Communication systems and entanglement

[UChr]

Those who are against superluminal communication often choose to look at a single set of 'entangled' particles as an example of communication between A(lice) and B(ob). For example, Patrick Van Esch: 'EPR, density matrices, and FTL signaling' that sees the two particles as ‘clearly defined subsystems’ - which seems surprising if they shares a common superposition.

Would it not be more appropriate to look at a communicative situation which taking some time and are based on agreements between A and B?

For example:
A and B are measuring corresponding particles from pairs of quantum mechanically entangled photons - so-called Bell-couples.
The distance between the transmitter and the source are suitably much shorter than between the source and the receiver, so with synchronized watches the transmitter will detect its twin particle before the other twin reaches the receiver.

The transmitter can change its measuring setup by inserting a mirror or not – choice situation, T(1) or T(0). It keeps its choice for an agreed period – for instance 1 / 300.000 sec.
The receiver has a fixed preset setup. It should by measuring its part of the pairs with at least 99% probability, guess the Transmitters choice.

As the exchange between the entangled particles takes place instantaneous it will for a growing distance between A and B create superluminal communication.

 

[SpectraCat]

Those who are against superluminal communication often choose to look at a single set of 'entangled' particles as an example of communication between A(lice) and B(ob). For example, Patrick Van Esch: 'EPR, density matrices, and FTL signaling' that sees the two particles as ‘clearly defined subsystems’ - which seems surprising if they shares a common superposition.

Would it not be more appropriate to look at a communicative situation which taking some time and are based on agreements between A and B?

For example:
A and B are measuring corresponding particles from pairs of quantum mechanically entangled photons - so-called Bell-couples.
The distance between the transmitter and the source are suitably much shorter than between the source and the receiver, so with synchronized watches the transmitter will detect its twin particle before the other twin reaches the receiver.

The transmitter can change its measuring setup by inserting a mirror or not – choice situation, T(1) or T(0). It keeps its choice for an agreed period – for instance 1 / 300.000 sec.
The receiver has a fixed preset setup. It should by measuring its part of the pairs with at least 99% probability, guess the Transmitters choice.

As the exchange between the entangled particles takes place instantaneous it will for a growing distance between A and B create superluminal communication.

Nope. The transmitters choice can be re-phrased as "measure, or not measure". The receive must always measure to get a value. How will the receiver be able to tell if they are measuring a value that was "predetermined" by the transmitter's action, or if they themselves determined the state from their own measurement, because the transmitter chose not to measure that particular pair?

 

[UChr]

Times for communication be agreed regularly. A transmits to B at certain times - and B transmits its response to the agreed times.

 

[DrChinese]

What do you expect the receiver to see differently based on what the sender does? All that the receiver ever sees it a random string of + - + + - + + - - etc.

 

[SpectraCat]

Times for communication be agreed regularly. A transmits to B at certain times - and B transmits its response to the agreed times.

That is irrelevant ... please read my post again. The issue is not about time correlation, it's about being able to tell a 0 from a 1 in the supposed transmitted data stream. The only way it would work is if the receiver can somehow know the state of the transmitter's system, and I explained why that is not possible in my first post.

 

[UChr]

If the receiver has two detectors D+ and D- output will be something like + + - + - - etc.
In case T(0), I expect for example a distribution about 50% / 50%.
For T(1) another distribution - for example 25% / 75% .

And this must be translated by the receiver to a range of 0 and 1.

 

[SpectraCat]

If the receiver has two detectors D+ and D- output will be something like + + - + - - etc.
In case T(0), I expect for example a distribution about 50% / 50%.
For T(1) another distribution - for example 25% / 75% .

And this must be translated by the receiver to a range of 0 and 1.

That is not how entangled systems behave. Local detection statistics are always 50-50 ... it is only by comparing coincident statistics between "transmitter" and "receiver" that correlations could be established.

It seems like you either don't fully understand quantum entanglement, or you haven't thought your model through completely. I urge you to at least do the latter .. think through *in detail* exactly what experiments will be performed by the transmitter and receiver, and what the results should be .. keeping in mind that there is no such thing as passive detection in quantum systems.

