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Old Sep 04, 2009, 04:11 PM   #1
SS-18 ICBM
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Arrow Magnetic Monopoles Detected for the First Time

Magnetic Monopoles Detected In A Real Magnet For The First Time

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ScienceDaily (Sep. 4, 2009) — Researchers from the Helmholtz-Zentrum Berlin für Materialien und Energie have, in cooperation with colleagues from Dresden, St. Andrews, La Plata and Oxford, for the first time observed magnetic monopoles and how they emerge in a real material.

Results of their research are being published in the journal Science.

Magnetic monopoles are hypothetical particles proposed by physicists that carry a single magnetic pole, either a magnetic north pole or south pole. In the material world this is quite exceptional because magnetic particles are usually observed as dipoles, north and south combined. However there are several theories that predict the existence of monopoles. Among others, in 1931 the physicist Paul Dirac was led by his calculations to the conclusion that magnetic monopoles can exist at the end of tubes – called Dirac strings – that carry magnetic field. Until now they have remained undetected.

Jonathan Morris, Alan Tennant and colleagues (HZB) undertook a neutron scattering experiment at the Berlin research reactor. The material under investigation was a single crystal of Dysprosium Titanate. This material crystallises in a quite remarkable geometry, the so called pyrochlore-lattice. With the help of neutron scattering Morris and Tennant show that the magnetic moments inside the material had reorganised into so-called 'spin-spaghetti'. This name comes from the ordering of the dipoles themselves, such that a network of contorted tubes (strings) develops, through which magnetic flux is transported. These can be made visible by their interaction with the neutrons which themselves carry a magnetic moment. Thus the neutrons scatter as a reciprocal representation of the Strings.

During the neutron scattering measurements a magnetic field was applied to the crystal by the researchers. With this field they could influence the symmetry and orientation of the strings. Thereby it was possible to reduce the density of the string networks and promote the monopole dissociation. As a result, at temperatures from 0.6 to 2 Kelvin, the strings are visible and have magnetic monopoles at their ends.

The signature of a gas made up by these monopoles has also been observed in heat capacity measured by Bastian Klemke (HZB). Providing further confirmation of the existence of monopoles and showing that they interact in the same way as electric charges.

In this work the researchers, for the first time, attest that monopoles exist as emergent states of matter, i.e. they emerge from special arrangements of dipoles and are completely different from the constituents of the material. However, alongside this fundamental knowledge, Jonathan Morris explains the further meaning of the results: "We are writing about new, fundamental properties of matter. These properties are generally valid for materials with the same topology, that is for magnetic moments on the pyrochlore lattice. For the development of new technologies this can have big implications. Above all it signifies the first time fractionalisation in three dimensions is observed."
Link to research abstract.

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While sources of magnetic fields—magnetic monopoles—have so far proven elusive as elementary particles, several scenarios have been proposed recently in condensed matter physics of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin ice state is argued to be well-described by networks of aligned dipoles resembling solenoidal tubes—classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defect looks like a magnetic monopole. We demonstrate, by diffuse neutron scattering, the presence of such strings in the spin ice Dy2Ti2O7. This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.
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Old Sep 04, 2009, 07:13 PM   #2
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Well this is huge news if confirmed.

Ah wait...[reading the links] Looks like a clever construct that makes dipoles look like a monopole. How odd, interesting stuff.
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Old Sep 05, 2009, 04:12 AM   #3
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Helmholtz-Zentrum Berlin für Materialien und Energie
A friend of mine is working there at the moment.

Interesting news, though it doesn't really seem to be "the real big thing".

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Originally Posted by wiki
While a magnetic monopole particle has never been observed, there are a number of phenomena in condensed-matter physics where a material, due to the collective behavior of its electrons and ions, can show emergent phenomena that resemble magnetic monopoles in some respect.[16][17][18][19] These should not be confused with actual monopole particles; in particular, the divergence of the microscopic magnetic B-field is zero everywhere in these systems, unlike in the presence of a true magnetic monopole particle. The behavior of these quasiparticles would only become indistinguishable from true magnetic monopoles -- and they would truly deserve the name -- if the so-called magnetic fluxtubes connecting these would-be monopoles became unobservable which also means that these flux tubes would have to be infinitely thin, obey the Dirac quantization rule, and deserve to be called Dirac strings.

In a paper published in Science in September 2009, researchers Jonathan Morris and Alan Tennant from the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) along with colleages from Dresden University of Technology, St. Andrews, La Plata, and Oxford University describe the observation of quasiparticles resembling monopoles. A single crystal of dysprosium titanate in a highly frustrated pyrochlore lattice (F d -3 m) was cooled to 0.6 to 2 K. Using neutron scattering, the magnetic moments were shown to align in the spin ice into interwoven tube-like bundles resembling a Dirac strings. At the defect formed by the end of each tube, the magnetic field looks like that of a monopole. Using an applied magnetic field to break the symmetry of the system, the researchers were able to control the density and orientation of these strings. A contribution to the heat capacity of the system from an effective gas of these quasiparticles is also described.
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Old Sep 05, 2009, 04:57 AM   #4
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Well this is huge news if confirmed.
Just wondering, is something physicist have been searching for, like Higgs boson?

