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Chinese scientists test quantum entanglement over unprecedented distance
- fsiefken 9y agoCould you use this for untraceable communication with hidden non-traceable submerged subs? That would be a military advantage.
- indolering 9y agoNo because they are only using entanglement to ensure no-one has intercepted the particle. This way you can send your symmetric keys and know they weren't intercepted. This is a real logistics issue for governments, who still physically move symmetric keys between locations.
- comboy 9y agoAs long as you have a fiber between them..
- JPLeRouzic 9y agoThanks to your comment I am now daydreaming of a neutrino radio, with a design inspired from a Fusor!
- Illniyar 9y agoI thought quantum entanglement is the idea that two quantum particles separated by distance will behave the same at the same time regardless od distance. Why is sending photons over distances a verification of quantum entanglement? Can someone elaborate on what this is?
- indolering 9y agoThey are breaking a record, that's all.
- EGreg 9y agoProbably it is similar to what has been done here: http://www.cbc.ca/beta/news/canada/calgary/calgary-teleportation-quantum-networking-city-hall-1.3770440 http://www.cbc.ca/beta/news/canada/calgary/calgary-teleporta... Information can't travel faster than the speed of light. You have to actually take the photons and move them away from one another, then check one which will modify both.
- djsumdog 9y agoI too am wondering about this. I thought entanglement couldn't be used for communication because observing both particles simultaneously will reveal that they have opposite spins. It's a conformation after observation, based on what the quantum superposition collapses into once you observe the state. But the actual state is also unknown until you observe it. I'm not a physicist, but I'm sure there're be one on HN that will tell us what this study really means.
- yorwba 9y agoNot a physicist either, but as I understand it, entanglement is not useful for communication on its own, but allows for tamper-proof key exchange. Basically, you generate a pair of entangled particles. Keep one of the pair and send the other away. Now both you and your partner randomly select a basis to measure the particle in. After a few repetitions, you tell each other (over a classic channel) how you measured and discard measurements made in different bases. The remaining results will be strongly correlated, depending on the quality of the entanglement. By comparing a small part, you can find out exactly how much. If the correlation is lower than expected, you might have some dust in your measurement apparatus, or an eavesdropper has intercepted a few quanta. If the correlation is good enough, you now both have a value that is secret to anyone who did not measure the particles. The secret value can then be used as a key to encrypt your communication over the classic channel. If this description is not satisfying, maybe the Wikipedia article explains it better: https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/Quantum_key_distribution
- RugnirViking 9y agoIsn't that no better than a one-time pad if you need a classic channel?
- yorwba 9y agoQuantum key-exchange solves the distribution problem for one-time pads. And a one-time pad is the best security you could possibly get, so I'm not sure what you mean by "no better", since that's a given.
- tim333 9y agoIt's more subtle than that. In this case with photons it's that the correlation between a photon going through a polarizer at point A and it's entangled pair going through a polarizer at point B is a function of the angle between the polarizers. The odd thing is it depends on the relative angle of the polarizers at the time the photons go through even if they are far apart. So if you use the analogy of God rolling a dice to determine if the photon goes through or not then He has to know the angle of the other polarizer in a faster than light way even if us mortals can not know that.
- pacman128 9y agoAnother factor to consider is that relativity showed that whether two events at different locations are simultaneous depends on the observer's reference frame. See (https://en.wikipedia.org/wiki/Relativity_of_simultaneity https://en.wikipedia.org/wiki/Relativity_of_simultaneity). So you can't even say which measurement of the state is the one that collapses the waveform. Observers in different reference frames would disagree.
- kiliankoe 9y agoAs a child I dreamt of having two futuristic walkie-talkies sharing several pairs of entangled particles making perfect instant communication across the galaxy possible. Later my physics teacher crushed my dreams by telling me it's far from as easy as that and probably impossible due to Heisenberg's ... (no clue what it's called in English). It's pretty awesome to hear that something similar is actively being worked on and seems possible, although being a huge challenge.
