Unconditional quantum teleportation?

[Dancing David]

For cryptography, you want a random key. QM offers many sources of true randomness.
When entangled particles are measured in the same way at different locations, then the results will be random but complementary.

I think you could say that the key is generated in both locations at once.

If someone intercepts and measures one of the entangled particles, then there won't be matching keys generated. If the person prepares a particle with the correct state and sends it on, then this will be detected via Bell's inequalities. That's a bit of a long story.


Functional fixedness is a psychological bias. We tend to think of tools as for one specific purpose and find it difficult to conceive of other uses.
You originally doubted the usefulness of entanglement. However, your posts since then suggest that you did not consider entanglement in any other context but for communicating with (Which is a shame since that is the one thing it certainly can't be used for, according to current theory). I speculate that this may have been an example of aforementioned bias.

My statements did not state that there are no ways to use entanglement, but about teleportation and then about something related.

Is mind reading something you do often?

Or is that just my bias again?

 

[Dancing David]

It depends if there is a practical limitation to the distance between the particles, and how fast and easy it becomes to change and read their states.

If we become able to change and read their states in a millisecond, and have no limit to the distance, then it could be very useful. Imagine having real time communications with a team of explorers on the Martian surface, or with a satellite around Neptune.

True it might not be possible, but each step is another one toward understanding the possible uses of this "spooky action".

Um that is a good example of what i am saying would be very difficult, especially the maintenance of entangled pairs.

 

[steenkh]

That's quantum teleportation.

Why is this called teleportation? It has nothing to do with the traditional meaning of the word. Not a single atom is transported.

 

[GnaGnaMan]

My statements did not state that there are no ways to use entanglement, but about teleportation and then about something related.

Your initial statement was this:

The issue is that quantum entanglement will not lead to anything really useful. It usually is only over limited distances, very particular conditions. And as communication it has extreme limitations, in that codes would have to be arranged in advance and the the entangled bit moved to location.

---

Is mind reading something you do often?

Never.

Or is that just my bias again?

Do you think it was that bias then?

 

[GnaGnaMan]

Why is this called teleportation? It has nothing to do with the traditional meaning of the word. Not a single atom is transported.

I'd like to know that, too. I always figured that nerds really like Star Trek.

In Star Trek, the original is destroyed, beamed elsewhere and recreated there. That's a lot like what happens in quantum teleportation.
What's missing in quantum teleportation is the "beaming" of the orginal matter. That part is pointless as it is generally held that all particles of a kind are the same (except for state and location).

 

[Dancing David]

Your initial statement was this:

---


Never.


Do you think it was that bias then?

Um, I concede that your piss flows much farther and with greater force than mine.

Thanks for the edit, but even granted the HIP I shall not engage in urine streaming competitions with you.

 

[steenkh]

I
In Star Trek, the original is destroyed, beamed elsewhere and recreated there. That's a lot like what happens in quantum teleportation.

What's missing in quantum teleportation is the "beaming" of the orginal matter. That part is pointless as it is generally held that all particles of a kind are the same (except for state and location).

I do not mind that the 'beaming' is missing, but as far as I know not a single atom has been reconstructed at the other end.

 

[GnaGnaMan]

I do not mind that the 'beaming' is missing, but as far as I know not a single atom has been reconstructed at the other end.

Photons or atoms, does it really matter?

Anyways:
http://www.nature.com/nature/journal/v429/n6993/abs/nature02570.html

 

[Anders Lindman]

"These results establish diamond spin qubits as a prime candidate for the realization of quantum networks for quantum communication and network-based quantum computing." -- http://www.sciencemag.org/content/early/2014/05/28/science.1253512

"Teleportation of quantum information has been accomplished before, but the process was not close to reliable, typically working once in every 100 million attempts. The new method achieves that feat every time." -- http://www.techtimes.com/articles/7817/20140530/quantum-teleportation-made-possible-data.htm

Impressive, but quantum computing is very limited today. The main problem is that it's tricky to deal with more than a few qubits at a time.

"A qubit has a few similarities to a classical bit, but is overall very different. Like a bit, a qubit can have two possible values—normally a 0 or a 1. The difference is that whereas a bit must be either 0 or 1, a qubit can be 0, 1, or a superposition of both." -- http://en.wikipedia.org/wiki/Qubit

 

[Roboramma]

I do not mind that the 'beaming' is missing, but as far as I know not a single atom has been reconstructed at the other end.

What's "teleported" is the state of the particle. You start with a particle here in a certain state, and you end up with a particle there in that same state. There is still a particle here, but it's no longer in that state. There was a particle there to begin with, but it wasn't in that state originally.

As I understand it, anyway...

 

[Roboramma]

I think the issue that Einstein had with entanglement was as follows:

If you take two entangled particles and separate them, you can have them in a state that's something like, 50% Up, 50% Down for both (these are probabilities). When you measure one and find that it's up, it tells you that the other is down.

But let's day that we arrange it so that I keep particle A and you take particle B somewhere far away.
Now, we arrange it so that I first measure A then 1 second later you measure B. I find A is Up, and then 1 second later you necessarily measure B to be down. It seems that A and B were both in an indeterminate superposition of states until I measured A, which caused them both to be in a definite state (A=Up, B=Down).