 

[UChr]

No, I do not fully understand entanglement ... I discuss, inter alia, to become wiser.

The particles are not in a superposition when they reach the receiver - it stops before, when detected by the transmitter.

Yes I have some private ideas on how I avoid this 50% - 50% issue.

 

[SpectraCat]

The particles are not in a superposition when they reach the receiver - it stops before, when detected by the transmitter.

I'll try this one more time ...

Explain how you will "encode" a signal when you disrupt the entanglement of EVERY pair at the "transmitter"? (If you do not disrupt EVERY pair, then some will still be entangled when they reach the receiver, won't they?) What will the "transmitter" do *specifically* that you think the "receiver" will be able to decipher? How precisely will the "receiver" probe their beam experimentally in order to read the "data", and how will they tell "data" from noise?

Once you have tried to come up with a specific set up, rather than a vague conception, you will understand what we have been telling you ... that this is fundamentally impossible ... as opposed to just being technically difficult.

 

[UChr]

OK
Idea 1 is to create interference or non interference.

More fundamentally, however, idea 2 - if it is correct - so I will start with 2:

The building block is a polarizing beam splitter = PBS (v) that transmits light polarized in the direction v and reflects light polarized perpendicular to v.
The beam splitter is not a measurement on the photons. The entangled pair should therefore remain in a superposition although one of the twins encounters one or more PBS’s.

T (0) = the receiver R: a polarizing beam splitter = PBS (0) followed by two photo detectors.
(R measuring approximately 50% / 50%, then T (0) could also simply be to do nothing.)

T (1) starts with a polarizing beam splitter = PBS (0).
The horizontal beam (0 degree) meets after sufficiently long times a detector.
The vertical beam meets a PBS (+45) followed by two detectors.

How T(1) should work:
The PBS (0) splits the beam into two beams with the distribution 50% to 50%.
The vertical beam meets next a PBS (+45) and must choose between +45 degrees = diagonally to the right or perpendicular to it = diagonally to the left. It will be a fifty - fifty situation. Together we should get: Horizontal / vertical /diagonally to the right / left = 50 % / 0% / 25 % / 25 %.

When the transmitter has measured its photon in the entangled pair as polarized in a certain direction stops the common superposition. The ‘twin’ will result in theory; behave as polarized perpendicular to the measured.
In case T (1) would beam towards the receiver have the following distribution:
Horizontal / vertical / diagonally right / left = 0 % / 50 % / 25 % / 25 %.
The vertically polarized photons will pass through the vertical path to detector D2. So from this part of the beam: D1 / D2 = 0 % / 50 %.
The beam polarized diagonally to the right and left must choose between vertical and horizontal. This is a fifty - fifty situation. So from this part: D1 / D2 = 25 % / 25 %. Totally we should get: D1 / D2 = 25 % / 75 % - ie in case T (0) is the probability of D2 = 0.5. In case T (1) = 0.75.

 

[SpectraCat]

OK
Idea 1 is to create interference or non interference.

More fundamentally, however, idea 2 - if it is correct - so I will start with 2:

The building block is a polarizing beam splitter = PBS (v) that transmits light polarized in the direction v and reflects light polarized perpendicular to v.
The beam splitter is not a measurement on the photons. The entangled pair should therefore remain in a superposition although one of the twins encounters one or more PBS’s.

T (0) = the receiver R: a polarizing beam splitter = PBS (0) followed by two photo detectors.
(R measuring approximately 50% / 50%, then T (0) could also simply be to do nothing.)

T (1) starts with a polarizing beam splitter = PBS (0).
The horizontal beam (0 degree) meets after sufficiently long times a detector.
The vertical beam meets a PBS (+45) followed by two detectors.

How T(1) should work:
The PBS (0) splits the beam into two beams with the distribution 50% to 50%.
The vertical beam meets next a PBS (+45) and must choose between +45 degrees = diagonally to the right or perpendicular to it = diagonally to the left. It will be a fifty - fifty situation. Together we should get: Horizontal / vertical /diagonally to the right / left = 50 % / 0% / 25 % / 25 %.

