# Proof that FTL communication quantum protocol is impossible?

• Euclid's rat
In summary, the conversation discusses the existence of a quantum protocol for faster-than-light communication and whether there is a self-contained proof that it is impossible. The speaker also mentions using two different proofs to show that a certain problem cannot be solved by any quantum algorithm. They are interested in finding a direct proof of the impossibility of using EPR pairs to transmit information without physical carriers. Two references are provided on this topic.

#### Euclid's rat

Hi all,

I am reading pretty much everywhere that no quantum protocol for faster-than-light communication can exist.

Now, clearly neither super-dense coding nor any other quantum protocol I know of can be used for FTL communication - but is there a self-contained proof that no such protocol can exist? And if yes, where can I find it?

I am asking this because last week I had to prove, for one of my courses, that a certain problem can not be solved by any quantum algorithm: I managed to prove that if the problem had a solution then FTL communication would be possible, and therefore I concluded that no algorithm could solve the problem.

I also found -and included in my homework- a different proof of the same result by means of the no-deleting theorem, but it was definitely clunkier and less elegant than my first one.

So, I ended up using both proofs, and justifying the first one by saying that FTL communication (and hence, the original problem) can not be performed because, in a relativistic framework, it would lead to violations of the principle of causality.

But I wonder if a direct proof of the impossibility of using EPR pairs to transmit information without physical carriers exists - I just started taking an interest in quantum information theory, and for all I know there could be a fairly well-known theorem stating exactly this

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Thank you for the references!

## 1. Is it possible for information to travel faster than the speed of light?

No, according to Einstein's theory of relativity, nothing can travel faster than the speed of light in a vacuum. This means that any form of communication, including quantum protocols, cannot exceed the speed of light.

## 2. Can quantum entanglement be used for faster-than-light communication?

No, while quantum entanglement allows for instantaneous communication between two entangled particles, it does not violate the speed of light. The information is still transmitted at the speed of light, but the correlation between the particles can be observed instantly.

## 3. What about the phenomenon of quantum tunneling?

Quantum tunneling, the ability of particles to pass through barriers they normally couldn't, also does not violate the speed of light. It is a probabilistic phenomenon and does not allow for the transfer of information faster than the speed of light.

## 4. Are there any loopholes or exceptions that could allow for FTL communication using quantum protocols?

As of now, there are no known loopholes or exceptions that would allow for FTL communication using quantum protocols. The laws of physics, including the speed of light, have been extensively tested and no evidence has been found to suggest that they can be violated.

## 5. Could advancements in technology or future discoveries change our understanding of the impossibility of FTL communication?

While it is always possible for new technologies or discoveries to change our understanding of the universe, at this time there is no indication that FTL communication using quantum protocols is possible. Any future advancements would need to adhere to the current laws of physics, including the speed of light.