Brian Green's Beam Splitter Experiments

[selfAdjoint]

Hi mf, Yes I see the asymmetry argument but I still don't see the how Cramerite satz works in the asymmetric case. Originally the retarded quantum waves went into the future, and the advanced waves went into the past, and both were reflected by the supposed abosrbers, handwavingly (as far as I ever saw) identified with the big bang and the big crunch. Then the relected waves interfered, and here he did calculations in the simple cases at least to show that the famous quantum behavior resulted. But if there is no reflection for the retarded waves how does this work?

As far as "explaining reality" goes, I am of two minds currently. One is that quantum mechanics was never built for that purpose, it's complete in itself but it is a machine that gives accounts of behavior, not explanations, and to attempt to use it for that incorrect purpose results in science-fiction - Cramer's time travel or Everett's multiple universes.

My other mind leads me to look into the combination of decoherence and relational quantum mechanics, to see how much can be retrieved there. Decoherence can explain how the classical world automatically results from the quantum world, but it doesn't address the measurement problem. RQM is one way of addressing the measurement problem, but it seems to me very much a work in progress at this point. I don't really like Consistent Histories because it seems to be just SUAC in disguise.

 

[Farsight]

Thanks for that rather sad feedback, selfAdjoint. Could you recommend any papers/links on Aspect or EPR explaining why classical and hidden variables must be eliminated?

moving finger: I tried combining D1 and D2 via manual dotting and got myself a mess - there's a displacement that I missed. Maybe I'll try printing two copies and sticking through the top one with a pin. I have to say I don't like the sound of throwing away data points.

 

[selfAdjoint]

Thanks for that rather sad feedback, selfAdjoint. Could you recommend any papers/links on Aspect or EPR explaining why classical and hidden variables must be eliminated?

I don't think you can go wrong with https://www.amazon.com/gp/product/0521523389/?tag=pfamazon01-20 by Bell and Aspect themselves. It's a collection of papers at different levels of technical difficulty, including some that require no math at all (though they all require you to keep your wits carefully about you as if your were solving a difficult puzzle!).

Currently my favorite hard-nosed popular account of the issues with quantum mechanics is Where Does the Weirdness Go? by David Lindley, which I excerpted a biut earlier in this thread.

 

[physicsmasta]

I too read the book in question. But the answer to that question has evaded me also. I would love to if you find out anything surrounding the book.

 

[physicsmasta]

I just read, "Beyond the Quantum" and in it it suggest that light particles have mass and all we have to do measure speed, position and force simutamelously is to measure the mass of light in the presence of gravity on earth. Do you believe this would work please reply!

 

[Reagle]

I have read through this thread and I would respectfully like to verify a few conclusions I have reached regarding the whole

"delayed choice quantum eraser"

phenomenon.

My questions relate to Yoon-Ho Kim, R. Yu, S.P. Kulik, and Y.H. Shih fairly famous paper calledhttp://xxx.lanl.gov/PS_cache/quant-ph/pdf/9903/9903047.pdf"

As noted in this thread this paper is the subject of comments made by Ross Rhoades in his http://www.bottomlayer.com/bottom/ki...scully-web.htm" at Wikipeadia.

Here are my conclusions about this paper:

1.

It makes no difference what is at D3.

If the idler photon was sent to D3, and D3 had been a coffee cup (instead of a detector), then the interference pattern would be still destroyed.

2. If conclusion 1 is true then the interference pattern at DO is dependent on the existance of which path information, even if which path information is impossible to recover (such as a photon hitting a coffee cup at D3).

3. If conclusion 1 and 2 are true then a lot of people like to make overreaching assumptions about this paper, leading to unsupportable conclusions. Especially people like the producers of the "[MEDIA=youtube[/URL]. These people are interpreting the interference effect as being determined by "what an observer knows", when it really has nothing to do with an observer at all and only has to do with the existence, or non existence, of which path information.

Am I right or wrong regarding these 3 observations?

 

[selfAdjoint]

Here are my conclusions about this paper:

1.
Quote:
It makes no difference what is at D3.

If the idler photon was sent to D3, and D3 had been a coffee cup (instead of a detector), then the interference pattern would be still destroyed.

2. If conclusion 1 is true then the interference pattern at DO is dependent on the existence of which path information, even if which path information is impossible to recover (such as a photon hitting a coffee cup at D3).

3. If conclusion 1 and 2 are true then a lot of people like to make overreaching assumptions about this paper, leading to unsupportable conclusions. Especially people like the producers of the "What the bleep clip here", and even Ross Rhoades in this video. These people are interpreting the interference effect as being determined by "what an observer knows", when it really has nothing to do with an observer at all and only has to do with the existence, or non existence, of which path information.

Am I right or wrong regarding these 3 observations?

Sure looks right to me. "What the bleep.." is a notoriouus new age commercial that has been complained about by just about every physicst with a blog. Would that newspaper journalists would pick up on that.

And yes a whole lot of people have egg on their faces, not just mystigogical cranks.

In my mind (and here I am treading on sacred professional ground) is that the whole personalizing thing in QM (as in using "observation" instead of "interaction" to describe whatever it is that generates real number observable values) should be abandoned. It was introduced by Bohr who was a famous mutterer and "guru" to three generations of physicsists including some of the great ones, but it's time to see it for what it is, a crutch, and a broken one that is droppiing us on our keisters at that.

 

[Hurkyl]

Maybe you've figured this out already, but this is something that wasn't clear to me when I was trying to figure out the delayed choice eraser experiment.

If you're just looking at D0, there is no interference pattern. The "interference pattern" only surfaces when split all the photons striking D0 into two groups, each group corresponding to having its pair strike D3 or D4.

 

[moving finger]

Thanks for that rather sad feedback, selfAdjoint. Could you recommend any papers/links on Aspect or EPR explaining why classical and hidden variables must be eliminated?

moving finger: I tried combining D1 and D2 via manual dotting and got myself a mess - there's a displacement that I missed. Maybe I'll try printing two copies and sticking through the top one with a pin. I have to say I don't like the sound of throwing away data points.

isn't that what destructive interference is all about? take two waves 180 degrees out of phase, and you end up with no wave.

the whole experiment is about throwing away (or deleting) information - delete the "which way" information (by randomising with a beamsplitter) and you see the interference - but retain the information and you don't see the interference. It just seems to me that the phase shift between the D1 and D2 data is just enough so that when combined these two signals destructively interfere. Is that significant, or irrelevant?

