Interferometers and Superposition

[Dalo]

Just now, swansont said:

I am telling you that you are wrong. A general representation of an interferometer is not going to be a "which path" experiment. You are wrong to assume that it is.

Presenting misinformation and holding a misconception certainly can't help with that.

But they were using a which-path experimental setup, and not a "simple" MZI which you claimed gives no interference pattern.

Let us try and clear up any misunderstanding. Which drawings are you considering as not which-path experiments, and therefore not relevant to the discussion of the pdf file you suggested. What makes them not acceptable for the discussion at hand.

[studiot]

Personally I blame the Kellog brothers and their sunshine breakfast for the confustion.

I mean, depicting that Sun with all those rays coming off!

Well!

 

The lines or rays that are drawn are not the paths of light waves.

They are geometrical lines drawn for mathematical construction purposes.

In particular they are drawn perpendicular to wavefronts, which therefore exist in dimensions perpendicular to those rays.

 

Edited December 15, 2017 by studiot

[Dalo]

1 hour ago, swansont said:

Interferometers and which-path experiments are not synonymous.

This seems quite obvious to me. It wouldn't help to use a Michelson interferometer to discuss of the role of observation in an experiment. But the MZI is used in trying to determine how finding out through which path photons are passing can create ambiguity as to where they came from

I agree with you that it is not a matter of interference pattern disappearing but of which-path information. That is exactly what I was discussing in the first posts when dealing with Scariani.

Concerning the pdf file you suggested, the trouble I have is to relate it to the first part of the thread, dealing with Scariani. I have not in any way drawn any conclusion regarding the relationship between interference patterns and which-path information. All I have been doing is trying to clarify the meaning of the drawings used in the pdf file, and the explanations of the authors.

I therefore do not understand why you are objecting to my analysis at this stage. I have not expressed any opinion yet about the pdf file

If you do not agree with my analysis of Scariani's own presentation, then you should make that explicit, and distinct from the second part concerning the pdf file.

[swansont]

1 hour ago, Dalo said:

Let us try and clear up any misunderstanding. Which drawings are you considering as not which-path experiments,

There is only one which-path experimental setup you have posted. The actual diagram from the lab report. Fig1, unedited.

The setup from the book is just an interferometer, as is your simplified drawing.

1 hour ago, Dalo said:

and therefore not relevant to the discussion of the pdf file you suggested. What makes them not acceptable for the discussion at hand.

I'm not saying they are unacceptable or irrelevant, but you can't misrepresent them and what you can learn from them.

28 minutes ago, Dalo said:

This seems quite obvious to me. It wouldn't help to use a Michelson interferometer to discuss of the role of observation in an experiment. But the MZI is used in trying to determine how finding out through which path photons are passing can create ambiguity as to where they came from

The MZI is used, but the polarizers play a critical role in this. Without the polarizers (your simplified drawing) you can't determine which path the photons took. Your "simplified MZI" is not a which-path device.

 

28 minutes ago, Dalo said:

I agree with you that it is not a matter of interference pattern disappearing but of which-path information. That is exactly what I was discussing in the first posts when dealing with Scariani.

The figure from Scariani does not show a which-path configuration.

so when you say

"Look at Fig. 1.3. Where would we place detectors to determine the path each particle has taken? Well, without even looking at the detectors, we know that we will be unable to determine the path taken to RT or TR, just as we have no way of knowing if the photon would have hit TT or RR.
Fig. 1.3 is therefore inherently ambiguous."

the conclusion is bogus. It's not a which-path setup, so it should come as no surprise that you can't use it as such. It is not ambiguous. It's like having a phillips head screwdriver for a slotted screw. Wrong tool configuration. 

28 minutes ago, Dalo said:

Concerning the pdf file you suggested, the trouble I have is to relate it to the first part of the thread, dealing with Scariani. I have not in any way drawn any conclusion regarding the relationship between interference patterns and which-path information. All I have been doing is trying to clarify the meaning of the drawings used in the pdf file, and the explanations of the authors.

You are comparing two different things. Maybe your focus should be on understanding the difference, rather than forging ahead when you don't really know what you are talking about.

