Communicating Via Quantum Entanglement Using Time Differentiated Pulse

[ray3400]

TL;DR Summary

Question about trying to utilize quantum entanglement to create a communication protocol.

Which of these premises is impossible or incorrect according to our current understanding of quantum entanglement?

Given 2 entangled particles, p1 and p2:

• Observing paired particle p1 induces a change in spin on paired particle p2.
• There a way of detecting a change in spin on particle p2 without observing its starting point.

If these two premises can be held as true, someone can theoretically build a functional communication protocol using quantum entanglement. Even though the spins are randomized, all one needs is to generate an event trigger from the sender to the receiver. I.e. when p1 is observed, p2 changes its spin. The change in spin generates a 5v signal on a wire (the direction of the spin is arbitrary). Data can be encoded using time differentiation between the signals - I.e. a 1 ms delay is a binary 0, a 2 ms delay is a binary 1.

 

[phinds]

• There a way of detecting a change in spin on particle p2 without observing its starting point.

In order to "detect a change in spin on p2", you have to be OBSERVING p2's spin and any observation of the spin on either p1 or p2 breaks the entanglement.

 

[PeterDonis]

Which of these premises is impossible or incorrect

Both of them are incorrect.

#1 is incorrect because of relativity: if the two spin measurements are spacelike separated, their time ordering is not invariant, so there is no invariant fact of which one was first. The only invariant is that the measurement results are independent of which one is first. Which means there is no valid way to interpret either one as triggering a change in the other.

#2 is incorrect because it depends on #1 being correct, and #1 is incorrect.

 

[ray3400]

In order to "detect a change in spin on p2", you have to be OBSERVING p2's spin and any observation of the spin on either p1 or p2 breaks the entanglement.

What qualifies as "observing"? What if I observed the effects of the spin of p2 without observing it directly? Would that still break entanglement?

 

[ray3400]

Both of them are incorrect.

#1 is incorrect because of relativity: if the two spin measurements are spacelike separated, their time ordering is not invariant, so there is no invariant fact of which one was first. The only invariant is that the measurement results are independent of which one is first. Which means there is no valid way to interpret either one as triggering a change in the other.

#2 is incorrect because it depends on #1 being correct, and #1 is incorrect.

Thanks for the answer. I am still having a hard time understanding.

If I have a set of paired particles that must have the opposite spin.
t1 - Both particles spins are undetermined (p2's state is undetermined spin)
t2 - Particle p1 is observed and has an upward spin, and therefore particle p2's spin is determined instantaneously to have a downward spin (p2's state is downward spin)

There are, in this example, two states for particle p2 (undetermined spin and downward spin), which happen in chronological order. Is there a way to detect p2 going from state 1 (undetermined) to state 2 (determined) without observing the particle directly? I.e. observing the secondary effects of the state transition rather than observing the particle itself?

 

[phinds]

What qualifies as "observing"? What if I observed the effects of the spin of p2 without observing it directly? Would that still break entanglement?

You either know what the spin is or you don't. If you know, you have observed it, so your question exactly amounts to "what if I know the spin without knowing it?" It just doesn't make any sense.

Also, reread post #3 until you understand it, so that you can move on from your mistaken belief that you can use quantum entanglement for communication.

 

[ray3400]

You either know what the spin is or you don't. If you know, you have observed it.

A magnet moves through a coiled wire and creates a voltage in the wire. By measuring the voltage of the wire I can deduce that a magnet must have moved through it without actually having to physically observe the magnet itself.

If there was a measurable, secondary effect of the particle spin, would measuring that secondary effect break entanglement? What constitutes an observation?

 

[PeterDonis]

If I have a set of paired particles that must have the opposite spin.

Then you have an entangled state that does not work like anything you are used to. In particular, neither particle has a well-defined state by itself. It's not even correct to say that either particle has "undetermined spin". You simply cannot reason about the state of either particle in isolation the way you are trying to. You cannot rely on any of your intuitions. You have to actually do the math of QM and see what it predicts.

observing the secondary effects of the state transition

There is no "state transition"; this is an example of the kind of reasoning about the state of one of the particles in isolation that you simply cannot do when the particles are entangled.

