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posted by cmn32480 on Wednesday January 20 2016, @01:14AM   Printer-friendly
from the is-it-a-granny-knot? dept.

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)


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  • (Score: 1, Informative) by Anonymous Coward on Wednesday January 20 2016, @02:55AM

    by Anonymous Coward on Wednesday January 20 2016, @02:55AM (#291916)

    So if I tied my shoe into a quantum knot and looked at it then I would have to tie it again? But as long as I don't look at it it will stay tied and I have nothing to worry about right? What if someone else looks at it? Then does it stay tied for me but untied for them? Does that mean they can trip on it but I can't?

    • (Score: 5, Informative) by Zz9zZ on Wednesday January 20 2016, @03:54AM

      by Zz9zZ (1348) on Wednesday January 20 2016, @03:54AM (#291948)

      1. So if I tied my shoe into a quantum knot and looked at it then I would have to tie it again?
          - No guarantee of delivering a force with the knot, but if so then untying would probably require a similar force as what's holding it together.
          - In this case "looking" means applying energy to the system and observing the result. If you were actually looking at the knot, then just the light in the room would have enough energy to break the knot. Quantum systems are delicate (so far)
      2. But as long as I don't look at it it will stay tied and I have nothing to worry about right?
          - Depends on your worries, tripping in this context, is an unlikely result.
      3. What if someone else looks at it?
          - It unties when they "look" at it.
      4. Then does it stay tied for me but untied for them? Does that mean they can trip on it but I can't?
          - Untied for both of you, unless it created a quantum fissure in space time which splits your reality from the person who just untied it.
          - The resulting paradox would rip apart the very fabric of reality itself! quoth the delorean

      Your analogy suffers the same fate as the old cat in the box. These are real atoms in the universe, the effects are measurable, but our human senses and common logic aren't developed for contemplating subatomic particles. So "looking" and "measuring" are simply methods of "poking" the system to make sure its still there and in what state its in. But "poking" has a high chance of affecting the quantum system, thus measuring the system changes the system; here it is untying the knot.

      --
      ~Tilting at windmills~
  • (Score: 1) by YeaWhatevs on Wednesday January 20 2016, @03:28AM

    by YeaWhatevs (5623) on Wednesday January 20 2016, @03:28AM (#291929)

    in a knot tying contest?

    • (Score: 4, Interesting) by aristarchus on Wednesday January 20 2016, @07:51AM

      by aristarchus (2645) Subscriber Badge on Wednesday January 20 2016, @07:51AM (#292000) Journal

      "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.

      --
      If you could ensure that your submissions are balanced, accurate and unbiased, you might stand a better chance