Delayed Choice Quantum Eraser Experiment

[josephpalazzo]

Well I am in total agreement with you here. There are however some extra things that both Eraser and Delayed Choice Experiments teach us that the double-slit experiment by itself cannot.

A Quantum Eraser for instance shows us that the measuring device alone does not cause collapse unless a conscious observer is able to obtain the which-path information from it.

It's a speculation that is not borne by the facts. All the measurements are made by detectors. Those results are there whether there is a conscious being reading the results on the detectors or not.

If a measuring device makes a measurement and then the which-path information is made unretrievable (no conscious observer will ever see it), the interference pattern remains as if no measurement had ever taken place. The double-slit alone could not have told us that.

The which-path goes to detectors 1 and 2. It matters not if there is a conscious being to observe it. The interference will take place. But we only know this when we look at the oscilloscope that shows the inference pattern.  The detector by interacting with the photon to make the measurement has already influenced the result. But in no way, our decision to look at the detector will affect the results. I don't think you know what's involved in the experiment, otherwise you would not make such an implausible statement.

Also the Delayed Choice experiment shows us that the wave or particle behavior is not dependent on space-time and violates causality.

No it doesn't. The original paper made that claim. Subsequently that idea was abandoned as it would make no sense. There has never been any experiment that has ever showed that causality is violated. Not to confuse with violations of Bell's theorem, as this is an altogether different thing.

Again I won't answer any of your quote-mine as they are irrelevant to this discussion. What Wheeler said in the 1960's or Einstein in the 1930's is quite irrelevant if we have moved on to better ideas.

[stromboli]

You've only got a lousy PHD, JP. You ain't got a chance.

 

[josephpalazzo]

You've only got a lousy PHD, JP. You ain't got a chance.

 

At this stage I'm wondering if Casparov has ever walked into a physics lab.

[Casparov]

It's a speculation that is not borne by the facts. All the measurements are made by detectors. Those results are there whether there is a conscious being reading the results on the detectors or not.


The which-path goes to detectors 1 and 2. It matters not if there is a conscious being to observe it. The interference will take place. But we only know this when we look at the oscilloscope that shows the inference pattern.  The detector by interacting with the photon to make the measurement has already influenced the result. But in no way, our decision to look at the detector will affect the results. I don't think you know what's involved in the experiment, otherwise you would not make such an implausible statement.

Kind sir, are you meaning to tell me that once the signal photon is detected, registered, and scanned at detector D0 according to its position, that no matter what happens beyond this, "the detector by interacting with the photon to make the measurement has already influenced the result," meaning that no matter if we ever know the which-path information or not the wave function will be collapsed every single time because the "unconscious measuring device" made an observation already?

Is this your argument? Because you seem to be implying that measuring devices cause the collapse regardless of whether or not they relay information to a conscious observer or not. If you are correct, then the very first measurement that occurs in the experiment should suffice to collapse the wave function every single time, and we should never get an interference pattern.

You say, "But in no way, our decision to look at the detector will affect the results." Your words are cryptic here. I am assuming that you mean that if the which-path information is not erased, and is made available, no matter if we look at the results or not we will still get a collapsed wave function. This is true, but it might not be what you are saying. On the other hand you could be saying that whether or not the detecter erases or relays the which-path information does not effect the results, and this would be definitely false. So which are you saying? Please clarify.

No it doesn't. The original paper made that claim. Subsequently that idea was abandoned as it would make no sense. There has never been any experiment that has ever showed that causality is violated. Not to confuse with violations of Bell's theorem, as this is an altogether different thing.

Yes there has, it is the experiment called "Quantum Eraser With a Causally Disconnected Choice" completed last year. The fact that wave or particle like behavior is determined by a "Causally disconnected choice" is a demonstration of causality being violated. Since you are an educated man, you should be able to read the paper and deduce this yourself. It is quite straight forward that Causality is conclusively violated: You are not allowed to view links. Register or Login

I am just happy to be speaking with someone on this forum who seems to actually be willing to discuss the evidence. 

