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Bill S. Offline OP
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http://www.engadget.com/2015/03/30/spooky-experiment-proves-quantum-entanglement-is-real/

Interesting article, but it raises a few questions.

...a particle in superposition effectively exists in both places at once.

My understanding was that it is only the wave function that exists in both places, and that the particle does not exist as a specific object until it is observed, when it is just in one place.

Upon analysis, they found that the particle not only exists in a superposition state until its observed but that it never showed up in both labs at the same time.

Doesnt this indicate that a particle is not in fact in two places at once?

the team split a single photon in half..

If a photon is a quantum of energy; what is half a photon? How can you have half a quantum?


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Bill S,

In the non layman link it said "A single quantum particle can be described by a wavefunction that spreads over arbitrarily large distances; however, it is never detected in two (or more) places.".

It irks me that "layman" science writers don't seem to be precise. Which causes great confusion to those of us that haven't had a science course in decades.

Also the scientific definitions are not necessarily those of common usage.
Terms such as "exist", "place" and "at once".

All for now.

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Not sure what you mean Pokey it is precise ... lets see if I can rephrase it

"A single quantum particle can be described by a wavefunction that spreads over arbitrarily large distances; however, it is only ever detected in one place at which point the waveform collapses to a zero in all other places the waveform spread."

Last edited by Orac; 05/04/15 03:00 AM.

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Originally Posted By: Bill S.
Doesnt this indicate that a particle is not in fact in two places at once?

Correct and that is what QM says the waveform exists in both places but not the particle (the observed state). This is sort of falsifying interpretations of QM that somehow make the actual particle in both places at the same time. Remember there are arguments with people who want the classical world restored as well as other interpretations of QM, it isn't a single sided argument.

Originally Posted By: Bill S.
the team split a single photon in half..

If a photon is a quantum of energy; what is half a photon? How can you have half a quantum?

You are correct the process must conserve energy ... UV in 2xIR photons out smile

The fact the 2 photons are entangled and still heavily connected is why they are called "split". If you don't like the terminology replace it with 2 connected photons it makes no real difference, the terminology does not change the result.

Does this help:
http://www.learner.org/courses/physics/visual/animation.html?shortname=entangled_energy

The old normal way to do the process was spontaneous parametric down-conversion (http://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion).

In the experiment above they use a fock state setup (http://en.wikipedia.org/wiki/Fock_state) which produces a split photon pair probably using SPDC with a heralded photon.

You can get these things on a semiconductor chip now
https://uwaterloo.ca/research/waterloo-c...tum-information

Bonus question: Do you think it would be possible to combine two photons in sort of the reverse process.
Hint: You have discussed this relative to an article on Rydberg blockade but may not have recognized what it was doing.

For the record both process where predictions of Quantum Field theory with conventional assumptions and why science went looking for it.

No QM was harmed in the making of this experiment smile

Last edited by Orac; 05/04/15 09:49 AM.

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Originally Posted By: Orac
You have discussed this relative to an article on Rydberg blockade but may not have recognized what it was doing.


I don't recall being involved in a discussion about Rydberg blockade, In fact I don't know what it is.


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This was sort of the glossy science media version and I thought you were involved in the discussion it carried a lovely photo of the starwars light saber smile

http://www.natureworldnews.com/articles/4178/20130926/new-state-matter-created-fusing-photons.htm
http://www.independent.co.uk/news/scienc...rs-8841612.html

What they are doing is binding two or more photon behaviours together in a very different way than entanglement.

Wikipedia has a reference on the process now:
http://en.wikipedia.org/wiki/Photonic_molecule

This work was really an extension of earlier works to create super photons.
http://www.zmescience.com/science/physics/super-photons-bose-einstein-condensate-27112010/

The latest extension of these sorts of ideas is a new proposal to test BreitWheeler process and make matter directly from light.
http://www.theguardian.com/science/2014/may/18/matter-light-photons-electrons-positrons

It's all just standard QM with a bit of very clever thinking to setup challenging almost unnatural situations that produce some very strange results.

What is common to all the processes is micro-cavities with really exotic control of conditions.

So the bonus question answer was you can bind together photons in more unusual ways than entanglement and it may even be able to produce matter from it .... we will know in the near future.

Last edited by Orac; 05/07/15 05:47 AM.

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