# The Naked Scientists Forum

### Author Topic: Can we communicate via entangled particles?  (Read 9214 times)

#### jeffreyH

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##### Can we communicate via entangled particles?
« on: 16/04/2015 18:18:08 »
Take a transmitter of entangled particles. Assume for the moment that these particles can be directed precisely without disturbance of the entanglement. We then have two receivers an equal distance apart in directions exactly opposite each other with respect to the transmitter. As they both detect the particles they can then tell from their results exactly what the other observer should have detected. This must be wrong somehow because it is off the top of my head.

EDIT: You then tell each receiver what states represent true and false, except that it is the opposite way round for each one.
« Last Edit: 16/04/2015 18:20:14 by jeffreyH »

#### chiralSPO

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##### Re: Can we communicate via entangled particles?
« Reply #1 on: 16/04/2015 20:20:23 »
I don't think there is any information transferred from one receiver to the other in this scenario.

#### PmbPhy

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##### Re: Can we communicate via entangled particles?
« Reply #2 on: 16/04/2015 21:56:29 »
Take a transmitter of entangled particles. Assume for the moment that these particles can be directed precisely without disturbance of the entanglement. We then have two receivers an equal distance apart in directions exactly opposite each other with respect to the transmitter. As they both detect the particles they can then tell from their results exactly what the other observer should have detected. This must be wrong somehow because it is off the top of my head.

EDIT: You then tell each receiver what states represent true and false, except that it is the opposite way round for each one.
This is the subject of quantum teleportation. See:
http://en.wikipedia.org/wiki/Quantum_teleportation

#### jeffreyH

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##### Re: Can we communicate via entangled particles?
« Reply #3 on: 16/04/2015 22:21:03 »
Thanks Pete. I thought I was going to be shot down in flames. I really need to start learning quantum physics. I hope it isn't like some of the other stuff I have been learning. I can't get my head round some of it yet.

#### evan_au

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##### Re: Can we communicate via entangled particles?
« Reply #4 on: 16/04/2015 22:36:21 »
This is also the mechanism of quantum encryption.

However, because we currently don't have efficient ways to generate entangled particles, the degree of entanglement is quite low. The entanglement is often lost over the transmission path ("decoherence"), so the achievable data rates are extremely low.

At present, quantum encryption is not used to transmit the message itself, but only to securely transmit the encryption keys by which the real message will be encrypted.

Ever since Einstein's feared "spooky action at a distance" has been demonstrated in the laboratory, people have wished for faster-than-light communication by distribution of entangled photons (this would supposedly allow instant communication within a sphere which expands at the speed of light from your entangled photon generator).

However, people who know much more about this than I do tell me that you can't communicate faster than the speed of light with entangled photons (as much as high-volume stock traders would like to do it!).

#### jccc

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##### Re: Can we communicate via entangled particles?
« Reply #5 on: 17/04/2015 00:26:03 »

However, people who know much more about this than I do tell me that you can't communicate faster than the speed of light with entangled photons (as much as high-volume stock traders would like to do it!).

who knows it much more? did he told you why? did you asked him?

#### PmbPhy

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##### Re: Can we communicate via entangled particles?
« Reply #6 on: 17/04/2015 02:14:40 »

However, people who know much more about this than I do tell me that you can't communicate faster than the speed of light with entangled photons (as much as high-volume stock traders would like to do it!).

who knows it much more? did he told you why? did you asked him?
Yes. That information is readily available online if you simple search for it. I posted those links for someone else recently on this topic.

#### PmbPhy

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##### Re: Can we communicate via entangled particles?
« Reply #7 on: 19/04/2015 15:33:33 »
Jeff - I found a text which can help you understand this subject. It's called Quantum Mechanics and Quantum Information by Moses Fayngold and Vadim Fayngold, Wiley-VCH, (2013). You can download if from here:
http://bookos-z1.org/book/2160475/e06720

In particular you'd want to read the section entitled 24.3 Quantum Teleportation. It starts off with
Quote
We look here at a pair of separated but still entangled particles. The correlations between measurement results performed on the particles are nonlocal, which seems to demonstrate the existence of faster than light (FTL) communication between distant objects. The whole phenomenon of quantum nonlocality is so impressive and difficult to accept that it appears to be on the verge of mystical. It has been widely discussed from the early days of QM up to this day. Its most characteristic features have been confirmed in experiments by Aspect et al.

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##### Re: Can we communicate via entangled particles?
« Reply #7 on: 19/04/2015 15:33:33 »