[Solitary]

Oh my goodness, it isn't the detector or observer that causes the results to be different, it is light itself that makes the difference. Caparov, take a course in quantum mechanics so you don't keep making a fool out of your self by committing the logical fallacy of Appeal to ignorance (Argumentum Ad Ignorantum) which is advancing the position that if one conclusion in an argument cannot be established convincingly to a debater, then their opposing view can be accepted. Everyone here has shown you your wrong because you don't have a clue about quantum mechanics and parrot all the New Age philosophical speculation on how it operates. Do you have a high degree in math and physics like Joseph Palazzo has, or studied all the higher mathematics and physics like I have? If no, you have no idea what you are talking about, because without understanding the math and physics you can't possibly know because it requires abstract thinking that has to be learned and not intuitive thinking and mere speculation that is used in philosophy. Solitary

Casparov, can you do this equation? You are not allowed to view links. Register or Login

[josephpalazzo]

Kind sir, are you meaning to tell me that once the signal photon is detected, registered, and scanned at detector D0 according to its position, that no matter what happens beyond this, "the detector by interacting with the photon to make the measurement has already influenced the result," meaning that no matter if we ever know the which-path information or not the wave function will be collapsed every single time because the "unconscious measuring device" made an observation already?

Is this your argument? Because you seem to be implying that measuring devices cause the collapse regardless of whether or not they relay information to a conscious observer or not. If you are correct, then the very first measurement that occurs in the experiment should suffice to collapse the wave function every single time, and we should never get an interference pattern.

Here is what you get on the detectors:

You are not allowed to view links. Register or Login

It doesn't matter if a conscious being looks at the detectors or not, the detectors will show those patterns.

To explain the data:

The interference occurs at D₁ and D₂, these are the paths in which we don't know if the photon comes from A or B.  This is the same as a double-slit experiment, where we are not trying to know where the photon went through.

However for D₃, the photon went through the beam splitter BS_a making an angle, while for D₁, it went right through - follow the diagram carefully. This is the same as adding a detector in a double-slit experiment to figure out which slit the photon went through. By gaining this knowledge with an additional interaction, the interference disappears. Ditto for D₄.

[Solitary]

  Can't wait for  . Solitary

[Casparov]

I am glad we are having this conversation JosephPalazzo because you are the first person willing to discuss the actual evidence and it's conclusions with me. We disagree but that is fine, let's come to an agreement based on this experiment:

Here is what you get on the detectors:

You are not allowed to view links. Register or Login

It doesn't matter if a conscious being looks at the detectors or not, the detectors will show those patterns.

To explain the data:

The interference occurs at D₁ and D₂, these are the paths in which we don't know if the photon comes from A or B.  This is the same as a double-slit experiment, where we are not trying to know where the photon went through.

However for D₃, the photon went through the beam splitter BS_a making an angle, while for D₁, it went right through - follow the diagram carefully. This is the same as adding a detector in a double-slit experiment to figure out which slit the photon went through. By gaining this knowledge with an additional interaction, the interference disappears. Ditto for D₄.

All of this is correct as I understand it but you have omitted the key part of it.

Before any particle arrives at either (D1 and D2) or (D3 and D4), D0 detects, scans, and registers either an interference or a particle pattern. D0 makes a measurement of particle or wave-like behavior before D1, D2, D3, D4 ever do anything.

Now if the photon arrives at (D1 and D2), since we do not have which path information, we get an interference pattern at both of these detecters as you rightly said, but what you omitted was that we also get an interference pattern from D0 with this scenerio as well.

If the photon arrives at (D3 and D4), because we do have which-path information, we get no interference pattern at both of these detecters as you rightly said, but what you omitted was that we also get no interference pattern from D0 with this scenerio as well.

The Coincidence Counter correlates the arrival of a signal photon at detector D0 with the arrival of its twin at D1, D2, D3, or D4. If the correlation is with an idler arriving at D3 or D4, then we know (after-the-fact) the which-path information of the signal photon that arrived earlier at D0. If the correlation is with an idler arriving at D1 or D2, then we have no which-path information for the signal photon that arrived earlier at D0.

QM predicts that if which-path information is not available "at the time of measurement", the pattern will be an interference pattern. This is the case at detector D0 at all times.

QM also predicts that if which-path information is available "at the time of measurement", there will be a particle pattern and no interference pattern.

Therefore, based on the results of this experiment we can only conclude that, "the time of measurement," is after the correlation of the joint detections, which takes place at the Coincidence Counter. However, the count of photon hits that will be displayed, just as your pictures show, represents hits at D0 registered earlier. Proving that a measuring device's "observation" does not cause collapse simply by "interfering with the particle", but rather the cause of collapse is the availability of which-path information "at the time of measurement." Period.

You say, "It doesn't matter if a conscious being looks at the detectors or not, the detectors will show those patterns." But this is not a testable hypothesis. The only way you can ever know "the detectors will show those patterns" is if a conscious being looks.

Question: Do agree you that "the time of measurement" is at the Coincidence Counter?

