Can entangled photons transmit information faster than the speed of light?

[DrChinese]

... There is simply NOTHING that Bob can do to his detection set up that will change the *single-photon* results of Alice's measurement. ...

Right you are, and nature is quite clever in that regard.

 

[UChr]

This has been a common thread in all of the answers you have received on this thread, but you appear not to have absorbed the significance of the point. There is simply NOTHING that Bob can do to his detection set up that will change the *single-photon* results of Alice's measurement. The changes will only be reflected in the *two-photon* (i.e. coincidence counting) results, which can ONLY be created by comparing the measurements made at BOTH detectors.

It is clear that we disagree.

It is to get behind the postulates that we look at concrete examples and texts - here is Dopfer interesting because she beyond two-photon experiment also is considering a one-photon experiment.

Most - like Walborn - look only at two-photon part, because they so: a) avoids the noise, b) can easily select different subsets, -, and 3) because of the complementarity between one and two - photons, so it is difficult to obtain reasonably good results by both with the same setup.

By the way - I never got any comments about:
# 13: ‘Why I think the order may be important in some types of experiments: ...’

 

[DrChinese]

By the way - I never got any comments about:
# 13: ‘Why I think the order may be important in some types of experiments: ...’

You did, but you choose to ignore it. Ordering makes no difference, as every delayed-choice experiment clearly shows.

 

[SpectraCat]

It is clear that we disagree.

Whether or not you "agree" is completely irrelevant. The statement I gave summarizes the current understanding of how this works within the framework of Quantum Mechanics .. it was not simply my opinion.

What you are claiming (i.e. that the single-photon results at Alice or Bob can be affected by measurements done at the other end) goes against the predictions of quantum mechanics ... if you think differently, then please provide a derivation or a reference to support your statement.

So is it your contention that QM is wrong about this? That is of course possible, which is why people put some effort into testing this experimentally. So far nothing they have found indicates any kind of disagreement with QM predictions. What you appear to by trying to do is to propose a new experiment that will reveal this "new physics" to allow FTL communication. The problem with this is that you aren't really proposing anything new .. you are combining well-understood measuring devices in a fairly simple way, such that the experimental results can be easily predicted from basic principles, and by analogy with experiments that have already been done.

 

[UChr]

You did, but you choose to ignore it. Ordering makes no difference, as every delayed-choice experiment clearly shows.

Example of experiment type where the order of the measurements are important:
Quantum teleportation where the first measured by Alice 2nd mailed to Bob 3rd Bob responds.

At Walborn it could have been interesting if he had measured the s photons circled right or left. It could possibly have given a difference when p is measured after s.

Wikipedia believes that a measurement of one photon breaks entanglement - and as I understand it, it is the most common perception. Furthermore, there are indeed made some attempt to show that the adjustment between the photons is very fast.
So who claim (reviewed) that the order of measurements can never have meaning for an experiment?

 

[DrChinese]

So who claim (reviewed) that the order of measurements can never have meaning for an experiment?

The order of measurements on entangled particles never changes the outcome in any discernible manner. This is basic. There are no experiments saying otherwise, including those in which there is entanglement swapping.

http://arxiv.org/abs/quant-ph/0201134

P.S. Wiki is not considered a reference for matters in dispute. Neither is Scientific American, etc.

 

[UChr]

The order of measurements on entangled particles never changes the outcome in any discernible manner. This is basic. There are no experiments saying otherwise, including those in which there is entanglement swapping.

http://arxiv.org/abs/quant-ph/0201134

Although the order is indifferent in 'Entanglement swapping' - it is not trivial at 'Quantum teleportation’ - see for example:

Nicolas Gisin and Rob Thew: ‘Quantum Communication’
http://arxiv.org/PS_cache/quant-ph/pdf/0703/0703255v1.pdf

“FIG. 4: Quantum teleportation. Alice performs a BSM, a joint measurement, on the unknown qubit […] and one photon from the entangled state […]. The result does not reveal the state of the qubit but is sent to Bob who performs a result-dependent operation U to complete the teleportation.”


? Did Luiz Carlos Ry have a point in: “Comment on \Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping"
http://cdsweb.cern.ch/record/608852/files/0303082.pdf
- Or is he a questionable source?

 

[UChr]

Related to the possibility of obtaining interference = the need for relatively nice single-photon coherence:

In the last post mentioned Gisin + Thew: ‘Quantum Communication’: p. 5; section V:

“Consequently, some of the next steps will require detectors with improved jitter [43, 71] as well as compact sources of entangled photons with significantly increased single-photon coherence.”

- So the idea about compact sources of entangled photons with a robust single-photon coherence is not theoretically impossible.

 

[Cthugha]

- So the idea about compact sources of entangled photons with a robust single-photon coherence is not theoretically impossible.

Why do you rip short sentences out of context? Gisin is discussing the need for stabilization on the timescales of the coherence times of the light. This is a discussion about coherence times which is the kind of coherence you need if you want to see interference in a Michelson interferometer. It is not about transversal coherence length which is the kind of coherence you need in a double slit.

 

[UChr]

Why do you rip short sentences out of context? Gisin is discussing the need for stabilization on the timescales of the coherence times of the light. This is a discussion about coherence times which is the kind of coherence you need if you want to see interference in a Michelson interferometer. It is not about transversal coherence length which is the kind of coherence you need in a double slit.

A tough question - among others due
a) Zeilinger in his famous experiment with quantum teleportation using polarization.
b) Wishful thinking. It would be nice to do without coincidence counters - even something like Walborn’s experiment could test most of the idea behind my experiment.