Does this news, if confirmed, change any current ideas about electromagnetism or particle physics ? or is it just evidence backing up what was already thought ?
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Old Sep 05, 2009, 05:03 AM   #5
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If that is true it would indeed be one of the most important findings in experimental physics ever.
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Old Sep 05, 2009, 06:59 AM   #6
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Originally Posted by Tabster View Post
Just wondering, is something physicist have been searching for, like Higgs boson?

Does this news, if confirmed, change any current ideas about electromagnetism or particle physics ? or is it just evidence backing up what was already thought ?
Yes, monopoles were searched for extensively.

True monopoles would mess up physics in a serious way, they invalidate one of Maxwell's equations that the divergengence of a mag field must be zero(for background: there are 4eqts called Maxwells equations that completely sum up all electromagnetic phenomena and Special relativity is a consequence of Maxwell's eqts).

However, the articles do not point to "real" monopoles. They are a clever collection of dipoles that happen to look like a monopole at the right length scale.
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Old Sep 05, 2009, 07:15 AM   #7
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Originally Posted by Atrebates View Post
However, the articles do not point to "real" monopoles. They are a clever collection of dipoles that happen to look like a monopole at the right length scale.
It is actually simple to find out whether a black box contains several magnetic dipoles or a magnetic monopole. I agree that this is probably a clever collection of dipoles but they have obviously found some weird quantum thing that makes them look like a monopole. I wonder how far two monopoles can be departed from each other.
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Old Sep 05, 2009, 07:39 AM   #8
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Read the links in the OP.

They don't 100% explain but it looks like a solid state trick whereby (in a given crystal) the dipoles are aligned into a stucture a bit like a carbon nanotube, and there is a blob of monopole at each end of the tube.

Now that's clearly not quite what's going on because that will never satisfy the divB=/=0 (for any gaussian surface) that defines a monopole.
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Old Sep 05, 2009, 07:54 AM   #9
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Originally Posted by Atrebates View Post
Read the links in the OP.

They don't 100% explain but it looks like a solid state trick whereby (in a given crystal) the dipoles are aligned into a stucture a bit like a carbon nanotube, and there is a blob of monopole at each end of the tube.

Now that's clearly not quite what's going on because that will never satisfy the divB=/=0 (for any gaussian surface) that defines a monopole.
I read it. They wouldn't claim to have a monopole if the thing does not behave like a monopole.
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Old Sep 06, 2009, 03:49 PM   #10
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If that is true it would indeed be one of the most important findings in experimental physics ever.
Understatement much?

But this is actually really interesting news, I followed Atrebates' advice and what he got out of the article seems to be what I've gotten - it's a very interesting effect but doesn't seem like a true monopole.
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Old Sep 07, 2009, 04:41 AM   #11
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Originally Posted by Gigaz View Post
I read it. They wouldn't claim to have a monopole if the thing does not behave like a monopole.

Are you kidding? They make statements that get taken out of context by journalists all the time. Remember "quantum teleportation"? Nice phrase, except that it only communicates information. If communication were teleportation, then whoever sent the first smoke signal did it. Nor is it instantaneous - it can only work in conjunction with some other communication medium, such as a telephone line or radio transmission (or even smoke signals!), and in terms of communication, is limited by the speed and bandwidth of that communication. What it really is, is quantum encryption.

If you said to a journalist "well, I'm oversimplifying in order to explain it in lay terms, but in a sense, you could think of it as being vaguely like X, however ..." the headline will say "Scientists discover X!!"
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Old Sep 07, 2009, 06:54 AM   #12
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Are you kidding? They make statements that get taken out of context by journalists all the time. Remember "quantum teleportation"? Nice phrase, except that it only communicates information. If communication were teleportation, then whoever sent the first smoke signal did it. Nor is it instantaneous - it can only work in conjunction with some other communication medium, such as a telephone line or radio transmission (or even smoke signals!), and in terms of communication, is limited by the speed and bandwidth of that communication. What it really is, is quantum encryption.
"Quantum teleportation" does not communicate information. It is however instantaneous and that's where the "teleportation" comes from. Science journalism is notoriously bad, but in this case I don't blame them. Entanglement is a difficult subject and it's easy to get it wrong.

If you compare quantum entanglement to smoke signals, then you badly missed the point of it.
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Old Sep 07, 2009, 09:30 AM   #13
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"Quantum teleportation" does not communicate information.
That's precisely what it does.

