# Quantum entanglement and communication

#### DanCarpenter

Quantum entanglement is a concept that has captured my imagination and has intrigued me very much in the past few years in which I've become interested in quantum physics. Immediately upon reading about it for the first time, I realized that quantum entanglement could be applied in a new communication technique where a message is conveyed instantly. After doing some research on the matter, I've come to have some understanding of entanglement. For example, I know that when two electrons are entangled, they are always in opposite spin states. If one's state were to be changed, the other would also switch states. This switch happens immediately no matter how far apart the electrons are in space. I was thinking that this could be implemented in a pair of devices to allow for instantaneous communications between satellites or space vessels and mission control (the two devices can only communicate with each other, however). An early prototype of such a device could be a single pair of electrons, one at mission control, and one on vessel. Communication can be achieved by morse code, where either electron's spin state is switched in a morse code-type sequence. For another prototype, a pair of devices could have two sets of 26 pairs of electrons, each one coding for a letter in the alphabet. This way, a message from a ship could be typed up, then the device would switch the spin state of each electron accordingly, thus changing the other paired electrons in the device at mission control, and that device would decide the message. This technology could be helpful in an regency where an astronaut would require immediate technical support, or blueprints could be relayed to a 3d printer if they needed a new part or tool. This technology could also advance to allow for instant video communication, with each paired electron coding for a pixel on a screen.

Also: quantum entanglement has constantly baffled scientists, because nothing should be able to travel faster than the speed of light. However, I believe that the reason why the switch is instantaneous, it that the paired particles become juxtaposed on a sub dimensional field. This could also have practical applications.

Are these ideas plausible? I want to hear some other thoughts and opinions.

Note: please forgive any flaws or inaccuracies in my reasoning. I only just finished my junior year in high school and I don't know where else to share my thoughts with someone who is also knowledgeable of the subject.

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#### DanCarpenter

I just joined the site and on mobile. Sorry for any mistakes

#### king vitamin

Gold Member
No, you've completely misunderstood quantum entanglement. When two electrons are entangled, you don't know what spin state either is in before you measure it. However, once you do measure, they will be measured to have opposite spins with 100% probability.

Then they're not entangled. You can only measure an element of the entangled pair once, then they're just two boring electrons with no further relation to each other. Your morse code idea would not work.

#### DanCarpenter

What about with other particles or objects? I know that relatively recently, they were able to entangle two macroscopic diamonds. They were able to tell that the two were entangled, because when white light was emitted into them, light exiting one of the diamonds was blue-shifted. I don't think that measuring them caused them to no longer be entangled?

#### phinds

Gold Member
What about with other particles or objects? I know that relatively recently, they were able to entangle two macroscopic diamonds. They were able to tell that the two were entangled, because when white light was emitted into them, light exiting one of the diamonds was blue-shifted. I don't think that measuring them caused them to no longer be entangled?
There are numerous threads on this topic, one very recent and ongoing. FTL communication is impossible.

#### king vitamin

Gold Member
What about with other particles or objects? I know that relatively recently, they were able to entangle two macroscopic diamonds. They were able to tell that the two were entangled, because when white light was emitted into them, light exiting one of the diamonds was blue-shifted. I don't think that measuring them caused them to no longer be entangled?
If you give me a reputable source on how these diamonds were entangled and your proposed mechanism on how this entanglement can cause FTL transmission, I can explain to you how you've misunderstood the system. I can't comment without these specifics (and you can't transmit FLT info without them either!).

#### DanCarpenter

If you give me a reputable source on how these diamonds were entangled and your proposed mechanism on how this entanglement can cause FTL transmission, I can explain to you how you've misunderstood the system. I can't comment without these specifics (and you can't transmit FLT info without them either!).
http://physicscentral.com/explore/action/entangled-diamonds.cfm

And like I said, I believe that it's not FTL, because that's impossible; they are juxtaposed next to each other on a sub dimensional field, and the distance between them on that field is much smaller than in actual space

#### DennisN

Hi DanCarpenter, and welcome to PF!
You could also have a look at this thread, "Two Questions on Black Holes", which involved a question about an entanglement communication scheme quite like yours (and this type of communication suggestion often comes up here in the quantum mechanics forum ). I suggest you read post #1 to post #9 in particular in that very thread.