- brobinson 9y agoHeisenberg's uncertainty principle https://en.wikipedia.org/wiki/Uncertainty_principle https://en.wikipedia.org/wiki/Uncertainty_principle
- adrianN 9y agoYou can't communicate (FTL) with entangled particles unless fundamental assumptions in quantum mechanics are wrong.
- guelo 9y agoYour dreams are still crushed. This research is about encrypting normal-speed communication. Instant communication is still impossible.
- pulse7 9y agoThe interesting part of "quantum communications" is the impact on security and surveillance. Does "quantum communications" even needs switches and routers? Backdoors don't seem to be possible...
- yorwba 9y agoQuantum communication works best if you have a direct connection, because the entanglement is easily destroyed if the particles interact with anything. This is the whole point, you can't intercept it without completely degrading the connection. If you try to redirect your particles through a network of switches and routers, be prepared for lots of dropped packets.
- yozel 9y agoWhat if quantum communication is a backdoor? Wireless, undetectable bugs!
- sliken 9y agoA staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. By my understanding that's impossible, although I always wondered if you could coordinate FTL, by detecting when a particle was no longer entangled. Can someone with the background comment?
- indolering 9y agoDamn, all of these explanations are overly complex! The most basic reason it doesn't work is because measuring your particle breaks the entanglement. So you would know that your partner has the opposite spin (or whatever) but you can't bootstrap any sort of communication system with that.
- pishpash 9y agoNot overly complex, but overly simple. I wish people talking about physics learn for the last time that analogies are a horrible way to explain a complex concept that at best adds an unnecessary translation layer increasing cognitive load and at worst hand waves away the most critical parts.
- indolering 9y agoThey just get too excited : )
- MichaelBurge 9y agoIt's about as likely as reading a byte from an initialized /dev/urandom and measuring its entropy to see if someone removed a hardware RNG.
- posterboy 9y agoI'd guess it's impossible without measuring both particles and communication to compare the results.
- deleted 9y ago
- EGreg 9y agoWikipedia says: "If Bohmian Mechanics as an non-local hidden variables interpretation of quantum mechanics is accurate it should allow quantum computers to implement a search of an N-item database at most in O ( N 3 ) {\displaystyle O({\sqrt[{3}]{N}})} steps. This is slightly faster than the O ( N ) O({\sqrt {N}}) steps taken by Grover's algorithm using standard interpretations of quantum mechanics. Neither search method will allow quantum computers to solve NP-Complete problems in polynomial time.[4]" I thought there was no way to figure out which interpretation of QM is correct. Can someone explain?
- indolering 9y agoTry physics.stackoverflow.com.
- Strilanc 9y agoIt's just a wrong statement. Follow the reference to the paper and see: > [...] we show that if we could examine the entire history of a hidden variable, then we could efficiently solve [...] Bohmian mechanics doesn't give you access to the entire history of a hidden variable.
- EGreg 9y agoBut in principle could we access the history?
- Strilanc 9y agoHow? You can't just keep measuring the position of the particle and keep a list. Recording quantum information entangles the recorder and the system under test, which affects how interference plays out, which affects the later parts of the path in a way that makes your path-computer not work.
- EGreg 9y agoHow? Think a bit harder. It's pretty obvious once you get it. John Titor explained it to me last year. I'm just kidding. Yeah, what you said makes sense. How do we know though that IN PRINCIPLE we can't figure out which QM interprtation is correct? Because we are sure there is no additional data/math that can be developed?
- splicer 9y agoImagine being able to explore distant planets with robots and VR googles in real time!
- blazespin 9y agoQuantum entanglement obeys the speed limits.
- chibaozi 9y agowe can use quantum tech to break the GFW firewall
- ozy 9y agoNote that while particles can be entangled, the special/useful thing is the postponement of further entanglement (with the rest of the world).
- gozur88 9y agoUseful for what? Every time I see someone propose a use for QE someone else comes along and assures us it won't work.
- dynofuz 9y agoSo if quantum entanglement does not enable FTL communication, what is it good for? How do you keep getting entangled particles from one place to another?