Delayed Choice Quantum Eraser Experiment

Started by josephpalazzo, May 07, 2014, 11:37:40 AM

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Casparov

Quote from: josephpalazzo on May 10, 2014, 07:20:01 AM
BTW, did you read up on  LuboÅ¡ Motl at http://motls.blogspot.ca/2010/11/delayed-choice-quantum-eraser.html , he has an extensive explanation on Delayed Choice Quantum Eraser experiments. You won`t find better explanation.

I read this blog, thank you for the link. He seems to be saying over and over again that the only reason people think Quantum Mechanics is counter-intuitive is if they assume Realism is true. We cannot say what the real properties of the system are prior to measurement. If we attempt to, counter-intuitive things like retro-causality seem to be taking place. Quantum Mechanics teaches us that we cannot assume that Realism is true, and thus when we simply refuse to make that assumption, all of the counter-intuitiveness goes away. I agree with this assessment.

Realism - all measurement outcomes are determined by pre-existing properties of particles independent of the measurement; a viewpoint according to which an external reality exists independent of observation
“The Fanatical Atheists are like slaves who are still feeling the weight of their chains which they have thrown off after hard struggle. They are creatures whoâ€"in their grudge against traditional religion as the "opium of the masses"â€"cannot hear the music of other spheres.” - Albert Einstein

josephpalazzo

Quote from: Casparov on May 11, 2014, 04:36:11 AM
I am aware of Young's Double Slit Experiment. Thank you. You seem to be suggesting that the mere presence of a detector causes the interference pattern to disappear.

It is NOT a suggestion, it is a FACT.


Quote
If the detector records which-path information and then erases it, does the detector's mere presence still cause the interference pattern to disappear?

You've missed out on what I said earlier. Let me make it clearer for you:1) every double-slit experiment, 2)every delayed choice experiment, 3)every quantum eraser experiment, 4) every experiment that combines any of 1,2, 3 show exactly the same results - if the which-path is known, no interference; if the which-path is not known, there is interference.


josephpalazzo

#62
Quote from: Casparov on May 11, 2014, 05:17:55 AM
I read this blog, thank you for the link. He seems to be saying over and over again that the only reason people think Quantum Mechanics is counter-intuitive is if they assume Realism is true.

I've read that blog and nothing you say is in that blog. You are extracting what you think he should be saying. I hate to tell you this but you make a poor student. Did I say I have been teaching physics for more than 25 years? In those years I've seen all kinds, bright students, average students, students who didn't belong in my classes. Regrettably you would fail all my courses, not because you're not smart but because you have blinders that prevent you from absorbing the material.

QuoteWe cannot say what the real properties of the system are prior to measurement. If we attempt to, counter-intuitive things like retro-causality seem to be taking place.

You're partly right but you extract the wrong conclusion. Let me give an analogy. Suppose you want to measure the velocity of a car. What you do is take its position versus a clock. You plot that on a graph, draw the best curve, joining all the data, and from there, you can calculate the velocity. There is one assumption that is left out: for you to see the car at different positions, photons had to strike the car, bouncing off  and then reach your eyes (or a detector). Those photons bouncing off the car don't disturb the car - well they do, but the effect is so small, you can safely ignore that effect. However, should you do the same for an electron, the effect of the bouncing photons would have great effect, so much so that any attempt to find the position at any given time is almost an impossible task. That's reality - at subatomic scale, any measurement you are trying to observe affect the system to such an extent that it destroys what you are trying to accomplish - this is something you cannot circumvent. Fortunately, people of great imagination and creativity were able to come up with a theory to deal with those situations, but there is a cost: we can only calculate probabilities, and that theory is quantum mechanics.

Now that is not the only problem the early pioneers of QM were faced. Another problem was that these objects (photons, electrons, etc) were exhibiting both particle and wave characteristics. Again, QM can handle that, but there is a cost: there are certain properties which are incompatible, meaning: if you know the position of those objects, there is an uncertainty in the momentum, or, if you know one component of the spin, there is an uncertainty in the other components of the spin, and what you get in those experiments we have been talking about- double-slit, delayed choice, quantum eraser - if you know the path, you get no interference, meaning large uncertainties in the momentum.


