DCQE - how does/can the pattern change?

[San K]

Cthugha's analysis is clearly correct at least about one thing.
Postselection by coincidence counter has a key role in appearance of interference pattern.

That can be easily seen if you replace polarizer in idler beam with polarization beam splitter. Then you will have fringe and antifringe pattern at the same time just by looking at coincidences between signaling detector and one of the two detector at different outputs of PBS.

Ah...this explains it well...good one

 

[unusualname]

Cthugha's analysis is clearly correct at least about one thing.
Postselection by coincidence counter has a key role in appearance of interference pattern.

That can be easily seen if you replace polarizer in idler beam with polarization beam splitter. Then you will have fringe and antifringe pattern at the same time just by looking at coincidences between signaling detector and one of the two detector at different outputs of PBS.

Ah...this explains it well...good one

Yes he's correct in that one thing.

 

[SpectraCat]

what do you mean by "generated" above? did you mean filtered?

because the s-photon position has been generated, the s-quantum has been registered.

the only thing that is to be done is filtering out from the noise (via coincidence counter) to get the proper sub-sample.

No, the coincidence counter is not a simple noise filter ... it is required for proper identification of the photons that were generated as entangled pairs. Since the photon's travel different distances through the apparatus, they arrive at their respective detectors at different times. To keep it simple, consider a case where the A photon travels 2.9979 m to its detector, and the B photon travels twice as far to its detector. In that case there will be a delay of 1.0000 ns between emission and detection of the A photon, and a delay of 2.0000 ns for the B photon. The coincidence counter compensates for these delays so that the proper pair of photon detection events (separated by 1.0000 ns in this case) are paired in the analysis.

So, in order to see the interference pattern in these experiments, you have to wait until both the s-detector and p-detector events for each entangled pair have been registered before they can be properly compared via the coincidence counter. If the polarizer is in place (and set to the appropriate angle), then you will see the interference pattern revealed as an oscillation in the coincidence counts as a function of the s-detector position.

 

[San K]

No, the coincidence counter is not a simple noise filter ... it is required for proper identification of the photons that were generated as entangled pairs. Since the photon's travel different distances through the apparatus, they arrive at their respective detectors at different times. To keep it simple, consider a case where the A photon travels 2.9979 m to its detector, and the B photon travels twice as far to its detector. In that case there will be a delay of 1.0000 ns between emission and detection of the A photon, and a delay of 2.0000 ns for the B photon. The coincidence counter compensates for these delays so that the proper pair of photon detection events (separated by 1.0000 ns in this case) are paired in the analysis.

So, in order to see the interference pattern in these experiments, you have to wait until both the s-detector and p-detector events for each entangled pair have been registered before they can be properly compared via the coincidence counter. If the polarizer is in place (and set to the appropriate angle), then you will see the interference pattern revealed as an oscillation in the coincidence counts as a function of the s-detector position.

ok... so instead of "generated" we can say "identified/paired" (by the coincidence counter)

because when you said generated, one could assume...as "created"...it can give the sense that position is generated/created...

once s-quantum is registered at Ds, its position is locked, it won't change, right?

thus s-photon/position is not generated but identified (via pairing through coincidence counter)

 

[SpectraCat]

er, you're being funny right?. No, in QM a phase is assigned to a complex probability amplitude that evolves according to the Schrödinger eqn., in classical EM it is assigned to a wave described my Maxwell's equations.

Yeah, that's what I thought .. you don't understand what you are talking about. Phase is just an expression of the relative position of a wave in its cycle ... that's why it is expressed as an angle. So any system with wave-like properties will have a phase, regardless of whether it is quantum or classical. Coherence in any system can be expressed as the persistence of a well-defined phase relationship in time and/or space. So, the spatial coherence that is observed in the double-slit experiment (of which the DCQE is just an extension), occurs because the photon (or massive particle) is interfering with itself, and thus the different paths through the apparatus always have a well-defined phase relationship. The DCQE is more complicated, because it involves phase relationships of the two-photon entangled state as well, but that can still be accounted for, as Cthugha showed in his analysis.

