Quantum Physics ?

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  • #1
SDetection
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Hi, as my previous thread was closed, I'd like to continue asking some questions here regarding QM (of course if the mentors don't mind that ?).
This experiment and a zillion other tests of the HUP have demonstrated it is indeed correct. Every day, new and sophisticated experiments are performed on entangled particles and their behavior must follow the HUP to obtain the expected results. So the scientific community is actually performing ongoing experiments in this regard daily.
So, has entanglement been experimentally proven?.
 

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  • #2
DrChinese
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Hi, as my previous thread was closed, I'd like to continue asking some questions here regarding QM (of course if the mentors don't mind that ?).

So, has entanglement been experimentally proven?.

Yes, in literally thousands of experiments covering dozens of ways that particles can be entangled.

Entanglement can be verified a number of ways. The usually starting point is to generate a stream of particle pairs that exhibit a maximum of "perfect correlations". Only entangled pairs exhibit this, which is the cos^2(theta) function for photons. That reachs its max of 1 at theta=0 or 90 degrees. Unentangled photons follow a different correlation function, with a max of only .75 at those angles. The unentangled function is .25+.5(cos^2(theta)).

The next step is usually to form a Bell Inequality and demonstrate its violation. Obviously, for both the first step and the second step, the exact functions are dependent of the particle types, the setup, what is being measured, number of particles (entanglement can be 2 or more), etc. So the exact methodlogy varies, but is always described.
 
  • #3
whybother
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So, has entanglement been experimentally proven?.

Yes.

In the early 80s http://en.wikipedia.org/wiki/Alain_Aspect" [Broken] that confirmed entanglement.
 
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  • #5
SDetection
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I still don't get it, could someone explain to me, from physics point of view, how Bell's experiment proved entanglement?.
 
  • #6
Fredrik
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You don't prove a thing like entanglement (or gravity). What you do is to compare the predictions of different theories to see if you can dismiss some of those theories.

A large class of hidden variable theories make predictions that satisfy Bell inequalities. Quantum mechanics makes predictions that violate those inequalities. Experiments were performed, and the results weren't even close to satisfying the Bell inequalities. Therefore, those hidden variable theories have been falsified.
 
  • #7
ZapperZ
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So, has entanglement been experimentally proven?.

Note that violation of Bell inequality is only ONE aspect of the test of quantum entanglement. The other is the breaking of the diffraction limit using these entangled particles.

http://physicsworld.com/cws/article/news/19514

Such experiments were done 5 years ago!

Zz.
 
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  • #8
SDetection
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Note that violation of Bell inequality is only ONE aspect of the test of quantum entanglement. The other is the breaking of the diffraction limit using these entangled particles.

http://physicsworld.com/cws/article/news/19514

Such experiments were done 5 years ago!

Zz.
OK, but do the loopholes still apply to those new experiments, specifically http://physicsworld.com/cws/article/print/1332" [Broken]?:
physicsworld.com said:
Bell himself was worried that, according to special relativity, the nonlocal (faster than light) influence demonstrated in the Aspect experiment could involve propagation backward in time in other inertial reference frames of equal status. What he called the "cheapest resolution" to this problem was to return to the Lorentz (i.e. pre-Einstein) approach to relativity in which an ether is retained. In other words, there is a preferred frame of reference in which a real causal sequence may be defined (see Bell's contribution to The Ghost in the Atom in further reading). Propagation backward in time in other frames may then be dismissed as "unreal" or "apparent". More generally, however, Bell hoped for better theories than the ones we have now, and insisted that our current version of quantum theory was no more than a temporary expedient.
 
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  • #9
ZapperZ
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OK, but do the loopholes still apply to those new experiments, specifically http://physicsworld.com/cws/article/print/1332" [Broken]?:

There are no loopholes in the diffraction limit experiments.

Zz.
 
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  • #10
SDetection
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There are no loopholes in the diffraction limit experiments.

Zz.

I'm sorry, I meant do the diffraction limit experiments (as Bell's experiments) favor the completeness of QM?. If so do the loopholes still apply to them?.
Thanks.
 
  • #11
ZapperZ
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I'm sorry, I meant do the diffraction limit experiments (as Bell's experiments) favor the completeness of QM?. If so do the loopholes still apply to them?.
Thanks.

You are no longer making any sense.

At some point, YOU have to do your own homework. We have arrive at that point where you have to read those experiments yourself, understand the physics, and then figure out if your question makes any more sense.

Zz.
 
  • #12
SDetection
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  • #13
ZapperZ
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These are not "tiny holes"!!

