5 ms·

Hi all! I'm one of the co-authors. Honestly it's a dream to end up on HN with my research. As mentioned in the video we made, it has been a long road (6-7 years

Hi all! I'm one of the co-authors. Honestly it's a dream to end up on HN with my research. As mentioned in the video we made, it has been a long road (6-7 years) to achieve this absolute moonshot of a project. I think we'll look back on this demonstration as the first experiment that truly made a distributed and real-world deployed quantum network. Not only did we use a (quantum) hardware platform capable of quantum processing, we also generated the entanglement in a way that it can be used in further quantum computations. In order for all this to work on a distributed network, we had to fully design and build the architecture to support that, both hard- and software. And we did it successfully! Besides hard-working PhD students, another key ingredient that our research institute QuTech facilitated, was the collaboration with expert hardware and software engineers, allowing us to quickly transform new ideas into (deployable) products. A great show of what's possible when academia mixes with professional engineering. But of course there was enough hacking and tinkering going on that it warrants to be on HN ;) You can reply here if you have any questions, I'll be checking throughout the day. Thanks!

Havoc 2y ago
It says over fiber. I assume that has to be a straight shot point to point non-routed? Or could this deal with repeaters and routers etc
- pclmulqdq 2y ago
  All of the quantum networking stuff is point-to-point. It's not clear to me whether fiber amplifiers are even allowed on these links.
  - dwnw 2y ago
    Amplification would absorb one photon and replace it with one or more new photons. Definitely not quantum. Personally, I always wonder why point-to-point connections are called "networks". The information is not quantum at any node, even if there are multiple nodes in a system. Then there's "quantum internet", which makes no sense at all. What are we going to do, run direct fiber from every computer to every other computer directly? You can't hop safely or anything. Don't get me started on the total bullshit that is the "quantum repeater", now we need "quantum switch" too? We call serial port connections things like "link", "connection", etc. We typically don't call them networks until we start linking them all together with simple routing logic that doesn't inherently require access to all the unencrypted information the packets contain and such. To me these are all just signs that the whole scheme is/was and will forever be mostly crankery. Quantum networking is an oxymoron. It doesn't allow end-to-end encryption and in exchange gives back extremely fragile single link security properties.
    - eigenket 2y ago
      I don't think it's completely clear (to me) that quantum networking is an oxymoron. I would enthusiastically agree that its very complicated and the real world use cases are incredibly limited. As far as your routing/switching qualms go I think they are mostly addressed by entanglement swapping? Person A and person B can each make an entangled pair and send me half, and I can (locally) do stuff which leads to the halves they keep at home becoming entangled. Then they can use teleportation or whatever to do whatever they want between themselves without me knowing anything about it.
      - dwnw 2y ago
        Lots of handwaving there. Particularly with "and I can (locally) do stuff" Good luck with all of that.
        eigenket 2y ago
        The I can locally do stuff is completely understood theoretically/mathematically. I hand waved because this isn't a forum where those technicalities are particuarly relevant. Its been well understood since at least 1993 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.71.4287 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.71...
    - Strilanc 2y ago
      > What are we going to do, run direct fiber from every computer to every other computer directly? No, you don't have to do that. A quantum network would be a web of point-to-point quantum links, with paths formed by routers choosing links. Same as a classical network. To be a bit more concrete what an operating quantum network would look like is a bunch of routers using links to build up entanglement with their neighbors. When an endpoint wants to send a message across the network, a path from source to destination would be determined and entanglement across the links of that path would be consumed to move the message across the network [1][2]. The reason it's done this way, instead of directly sending the message, is that entanglement can be cross-checked before using it [3] and quantum networks really don't like dropping packets due to the no-cloning theorem. > We typically don't call them networks until we start linking them all together with simple routing logic Yeah I agree that it would be more accurate for this press release to say they made a quantum link. > To me these are all just signs that the whole scheme is/was and will forever be mostly crankery. Don't confuse difficulty with crankery. It'll be awhile before anyone reports an experimental realization of a true quantum network, because it'll be awhile because anyone can make a quantum router. The issue is that a quantum router is for all intents and purposes a fault tolerant quantum computer, and that is its own hard challenge being worked on separately. In particular, a quantum router needs to be able to store qubits reliably for non-trivial amounts of time, and to perform reliable operations on those qubits in order to cross-check stored entanglement. [1]: https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation [2]: https://en.wikipedia.org/wiki/Quantum_entanglement_swapping https://en.wikipedia.org/wiki/Quantum_entanglement_swapping [3]: https://en.wikipedia.org/wiki/Entanglement_distillation https://en.wikipedia.org/wiki/Entanglement_distillation
andai 2y ago
Layman 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.
- metropolbadger 2y ago
  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 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).
  - ricardobeat 2y ago
    The article says > which means they share a quantum connection enabling instant correlations, no matter the distance But per your response this is not true, i.e. information transmission is still limited by the speed of light?
Strilanc 2y ago
How hard do you expect it would be to improve the heralded infidelity from 45% to 10%? In figure 3 of the paper [1] the heralded infidelity of entanglement is reported to be around 45%. That's not good enough for computation, but it's less than 50% which means it makes purification to arbitrarily low infidelity possible. However, the conversion rates would be pretty brutal for such a high infidelity start (e.g. millions of physical pairs consumed per logical pair good enough for use in a fault tolerant computation e.g. a target logical infidelity of 1e-6 or 1e-9). 1: https://arxiv.org/pdf/2404.03723#page=4 https://arxiv.org/pdf/2404.03723#page=4