When the transmitter has measured its photon in the entangled pair as polarized in a certain direction stops the common superposition. The ‘twin’ will result in theory; behave as polarized perpendicular to the measured.
In case T (1) would beam towards the receiver have the following distribution:
Horizontal / vertical / diagonally right / left = 0 % / 50 % / 25 % / 25 %.
The vertically polarized photons will pass through the vertical path to detector D2. So from this part of the beam: D1 / D2 = 0 % / 50 %.
The beam polarized diagonally to the right and left must choose between vertical and horizontal. This is a fifty - fifty situation. So from this part: D1 / D2 = 25 % / 25 %. Totally we should get: D1 / D2 = 25 % / 75 % - ie in case T (0) is the probability of D2 = 0.5. In case T (1) = 0.75.

That is an interesting construction, and I think I see where you are coming from, but you have misunderstood what is meant by "the polarization of the entangled twin will always be antiparallel to it's partner". Those designations are with respect to the polarizations when the photons are generated ... one will be |H>, the other |V> .. you cannot know which until you measure one of them. All of the manipulations you propose with T(1) only change the polarization detection basis for the photon going to the transmitter ... they do not change the polarization basis for the entanglement, or the detection basis at the receiver. Say that the photon going to T(1) is resolved by the first PBS as |V>, so that it goes to your 2nd 45º PBS .. that means that you will have rotated the detection basis so that you will see |L> or |R>. However the photon going to the receiver is unchanged .. it is still |H>. So the detection statistics at the receiver will still be 50/50 between |H> and |V>. What will be different for the case that you have devised is the coincidence statistics between the two setups. Let's call the photon to the transmitter A, and the one to the receiver B. If you compare the results for A and B you would see:

T(0)
case I: A=|H>, B=|V> 50% chance
case 2: A=|V>, B=|H> 50% chance

T(1)
case I: A=|H>, B=|V> 50% chance
case 2: A=|L>, B=|H> 25% chance
case 3: A=|R>, B=|H> 25% chance

But of course in order to compare the statistics, you would have to communicate the results from transmitter to receiver by some other lightspeed or slower method.

 

[UChr]

I'm trying to understand your point - so I have 2.5 questions:

1: A circularly polarized photon is measured as horizontally polarized by the first PBS. Its twin still should react as a vertically polarized when it later meets the receiver ??

2: I use my T(1) but modify the receiver to a PBS (+45).
After awhile, I look at the coincidence statistics.
All of which is detected as' +45' at T(1) ought to be detected as' -45 'at R ??

2.5: Are there made experiments - as you know - which is about equivalent to 2 ?

 

[SpectraCat]

Hmmm ... after further consideration, I don't think the explanation in my previous post was correct. Specifically, the stuff about the polarization basis for the entanglement not changing seems incorrect ... I have been arguing with local realists on another thread and may have ended up confusing myself .

I still stand by my statement that the receiver cannot know about the measurement choices made by the transmitter, but I have to admit that all I have to go on right now is dogma. I will continue to think about your example and see if I can come up with a correct, detailed explanation for why the receiver will always see a 50-50 distribution between polarization states.

 

[UChr]

Concerning Dogma: I feel the opposite; entanglement must necessarily lead to superluminal communication - otherwise entanglement should be reviewed.
Concerning my own ideas of superluminal communication: They have survived the first week in the forum !

 

[zonde]

The beam splitter is not a measurement on the photons. The entangled pair should therefore remain in a superposition although one of the twins encounters one or more PBS’s.

In order for photons to be in so called polarization entangled state there should be mixture of H and V photons in single beam. After first PBS you have only H or V in your beam and so they are not entangled any more just classically correlated.

 

[SpectraCat]

Concerning Dogma: I feel the opposite; entanglement must necessarily lead to superluminal communication - otherwise entanglement should be reviewed.
Concerning my own ideas of superluminal communication: They have survived the first week in the forum !

