div B <> 0 everywhere...

Dirac monopoles in lab.

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div B <> 0 everywhere...

#1  Postby newolder » May 18, 2017 3:49 pm

"Experimental realization of a Dirac monopole through the decay of an isolated monopole"
T. Ollikainen, K. Tiurev, A. Blinova, W. Lee, D. S. Hall, and M. Möttönen

available in the arxiv and published in Physical Review X
We experimentally observe the decay dynamics of deterministically created isolated monopoles in spin-1 Bose-Einstein condensates. As the condensate undergoes a change between magnetic phases, the isolated monopole gradually evolves into a spin configuration hosting a Dirac monopole in its synthetic magnetic field. We characterize in detail the Dirac monopole by measuring the particle densities of the spin states projected along different quantization axes. Importantly, we observe the spontaneous emergence of nodal lines in the condensate density that accompany the Dirac monopole. We also demonstrate that the monopole decay accelerates in weaker magnetic field gradients.


Write-up at Physicsworld.com

ETA attribution.

ETA Paul Dirac talks us through the theory in this youtube.
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Re: div B <> 0 everywhere...

#2  Postby DavidMcC » May 18, 2017 4:12 pm

Physics world article wrote:While isolated monopoles have never been seen, physicists have been able to create several different collective excitations in condensed-matter systems that resemble monopoles.


It's a fair bet that isloated magnetic monopoles will continue never to be seen, but anything is possible in a crystal lattice, such as negative mass charge carriers, etc.
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Re: div B <> 0 everywhere...

#3  Postby DavidMcC » May 18, 2017 4:12 pm

Duplicate post. Sorry.
Last edited by DavidMcC on May 18, 2017 4:14 pm, edited 1 time in total.
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Re: div B <> 0 everywhere...

#4  Postby DavidMcC » May 18, 2017 4:13 pm

Another duplicate post!
Last edited by DavidMcC on May 18, 2017 4:15 pm, edited 1 time in total.
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Re: div B <> 0 everywhere...

#5  Postby DavidMcC » May 18, 2017 4:13 pm

Yet another duplicate post. The site + my browser was very slow .
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Re: div B <> 0 everywhere...

#6  Postby DavidMcC » May 18, 2017 4:20 pm

newolder wrote:Experimental realization of a Dirac monopole through the decay of an isolated monopole

...

You are confused. A monopole within a crystal lattice can hardly be called "isolated" - it's surrounded by a whole crystal lattice.
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Re: div B <> 0 everywhere...

#7  Postby newolder » May 18, 2017 4:24 pm

Conclusion
...
We have also identified spontaneously appearing nodal lines associated with the emergent Dirac monopole. Numerical simulations are in agreement with these experimental results with no free parameters. The decay of the monopole is observed to be faster in weaker magnetic fields.

To date, the experimental studies of spatially localized monopoles in the context of spinor BECs have been limited to two publications [19,20] (see also Ref. [45]). Our work further verifies the existence of both isolated and Dirac monopoles through reproduction and in-depth characterization.
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Re: div B <> 0 everywhere...

#8  Postby newolder » May 18, 2017 4:25 pm

DavidMcC wrote:
newolder wrote:Experimental realization of a Dirac monopole through the decay of an isolated monopole

...

You are confused. A monopole within a crystal lattice can hardly be called "isolated" - it's surrounded by a whole crystal lattice.

How can I be confused? It's not my title.
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Re: div B <> 0 everywhere...

#9  Postby DavidMcC » May 18, 2017 4:33 pm

newolder wrote:
DavidMcC wrote:
newolder wrote:Experimental realization of a Dirac monopole through the decay of an isolated monopole

...

You are confused. A monopole within a crystal lattice can hardly be called "isolated" - it's surrounded by a whole crystal lattice.

How can I be confused, it's not my title?

But you failed to explain how misleading the title is. A monopole in a crystal lattice is NOT isolated, just as a charge carrier in a crystal isn't really a free electron!
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Re: div B <> 0 everywhere...

#10  Postby newolder » May 18, 2017 4:42 pm

DavidMcC, If you want to shoot the messenger, go right ahead. If you want to argue the toss with the authors, that's up to you. Have you seen my field of fucks? It's empty.
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Re: div B <> 0 everywhere...

#11  Postby Calilasseia » May 18, 2017 4:57 pm

The mere fact that an observable monopole has been generated in the laboratory, on its own, is headline news for me.

