191–200 of 219 posts
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Why the assumption that teleportation means faster than light travel?
Because Anton Zeilinger has proven in his experiments that "teleportation" can happen faster than speed of light. It's what Einstein said was "spooky" about "quantum teleportation" that it contradicts theory of relativity.
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>>But if you have a secure way of getting your quantum bits to Bob, couldn't you get your OTP there in the same way? No, because you do not choose the information to be verified on either side. You're not choosing a key and "encoding" it into "quantum bits", you're measuring the quantum state of two entangled particles. If the quantum state matches, you have provably secure transmission. If the transmission were inte…
Is it possible to know when particles were prematurely untangled? Wouldn't that constitute transmitting information? How would you tell the difference between a set of qbits entangled with the right other set of qbits, and with a different set of qbits? If an attacker were to intercept the whole stream/set of entangled particles, wouldn't he be able to perform a MITM attack by sending you particles entangled with his…
A third party also viewing the entangled qubit would necessarily modify the measurements also, causing correlation failure. A man-in-the-middle attack would only be effective if they also intercepted the measurement information and replaced it with their own. In which case, yes naturally someone who can intercept all your communication and replace it arbitrarily can arbitrarily control your communication.
As is used today, signing the measurement information would be an effective mechanism for preventing this. The attacker should be unable to correctly sign their own measurement information, and so you will be able to detect that the key transfer is unreliable.
Once the key is reliably transferred, then it's theoretically a secure one-time pad. That is, you know that it was transferred to the party at the other end of the entangled qubit, and that it was not intercepted along the way.
Not quite as impressive when you know, and if you don't you should before opening this link, that "quantum teleportation" is not teleportation. It was a cool-sounding name at the time, but has nothing to do with sci-fi style teleportation: nothing disappears from one place and then shows up in another. "Quantum teleportation" is a process of information duplication using particles that already exist, and have been po…
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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…
> The particles when measured will result in the other particle ending up in the opposite of the measured state, and this inversion persists even if we do operations that preserve the quantum state. This is the part that I don't get - what's the physics mechanism behind this? It sounds very Schrodinger's cat. It also sounds like a great way to tell if your information has been unknowingly accessed when it's travellin…
> It also sounds like a great way to tell if your information has been unknowingly accessed when it's travelling between two supposedly secure locations.
That's actually one of the currently possible applications of quantum mechanics to cryptography[1]. There are already multiple commercial implementations!
In short, quantum entanglement is an effect that causes two quantum particles to share state instantaneously over arbitrary distances. It can not be used to transmit information faster than the speed of light, essentially because while it is possible to manipulate the particle at one end, it is not possible to arbitrarily set it to a chosen state (and as described fully in the no communication theorem)[1].
Quantum teleportation is a way to transmit quantum information, ie the quantum state of a 'qubit', using both quantum entanglement and a classical communication channel. Because classical communication is required, no faster than light communication is possible. However, quantum teleportation is necessary if you want to transmit quantum information.
To very briefly sum up how it works, you start with a qubit whose state you want to transmit, along with two entangled particles, and a 'receiving' qubit that will receive the state of the sending qubit. Through an interaction between the sending qubit and the entangled particle on the sending side, the quantum state of the entangled particles is set to one of four possibilities. Which of the four possibilities resulted is sent via the classical communication channel from sending to receiving end. The receiving end then uses that information, along with the receiving-end entangled particle, to manipulate the receiving qubit into the identical state as the sending qubit, thereby 'teleporting' that state from sending to receiving end. The Wikipedia article has a more thorough layman's description, as well as the underlying math[2].
Caveat: I'm an engineer, not a physicist, so I may have made a mistake here as well, but the main take-away is that quantum teleportation is not the same thing as quantum entanglement, and its purpose is not FTL communication, but rather communication of quantum states.
[1] https://en.wikipedia.org/wiki/No-communication_theorem [2] https://en.wikipedia.org/wiki/Quantum_teleportation
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Actually, I find it very intuitive that reality is just information. It's much easier than setting it apart as ineffable.
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.…
But yes, I think phenomena are the atomic building blocks of science. The logical positivists at least got that right.
Not quite as impressive when you know, and if you don't you should before opening this link, that "quantum teleportation" is not teleportation. It was a cool-sounding name at the time, but has nothing to do with sci-fi style teleportation: nothing disappears from one place and then shows up in another. "Quantum teleportation" is a process of information duplication using particles that already exist, and have been po…
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…
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?
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Isn't that how actual sci-fi teleportation would work behind the scenes as well? Basically, if I wanted to teleport myself from one city to another. I'd actually die and disappear, and an exact copy myself would be created instantly in the other city. It would be teleportation for the rest of the world but for me it would be death.
If they relied on quantum teleportation: no, not in the slightest. In order to QT a particle (explicitly not using the verb "teleport" here, because it's a very different thing) you need three additional particles for every particle you're QTing. A pair of entangled particles that act as your fascilitator, and a spare particle on the other end to take on the information state of the one you're QTing. So unless your s…
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right, "quantum teleportation" is a woefully misleading name, however this is still an impressive advancement and quantum teleportation will play a key role in wide-area quantum information networks
Since nobody has mentioned it, maybe I didn't understand the implications, but does this mean there is a chance in the future we won't have "bandwidth"? I could replicate data from a server into my personal computer instantly?
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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?
If you don't get the classical information on the receiving end, any attempts to read the quantum state will garble the quantum transmission such that it'll be indistinguishable from random noise. Since those classical bits are limited by the speed of light, so is the overall transmission of the state.