 

[ray3400]

Then you have an entangled state that does not work like anything you are used to. In particular, neither particle has a well-defined state by itself. It's not even correct to say that either particle has "undetermined spin". You simply cannot reason about the state of either particle in isolation the way you are trying to. You cannot rely on any of your intuitions. You have to actually do the math of QM and see what it predicts.
There is no "state transition"; this is an example of the kind of reasoning about the state of one of the particles in isolation that you simply cannot do when the particles are entangled.

Is it not the case that the observation of one of the particles implies an absolute quality of the other entangled particle? If this is not the case, what is the significance of "entanglement" at all? It would mean nothing.

State 1: "Both particles are not well-defined"
Observation of particle 1
State 2: "Both particles are well-defined"

"Both particles are not well defined" -> "Particle 2 is not well defined"
"Both particles are well defined" -> "Particle 2 is well defined"

State 1: "Particle 2 is not well-defined"
Observation of particle 1
State 2: "Particle 2 is well-defined"

There is a change in states for particle 2, whether there is a "transition" or not, there is a change in states. Detecting "state 2 and not state 1" for particle 2 would be the mechanism for determining a signal. It doesn't matter whether the change from state 1 to state 2 is instantaneous or not. At one point in time particle 2 is in state 1, and at a later point in time it is in state 2. This is all that's needed.

The question then becomes whether you can detect that an entangled particle is "not well-defined" without observing it.

 

[phinds]

The question then becomes whether you can detect that an entangled particle is "not well-defined" without observing it.

It's not really a question for anyone here but you. You clearly aren't going to give up on this, but it seems pretty pointless for you to keep asking the same question without listening to the answers.

 

[PeterDonis]

Is it not the case that the observation of one of the particles implies an absolute quality of the other entangled particle?

No, because nothing requires the two particles to have their spins measured in the same direction. The entangled state of the two-particle system entails a lot more: it entails a precise level of correlation between spin measurements at all possible combinations of directions, not just the single case where the two measurements are in the same direction.

Again, you cannot use your intuition for this. You need to actually look at the math.

There is a change in states for particle 2

Wrong. Particle 2 does not even have a well-defined state when the two particles are entangled. Continuing to repeat your erroneous statements will simply lead to the thread being closed.

At one point in time particle 2 is in state 1, and at a later point in time it is in state 2.

Wrong. See above.

 

[PeterDonis]

an absolute quality

This wording suggests that you are imagining a local hidden variable model of the sort that Bell's Theorem rules out. You would be well advised to read up on Bell's Theorem.

 

[ray3400]

It's not really a question for anyone here but you. You clearly aren't going to give up on this, but it seems pretty pointless for you to keep asking the same question without listening to the answers.

When you say "There is no state transition" how is that the case given what I just said? There is a point in time when the particle is not well-defined and a point in time when the particle is well-defined.

No, because nothing requires the two particles to have their spins measured in the same direction. The entangled state of the two-particle system entails a lot more: it entails a precise level of correlation between spin measurements at all possible combinations of directions, not just the single case where the two measurements are in the same direction.

Again, you cannot use your intuition for this. You need to actually look at the math.
Wrong. Particle 2 does not even have a well-defined state when the two particles are entangled. Continuing to repeat your erroneous statements will simply lead to the thread being closed.
Wrong. See above.

Prior to observation:
"Both particles are not well defined" -> "Particle 2 is not well defined"

After observation:
"Both particles are well defined" -> "Particle 2 is well defined"

How is this not correct? Are both particles not defined prior

Just look at the math? Don't you think the math has to fit some sort of logical framework?

Also, let me try to narrow this down to a fundamental question:
What role does observation play

No, because nothing requires the two particles to have their spins measured in the same direction. The entangled state of the two-particle system entails a lot more: it entails a precise level of correlation between spin measurements at all possible combinations of directions, not just the single case where the two measurements are in the same direction.

Again, you cannot use your intuition for this. You need to actually look at the math.
Wrong. Particle 2 does not even have a well-defined state when the two particles are entangled. Continuing to repeat your erroneous statements will simply lead to the thread being closed.
Wrong. See above.

If you followed what I said I was asking if particle 2 would have a well-defined state after particle 1 has been observed. Not while they are still in an entangled state.

And I would think the math has to work within some logical framework in order for it to parallel what is seen with real-world experiments.

