Why can't we use quantum bit entanglement for FTL information?

[Gigasoft]

Well, you really don't get it, do you. The entanglement of the particles has no effect on your scenario. Nothing in your scenario requires that the particles are in an entangled state. You could send him a copy of the script to a Days of our Lives episode, and it would serve the exact same purpose as your particles. Or, you could send him a diskette with a photograph of the president as a JPEG image, and use the image bits as the decryption key. Most importantly, you could send him particles prepared in a known state, without ever producing any entangled pairs. Your friend won't know the difference, and the police won't know the difference either.

 

[NetMage]

"Lets pretend that you're going back in time and for some crazy reason you want to make sure that the Nazis win WWII. You remember that one of the biggest coups for the Allied forces was intercepting the code device on a U-Boat. You don't care about faster than light comms, but you want it to be instant, and SECURE. So, you bring the technology to use entangled photons to send information, but to keep it secure you can't verify by radio. You make sure that the captain and first officer of each U-Boat knows what "signal 1" "signal 2" and so forth means with their entangled photons. It doesn't matter if they get a 0 or 1, because each time there is a spin flip, they call to memory a conversation they had with their commanding officers at base. They now have completely secure signaling devices, even if they can't send so much as the message "hello" via direct means.

This is the simplest use of a single entangled pair, but there is such a thing as using quantum means of communication at less than c, which would be altered by any spying (or any perturbation). In this case, it's not the speed, but the security that's so desirable. In essence, the benefits of QM comms are many, but FTL isn't one of those benefits."

Maybe you can wrap your brain around this...it is the same concept. Stated by another person from this forum.

 

[unusualname]

@NetMage , the thread is titled "why can't we use quantum bit entanglement for FTL information?", I think it's well-known that there may be applications in subluminal communication scenarios, in fact, as well as security it can be used to improve efficiency of communication channels (dense coding) and in pooled-data situations eg see the article by W Wooters "Quantum entanglement as a resource for communication" (from this book, or do a google search)

but FTL communication is ruled out, (jambaugh posted a detailed argument above for those who don't like the simplistic "cos it's random" type reply)

 

[Gigasoft]

No, what you quoted does not constitute a secure means of communication using quantum entanglement. With only 1 bit measured, it is of course impossible to detect that the message has been tampered with or spied on. In fact, it is not even communication, since no information is transferred from the first submarine to the second (assuming that I interpreted his post correctly).

I recommend that you read up on http://en.wikipedia.org/wiki/Quantum_key_distribution" . What is essential in secure communication using quantum entanglement is that enough bits are transferred that it can be detected with high probability that an attempt at eavesdropping has taken place, and that an eavesdropper doesn't know how the particles will be measured, until the recipient is already in possession of the particles.

 

[NetMage]

Yes I realize all of this, in my original post on here I spoke of entanglement not being a tool for FTL comm. But instead stated as to what it could be used for ie security purposes etc. Then I got tangled up in a ridiculous hijacking of the thread thanks to gigasofts absurd posts.

 

[NetMage]

Gigasoft...you cannot eavesdrop on entangled particles...EVEN IF someone was able to find out measurements of the particles...it does not matter, because the REAL information was already pre determined, the entanglement only gives commands in order to execute the information that was exchanged b4 hand. The only people that even know what the corresponding entangled particles mean, is the people who are using them and understand what information they represent. No one else COULD know.

 

[NetMage]

Basically the purpose is that no one could intercept the information.

 

[Gigasoft]

"The only people that even know what the corresponding entangled particles mean, is the people who are using them and understand what information they represent. No one else COULD know."

"The only people that even know what the corresponding letters in the script to Days of our Lives mean, is the people who are using them and understand what information they represent. No one else COULD know."

Do you believe that there is a conceptual difference between these two lines of reasoning?

 

[NetMage]

I believe you sound ridiculous.