I figured out the problem .. the explanation I gave in post #11 WAS correct, I just temporarily forgot the reason why. When the transmitter photon hits the first PBS, it becomes entangles with the spatial paths in the device, which breaks the entanglement with the photon going to the receiver. Therefore the interaction with the first PBS *does* determine the measurement basis for the receiver photon, and the statistics will be exactly as I laid out.

 

[UChr]

About a PBS acts as a measurement and stops entanglement?
(This question is crucial for my argument, so I focus here on this issue.)

A: Usually you can assemble a beam again after a beam splitter (BS). After a PBS(v) use two mirrors that the two parts of the beam form a rectangle and a one-way mirror '- especially a PBS(v+90) - which transmits the part of the beam which was previously reflected and reflects the portion of the beam which was first transmitted. Then we're back to the beam before. (The first BS - may corrected with a few mirrors so the direction is exactly as before.) This is interpreted as an argument against that there has been a decisive intervention in the beam.

B: As I understand it follows a photon not a single path through a BS but both - in less the probability of one is 0%.

C: I do not recall having read that a BS stops entanglement unless it is followed by at least one detector. Do you have any reference?

 

[SpectraCat]

About a PBS acts as a measurement and stops entanglement?
(This question is crucial for my argument, so I focus here on this issue.)

A: Usually you can assemble a beam again after a beam splitter (BS). After a PBS(v) use two mirrors that the two parts of the beam form a rectangle and a one-way mirror '- especially a PBS(v+90) - which transmits the part of the beam which was previously reflected and reflects the portion of the beam which was first transmitted. Then we're back to the beam before. (The first BS - may corrected with a few mirrors so the direction is exactly as before.) This is interpreted as an argument against that there has been a decisive intervention in the beam.

Yes, the PBS does not destroy the entanglement entirely, however the photon that interacts with the PBS becomes entangled with the spatial paths in the apparatus (see below), and is no longer entangled with its original partner photon. This is used in some of the delayed choice quantum eraser (DCQE) experiments that have been performed. If at a later time, you recombine the two beams, you can reconstruct the entangled state. However, if you put detectors in one or both of the two paths (as in your example), then you have which way information, which means the entanglement is broken. The way that this is often explained is that you have to consider the entire experimental context in order to understand the results.

B: As I understand it follows a photon not a single path through a BS but both - in less the probability of one is 0%.

Yes, that's right .. that's why we say that the photon becomes entangled with the apparatus. The |H> polarization state becomes entangled with the path an |H> photon will take through the apparatus, and likewise for the |V> polarization state.

C: I do not recall having read that a BS stops entanglement unless it is followed by at least one detector. Do you have any reference?

That's right .. and the PBS *is* followed by a detector in your example.

As for the reference, that's a bit tricky ... I know I have run across the above explanation several times, but I am not sure if it has been from experts on PF, or from the original papers themselves. Try searching DCQE on here and reading through some of the threads. There is a particular experimental setup called a Mach-Zehnder interferometer ... one of the DCQE experiments uses such a setup. That is the context in which I remember this stuff being discussed.

 

[zonde]

About a PBS acts as a measurement and stops entanglement?
(This question is crucial for my argument, so I focus here on this issue.)

A: Usually you can assemble a beam again after a beam splitter (BS). After a PBS(v) use two mirrors that the two parts of the beam form a rectangle and a one-way mirror '- especially a PBS(v+90) - which transmits the part of the beam which was previously reflected and reflects the portion of the beam which was first transmitted. Then we're back to the beam before. (The first BS - may corrected with a few mirrors so the direction is exactly as before.) This is interpreted as an argument against that there has been a decisive intervention in the beam.

When you have beams of photons with definite polarization they are not entangled. They are in product state. PBS does exactly that - it separates H/V beam into H and V beam.
Let's say it's not measurement but entanglement stops just the same.

C: I do not recall having read that a BS stops entanglement unless it is followed by at least one detector. Do you have any reference?