28 minutes ago, Dalo said:

I therefore do not understand why you are objecting to my analysis at this stage. I have not expressed any opinion yet about the pdf file

Sure you did. You claimed that there would be no interference pattern based on a drawing from the pdf that you modified.

28 minutes ago, Dalo said:

If you do not agree with my analysis of Scariani's own presentation, then you should make that explicit, and distinct from the second part concerning the pdf file.

I have done so. I have pointed out that Scariani's drawing is of an interferometer, not a which-path experiment, and you should not be making any claims about which-path information based on that drawing. That is true independent of the pdf.

[Dalo]

9 minutes ago, swansont said:

There is only one which-path experimental setup you have posted. The actual diagram from the lab report. Fig1, unedited.

The setup from the book is just an interferometer, as is your simplified drawing.

I'm not saying they are unacceptable or irrelevant, but you can't misrepresent them and what you can learn from them.

I will wait until you answer my last post. Because I still have no idea what you mean exactly. Please be precise:  "only one which-path...." is not helping me any. I still do not know what is wrong with with I have presented because you have not said anything except damning the whole thread.

 

Edited December 15, 2017 by Dalo

[swansont]

Just now, Dalo said:

I will wait until you answer my last post. Because I still have no idea what you mean exactly. Please be precise:  "only one which-path...." is not helping me any.

The unmodified MZI form the pdf (labeled fig 1) is the ONLY schematic presented thus far that will give which-path information.

Scariani's drawing (fig 1.3), and your "simplified" MZI are just interferometers. They are not "which path" experimental layouts.

[Dalo]

Just now, swansont said:

The unmodified MZI form the pdf (labeled fig 1) is the ONLY schematic presented thus far that will give which-path information.

Scariani's drawing (fig 1.3), and your "simplified" MZI are just interferometers. They are not "which path" experimental layouts.

repeating the same thing over and over again does not make anything clearer. What is wrong with the drawings? Specifically.

[Mordred]

He is explaining the correct meaning of those drawings. Which he is forced by you to repeat, by your not continuing to listen.

 

[Dalo]

I am listening all right. But he is not saying anything except that it is not a which-path experiment, talking about Scarani: which is flagrantly false. Maybe he should read the book and find out.

For the pdf file, I am supposed to have done everything wrong, but what exactly?

I can do nothing with this kind of criticism. You are welcome to be more specific.

[Mordred]

That article is very easy to understand. I'm positive Swansont has read it. So have I and we both agree your interpretation is wrong. In one case there is no "self interference" in the other case there is. Try to read the book and identify which case is which. The book is very clear on this.

Edited December 15, 2017 by Mordred

[Dalo]

Just now, Mordred said:

That article is very easy to understand. I'm positive Swansont has read it. So have I and we both agree your interpretation is wrong.

Fine. Now, tell me why.

[Mordred]

It will have to be after work, unless someone else has time before then. However the clue is "What happens when you polarize light"

Edited December 15, 2017 by Mordred

[swansont]

4 minutes ago, Dalo said:

repeating the same thing over and over again does not make anything clearer. What is wrong with the drawings? Specifically.

You keep asking the same thing.

The polarizers allow one to possibly determine which path. (It's why the polarizer that's added or removed has an effect)

[studiot]

4 minutes ago, swansont said:

You keep asking the same thing.

 

It's called the broken record technique.

[Dalo]

2 hours ago, swansont said:

I am telling you that you are wrong. A general representation of an interferometer is not going to be a "which path" experiment. You are wrong to assume that it is.

Presenting misinformation and holding a misconception certainly can't help with that.

But they were using a which-path experimental setup, and not a "simple" MZI which you claimed gives no interference pattern.

You have convinced me that you have not read Scariani. His main argument, which by the way you would subscribe to because it is the orthodox Bohrian interpretation, is that knowing the path (isn't that what which-path information is about?) changes the percentages of photons detected by the different detectors. 