Solitary

I'm getting bored like I do with children who beieve their fantasies are real. Solitary
There is nothing more frightful than ignorance in action.

Casparov

Quote from: josephpalazzo on May 11, 2014, 07:27:34 AM


It is NOT a suggestion, it is a FACT.


You've missed out on what I said earlier. Let me make it clearer for you:1) every double-slit experiment, 2)every delayed choice experiment, 3)every quantum eraser experiment, 4) every experiment that combines any of 1,2, 3 show exactly the same results - if the which-path is known, no interference; if the which-path is not known, there is interference.

Mr. Palazzo, I agree with you, but you don't seem to be answering my question. I agree that all of these experiments show that: "if the which-path is known, no interference; if the which-path is not known, there is interference." We agree We agree we agree. there should be no need to go over this point any longer because we agree.

The point in question is: "if which-path is known or unknown" by what? Measuring devices or conscious observers? What if a measuring device "knows" the which-path information but makes it absolutely impossible for any conscious observers to "know" the which path? Do we get an interference or no?

I am not trying to force my layman opinion on you and I am not quote mining for passages that agree with me. I am sincerely trying to understand the results of these experiments. You seem to be saying that "the observer" need not be a conscious being, but I find that this is inconsistent with the results of these experiments. If unconscious detectors are observers then why does the interference or no interference result depend on whether or not these detectors relay their information to conscious beings? Why is it not the case that if a detector is present and records which-path information, no matter if the which-path information later gets relayed to conscious observers or erased, there will always be no interference pattern as a result of the detector's "observation" alone?

The detectors detecting does not seem to be the cause of the no interference patter result. The cause seems to be whether or not these detectors relay which-path information to conscious observers. You have not addressed why this is so. The question: "If detectors are the observers, why does the interference pattern remain after detectors have "observed" but neglected to relay which-path information to any conscious being?"

If all you do is repeat: "if the which-path is known, no interference; if the which-path is not known, there is interference." Am I allowed to assume that by "known" you mean "known by the experimenters"? It is the experimenters knowledge (even if just in principle, because it is obtainable) of which-path information that results in no interference? If this is what you are saying I agree.
“The Fanatical Atheists are like slaves who are still feeling the weight of their chains which they have thrown off after hard struggle. They are creatures whoâ€"in their grudge against traditional religion as the "opium of the masses"â€"cannot hear the music of other spheres.” - Albert Einstein

Casparov

Quote from: josephpalazzo on May 11, 2014, 08:03:02 AM
I've read that blog and nothing you say is in that blog. You are extracting what you think he should be saying.

He never says, "We should not assume that Realism is true" outright and blatantly like that of course, but this is essentially what he keeps saying over and over. If we assume that Realism is true, then that would mean that the past of this particle would be effected by a decision that is made in it's future. He says, don't assume that Realism is true, we can say nothing about the past of the particle as if it had real properties before the measurement takes place. Assume Realism is true and all kinds of counter-intuitive things seem to be taking place, locality being violated, causality being violated, etc. Refuse to assume that Realism is true and all of these counter-intuitive things are no longer a problem. This is the message of his blog, only without using the actual word "realism."

QuoteI hate to tell you this but you make a poor student. Did I say I have been teaching physics for more than 25 years? In those years I've seen all kinds, bright students, average students, students who didn't belong in my classes. Regrettably you would fail all my courses, not because you're not smart but because you have blinders that prevent you from absorbing the material.

With all due respect, I am not a student who has paid to be taught by you in a classroom setting. I am an equal human being trying to understand very complex ideas that even the experimenters themselves may not understand. I am speaking to you as an equal, yet I am open to learning from you if you have something to teach. If you do not make sense or fail to adhere to the evidence I am not just going to quietly accept that and swallow my tongue because there is no test on monday and you don't get to decide if I pass or fail.