Best Regards

 

[Reagle]

Thank you selfAdjoint, for your feedback. I had an unresolved question in my mind regarding this paper. So let me respectfully ask one more question:

Q) The whole point of Yoon-Ho Kim, R. Yu, S.P. Kulik, and Y.H. Shih's fairly famous paper calledhttp://xxx.lanl.gov/PS_cache/quant-ph/pdf/9903/9903047.pdf"
is that the position of the signal photon impact on detector D0 is belatedly dependent on if the idler photon goes to D3 (which establishes which path information) or goes to either D0 or D1 (which erases which path information).
This is a pretty standard delayed quantum eraser setup with entangled pairs.

But in my simple mind this is totally impossible, since once the location of the D0 signal photon impact has been recorded, it can not change.

What am I missing here?

 

[moving finger]

Hi mf, Yes I see the asymmetry argument but I still don't see the how Cramerite satz works in the asymmetric case. Originally the retarded quantum waves went into the future, and the advanced waves went into the past, and both were reflected by the supposed abosrbers, handwavingly (as far as I ever saw) identified with the big bang and the big crunch. Then the relected waves interfered, and here he did calculations in the simple cases at least to show that the famous quantum behavior resulted. But if there is no reflection for the retarded waves how does this work?

I agree it seems like handwaving. As far as I can see Cramer is suggesting the advanced waves get reflected at T0, and thereby constructively interfere with retarded waves (see figure 2 in his paper attached to this post as a GIF file – I can’t explain it any better than he shows it in his figures).

This explains why we see retarded waves. That there is no future singularity then (according to Cramer) means that there is no future point of reflection, hence why we see asymmetry (we see waves going from past to future, but not from future to past). In other words, an ever-expanding universe with no future singularity (rather than being a problem because of future transparency and hence lack of absorbers) is actually necessary for the emergence of the electromagnetic arrow of time.

As far as "explaining reality" goes, I am of two minds currently. One is that quantum mechanics was never built for that purpose, it's complete in itself but it is a machine that gives accounts of behavior, not explanations, and to attempt to use it for that incorrect purpose results in science-fiction - Cramer's time travel or Everett's multiple universes.

OK, I can go along with this as far as it goes – this is the Shut Up & Calculate approach. But to me not a very useful philosophy.

My other mind leads me to look into the combination of decoherence and relational quantum mechanics, to see how much can be retrieved there. Decoherence can explain how the classical world automatically results from the quantum world, but it doesn't address the measurement problem.

Neither, it seems to me, does it address the delayed choice problem.

RQM is one way of addressing the measurement problem, but it seems to me very much a work in progress at this point. I don't really like Consistent Histories because it seems to be just SUAC in disguise.

I’m not familiar with RQM – does this address the delayed choice problem?

Currently my favorite hard-nosed popular account of the issues with quantum mechanics is Where Does the Weirdness Go? by David Lindley, which I excerpted a biut earlier in this thread.

Yes, this is a good book – from memory though doesn’t it say “decoherence is the answer”? How does decoherence address the delayed choice issue?

I just read, "Beyond the Quantum" and in it it suggest that light particles have mass and all we have to do measure speed, position and force simutamelously is to measure the mass of light in the presence of gravity on earth. Do you believe this would work please reply!

Light does have a “mass-equivalent” in the sense of E=mc^2 where E = hf in the case of light (f = frequency), but light does not have rest mass. Is this what you mean?

1. It makes no difference what is at D3.

If the idler photon was sent to D3, and D3 had been a coffee cup (instead of a detector), then the interference pattern would be still destroyed.

Agreed. That’s an important point (but we would have no way of detecting and displaying that destroyed pattern any more, because we’ve now lost our detector and substituted a cup of coffee instead).

2. If conclusion 1 is true then the interference pattern at DO is dependent on the existence of which path information, even if which path information is impossible to recover (such as a photon hitting a coffee cup at D3).

The interference pattern is not “at D0”, it is in the coincidence between detections at D0 and D1 (or D0 and D2). There is no interference pattern in the D0 data alone. But the detections at D0, D1 and D2 do not contain any which-path information – this information is only in the coincidence between detections at D0, D3 and D4 (which do not show interference fringes). If we replace D3 / D4 with a cup of coffee then we cannot recover any coincidence detections between these cups of coffee and D0, hence the which path information would be lost. But the interference at D0/D1 and D0/D2 would still exist. The presence of interference fringes at D0/D1 and D0/D2 has nothing whatsoever to do with what happens at D3 and D4 – different idler (and signal) photons are involved.

If you're just looking at D0, there is no interference pattern. The "interference pattern" only surfaces when split all the photons striking D0 into two groups, each group corresponding to having its pair strike D3 or D4.

That’s correct.

For each signal photon hitting D0, there is an idler photon which either goes to D1, D2, D3 or D4. The interference fringes emerge only when we look at the coincidence detections between D0 and D1, or between D0 and D2. The which way information only emerges when we look at the coincidence detections between D0 and D3, or between D0 and D4.

Q) The whole point of Yoon-Ho Kim, R. Yu, S.P. Kulik, and Y.H. Shih's fairly famous paper called "A Delayed Choice Quantum Eraser"
is that the position of the signal photon impact on detector D0 is belatedly dependent on if the idler photon goes to D3 (which establishes which path information) or goes to either D0 or D1 (which erases which path information).

This is a pretty standard delayed quantum eraser setup with entangled pairs.

But in my simple mind this is totally impossible, since once the location of the D0 signal photon impact has been recorded, it can not change.

Imho your “simple mind” interpretation is correct – this is impossible. I do not believe we can understand what is going on by saying the position on D0 is “belatedly dependent” on what happens later at D1, D2, D3 or D4. In terms of temporal sequence, the signal photon hits D0 BEFORE the idler photon has “decided” whether to go for D1, D2, D3 or D4. Whatever happens to that idler cannot (imho) then retrospectively cause the detection position on D0 to change – EXCEPT in the Transactional Interpretation sense that an advanced wave may be sent out by D1/2/3/4 which (travelling backwards in time) somehow then “causes” the signal photon to land at a certain point on D0.

It seems to me that the only way to explain what is going on is either that there is some backwards-in-time correlation between entangled states, or that the world is super-deterministic via hidden variables (whatever it is that causes the signal photon to land at a particular position on D0 also cause the twin idler to hit either D1/2/3 or 4).

If anyone has another explanation I’m all ears….