Also, since photons are intrinsically quantum mechanical objects, it seems silly to talk about the phase relationships that Cthugha is presenting as classical. The polarization of photons is ALSO quantum mechanical, however it is analogous to the Jones vector for the classical description of EM radiation.

In measurements the intensity predicted by Maxwell's eqns matches the probability predicted by quantum (field) theory, but this is misleading, the Maxwell EM wave is not an ontological wave traveling through space with a well defined phase at all times (so that you might think you can naively interpret phase diagrams for single photons)

I have no idea what you tried to express above .. what is a "phase diagram" for a single photon?

The fact that you think DCQE can be explained by a classical phase argument.

Nope, I sure don't ... for the umpteenth time, if Cthugha's argument were classical, then a) we would not be talking about photons, and b) there could never be a well-defined phase relationship between the entangled photons, because there is no way of describing that classically.

 

[SpectraCat]

ok... so instead of "generated" we can say "identified/paired" (by the coincidence counter)

because when you said generated, one could assume...as "created"...it can give the sense that position is generated/created...

once s-quantum is registered at Ds, its position is locked, it won't change, right?

Yes, of course.

thus s-photon/position is not generated but identified (via pairing through coincidence counter)

I never said the s-photon position was generated .. I said that the interference pattern is only evident in the coincidence counts, which cannot be generated until detection events for both photons have been registered.

 

[unusualname]

Yeah, that's what I thought .. you don't understand what you are talking about. Phase is just an expression of the relative position of a wave in its cycle ... that's why it is expressed as an angle. So any system with wave-like properties will have a phase, regardless of whether it is quantum or classical. Coherence in any system can be expressed as the persistence of a well-defined phase relationship in time and/or space. So, the spatial coherence that is observed in the double-slit experiment (of which the DCQE is just an extension), occurs because the photon (or massive particle) is interfering with itself, and thus the different paths through the apparatus always have a well-defined phase relationship. The DCQE is more complicated, because it involves phase relationships of the two-photon entangled state as well, but that can still be accounted for, as Cthugha showed in his analysis.

haha, what more can I say, maybe you can use a similar analysis for GHZ states.

Also, since photons are intrinsically quantum mechanical objects, it seems silly to talk about the phase relationships that Cthugha is presenting as classical. The polarization of photons is ALSO quantum mechanical, however it is analogous to the Jones vector for the classical description of EM radiation.

yes of course it is, you guys are right there is no mystery in the DCQE, what was I thinking?

I have no idea what you tried to express above .. what is a "phase diagram" for a single photon?

Nope, I sure don't ... for the umpteenth time, if Cthugha's argument were classical, then a) we would not be talking about photons, and b) there could never be a well-defined phase relationship between the entangled photons, because there is no way of describing that classically.

No there isn't, well done.

 

[Cthugha]

edit: it must be this one ----> http://arxiv.org/abs/1010.1236

Yes, I mean this one. Sorry, I thought it was easy to find as I mentioned it only a few posts earlier. Besides section 6, also section 4.2 about ghost interference might help you understand the details better.

Well I don't think you're correct there, in the Walborn experiment they adjust the p-photon arm by a couple of meters, no worrying about planes there. In recent experiments they have done this stuff across Canary Islands, where I think it would be difficult to accurately find the "Fourier Plane". And I believe fibre optics are/will be used which makes the idea of your planes not really relevant.

As I said before you need to create a momentum eigenstate and using the Fourier plane is one of the possibilities. You can also go to far field conditions like in the double slit quantum eraser experiment. The result is the same. You decrease the angular size of the source, get a better defined momentum of your subset and increase spatial coherence. You just need the Fourier plane if you don not wan t to work at far field conditions.

Yeah, I have no doubt the pattern moves around, but we're investigating delayed eraser so all we really want is no pattern/some pattern as we remove/put in place the eraser.

Fine, then you agree with my explanation because if you do not use coincidence counting you will just measure a superposition of all these moced patterns which gives no pattern at all. From this point on the inserting/removing the eraser thing is trivial.

