about entanglement/teleportation

[Itoero]

hi,

I have some questions about quantum entanglement/teleportation.

 

The idea is that correlation does not imply causation, concerning entangled particles.

That's shown in the fact that entangled particles are described as single wave functions.

We know there are channels between entangled particles which enable teleportation.

So why don't those channels cause the correlation?

Why can't entanglement be about causality?

If it is, then entangled particles would copy information, which goes in against the no-cloning theorem.

 

How can you know you are transmitting and not copying information during a teleportation?

Teleportation collapses the entanglement, it collapses the wave function...so can you really know what happens with the information?

Isn't Heisenberg's uncertainty principle all over such an experiment?

[swansont]

hi,

I have some questions about quantum entanglement/teleportation.

 

The idea is that correlation does not imply causation, concerning entangled particles.

That's shown in the fact that entangled particles are described as single wave functions.

We know there are channels between entangled particles which enable teleportation.

So why don't those channels cause the correlation?

The correlation is present before the teleportation.

 

Why can't entanglement be about causality?

If it is, then entangled particles would copy information, which goes in against the no-cloning theorem.

 

How can you know you are transmitting and not copying information during a teleportation?

Teleportation collapses the entanglement, it collapses the wave function...so can you really know what happens with the information?

Isn't Heisenberg's uncertainty principle all over such an experiment?

In teleportation, the information contained in the original particle is destroyed. There is no cloning going on.

[Itoero]

Ok, but we know there are channels between entangled particles, otherwise teleportation could not happen.

Why are those channels not the cause for the correlation?

Are those channels non existent until you try to teleport?

[swansont]

Ok, but we know there are channels between entangled particles, otherwise teleportation could not happen.

Why are those channels not the cause for the correlation?

Are those channels non existent until you try to teleport?

 

What channel is there between the entangled particles? I think you're assuming something that isn't true.

[Itoero]

There is a quantum and classical channel between entangled particles.

[swansont]

There is a quantum and classical channel between entangled particles.

 

No, there isn't. One of the (unsettling, to some) things about teleportation is that there is no communication channel between the particles. The results of the entanglement have been observed nearly simultaneously. If there was some communication channel it would require the communication happen at many times the speed of light.

 

There is discussion of requiring channels for teleportation; you have to send information via a classical channel in order to do the teleportation, and this is limited to c, which is why you can't use this for superluminal communication.

 

You might need to take a step back and firm up your understanding of entanglement and teleportation and what is involved.

[Itoero]

Another physicist told me something different.

He said teleportation demands a classical and quantum channel.

Teleportation works with entangled particles, so entangled particles show the same channels.

In Wikipedia there is a Quantum teleportation diagram that shows this.

[swansont]

Another physicist told me something different.

He said teleportation demands a classical and quantum channel.

 

That's not really different than what I said. Teleportation requires the classical channel to send certain information; I assume the "quantum" channel being referred to is the signal (particle) that's sent that teleports the state.

 

Teleportation works with entangled particles, so entangled particles show the same channels.

In Wikipedia there is a Quantum teleportation diagram that shows this.

Teleportation requires entanglement, but entanglement can occur in situations that do not involve teleportation.

[Itoero]

ok

Can you give an example in which entanglement doesn't enable teleportation?

[swansont]

ok

Can you give an example in which entanglement doesn't enable teleportation?

 

Bell test experiments do not involve teleportation. Just detecting the entangles particles.

https://en.wikipedia.org/wiki/Bell_test_experiments

 

Quantum eraser experiments

https://en.wikipedia.org/wiki/Quantum_eraser_experiment

 

Also the tests that show the wave function collapses faster than would be allowed by communication limited by the speed of light (possibly similar to Bell tests)

http://www.nature.com/nature/journal/v454/n7206/edsumm/e080814-10.html

 

No teleportation involved.

[Itoero]

Measuring a particle or teleportation causes the wave to collapse.

So the idea that information is transmitted faster then the speed of light (via privileged frame?) does it come from the speed in which the wave collapses?

 

If measuring one of the entangled particles makes the wave to collapse, then how can you detect entanglement between 2 particles?

Doesn't Heisenbergs uncertainty prevents measuring entangled particles?

Edited October 27, 2015 by Itoero

[swansont]

Measuring a particle or teleportation causes the wave to collapse.