Best Regards

Below for selfAdjoint is attached figure 2 from Cramer's paper on The Arrow of Electromagnetic Time and Generalized Absorber Theory, showing advanced wave reflection at the T0 singularity. The caption to this figure is :

Figure 2: Minkowski diagram showing an open-ended emission transaction. The conventions used here are the same as those used in Fig. 1. The advanced waves propagate backward in time to the T=0 origin, where they are subject to a reflection boundary condition. The reflected wave arising from the boundary condition cancels the advanced wave up to the emission event, and at times after emission it reinforces the retarded wave from the emitter.

 

[selfAdjoint]

Hi mf, Yes I see the asymmetry argument but I still don't see the how Cramerite satz works in the asymmetric case. Originally the retarded quantum waves went into the future, and the advanced waves went into the past, and both were reflected by the supposed abosrbers, handwavingly (as far as I ever saw) identified with the big bang and the big crunch. Then the relected waves interfered, and here he did calculations in the simple cases at least to show that the famous quantum behavior resulted. But if there is no reflection for the retarded waves how does this work?

I agree it seems like handwaving. As far as I can see Cramer is suggesting the advanced waves get reflected at T0, and thereby constructively interfere with retarded waves (see figure 2 in his paper attached to this post as a GIF file – I can’t explain it any better than he shows it in his figures).

This explains why we see retarded waves. That there is no future singularity then (according to Cramer) means that there is no future point of reflection, hence why we see asymmetry (we see waves going from past to future, but not from future to past). In other words, an ever-expanding universe with no future singularity (rather than being a problem because of future transparency and hence lack of absorbers) is actually necessary for the emergence of the electromagnetic arrow of time.

And does Cramer have a detailed account of his approach dealing with the delayed choice quantum eraser?

As far as "explaining reality" goes, I am of two minds currently. One is that quantum mechanics was never built for that purpose, it's complete in itself but it is a machine that gives accounts of behavior, not explanations, and to attempt to use it for that incorrect purpose results in science-fiction - Cramer's time travel or Everett's multiple universes.

OK, I can go along with this as far as it goes – this is the Shut Up & Calculate approach. But to me not a very useful philosophy.

You and vanesch both complain about that. Who says nature has to be fully explained in 2006? What justification does "needing a useful philosophy" give for forcing the QM formalism into doing things it was never intended to?

My other mind leads me to look into the combination of decoherence and relational quantum mechanics, to see how much can be retrieved there. Decoherence can explain how the classical world automatically results from the quantum world, but it doesn't address the measurement problem.

Neither, it seems to me, does it address the delayed choice problem.

Since I think the delayed choice quantum eraser (DCQE) is a sub-problem of the measurement problem (being a combination of double slit with entanglement), it would follow that decoherence doesn't address this. Decoherence is not a complete explanation for quantum effects but a useful part of any complete explanation.

RQM is one way of addressing the measurement problem, but it seems to me very much a work in progress at this point. I don't really like Consistent Histories because it seems to be just SUAC in disguise.

I’m not familiar with RQM – does this address the delayed choice problem?

On the Beyond the Standard Model board, vanesch and I have discussed a paper detailing the RQM account of the entanglement problem. I am sure they can do double slit too, so it seems to me that if someone wanted to work it out, they could do DCQE as well. The basic principle is that quantum systems are only real in the process of interaction; that's where their observables take on real number values. And each interacting system sees the other's values relative to itself. This gets into the point that the photon doesn't have any spacetime real position between interactions, hence asking "which path did it go down" is a meaningless noise.

Currently my favorite hard-nosed popular account of the issues with quantum mechanics is Where Does the Weirdness Go? by David Lindley, which I excerpted a biut earlier in this thread.

Yes, this is a good book – from memory though doesn’t it say “decoherence is the answer”? How does decoherence address the delayed choice issue?

Lindley likes decoherence and uses it to show that some old chestnuts like Schroedinger's cat and whether the moon is there when nobody is looking are bunk. He doesn't use it for the quantum eraser. For his account of that see the long excerpts I copied earlier in this thread. His explanation there is basically what you might call "highly motivated SUAC" One possible caveat; I think Lindley's discussion is pre-delayed choice, but I don't think that changes the argument much.

 

[jjalexand]

Alternate Universes interpretation

I'm a non-physicist, but it seems to me that making an observation could be seen as akin to locking oneself into a sub-set or an otherwise larger set of previously possible universes. I.e., by making an observation (or even by having been able to make that observation perhaps) the observer becomes "racheted-in" to a new smaller (but diverging?) subset of alternate universes?

In other words, all possible universes co-exist but you chose to increment your path through them every time you make an observation.

Alternatively you could be seen as being in the middle of a small personal subset that swung in a different direction every time your attention focussed on something! :)

 

[Cane_Toad]

I'm still trying to get a handle on this sort of thing. My 2 cents worth:

It is a serious mistake to take the descriptions given by quantum functions literally. Quantum theory describes *HOW* things work, not *WHY*. When people start adding *WHY* they are engaging in philosophical speculation. As far as I know, the why of the quantum world is still unknown.

Popular science writers have been doing a disservice to the field by selling their books based on the sensationalist views of the various "whys", i.e. many universes, human conscious interaction with wave collapse, etc., which are all great fun to think about, but are meaningless in the scientific sense of testability The process of trying to understand the "why" of quantum mechanics by the experts, which can be fantastical, has been translated to the public (often) without the realistic counter-point that these are only attempts at putting a framework around all the odd mathematical behavior.

So with the interference experiment, you can choose to *believe* that the experimenter's knowledge of an event affects correlated/entangled/etc. events. You can also choose to believe anything you want, but that's not science. Again, the mistake is to confuse a mathematical description of a behavior with reality.

People will always gravitate towards the mysterious, and promoting a book, paper, theory, etc. based on this, is taking advantage of non-experts who don't have the background frame their own skepticism (even if the author *believes* it him/herself).

My guess is that some day if we ever do understand what is going on at the sub-atomic level (my use of "why" above), we will find that quantum/string/brane/etc theories were good *models* of the physical world, but flawed in the long run just as Newton/Einstein/etc. have broken down at deeper/lower levels.

As one who once thought quantum mechanics was connecting the spiritual to the physical world, I have been (contentedly) disillusioned since then. It was akin to the disappointment/fascination at discovering that Santa Claus was really daddy in a red suit. The problem is that quantum theory is a much more difficult puzzle than Santa Claus.