The correct answer to the question "Why are coincidence counters used?" is that QM is probabilistic. Even if you could remove all background effects and have an efficient entangled pair source you still have the fact that ~50% of the p-photons will pass through the eraser probabilistically. There is no deterministic way round it, not by phase matching or other weird calculation, otherwise FTL signalling would be possible since you wouldn't need a coincidence match to determine if the eraser was in place or not.

This is easily refuted because coincidence counting is also needed in experiments without DCQE or polarizers which just rely on basic conditional interference patterns or ghost imaging. The simple fact that relative phases leading to two-photon interference require coincidence counting, is all there is to it. This is not specific to DCQE. Again this is a result explained around equation 96 in Walborn's paper. You still did not tell me where he is wrong. The thing that prevents FTL signaling is the single-photon phase which is not well defined on average and therefore prevents information transfer. It is generally accepted that two-photon interference and single photon-interference are complementary due to the reasons I gave and information contained in coincidence counts therefore cannot be carried by one of these photons alone. I already gave you the references. Do you have any supporting your claim?

No I already understand that QM is either non-local and/or non-separable so I have no problem interpreting the experiment.

You seem to have found a different interpretation that doesn't require non-locality and/or non-separability. You should try to publish this discovery, really.

You do not seem to grasp where non-locality or non-seperability stems from. It comes into play because of the second and the first photon ending up in "compatible" states according to the rules of entanglement even if the second detection is not in the light cone of the first one and that is all there is to it. Most DCQE experiments indeed are not a proof of nonlocality as no Bell tests are performed. The first experiments on DCQE really showing that came in 2004 according to Walborns review paper.

No, in QM a phase is assigned to a complex probability amplitude that evolves according to the Schrödinger eqn., in classical EM it is assigned to a wave described my Maxwell's equations. In measurements the intensity predicted by Maxwell's eqns matches the probability predicted by quantum (field) theory, but this is misleading, the Maxwell EM wave is not an ontological wave traveling through space with a well defined phase at all times (so that you might think you can naively interpret phase diagrams for single photons)

You are wrong here. The phase is (somewhat) well defined in each run of the experiment. It is, however, usually not defined well on average, that means the phase will be different in every run of the experiment. Besides that you can map two-photon Fourier optics to classical Fourier optics using Klyshko's picture as mentioned in the Scarcelli et al. paper I already cited.

 

[unusualname]

OK, Cthuga I'm out, otherwise I may incur further warnings and infractions.

I would suggest you guys put together your explanations of the DCQE (since they are not widely known) in a paper, even just on arXiv so at least it may be argued on a more professional level.

 

[Drakkith]

The correct answer to the question "Why are coincidence counters used?" is that QM is probabilistic. Even if you could remove all background effects and have an efficient entangled pair source you still have the fact that ~50% of the p-photons will pass through the eraser probabilistically. There is no deterministic way round it, not by phase matching or other weird calculation, otherwise FTL signalling would be possible since you wouldn't need a coincidence match to determine if the eraser was in place or not.

I don't see what the 50% has anything to do with a counter. Take the eraser away and you would still need the counter to determine which photons were entangled, correct? It looks like its only job is to count when events are detected at the detectors. Nothing else. Take the counter away, run the experiment, and take the times from each detector for the detection events and compare them to match up the events. You just became a coincidence counter. Correct?

Also, can someone tell me what this purpose of these DCQE's are? Are they to determine if the photons can communicate with each other once one interacts and has to go to a set quantum state after the other one has already been detected?

 

[Cthugha]

Take the counter away, run the experiment, and take the times from each detector for the detection events and compare them to match up the events. You just became a coincidence counter. Correct?

Yes, modern coincidence counters really allow to do so and also offer a mode which gives only timestamps of detections from each photo diode and allows to do the analysis by hand. However, this mode is rarely used as the count rates from each diode are usually on the order of 10^6 per second at least and recording timestamps for every detection piles up huge amounts of data which need to be written to a hard disk quickly.

Also, can someone tell me what this purpose of these DCQE's are? Are they to determine if the photons can communicate with each other once one interacts and has to go to a set quantum state after the other one has already been detected?