Look at the nature of the detector. In many cases, these are CCD detectors. It means that whatever is triggering it has a finite "boundary" of detection.

If I make the CCD camera pixels bigger, you get bigger "holes".

Zz.
 
  • #14
Doc Al
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Ok, Here is why I think so. Electrons interference pattern :

Photons interference pattern:

But why this happens?.
If you are asking about why the patterns are different, it looks to me that the electrons were diffracted through slits while the photons were diffracted through holes. :wink:
 
  • #15
SDetection
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These are not "tiny holes"!!
I know, I didn't mean that. If you compare the two patterns, you will notice that when photons go through the slits, they are more concentrated at one entrance point (tiny hole) along the slits axis unlike electrons.

If you are asking about why the patterns are different, it looks to me that the electrons were diffracted through slits while the photons were diffracted through holes. :wink:
No!, if you are sure about that, you would have said this before :smile:.
 
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  • #16
Doc Al
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No!, if you are sure about that, you would have said this before :smile:.
Huh? Did you show these pictures before? Do you know what they represent?
 
  • #17
DrChinese
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There are no loopholes in the proof of entanglement. What you are trying to refer to is the alleged loopholes in tests of Bell's inequality, which is used to rule out local realism. These are not the same things as proof of entanglement. Even folks that assert local realism is not ruled out by these tests must acknowledge that entangled pairs do NOT act like unentangled pairs.
 
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  • #18
SDetection
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Huh? Did you show these pictures before? Do you know what they represent?
I meant that you saw pictures of photons/electrons interference pattern before?.
There are no loopholes in the proof of entanglement. What you are trying to refer to is the alleged loopholes in tests of Bell's inequality, which is used to rule out local realism. These are not the same things as proof of entanglement. Even folks that assert local realism is not ruled out by these tests must acknowledge that entangled pairs do NOT act like unentangled pairs.

Yeah, I know, maybe I should have said "entanglement interpretation". But have all the alleged loopholes been argued as not happening in Bell's experiment?.
 
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  • #19
Doc Al
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I meant that you saw pictures of photons/electrons interference pattern before?.
I have certainly seen them before. What's your point?
 
  • #20
SDetection
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I have certainly seen them before. What's your point?
I'm sorry, it was maybe a misunderstanding.
 
  • #21
lightarrow
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Ok, Here is why I think so. Electrons interference pattern :
http://www.hitachi.com/rd/research/em/doubleslit.html" [Broken]

Photons interference pattern:
http://ophelia.princeton.edu/~page/single_photon.html"

But why this happens?.
Are you perhaps referring to the fact that in the second picture the light source is more collimated (maybe a laser beam)?
 
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  • #22
whybother
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This thread is really hard to read. I'm surprised it hasn't been locked yet.
 
  • #23
Doc Al
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Are you perhaps referring to the fact that in the second picture the light source is more collimated (maybe a laser beam)?
It is definitely a laser beam passing through a double slit.
 
  • #24
feynmann
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The usually starting point is to generate a stream of particle pairs that exhibit a maximum of "perfect correlations". Only entangled pairs exhibit this, which is the cos^2(theta) function for photons. That reachs its max of 1 at theta=0 or 90 degrees. Unentangled photons follow a different correlation function, with a max of only .75 at those angles. The unentangled function is .25+.5(cos^2(theta)). .

If the stream of particle pairs are photons, perhaps we can explain the entanglement using "special relativity". Per SR, from the photon's point of view, the distance between the pair is always zero and time stands still, then the entanglement is not so perplexing
 
  • #25
SDetection
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Are you perhaps referring to the fact that in the second picture the light source is more collimated (maybe a laser beam)?
It is definitely a laser beam passing through a double slit.
Yeah, it's a laser source, but the mean distance between consecutive photons is 2 km.
This thread is really hard to read. I'm surprised it hasn't been locked yet.
Come on!, don't put ideas in the mentors minds. As I'm still learning, and this is a public forum, I'd like to know what you think is so hard to read, quote me, and I'll try to improve the writing.
 
  • #26
SDetection
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This thread is really hard to read.

Maybe it's hard to read for you because some posts here are in the context of a prior discussion.
 
  • #27
lightarrow
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Yeah, it's a laser source, but the mean distance between consecutive photons is 2 km.
Ok, but what I intended is: are you referring to the fact the two pictures are different because in the second case the laser beam's cross section area is lower than the slits' dimensions?
 