 

******************************************************

The pdf file can be summarized as follows:

Which-path information preserved - no polarizer - no interference pattern

Which-path information destroyed -    polarizer -    interference pattern

The important question in the interpretation of Fig.5 of the pdf file, is how the interference patterns are related to the which-path information. The quote of p.6 might contain the answer. Here it is again:

"We observed that without a polarizer no interference pattern was observed because light exiting the interferometer contained which-path information."

If we look at the the second simplified drawing, the one with no polarizer, we immediately understand the meaning of this assertion.
The polarizing beam splitter divides the photons in two groups, one is vertically polarized, the other horizontally. In other words, even though no human could distinguish between them, the information is there. In principle, and in a very abstract way, we could know of each photon, whether it is vertically or horizontally polarized. And that in itself would be, according to the authors, sufficient to destroy the interference patterns.

When using an extra polarizer at the end of the MZI, we scramble the information contained in each photon in the form of vertical or horizontal polarization. All photons acquire the same polarization before hitting the screen and being registered by the camera. They become therefore indistinguishable from each other, and there is no way anymore of knowing through which path they reached the screen. Which means that the interference patterns are present.

The question now is, what is the value of this argumentation?

edit: here is another quote that confirms my analysis.

"As long as no polarizer is present the path that a photon took is encoded into its polarization state. Thus, it is not free to take both paths and cannot interfere with itself. As soon as another polarizer is introduced at the exit of the system, the information about which path the photon took is destroyed because it has a new polarization." p.4

 

Edited December 15, 2017 by Dalo

[swansont]

26 minutes ago, Dalo said:

You have convinced me that you have not read Scariani.

No, I haven't, and never claimed to. But then, that's not supposed to be a requirement for participation in the discussion.

26 minutes ago, Dalo said:

His main argument, which by the way you would subscribe to because it is the orthodox Bohrian interpretation, is that knowing the path (isn't that what which-path information is about?) changes the percentages of photons detected by the different detectors. 

At this point I don't trust that any of your interpretations are correct, because some of the basic information you have presented is incorrect.

26 minutes ago, Dalo said:

******************************************************

The pdf file can be summarized as follows:

Which-path information preserved - no polarizer - no interference pattern

Which-path information destroyed -    polarizer -    interference pattern

The important question in the interpretation of Fig.5 of the pdf file, is how the interference patterns are related to the which-path information. The quote of p.6 might contain the answer. Here it is again:

"We observed that without a polarizer no interference pattern was observed because light exiting the interferometer contained which-path information."

If we look at the the second simplified drawing, the one with no polarizer, we immediately understand the meaning of this assertion.
The polarizing beam splitter divides the photons in two groups, one is vertically polarized, the other horizontally. In other words, even though no human could distinguish between them, the information is there. In principle, and in a very abstract way, we could know of each photon, whether it is vertically or horizontally polarized. And that in itself would be, according to the authors, sufficient to destroy the interference patterns.

Yes. Not particularly abstract, though.

26 minutes ago, Dalo said:

When using an extra polarizer at the end of the MZI, we scramble the information contained in each photon in the form of vertical or horizontal polarization. All photons acquire the same polarization before hitting the screen and being registered by the camera. They become therefore indistinguishable from each other, and there is no way anymore of knowing through which path they reached the screen. Which means that the interference patterns are present.

The question now is, what is the value of this argumentation?

It answers your inquiry about whether someone has done a "which-path" experiment.

[Dalo]

31 minutes ago, swansont said:

No, I haven't, and never claimed to. But then, that's not supposed to be a requirement for participation in the discussion.

It is if you insist that his drawing does not represent a which-path experiment while he explicitly states that knowing which path the photon has taken changes the outcome of an experiment.

 

31 minutes ago, swansont said:

At this point I don't trust that any of your interpretations are correct, because some of the basic information you have presented is incorrect.

you have not yet given me a single reason to take your objection seriously.

 

31 minutes ago, swansont said:

It answers your inquiry about whether someone has done a "which-path" experiment.

Scariani does the same, but instead of using interference patterns and polarization, he uses percentages. There are many forms of MZI's, and many forms of which-path experiments. Apparently you have fixated on the form given by the pdf file and refuse to acknowledge any alternative given by other authors.