The best reference I could find for the point I am making is this:
From http://arxiv.org/abs/quant-ph/9810003" :
"In several earlier experiments downconversion photon pairs of definite polarization were incident on a beamsplitter, and nonclassical correlations observed for those post-selected events in which photons traveled to different output ports [11]. However, the photons were actually created in polarization product-states."
Under [11] there are three references. I looked into first and I could not find anything about correlations between photons with definite polarizations, only about entangled photons produced after BS.

I suppose that classical correlations are not considered very interesting and so they are not getting much attention in papers.

 

[DrChinese]

I think everyone is saying almost the same thing - though I may slightly mislabel who is saying what. It is true that the detector (or similar) is required to end entanglement as SpectraCat says. It is also true that the PBS can be said to end the entanglement if it is subsequently detected. You cannot distinguish between the above statements as one being true and the other false. It is also true, as UChr says, that the beams can be reassembled to restore entanglement. And that is true EVEN IF the entanglement was broken on the other end already. (Shock!)

In all cases, the receiver sees a 50/50 split and that never changes as long as the ultimate source was entangled photons. There is no superluminal communication. I don't really follow what the UChr setup is that would prompt UChr to think anything else results. Because it won't.

 

[UChr]

OK - it looks like that this proposal for superluminal communication is in a serious crisis.

 

[UChr]

There is no superluminal communication.

Why would it not be an open question?

 

[SpectraCat]

There is no superluminal communication.

Why would it not be an open question?

Because we believe that the theory of relativity is correct, and information cannot travel faster than lightspeed.

 

[UChr]

Beliefs and dogma are indispensable - but they are non evidence and therefore naturally open questions for discussion. Entanglement - that seems to work non local - is in itself a challenge to some aspects of the theory of relativity

 

[SpectraCat]

Beliefs and dogma are indispensable - but they are non evidence and therefore naturally open questions for discussion. Entanglement - that seems to work non local - is in itself a challenge to some aspects of the theory of relativity

No, I am not relying on dogma ... I have *explained* already why that is not correct as far as we know. Everything about entanglement seems to obey the principle of relativity. There are other ways of getting "speeds" that are faster than lightspeed (cf. group velocity), but there is never any information transfer associated with those processes either.

 

[IllyaKuryakin]

Yes, it's frustrating, isn't it? It's possible to establish an instant correlation between two particles at any arbitrary distance, but any attempt to use it for information transfer is frustrated by the detailed physics. I think everyone goes through this at some point. Some just accept the rules that GR does not allow the transfer of information FTL and move on to other things. Some dig very deeply creating ever more complex arrangements to try to turn the correlation into communication, and learn lots of physics in the process. But in the end, we all wind up at the same point, GR holds and information cannot be transferred faster than light. If you choose the more difficult path, of trying to create FTL communications, you'll gain a very deep understanding of physics in the process of understanding why it will not work, so I wouldn't necessarily discourage it. But don't let it frustrate you, there's so much more to learn and understand, and it's great fun, isn't it?

I'm with you on the dogma thing. I despise dogma. But, there are physical facts that are more than mere dogma. I discern the difference between dogma and physical facts with experimental data. If one can't produce experimental data to justify their belief, I consider it dogma, or mysticism. Since there is a huge body of experimental data supporting Relativity, I consider it a physical fact, no matter how frustrating it may be with regards to my spaceships moving faster than light and even more importantly, being able to send stock prices into the past

 

[skippy1729]

Yes, it's frustrating, isn't it? It's possible to establish an instant correlation between two particles at any arbitrary distance, but any attempt to use it for information transfer is frustrated by the detailed physics. :

One solution to the frustration is that there is no instant correlation of particles. Consider the following two possible assumptions:

A. A quantum state is characterized by the probabilities of the various outcomes of every conceivable test. It is a mathematical tool created by and used by physicists. The quantum state exists in Hilbert space, not spacetime.

B. The quantum system, which we call a particle, is physically equivalent to the quantum state which describes it.

Without going into details it is easy to see that assuming A only, it is not possible to have instant correlation of particles.

