# Can someone explain in a simple manner that How can we use Quantum entanglement to transfer data instantly when we seperate photons? [duplicate]

So I'm an IT engineer and i just watched a video about Quantum entanglement, that somehow when we split the entangled photons, any change happening to one of them will be reflected to the other one INSTANTLY, and therefore we can use this technology to transfer data from one point to the other instantly, basically even faster than the speed of light because no travel is required so we can even send data without the need of encryption!!

and China has developed a technology like this too https://www.inverse.com/article/34027-quantum-teleportation-entanglement-computing-internet-china

so since i have 0 knowledge about quantum physics and this blows my mind, can someone here explain this in a simple manner that how is this possible? and does this mean we can communicate with other planets INSTANTLY no matter how far they are ? doesn't this change everything?

also what is this technology called? where we separate the entangled photons and use them to communicate, basically can you guys also tell where should i start because i want to know everything about this technology, but I'm not sure where to start!

## marked as duplicate by Martin, WillO, stafusa, sammy gerbil, Kyle KanosJul 26 '18 at 16:13

• Possible duplicate of Why is quantum entanglement considered to be an active link between particles? – Martin Jul 25 '18 at 14:46
• If you would like to learn more about this technology -- although Martin is completely correct that it does not transfer information the way you describe -- you should look up "quantum key distribution." – zeldredge Jul 25 '18 at 14:52
• John, that article says that it is not FTL communication. Which it isn't. Usual comic link: xkcd.com/1591 – dmckee Jul 25 '18 at 14:56
• @JohnP It seems you didn't read the answer on the "duplicate" question. It is physically impossible, not technologically. So unless we discovered new physics ... – Norbert Schuch Jul 25 '18 at 18:20

You can't use quantum entanglement to send messages instantly. Thus, there is no such technology.

The nature of entanglement experiments is as follows.

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

You have a central source of two particles in an entangled state. One particle goes left, the other right. When you detect one at detector A, and the other at detector B, then you will find that the result at this detector and that detector are correlated. And you will find that the correlation is not compatible with causal-deterministic parameters. This is Bell's theorem.

But notice that it does not say you can determine some message and send it. Consider.

Suppose you are here with detector A, and your compatriot is on some distant planet with detector B. And suppose we even have some pre-arranged source of entangled particles, such that if detector A sees a spin up, detector B must see a spin down, and the reverse at both also.

There is still no way to send a message. If your friend sits at B and carefully observes particles, he won't be able to discern from what he sees anything about any message you want to send. If you get an up he must get a down. But you cannot predict what you will get from the entangled pair. If you want to send "up up up down" to indicate 1110, you can't. Because the next thing you detect is equally likely to be up or down.

So you will get a random stream of up-down values. And he will get the corresponding stream of exactly opposite values. But there is no message here.

The thing that $seems$ to go instantly is the correlation. If you get a down, he must have an up. But you can't tell that until you compare the results. Your friend cannot even tell, from $only$ his stream of measurements, whether your detector is even working. Or whether it still exists.

Try it this way. Imagine that between the two planets there was a random source of red and blue light flashes. Even supposing you can tell the flashes apart, so that you know when you see "red red red blue" that so did your friend. You can't control when the flashes are red or blue. So you can't sit at your detector and say "I want to send red red red blue to indicate 1110" because your friend can't tell, from the flashes alone, which sequence is your message. And you can't choose what the next flash will be, so you may see an arbitrarily long sequence of flashes that does not correspond to 1110. You can't use this to send a message.

• @JohnP China had a particle here and a particle in their space station. When they measured one, they could see that the state of the other had changed despite the distance between them. That's the "easy" part today. The challenge is what we've been discussing here, having the ability to force the state of the one (in turn changing the state of the other) without breaking the entanglement. – Joshua Schlichting Jul 25 '18 at 15:23
• INSTANTLY dudes. You can use entanglement to send messages at boring old speed-of-light. That's no problem at all. And that's what the phys.org article is referring to. It's useful for security, encryption, and error correction. But not faster than light. – user93146 Jul 25 '18 at 15:45