In quantum teleportation, an unknown quantum state is faithfully transferred from a sender (Alice) to a receiver (Bob). To perform the teleportation, Alice and Bob must have a classical communication channel and must also share quantum entanglement -- in the protocol we employ*, each possesses one half of a two-particle entangled state. Alice makes an appropriate projective measurement (Bell measurement) of the unknown state together with her component of the shared entangled state. The result of this measurement is a random piece of classical information which Alice sends to Bob over their classical communication channel. Bob uses this information to choose a unitary transformation which he performs on his component of the shared entangled state, thus transforming it into an output state identical to the original (unknown) input.

http://www.its.caltech.edu/~qoptics/teleport.html

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It is however instantaneous and that's where the "teleportation" comes from.
No, see the abstract above. It has to do with the relational state being changed in two distant locations via entanglement. In this sense it is action at a distance. However, the only use is the transfer of information - no thing is being removed from one place and relocated at another, there is only a relation between two things at a distance that is maintained.

The idea of teleportation doesn't come from the speed of the thing. It comes from the fact that, with no intermediate action occuring, a change in state in one particle is reflected by a change in state in another particle. A relation or state is changing at a distance. This does not mean you can send apples or any physical thing from one place to another ... it only means you can have a particle's spin state in one location reflected in another location.

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If you compare quantum entanglement to smoke signals, then you badly missed the point of it.
You missed the point if you think I was comparing them. Quantum "teleportation" requires a conventional medium to make use of the information being transferred. Technically, one could use smoke signals or any other conventional medium. In the example above, Alice could send the classical information by smoke signal. Or farting in Morse code, or whatever.

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Old Sep 07, 2009, 02:42 PM   #14
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That's precisely what it does.
No, you're reading it wrong. The point of quantum teleportation is the instantaneous transfer of a quantum mechanical state. This is not equivalent to information. Actually all information is going over the classical channel in these protocolls. If any information traveled through the quantum channel, you could use this for instantaneous communication.

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No, see the abstract above. It has to do with the relational state being changed in two distant locations via entanglement. In this sense it is action at a distance. However, the only use is the transfer of information - no thing is being removed from one place and relocated at another, there is only a relation between two things at a distance that is maintained.
Actually the state is relocated. At the original site it is destroyed and then created at the other site.

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The idea of teleportation doesn't come from the speed of the thing. It comes from the fact that, with no intermediate action occuring, a change in state in one particle is reflected by a change in state in another particle. A relation or state is changing at a distance. This does not mean you can send apples or any physical thing from one place to another ... it only means you can have a particle's spin state in one location reflected in another location.
Yes, you cannot send any physical thing by quantum teleportation. However you cannot send any information either. What you can do is transfer a qunatum mechanical state in such a way that it doesn't exist at it's original place any more. And this happens instantaneously. Hence "quantum teleportation".


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You missed the point if you think I was comparing them. Quantum "teleportation" requires a conventional medium to make use of the information being transferred. Technically, one could use smoke signals or any other conventional medium. In the example above, Alice could send the classical information by smoke signal. Or farting in Morse code, or whatever.
Again you missed the point: You don't need the conventional medium to make use of the information, you need the conventional medium to transfer any information at all.
No matter how slow that conventional medium is, be it electric signals, smoke signals or snail mail, the actual transfer, the exciting thing, happens instantaneously (Well, assuming that you can keep the state alive until the snail arrives...).
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Old Sep 08, 2009, 02:15 AM   #15
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No, you're reading it wrong. The point of quantum teleportation is the instantaneous transfer of a quantum mechanical state.
Yes, but the only use of that is qubits.

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Actually all information is going over the classical channel in these protocolls.
No. If a state is being transferred - actually if anything detectable at all is being transferred - it can be used to send information. Alice and Bob have entangled particles; Alice sends Bob classical bits from her measurement of the particle, which Bob can use to reproduce qubits on Alice's end.

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If any information traveled through the quantum channel, you could use this for instantaneous communication.
Information is being passed through the quantum channel, because a state is information. If anything measurable is being passed, information is being passed, because any measurement is an expression of value and expressions of value are information. However, instantaneous communication is not possible because it is necessary for Alice to send her measurements to Bob before he can decipher, with accurate fidelity, these states as qubits.

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Again you missed the point: You don't need the conventional medium to make use of the information, you need the conventional medium to transfer any information at all.
No matter how slow that conventional medium is, be it electric signals, smoke signals or snail mail, the actual transfer, the exciting thing, happens instantaneously (Well, assuming that you can keep the state alive until the snail arrives...).
True, but in practical terms, there's no violation of the no-communication theorem because of the need for a classical communications channel.

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Old Sep 08, 2009, 06:35 AM   #16
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No. If a state is being transferred - actually if anything detectable at all is being transferred - it can be used to send information. Alice and Bob have entangled particles; Alice sends Bob classical bits from her measurement of the particle, which Bob can use to reproduce qubits on Alice's end.

Information is being passed through the quantum channel, because a state is information. If anything measurable is being passed, information is being passed, because any measurement is an expression of value and expressions of value are information.
You cannot equate a state or a qubit with classical information, because one state cannot be measured. Any classical information about that state is generated at Bob's place. Alice doesn't know anything about the state, until Bob tells her about his measurements. How can Alice transfer information, that doesn't even exist yet?

You could define a qubit as "quantum information" and could say that quantum information was transferred. But this is not equal to classical information and these shouldn't be confused.
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