Anyway, that's my world view, though I'm always ready to change it (via the school of hard [mental] knocks :-)

 

[MojaveJoe]

3. If conclusion 1 and 2 are true then a lot of people like to make overreaching assumptions about this paper, leading to unsupportable conclusions. Especially people like the producers of the "[MEDIA=youtube[/URL]. These people are interpreting the interference effect as being determined by "what an observer knows", when it really has nothing to do with an observer at all and only has to do with the existence, or non existence, of which path information.[/QUOTE]

That sounds good, but only if you don't think about it too closely. What is which path information? It is when the data has "meaning" aka...knowledge. There are plenty of points in the experiment where the data has no meaning and we see the interference pattern...it is only when we are able to analyze the data and arrive at a conclusion about the data that the pattern changes.

It was posited earlier in the thread that software that could "analyze" the which path data without any human interaction would also destroy the interference pattern. Even if this is the case, it seems to me that we still have a hugely significant problem in that knowledge (whether using a human mind or a "pseudo" mind like a computer) would appear to have an effect on our physical universe.

Edit:
Something similar to an artifact is what I initially thought was happening in these experiments...and I still think something similar to this is happening. However, I don't see how this can be the case at least looking at the initial Scully and Druhl experiments (which is where I got this question from originally). This is a quote from wikipedia as I don't have the book in front of me:

[Quote=wikipedia]In the double-slit experiment, the common wisdom is that the Heisenberg Uncertainty Principle makes it impossible to determine which slit the photon passes through without at the same time disturbing it enough to destroy the interference pattern. However, in 1982, Scully and Druhl found a way around the position-momentum uncertainty obstacle and proposed a quantum eraser to obtain which-path or particle-like information without introducing large uncontrolled phase factors to disturb the interference. They found that the interference pattern disappears when which-path information is obtained, even if this information was obtained [B]without directly observing[/B] the original photon. Even more surprising was that, if you somehow "erase" the which-path information, the interference pattern reappears! And, perhaps most provocative of all, you can delay the "choice" to "erase" or "observe" the which-path information and still restore the interference pattern, even after the original photon has been "observed" at the primary detector!
[/Quote]

As a non-physicist (wish I had made some different choices at university - granted I'd properly be a lot poorer!) I can imagine that these experiments are exceedingly delicate - we are dealing with virtually massless particles after all, and it seems to me that an artifact is very possible. But that is simply not what the experiment says...the experiment says otherwise.

[Quote=selfAdjoint]Sure looks right to me. "What the bleep.." is a notoriouus new age commercial that has been complained about by just about every physicst with a blog. Would that newspaper journalists would pick up on that.

And yes a whole lot of people have egg on their faces, not just mystigogical cranks.
[/Quote]

I'm at work so I cannot look at those "commercials". However, it seems to me that a physicist who posits an esoteric theory and then faces some (probably not all unjustified!) criticism in an attempt find an answer to this quandry is not entirely unadmirable.

Edit#2: Provided they understand the data and don't knowingly misrepresent it of course!

Cheers!

 

[MojaveJoe]

Popular science writers have been doing a disservice to the field by selling their books based on the sensationalist views of the various "whys", i.e. many universes, human conscious interaction with wave collapse, etc., which are all great fun to think about, but are meaningless in the scientific sense of testability The process of trying to understand the "why" of quantum mechanics by the experts, which can be fantastical, has been translated to the public (often) without the realistic counter-point that these are only attempts at putting a framework around all the odd mathematical behavior.

I disagree with this as far as it pertains to Brian Greene's book Fabric of the Cosmos. Mr. Greene made no claims about the original question in the book, it was simply my own thought derived from his explanation of the Scully/Druhl's experiments. It was a rather obvious thought to be honest and I simply asked for some clarification. Whether Mr. Greene agrees/disagrees with this position is never clarified - indeed that's why I came to this board to ask!

Cheers!

 

[Cane_Toad]

I disagree with this as far as it pertains to Brian Greene's book Fabric of the Cosmos. Mr. Greene made no claims about the original question in the book, it was simply my own thought derived from his explanation of the Scully/Druhl's experiments. It was a rather obvious thought to be honest and I simply asked for some clarification. Whether Mr. Greene agrees/disagrees with this position is never clarified - indeed that's why I came to this board to ask!

Cheers!

Interesting. Does he put forth any ramifications?


Also, in trying to understand this experiment, I'm wondering why there was any surprise when they found that getting which-path information killed the interference pattern ... after all, they were measuring an entangled photon, whose function interacts with the other photon. It was already known that measurements, by definition in the small world, affect the item measured, and thus break the interference pattern experiments.

It seems like the Scully/Druhl was a *failed* attempt to get information without interacting. They simply found that you can't cheat by using entangled photons. It isn't presented that way though.

Now, if somebody would just explain what the hell entangled photons are, I'd be happy. They imply that at the quantum level, distance is meaningless, and the only thing that holds up the universe is that God continues to care to throw the dice (i.e. nothing is real but probability functions). It does bring to mind the idea of these entangled photons being a single N-dimensional object projected into 3D space. Is this discussed somewhere?

 

[Cane_Toad]

Another question...

In that silly cartoon link posted earlier, it explained the experiment using electrons instead of photons, and using some (what?) kind of detector in the path of the electron before the double slit. I can only guess that it must measure some wiggle in the field of a passing electron, since the electron isn't consumed?

Anyway, if this is true (and the cartoon isn't completely bogus), then I have no clue when a probability function becomes un-collapsed(term??) for something. It suggests that any material close enough to the path of the electron would collapse it, acting like the detector. When the electron is first emitted, it is immediately in the vacinity of the emitter and other surrounding EMF. Why isn't its probability function collapsed just after it starts moving?

When does the electron regain its un-collapsed state? Presumably when it enters a shell in an atom, but why? What's special about that? Is an atom a probability generator? Has anybody tried to un-collapse anything?

 

[MojaveJoe]

Interesting. Does he put forth any ramifications?

Nope, its pretty much a survey book. He's partial to certain theories (like String) and does try to give attention to possible theories where they are noteworthy...he didn't give any attention to this particular theory though - maybe he didn't think it noteworthy.

Also, in trying to understand this experiment, I'm wondering why there was any surprise when they found that getting which-path information killed the interference pattern ... after all, they were measuring an entangled photon, whose function interacts with the other photon. It was already known that measurements, by definition in the small world, affect the item measured, and thus break the interference pattern experiments.

I would imagine the surprise comes because it was assumed that there is some "unknown" physical interaction (see the wikipedia quote I included) on the part of the observer and this experiment made that position very difficult to maintain. Indeed, if you leave out a physical interaction the only explanation of what is causing the wave to collapse is the knowledge of the which-path which is the question of this thread.

It seems like the Scully/Druhl was a *failed* attempt to get information without interacting. They simply found that you can't cheat by using entangled photons. It isn't presented that way though.