QuoteYou're partly right but you extract the wrong conclusion. Let me give an analogy. Suppose you want to measure the velocity of a car. What you do is take its position versus a clock. You plot that on a graph, draw the best curve, joining all the data, and from there, you can calculate the velocity. There is one assumption that is left out: for you to see the car at different positions, photons had to strike the car, bouncing off  and then reach your eyes (or a detector). Those photons bouncing off the car don't disturb the car - well they do, but the effect is so small, you can safely ignore that effect. However, should you do the same for an electron, the effect of the bouncing photons would have great effect, so much so that any attempt to find the position at any given time is almost an impossible task. That's reality - at subatomic scale, any measurement you are trying to observe affect the system to such an extent that it destroys what you are trying to accomplish - this is something you cannot circumvent. Fortunately, people of great imagination and creativity were able to come up with a theory to deal with those situations, but there is a cost: we can only calculate probabilities, and that theory is quantum mechanics.

Mr. Palazzo, what are you suggesting? Measuring devices interfere with the particle because photons must strike it in order for an observation to be made?

Consider this:

Scenerio #1: Run the Young Double slit experiment with no detector present. Send a single particle towards the slits and it seems to travel through both Slit A and Slit B simultaneously as a wave which interferes with itself and produces the interference pattern at the back slide.

Scenerio #2: Now place a Detector at Slit A which will detect the particle if it goes through Slit A by emitting a photon which must strike the particle in order to detect it. Send a single particle towards the slits and if it goes through Slit B, it was never struck by any photon and the detector at Slit A will not have detected anything, and yet the interference pattern will have disappeared and we will know that the particle travelled through Slit B.

Even though no photon struck the particle, we have extracted which-path information because the detector at Slit A detected nothing, therefore it went through Slit B. The cause of the interference pattern disappearing is that we the experimenters can know the which path information, it has absolutely nothing to do with the measuring device striking the particle with a photon.

QuoteNow that is not the only problem the early pioneers of QM were faced. Another problem was that these objects (photons, electrons, etc) were exhibiting both particle and wave characteristics. Again, QM can handle that, but there is a cost: there are certain properties which are incompatible, meaning: if you know the position of those objects, there is an uncertainty in the momentum, or, if you know one component of the spin, there is an uncertainty in the other components of the spin, and what you get in those experiments we have been talking about- double-slit, delayed choice, quantum eraser - if you know the path, you get no interference, meaning large uncertainties in the momentum.

You speak of The Uncertainty Principle. If you have 100% certainty of it's position you have 0% certainty about it's momentum and vice versa. If you have 100% certainty about it's energy you have only 0% certainty about how long it had or will have that charge for and vice versa. I thought we were having a conversation about what constitutes an "observation" though? I say which path information available to a conscious observer prevents interference patterns, you say it doesn't have to be a conscious observer it could just be an unconscious detector. Why are you teaching me about The Uncertainty Principle all of a sudden?
“The Fanatical Atheists are like slaves who are still feeling the weight of their chains which they have thrown off after hard struggle. They are creatures whoâ€"in their grudge against traditional religion as the "opium of the masses"â€"cannot hear the music of other spheres.” - Albert Einstein

josephpalazzo

#66
Quote from: Casparov on May 12, 2014, 02:59:19 AM

He never says, "We should not assume that Realism is true" outright and blatantly like that of course, but this is essentially what he keeps saying over and over.

Like I said before, that is YOUR interpretation.

QuoteIf we assume that Realism is true, then that would mean that the past of this particle would be effected by a decision that is made in it's future.

Another interpretation not borne by the facts.

QuoteHe says, don't assume that Realism is true, we can say nothing about the past of the particle as if it had real properties before the measurement takes place. Assume Realism is true and all kinds of counter-intuitive things seem to be taking place, locality being violated, causality being violated, etc. Refuse to assume that Realism is true and all of these counter-intuitive things are no longer a problem. This is the message of his blog, only without using the actual word "realism."