  • #28
SDetection
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Ok, but what I intended is: are you referring to the fact the two pictures are different because in the second case the laser beam's cross section area is lower than the slits' dimensions?
Yes but not exactly:
I know, I didn't mean that. If you compare the two patterns, you will notice that when photons go through the slits, they are more concentrated at one entrance point (tiny hole) along the slits axis unlike electrons.
 
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  • #29
ZapperZ
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This thread has really become VERY confusing, but it is due to your own fault. Note that it started simple with issues about entanglement, and now it is nothing more than going back to going around in circles about standard diffraction and interference.

It appears that even after repeated attempts in this and the other previous threads, you clearly have not understood (or want to understand) the QM picture of interference. And now, you are trying to pick on some apparent "details" about the interference. Let me just say that the mathematical description for BOTH types of interference does NOT differ. Unless you can show otherwise, you are barking up the wrong tree of ignorance here.

Do not attempt to go after non-existent effect or entity by simply making wild guesses. We draw the line right there in this forum. While we welcome people who sincerely want to learn, we do NOT cater to someone who is simply shooing empty bullets in all directions hoping to make one sticks. There have been many people who have responded to your ORIGINIAL question hoping that you wanted to learn about entanglement, and somehow, it has degenerated back to some nonsensical in-detail examination of the interference pattern.

Either this goes back to discussing what you asked for in the beginning of the thread, or this thread is done. It is your call.

Zz.
 
  • #30
SDetection
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This thread has really become VERY confusing, but it is due to your own fault.
I'm sorry but I don't know how this thread is confusing!, it's an open and ongoing discussion. If someone thinks that something is confusing, he/she just have to refer to it and explain why it's so. I don't post and run away, I'm very committed here.
Note that it started simple with issues about entanglement, and now it is nothing more than going back to going around in circles about standard diffraction and interference.
But as the thread title implies, I want to discuss all aspects of quantum physics, not just entanglement. Also correct me if I'm wrong, Diffraction and interference in the slits experiments are very important aspects of quantum physics, right?. Also I was responding to question by a member regarding why I think photons can be more concentrated at a tiny hole unlike electrons.
It appears that even after repeated attempts in this and the other previous threads, you clearly have not understood (or want to understand) the QM picture of interference. And now, you are trying to pick on some apparent "details" about the interference.
Correct me if I'm wrong, but quantum physicists themselves don't understand that?.
Let me just say that the mathematical description for BOTH types of interference does NOT differ. Unless you can show otherwise, you are barking up the wrong tree of ignorance here.
When it comes to the mathematics, I assure you that I'm very convinced, but I'm only concerned with quantum physics. Also which "types of interference" you are referring to if the "mathematical description" for them is the same?.

Do not attempt to go after non-existent effect or entity by simply making wild guesses. We draw the line right there in this forum. While we welcome people who sincerely want to learn, we do NOT cater to someone who is simply shooing empty bullets in all directions hoping to make one sticks.
I'm sorry, but it's divide and conquer, a very good learning technique, I'm not "shooting empty bullets", my arguments are based on logic and reasoning even if they were scientifically wrong in the beginning. Also I didn't hold my position on any argument that was proven scientifically wrong, which means that I want to learn and I actually did. Also I'm not questioning QM successful predictions but I want to come up with a non counterintuitive interpretation.

There have been many people who have responded to your ORIGINIAL question hoping that you wanted to learn about entanglement, and somehow, it has degenerated back to some nonsensical in-detail examination of the interference pattern.
As I said I want to discuss all aspects of quantum physics, I'm not going off-topic here. I'm reading about entanglement and I'll not drop it from the discussion.

Either this goes back to discussing what you asked for in the beginning of the thread, or this thread is done.
But my original question was "do the mentors mind me asking any questions regarding QM?":
I'd like to continue asking some questions here regarding QM (of course if the mentors don't mind that ?).

So, has entanglement been experimentally proven?.

It is your call.
No, It's yours :smile:, and I know that you're open-minded and won't close this thread.
 
  • #31
ZapperZ
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It has nothing to do with having an "open mind". And open mind is a dangerous thing to have. Flies might fall into it.

The best and most effective use of a forum such as this is if one focuses on a particular, narrow topic, not some broad topic such as wanting to learn quantum mechanics, which one does in a standard college course. You cannot expect to be schooled in something that broad, and in, of all places, a public forum! This is pure laziness!

If you truly want to learn about QM, then open a QM text and learn from it. If you have specific questions, then ask that specific question on here after you've made an honest attempt at understanding it. That is the most effective way of learning anything, if that is what you really want to do.

A broad, open-ended, vague, and often meandering thread like this isn't the way to do it. It is now closed.

Zz.
 

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