Havoc 2y ago

It says over fiber. I assume that has to be a straight shot point to point non-routed? Or could this deal with repeaters and routers etc

pclmulqdq 2y ago
All of the quantum networking stuff is point-to-point. It's not clear to me whether fiber amplifiers are even allowed on these links.
- dwnw 2y ago
  Amplification would absorb one photon and replace it with one or more new photons. Definitely not quantum. Personally, I always wonder why point-to-point connections are called "networks". The information is not quantum at any node, even if there are multiple nodes in a system. Then there's "quantum internet", which makes no sense at all. What are we going to do, run direct fiber from every computer to every other computer directly? You can't hop safely or anything. Don't get me started on the total bullshit that is the "quantum repeater", now we need "quantum switch" too? We call serial port connections things like "link", "connection", etc. We typically don't call them networks until we start linking them all together with simple routing logic that doesn't inherently require access to all the unencrypted information the packets contain and such. To me these are all just signs that the whole scheme is/was and will forever be mostly crankery. Quantum networking is an oxymoron. It doesn't allow end-to-end encryption and in exchange gives back extremely fragile single link security properties.
  - eigenket 2y ago
    I don't think it's completely clear (to me) that quantum networking is an oxymoron. I would enthusiastically agree that its very complicated and the real world use cases are incredibly limited. As far as your routing/switching qualms go I think they are mostly addressed by entanglement swapping? Person A and person B can each make an entangled pair and send me half, and I can (locally) do stuff which leads to the halves they keep at home becoming entangled. Then they can use teleportation or whatever to do whatever they want between themselves without me knowing anything about it.
    - dwnw 2y ago
      Lots of handwaving there. Particularly with "and I can (locally) do stuff" Good luck with all of that.
      - eigenket 2y ago
        The I can locally do stuff is completely understood theoretically/mathematically. I hand waved because this isn't a forum where those technicalities are particuarly relevant. Its been well understood since at least 1993 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.71.4287 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.71...
  - Strilanc 2y ago
    > What are we going to do, run direct fiber from every computer to every other computer directly? No, you don't have to do that. A quantum network would be a web of point-to-point quantum links, with paths formed by routers choosing links. Same as a classical network. To be a bit more concrete what an operating quantum network would look like is a bunch of routers using links to build up entanglement with their neighbors. When an endpoint wants to send a message across the network, a path from source to destination would be determined and entanglement across the links of that path would be consumed to move the message across the network [1][2]. The reason it's done this way, instead of directly sending the message, is that entanglement can be cross-checked before using it [3] and quantum networks really don't like dropping packets due to the no-cloning theorem. > We typically don't call them networks until we start linking them all together with simple routing logic Yeah I agree that it would be more accurate for this press release to say they made a quantum link. > To me these are all just signs that the whole scheme is/was and will forever be mostly crankery. Don't confuse difficulty with crankery. It'll be awhile before anyone reports an experimental realization of a true quantum network, because it'll be awhile because anyone can make a quantum router. The issue is that a quantum router is for all intents and purposes a fault tolerant quantum computer, and that is its own hard challenge being worked on separately. In particular, a quantum router needs to be able to store qubits reliably for non-trivial amounts of time, and to perform reliable operations on those qubits in order to cross-check stored entanglement. [1]: https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation [2]: https://en.wikipedia.org/wiki/Quantum_entanglement_swapping https://en.wikipedia.org/wiki/Quantum_entanglement_swapping [3]: https://en.wikipedia.org/wiki/Entanglement_distillation https://en.wikipedia.org/wiki/Entanglement_distillation

andai 2y ago

Layman 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.

metropolbadger 2y ago
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 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).
- ricardobeat 2y ago
  The article says > which means they share a quantum connection enabling instant correlations, no matter the distance But per your response this is not true, i.e. information transmission is still limited by the speed of light?

Strilanc 2y ago

How hard do you expect it would be to improve the heralded infidelity from 45% to 10%? In figure 3 of the paper [1] the heralded infidelity of entanglement is reported to be around 45%. That's not good enough for computation, but it's less than 50% which means it makes purification to arbitrarily low infidelity possible. However, the conversion rates would be pretty brutal for such a high infidelity start (e.g. millions of physical pairs consumed per logical pair good enough for use in a fault tolerant computation e.g. a target logical infidelity of 1e-6 or 1e-9). 1: https://arxiv.org/pdf/2404.03723#page=4 https://arxiv.org/pdf/2404.03723#page=4