Lubos doesn't say any of that stuff, and it is very dishonest on your part to put your "words" into his mouth.



QuoteWith all due respect, I am not a student who has paid to be taught by you in a classroom setting. I am an equal human being trying to understand very complex ideas that even the experimenters themselves may not understand. I am speaking to you as an equal, yet I am open to learning from you if you have something to teach. If you do not make sense or fail to adhere to the evidence I am not just going to quietly accept that and swallow my tongue because there is no test on Monday and you don't get to decide if I pass or fail.

Sorry to rain on your parade, but in matters of physics, you are NOT my equal.


Quote
Mr. Palazzo, what are you suggesting? Measuring devices interfere with the particle because photons must strike it in order for an observation to be made?

Consider this:

Scenerio #1: Run the Young Double slit experiment with no detector present. Send a single particle towards the slits and it seems to travel through both Slit A and Slit B simultaneously as a wave which interferes with itself and produces the interference pattern at the back slide.

Scenerio #2: Now place a Detector at Slit A which will detect the particle if it goes through Slit A by emitting a photon which must strike the particle in order to detect it. Send a single particle towards the slits and if it goes through Slit B, it was never struck by any photon and the detector at Slit A will not have detected anything, and yet the interference pattern will have disappeared and we will know that the particle travelled through Slit B.

Even though no photon struck the particle, we have extracted which-path information because the detector at Slit A detected nothing, therefore it went through Slit B. The cause of the interference pattern disappearing is that we the experimenters can know the which path information, it has absolutely nothing to do with the measuring device striking the particle with a photon.

It doesn't happen this way. When you send single particles, you get single dots on the screen. It's only after there are thousands of these dots that we see the interference pattern. During that process, some of these will pass through slit A where there is a detector, and some will pass though slit B where there is no detector. And QM can describe this very well, and it does that without any of your arguments that you keep repeating which has nothing to do with how QM was built to describe what classical physics had failed to do.

QuoteYou speak of The Uncertainty Principle. If you have 100% certainty of it's position you have 0% certainty about it's momentum and vice versa. If you have 100% certainty about it's energy you have only 0% certainty about how long it had or will have that charge for and vice-versa. I thought we were having a conversation about what constitutes an "observation" though? I say which path information available to a conscious observer prevents interference patterns, you say it doesn't have to be a conscious observer it could just be an unconscious detector. Why are you teaching me about The Uncertainty Principle all of a sudden?

This is another instance that illustrates you don't pay attention to the arguments. In post #28, I wrote about the Heisenberg Uncertainty Principle: "Sorry to disagree, but as I have already stated there is only one conclusion from all DCQE experiments: if you know the which-path there is no interference; if you do not know it, there will be interference. Any contrary result would be an exception to the Heisenberg Uncertainty Principle, and that would be so big, so huge, it would have hit the headlines of all the major papers and that person would be in line for the Nobel.".  All experiment in which you would know the which-path,  there is no interference, and by the HUP, you get large uncertainties in the momentum. The HUP is at the core of QM. As I said before, and repeating what seems to be a million times, as you are very slow to make the connection, there is no exception to the HUP. All of these experiments are confirming the HUP, and by de facto, QM.



Casparov

Quote from: josephpalazzo on May 12, 2014, 08:02:34 AM
It doesn't happen this way. When you send single particles, you get single dots on the screen. It's only after there are thousands of these dots that we see the interference pattern. During that process, some of these will pass through slit A where there is a detector, and some will pass though slit B where there is no detector. And QM can describe this very well, and it does that without any of your arguments that you keep repeating which has nothing to do with how QM was built to describe what classical physics had failed to do.