The appeal of assumption B, in my opinion, is largely psychological: For example, the beautiful Hydrogen wave functions must be a glimpse of the underlying physical system. We all want to know what the magician is doing behind the curtain. When Mother Nature is the magician it is easy to ascribe physical reality to mathematical tools. A good portion, but not all, of the quantum mysteries stem from this assumption which has no experimental basis e.g nonlocality, contextuality, Schrodinger's cat, crypto-determinism.

 

[IllyaKuryakin]

One solution to the frustration is that there is no instant correlation of particles. Consider the following two possible assumptions:

A. A quantum state is characterized by the probabilities of the various outcomes of every conceivable test. It is a mathematical tool created by and used by physicists. The quantum state exists in Hilbert space, not spacetime.

B. The quantum system, which we call a particle, is physically equivalent to the quantum state which describes it.

Without going into details it is easy to see that assuming A only, it is not possible to have instant correlation of particles.

The appeal of assumption B, in my opinion, is largely psychological: For example, the beautiful Hydrogen wave functions must be a glimpse of the underlying physical system. We all want to know what the magician is doing behind the curtain. When Mother Nature is the magician it is easy to ascribe physical reality to mathematical tools. A good portion, but not all, of the quantum mysteries stem from this assumption which has no experimental basis e.g nonlocality, contextuality, Schrodinger's cat, crypto-determinism.

Well, I like the idea that a quantum state does not exist in spacetime. Therfore, space and time do not enter into the math of the entanglement. There are not even terms for them that can't be eliminated in the math of entanglement! So, if the quantum state does not exist in regular spacetime, where does the math reside? Just in our heads? No, I don't think so, Non-locality is a well proven mathematical concept. It's been demonstrated in hundreds of experiments and in many different fashions.

I think the math is real. In fact, I believe only the math is real. What we consider to be reality is simply our interpretation of the math. The math runs on the quantum computer we call the Universe.

So, when we see a nice piece of candy on the table, it's really not candy. It's the math of the surface causing the math of the photons to reflect into the math of our optic nerve and processed by a massively parallel computer in our head, which is really just some extremely complex transfer functions, to produce the holographic mathmatetical concept of a piece of candy. It's sort of like a "Matrix" concept. Reality isn't real. Only the math is real and we use it as a tool to create what we call reality. It all works fine until the math tells us something is true that can't possibly fit into our construct of reality.

That happened with the discovery of QM about a century ago and we still have not been able to rearrange our construct of reality to fit the math. But eventually we will, even if we have to go so far as revise our construct from physical reality to pure mathematics, like the guy watching the numbers fly by in the Matrix and seeing it's meaning. Now I'm hungry. Gone for a snack. The math of the cookies and milk exchanging electrons with the math of my taste buds will create some very satisfying equations representing satisfaction in my massively parallel computer

 

[StevieTNZ]

Has anyone else picked up the similar themes in these 'new peoples' posts, and what Varon seems to be asking. I wonder if they're the same person, just with different usernames.

I picked up Varon seems to have an unhealthy obsession with interpretations of QM, and he later posted not knowing which one is correct is insanity, at least to him.

 

[skippy1729]

So, if the quantum state does not exist in regular spacetime, where does the math reside? Just in our heads? No, I don't think so, Non-locality is a well proven mathematical concept. It's been demonstrated in hundreds of experiments and in many different fashions.

No, it has not been demonstrated in any experiment UNLESS you accept the identification of the statistical description of all possible interactions with the thing (THE QUANTUM STATE VECTOR) with the thing in itself (THE PARTICLE).

Alice and Bob prepare a pair of entangled particles and Bob takes one with him on his trip to never-never-land. Alice performs a measurement on her particle and immediately can assign a new state (Alice's state vector) to Bob's particle. No experiment can detect a physical change in Bob's remote lab. Until Bob performs a measurement or receives a message from Alice (along a timelike curve) his state vector is unchanged. At this point all that can be said is that Alice has better information about Bob's particle than Bob has.

