Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Sustained, high-fidelity quantum teleportation

news.fnal.gov

Post reply on HN
Print view View original

81–90 of 169 posts

Re: Sustained, high-fidelity quantum teleportation

#81

Post by 8note »

tgb wrote: post #26
junon wrote: post #20

Earlier quoted context omitted.

This makes zero sense. If the information must be conveyed classically anyway, what's the point?

If you want to transmit 1 quantum bit (qubit), then you need to transmit 2 classical bits. Why is this useful? Because otherwise you have to carry the qubit over by hand. It's really just "quantum ethernet" not "quantum teleportation". There are actually other uses, too, about error tolerance, allowing you to quality-control some steps of the computation and repeat them if necessary without risking damaging the resul…

You still have to carry the qubit over by hand, but you can do it asynchronously to the change

Re: Sustained, high-fidelity quantum teleportation

#82

Post by 8note »

junon wrote: post #20
pontus wrote: post #5

Earlier quoted context omitted.

You entangle two systems but in order to actually complete the teleportation you need to measure one system and then convey the outcome of that measurement to the other party. This information is needed by the second party in order for them to be able to correctly collapse the state of their system into one that is identical to the original system being teleported. The information that the first party must convey to…

This makes zero sense. If the information must be conveyed classically anyway, what's the point?

Supposing we get enough qubits to support teleporting you, we can regularly entangle qubits and ship them around the world, then when you want to travel, we can teleport you, and the trip time will be how long it takes to send the message. This cuts your trip time down from hours long flights to seconds long trips

Re: Sustained, high-fidelity quantum teleportation

#83

Post by stakkur »

pontus wrote: post #75
edge17 wrote: post #51

Earlier quoted context omitted.

Maybe I'm dense, but I still don't understand. The cloning explanation made sense to me, but to the original question - how does the recipient know the message is done being sent without the sender picking up the phone and calling the recipient...? i.e. Is there some equivalent of a termination code/header sort of thing that the recipient is looking for in the 'bit stream' or whatever? Or am I not even thinking about…

The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics. So, the two people communicating would e.g. start out together and create a pair of…

It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics.

Yes. This is the key point, I think, and it didn't seem well-communicated in the article.

Re: Sustained, high-fidelity quantum teleportation

#84

Post by edge17 »

pontus wrote: post #75
edge17 wrote: post #51

Earlier quoted context omitted.

Maybe I'm dense, but I still don't understand. The cloning explanation made sense to me, but to the original question - how does the recipient know the message is done being sent without the sender picking up the phone and calling the recipient...? i.e. Is there some equivalent of a termination code/header sort of thing that the recipient is looking for in the 'bit stream' or whatever? Or am I not even thinking about…

The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics. So, the two people communicating would e.g. start out together and create a pair of…

Got it, thanks for the explanation.

Also, not to get ahead of ourselves (understanding this is research), but what is the use/benefit of this method? We can already send and receive information over great distances with and without wires at seemingly high speeds. Is this a new level of speed? Are there some previous limitations of distances that are now surmountable? Is the power or cost envelope required somehow reduced in some obvious way (not today, but in some future commercial implementation)?

Re: Sustained, high-fidelity quantum teleportation

#85

Post by foobiekr »

lscharen wrote: post #35
ed25519FUUU wrote: post #21

Earlier quoted context omitted.

It clearly makes no practical sense at the moment outside of research.

There are quantum communication links for satellites that guarantee that the data streams are not tampered with. https://directory.eoportal.org/web/eoportal/satellite-missio... https://spectrum.ieee.org/tech-talk/computing/networks/quant...

Less "tampered with" (because they can be trivially blocked or corrupted) and more "uninspected."

Re: Sustained, high-fidelity quantum teleportation

#86

Post by metadaemon »

pontus wrote: post #75
edge17 wrote: post #51

Earlier quoted context omitted.

Maybe I'm dense, but I still don't understand. The cloning explanation made sense to me, but to the original question - how does the recipient know the message is done being sent without the sender picking up the phone and calling the recipient...? i.e. Is there some equivalent of a termination code/header sort of thing that the recipient is looking for in the 'bit stream' or whatever? Or am I not even thinking about…

The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics. So, the two people communicating would e.g. start out together and create a pair of…

I know this is probably a stupid question, but would a text message be considered classical in terms of communication?

Re: Sustained, high-fidelity quantum teleportation

#87

Post by dodobirdlord »

djxfade wrote: post #15
magicalhippo wrote: post #9

Earlier quoted context omitted.

The whole point is the other party needs to know the result of your measurement, and you don't know that before you measured (otherwise the particles wouldn't be entangled).

So what can this really be useful for?

Another response already mentioned one aspect of how this can be used for secure communication, for detecting signal interception. But there’s a second aspect as well. Since the signaling is broken up into two parts (send the entangled state, send the measurement result), both parts have to be intercepted to decode the communication. The entangled state can be sent over a secure channel in advance, and the measurement sent over an insecure channel at the time of information transmission. This is analogous to sharing a one-time pad in advance, but the key distinction is that the no-cloning theorem guarantees that it’s impossible for someone to have stolen a copy of your one-time pad. They can only have stolen your one time pad, in which case you would notice.

Re: Sustained, high-fidelity quantum teleportation

#88

Post by _underfl0w_ »

bluesign wrote: post #54
cambalache wrote: post #14

Earlier quoted context omitted.

No communication is possible BUT, I have this toy scenario where a "quasi-communication" may be possible in FTL speed. "2 generals command 2 armies hundreds of km apart. They want to attack a common enemy, there are 2 options, A) And all-front attack. B) From the flanks. The generals want the plans to remain uncertain until the last second before the attack. So from an intermediate point, they send two "entangled coi…

Sorry but this example doesn't make sense, how it is faster than light?

I think key is that both generals have already agreed on a predetermined "meaning" of each coin flip outcome, rather than having to communicate it on a different, slower medium after the coin has been flipped.

So really it just front-loads that portion (I.e. removes it from consideration as part of the proposed solution) instead of allowing it to slow down solving the overall problem. It requires precomputation/agreement beforehand, rather than during the time allotted to the problem.

The speed of that precomputation would still be unchanged, and still be the slowest portion.

Re: Sustained, high-fidelity quantum teleportation

#89

Post by phyalow »

c22 wrote: post #47
Avtomatk wrote: post #37

Earlier quoted context omitted.

But if they destroy you and recreate you, are you still alive or die in the process?

If you're entangled before you're destroyed have you really been destroyed?

https://en.wikipedia.org/wiki/Ship_of_Theseus

Re: Sustained, high-fidelity quantum teleportation

#90

Post by FeepingCreature »

pontus wrote: post #44
sebmellen wrote: post #42

Earlier quoted context omitted.

Very interesting. If I understand correctly, does this mean cloning is a functionally impossible task? I've always been entertained by the paradoxes where someone is teleported ala Michael Crichton's Timeline , and is then (due to some glitch) "duplicated", leading to interesting quandaries about "who is who". If Penrose is right about consciousness [0], this means all these fantastical paradoxes are just fantasy, ri…

Correct, cloning in even the simplest sense of a single particle state (let alone a whole human) is impossible in quantum mechanics.

Though cloning a human may be possible if the brain does not rely on quantum state. Obligatory "warm and wet" objection.
Post reply on HN