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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.
- To make this discovery we exposed a Rubidium condensate to rapid changes of a specifically tailored magnetic field, tying the knot in less than a thousandth of a second. After we learned how to tie the first quantum knot, we have become rather good at it. Thus far, we have tied several hundred such knots, says Professor David Hall, Amherst College.
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.
The knot only stays tied if you don't look at it.
Tying quantum knots (DOI: 10.1038/nphys3624)
(Score: 1) by YeaWhatevs on Wednesday January 20 2016, @03:28AM
in a knot tying contest?
(Score: 4, Interesting) by aristarchus on Wednesday January 20 2016, @07:51AM
"I'm a frayed knot!"
Throughout my overlong existence on this planet, I have learned many knots. Some "do's", but mostly knots. First: learn to tie a square knot correctly. You life could be saved, or at least your shoelaces. Both the standing and the bitter end should be together on both sides of the knot, or you have tied a "Granny". Grannies are bad both because they can fail under tension, and they are hard to untie. Ease of release is a virtue of a good knot.
And I always found that for competition purposes, while there are many "showoff" knots, the Carrick's Bend has much to recommend it. You make a loop, lay the other line over the loop, go around the standing end, and under the bitter end of the second line, and then worf your original lay! Distorts upon tension, but it's a darn good knot.
Every sailor, physicist, or programmer ought to be familiar with all the basic knots: Square knot (also called the "reef knot", due to its use in tying up sails on squareriggers). the Bowline, for a non-constricting loop (handy for hoisting the young boys aloft!), the Sheepshank, the Timberhitch, the Tautline, and of course, thehttps://www.youtube.com/watch?v=TUHgGK-tImY [youtube.com] Trucker's Hitch!
Of course, with quantum knots, it is possible to have a Trucker's Hitchhiker's Guide to the Galaxy. Ylvis rules.