So the idea that information is transmitted faster then the speed of light (via privileged frame?) does it come from the speed in which the wave collapses?

 

The mistaken notion that you can transmit information faster than c comes from the speed of the wave function collapse. But it sends no information — all of the information about the system is there in the first particle — you already know they're entangled. Sorta like rolling an enormous die or flipping a giant coin. Knowing what's on the side facing you instantly tells you what's on the opposite side, even though if these things were big (say, 1/3 of a meter thick), information from the other side would take an extra nanosecond to get to you. Or scale that up as much as you want. You still know the correlation between heads and tails before the experiment is done, so that information doesn't need to be transmitted to you.

 

What you don't know is the answer you will get when you make the measurement.

 

If measuring one of the entangled particles makes the wave to collapse, then how can you detect entanglement between 2 particles?

Doesn't Heisenbergs uncertainty prevents measuring entangled particles?

Take a spin-1/2 system for example. Once you've set the coordinate system, spin is either up or down, so you could entangle particle to have the same or opposite spin. These are not subject to the HUP; they are not conjugate variables of the same system. Different spin projection of the same particle are — you can't measure the spin projection along two different axes at the same time to better than the HUP limit. But measuring only the spin, along only one axis? No limitation.

 

You detect the entanglement by noting the correlation between the two measured particles. It will be much better than some limit, which is dictated by the details of the experiment and what you're trying to show. You might expect particle B to be identical (or opposite) to A half the time, for example, if things were random. But it's larger, (possibly 100% within experimental limitations, but at the very least the uncertainty excludes the lower limit from being possible), and that's how you know they were entangled.

[Itoero]

1/2 spin..those are fermions?

Why aren't they subject to HUP?

I don't understand how you can say particles are entangled without intervening.

Are there loopholes concerning HUP?

 

If all the information is present in the first particle, does that mean the information is superposed in the wave?

Changing the quantum state (by measuring) collapses the wave.

When the wave collapses, does the superposed information go to one of the ex-entangled particles where it forms a new superposition which you can interpret as teleported information?

 

You have a very good way of explaining things.

Edited October 27, 2015 by Itoero

[swansont]

1/2 spin..those are fermions?

Why aren't they subject to HUP?

I don't understand how you can say particles are entangled without intervening.

Are there loopholes concerning HUP?

 

If all the information is present in the first particle, does that mean the information is superposed in the wave?

Changing the quantum state (by measuring) collapses the wave.

When the wave collapses, does the superposed information go to one of the ex-entangled particles where it forms a new superposition which you can interpret as teleported information?

 

You have a very good way of explaining things.

 

The HUP says that certain variable pairs can't be exactly determined simultaneously for a particle. Position and momentum, for example. If you prepared an ensemble of particles exactly the same and measure the position of half and momentum of half, you would be limited in your precision by the HUP.

 

But you aren't measuring a pair of variables. We're measuring the same variable.

 

The wave function contains all the information about both particles. When you make the measurement, you are getting all that information.

[Itoero]

So the wave function contains info about both particles.

By measuring one of the entangled particles(A), you get all the info and the wave collapses.

But then what happens with the quantum state of the other particle(B) if all info is measured in A?

 

If it's possible to simultaneously measure both entangled particles.

Then what will the measurements give?

 

edit

On internet I read that "neither of entangled particles has a definite state until one is measured, which causes the other particle to assume a corresponding state."

=>How is that possible when measurement of one of the particles breaks the wave?

Edited October 28, 2015 by Itoero

[swansont]

So the wave function contains info about both particles.

By measuring one of the entangled particles(A), you get all the info and the wave collapses.

But then what happens with the quantum state of the other particle(B) if all info is measured in A?

 

If it's possible to simultaneously measure both entangled particles.

Then what will the measurements give?

 

edit

On internet I read that "neither of entangled particles has a definite state until one is measured, which causes the other particle to assume a corresponding state."

=>How is that possible when measurement of one of the particles breaks the wave?

The measurement collapses the wave function. It goes from the superposition to a specific eigenstate, for each particle. Spin up and spin down, for example.

[Itoero]

ok

I've read several times that space time is built by or emerges from entanglement.

I there a simple way of explaining this?

Hirosi Ooguri has written a paper about it.

Edited October 31, 2015 by Itoero

[imatfaal]

ok

I've read several times that space time is built by or emerges from entanglement.