Well, from a historical point of view quantum erasers and its delayed choice version were introduced by Scully in 1982. Back then this experiment was aimed at answering the question whether uncertainty or complementarity is more fundamental. So they were aiming at showing that it is not the uncontrolled disturbance introduced by a position measurement in the common double slit experiment that causes the interference pattern to disappear in the double slit experiment and thought of a reversible way to mark the way. The delayed choice version of the quantum eraser was introduced in the same paper - mainly because Aspect's idea of delayed choice experiments in general were intensely debated at that time.

 

[San K]

So they were aiming at showing that it is not the uncontrolled disturbance introduced by a position measurement in the common double slit experiment that causes the interference pattern to disappear in the double slit experiment and thought of a reversible way to mark the way.

it is not the uncontrolled disturbance but rather the way (rules/methods) the sub-samples of photons are chosen/identified ? ...that causes interference pattern to appear/disappear

 

[zonde]

yeah, you are probably right, it would be interesting to see an experiment done this way rather than using a coincidence counter, afaik there is no such published experiment.

There is. Weihs et al experiment http://arxiv.org/abs/quant-ph/9810080"

"Each observer station featured a PC which stored the tables of time tags accumulated in an individual measurement. Long after measurements were finished we analyzed the files for coincidences with a third computer."

 

[Drakkith]

Well, from a historical point of view quantum erasers and its delayed choice version were introduced by Scully in 1982. Back then this experiment was aimed at answering the question whether uncertainty or complementarity is more fundamental. So they were aiming at showing that it is not the uncontrolled disturbance introduced by a position measurement in the common double slit experiment that causes the interference pattern to disappear in the double slit experiment and thought of a reversible way to mark the way. The delayed choice version of the quantum eraser was introduced in the same paper - mainly because Aspect's idea of delayed choice experiments in general were intensely debated at that time.

What did they find out?

 

[unusualname]

yeah, you [SpectraCat] are probably right, it would be interesting to see an experiment done this way rather than using a coincidence counter, afaik there is no such published experiment.

There is. Weihs et al experiment http://arxiv.org/abs/quant-ph/9810080"

"Each observer station featured a PC which stored the tables of time tags accumulated in an individual measurement. Long after measurements were finished we analyzed the files for coincidences with a third computer."

Thanks zonde, I assume this should be easier now than in 1998, but the lengths the experimenters go to close "loopholes" is impressive.

 

[zonde]

There is something puzzling for me about Walborn Quantum eraser experiment.

Without quarter wave plates coincidence postselection increases spatial coherence. Otherwise interference is just a single beam interference.
At least that's how it seems from Walborn explanation (http://arxiv.org/abs/1010.1236" 4.1)

But in that case placing polarizer in idler beam when there are no quarter wave plates before slits should change nothing. Interference pattern should still be there.

Does it seems right?

 

[SpectraCat]

There is something puzzling for me about Walborn Quantum eraser experiment.

Without quarter wave plates coincidence postselection increases spatial coherence. Otherwise interference is just a single beam interference.
At least that's how it seems from Walborn explanation (http://arxiv.org/abs/1010.1236" 4.1)

But in that case placing polarizer in idler beam when there are no quarter wave plates before slits should change nothing. Interference pattern should still be there.

Does it seems right?

Yes, that is correct. Note also that with the QWP's in place, the angles of the QWP's seem to define a preferred basis for the polarizer to recover the interference patterns. The authors only report results for the polarizer in the QWP basis (45 and 135 degrees), but it would be interesting to see how changing the angle of the polarizer changes the experimental results. From an (admittedly casual) analysis of the mathematical treatment earlier in the paper, it seems like moving the polarizer angle away from 45 towards 90 would cause the interference fringes to gradually lose intensity, and eventually disappear at 90 (or 0) degrees. The reason I find this somewhat striking (assuming it is correct) is that it seems to work in the opposite sense of other experiments where a particular polarization basis is associated with "which path" information, in that interference is not observed in those cases until the polarizer angle is chosen to mix the basis states.

