5 ms·
Does this mean information can be transmitted faster than light speed?
by sreejithr 6y ago
Does this mean information can be transmitted faster than light speed?
- moron4hire 6y agoNo. Long range quantum networking means that guarantees on the security of communication between quantum computers in the network can be made. Short range means that quantum compute clusters can be made, to make quantum computers that can process more qubits. https://en.m.wikipedia.org/wiki/Quantum_network https://en.m.wikipedia.org/wiki/Quantum_network
- pontus 6y agoNo, while entanglement acts instantaneously across a large distance, there's no way for that "signal" to carry any information. In order to complete the teleportation the two parties must somehow communicate in order to convey an additional piece of information. This communication would be classical and slower than light.
- Mizza 6y agoAny chance that communication could happen _before_ the measurement? Entangle some matter, give half of it to the space team and then have inter-stellar walkie talkies?
- magicalhippo 6y agoThe whole point is the other party needs to know the result of your measurement, and you don't know that before you measured (otherwise the particles wouldn't be entangled).
- lemonspat 6y agoI think OP is asking, can you entangle, measure, discuss, and then go travel to another galaxy with real time communications? Edit: or can the communication only happen once and then you need to remeasure over classic communication?
- magicalhippo 6y ago> travel to another galaxy with real time communications? As I said, no. How would you relay your measurement results in real-time? Without those measurement results, the receiver would in essence just hear white noise. That's the perplexing part of entanglement. Somehow it feels like information is instantaneously transferred from A to B, yet the information content is somehow zero so can't be used for proper communication.
- lemonspat 6y agoSo you have to measure every time you want to transmit?
- rodiger 6y agoThere is no "transmission." When you measure you learn the state of one of the particles, and you can use that information to deduce the state of the other (which until measurement is indeterminate). You can see that this information is useless unless communicated classically.
- magicalhippo 6y agoNo, you have to transmit every time you want to transmit. When measuring one particle of an entangled pair and you get say "spin up", you know immediately that if someone measures the other particle (with the same measurement settings) they'll get "spin down", and vice versa. The chance that you get "spin up" or "spin down" is 50/50 and, as far as we know, cannot be affected or determined in advance. So, on the receiving end, they measure some random combination of "spin up" and "spin down". Without anything else, this information is for all intents and purposes noise. What you can do however, is to send a message using regular means with what you measured: "up, down, down, up, down". Ok, at least now they can check that what they got was the exact opposite. However that still doesn't tell them anything. So instead what you do is that you change the measurement settings, and send via regular means not just your measurement results but also your measurement settings. So you'll send "H left, V down, V up, H left, H right". The recipient will then take the measurement settings (H or V) and measure the entangled particles in the same way you did, and then note down that they get the opposite. Note now that you suddenly got a way to communicate some actual information. By agreeing in advance that a Vertical measurement means 0 and a Horizontal measurement means 1, you can send information to the recipient. However also note that you had to make a measurement of your particles and then send the results using regular means, limited by the speed of light. So why bother with this complicated setup? Why not just send the data without all this entangled stuff? And indeed, for just sending plain messages it makes no sense to use entangled pairs. However as I noted in my other post, the inability to clone entangled states means an eavesdropper can be detected using the entangled setup.
- djxfade 6y agoSo what can this really be useful for?
- magicalhippo 6y agoI'm no expert, but AFAIK one thing is secure communication, in the sense that the recipient can detect if anyone is eavesdropping. As I've understood it, to "listen in" the eavesdropper has to destroy the entangled state by measuring it, and there's no way to perfectly clone the entangled state before doing that. The recipient can compare the entangled data with the measurement results (sent via classical means) and detect statistical inconsistencies if there is an eavesdropper. edit: I see their page[1] mentions quantum metrology, which I found reference to in a page[2] describing work to improve GPS and similar detection using quantum entanglement. Not sure if it's directly related but seems like there should be room for some interesting work using this quantum network in this area. [1]: https://ieqnet.fnal.gov/ https://ieqnet.fnal.gov/ [2]: https://news.engineering.arizona.edu/news/quantum-entanglement-offers-unprecedented-precision-gps-imaging-and-beyond https://news.engineering.arizona.edu/news/quantum-entangleme...
- dodobirdlord 6y agoAnother response already mentioned one aspect of how this can be used for secure communication, for detecting signal interception. But there’s a second aspect as well. Since the signaling is broken up into two parts (send the entangled state, send the measurement result), both parts have to be intercepted to decode the communication. The entangled state can be sent over a secure channel in advance, and the measurement sent over an insecure channel at the time of information transmission. This is analogous to sharing a one-time pad in advance, but the key distinction is that the no-cloning theorem guarantees that it’s impossible for someone to have stolen a copy of your one-time pad. They can only have stolen your one time pad, in which case you would notice.