Yup. Cheaters never prosper

The nature of that interaction is the $64,000 question.

Cheers!

 

[MojaveJoe]

Another question...

In that silly cartoon link posted earlier, it explained the experiment using electrons instead of photons, and using some (what?) kind of detector in the path of the electron before the double slit. I can only guess that it must measure some wiggle in the field of a passing electron, since the electron isn't consumed?

Anyway, if this is true (and the cartoon isn't completely bogus), then I have no clue when a probability function becomes un-collapsed(term??) for something. It suggests that any material close enough to the path of the electron would collapse it, acting like the detector. When the electron is first emitted, it is immediately in the vacinity of the emitter and other surrounding EMF. Why isn't its probability function collapsed just after it starts moving?

When does the electron regain its un-collapsed state? Presumably when it enters a shell in an atom, but why? What's special about that? Is an atom a probability generator? Has anybody tried to un-collapse anything?

I think it may not be a good idea to think of "collapse" or "uncollapse" as pertaining to an individual electron cloud but rather look at it as a large collection of particles and their distribution on a detector screen. Collapse would be seen simply as the disappearance of an interference pattern (wavelike behavior) on the detection screen and the appearance of a standard curve (particle behavior). Uncollapse would be the opposite - and in fact does happen...that's the eraser part of the experiment.

Cheers!

 

[selfAdjoint]

I'm at work so I cannot look at those "commercials". However, it seems to me that a physicist who posits an esoteric theory and then faces some (probably not all unjustified!) criticism in an attempt find an answer to this quandry is not entirely unadmirable.

Edit#2: Provided they understand the data and don't knowingly misrepresent it of course!

"What the bleep" was not produced by any kind of physicists; it is the product of a community of disciples of some "ascended master" and the quantum statements in it are new age pap. One physicist who was interviewed protested this on camera, but his protests were cut from the distributed film.

 

[MojaveJoe]

"What the bleep" was not produced by any kind of physicists; it is the product of a community of disciples of some "ascended master" and the quantum statements in it are new age pap. One physicist who was interviewed protested this on camera, but his protests were cut from the distributed film.

Ascended masters

Sounds pretty terrible. I think the idea is to posit as many non-metaphysical theories as possible because how the heck can you test anything else?

Cheers!

Edit: Your point about non-starter theories earlier in the thread strikes me as pretty important.

 

[Reagle]

Originally Posted by Reagle

1. It makes no difference what is at D3.

If the idler photon was sent to D3, and D3 had been a coffee cup (instead of a detector), then the interference pattern would be still destroyed.

Reply by Moving Finger

Agreed. That’s an important point (but we would have no way of detecting and displaying that destroyed pattern any more, because we’ve now lost our detector and substituted a cup of coffee instead).

Reply by Reagle

I don't find it so easy to understand what the author’s mean by "joint detection counting rates". Here is a quote for http://qopt.phys.msu.su/kulik/Papers/p1_1.pdf" on the subject.

It is easy to see that
these “joint detection” events must have resulted from the
same photon pair. It is predicted that the joint detection
counting rate R01 (joint detection rate between D0 and D1)
and R02 would show an interference pattern as a function
of D0’s position on its x axis. This reflects the wave
nature (both-path) of photon 1. However, no interference
fringes would be observed in the joint detection counting
events R03 and R04 during the same scan of detector D0
along its x axis. This is as would be expected because
we have now inferred the particle (which-path) property
of photon 1. It is important to emphasize that all four
joint detection rates R01, R02, R03, and R04 are recorded
at the same time during one scanning of D0. That is, in
the present experiment we “see” both wave (interference)
and which-path (particle like) with the same measurement
apparatus.
Different from

I thought the only thing that mattered, since the photon has traveled through a double slit, was that the position of arrival of the photon at D0 thus determining if the location coincides to an interference pattern.

Could someone who understands please explain what the "joint detection counting rates" are.

Thanks!
Reagle


http://qopt.phys.msu.su/kulik/Papers/p1_1.pdf"

 

[Farsight]

I don't know if it's relevant, but if you print two copies of page 10, figures 3 and 4 tally better if you turn one page over. They appear to be mirror images of one another. Then if you cut out figure 4 and align it carefully over figure 3, the peaks fill the troughs.

http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm

Selfadjoint, thanks for the info re:

Speakable and Unspeakable in Quantum Mechanics by Bell and Aspect and
Where Does the Weirdness Go? by David Lindley.

Much appreciated.

 

[selfAdjoint]

I don't know if it's relevant, but if you print two copies of page 10, figures 3 and 4 tally better if you turn one page over. They appear to be mirror images of one another. Then if you cut out figure 4 and align it carefully over figure 3, the peaks fill the troughs.

http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm

Selfadjoint, thanks for the info re:

Speakable and Unspeakable in Quantum Mechanics by Bell and Aspect and
Where Does the Weirdness Go? by David Lindley.

Much appreciated.

You're very welcome, and thank YOU for the suggestion re the diagram. Anything we can do to make this experiment as clear as possible will help everybody.

 

[MojaveJoe]

On the Beyond the Standard Model board, vanesch and I have discussed a paper detailing the RQM account of the entanglement problem. I am sure they can do double slit too, so it seems to me that if someone wanted to work it out, they could do DCQE as well. The basic principle is that quantum systems are only real in the process of interaction; that's where their observables take on real number values. And each interacting system sees the other's values relative to itself. This gets into the point that the photon doesn't have any spacetime real position between interactions, hence asking "which path did it go down" is a meaningless noise.

I guess this bothers me because isn't quantum theory supposed to explain the universe on a micro level? It seems to me that this is simply saying Quantum Theory is useless.

Cheers!

 

[MeJennifer]

I guess this bothers me because isn't quantum theory supposed to explain the universe on a micro level? It seems to me that this is simply saying Quantum Theory is useless.

Well a theory is supposed to give calculable results that are in accordance with experiments.

 

[Farsight]

Isn't that why we're all here? Because "Quantum Theory" predicts things correctly, but doesn't really explain what's going on under the covers in terms that the layman can understand?

 

[selfAdjoint]

Well a theory is supposed to give calculable results that are in accordance with experiments.

Exactly. In all the history of 20th century particle physics, people again and again started out hoping the latest thing "explained reality" and were disillusioned in one way or the other. But the ability to predict what experiments would see just got better and better. This is not lost on the physicists, hence the popularity of "SUAC".

