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Oh it's better than that! The term "quantum teleportation" is horribly misleading but that would be a major application of this. What "quantum teleportation" sh

by tgb 8y ago

Oh it's better than that! The term "quantum teleportation" is horribly misleading but that would be a major application of this. What "quantum teleportation" should maybe be thought of is allowing you transmit a quantum bit to someone else by instead (A) sharing an entangled particle pair ahead of time and (B) transmitting two (non-quantum) bits to them over, say, ethernet. If you prepare your half of the entagled particle pair properly and send them the right two (classical) bits, then they will be able to reconstruct your original quantum bit out of their entangled particle. So it's a way of getting my quantum bit to your quantum computer without having to pick it up and move it over there. It doesn't happen faster than the speed of light since it still involves transferring 2 regular bits. And it's not really teleportation, unless I "teleport" an image to you by sending emailing it to you. The main difference with sending regular bits is that you inherently destroy your original quantum bit before you "teleport" it, which is presumably where the name comes from. Since copying quantum bits is impossible (the "no-clone theorem"), you can't work around that destruction either.

jfoutz 8y ago
I know, like, nothing about this. But my wiki reading makes me think this is essentially a one time pad. you share the entangled bits, you send a message, the message tells you what to do if your entangled bit is one, or zero. nobody can mess with the entangled bits, or they lose entanglement, and the message becomes random. i dunno, it seems like if you had a bunch of them you could make a secure channel.
- marcosdumay 8y ago
  > i dunno, it seems like if you had a bunch of them you could make a secure channel. I don't think anybody solved man in the middle attacks against it yet. If the attacker takes hold of both the entangled channel and the classical channel, he can impersonate both parties and keep the conversation going. And you can't store those pairs. All those articles are about people that made them survive long enough for transmission. So you can't distribute them in person.
  - AlexCoventry 8y ago
    That MITM attack is considerably more fragile than just reading a one-time pad during transit, though.
    - marcosdumay 8y ago
      Asymmetric encryption is cheaper, survives storage, requires only the transmission of public data, and is not fundamentally flawed like that. It is also more versatile.
      - akvadrako 8y ago
        But non-quantum encryption hasn't been mathematically proven to be secure. In the real world, you'll probably always use both and only if large quantum computers become available.
        marcosdumay 8y ago
        Quantum computers are not needed for quantum encryption, and quantum computers do not break classical encryption in general, just the most used algorithms. They simply don't change the overall picture on this. Yes, non-quantum encryption has not been proven secure. That beats a known insecure systems at any time. You are also underestimating the cost of quantum crypto - it will only work on direct fiber, it can never be routed.
        akvadrako 8y ago
        Maybe some classical algorithm is immune to quantum computers, but none have been proven to be, unlike quantum encryption. Also, the Chinese have already demonstrated quantum channels over satellites - it doesn’t need fiber. The satellites are certainly acting as routers too.
        marcosdumay 8y ago
        Quantum encryption is broken today. Classical encryption may be broken, nobody knows. None of those is perfect, but one is better than the other.
- Strilanc 8y ago
  Quantum teleportation is in fact a quantum generalization of the classical one time pad. And it does form a secure channel, but with the same caveats as in the classical case (e.g. it's not authenticated). Many quantum things have classical analogues. For example, there is classical no cloning [1] and classical delayed erasure [2], though people will debate if these classical versions have really captured the "essence" of the quantum things. 1: https://marozols.wordpress.com/2012/05/21/three-myths-about-quantum-computing-part-2/ https://marozols.wordpress.com/2012/05/21/three-myths-about-... 2: http://algassert.com/post/1720 http://algassert.com/post/1720

by tgb 8y ago

jfoutz 8y ago

I know, like, nothing about this. But my wiki reading makes me think this is essentially a one time pad. you share the entangled bits, you send a message, the message tells you what to do if your entangled bit is one, or zero. nobody can mess with the entangled bits, or they lose entanglement, and the message becomes random. i dunno, it seems like if you had a bunch of them you could make a secure channel.

marcosdumay 8y ago
> i dunno, it seems like if you had a bunch of them you could make a secure channel. I don't think anybody solved man in the middle attacks against it yet. If the attacker takes hold of both the entangled channel and the classical channel, he can impersonate both parties and keep the conversation going. And you can't store those pairs. All those articles are about people that made them survive long enough for transmission. So you can't distribute them in person.
- AlexCoventry 8y ago
  That MITM attack is considerably more fragile than just reading a one-time pad during transit, though.
  - marcosdumay 8y ago
    Asymmetric encryption is cheaper, survives storage, requires only the transmission of public data, and is not fundamentally flawed like that. It is also more versatile.
    - akvadrako 8y ago
      But non-quantum encryption hasn't been mathematically proven to be secure. In the real world, you'll probably always use both and only if large quantum computers become available.
      - marcosdumay 8y ago
        Quantum computers are not needed for quantum encryption, and quantum computers do not break classical encryption in general, just the most used algorithms. They simply don't change the overall picture on this. Yes, non-quantum encryption has not been proven secure. That beats a known insecure systems at any time. You are also underestimating the cost of quantum crypto - it will only work on direct fiber, it can never be routed.
        akvadrako 8y ago
        Maybe some classical algorithm is immune to quantum computers, but none have been proven to be, unlike quantum encryption. Also, the Chinese have already demonstrated quantum channels over satellites - it doesn’t need fiber. The satellites are certainly acting as routers too.
        marcosdumay 8y ago
        Quantum encryption is broken today. Classical encryption may be broken, nobody knows. None of those is perfect, but one is better than the other.
Strilanc 8y ago
Quantum teleportation is in fact a quantum generalization of the classical one time pad. And it does form a secure channel, but with the same caveats as in the classical case (e.g. it's not authenticated). Many quantum things have classical analogues. For example, there is classical no cloning [1] and classical delayed erasure [2], though people will debate if these classical versions have really captured the "essence" of the quantum things. 1: https://marozols.wordpress.com/2012/05/21/three-myths-about-quantum-computing-part-2/ https://marozols.wordpress.com/2012/05/21/three-myths-about-... 2: http://algassert.com/post/1720 http://algassert.com/post/1720