I there a simple way of explaining this?

Hirosi Ooguri has written a paper about it.

 

Certainly not. To begin with it is not an established concept - General Relativity and spacetime (ie that gravity is the intrinsic curvature of spacetime in which time is a dimension along with three spatial dimensions which form a 4 dimensional space time) is purely classical whereas entanglement (the superposition of states across multiple particles which are spatially separate) is quintessential quantum mechanical. Any crossover is at the cutting edge of physics in the search for a quantum mechanical theory of gravity. To illustrate - spacetime is thought of as the geometry, the assemblage, and relationships between all events; it is not considered as a medium within which we exist. In and of itself this idea is not simple - to consider spacetime as something concrete which is created by particles is mind-bending.

 

Furthermore neither of the individual concepts has a "simple" way of explaining it - there are cutdown analogies that help you visualise a part of the idea; but the actual theories in their working form are very hard graduate physics with mathematics which would make your teeth ache. You can read in various threads in the Relativity forum at present the danger of taking these analogies too far - you can neither test nor expand the physics without getting to grips with it and that means leaving the simplifications behind and tackling the maths.

 

No overarching explanation of the universe can be without quantum mechanics because at the energetic and small levels it rules - but at large distances and when dealing with great masses we must also consider gravity; at present we don't even have a handle on how to merge these two disparate theories. We hypothesize about soon after the big bang and near black holes because these are areas where we realise that both the curvature of spacetime predicted by General relativity AND the quantum mechanical effects will both be influential and unable to be ignored - the rest of the time we look at one or the other but not both.

[Starfield]

But he is not asking about quantum mechanics in general, he is asking about quantum entanglement. The sad thing about entanglement, is that it is real at some level, but it is fully not understood. Even the people who are doing experiments, do not know what is happening. So the question is valid, but all direct answers are just theoretical.

[swansont]

But he is not asking about quantum mechanics in general, he is asking about quantum entanglement. The sad thing about entanglement, is that it is real at some level, but it is fully not understood. Even the people who are doing experiments, do not know what is happening. So the question is valid, but all direct answers are just theoretical.

 

The experimenters know what is happening, as in what results they will get. What they don't know is why that happens, at a fundamental level. But that's true of QM in general, though. Physics overall, really. There's a level below which you can't explain why something works the way it does.

[Itoero]

Entanglement goes seemingly a lot faster then the speed of light....so that's I suppose why they assume entangled particles are connected with a wormhole.

A wormhole is a hole trough space time, caused by the warping of space time.

Isn't it more logic to think that a wormhole is not a hole trough space time and it does not bend space time.

A wormhole is just a connection between particles that does not use space time as a medium....it uses a privileged frame.

Wouldn't that explain why space time is not the medium we live in?

Edited November 8, 2015 by Itoero

[swansont]

A privileged frame is contrary to the physics we know.

[Itoero]

Yes, but in the physics we know, space time is a fundamental force.

A wormhole is a hypothetical feature that basically explains how matter or information can travel seemingly faster then the speed of light with space time as fundamental force/medium.

If Hirosi Ooguri is right, then the superposed information between entangled particles does not use space time as fundamental force so there can't be a wormhole or other gravitational forces...yet it goes seemingly a lot faster then the speed of light.

 

Hirosi wrote a paper about entanglement and space time.

There is an arXiv preprint of that paper, it's called 'Tomography from Entanglement.'

I can't copy/paste...

[swansont]

Yes, but in the physics we know, space time is a fundamental force.

It is? What's the exchange particle for this force?

 

A wormhole is a hypothetical feature that basically explains how matter or information can travel seemingly faster then the speed of light with space time as fundamental force/medium.

If Hirosi Ooguri is right, then the superposed information between entangled particles does not use space time as fundamental force so there can't be a wormhole or other gravitational forces...yet it goes seemingly a lot faster then the speed of light.

 

Hirosi wrote a paper about entanglement and space time.

There is an arXiv preprint of that paper, it's called 'Tomography from Entanglement.'

I can't copy/paste...

How did wormholes get into this? That's discussed another thread, and IIRC it was only broached in the context of the black hole firewall problem. You're extrapolating from multiple hypotheses that have no experimental evidence to support them.

[Itoero]

I read an article about a paper in which Juan Maldacena and Leonard Susskind found a link between Wormholes and entanglement.