Here are some quotes from Scariani:

"Interference appears when a particle can take several paths in order to
arrive at the same detector, and the paths are indistinguishable after
detection."

Let’s put the principle to work on the phenomena we have already
described. In apparatus 1 and 2, there is only one path leading to
each detector; consequently, when a particle is detected we know
exactly which path it must have taken. It is a situation of distinguishability and no interference effect is apparent.

In apparatus 3 and 4, on the other hand, when a particle is detected after the second beam splitter, we have no way of knowing by which path it arrived, since two paths are possible. These two paths are therefore indistinguishable, and the effects of interference are present."  p.10-11

Edited December 15, 2017 by Dalo

[swansont]

31 minutes ago, Dalo said:

It is if you insist that his drawing does not represent a which-path experiment while he explicitly states that knowing which path the photon has taken changes the outcome of an experiment.

Both of those statements are true. Knowing the path changes the outcome, and the device depicted does not allow you to know which path is taken.

Quote

you have not yet given me a single reason to take your objection seriously.

You can lead a horse to water...

Quote

Scariani does the same, but instead of using interference patterns and polarization, he uses percentages. There are many forms of MZI's, and many forms of which-path experiments. Apparently you have fixated on the form given by the pdf file and refuse to acknowledge any alternative given by other authors.

You haven't presented any alternatives. You were the one who wasn't sure such experiments existed, remember?

I'm "fixated" on one because it was the first one I found, and it's usually a disaster when you start discussing variants on an experiment, since the different versions get mixed up. (much the same as you are peobably "fixated" on Scariani, i.e. you aren't, but that's a book you have available and there's no point in finding another reference with some superficial differences that have no effect on the concepts)

[Dalo]

57 minutes ago, swansont said:

I'm "fixated" on one because it was the first one I found, and it's usually a disaster when you start discussing variants on an experiment, since the different versions get mixed up. 

Yes, I can understand that. I also prefer to stick to one path. That is why I did not want to discuss MZI's  in the other thread, and preferred to stick to double slit experiments.

In this case though, both versions were completely separate. You started denying that Scariani was talking about which-path experiments right away. And you refused to bulge from your position. I hope it is behind us now.

 

************************************************************

In the case of the use of an extra polarizer the whole set up becomes equivalent to a much simpler one: one light source, a polarizer, and then a screen + camera. We can leave out all the rest, that is, the polarizing and non-polarizing beam splitters, and the two mirrors.

There would be then no which-path information involved, simply because there is for all practical purposes only one path. But since there is no ambiguity as to where the photons came from, there should be no interference patterns present. And still there is.
One way that we could explain the difference between the complex and simple form is accepting the mystical idea that the photons somehow know where they are coming from and choose not to interfere with each other, as they would if we used the simpler form, or the other form with no extra polarizer.

It would be interesting to see if the simpler form would be equivalent to the first (no extra polarizer) or the other  setup (an extra polarizer).

If it gives a similar result to the second form, then we will know for sure that it is not the presence or absence of which-path information that determines the presence or absence of interference patterns.
The only factor then eligible for a rational explanation would be the presence or absence of an extra polarizer.

If my analysis is correct, then so is my claim that there is no superposition of particles, and that observation does not change the outcome of an experiment. Which also means that particles do not change their behavior unless there is an external cause, in this case a polarizer in the path of the beam.
 

Edited December 15, 2017 by Dalo

[swansont]

2 hours ago, Dalo said:

You have convinced me that you have not read Scariani. His main argument, which by the way you would subscribe to because it is the orthodox Bohrian interpretation, is that knowing the path (isn't that what which-path information is about?) changes the percentages of photons detected by the different detectors. 

Bohrian?

[Dalo]

Just now, swansont said:

Bohrian?

Should it be Bohrean? Anyway, Niels Bohr.

[swansont]

54 minutes ago, Dalo said:

You started denying that Scariani was talking about which-path experiments right away.

Stop already. I never said anything about what Scarani was talking about. All I said was that the figure you posted from the book does not depict a which-path experiment.

54 minutes ago, Dalo said:

And you refused to bulge from your position. I hope it is behind us now.