Plus, doesn't 'isolated' in this context have a pretty precise meaning? As in 'persistently present without being annihilated by its opposite number, and widely separated from any other like entities'?
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Re: div B <> 0 everywhere...

#12  Postby Calilasseia » May 18, 2017 5:16 pm

Ah, just done some checking. Apparently, the phenomena observed in condensed matter systems are not true monopoles at all. Instead, they are quasi-particles exhibiting monopole-like behaviour.

Somehow I thought I'd have alighted upon discovery of genuine observable monopoles before now, if this had happened. Because a true magnetic monopole would constitute a new fundamental particle, and would be headline news.
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Re: div B <> 0 everywhere...

#13  Postby newolder » May 18, 2017 7:07 pm

The "popular summary" at the Physical Review X site relates:
All known magnets have two distinct ends: a north pole and a south pole. North and south poles by themselves—known as magnetic monopoles—have never been observed in nature, though their existence has been theoretically predicted for decades. Some of their properties have been deduced in recent experiments that simulate monopoles in a Bose-Einstein condensate, a dilute gas of atoms chilled to near absolute zero. One experiment investigated properties of a magnetic monopole first described by Dirac more than 80 years ago; another studied a different type of monopole in the quantum field that describes the gas. Several questions remain about the properties of these monopoles. Our new experiments in the condensate show that a quantum monopole decays into a Dirac monopole.

We create the quantum monopole by subjecting a Bose-Einstein condensate of rubidium atoms to a slowly varying magnetic field, which imprints magnetic order onto the condensate. We then record the resulting dynamics. The initially nonmagnetized phase of the condensate evolves into a magnetized, or ferromagnetic, phase. Consequently, the quantum monopole is destroyed and replaced by a Dirac monopole. A vortex line of vanishing particle density, akin to a tiny tornado, spontaneously appears in the new phase, closely agreeing with Dirac’s early theoretical work. We subsequently study the Dirac monopole in detail, providing, for the first time, experimental information on its full three-dimensional magnetic structure.

Our work provides the first experimental results on the stability of quantum monopoles and new evidence concerning the properties of Dirac monopoles in condensates. These findings establish fertile conditions for future studies of monopole dynamics in quantum matter.


The researchers build and study both "quantum" and "Dirac" monopoles in isolated condensates in this work.
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Re: div B <> 0 everywhere...

#14  Postby crank » May 18, 2017 7:44 pm

It's unfortunate they didn't take the time to remove that hum in the video, it's pretty much unwatchable for me as is, I might go dick with it myself, it shouldn't be all that difficult to filter out.
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Re: div B <> 0 everywhere...

#15  Postby DavidMcC » May 19, 2017 11:44 am

newolder wrote:DavidMcC, If you want to shoot the messenger, go right ahead. If you want to argue the toss with the authors, that's up to you. Have you seen my field of fucks? It's empty.

We are not supposed to be merely messengers here, newolder. You are assumed to have a reason for posting a link.
As for your "field of fucks" being empty - pull the other one! (Think of your angry storming out of the "FTL at JPL" thread)
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Re: div B <> 0 everywhere...

#16  Postby DavidMcC » May 19, 2017 1:55 pm

Calilasseia wrote:Ah, just done some checking. Apparently, the phenomena observed in condensed matter systems are not true monopoles at all. Instead, they are quasi-particles exhibiting monopole-like behaviour.

...

Exactly. It's equivalent to negative mass charge carriers - an artifact of treating a crystal lattice as if it was free space.
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Re: div B <> 0 everywhere...

#17  Postby newolder » May 20, 2017 1:18 pm

Further discussion/report on this latest work here (sciencealert)
...
"This discovery nicely ties together the monopoles we have been producing over the years."

What this means for their search for a real magnetic monopole is not yet clear, but now the researchers have a tantalising lead for where the two types of analogues could meet in the middle to resemble a true magnetic monopole even more closely.

Like the elusive dark matter, if we could find a magnetic monopole, it would open the door to a whole new world of physics. And these researchers are closer than anyone's ever gotten to figuring out how to close some big gaps in our understanding of the Universe.
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Re: div B <> 0 everywhere...

#18  Postby DavidMcC » May 20, 2017 1:39 pm

Even an electric monopole (ie, an electric charge) isn't truly isolated, because the electric field lines have to terminate somewhere, even if it's very remotely. I suspect that the same would be true of a magnetic monopole. Thus, the "gap" may be largely an imagined one.
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