 

[zonde]

Yes, that is correct. Note also that with the QWP's in place, the angles of the QWP's seem to define a preferred basis for the polarizer to recover the interference patterns. The authors only report results for the polarizer in the QWP basis (45 and 135 degrees), but it would be interesting to see how changing the angle of the polarizer changes the experimental results. From an (admittedly casual) analysis of the mathematical treatment earlier in the paper, it seems like moving the polarizer angle away from 45 towards 90 would cause the interference fringes to gradually lose intensity, and eventually disappear at 90 (or 0) degrees. The reason I find this somewhat striking (assuming it is correct) is that it seems to work in the opposite sense of other experiments where a particular polarization basis is associated with "which path" information, in that interference is not observed in those cases until the polarizer angle is chosen to mix the basis states.

Well, I am quite sure that source determines preferred basis. Source produces H and V modes in certain basis. QWP mixes H and V modes so that interference (at detector) happens between them. And polarizer at +45° or -45° mixes H and V modes in similar way as two QWPs.
When you rotate polarizer you get more of one mode and less of the other. Finally at 0° and 90° you get pure H or V mode (so no interference between modes after polarizer).

That's how I see it.

 

[SpectraCat]

Well, I am quite sure that source determines preferred basis. Source produces H and V modes in certain basis. QWP mixes H and V modes so that interference (at detector) happens between them. And polarizer at +45° or -45° mixes H and V modes in similar way as two QWPs.
When you rotate polarizer you get more of one mode and less of the other. Finally at 0° and 90° you get pure H or V mode (so no interference between modes after polarizer).

That's how I see it.

No .. the source is entangled, so there is no preferred basis for detection until the QWP's are added. This is the fundamental results showed by the Aspect experiments, and since confirmed many times.

 

[San K]

There is something puzzling for me about Walborn Quantum eraser experiment.

Without quarter wave plates coincidence postselection increases spatial coherence. Otherwise interference is just a single beam interference.
At least that's how it seems from Walborn explanation (http://arxiv.org/abs/1010.1236" 4.1)

But in that case placing polarizer in idler beam when there are no quarter wave plates before slits should change nothing. Interference pattern should still be there.

Does it seems right?

Well then in this case you are getting which-way (via polarizer in idler) and also getting interference pattern...

 

[San K]

Well then in this case you are getting which-way (via polarizer in idler) and also getting interference pattern...

edit: on second thoughts...ah well you are not getting which-way...because you cannot get which-way by just a polarizer, you need to compare with s-photon

 

[San K]

in conclusion (to the title of this topic):

the position of the s-photon (or the p-photon or anything in the world for that matter) on the detector/screen never changes...once registered...(i.e. the past doesnot/cannot be changed)

the interference pattern is created/emerges when we "sample/filter out" the detections/photons lying on the blank spaces between the fringes...

or in other words...

the non-interference pattern is blob...out of the blob...we filter out (via coincidence counter) the markings/photons that don't lie on the interference fringes...

the non-interference blob contains the fringes hidden within it as a sub-set/sub-sample...

on a separate but related note:

also you can go from an (original) non-interference pattern to a interference pattern

but not vice-versa, i.e.

you cannot get/go from an (original) interference pattern to a non-interference pattern

because: the interference pattern is a sub-set of the non-interference pattern

Walborn does not discuss this, nor does he mention why they do the experiment only one-way...i.e. from non-interference blob to interference fringes...

 

[unusualname]

It's easier to explain if you just accept a QM explanation, and not try to make it "intuitive", in case you disagree perhaps try to explain this experiment:

Experimental realization of Wheeler's delayed-choice Gedanken Experiment (Science, 2007)

 

[San K]

It's easier to explain if you just accept a QM explanation, and not try to make it "intuitive", in case you disagree perhaps try to explain this experiment:

Experimental realization of Wheeler's delayed-choice Gedanken Experiment (Science, 2007)

Cthuga/SpectraCat and I are advocating non-local phenomena with sub-sampling as explanation for the patterns in DCQE.

you said, that you agreed with Cthuga/SpectraCat and San K.

