7 ms·

Quantum teleportation achieved over record distances

49 points by ananyob 14y ago

zrgiu_ 14y ago
I know this is a long long time away but .. Could this be used to communicate faster with stuff like the Curiosity rover ? I mean, once it becomes easier to reproduce without big laboratories to actually read the quantum state of the photons.
- darkstalker 14y ago
  And although part of the transfer happens instantaneously, the steps required to read out the teleported quantum state ensure that no information can be communicated faster than the speed of light. Seems not.
  - pavel_lishin 14y ago
    It might increase bandwidth, though.
- stordoff 14y ago
  My understanding is that current quantum teleportation methods need a classical channel to transmit information (and so is limited to the speed of light). See the Protocol section of Wikipedia - https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation . To my knowledge, there is no particular reason to believe that this limitation can be removed. The simplest way to see this is to consider a state such as a|0> + b|1>, which is the quantum state of the particle we wish to teleport from Alice to Bob. If Alice does the measurements needed to teleport it, Bob might end up with either a|0> + b|1> or a|0> - b|1> (or two other similar states) with equal probability. To actually get the correct state we began with, which is the only way to transmit something meaningful, then he needs the results of Alice's measurements to make a correction. These can only be transmitted at the speed of light, so speed of information transfer is still limited to the speed of light.
RockofStrength 14y ago
This phenomenon is explained by many-worlds: The two photons have both polarization orientations in the multiverse. We are limited to a single instance of the multiverse, and any interaction whatsoever between the photons and our universe will force them into a single instance of polarization orientation, as this is all we can experience, being interacting beings ourselves. Reality is really an immense interconnected binary tree, and we must always travel along a single path. It has the property that reconciling paths (paths that diverged but met up again with no interaction in our universe) will again be accessible to us. As Galileo was prosecuted for supporting Copernicus' heliocentric theory (more specifically for championing reason over faith), the Church's default stance was that the planets moved around the sky 'as if' they orbited the Sun. We are in a similar position now with many-worlds vs. 'as if' many-worlds, based on experimental evidence such as the Mach-Zehnder interferometer results.
- Symmetry 14y ago
  Of course the phenomenon is explained by Many Worlds, that's an interpretation of QM that should be consistent with the evidence we have in all cases if it's not to be discarded. Many Worlds is also hardly a persecuted viewpoint, it may not have penetrated into the popular consciousness but I seem to recall evidence that most actual physicists don't use a collapse postulate. I certainly know that my of my physicist friends here in the MIT community everyone holds with some sort of non-collapse interpretation. EDIT: Wait, I just remembered one dual physics/philosophy major who believes in quantum collapse. But even she thinks that the Copenhagen Interpretation, the one you usually see in the media, is ridiculous. I'll say that, personally, I find it much easier to make sense of situations involving long range entanglements when I think about them in terms of Many Worlds than when I think about them in terms of waveform collapse. And the term "teleportation" as applied to these results really does annoy me.
  - RockofStrength 14y ago
    Thank you - it is nice to get feedback from someone in the community. I agree that Many Worlds is not literally persecuted, but it is viewed as something of an absurdity by the layman, and seems to be a bit taboo among the elders in the field. The preference of a public panel is often to throw up one's hands at the mystery of it all, which encourages people like Deepak Chopra to muse on the magic of consciousness' power to collapse the wave function.
Mitt 14y ago
Often “why”-questions are interpreted as criticism. I would like to ask one, just because I am curious: why are people interested in this for communication? With current technology we can communicate with within the limits of the speed of light. We can also encrypt communication. So, what makes this technology so interesting, that people may want to use it in the future? Will it be cheaper? Faster? More secure/better encrypted?
- thomaslangston 14y ago
  From the article: Teleportation can also securely transmit quantum information even when Alice does not know where Bob is. Bob can take his entangled particle wherever he pleases, and Alice can broadcast her instructions for how to ungarble the teleported state over whatever conventional channels — radio waves, the Internet — she pleases. That information would be useless to an eavesdropper without an entangled link to Alice.
  - JeremyBanks 14y ago
    As far as I can tell, this just seems like an obscenely overcomplicated one time pad. Instead of Alice giving Bob a string of bits that are known in advance, she gives Bob an entangled particle that can be collapsed to determine a string of bits at a later date. I can't see any security benefit. This is very neat from a purely scientific perspective. It seems pointless and misleading to try to present it as having direct practical value.
    - BerislavLopac 14y ago
      This is very neat from a purely scientific perspective. It seems pointless and misleading to try to present it as having direct practical value. If I had a buck for every time this was said about a scientific discovery, I would be quite well off...
    - jvdongen 14y ago
      For one thing, AFAIK, Alice can be sure that Bob's 'pad' is the only copy in existence because no one can copy Bob's 'pad' without destroying the entanglement. For a 'regular' one time pad this is not the case. Someone could have copied it and both Alice and Bob would be none the wiser until it's too late. One-time pad based encryption schemes are theoretically unbreakable - one of the things (the thing?) holding back wide spread adoption is the difficulty of proper key management. This has the potential to solve that issue.
jaekwon 14y ago
If you can't retrieve the information "quantum teleported" until something else bridges the gap afterwards, then how can you say that anything was teleported at all? There would have to be a qualitative or quantitative difference between what was supposedly teleported and the "key" that must be transfered afterwards. Either you can teleport a gigabyte of information and retrieve it with a kilobyte key, or you can teleport a material thing with a "key" comprised of less information needed to encode its molecular structure. Otherwise, teleportation seems to be a misnomer.
- srl 14y ago
  > Otherwise, teleportation seems to be a misnomer. It is. People call it teleportation because when you attempt to mesh the results you get from experiments involving quantum entanglement with our intuitive model of physics, it looks like something has been teleported instantaneously (the state of the photon or what have you). But in reality, no information is transmitted faster than the speed of light, and there's no good reason that will change.
  - greeneggs 14y ago
    People call it teleportation because it moves the state of a system from one place to another, without going through the intermediate positions. I'm not sure where this idea came from that teleportation has to be "instantaneous." From special relativity, we know that the word "instantaneous" isn't even well-defined, except in a fixed reference frame. Basically, quantum teleportation takes the quantum state of a system, measures it. The measurement destroys the system and converts it into classical information that can be sent over a phone line. The information, once received, can be used to reconstruct the initial state. If you think of a classical system, as computer scientists usually do, this is not very surprising. It seems obvious that in principle you could look very carefully at a complicated classical system, a human being for example, write down all of its details down to the positions of the individual atoms as a long classical string, and send this information down a phone line to reconstruct the person at the other end. It is only surprising because quantum teleportation works with quantum systems, and we know that there is no physical way of extracting all the details of a quantum system as a long classical string (Heisenberg's uncertainty principle, etc.).