I am not going to "budge" when this is simply a straw-man argument. 

59 minutes ago, Dalo said:

 

In the case of the use of an extra polarizer the whole set up becomes equivalent to a much simpler one: one light source, a polarizer, and then a screen + camera. We can leave out all the rest, that is, the polarizing and  non-polarizing beam splitters, and the two mirrors.

How would one observe interference with this device? if there is no possibility of interference, then this is not equivalent.

59 minutes ago, Dalo said:

There would be then no which-path information involved, simply because there is for all practical purposes only one path. But since there is no ambiguity as to where the photons came from, there should be no interference patterns present. And still there is.

Where is the interference pattern? Give a reference to the experiment where interference is observed with that configuration.

 

[Dalo]

1 hour ago, Dalo said:

If my analysis is correct, then so is my claim that there is no superposition of particles, and that observation does not change the outcome of an experiment. Which also means that particles do not change their behavior unless there is an external cause, in this case a polarizer in the path of the beam.

In case my edit goes unnoticed

********************************

I find it interesting that in the case of Scariani's experiments, the external factor that could rationally explain the different percentages was the difference in length of the two main paths, while in this second case, it is the presence, or absence, of a polarizing filter.

In both cases, an external factor can be put forward to explain the change of behavior of the photons.

A model I can certainly live with, even though I have no idea how both factors work.

Edited December 15, 2017 by Dalo

[swansont]

2 hours ago, Dalo said:

 Here are some quotes from Scariani:

"Interference appears when a particle can take several paths in order to
arrive at the same detector, and the paths are indistinguishable after
detection."

Let’s put the principle to work on the phenomena we have already
described. In apparatus 1 and 2, there is only one path leading to
each detector; consequently, when a particle is detected we know
exactly which path it must have taken. It is a situation of distinguishability and no interference effect is apparent.

In apparatus 3 and 4, on the other hand, when a particle is detected after the second beam splitter, we have no way of knowing by which path it arrived, since two paths are possible. These two paths are therefore indistinguishable, and the effects of interference are present."  p.10-11

You are citing 4 devices. Are these the 4 you have presented? Because the first two are not interferometers (fig 1.1 and 1.2), in which case they are moot. The author points out that there is no interference.

If 3 and 4 represent 1.3 and 1.4, they are interferometers, and the author has declared that they are not which-path devices (and where have we heard that before?)

[Dalo]

2 hours ago, swansont said:

The author points out that there is no interference.

 

2 hours ago, swansont said:

You are citing 4 devices. Are these the 4 you have presented? Because the first two are not interferometers (fig 1.1 and 1.2), in which case they are moot. The author points out that there is no interference.

If 3 and 4 represent 1.3 and 1.4, they are interferometers, and the author has declared that they are not which-path devices (and where have we heard that before?)

Only Fig.1.3 and Fig.1.4 represent MZI's. The others are there to explain why the results given by the two MZI's are strange and need explanation. They build up the case as it were.

Where did the author say that they are not which-path devices?

edit: if you do not trust the quotes I am giving of the text, then it will remain a difficult discussion. Maybe you should check it for yourself.

"how does it work, that in changing
only one of the two paths, we manage to change the behaviour of
all of the particles? How is it that the particles that travel by the
path that we have not modified can know about the modification?" p.9

I do not know how many quotes will convince you, so let me say it plainly and then you can decide for yourself:

Fig1.3 and 1.4 represent MZI's, and which-path devices. The whole set up of the book is to show the effect of which-path information on the results of the experiments done with those two devices. Scarani is trying to prove that the photons somehow know which path they have taken and behave accordingly. An explanation that all supporters of orthodox quantum theory support.

So either you accept that and look at my own analysis to criticize it, or you keep doubting what the author is saying and with whom I expect that you will be in complete agreement.

Please read at least the first 15 pages of the book and form your own opinion on whether I have presented the author's views correctly, and whether you agree with him. Then you can look at my own analysis and present valid arguments why you do not agree with me.

I have until now only defended the author with whom, and I cannot stress it enough, I expect you will be in perfect accordance!

Edited December 15, 2017 by Dalo