I am ok with the explanation above, did you go through it?

There is nothing surprising in the paper, you mentioned, as I see it.

When we try which-way the photon wave function collapses and it follows a non-interference path.

The wave function can collapse well after the slits. It collapses when we try to detect the photon.

In my, long held, hypothesis:

the photon, always carries both options - particle and wave.

It depends upon which aspect we want the photon to manifest.

 

[unusualname]

Cthuga/SpectraCat and I are advocating non-local phenomena with sub-sampling as explanation for the patterns in DCQE.

you said, that you agreed with Cthuga/SpectraCat and San K.

I am ok with the explanation above, did you go through it?

However I will go through the link you provided.

If you want to assume an explicit non-local explanation then fine, but be aware that it is just an assumption and many people don't like explicit non-local interpretations of QM.

 

[unusualname]

There is nothing surprising in the paper, you mentioned, as I see it.

When we try which-way the photon wave function collapses and it follows a non-interference path.

The wave function can collapse well after the slits. It collapses when we try to detect the photon.

In my, long held, hypothesis:

the photon, always carries both options - particle and wave.

It depends upon which aspect we want the photon to manifest.

Yeah, ok, but that's not an explanation it's just an advertisement of your philosophical pondering, and doesn't really make any sense to me. But QM is tricky and people have all kinds of weird ideas all over the place ;-)

 

[San K]

If you want to assume an explicit non-local explanation then fine, but be aware that it is just an assumption and many people don't like explicit non-local interpretations of QM.

ya agreed...:), Einstein was one of them...

 

[SpectraCat]

Cthuga/SpectraCat and I are advocating non-local phenomena with sub-sampling as explanation for the patterns in DCQE.

Yeah, ok, but that's not an explanation it's just an advertisement of your philosophical pondering, and doesn't really make any sense to me. But QM is tricky and people have all kinds of weird ideas all over the place ;-)

Just to clarify, there is a phase-based quantum explanation of the 2007 Aspect delayed-choice experiment as well, and just as with the DCQE, it serves to dispel much of the apparent mysticism associated with the popular analysis.

The 2007 Aspect experiment can be explained using an even simpler phase-based argument than the DCQE experiments. In this case, there is only one-photon. Interaction with the first 45º-polarized photon into a superposition state, which becomes entangled with the two spatial paths in the interferometer .. one polarization state (S or P) travels down each arm. At the detector, we have two choices based on the setting of an electo-optic modulator (EOM)

1) in the open configuration, the (EOM) does not affect the two orthogonally polarized beams, and they are sent through to a Wollaston-prism which collapses the spatial-entanglement, with a 50-50 probability distribution between the two detection channels, irrespective of the phase of the interferometer.

2) in the closed configuration, the (EOM) acts like a second beamsplitter in a Mach-Zender interferometer, converting the spatially-entangled state back into a polarization-entangled state in a *phase-sensitive fashion*. That is, since the quantum state is coherent, there is a well-defined phase relationship between the two polarization components as they travel through the two arms of the interferometer. These two paths have different lengths (controlled by tilting an optic on the detection stage in this experiment), and therefore the two output beams have different phases, and interfere with each other, causing their associated polarization components to have different contributions to the final superposition, and this gives rise to the different intensities in the S & P channels after the Wollaston-prism, depending on the phase difference between the interferometer arms.

There are two important things to notice about this interpretation. First, it is inherently NON-LOCAL .. it relies on the entanglement of the photon along two spatially separated paths through the interferometer. Second, it relies on the COHERENCE of the quantum superposition throughout the apparatus. Both of those are features that are exclusive to quantum mechanics, and cannot be explained by a classical interpretation.

Another important thing to notice about the explanation is that it completely removes any question of whether there is a causality violation in the experiment. Since the photon always travels through both arms of the interferometer, there is no paradox about "which path" information being selected "after" the photon has "chosen a path". With all due respect to Prof. Wheeler, it is my opinion that those are features of a classically-based MIS-interpretation of the experiment.

