6 ms·

Can someone with more knowledge on this topic speak to whether this is likely to take off, or is it just a research toy?

lallysingh 8y ago
Yes. Can these be used in cases where traditional radio systems can't be used? Like deeply submerged submarines?
- roywiggins 8y ago
  Having a bunch of entangled particles doesn't actually let you communicate. You still need to exchange particles with your interlocutor. If you can't communicate classically, you can't communicate with quantum states either- this is the no-communication theorem. Quantum mechanics allows for superdense coding, where you get a bit more than one bit per particle, but it's probably not really helpful.
  - lallysingh 8y ago
    But you can then twiddle with these photons after exchange right? Use them to communicate after? Otherwise what's the point?
    - deleted 8y ago
      [deleted]
    - Strilanc 8y ago
      > Having a bunch of entangled particles doesn't actually let you communicate. [...] this is the no-communication theorem.
    - roywiggins 8y ago
      The theorem says that you specifically can't communicate with entanglement alone. It's spooky, but just non-spooky enough to forbid building an ansible. If you poke one part of an entangled pair, you can't actually force which state you will get. You will get a measurement, and the other can be measured as well and they will both be observed in some state- but you can't push one leftwards to get the other to go rightwards. If you could, high speed traders would not bother with microwave links. Quantum networks are (in theory) impossible to snoop on without detection, so they are useful for distributing cryptographic keys. They might be useful to pass quantum states around between quantum computers if they're reliable enough.
n4r9 8y ago
Well, there's supposedly a much longer network in China: https://www.opengovasia.com/articles/8091-worlds-longest-unhackable-quantum-communications-link-opened-between-beijing-and-shanghai https://www.opengovasia.com/articles/8091-worlds-longest-unh... The theory is sound and the technology is getting there. The question is really whether there's enough commercial interest. Joe Public doesn't care too much about this level of security, but governments, journalists, intelligence groups, and companies with a lot of intellectual property do. I predict that there will be some commercial uptake of this tech in 20 or so years time, but I don't think it'll be that exciting in terms of practical application. It's already possible to be confident that the pure algorithm is secure, i.e. communications can't be read without some sort of social engineering, backdoors or the like.
Moodles 8y ago
It's not likely to take off. Do you want pre-shared secrets and the expense of a quantum network to, in theory, have infinite security (in theory!), or are you okay with tried and tested RSA which gives you >1000000000 years security at a much cheaper cost, that actually works in practice?
- OscarCunningham 8y ago
  Well not RSA, that will be broken by quantum computers. But there are some classical encryption methods that quantum computers are not known to break.

lallysingh 8y ago

Yes. Can these be used in cases where traditional radio systems can't be used? Like deeply submerged submarines?

roywiggins 8y ago
Having a bunch of entangled particles doesn't actually let you communicate. You still need to exchange particles with your interlocutor. If you can't communicate classically, you can't communicate with quantum states either- this is the no-communication theorem. Quantum mechanics allows for superdense coding, where you get a bit more than one bit per particle, but it's probably not really helpful.
- lallysingh 8y ago
  But you can then twiddle with these photons after exchange right? Use them to communicate after? Otherwise what's the point?
  - deleted 8y ago
    [deleted]
  - Strilanc 8y ago
    > Having a bunch of entangled particles doesn't actually let you communicate. [...] this is the no-communication theorem.
  - roywiggins 8y ago
    The theorem says that you specifically can't communicate with entanglement alone. It's spooky, but just non-spooky enough to forbid building an ansible. If you poke one part of an entangled pair, you can't actually force which state you will get. You will get a measurement, and the other can be measured as well and they will both be observed in some state- but you can't push one leftwards to get the other to go rightwards. If you could, high speed traders would not bother with microwave links. Quantum networks are (in theory) impossible to snoop on without detection, so they are useful for distributing cryptographic keys. They might be useful to pass quantum states around between quantum computers if they're reliable enough.

n4r9 8y ago

Well, there's supposedly a much longer network in China: https://www.opengovasia.com/articles/8091-worlds-longest-unhackable-quantum-communications-link-opened-between-beijing-and-shanghai https://www.opengovasia.com/articles/8091-worlds-longest-unh... The theory is sound and the technology is getting there. The question is really whether there's enough commercial interest. Joe Public doesn't care too much about this level of security, but governments, journalists, intelligence groups, and companies with a lot of intellectual property do. I predict that there will be some commercial uptake of this tech in 20 or so years time, but I don't think it'll be that exciting in terms of practical application. It's already possible to be confident that the pure algorithm is secure, i.e. communications can't be read without some sort of social engineering, backdoors or the like.

Moodles 8y ago

It's not likely to take off. Do you want pre-shared secrets and the expense of a quantum network to, in theory, have infinite security (in theory!), or are you okay with tried and tested RSA which gives you >1000000000 years security at a much cheaper cost, that actually works in practice?

OscarCunningham 8y ago
Well not RSA, that will be broken by quantum computers. But there are some classical encryption methods that quantum computers are not known to break.