Quantum entanglement can not be used for FTL communication.

#### DennisN

they are juxtaposed next to each other on a sub dimensional field, and the distance between them on that field is much smaller than in actual space
(my boldings)

What does "juxtaposed" mean?
What does "sub dimensional field mean"?

#### king vitamin

Gold Member
http://physicscentral.com/explore/action/entangled-diamonds.cfm

And like I said, I believe that it's not FTL, because that's impossible; they are juxtaposed next to each other on a sub dimensional field, and the distance between them on that field is much smaller than in actual space
The key point is that they do not know which diamond is in the higher vibrational state. Now try to separate the diamonds by some vey large distance (presuming you can maintain entanglement, even though your article says decoherence occurs on a timescale of 7 picoseconds). Now, if you check to see if one diamond is in the higher state, and you find that it is, you know right away that the other does not have that state. But you've killed the entanglement - you cannot do "Morse code" and excite a state hoping that it does something to the other diamond far away.

#### StevieTNZ

Nor can you control what spin you get when you measure an electron. Its random; 50% probability of up, 50% probability of down.

#### Water nosfim

Mr Stevietnz you can influance the spin up or down if you chek it in angel of the polarity and get someting like 60% and not 50% and influance the outcume too , and by that get percentage of bite trancfer .thanks

#### Nugatory

Mentor
Mr Stevietnz you can influance the spin up or down if you chek it in angel of the polarity and get someting like 60% and not 50% and influance the outcume too , and by that get percentage of bite trancfer .thanks
That does not work. Even if I am measuring at an angle while the other guy is measuring straight up and down, he'll get a 50/50 mix of up and down measurements.

#### Water nosfim

As i see it , if you measuring at angle and the other guy measuring straight you get close to 50/50 not 50/50 at both side , and it tranfer data

#### DrChinese

Gold Member
As i see it , if you measuring at angle and the other guy measuring straight you get close to 50/50 not 50/50 at both side , and it tranfer data
Welcome to PhysicsForums!

Not sure what you are imagining, but there is no way to influence the outcome of a spin measurement on a spin-entangled particle. You can influence the basis that collapse occurs, but not the outcome.

#### Water nosfim

Well , the spin can be influence by fild in one side , and it entangled , influence statistic but influence as i see it , well ?

#### DrChinese

Gold Member
Well , the spin can be influence by fild in one side , and it entangled , influence statistic but influence as i see it , well ?
If a spin-entangled photon encounters a polarizer, it will come out polarized either + or - at that angle. So 50-50 over the long run, with no way to influence it either to the + or - side.

You can "influence" the spin of a photon with a known polarization, but that photon will not be spin entangled.

#### Nugatory

Mentor
Well , the spin can be influence by fild in one side , and it entangled , influence statistic but influence as i see it , well ?
Try calculating it... Let's take the angle between my measurement and the other guy's measurement to be 60 degrees and use entangled polarized photons, mainly because that way the calculations are easy to do in my head. Take the angle of my polarizer to be zero and his to be 60 degrees.

One-half the time my photon clears my polarizer, and then I know that the other photon is at 90 degrees, which is 30 degrees relative to his polarizer. Cosine of 30 degrees is $\sqrt{3}/2$, so there is 3/4 chance that his photon will clear his polarizer, 1/4 that it will not.

One-half the time my photon does not clear my polarizer, and then I know that the other photon is at 0 degrees, which is 60 degrees relative to his polarizer. Cosine of 60 degrees is 1/2, so there is a 1/4 chance that his photon will clear his polarizer, 3/4 that it will not.

Total probability that his photon clears his polarizer? $\frac{1}{2}\frac{3}{4}+\frac{1}{2}\frac{1}{4} = \frac{1}{2}$.

Now, if I could control the result of my measurement... Then I could transmit information. But my results are just a stream of random pass/no-pass results, and so are his. It is only if we could get together and compare our results that we could work backwards to the conclusion that my polarizer was at 60 degrees to his.

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