 

[unusualname]

You're still not getting it SpectraCat. You are trying to explain what is "happening" via some convoluted argument about phase relationships which doesn't, and can't possibly explain what is "happening".

You are not dispelling any "mysticism" you are simply promoting an interpretative explanation.

 

[SpectraCat]

You're still not getting it SpectraCat. You are trying to explain what is "happening" via some convoluted argument about phase relationships which doesn't, and can't possibly explain what is "happening".

You are not dispelling any "mysticism" you are simply promoting an interpretative explanation.

Nope .. I am definitely "getting it". As I understand it, the principal question with delayed choice is whether or not it violates causality. My analysis above, which is not really convoluted but is rather simple once you understand it, uses the principles of quantum mechanics to show unequivocally why the answer is, "no, delayed choice does not violate causality".

[EDIT] By the way, you characterized this as an "alternative explanation" .. what other explanations are there that are consistent with QM?

[EDIT2] Also, in what way does the explanation I gave fail to explain what happens in the experiment?

 

[unusualname]

Nope .. I am definitely "getting it". The principal question with delayed choice is whether or not it violates causality. My analysis above, which is not really convoluted but is rather simple once you understand it, uses the principles of quantum mechanics to show unequivocally why the answer is, "no, delayed choice does not violate causality".

Er, yeah right, that was what the argument was about all along was it, I don't think so..

Your "explanation" is zero-value, it adds nothing apart from a vacuous and unnecessary analysis of how "phases" might exist in the experiment. You might as well argue about the statistical thermal properties of the apparatus, I'm sure they could be made to seem relevant by a similar convoluted "analysis", but totally irrelevant.

 

[unusualname]

[EDIT] By the way, you characterized this as an "alternative explanation" .. what other explanations are there that are consistent with QM?

[EDIT2] Also, in what way does the explanation I gave fail to explain what happens in the experiment?

edit1: i wrote "interpretative"

edit2: you can't explain what happens in the experiment, you can calculate it and you can interpret it, that's all.

 

[San K]

Just to clarify, there is a phase-based quantum explanation of the 2007 Aspect delayed-choice experiment as well, and just as with the DCQE, it serves to dispel much of the apparent mysticism associated with the popular analysis.

The 2007 Aspect experiment can be explained using an even simpler phase-based argument than the DCQE experiments. In this case, there is only one-photon. Interaction with the first 45º-polarized photon into a superposition state, which becomes entangled with the two spatial paths in the interferometer .. one polarization state (S or P) travels down each arm. At the detector, we have two choices based on the setting of an electo-optic modulator (EOM)

1) in the open configuration, the (EOM) does not affect the two orthogonally polarized beams, and they are sent through to a Wollaston-prism which collapses the spatial-entanglement, with a 50-50 probability distribution between the two detection channels, irrespective of the phase of the interferometer.

2) in the closed configuration, the (EOM) acts like a second beamsplitter in a Mach-Zender interferometer, converting the spatially-entangled state back into a polarization-entangled state in a *phase-sensitive fashion*. That is, since the quantum state is coherent, there is a well-defined phase relationship between the two polarization components as they travel through the two arms of the interferometer. These two paths have different lengths (controlled by tilting an optic on the detection stage in this experiment), and therefore the two output beams have different phases, and interfere with each other, causing their associated polarization components to have different contributions to the final superposition, and this gives rise to the different intensities in the S & P channels after the Wollaston-prism, depending on the phase difference between the interferometer arms.

There are two important things to notice about this interpretation. First, it is inherently NON-LOCAL .. it relies on the entanglement of the photon along two spatially separated paths through the interferometer. Second, it relies on the COHERENCE of the quantum superposition throughout the apparatus. Both of those are features that are exclusive to quantum mechanics, and cannot be explained by a classical interpretation.

Another important thing to notice about the explanation is that it completely removes any question of whether there is a causality violation in the experiment. Since the photon always travels through both arms of the interferometer, there is no paradox about "which path" information being selected "after" the photon has "chosen a path". With all due respect to Prof. Wheeler, it is my opinion that those are features of a classically-based MIS-interpretation of the experiment.

