knots from all kinds of surprising things, including DNA, light and water. Now Mikko Möttönen of Aalto University in Finland and his colleagues have tied up a more exotic material: a type of quantum matter called a Bose-Einstein condensate (BEC).

BECs are an unusual kind of gas in which the atoms have been cooled to near absolute zero, putting them all into a single quantum state. Using a carefully changing magnetic field, Möttönen’s team coaxed a BEC made from rubidium atoms into a complex knot called a Hopf fibration, a tangle of interlocking circles in the shape of a doughnut.


“These knots are inspiring and visually rich,” he says. “After having worked with them, you start to really appreciate their elegance.”

But the knots may be more than just pretty. The 19th century physicist Lord Kelvin thought that atoms were knots in the ether, a now debunked fluid thought to permeate the universe. More recently, similar ideas have inspired topological quantum field theories, in which particles are described by mathematical shapes similar to knots within quantum fields that fill the universe.

“These quantum knots are great because of their fundamental importance,” says Möttönen. “They show that these structures are possible in quantum fields.”

It may even be possible to use these kinds of knots in advanced devices called topological quantum computers, which even the likes of Microsoft are taking seriously as a future direction for computing. “I hope our results boost this promising field of study,” says Möttönen.

Journal reference: Nature Physics DOI: 10.1038/nphys3624

Image information, from top: Artistic impression of a quantum-mechanical knot soliton (Heikka Valja); the equipment used to create the quantum knots (Marcus DeMaio/Amherst College April 2015)