You will note in this example that there are two state vectors for the same particle; Alice's state vector and Bob's state vector. They evolve independently as Alice and Bob acquire new information. In a sense they reside in Alice's mind and Bob's mind. But this is not some kind of absurd consciousness causing the collapse of an objective state vector which exists in the real world.

Skippy

 

[IllyaKuryakin]

Has anyone else picked up the similar themes in these 'new peoples' posts, and what Varon seems to be asking. I wonder if they're the same person, just with different usernames.

I picked up Varon seems to have an unhealthy obsession with interpretations of QM, and he later posted not knowing which one is correct is insanity, at least to him.

Said in jest Stevie. No offence meant, I hope none taken.

 

[UChr]

I will still present my second suggestion (Despite possible frustration)
The idea - as previously mentioned: interference / non-interference.

I compare with the Walborn's experiment: 'A double-slit quantum eraser' which has been discussed in the forum.
I transmit from ‘p to s’: p measured first - and even before the s-twin reaches the 'double slit'.
Transmitter - position 0:
Instead of Dp I place a polarizing beam splitter PBS(0) that transmits light polarized in the direction 0 degree = horizontal and reflects vertical light (90 degrees). This is followed by two detectors Dp(0) and Dp(90).
At Walborn should a coincidence counter between Dp(0) and Ds gives fringes - and between Dp(90) and Ds gives anti-Fringe (or vice versa).

Receiver:

When photon p is measured (0 or 90) the twin s will be set perpendicular - ie vertically / horizontally.
The receiver starts with a PBS(0).

All the now horizontal = ‘Dp (90)’ are transmitted and meets now a double slit with a detector. That should give anti-Fringes by this detector.

All the now vertical = initial horizontal = Dp(0) are reflected and meets another double slit with a detector. This should give fringes.

All in all: Interference by both double slit.



Transmitter position 1 - follow - if the above seem ok.

 

[DrChinese]

I will still present my second suggestion (Despite possible frustration)
The idea - as previously mentioned: interference / non-interference.

I compare with the Walborn's experiment: 'A double-slit quantum eraser' which has been discussed in the forum.
I transmit from ‘p to s’: p measured first - and even before the s-twin reaches the 'double slit'.
Transmitter - position 0:
Instead of Dp I place a polarizing beam splitter PBS(0) that transmits light polarized in the direction 0 degree = horizontal and reflects vertical light (90 degrees). This is followed by two detectors Dp(0) and Dp(90).
At Walborn should a coincidence counter between Dp(0) and Ds gives fringes - and between Dp(90) and Ds gives anti-Fringe (or vice versa).

Receiver:

When photon p is measured (0 or 90) the twin s will be set perpendicular - ie vertically / horizontally.
The receiver starts with a PBS(0).

All the now horizontal = ‘Dp (90)’ are transmitted and meets now a double slit with a detector. That should give anti-Fringes by this detector.

All the now vertical = initial horizontal = Dp(0) are reflected and meets another double slit with a detector. This should give fringes.

All in all: Interference by both double slit.



Transmitter position 1 - follow - if the above seem ok.

I don't follow your example. Are you trying to say that the transmitter does something (it is not clear what) and the receiver sees something different (also not clear what)? Because the pattern will actually be the same regardless. But can you clarify?

 

[San K]

It is also true, as UChr says, that the beams can be reassembled to restore entanglement. And that is true EVEN IF the entanglement was broken on the other end already. (Shock!)

you mean entanglement is restored non-locally?...you mean entanglement is restored between "unconnected" photons separated by time-space and not connected to/by any common source?

in my opinion the entanglement is not restored (and cannot be restored).

the re-appearance of the fringes (or anti-fringes) can be explained by sub-samples...(via coincidence counter)

 

[DrChinese]

you mean entanglement is restored non-locally?...

As "non-locally" as it was broken, yes. No one actually knows the point in time at which the superposition ceases. We speak as if it ends when the first observation is performed, and in a sense that is true. But really, that is more of a convenience for discussion than anything else.