- roywiggins 6y agoYou can't use entanglement (on its own) to communicate at all. https://en.wikipedia.org/wiki/No-communication_theorem https://en.wikipedia.org/wiki/No-communication_theorem
- moron4hire 6y agoWhat's funny to me is that this topic comes up A LOT. Like, people hear about entanglement, and then decide they are smarter than those dumb physicists and have figured out FTL communication in 15 minutes. Why is that? This keeps happening. Quantum entanglement is not a new concept. It's almost certainly older than 99.9% of the people on this site. Yet the myth that it could enable FTL communcation continues to persist.
- pontus 6y agoIn some sense the two systems that are entangled are connected instantaneously. The problem is that the information doesn't reside in either system but rather in them as a whole. So, if you were in space with one part of your "walkie talkies" you wouldn't be able to make sense of the information unless you have access to the other system. This access would usually occur through some slower than light channel. Imagine that you have 2 coins and give one to someone on earth to flip and one to someone on the moon to flip. The outcomes in either location is random 50/50, but interestingly they are perfectly correlated (H<->H, T<->T). When you flip a coin you don't have the ability to pick it's outcome. The only thing you can pick is whether or not to flip it at all. So, imagine you want to communicate one bit of information from earth to the moon and decide that a 1 will be encoded as "flip the coin" and 0 as "don't flip the coin". When you're standing on the moon and want to reveal the information you flip the coin and see e.g. H. There are two ways this could have happened: either the earth coin had already been flipped and showed H or the earth coin had not yet been flipped and you just randomly got a H. In other words, the outcome by the flip is useless by itself.
- cambalache 6y agoNo communication is possible BUT, I have this toy scenario where a "quasi-communication" may be possible in FTL speed. "2 generals command 2 armies hundreds of km apart. They want to attack a common enemy, there are 2 options, A) And all-front attack. B) From the flanks. The generals want the plans to remain uncertain until the last second before the attack. So from an intermediate point, they send two "entangled coins" , one to each general, the coins will arrive at both sites at the exact start of the battle.Both will show the same face when "measured". The generals have agreed previously that if they turn out "heads" they will both attack from the flank, in the other case, they will do a front-attack. Of course you dont need a quantum system for this, you could have agreed on other stuff (like it if it is raining that day at certain place or sending a framed coin by regular mail) but I think the quantum solution is the more elegant, assuming no 3rd party snooping.
- roywiggins 6y agoThere are game theoretical proofs that show that you can use entanglement to enable better-than-classical performance on games that reward cooperation but disallow actual communication. https://en.m.wikipedia.org/wiki/Quantum_pseudo-telepathy https://en.m.wikipedia.org/wiki/Quantum_pseudo-telepathy
- bluesign 6y agoSorry but this example doesn't make sense, how it is faster than light?
- _underfl0w_ 6y agoI think key is that both generals have already agreed on a predetermined "meaning" of each coin flip outcome, rather than having to communicate it on a different, slower medium after the coin has been flipped. So really it just front-loads that portion (I.e. removes it from consideration as part of the proposed solution) instead of allowing it to slow down solving the overall problem. It requires precomputation/agreement beforehand, rather than during the time allotted to the problem. The speed of that precomputation would still be unchanged, and still be the slowest portion.
- boie0025 6y agoThis reveals my severe ignorance about quantum mechanics; but I've always wondered if entanglement could be used to transmit binary data by way of timing and presence or lack of presence of a transmission. So maybe every 1ms is a position, and either something is sent or not.
- tgb 6y agoQuantum teleportation is a process that both sender and receiver have to coordinate. Part of that coordination is that the sender measures 2 classical bits of information on their entangled qubit and transmits those two classical bits to the receiver. Then the receiver uses those two bits to perform certain operations on their half of the entangled qubit pair in such a way that their qubit is now exactly the same as sender's original qubit. As you can see, there's no way to use timing in this, other than the timing of the classical bits being transferred.
- deleted 6y ago[deleted]
- roywiggins 6y agoYou can't. There's a theorem and everything. If there is some way to do it, QM must be wrong. https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem
- walkerbrown 6y agoThank you. For me, this clears up a long held misconception.
- boie0025 6y agoThanks for the link; I had no idea what to even search for to understand this.
- jv22222 6y agoWhey can't they just have an agreed upon stop point? Like, keep parsing the incoming information until you see a period (for example). (I know it's not using actual characters, just using the idea to illustrate the point).
- thwd 6y agoYou have a box with random garbage in it. I have a box with a football in it. We entangle the football and the garbage. You stand far away from me. If you randomly open your box now, you may either see a football or random garbage. If I call you on the phone (classically) and tell you to open the box tonight at precisely 8:12pm, you're guaranteed to find a football then and hence, I will have the garbage. There's no parsing; it's all or nothing.
- pif 6y agoYes and no. Yes, information can travel with infinite speed. No, cause-effect relationship cannot travel faster than light. https://en.wikipedia.org/wiki/Quantum_nonlocality https://en.wikipedia.org/wiki/Quantum_nonlocality
- kazinator 6y ago> Yes and no. Could a QM answer be otherwise?
- mathgenius 6y agoCorrelations are "transmitted" faster than light speed. You could call this information. Quantum information theory is way more complicated (and many open questions) than Shannon information theory.