49 points by ananyob 14y ago

I know this is a long long time away but .. Could this be used to communicate faster with stuff like the Curiosity rover ? I mean, once it becomes easier to reproduce without big laboratories to actually read the quantum state of the photons.

darkstalker 14y ago
And although part of the transfer happens instantaneously, the steps required to read out the teleported quantum state ensure that no information can be communicated faster than the speed of light. Seems not.
- pavel_lishin 14y ago
  It might increase bandwidth, though.
stordoff 14y ago
My understanding is that current quantum teleportation methods need a classical channel to transmit information (and so is limited to the speed of light). See the Protocol section of Wikipedia - https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation . To my knowledge, there is no particular reason to believe that this limitation can be removed. The simplest way to see this is to consider a state such as a|0> + b|1>, which is the quantum state of the particle we wish to teleport from Alice to Bob. If Alice does the measurements needed to teleport it, Bob might end up with either a|0> + b|1> or a|0> - b|1> (or two other similar states) with equal probability. To actually get the correct state we began with, which is the only way to transmit something meaningful, then he needs the results of Alice's measurements to make a correction. These can only be transmitted at the speed of light, so speed of information transfer is still limited to the speed of light.

RockofStrength 14y ago

This phenomenon is explained by many-worlds: The two photons have both polarization orientations in the multiverse. We are limited to a single instance of the multiverse, and any interaction whatsoever between the photons and our universe will force them into a single instance of polarization orientation, as this is all we can experience, being interacting beings ourselves. Reality is really an immense interconnected binary tree, and we must always travel along a single path. It has the property that reconciling paths (paths that diverged but met up again with no interaction in our universe) will again be accessible to us. As Galileo was prosecuted for supporting Copernicus' heliocentric theory (more specifically for championing reason over faith), the Church's default stance was that the planets moved around the sky 'as if' they orbited the Sun. We are in a similar position now with many-worlds vs. 'as if' many-worlds, based on experimental evidence such as the Mach-Zehnder interferometer results.