But according to relativity there is no such thing as simultaneity. If we're far enough apart, as measured from a different reference frame, you measured B before I measured A. So, which measurement caused the collapse of the wave function, yours or mine?

Thus, Einstein figured that they must both originally be in a definite state, we just don't know all the details of that state, and thus can't calculate the outcome of any particular experiment, but those "hidden" details must be there. That's hidden variables.
However, Bell's inequality shows that there can't be hidden variables.

 

[annnnoid]

I think the issue that Einstein had with entanglement was as follows:

If you take two entangled particles and separate them, you can have them in a state that's something like, 50% Up, 50% Down for both (these are probabilities). When you measure one and find that it's up, it tells you that the other is down.

But let's day that we arrange it so that I keep particle A and you take particle B somewhere far away.
Now, we arrange it so that I first measure A then 1 second later you measure B. I find A is Up, and then 1 second later you necessarily measure B to be down. It seems that A and B were both in an indeterminate superposition of states until I measured A, which caused them both to be in a definite state (A=Up, B=Down).

But according to relativity there is no such thing as simultaneity. If we're far enough apart, as measured from a different reference frame, you measured B before I measured A. So, which measurement caused the collapse of the wave function, yours or mine?

Thus, Einstein figured that they must both originally be in a definite state, we just don't know all the details of that state, and thus can't calculate the outcome of any particular experiment, but those "hidden" details must be there. That's hidden variables.
However, Bell's inequality shows that there can't be hidden variables.

...but there also can't be instantaneous 'communication'. Yet according to the results of these experiments instant 'communication' is exactly what occurs.

 

[xtifr]

...but there also can't be instantaneous 'communication'. Yet according to the results of these experiments instant 'communication' is exactly what occurs.

Why can't there be instantaneous communication? Relativity says that matter and energy can't travel faster than the speed of light, but that's not what's happening here. Nothing physical is moving; no energy is transmitted.

 

[Roboramma]

...but there also can't be instantaneous 'communication'. Yet according to the results of these experiments instant 'communication' is exactly what occurs.

Actually, they don't show that instantaneous communication occurs. They just show that the situation isn't classical.

See, for instance, the many worlds interpretation of QM. http://en.wikipedia.org/wiki/Many_worlds

If looked at from this perspective it becomes quite clear that there's no transfer of information involved.

 

[steenkh]

What's "teleported" is the state of the particle. You start with a particle here in a certain state, and you end up with a particle there in that same state. There is still a particle here, but it's no longer in that state. There was a particle there to begin with, but it wasn't in that state originally.

As I understand it, anyway...

That is also how I understand it. I would just have called it quantum communication. It seems to me that the PR department wanted to find some expression that could more easily grab the imagination.

Anyway, I think I made my point, so I will stop flogging this half-dead horse now.

 

[GnaGnaMan]

That is also how I understand it. I would just have called it quantum communication.

That seems even worse to me. What communication happens is classical, using conventional means.

It seems to me that the PR department wanted to find some expression that could more easily grab the imagination.

I doubt that PR departments provide input on basic research in Q physics.

 

[sol invictus]

Why can't there be instantaneous communication? Relativity says that matter and energy can't travel faster than the speed of light, but that's not what's happening here. Nothing physical is moving; no energy is transmitted.

According to relativity, the time-ordering of events that are instantaneous in one frame of reference will be backwards in time in another. Hence instantaneous information transfer leads to causal paradoxes (you can talk to your past self, but you don't remember talking to your future self) and is impossible.

Fortunately, quantum teleportation (and QM in general) does not allow instantaneous communication. To teleport a QM state requires classical information, which travels at the speed of light.

 

[Anders Lindman]

I have an awesomely simple theory for quantum entanglement. Entangled particles are the same shared waveform. So two entangled particles are the same wave packet stretched out. Change on one side affects the other side instantaneously, regardless of the distance between the two sides.

Here is a single wave packet broken down into individual "nonlocal" components (sine waves): http://4.bp.blogspot.com/-w8OiIwxYgvM/UGKP6Z57j6I/AAAAAAAACLI/24J-q_n3wpc/s1600/wpac5.gif

Two wave packets are still one single waveform: http://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Wave_packets.png/400px-Wave_packets.png

 

[xtifr]

According to relativity, the time-ordering of events that are instantaneous in one frame of reference will be backwards in time in another. Hence instantaneous information transfer leads to causal paradoxes (you can talk to your past self, but you don't remember talking to your future self) and is impossible.

Fortunately, quantum teleportation (and QM in general) does not allow instantaneous communication. To teleport a QM state requires classical information, which travels at the speed of light.

Really? I thought that it was the fact that the information is random and non-deterministic is why it didn't violate causality. Maybe I'm mixing up measuring the state of one of an entangled pair with actually "teleporting" the state. But the former case seems to involve information transfer at more than the speed of light.

 

[Soapy Sam]

According to relativity, the time-ordering of events that are instantaneous in one frame of reference will be backwards in time in another. Hence instantaneous information transfer leads to causal paradoxes

Why? If in my frame A precedes B , but from yours B precedes A, there must be some frame in which A and B are simultaneous?
Why is that more paradoxical than B preceding A? (Which I'm jolly sure it didn't!)