Sometimes I wonder if all this marvelous ability to predict counterintuitive behavior rationally(as in this experiment!) is a sign of a deeper level of causality, and what we are seeing is the behavior of that level, which is counterintuitive but has these rational patterns to it. But what that deeper level might be like hasn't showed up yet. We do know (if the Aspect and other entanglement experiments hold up - again including this one) is that it isn't a naive classical theory. You have to break classicality some way or other to get the result to behave like QM. 't Hooft for example is experimenting with a huge gauge group; he puts Hamiltonian mechanics through that and comes out with something that behaves like quantum mechanics. But he can't do fermions, and hasn't calculated beyond the simplest behavior. There are other workers in this field, including of course all those QG people, who are starting to get to "coupling matter", which means deriving QM from their various ansatzen.

 

[selfAdjoint]

I just had a thought. Vanesch, in a post on another thread you said that Aspect-type tests of quantum entanglement had some irreducible uncertainty because detectors with fast enought switching time did not exist.

Isn't the DCQE interpretable as a test of quantum entanglement? And doesn't it get around the switching time problem?

 

[Farsight]

I bumped into this post from vanesch, third one down. Maybe it's relevant. Calling vanesch!

https://www.physicsforums.com/archive/index.php/t-59501.html

"Although it is a nice experiment and so on, I think it is a bit "oversold". You can give it the interpretation given by the authors if you want to, but in fact, something much simpler is going on. When you look at figure 3, you get an interference pattern, because you SELECT A SUBSAMPLE from all impacts at D0, which are coincident with a hit at D1. When you look at ANOTHER SUBSAMPLE, namely the impacts at D0 which are coincident with D2 (figure 4) you get a shifted interference pattern. This shift comes about, if you trace it back, to a difference in optical pathlengths in the polarizing beamsplitter, and this shift is utterly important..."

 

[moving finger]

And does Cramer have a detailed account of his approach dealing with the delayed choice quantum eraser?

I’ve not seen any. Applying the Transactional Interpretation (TI) to entangled entities such as the signal & idler photon would entail that advanced waves for both the signal & idler are sent back in time (the advanced wave for the signal from D0, and for the idler from either D1, D2, D3 or D4), these two advanced waves then arriving at the “source” at the same point in time (I guess this is a problem for the TI – how do two initially uncorrelated advanced waves arrange to travel back in time and arrive at the source at the same moment?). If this problem can be overcome, then the advanced waves “explain” how the signal photon “knows in advance where to land” on D0.

You and vanesch both complain about that. Who says nature has to be fully explained in 2006? What justification does "needing a useful philosophy" give for forcing the QM formalism into doing things it was never intended to?

I’m not suggesting forcing the QM formalism into doing any kind of things it was never intended to do - I’m interested in trying to find out what meaning, if any, lies behind the empirical data from quantum mechanics experiments, and whether we can understand more about what is really going on than what the QM formalism is currently telling us. The Copenhagen approach is great – for physicists. It’s not so very useful for most philosophers.

On the Beyond the Standard Model board, vanesch and I have discussed a paper detailing the RQM account of the entanglement problem. I am sure they can do double slit too, so it seems to me that if someone wanted to work it out, they could do DCQE as well. The basic principle is that quantum systems are only real in the process of interaction; that's where their observables take on real number values. And each interacting system sees the other's values relative to itself. This gets into the point that the photon doesn't have any spacetime real position between interactions, hence asking "which path did it go down" is a meaningless noise.

I disagree. Asking “which path did it go down” has meaning if and only if one measures which path it goes down – as the DCQE itself demonstrates. This fits with your description of RQM – that quantum systems are real only in the process of interaction. In other words – whether a quantum entity is manifest as a wave or a particle depends on how you measure it.

Could someone who understands please explain what the "joint detection counting rates" are.

For any given entangled (signal plus idler) state, both “parts” of that state leave the source (the slit) at the same time. We know the distances to the various detectors, therefore for any signal photon detected at D0, we can calculate the exact time that its partner idle photon should reach each of D1, D2, D3 and D4. But that particular idler only reaches one of these detectors – therefore by “looking” for an idler arriving at either of D1, D2 D3 or D4 at just the right time (the effective coincidence time as calculated from D0) we can determine which detector (either D1, D2, D3 or D4) the idler photon went to.

Repeat the above for each entangled pair leaving the source – that way we build up a correlation of signal photons at D0 (with x-position information) with corresponding idler photons at either D1, D2, D3 or D4.

Sometimes I wonder if all this marvelous ability to predict counterintuitive behavior rationally(as in this experiment!) is a sign of a deeper level of causality, and what we are seeing is the behavior of that level, which is counterintuitive but has these rational patterns to it.

I like it! Sounds like super-determinism to me (but I’m not sure I agree it’s counterintuitive). Having been forced (thank you, selfAdjoint) to think about Cramer’s TI in more detail and especially to think about its application to entangled states, I’m leaning more towards hidden variables and the world being super-deterministic. It seems to me that this is the only way to explain the temporal sequence of how the signal photon in the DCQE “knows where to land” on detector D0, in advance of the idler photons “deciding which detector to go to” – the information telling the signal and idler where to go is already built-in at the start..

As far as I can see, no other “interpretation” can coherently “explain” the temporally asymmetric information inherent in the DCQE experiment.

Best Regards

 

[moving finger]

I bumped into this post from vanesch, third one down. Maybe it's relevant. Calling vanesch!

https://www.physicsforums.com/archive...p/t-59501.html

"Although it is a nice experiment and so on, I think it is a bit "oversold". You can give it the interpretation given by the authors if you want to, but in fact, something much simpler is going on. When you look at figure 3, you get an interference pattern, because you SELECT A SUBSAMPLE from all impacts at D0, which are coincident with a hit at D1. When you look at ANOTHER SUBSAMPLE, namely the impacts at D0 which are coincident with D2 (figure 4) you get a shifted interference pattern. This shift comes about, if you trace it back, to a difference in optical pathlengths in the polarizing beamsplitter, and this shift is utterly important..."

Agreed. Which is why I asked earlier in the thread what happens if one adds together the D1 and D2 data, and is this important?

Vanesch’s observation, however, does not explain what is going on. He claims that “something much simpler is going on”, but does not go on to explain exactly what is going on, or how the signal photon at D0 “knows” exactly where to land (the D0 data is spatial) in advance of the idler photon arriving at either of D1, D2, D3 or D4.

The phase shift is due to differences in optical path lengths, yes, but that does not explain why there is an interference pattern in the first place. It also does not explain why we see no interference pattern at all in the D3, D4 data.

