3 ms·

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.