Symmetry 14y ago
Of course the phenomenon is explained by Many Worlds, that's an interpretation of QM that should be consistent with the evidence we have in all cases if it's not to be discarded. Many Worlds is also hardly a persecuted viewpoint, it may not have penetrated into the popular consciousness but I seem to recall evidence that most actual physicists don't use a collapse postulate. I certainly know that my of my physicist friends here in the MIT community everyone holds with some sort of non-collapse interpretation. EDIT: Wait, I just remembered one dual physics/philosophy major who believes in quantum collapse. But even she thinks that the Copenhagen Interpretation, the one you usually see in the media, is ridiculous. I'll say that, personally, I find it much easier to make sense of situations involving long range entanglements when I think about them in terms of Many Worlds than when I think about them in terms of waveform collapse. And the term "teleportation" as applied to these results really does annoy me.
- RockofStrength 14y ago
  Thank you - it is nice to get feedback from someone in the community. I agree that Many Worlds is not literally persecuted, but it is viewed as something of an absurdity by the layman, and seems to be a bit taboo among the elders in the field. The preference of a public panel is often to throw up one's hands at the mystery of it all, which encourages people like Deepak Chopra to muse on the magic of consciousness' power to collapse the wave function.

Mitt 14y ago

Often “why”-questions are interpreted as criticism. I would like to ask one, just because I am curious: why are people interested in this for communication? With current technology we can communicate with within the limits of the speed of light. We can also encrypt communication. So, what makes this technology so interesting, that people may want to use it in the future? Will it be cheaper? Faster? More secure/better encrypted?

thomaslangston 14y ago
From the article: Teleportation can also securely transmit quantum information even when Alice does not know where Bob is. Bob can take his entangled particle wherever he pleases, and Alice can broadcast her instructions for how to ungarble the teleported state over whatever conventional channels — radio waves, the Internet — she pleases. That information would be useless to an eavesdropper without an entangled link to Alice.
- JeremyBanks 14y ago
  As far as I can tell, this just seems like an obscenely overcomplicated one time pad. Instead of Alice giving Bob a string of bits that are known in advance, she gives Bob an entangled particle that can be collapsed to determine a string of bits at a later date. I can't see any security benefit. This is very neat from a purely scientific perspective. It seems pointless and misleading to try to present it as having direct practical value.
  - BerislavLopac 14y ago
    This is very neat from a purely scientific perspective. It seems pointless and misleading to try to present it as having direct practical value. If I had a buck for every time this was said about a scientific discovery, I would be quite well off...
  - jvdongen 14y ago
    For one thing, AFAIK, Alice can be sure that Bob's 'pad' is the only copy in existence because no one can copy Bob's 'pad' without destroying the entanglement. For a 'regular' one time pad this is not the case. Someone could have copied it and both Alice and Bob would be none the wiser until it's too late. One-time pad based encryption schemes are theoretically unbreakable - one of the things (the thing?) holding back wide spread adoption is the difficulty of proper key management. This has the potential to solve that issue.

jaekwon 14y ago

If you can't retrieve the information "quantum teleported" until something else bridges the gap afterwards, then how can you say that anything was teleported at all? There would have to be a qualitative or quantitative difference between what was supposedly teleported and the "key" that must be transfered afterwards. Either you can teleport a gigabyte of information and retrieve it with a kilobyte key, or you can teleport a material thing with a "key" comprised of less information needed to encode its molecular structure. Otherwise, teleportation seems to be a misnomer.

srl 14y ago
> Otherwise, teleportation seems to be a misnomer. It is. People call it teleportation because when you attempt to mesh the results you get from experiments involving quantum entanglement with our intuitive model of physics, it looks like something has been teleported instantaneously (the state of the photon or what have you). But in reality, no information is transmitted faster than the speed of light, and there's no good reason that will change.
- greeneggs 14y ago
  People call it teleportation because it moves the state of a system from one place to another, without going through the intermediate positions. I'm not sure where this idea came from that teleportation has to be "instantaneous." From special relativity, we know that the word "instantaneous" isn't even well-defined, except in a fixed reference frame. Basically, quantum teleportation takes the quantum state of a system, measures it. The measurement destroys the system and converts it into classical information that can be sent over a phone line. The information, once received, can be used to reconstruct the initial state. If you think of a classical system, as computer scientists usually do, this is not very surprising. It seems obvious that in principle you could look very carefully at a complicated classical system, a human being for example, write down all of its details down to the positions of the individual atoms as a long classical string, and send this information down a phone line to reconstruct the person at the other end. It is only surprising because quantum teleportation works with quantum systems, and we know that there is no physical way of extracting all the details of a quantum system as a long classical string (Heisenberg's uncertainty principle, etc.).