If the idler (after the signal has landed on D0) goes to either D3 or D4 then there is no interference pattern observed in the coincidence data; whereas if the idler (after the signal has landed on D0) goes to either D1 or D2 then there is an interference pattern observed in the coincidence data. The interference pattern is encoded within the spatial distribution of the D0 data – ie where the signal photon lands on D0.

Since the interference pattern depends on the spatial information encoded within D0, and “idler arriving at D1 or D2” entails that there be an interference pattern, whereas “idler arriving at D3 or D4” entails no interference pattern, and the signal photon arrives at D0 BEFORE the idler “chooses” which detector to go to, how does the signal photon know exactly where it is to land on D0?

As selfAdjoint has pointed out, the QM formalism tells us how to calculate the numbers in a self-consistent fashion, but it seems that is all that the QM formalism can do for us – it does not provide any insight into what is “really happening” in this experiment. As far as I can see, nobody has so far come up with a coherent interpretation of what is going on which explains the time-dependence of the process.

Best Regards

 

[cesiumfrog]

Does anyone know of any similar experiment, except where the experimenter can actively choose whether or not to erase, and where (if the information is erased) the interference fringes are immediately observable without examining correlations?

I guess I'm basically wondering if there exist conditions where it would seem as though the choice could be delayed until after observation of whether interference occured.

In the paper referenced above, even if the first beamsplitters are replaced with mirrors (to always erase the which-path information), the aggregate data from the scanning detector (D0) would still appear featureless (until time-correlated with either D1 or D2). Can the phase difference between R01 and R02 be removed with a different experimental layout?

 

[gptejms]

I started two threads 'Prob. density in spacetime' and 'Earlier or later' in 2004 which I think are relevant to the present discussion.I suggest that you all read these and let me have your comments.The links are:-

https://www.physicsforums.com/showthread.php?t=45264
https://www.physicsforums.com/showthread.php?t=45267

 

[moving finger]

I started two threads 'Prob. density in spacetime' and 'Earlier or later' in 2004 which I think are relevant to the present discussion.I suggest that you all read these and let me have your comments.The links are:-

https://www.physicsforums.com/showthread.php?t=45264
https://www.physicsforums.com/showthread.php?t=45267

sorry, both these threads seem unreadable - is anyone else having the same problem?

Best Regards

 

[Brinx]

Yup, the first part of those threads look messy, like they use some script that isn't supported by the site anymore.

But anyway, I was also struggling with the matter of the delayed-choice quantum eraser after having read http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm . In particular, if the setup described on that page would be changed by firing, say, a thousand photons from the laser of which the signal photons would all be detected before any of the idler photons arrived at the other detector. Suppose the 'far' detector used for detecting the idler photons can be any of two detectors, namely one which does detect which-path information and one which doesn't.

Further, suppose the person controlling that far-away detector position was given the choice to install one of those two detectors after the time the thousand signal photons were registered, but before the idler photons would arrive at his location. No FTL communication would be necessary to enable the person manning the far-away detector station to know when the signal photons are registered in this setup of course, this way of working could have been planned in advance. As the fate of the idler photons is unknown (whether they will have their which-path information extracted or not, in other words) at the time of detection of all signal photons, I'm not sure what pattern will be visible at the signal photon detection screen. Either all the idler photons will have their which-path information determined (in which case the signal photon detector screen would have to show no interference pattern but instead a classical lumped distribution), or they will all be detected without their which-path information being known, in which case the signal photons should show an interference pattern - if my reasoning is correct.

The problem with this situation is that the person observing the signal photon detector after all signal photons are registered would know in advance which type of detector the person manning the far-away detector is going to choose! This sounds quite bizarre to me as it implies sending information back in time, but I can't find out where the fault lies within this line of reasoning.

 

[cesiumfrog]

... if the setup described on that page would be changed by firing, say, a thousand photons from the laser of which the signal photons would all be detected before any of the idler photons arrived at the other detector.

I don't think that change would work, because (see the PRL paper for some detail) the pattern only exists in the part of the signal data coincident with D1 or D2 (singularly):

If you're just looking at D0, there is no interference pattern

Nonetheless, this seems almost like some mere artifact of the final beamsplitter. Perhaps I can propose a different variation (entanglement + Wheeler's delayed choice):

Let the thousand entangled photons be produced (by pumping through a double slit, as in this DCQE experiment). Let all the signal photons be (almost immediately) observed on a nearby screen (or the scanning D0). Let all the idler photons propogate some (much greater) distance, to where an observer is located. The observer either places a screen in the path of all the idler photons (in which case, "surely" an interference pattern *will* be seen in the raw data, at both individual ends of the apparatus), or alternatively, the observer instead places a telescope focussed on just one of the slits (in which case "surely" potential time correlation would expose the which-path information for each photon, so there should be no reason to expect interference in the signal data).

Can this signal data reveal what choice the idler observer is going to make?

 

[Brinx]

Cesiumfrog, your suggestion sounds the same as mine did to me - although your description of the actual detectors used is more accurate. The question you pose is the one I was also wondering about, in any case. :)

 

[gptejms]

sorry, both these threads seem unreadable - is anyone else having the same problem?

Yep,the threads seem unreadable--may be you could try reading s.p.r. if you are a member.

 

[moving finger]

But anyway, I was also struggling with the matter of the delayed-choice quantum eraser after having read http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm . In particular, if the setup described on that page would be changed by firing, say, a thousand photons from the laser of which the signal photons would all be detected before any of the idler photons arrived at the other detector. Suppose the 'far' detector used for detecting the idler photons can be any of two detectors, namely one which does detect which-path information and one which doesn't.

Which other one or two detectors are you talking about here? There are 4 in the paper... D1, D2, D3 and D4. It's not clear which ones you intend to keep and which ones throw away.

Best Regards

 

[moving finger]

I need some help please.

In the commentary paper http://www.bottomlayer.com/bottom/ki...scully-web.htm it says :

Without more, we would expect the pattern developing at detector D0 to be an interference pattern. QM predicts that without which-path information, photons arriving from either A or B should interfere and distribute themselves one-by-one according to the statistical distribution of interfering waves.

In other words, it actually says that in absence of which path information, the pattern of signal photons at D0 should be an interference pattern. But we can get that pattern simply by removing mirrors BSB and BSA (remove these mirrors, and all idlers go to D1 or D2 via BS, hence no which path information).

But the original paper at http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9903/9903047.pdf also made it clear that the raw data at D0 does not contain any interference pattern, because the interference patterns from D1 and D2 are 180 degrees out of phase - thus we will only see the pattern when we deconvolve the D0 signal data by correlating it with the idler coincidence data. This 180 degree phase shift is not referred to at all in the commentary paper at http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm.

