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Researchers quantum teleport particle of light six kilometres

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Re: Researchers quantum teleport particle of light six kilometres

#51

Post by semi-extrinsic »

brazzledazzle wrote: post #42
jdmichal wrote: post #28

I posted this in a duplicate thread: For those thinking that this is a step towards faster-than-light (FTL) communication: As far as I know it's fairly certain that quantum entanglement will not allow for FTL communication. Basic principle is that while measurements between both sides will be correlated, it's not possible to tell how they are correlated until both sides compare measurements. https://en.wikipedia.org/…

Is "measurement" or "observation" a simplified term for a complex process? It can't be as simple as a human "looking" at something since there's nothing special about humans (that I know of). I really wish I had the time and capability to understood how quantum entanglement really works. It seems a lot like magic if you take the layman explanations at face value.

This is a Hard Problem, to define what process is a "measurement" and what is not. But if we think about it very simply: a photon hitting a detector (or analog film strip) can be a measurement.

Since this process converts quantum information to classical information (a digital or analog signal), we know that it must lose information. Only by making many measurements can we infer statistical properties of the entire quantum state. This is exactly what happens with the two-slit experiment.

I personally subscribe to the "shut up and calculate" interpretation of QM (or perhaps the projection-valued operator approach when I'm feeling mathematical). The above intuition has served me well so far.

Re: Researchers quantum teleport particle of light six kilometres

#52

Post by jdmichal »

brazzledazzle wrote: post #42
jdmichal wrote: post #28

I posted this in a duplicate thread: For those thinking that this is a step towards faster-than-light (FTL) communication: As far as I know it's fairly certain that quantum entanglement will not allow for FTL communication. Basic principle is that while measurements between both sides will be correlated, it's not possible to tell how they are correlated until both sides compare measurements. https://en.wikipedia.org/…

Is "measurement" or "observation" a simplified term for a complex process? It can't be as simple as a human "looking" at something since there's nothing special about humans (that I know of). I really wish I had the time and capability to understood how quantum entanglement really works. It seems a lot like magic if you take the layman explanations at face value.

Human observation is fine. The fact that observing a state changes it is one of the "weird" things about quantum physics. Again, as far as I know since I'm not an expert, this is related to the fact that observation forces the wave function to collapse to a specific value, which then eliminates the "waviness" of the particle.

This is demonstrated by the single-particle double-slit experiment [0] and the eraser variation [1].

[0] https://en.wikipedia.org/wiki/Double-slit_experiment#Interfe...

[1] https://en.wikipedia.org/wiki/Double-slit_experiment#Delayed...

Re: Researchers quantum teleport particle of light six kilometres

#53

Post by booleandilemma »

Rooster61 wrote: post #7
fizx wrote: post #4

Earlier quoted context omitted.

In other news, words can mean more than one thing.

True, but that doesn't mean you can use words that fundamentally change the meaning of the sentence and then pass it off as the same thing.

For all intensive purposes

Re: Researchers quantum teleport particle of light six kilometres

#54

Post by nabla9 »

phkahler wrote: post #3

>> Researchers teleport particle of light six kilometres I'm sure they did nothing of the sort. At best they transferred an unknown state of a photon to another photon six kilometers away, then confirmed via measuring both.

Not so fast.

There is a good reason to call it quantum teleportation and not quantum facsimile.

When you move matter from one place to another it moves, it's not copied. When move classical information (or state) , you can retain the original or multiply it many times.

Quantum teleport demonstrates interesing aspects of quantum information that makes it work like material thing. When information (quantum state) moves, it can't be copied (no-cloning theorem). You lose the original from the sending end just as you would lose a physical object you send to other place.

Quantum theorems like no-hiding theorem, no-deleting theorem, no-cloning theorem makes quantum information act more like material substance than classical information.

There is no physical of philosophical argument differentiate between "real" teleportation and "just moving state".

Re: Researchers quantum teleport particle of light six kilometres

#55

Post by d_theorist »

lmm wrote: post #43
d_theorist wrote: post #36

I had thought that quantum entanglement could not be used for communication because the state that is transmitted is random, and cannot be controlled at either end. But, there are quotes in this article to the contrary. e.g.: “Such a network will enable secure communication without having to worry about eavesdropping, and allow distant quantum computers to connect,” says Tittel. Was my understanding mistaken?

It isn't directly usable for communication, but you can use the shared random state as a one-time pad for provably-secure communication over nonsecure conventional channels.

Oh! Because both ends have access to the same random bits. Thanks.

Re: Researchers quantum teleport particle of light six kilometres

#56

Post by fu9ar »

d_theorist wrote: post #36

I had thought that quantum entanglement could not be used for communication because the state that is transmitted is random, and cannot be controlled at either end. But, there are quotes in this article to the contrary. e.g.: “Such a network will enable secure communication without having to worry about eavesdropping, and allow distant quantum computers to connect,” says Tittel. Was my understanding mistaken?

If all you send is more like a checksum or a quantum salt, a few bits of entirely-secure-in-transit entropy in the encryption key could be enough to guarantee secure end-to-end communications in the moment.

Re: Researchers quantum teleport particle of light six kilometres

#57

Post by aparent »

fillskills wrote: post #41

This might sound like a very naive question but I am curious as to how the data was actually transmitted.

Both ends of the experiment share entangled photons produced from a single source and sent both ways. The sender performs some operations and measurements on their two photons, i.e. the photon they wish to send, and their entangled photon. They then send the result of the measurements to the receiver (this can be done any normal way you can think of; for example over a classical network).

The receiver does some operation on their entangled photon based on the results of the senders measurements. After these operations their entangled photon will be in the exact same state as the sent photon.

So to answer your question, information is transmitted classically but that information would not be enough without the use of entanglement.

Re: Researchers quantum teleport particle of light six kilometres

#58

Post by tgb »

jdmichal wrote: post #39
tgb wrote: post #35

Earlier quoted context omitted.

As I always bring up in these threads, quantum teleportation requires the transmission of classical bits, which of course is done slower than the speed of light.

As far as I know, ctrl-j [0] is correct. The quantum entangled state transfer may be instantaneous. However, this merely results in a correlation of measurements. In order to determine a correlation, you need to have both measurements to compare. This is the part that must be transferred classically. See my top-level post for more information [1]. [0] https://news.ycombinator.com/item?id=12548712 [1] https://news.yco…

The second photon that the first's state is being teleported to is constructed by performing certain operations on it and which ones are performed are determined by the two classical bits that are measured from the first photon (hence destroying the firsts's state). So from the first photon being destroyed to the second gaining its state, there must be a speed of light delay as those two classical bits are transmitted.

Re: Researchers quantum teleport particle of light six kilometres

#59

Post by kbenson »

spdustin wrote: post #45
sowbug wrote: post #16

Earlier quoted context omitted.

I could care less.

Couldn't?

At the risk of being too pedantic, that's the point. The incorrect phrasing is often used to mean the original thing, when the incorrect phrasing fundamentally changes the actual meaning of the sentence.

That said, this is a chain of comments that skirts dangerously close to not-contributing IMO, since I'm not sure making cryptic comments that lead readers that don't happen to reach the right context sensitive interpretation to produce more comments asking about it aren't actually worse than a pure non sequitur, from a discussion point of view. Having a clever counter-example (as the GP does) is good. Leaving it unexplained and ambiguous is not.

Re: Researchers quantum teleport particle of light six kilometres

#60

Post by bbctol »

brazzledazzle wrote: post #42
jdmichal wrote: post #28

I posted this in a duplicate thread: For those thinking that this is a step towards faster-than-light (FTL) communication: As far as I know it's fairly certain that quantum entanglement will not allow for FTL communication. Basic principle is that while measurements between both sides will be correlated, it's not possible to tell how they are correlated until both sides compare measurements. https://en.wikipedia.org/…

Is "measurement" or "observation" a simplified term for a complex process? It can't be as simple as a human "looking" at something since there's nothing special about humans (that I know of). I really wish I had the time and capability to understood how quantum entanglement really works. It seems a lot like magic if you take the layman explanations at face value.

To "observe" can mean any sort of interaction between the particle and a larger, connected physical system. To observe something, you have to have a physical interaction with it (it is hit by a photon of light which then hits your eyes, to use the most basic example) and so its quantum state decoheres into a particular state.

Most scientists are fine with the idea that it doesn't matter if the larger physical system has any sort of "consciousness" or "observation"; isolated particles have quantum behaviors, interacting particles decohere towards more normal-seeming physics. However, there are theories that shouldn't be immediately discounted that do still ascribe a role to the particular observer, indicating everything from reality being relative to consciousness being a fundamental aspect of the universe. I wouldn't take these too seriously, but I wouldn't dismiss them out of hand either.

Of course, that's not addressing the worst thing about quantum mechanics: once you've finally rid yourself of the pseudoscience and poor metaphors that make it sound like magic, it seems for just a second like a normal, intuitive process that's just been obscured through poor explanation--then you learn a little more and realize it's far more bizarre than you'd imagined.

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