This is another instance that illustrates you don't pay attention to the arguments. In post #28, I wrote about the Heisenberg Uncertainty Principle: "Sorry to disagree, but as I have already stated there is only one conclusion from all DCQE experiments: if you know the which-path there is no interference; if you do not know it, there will be interference. Any contrary result would be an exception to the Heisenberg Uncertainty Principle, and that would be so big, so huge, it would have hit the headlines of all the major papers and that person would be in line for the Nobel.".  All experiment in which you would know the which-path,  there is no interference, and by the HUP, you get large uncertainties in the momentum. The HUP is at the core of QM. As I said before, and repeating what seems to be a million times, as you are very slow to make the connection, there is no exception to the HUP. All of these experiments are confirming the HUP, and by de facto, QM.

sigh.....


Okay Mr. Palazzo, you win. Realism is entirely compatible with QM, there is undeniable proof that unconscious measuring devices are the irreversible cause of the wave function collapse, whether or not we have which-path information is irrelevant if the detector has already made an "observation", and because of HUB all of this is easily explained and consistent with the world view that we exist in an objective observation independent universe just as described in terms of the Materialism of 19th century Newtonian physics. Naive Realism wins again. Man I'm so dense!

Thanks for all the free lessons on cognitive dissonance and dogmatism. I learned a lot. Cheers!
“The Fanatical Atheists are like slaves who are still feeling the weight of their chains which they have thrown off after hard struggle. They are creatures whoâ€"in their grudge against traditional religion as the "opium of the masses"â€"cannot hear the music of other spheres.” - Albert Einstein

josephpalazzo

Quote from: Casparov on May 13, 2014, 03:17:33 AM
sigh.....


Okay Mr. Palazzo, you win. Realism is entirely compatible with QM, there is undeniable proof that unconscious measuring devices are the irreversible cause of the wave function collapse, whether or not we have which-path information is irrelevant if the detector has already made an "observation", and because of HUB all of this is easily explained and consistent with the world view that we exist in an objective observation independent universe just as described in terms of the Materialism of 19th century Newtonian physics. Naive Realism wins again. Man I'm so dense!

Thanks for all the free lessons on cognitive dissonance and dogmatism. I learned a lot. Cheers!

I know you've written that response with sarcasm, but I'm not here to defend "realism" or any philosophical position. I'm not a philosopher, and don't pretend to be. I believe that many of the pioneers of QM turned themselves into self-proclaimed philosophers and by giving all sorts of interpretations to QM led many future generations down the wrong path. In my study of physics, I have learned to interpret physics as close as possible to what the equations  say, and learn how those equations were derived, including whatever assumptions were put into these derivations.  I cannot put it into simpler language: you can't do physics without a thorough knowledge of math.


Berati

Quote from: josephpalazzo on May 13, 2014, 06:22:19 AM
I know you've written that response with sarcasm, but I'm not here to defend "realism" or any philosophical position. I'm not a philosopher, and don't pretend to be. I believe that many of the pioneers of QM turned themselves into self-proclaimed philosophers and by giving all sorts of interpretations to QM led many future generations down the wrong path. In my study of physics, I have learned to interpret physics as close as possible to what the equations  say, and learn how those equations were derived, including whatever assumptions were put into these derivations.  I cannot put it into simpler language: you can't do physics without a thorough knowledge of math.

Well I for one am glad you took the time to respond as I found your answers very informative. Hopefully we can now leave the religious arguments aside because I have a few questions if you don't mind.

Is it correct to say that photons are always particles (since they make individual dots) and that their final position is determined by whether or not their movement occurs in a wave like fashion? Like water is always particles that sometimes move in a wavelike fashion.
I'm trying to understand the "waveform". If it's a "probability wave" then aren't we always talking about particles?
Carl Sagan
"It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring."

josephpalazzo

Quote from: Berati on May 13, 2014, 08:47:09 AM
Well I for one am glad you took the time to respond as I found your answers very informative. Hopefully we can now leave the religious arguments aside because I have a few questions if you don't mind.