[Berati]

I am glad we are having this conversation JosephPalazzo because you are the first person willing to discuss the actual evidence and it's conclusions with me. We disagree but that is fine, let's come to an agreement based on this experiment:

That is not true. Others have discussed the same thing with you, myself included, but you just don't like disagreement.
You still confuse an interpretation with proof and decide that however you and your New Ageist friends interpret QM is the ONLY way it can be interpreted.

[josephpalazzo]

You say, "It doesn't matter if a conscious being looks at the detectors or not, the detectors will show those patterns." But this is not a testable hypothesis. The only way you can ever know "the detectors will show those patterns" is if a conscious being looks.

Do you believe a tree exists if no one looks at it? Same thing for the patterns on those detectors. If you believe that trees have an existence independent of your perception, so with the patterns as they are registered by the detectors. Over the last 30 years there have been quite a few teams of researchers that have investigated DCQE experiments, and all the results give the same results: if there is no knowledge of where the photons have gone through one of the slits, there is interference; if you have knowledge by whatever clever devices you have schemed, there is no interference.  And it doesn't matter if the experiment is set up for the interference to happen before or after it arrives at d₀. If you find an experiment that says the contrary, please let me know.

If you want to learn more about this, you can go  to Luboš Motl at You are not allowed to view links. Register or Login

[Casparov]

Do you believe a tree exists if no one looks at it? Same thing for the patterns on those detectors. If you believe that trees have an existence independent of your perception, so with the patterns as they are registered by the detectors.

This is not a trivial question. Einstein asked Bohr, "Do you really believe the moon is not there when nobody looks?" To which Bohr replied, “Can you prove to me the contrary?” It is a serious question to ask.

Realism is the assumption that perceived objects have an existence independent of perception, and I believe that what quantum mechanics is showing us is that there is no need for that assumption. Unless someone can "prove to me the contrary?"

Over the last 30 years there have been quite a few teams of researchers that have investigated DCQE experiments, and all the results give the same results: if there is no knowledge of where the photons have gone through one of the slits, there is interference; if you have knowledge by whatever clever devices you have schemed, there is no interference.  And it doesn't matter if the experiment is set up for the interference to happen before or after it arrives at d₀. If you find an experiment that says the contrary, please let me know.

Yes but the claim I am refuting is the one which states, "the measuring devices themselves are the cause of the wave function collapse." These experiments disprove this claim outright. If unconscious measuring devices were the sole cause of the "observer effect" of collapsing wave functions, then whether or not the recorded which-path information is at a later time erased or not should have no effect. The wave function should stay collapsed because the unconscious measuring device made the "observation." Do you disagree?

Further I do believe there have been better Quantum Eraser Experiments since the one we are discussing from 1999. For instance You are not allowed to view links. Register or Login from 2005 which states:

In this context another novelty of our experiment is particularly important: a new type of detection scheme. In all previous quantum erasers, the observation or not observation of the interference pattern were associated to different experiments, or at least to different photoelec- tric detectors. Therefore even though the physics behind the erasure has been exploited, the implementation of the random delayed choice can still be improved. In our real- ization both the erasing choice and the reading choice are analyzed by a single detector. This characteristic stresses the interpretative difficulties of the quantum eraser. In fact in our experiment the particle-like and wave-like be- havior of the photon are recorded randomly and simul- taneously by the same pair of joint measurement devices in only one measurement process.

And also You are not allowed to view links. Register or Login a beautifully simple quantum eraser experiment from 2002 which states:

We have presented a quantum eraser that uses a Young double slit to create interference. The quarter-wave plates in
our experiment served as the which-path markers to destroy interference. We recovered interference using the entangle- ment of photons s and p. Our quantum eraser is very similar to the that of Scully, Englert, and Walther. We have shown that interference can be destroyed, by marking the path of the interfering photon, and recovered, by making an appropriate measurement on the other entangled photon. We have also investigated this experiment under the conditions of delayed erasure, in which the interfering photon s is de- tected before photon p. In as much as our experiment did not allow for the observer to choose the polarization angle in the time period after photon s was detected and before detectionof p, our results show that a collapse of the wave function due to detection of photon s does not prohibit one from ob- serving the expected results. Our experimental data agree with the proposal of Scully, Englert, and Walther that quan- tum erasure can be performed after the interfering particle has been detected.

In all these experiments, unconscious detecters can "measure" or "observe" the which-path information, but this does not cause collapse if that which-path information never makes it to a conscious observer. Thus, proving that unconscious detecters and measuring devices themselves are not the cause of wave function collapse, and not the cause of the "observer effect." Otherwise, no matter what happens after the measurement from an unconscious detector, the wave function would stay collapsed.