If we remove BSB and BSA, do we see interference at D0 even without coincidence correlations with D1 and D2? If not, why not?

Am I missing something here?

Best Regards

 

[Brinx]

Moving finger, I proposed to place only one detector in the path of the idler photons instead of the more complex setup used in the paper - namely either a detector which does not read which-path information (such as a lens with a screen behind it, similar to the detector for the signal photons in the paper setup), or a detector which does read which-path information (such as the telescope detector Cesiumfrog suggested).

I should make a sketch to clear things up. I'll do so later on.

 

[moving finger]

Moving finger, I proposed to place only one detector in the path of the idler photons instead of the more complex setup used in the paper - namely either a detector which does not read which-path information (such as a lens with a screen behind it, similar to the detector for the signal photons in the paper setup), or a detector which does read which-path information (such as the telescope detector Cesiumfrog suggested).

I should make a sketch to clear things up. I'll do so later on.

OK, my problem (see my last post above) is that the original paper points out that there is a 180 degree phase shift between the D1 and D2 interference data, which means (I believe) that the raw D0 data (ie the data you want to use) will show no interference at all - I don't understand this and need someone to explain what is going on!

Best Regards

 

[gptejms]

OK, my problem (see my last post above) is that the original paper points out that there is a 180 degree phase shift between the D1 and D2 interference data, which means (I believe) that the raw D0 data (ie the data you want to use) will show no interference at all - I don't understand this and need someone to explain what is going on!

Best Regards

I've just had a quick look at the paper.The paper discusses this point(see page 3 of the paper).The culprit seems to be the beam splitter BS-- reflected and transmitted waves have a phase difference.

 

[moving finger]

I've just had a quick look at the paper.The paper discusses this point(see page 3 of the paper).The culprit seems to be the beam splitter BS-- reflected and transmitted waves have a phase difference.

Yes, I know the original paper discusses this point :

http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9903/9903047.pdf

But the explanation paper does not :

http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm

My questions are :

The explanation paper says that :

QM predicts that without which-path information, photons arriving from either A or B should interfere and distribute themselves one-by-one according to the statistical distribution of interfering waves.

But this is obviously not true, since the pattern at D0 is a combination of the two interference patterns which are 180 degrees phase-shifted, so the "raw data" hitting D0 (in absence of any coincidence correlations with the other detectors) shows NO interference pattern.

If the phase shift is due to the beamsplitter BS, what happens if we remove BS - does the raw data at D0 suddenly show an interference pattern?

If the beamsplitter at BS causes a 180 degree phase shift between transmitted & reflected photons, then 50% of all photons reaching D1 and 50% of all photons reaching D2 should be phase-shifted relative to the other 50% - because half of all photons reach each detector are transmitted and half are reflected! Thus the explanation for the phase shift between D1 and D2 data cannot be due to phase shift diferences between reflection and transmission.

Best Regards

 

[gptejms]

But this is obviously not true, since the pattern at D0 is a combination of the two interference patterns which are 180 degrees phase-shifted, so the "raw data" hitting D0 (in absence of any coincidence correlations with the other detectors) shows NO interference pattern.

The joint detections D0,D1 or D0,D2 show intereference patterns--that is the only claim in either of the papers.Besides,I don't see how the phase shift is 180 degrees--seems to be 90 degrees to me(one term contains cos,the other sin).

If the beamsplitter at BS causes a 180 degree phase shift between transmitted & reflected photons, then 50% of all photons reaching D1 and 50% of all photons reaching D2 should be phase-shifted relative to the other 50% - because half of all photons reach each detector are transmitted and half are reflected! Thus the explanation for the phase shift between D1 and D2 data cannot be due to phase shift diferences between reflection and transmission.

Best Regards

I don't really know how a beam splitter works,but the situation may not be the same on either side of the beam splitter.Imagine the following situation:-reflection coeff. R,transmission coeff. 1-R on one side; reflection coeff. -R,transmission coeff. 1+R on the other side.If you work with this, you get the signs as in the paper.

 

[gptejms]

But this is obviously not true, since the pattern at D0 is a combination of the two interference patterns which are 180 degrees phase-shifted, so the "raw data" hitting D0 (in absence of any coincidence correlations with the other detectors) shows NO interference pattern.

The joint detections D0,D1 or D0,D2 show intereference patterns--that is the only claim in either of the papers.Besides,I don't see how the phase shift is 180 degrees--seems to be 90 degrees to me(one term contains cos,the other sin).

If the beamsplitter at BS causes a 180 degree phase shift between transmitted & reflected photons, then 50% of all photons reaching D1 and 50% of all photons reaching D2 should be phase-shifted relative to the other 50% - because half of all photons reach each detector are transmitted and half are reflected! Thus the explanation for the phase shift between D1 and D2 data cannot be due to phase shift diferences between reflection and transmission.

Best Regards

I don't really know how a beam splitter works,but the situation may not be the same on both sides of the beam splitter.Imagine the following situation:-reflection coeff. R,transmission coeff. 1-R on one side; reflection coeff. -R,transmission coeff. 1+R on the other side.If you work with this, you get the signs as in the paper.

 

[moving finger]

The joint detections D0,D1 or D0,D2 show intereference patterns--that is the only claim in either of the papers.Besides,I don't see how the phase shift is 180 degrees--seems to be 90 degrees to me(one term contains cos,the other sin).

The original paper (page 3) clearly says Pi radians phase-shift - that's 180 degrees. A 180 degree phase shift would mean complete loss of fringes (destructive interference) when the data are superimposed - which explains why there is no structure in the D0 data alone. A 90 degree phase shift would not lead to complete loss of interference fringes when you superimpose the data.

I don't really know how a beam splitter works,but the situation may not be the same on both sides of the beam splitter.Imagine the following situation:-reflection coeff. R,transmission coeff. 1-R on one side; reflection coeff. -R,transmission coeff. 1+R on the other side.If you work with this, you get the signs as in the paper.

OK, thanks for that

Best Regards

 

[gptejms]

The original paper (page 3) clearly says Pi radians phase-shift - that's 180 degrees. A 180 degree phase shift would mean complete loss of fringes (destructive interference) when the data are superimposed - which explains why there is no structure in the D0 data alone. A 90 degree phase shift would not lead to complete loss of interference fringes when you superimpose the data.


OK, thanks for that

Best Regards

Right you are--the phase difference is 180 degrees because of the terms being cos^2 and sin^2(not cos &. sin),but D0 data still has a sinc^2.Anyway,the claim in the paper(s) is about D0,D1 or D0,D2--so what's the problem?