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What are the implications of this experiment?

by StevieTNZ
Tags: experiment, implications
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StevieTNZ
#2
Jun3-11, 01:25 AM
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An article about the work: http://www.aip.org.au/Congress2010/A...ajectories.pdf
DAlden
#3
Jun3-11, 08:16 AM
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Please see the following article on BBC News: http://www.bbc.co.uk/news/science-environment-13626587

Researchers have apparently side-stepped one of the conclusions of the double-slit experiment, namely that we cannot know which slit a photon went through if we want to produce the diffraction pattern. By performing weak measurements they are able to observe both the particle nature and wave nature of light at the same time.

My question is does this effectively disprove the "many-worlds" interpretation of quantum mechanics, in which the photon was said to go through both slits in alternate quantum realities? It seems they are averaging over large numbers of photons, so I'm not sure they can say what any individual particle does, but it does seem to point to the notion that each particle does take a definite path. What do you think?

f95toli
#4
Jun3-11, 08:43 AM
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What are the implications of this experiment?

It doesn't really change anything. The results agree with ''standard'' QM and is independent of interpretation.
Note that they are performing a weak measurements, meaning their results do not tell you anything about the trajectory of an individual photon

From the paper (latest issue of Science)

For the experimentally reconstructed trajectories for our double slit (Fig. 3), it is worth stressing that photons are not constrained to follow these precise trajectories; the exact trajectory of an individual quantum particle is not a well-defined concept.
This experiment is actually more about the nature of weak measurements (which is still somewhat controversial), than about the nature of photons or even the double-slit experiment.
It is interesting work, but not in any way revolutionary.
Demystifier
#5
Jun3-11, 09:16 AM
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I agree with f95toli. See also my arguments against weak measurements on my blog
http://www.physicsforums.com/blog.php?b=1225
http://www.physicsforums.com/blog.php?b=1226
ibysaiyan
#6
Jun3-11, 05:18 PM
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Hi all
I just came across this article in which from what I have read is that the wave-particle nature has been observed though the whole technicality confused me a little.
Link
On the whole it seems they took the average photons into consideration ,can someone with more knowledge enlighten me ?
Regards,
ibysaiyan
phinds
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Jun3-11, 05:37 PM
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Quote Quote by ibysaiyan View Post
Hi all
I just came across this article in which from what I have read is that the wave-particle nature has been observed though the whole technicality confused me a little.
Link
On the whole it seems they took the average photons into consideration ,can someone with more knowledge enlighten me ?
Regards,
ibysaiyan
THere's already a thread on this experiment. Don't remember subject title but it's in QM so should be easy to find.
OmCheeto
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Jun3-11, 08:50 PM
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Quote Quote by f95toli View Post
Note that they are performing a weak measurements, meaning their results do not tell you anything about the trajectory of an individual photon
hmm... My sister had me all atwitter today when she sent me the article.

Though it looks like there's nothing to see.

Odd that their abstract seems to imply something contrary to what you are saying. I guess I'll have to read the full article.

We sent single photons emitted by a quantum dot through a double-slit interferometer and reconstructed these trajectories by performing a weak measurement of the photon momentum, postselected according to the result of a strong measurement of photon position in a series of planes.
And go back to school to find out what a "weak measurement" is.
Truecrimson
#9
Jun4-11, 03:06 PM
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An explanation: http://scienceblogs.com/principles/2...erfere_obs.php
IllyaKuryakin
#10
Jun5-11, 04:00 AM
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Really good stuff. If this holds up, and I expect it will, it answers many more questions than some might realize at first glance. Really foundational work. Congrats to Aephraim Steinberg and his team at the University of Toronto!
yoda jedi
#11
Jun5-11, 06:49 PM
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good news for Two-State Vector model and Aharonov.
StevieTNZ
#12
Jun5-11, 07:40 PM
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Quote Quote by f95toli View Post
It doesn't really change anything. The results agree with ''standard'' QM and is independent of interpretation.
Note that they are performing a weak measurements, meaning their results do not tell you anything about the trajectory of an individual photon
Yeah, I was thinking that when I read the article (wording "on average"). Plus something to do with momentum having an approximate value.
Demystifier
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Jun6-11, 02:51 AM
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Quote Quote by Truecrimson View Post
As said there, these MEASURED trajectories look exactly like Bohm trajectories. Which, of course, is not surprising:
http://www.physicsforums.com/showthread.php?t=252491
Phrak
#14
Jun6-11, 05:19 AM
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This line of reasoning will eventually bust quantum mechanics wide open---finally! A more primitive theory will emerge of continuous field. It won't be MWT nor Bohmian mechanics nor any of the host of suppositions commonly bantered about these days, including Aharanov's latest musings--though he is close. Temporal symmetry is at the heart of it. All of this is just my less-than-humble opinion, of course.
AntonL
#15
Jun6-11, 05:57 AM
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a fascinating article with lively reader contribution

http://physicsworld.com/cws/article/news/46193

An international team of researchers has, for the first time, mapped complete trajectories of single photons in Young’s famous double slit experiment. The finding takes an important first step towards measuring complimentary variables of a quantum system – which until now has been considered impossible as a consequence of the Heisenberg uncertainty principle

PS: I just noticed this is a double posting of the thread "What are the implications of this experiment?"
SpectraCat
#16
Jun6-11, 07:02 AM
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Quote Quote by AntonL View Post
a fascinating article with lively reader contribution

http://physicsworld.com/cws/article/news/46193




PS: I just noticed this is a double posting of the thread "What are the implications of this experiment?"
That quote is somewhat misleading .. in fact, I am pretty sure that in that article, the authors themselves say that mapping trajectories of individual photons is impossible. The paper describes the results of *weak* measurements, which still provide information about the average trajectories over large numbers of measurements. Another way of saying this is that the authors don't get "which path" information for the photons, so the interference pattern is still preserved.

So even though the particles do travel through the interferometer one at a time, saying that "...mapped complete trajectories of single photons", makes it sound like they can say, "Ok, photon 1 went this way, photon 2 went that way, ..." etc., and that is not correct.
Demystifier
#17
Jun6-11, 07:40 AM
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Spectracat is right.

For me, the main implication is the following:
Bohmian particle trajectories are much more than a part of a controversial interpretation of QM. Bohmian particle trajectories are a part of QM itself, irrespective of the interpretation. However, what different interpretations disagree on, is what these trajectories really "are".

In this sense, trajectories play a role in QM similar to the role of the wave function. All interpretations involve the wave function, but different interpretations disagree on what this wave function really "is".
Demystifier
#18
Jun6-11, 09:34 AM
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Or let me further refine the comment above. I believe that the main implication of this experiment is that Bohmian trajectories are no longer "hidden variables". Or more precisely, not more hidden than the wave function. For a more elaborated argument see my blog
http://www.physicsforums.com/blog.php?b=3077


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