What is the significance of entanglement - what connection must be held true between the two entangled particles? If there is no connection that is held, they are just random particles doing their own random things and there is no point in differentiating entangled particles from non-entangled particles.

 

[StevieTNZ]

According to QM, no definite state arises. Linear superposition evolves into linear superposition. When you "measure" a quantum system, for example, spin, all that happens is entanglement of the apparatus with the system.

 

[PeterDonis]

Just look at the math? Don't you think the math has to fit some sort of logical framework?

Not if "logical framework" requires it to agree with your intuitions.

What is the significance of entanglement - what connection must be held true between the two entangled particles?

Whatever connection is given by the entangled quantum state of the two-particle system.

If your next question is "what is the entangled quantum state of the two-particle system", then you need to spend some time working through a QM textbook. As I've said, you cannot use your intuition for this. You really do need to learn the math. There's no shortcut.

 

[PeterDonis]

When you measure a quantum system, for example, spin, all that happens is entanglement of the apparatus with the system.

That's the first thing that happens, yes. What happens after that, strictly speaking, is interpretation dependent.

However, for practical purposes, what happens is that you can reduce the quantum state to the term in the entangled apparatus-system state that corresponds to the observed measurement result.

 

[ray3400]

Not if "logical framework" requires it to agree with your intuitions.
Whatever connection is given by the entangled quantum state of the two-particle system.

If your next question is "what is the entangled quantum state of the two-particle system", then you need to spend some time working through a QM textbook. As I've said, you cannot use your intuition for this. You really do need to learn the math. There's no shortcut.

I never said the logical framework needed to agree with my intuition. It only has to adhere to the rules of logic.

Fair enough to redirect me to a quantum physics book. When I have a question about something typically I ask the question before reading an entire book on it. There's really no need to have a negative attitude when someone is asking questions. I'm not doing anything unethical or immoral in asking questions.

 

[StevieTNZ]

I never said the logical framework needed to agree with my intuition. It only has to adhere to the rules of logic.

Might be worth googling 'quantum logic'.

Fair enough to redirect me to a quantum physics book.

Try "Sneaking a Look at God's Cards" -- https://www.amazon.com/dp/069113037X/?tag=pfamazon01-20 , and/or try an intro to basic Maths - https://www.crcpress.com/Quantum-Reality-Theory-and-Philosophy/Allday/p/book/9781584887034

You may be interested in reading https://www.amazon.com/dp/3319054724/?tag=pfamazon01-20

 

[ray3400]

Might be worth googling 'quantum logic'.

Try "Sneaking a Look at God's Cards" -- https://www.amazon.com/dp/069113037X/?tag=pfamazon01-20 , and/or try an intro to basic Maths - https://www.crcpress.com/Quantum-Reality-Theory-and-Philosophy/Allday/p/book/9781584887034

You may be interested in reading https://www.amazon.com/dp/3319054724/?tag=pfamazon01-20

I hate calculus, I'm guessing "quantum math" uses quadruple integrals embedded in an infinite series with 16 dimensions. I'm more interested in understanding how it works conceptually. I'm an software engineer so I was curious as to how the Rules of Quantum Mechanics can be taken advantage of to build a new type of device. I am aware of quantum computers, I was wondering if entanglement could be somehow manipulated to communicate data.

I'm guessing from this thread that it is impossible and people have already tried different ways of making it work. I heard that it can't work because the data is random, but that's not the reason it can't work, random data can still be used as an event trigger. The reason it can't work is because it fundamentally relies on the receiving end knowing when the coupled quantum property goes from undetermined to determined, which apparently is impossible.

 

[PeroK]

I hate calculus, I'm guessing "quantum math" uses quadruple integrals embedded in an infinite series with 16 dimensions. I'm more interested in understanding how it works conceptually. I'm an software engineer so I was curious as to how the Rules of Quantum Mechanics can be taken advantage of to build a new type of device. I am aware of quantum computers, I was wondering if entanglement could be somehow manipulated to communicate data.

I'm guessing from this thread that it is impossible and people have already tried different ways of making it work. I heard that it can't work because the data is random, but that's not the reason it can't work, random data can still be used as an event trigger. The reason it can't work is because it fundamentally relies on the receiving end knowing when the coupled quantum property goes from undetermined to determined, which apparently is impossible.

Here's a crude analogy of entanglement using nature as a computer system.