Is it correct to say that photons are always particles (since they make individual dots) and that their final position is determined by whether or not their movement occurs in a wave like fashion? Like water is always particles that sometimes move in a wavelike fashion.
I'm trying to understand the "waveform". If it's a "probability wave" then aren't we always talking about particles?


If it were just particles, then putting a detector at one of the slit in the double-slit experiment should not affect the outcome. But it does, so something else has to happen. Secondly, when we shoot individual photons, one at a time, a particle shouldn't interfere with itself. Yet, we get an interference pattern even in that case. No particle model can describe adequately these observations, and neither a wave model.  In QFT, fields are the basic idea, yet, we must look at an electron as an object surrounded by a cloud of photons or pairs of electron/positrons, some of these interacting with each other, and even interacting with the vacuum. In my latest blog, The Path Integral Simplified], according to Feynman, particles traveling from point A to point B  take an infinite number of paths, and with that idea, you get the same results as in QFT. All in all, there is no simple answer to the particle/wave duality. We are dealing with microscopic objects that have no analogy to our macroscopic world.

Hijiri Byakuren

Quote from: Casparov on May 13, 2014, 03:17:33 AM
sigh.....


Okay Mr. Palazzo, you win. Realism is entirely compatible with QM, there is undeniable proof that unconscious measuring devices are the irreversible cause of the wave function collapse, whether or not we have which-path information is irrelevant if the detector has already made an "observation", and because of HUB all of this is easily explained and consistent with the world view that we exist in an objective observation independent universe just as described in terms of the Materialism of 19th century Newtonian physics. Naive Realism wins again. Man I'm so dense!

Thanks for all the free lessons on cognitive dissonance and dogmatism. I learned a lot. Cheers!
https://www.youtube.com/watch?v=4bijbF3gkNk
Black lives matter, feminism is good, religion is bullshit, and if you disagree with me on any of these points you are a fucking moron.

Sargon The Grape - My Youtube Channel

Berati

#73
Quote from: josephpalazzo on May 13, 2014, 09:23:01 AM
If it were just particles, then putting a detector at one of the slit in the double-slit experiment should not affect the outcome. But it does, so something else has to happen. Secondly, when we shoot individual photons, one at a time, a particle shouldn't interfere with itself. Yet, we get an interference pattern even in that case.
I've seen video's of water waves passing through two slits and forming interference patterns. I always thought that this was because the waves are propagating through a medium (water in this case) and that the medium is particles of water. The interference is that of peaks and troughs of the (water) particles affecting each other. Not sure if this is 100% correct from the view of physics.

The problem with photons (it seems to me) is that there appears to be no medium for the waves to be propagating through and this is especially true if there is only one particle at a time being fired through the slits. How could something interfere with itself? as you pointed out.

QuoteNo particle model can describe adequately these observations, and neither a wave model.  In QFT, fields are the basic idea, yet, we must look at an electron as an object surrounded by a cloud of photons or pairs of electron/positrons, some of these interacting with each other, and even interacting with the vacuum. In my latest blog, The Path Integral Simplified], according to Feynman, particles traveling from point A to point B  take an infinite number of paths, and with that idea, you get the same results as in QFT. All in all, there is no simple answer to the particle/wave duality. We are dealing with microscopic objects that have no analogy to our macroscopic world.

I had a crazy thought while watching Neil DeGrasse Tyson give a talk on relativity and I might as well ask you here. I'm probably not the first to consider this and I'm probably missing something important, but here it goes anyway.

Dr. Tyson made the point that a photon doesn't experience time from it's point of view because it travels at the speed of light. If photons don't experience time, why should it be considered odd that it could interfere with itself if time is not an issue for it?
Is it possible that the photons interfere with their timeless selves when left alone (they are their own medium), but experience time whenever a measurement of their actual position is made, thus preventing them from interfering with themselves?

Sorry if it's a silly question.





Carl Sagan
"It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring."

Berati

Carl Sagan
"It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring."