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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

#201

Post by ythl »

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/…

As far as I know, quantum entanglement is like two paper bags with two identical colored balls in them. You can separate the bags by a million miles, and yet if you look in one bag, you will know which color ball the other bag contains (because they contain the same color).

Can someone correct this analogy if I'm wrong?

Re: Researchers quantum teleport particle of light six kilometres

#202

Post by tgb »

dave_sullivan wrote: post #197
johncolanduoni wrote: post #135

Earlier quoted context omitted.

You've compounded their lazy science reporting by making quite a few mistakes yourself in your description: 1. There is no duplication or copying of information, the original particle's state is destroyed. Copying is impossible when dealing with general quantum states[1]. (You may be thinking of measuring an entangled pair to randomly produce a stream of classical bits on each side that is the precise inverse of what…

It's still the consensus that we can't (even theoretically) send a bit of information this way, right? Like, no quantum telegraph? So we measure the particles and find that they are in inverse states. I assume there's a reason for this, but why are we sure that we're not just reading off a random number generator that's set from the same seed?

Third time I'm writing this in this thread, but it causes so much confusion: in order to quantum teleport one qubit, you transmit two classical bits of information, say by ethernet. So there's no way to take this to work as a sneaky means of sending a classical bit.

It's my sacred duty to keep repeating this fact until the whole internet knows. (It's even in the first sentence of the wikipedia page on quantum teleportation!)

Re: Researchers quantum teleport particle of light six kilometres

#203

Post by salamisultan »

ars wrote: post #171
Ciantic wrote: post #118

Earlier quoted context omitted.

It's easier to think these as random number generators seeded with same value, taken six kilometers apart from each other, and then fetching values from them. No data is transmitted when fetching values from these.

> random number generators seeded with same value That's basically the https://en.wikipedia.org/wiki/Hidden_variable_theory

Not really. Entanglement isn't anything crazy. It's just a conserved quantity being split among particles during some type of constriction (half-silvered mirror would make the velocities of both deflected particles add up to a straight line for example)

The hidden variable theory makes it more complicated than it is.

If any type of interference or interaction happens to either of the particles after their initial mirror deflection, the correlation is gone. The complimentary nature of the measured values only applies when the particles remain untouched - thats why news articles a couple years ago were praising the ability to "entangle" particles for such a long distance/time. It's not easy to prevent all interaction.

The correlation is really just the undisturbed conservation of some quantity that was divided between the two particles.

In any "path" which splits a wave stream into x%/y% chance of trajectory/spin/polarization, etc, there will be an entanglement. All this means is that for every x% that went one way, y% went another, and the total is 100% ( conserved quantity.)

Re: Researchers quantum teleport particle of light six kilometres

#204

Post by trentlott »

johncolanduoni wrote: post #200
dave_sullivan wrote: post #197

Earlier quoted context omitted.

It's still the consensus that we can't (even theoretically) send a bit of information this way, right? Like, no quantum telegraph? So we measure the particles and find that they are in inverse states. I assume there's a reason for this, but why are we sure that we're not just reading off a random number generator that's set from the same seed?

Quantum teleportation is actually kind of the opposite. You transmit a quantum state (which if your particle is as simple as a photon, can be used to create a copy of the particle) by using an already-separated entangled pair and sending two classical bits any boring old way (fiber, wire, smoke signals). If you don't get the classical information on the receiving end, any attempts to read the quantum state will garbl…

So why does the reciver need the two bits?

I'm not prone to study too deeply because I've learned (apparently) very bad analogies or schemes for entanglement.

Re: Researchers quantum teleport particle of light six kilometres

#205

Post by wamatt »

duaneb wrote: post #196
eternalban wrote: post #176

Earlier quoted context omitted.

That's not what Bohr said. He said we can't know -- per Bell "have no right to know" -- what is "[objective] reality" [at the atomic scale]. I am personally not comfortable with using 'information'. I think Bohm's formulation "phenomena" is more appropriate. Note that, for example, the manifestation of wave/particle duality is an actual physical phenomena . The 'information' bit is our observation of this phenomena.…

Well, I'd put "can't know" squarely in the ineffable. But yes, I think phenomena are the atomic building blocks of science. The logical positivists at least got that right.

> I think phenomena are the atomic building blocks of science

Lacking context, this could seem somewhat opaque.

Would you mind clarifying which definition of "phenomenon" you are intending to convey? (eg Kantian or otherwise)

Re: Researchers quantum teleport particle of light six kilometres

#206

Post by johncolanduoni »

trentlott wrote: post #204
johncolanduoni wrote: post #200

Earlier quoted context omitted.

Quantum teleportation is actually kind of the opposite. You transmit a quantum state (which if your particle is as simple as a photon, can be used to create a copy of the particle) by using an already-separated entangled pair and sending two classical bits any boring old way (fiber, wire, smoke signals). If you don't get the classical information on the receiving end, any attempts to read the quantum state will garbl…

So why does the reciver need the two bits? I'm not prone to study too deeply because I've learned (apparently) very bad analogies or schemes for entanglement.

The teleportation process involves using a measurement to entangle the receiver's side of the pair with the original state in a useful way. Since measurements are probabilistic (and the measurement is along two qubits) there are four outcomes of this measurement with four different kinds of "garbling" of the transmission (one of which is no garbling).

The receiver needs the two bits to choose which of four kinds of garbling occurred, so it can correct them with the appropriate post-processing (if necessary).

Re: Researchers quantum teleport particle of light six kilometres

#208

Post by mratzloff »

johncolanduoni wrote: post #206
trentlott wrote: post #204

Earlier quoted context omitted.

So why does the reciver need the two bits? I'm not prone to study too deeply because I've learned (apparently) very bad analogies or schemes for entanglement.

The teleportation process involves using a measurement to entangle the receiver's side of the pair with the original state in a useful way. Since measurements are probabilistic (and the measurement is along two qubits) there are four outcomes of this measurement with four different kinds of "garbling" of the transmission (one of which is no garbling). The receiver needs the two bits to choose which of four kinds of g…

So it's kind of like a traditional error-correcting code, just sent along a separate channel?

Re: Researchers quantum teleport particle of light six kilometres

#210

Post by johncolanduoni »

mratzloff wrote: post #208
johncolanduoni wrote: post #206

Earlier quoted context omitted.

The teleportation process involves using a measurement to entangle the receiver's side of the pair with the original state in a useful way. Since measurements are probabilistic (and the measurement is along two qubits) there are four outcomes of this measurement with four different kinds of "garbling" of the transmission (one of which is no garbling). The receiver needs the two bits to choose which of four kinds of g…

So it's kind of like a traditional error-correcting code, just sent along a separate channel?

Sort of. The only issue with that interpretation is that either piece of data in isolation conveys none of the original information, even probabilistically. A better analogy would be sending two classical bits by different channels, with the desired bit being the XOR of the two, and one of the bits being chosen by a random number generator.
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