[Berati]

You say, "It doesn't matter if a conscious being looks at the detectors or not, the detectors will show those patterns." But this is not a testable hypothesis. The only way you can ever know "the detectors will show those patterns" is if a conscious being looks.

Completely wrong.
The information shows up on the detectors first, then the light from the detectors goes to your eyes. That is the order.
So your wrong. The patterns appear on the detectors first and it doesn't matter if a conscious being, a moth, or a video recorder is "observing" the detectors.

[Shol'va]

This is not a trivial question. Einstein asked Bohr, "Do you really believe the moon is not there when nobody looks?" To which Bohr replied, “Can you prove to me the contrary?” It is a serious question to ask.

Yes I can. How? Same way that we know black holes exist even though they cannot be observed directly. Their existence is inferred from the effect they have on everything around them.
I don't have to look at the moon directly to not only know that it exists, but to also demonstrate this.

Realism is the assumption that [...]

You keep saying this, and have also occasionally jumped to "if you can't know for sure, then realism is an unsupported assertion", as if regarding our existence in a physical universe as something that is axiomatic is based on absolutely no evidence at all.

[josephpalazzo]

This is not a trivial question. Einstein asked Bohr, "Do you really believe the moon is not there when nobody looks?" To which Bohr replied, “Can you prove to me the contrary?” It is a serious question to ask.

Realism is the assumption that perceived objects have an existence independent of perception, and I believe that what quantum mechanics is showing us is that there is no need for that assumption. Unless someone can "prove to me the contrary?"

Einstein and Bohr were discussing what is as old as philosophy: how do you prove "existence" with philosophical arguments? And the answer is: you can't.  That was the point in Bohr's reply. You either accept that the moon has an existence independent of your perception or you don't. Most reasonable person accept that it does, the other way is to fall into nihilism. But I'll be honest, philosophical discussions don't interest me.

Yes but the claim I am refuting is the one which states, "the measuring devices themselves are the cause of the wave function collapse." These experiments disprove this claim outright. If unconscious measuring devices were the sole cause of the "observer effect" of collapsing wave functions, then whether or not the recorded which-path information is at a later time erased or not should have no effect. The wave function should stay collapsed because the unconscious measuring device made the "observation." Do you disagree?

Sorry to disagree, but as I have already stated there is only one conclusion from all DCQE experiments: if you know the which-path there is no interference; if you do not know it, there will be interference. Any contrary result would be an exception to the Heisenberg Uncertainty Principle, and that would be so big, so huge, it would have hit the headlines of all the major papers and that person would be in line for the Nobel.

In all these experiments, unconscious detecters can "measure" or "observe" the which-path information, but this does not cause collapse if that which-path information never makes it to a conscious observer. Thus, proving that unconscious detecters and measuring devices themselves are not the cause of wave function collapse, and not the cause of the "observer effect." Otherwise, no matter what happens after the measurement from an unconscious detector, the wave function would stay collapsed.

I'm not a fan of the terminology "wave collapse" as it leads to all kinds of crazy interpretations. It's a term that came out of the 1930's when physicists believed that the wavefunction was real (Einstein was one of them). Subsequently, with the development of QFT in the 1960's, that picture changed.  I tend to look at the wavefunction as a mathematical tool that allows the calculation of probabilities. Beyond that, I refuse to give it more than that interpretation. 

[Berati]

Sorry to disagree, but as I have already stated there is only one conclusion from all DCQE experiments: if you know the which-path there is no interference; if you do not know it, there will be interference. Any contrary result would be an exception to the Heisenberg Uncertainty Principle, and that would be so big, so huge, it would have hit the headlines of all the major papers and that person would be in line for the Nobel.

I think you're going to confuse him with the use of the word "you" above.

Here is a thought experiment that may shed light on the situation.

Shimon Malin Phd. Professor Emeritus of Physics at Colgate University
"Suppose a measurement of an electron's spin component along some direction is being measured. The result can either be "up" or "down". The result of the measurement is automatically communicated to a printer that can either print "up" or "down". If human consciousness is what causes the collapse to the observed state, then the collapse would only occur when someone read the printout, and not before. Now suppose that the printer has just enough ink to print "up", and not enough ink to print "down". Furthermore, if the printer runs out of ink, a bell sounds in a secretary's office. If the secretary hears the bell, a collapse to "down" has clearly occurred before the bell sounded. If the secretary does not hear the bell, a collapse to "up" must have occurred--and no human interaction was necessary at all."