You have two particles, represented by messages. They get sent to two end-users. The messages are "sealed", so you have to invoke a process called "measurement" to see what's inside. The rule (that the system maintains) is that the messages are always the opposite of each other. Let's say "Yes" and "No".

Now, there are at least two ways that system could work. First, the system could simply randomly put "Yes" inside one message and "No" inside another. In QM terms this would be a "local hidden variable". The messages are predefined at the outset and, clearly, there is no way for one end user to send information to another end user simply by opening his message and seeing "Yes" or "No".

The other way is that the system could wait until someone opens a message and then decide. In a computer system this would involve communication, not between the end users, but between the end users computers and the central system. Also, in this case there is no way for one end user to communicate with another. It doesn't matter that the underlying system does some processing in "real time". The end users have no more control over the random choice of "Yes" or "No" that they get than in the previous example.

That's why you cannot communicate with someone using entanglement. You simply have absolutely no control over the data that the other user receives as a result of their measurement. Their measurements follow the same statistical pattern, regardless of what you do. Your measurements have no statistical influence on their measuerments.

In the above simple case, no matter what either user does, both users will get a simple, random sequence of equally likely "Yes" and "No" messages. If they get together afterwards, they will note that each sequence was a mirror of the other. But, there was never any way for one to influence what the other received. User A was never in a position to say: I want user B to get a "No" as the next message.

Note also that more sophisticated experiments (following Bell's theorem) have shown that in fact the simple model of local hidden variables cannot be what's happening. QM is more like the second example where the content of each message (somehow) is not decided until it is measured.

Now, re entanglement, this of course begs the question of how nature maintains this "real time" correlation of data? The answer is that no one knows and the question itself may not even be meaningful.

There was a thread on here a little while back about all the theoretical possibilities for how nature might maintain quantum entanglement. PS I've found it now - see below.

There's also a lecture here from the Royal Institution with a better analogy than mine, which might be worth watching:

 

[PeterDonis]

It only has to adhere to the rules of logic.

You are mistaken if you think it doesn't. But just adhering to the rules of logic isn't enough. You also have to be reasoning from correct premises. You are not, so you are getting incorrect answers.

When I have a question about something typically I ask the question before reading an entire book on it.

And sometimes the answer to the question is that there's way too much background information needed to be able to give it to you in a single discussion thread, and you need to take the time to work through a textbook to get it.

 

[PeroK]

@ray3400

PS here's the post on theorectical mechanisms for entanglement.

https://www.physicsforums.com/threads/question-about-an-entanglement-paper.966466/post-6135402

 

[DrChinese]

I'm guessing from this thread that it is impossible and people have already tried different ways of making it work. I heard that it can't work because the data is random, but that's not the reason it can't work, random data can still be used as an event trigger. The reason it can't work is because it fundamentally relies on the receiving end knowing when the coupled quantum property goes from undetermined to determined, which apparently is impossible.

A couple of points to consider. In your example, you assume that an earlier measurement on P1 causes a change to P2. It is equally "true" that later observing P2 causes a change to earlier P1 (a violation of causality). There is no *demonstrable* difference because time ordering is NOT a factor in entanglement*.

What does that mean to your example? It means that you CANNOT select which direction a (hypothetical) signal goes in. That wrecks your communication protocol. And yes, many different scenarios have been studied in entanglement. There have been 1000+ papers per year on the subject for the last 10+ years. This is June's list so far, per the preprint arxiv:

https://arxiv.org/find/quant-ph/1/AND+all:+jun+abs:+entanglement/0/1/0/2019/0/1?per_page=100*There are a number of experiments that exploit the time ordering issue to create some very strange situations. For example, particles can be entangled *after* they are detected. But none of these serve to create communication channels.

 

[PeroK]

This is June's list so far, per the preprint arxiv:

https://arxiv.org/find/quant-ph/1/AND+all:+jun+abs:+entanglement/0/1/0/2019/0/1?per_page=100

I hope you're going to read them all!

 

[DrClaude]

I hate calculus, I'm guessing "quantum math" uses quadruple integrals embedded in an infinite series with 16 dimensions.

Not for what you are inquiring about here. I suggest you get a copy of Quantum Mechanics by David H. McIntyre. The first four chapters cover all that you need here, and the first integral doesn't appear until chapter 5