# Communication by means of entanglement for the layman

1. Jun 6, 2013

### Demos Mirak

Hello, I'm currently working on the background for a science fiction collection of short stories I am working on, and communication by means of entanglement plays a big role in it, and I want to make sure that I get it right. So here it comes.

As I understand it, particles can become entanglement by various physical interactions, which causes particle 1 to have the opposing spin of particle 2 (clockwise and counterclockwise). Changing the spin of particle 1 changes the opposing spin of particle 2, thus allowing information to be send. Sadly, measuring the particles spin influences the atom, thus corrupting the data send. To circumvent this problem, I proposed to create an entangled pair, consisting of particle 1 and 2, and then entangle 2 with 3. I then only measure the state of particle 3, discarding it in the process, and creating a new 3 to replace the old one. Could this work?

I am no expert on the subject of physics, least of all quantum physics and neither is English my mother tongue, and so if any faults, of which I am sure there are many, in reasoning could be explained in laymanâ€™s terms, I would be very grateful.

The information that caused this idea can be found in this article: http://www.extremetech.com/extreme/...ntanglement-of-photons-through-space-and-time

2. Jun 6, 2013

### Staff: Mentor

Afraid not - there is this thing called the no cloning theorem:
http://en.wikipedia.org/wiki/No-cloning_theorem

But even if it were possible I cant see how it would work anyway. The problem with using EPR to send data is we only know correlations - we know its the same as what the guy at the other end measured but he has no idea what that will be so cant manipulate it to communicate anything.

If you want to imagine it for science fiction purposes you might like to work into the story line some breakthrough that allows, via some sub-quantum process, the ability to actually manipulate the spin of the photon at the transmitter.

A method if cloning was possible is detailed here:
http://en.wikipedia.org/wiki/Superluminal_communication

So another possibility is for you to imagine some breakthrough that allows cloning.

Thanks
Bill

Last edited: Jun 6, 2013
3. Jun 6, 2013

### Demos Mirak

So the no cloning theorem leads to a no communication theorem, which states that instantaneous transfer of information by means of entanglement alone is impossible and the no teleportation theorem, which states that quantum information cannot be transmitted by means of classical information channels. It is then said that a combination of both can make this possible, but that defeats the purpose of the superluminal communication. Is there any way around this? Is there a theoretical way to have a superluminal way of communication, which does not need help of a classical information channel.

I missed your edit there, thanks for the extra information.

4. Jun 6, 2013

### VantagePoint72

The no signalling theorem is not a consequence of the no cloning theorem. It is proved independently. There is no way around the no signalling theorem without falsifying quantum mechanics itself.

No. Superluminal communication is not possible with entanglement or any other aspects of quantum mechanics.

5. Jun 6, 2013

### wotanub

He could just make it so Alice calls Bob and tells the result of her Bell state measurement. Or something even more dramatic like "Phone calls are insecure! we need to transport the result personally, but Bob can only "freeze" the quantum state for a limited amount of time, so we need to hurry!" then throw something in about a coherence time or something.

I don't know your plot OP.

6. Jun 6, 2013

### VantagePoint72

That's complete nonsense. We already can manipulate quantum states by coupling them to interaction Hamiltonians. Doing so breaks the entanglement with other particles. "Sub-quantum process" is just technobabble for "not quantum mechanics". Of course, you can do whatever you like in a story, but what you are suggesting is equivalent to saying that the story exists in a world where the fundamental laws of physics as we know them have been overturned. At that point, it's just plain fiction.

7. Jun 6, 2013

### Staff: Mentor

Errrr. Not quite. It is possible that QM is an approximation to an even more fundamental theory that, for SF purposes, allows this to be done.

Greg Bear used this device in one of his SF stories where he called it noach or something like that.

SF does this sort of thing all the time - time travel is a common one. If you could do it all sorts of physical paradoxes are possible but we suspend belief for a good story line. In fact signalling FTL causes the same problem - you can violate causality.

Thanks
Bill

Last edited: Jun 6, 2013
8. Jun 6, 2013

### Demos Mirak

Thank you guys for your replies. My story does not involve spaceships or space travel, so the thing about large distances are irrelevant. The thing I was looking for was the fact that there was no physical interaction between the two objects, that there was not some signal going between the two and thus no interference from other factors.

9. Jun 6, 2013

### Ravi Mohan

Maybe you can use the concept of Quantum Teleportation http://en.wikipedia.org/wiki/Quantum_teleportation mainly because

1) It includes communication by entangled stuff (+ communication through classical channel which is must)
2) The name may fascinate the redears.
3) It is well tested and it works. We use it in Quantum Computation.