I will go over your post, in detail, later. You are not saying that sub-sampling & phase are competing theories, right?...because I think they are exclusive and non-competitive...

However don't we need all three, listed below, depending upon the experiment, to explain the observations?:

sub-sampling
phase (coherence/decoherence)
non-location

not sure what you mean by the below:

With all due respect to Prof. Wheeler, it is my opinion that those are features of a classically-based MIS-interpretation of the experiment.

it's not classically based, its non-local...not sure what you mean...

 

[SpectraCat]

i wrote "interpretative"

Well, that's even worse, because it's not even correct. The analysis I gave does not rely on any interpretation, just the usual mathematics of QM, which are actually quite simple for this case.

Er, yeah right, that was what the argument was about all along was it, I don't think so..

Your "explanation" is zero-value, it adds nothing apart from a vacuous and unnecessary analysis of how "phases" might exist in the experiment. You might as well argue about the statistical thermal properties of the apparatus, I'm sure they could be made to seem relevant by a similar convoluted "analysis", but totally irrelevant.

As before, until you have something of substance to offer in response to my posts, instead of just vague dogmatic objections, then all I can do is simply stop perpetuating this and allow the readers to draw their own conclusions. I presented a fairly simple and straightforward analysis that is consistent with the experimental results and with QM, and shows why there is no reason to expect that causality is violated in this experiment, which is the primary question the experiment was designed to address. If you want to show that my explanation is "vacuous" and "zero-value", then you need to explain in detail why it fails to show that causality is not violated. Otherwise you aren't adding anything to this thread.

Also, I'll point out that it's odd that you think that a phase-based analysis is somehow irrelevant to this experiment, when the entire experiment hinges on the observation of interference, i.e. spatial coherence, i.e. an experimental phenomenon that depends explicitly on phase.

 

[San K]

Just to clarify, there is a phase-based quantum explanation of the 2007 Aspect delayed-choice experiment as well, and just as with the DCQE, it serves to dispel much of the apparent mysticism associated with the popular analysis.

The 2007 Aspect experiment can be explained using an even simpler phase-based argument than the DCQE experiments. In this case, there is only one-photon. Interaction with the first 45º-polarized photon into a superposition state, which becomes entangled with the two spatial paths in the interferometer .. one polarization state (S or P) travels down each arm. At the detector, we have two choices based on the setting of an electo-optic modulator (EOM)

1) in the open configuration, the (EOM) does not affect the two orthogonally polarized beams, and they are sent through to a Wollaston-prism which collapses the spatial-entanglement, with a 50-50 probability distribution between the two detection channels, irrespective of the phase of the interferometer.

2) in the closed configuration, the (EOM) acts like a second beamsplitter in a Mach-Zender interferometer, converting the spatially-entangled state back into a polarization-entangled state in a *phase-sensitive fashion*. That is, since the quantum state is coherent, there is a well-defined phase relationship between the two polarization components as they travel through the two arms of the interferometer. These two paths have different lengths (controlled by tilting an optic on the detection stage in this experiment), and therefore the two output beams have different phases, and interfere with each other, causing their associated polarization components to have different contributions to the final superposition, and this gives rise to the different intensities in the S & P channels after the Wollaston-prism, depending on the phase difference between the interferometer arms.

There are two important things to notice about this interpretation. First, it is inherently NON-LOCAL .. it relies on the entanglement of the photon along two spatially separated paths through the interferometer. Second, it relies on the COHERENCE of the quantum superposition throughout the apparatus. Both of those are features that are exclusive to quantum mechanics, and cannot be explained by a classical interpretation.

Another important thing to notice about the explanation is that it completely removes any question of whether there is a causality violation in the experiment. Since the photon always travels through both arms of the interferometer, there is no paradox about "which path" information being selected "after" the photon has "chosen a path". With all due respect to Prof. Wheeler, it is my opinion that those are features of a classically-based MIS-interpretation of the experiment.

SpectraCat, Please post the link to the paper, diagrams etc. I tried searching.

i found this just now...http://www.nature.com/nature/journal/v446/n7138/box/446866a_BX1.html