The very first experimental observations of knots in quantum matter have just been reported in Nature Physics by scientists at Aalto University (Finland) and Amherst College (USA). The scientists created knotted solitary waves, or knot solitons, in the quantum-mechanical field describing a gas of superfluid atoms, also known as a Bose-Einstein condensate.
In contrast to knotted ropes, the created quantum knots exist in a field that assumes a certain direction at every point of space. The field segregates into an infinite number of linked rings, each with its own field direction. The resulting structure is topologically stable as it cannot be separated without breaking the rings. In other words, one cannot untie the knot within the superfluid unless one destroys the state of the quantum matter.
The scientists tied the knot by squeezing the structure into the condensate from its outskirts. This required them to initialize the quantum field to point in a particular direction, after which they suddenly changed the applied magnetic field to bring an isolated null point, at which the magnetic field vanishes, into the center of the cloud. Then they just waited for less than a millisecond for the magnetic field to do its trick and tie the knot.
Knots have been used and appreciated by human civilizations for thousands of years. For example, they have enabled great seafaring expeditions and inspired intricate designs and patterns. The ancient Inca civilization used a system of knots known as quipu to store information. In modern times, knots have been thought to play important roles in the quantum-mechanical foundations of nature, although they have thus far remained unseen in quantum dynamics.
In everyday life, knots are typically tied on ropes or strings with two ends. However, these kinds of knots are not what mathematicians call topologically stable since they can be untied without cutting the rope. In stable knots, the ends of the ropes are glued together. Such knots can be relocated within the rope but cannot be untied without scissors.
Mathematically speaking, the created quantum knot realizes a mapping referred to as Hopf fibration that was discovered by Heinz Hopf in 1931. The Hopf fibration is still widely studied in physics and mathematics. Now it has been experimentally demonstrated for the first time in a quantum field.
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The research article (This article should be credited as the source of stories covered.)
D. S. Hall, M. W. Ray, K. Tiurev, E. Ruokokoski, A. H. Gheorghe, and M. Möttönen
"Tying Quantum Knots"
Nature Physics , DOI: 10.1038/NPHYS3624
Link: http://dx.doi.org/10.1038/nphys3624
(The submitted version of the manuscript is openly available at http://arxiv.org/abs/1512.08981 )
Video and images
https://www.youtube.com/watch?v=fFIAINR6rTY
http://materialbank.aalto.fi:80/public/95cc3f59c88F.aspx
Contact details
Mikko Möttönen
Docent, Professor
mikko.mottonen@aalto.fi
358-50-594-0950 (Time zone: GMT +2)
Aalto University and University of Jyväskylä
http://physics.aalto.fi/en/groups/qcd/
Mikko Möttönen is the leader of the theoretical and computational part of the research. Theoretical insight and computational modelling was very important for the success of the creation of the knots. The modelling was carried out using the facilities at CSC -- IT Center for Science Ltd and at Aalto University (Aalto Science-IT project).
David S. Hall, Professor
Amherst College
mailto:dshall@amherst.edu
1-413-542-2072 (Time zone: GMT -5)
http://www3.amherst.edu/~halllab/
David S. Hall is the leader of the experimental part of the research. The quantum knots were created in the Physics Laboratories at Amherst College, United States of America.
Funding
This material is based upon work supported by the National Science Foundation under Grant No. PHY-1205822, the Academy of Finland (grant nos. 251748, 284621, 135794, and 272806), Finnish Doctoral Programme in Computational Sciences, and the Magnus Ehrnrooth Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Nature Physics