China manages a new record in quantum teleportation

[Instant Mix]

[QUOTE=Ardosos;52375273]That's what I don't get though, if any interaction whatsoever with an entangled particle causes it to collapse, why even call it a superposition? Why not just say "it is either state A or state B", rather than say "it is both state A and B until you measure it"? How do we know that superpositions even exist if there is no way for them to interact with the universe without collapsing?[/QUOTE]

[media]https://youtu.be/8anVNc0r_8o[/media]
A little bit more precise than Lenny's video if you aren't up for the 12 minutes, and explains a particular algorithm in detail that completely exploits superpositions. Shor's is an interesting algorithm for the above video as it actually isn't entirely quantum, it requires certain classical computations to work as well.

[JohnnyMo]

[QUOTE=Ardosos;52375273]That's what I don't get though, if any interaction whatsoever with an entangled particle causes it to collapse, why even call it a superposition? Why not just say "it is either state A or state B", rather than say "it is both state A and B until you measure it"? How do we know that superpositions even exist if there is no way for them to interact with the universe without collapsing?[/QUOTE]

That goes back to what I said above about Bell's inequalities. Say you're interested in some observable, maybe position, associated to a particle. Say position has two possible values, A or B. If the particle is in a superposition so that each of those states may be measured with 50% probability, and you say, "The particle is in position A or B, we just don't know which one," that is actually physically distinguishable from saying, "The particle is in a superposition of position eigenstates A and B," and it can be falsified under the right assumptions.

If you assume that such a thing is true, it's called a "hidden variable theory." In that case, the particle has definite values for every observable property, and the wave function is just our ignorance of what the values actually are. But nature is provably weirder than that. Any hidden variable theory satisfies the Bell inequalities, and those are demonstrably violated by quantum mechanics, hence quantum mechanics is not described by a hidden variable theory.

(Disclaimer: some hidden variable theories are actually viable via various loopholes. Many-worlds interpretation is a local hidden variable theory, and it gives up a property called counterfactual definiteness to stay viable. De Broglie-Bohm theory is a counterfactually definite hidden variable theory, but it gives up locality. Superdeterminism also gives up counterfactual definiteness.)

And it's true, you can't really know what state a particle is in before measurement for certain. The best you can do is measure an ensemble of similarly-prepared states and record the frequency with which you measure observables to get a statistical picture of what the state looked like before measurement. The state is essentially a probability distribution over possible values of observable properties.

[_RIley]

[QUOTE=V12US;52373658]Not long now before God makes a divine intervention and bans us from his universe simulator for trying to glitch abuse the system.[/QUOTE]

Would that make the rapture just one big VAC ban wave?

[Nebukadnezzer]

[QUOTE=JimmyBowen;52372453]Not well versed in quantum entanglement, why can't it be used for communication?[/QUOTE]

Because you can't control WHICH state the particle ends up in. You only know, faster than the speed of light, that the other particle is in the opposite state. But since it's random and uncontrollable, that information doesn't help you.

[Lenny.]

[hd]https://www.youtube.com/watch?v=o123zZh5h_k[/hd]

This is a really good explanation of it I think

[Nebukadnezzer]

[QUOTE=Helix Snake;52375071]Here's my question; if this can't be used for faster than light communication, what CAN it be used for?[/QUOTE]

unbreakable encryption

[Headhumpy]

[QUOTE=Helix Snake;52375071]Here's my question; if this can't be used for faster than light communication, what CAN it be used for?[/QUOTE]

getting grant money

[shodan]

[QUOTE=JimmyBowen;52372453]Not well versed in quantum entanglement, why can't it be used for communication?[/QUOTE]
You can't beat the speed of light. Don't even think of it, you can't.

[Deunan]

[QUOTE=Agent_Wesker;52372712]Yes, someone explain why you can't have 4 particles, flip 1 (first set) for no and 2 (second set) for yes... or something.[/QUOTE]

Because the moment you check up on B you flip it. If you could verify that B is in a superstate without forcing it outside of the superstate, you could create an information carrier based on the amount of flips. But you unobserve observe a particle. Quantum communication to be feasible would have to allow us to be able to change the state of a particle even after it already has a state.