alt Hacker NewsLayman here! I have no idea what's going on but I have many questions!
- Are the photons themselves carrying quantum information?
- Does the photon link result in entangled particles in Delft and Den Haag?
- Can these entangled particles be used for communication without the optical link?
Also, I tried looking this stuff up and ran into something about quantum "repeaters" and a plans for a whole quantum network. Is this research part of working towards that? How far are we now, and what steps are still missing? Thanks!
Edit: Looks like you guys built a multi-node quantum network 2 years ago! I will have to do some more reading.
All good! That was me 5 years ago :)
- Yes and no. The photons emitted and sent through the fiber are entangled with their electron counterparts. So we send simultaneously a photon state (entangled with electron) from Delft, and a photon state (entangled with electron) from Den Haag. Those states interfere in the midpoint (Rijswijk), and upon measurement of one photon (photon now is absorbed/measured/gone) we know that the _electrons_ of the nodes in Delft and Den Haag are entangled.
- The above also answers this question: yes!
- No. They can be used to transfer a quantum state from one place to the other, for example, which _consumes_ the entanglement (one-time use only, per pair of entangled particles). However, still classical feedback signals need to propagate for that to happen, so we still need _a_ link, preferably optical (for speed and distance). Wiki has actually a great page on teleportation: https://en.wikipedia.org/wiki/Quantum_teleportation
I'll answer to a different question on repeaters later in another comment, so check back :) Indeed, multi-node quantum network was an awesome experiment. This takes it to the next level of being able to distribute entanglement over large distances and between quantum nodes that are self-sufficient (no sharing of hardware resources between nodes).