7 ms·

Ok, does anyone have a simple guide to what it means?

eloff 7y ago
Yeah, I'm really waiting for some of the physics experts on HN to give their take on this. I have a limited understanding of the basic idea behind entanglement, but I can't extend it to this case. I gather this experiment somehow entangles photons from the sun with photons produced by the experimenters, but they're already here when that happens right? So how does the distance come into play. I think I'm probably looking at it too "classically".
- nicholsonpk 7y ago
  The diagrams helped clear it up for me (I think.) Yes, they are entangling them on Earth and this seems to be testing the idea that an atom created here is the same/similar enough to one from the sun for this to take place. "Figure 4: Entanglement fidelity measurement of the entangled photon pairs with no common history." It's something I would have assumed as a novice but it's interesting that they thought to test it. If you couldn't entangle them, what would that mean? It looks like the keyword in the title was light "sources" that are 150 Million Kilometers apart. I didn't catch that at first.
  - abdullahkhalids 7y ago
    > created here is the same/similar enough to one from the sun for this to take place Exactly. They are testing if photons on Earth are the same as those produced in the Sun - a very simple test of the translation invariance of the laws of quantum physics. > If you couldn't entangle them, what would that mean? If such experiments failed despite repeated efforts, then maybe the laws of quantum physics are not invariant under translation as far as 150M kilometers. Note that we communicate with Voyager crafts for instance using classical EM waves, so presumably the laws of classical EM work the same as far as the edge of the solar system.
    - wwarner 7y ago
      I'm not an expert, but I thought the paper was more novel than that, in that it challenges my picture of entanglement. The paper demontrates entangled behavior with photons with no common history. They are "identical" in their conserved properties, rather than "entangled" which to me implies that their conserved properties sum to the values that existed before the event that produced the entangled pair. To me, the surprise is that identical pairs always take the same path.
      - abdullahkhalids 7y ago
        This might challenge your picture of entanglement, but definitely not that of a physicist. Otherwise, I can't make head or tail of your statements.
        wwarner 7y ago
        I'll try to restate. I was under the impression that entanglement implied what the paper calls "common history", such as when an excited calcium atom decays to its ground state and produces two entangled photons. I also understood entanglement to be particles with some opposite properties, so that the sum of say the angular momentum of the system before and after the decay remains constant. So it was news to me that (a) photons without a common history, and (b) photons indistinguishable in all degrees of freedom could be entangled.
        abdullahkhalids 7y ago
        > So it was news to me that (a) photons without a common history, and (b) photons indistinguishable in all degrees of freedom could be entangled. Oh no. It is definitely possible to entangle two photons from two different sources. Say two hydrogen atoms emit a photon each; then you just need a non-linear crystal to entangle them, or use linear crystals and post-select good results. Here is a recent example for the latter for quantum repeaters [1], though this has been done for decades now. And making two different photon sources indistinguishable (or controllably-distinguishable) is like the first thing you do in a quantum optics lab. > I also understood entanglement... That's not a correct way to think of entanglement. Two particles are (maximally) entangled if (1) you do the same measurement on the two particles, the results are (perfectly) correlated. (2) if you do orthogonal measurements on the two particles, the results are (perfectly) uncorrelated. And all this happens in a way that no local classical theory can explain. [1] https://arxiv.org/pdf/1908.05351.pdf https://arxiv.org/pdf/1908.05351.pdf
bmcooley 7y ago
I have a limited understanding, but I think this is just further reproduction of the same science. I believe there's some controversy over non-locality in that entanglement and spooky action at a distance is still a result of hidden local variables. By increasing the distance between the sources of the photons, you would give more evidence to nonlocality. Please correct me if this is offbase.
- longtom 7y ago
  Non-locality means that the way the probability of presence (wave function) of a photon is determined is by trying out all possible paths through the entire universe at once rather than only in regions nearby the photons?
  - Misdicorl 7y ago
    The path integral formulation is the most prevalent and successful version of quantum physics (this is what you describe in the second half). Non locality is different; it supposes that there are hidden mechanisms we have not uncovered (and may but be able to uncover) instead which describes our world. It must be non local to get the observed experimental results. Non local means data about the universe is teleporting faster than (conventional) causality allows i.e. the speed of light
    - longtom 7y ago
      Either case seems to require faster-than-light or instant communication between alternative paths that are being tried out, so the distinction is whether the combination of different paths is mediated by another faster-than-light (non-local) particle or whether the combination is axiomatic to the laws of the universe without a particle mediating it?
      - Misdicorl 7y ago
        No, the path integral formulation does not require faster than light communication. Time is an explicit parameter
chews 7y ago
Imagine entangled data transmission... having a matrix of entangled particles, using known truths to illuminate what has up until now have been unknowable things. Wow, it’s an amazing time to be alive.

Yeah, I'm really waiting for some of the physics experts on HN to give their take on this. I have a limited understanding of the basic idea behind entanglement, but I can't extend it to this case. I gather this experiment somehow entangles photons from the sun with photons produced by the experimenters, but they're already here when that happens right? So how does the distance come into play. I think I'm probably looking at it too "classically".

nicholsonpk 7y ago
The diagrams helped clear it up for me (I think.) Yes, they are entangling them on Earth and this seems to be testing the idea that an atom created here is the same/similar enough to one from the sun for this to take place. "Figure 4: Entanglement fidelity measurement of the entangled photon pairs with no common history." It's something I would have assumed as a novice but it's interesting that they thought to test it. If you couldn't entangle them, what would that mean? It looks like the keyword in the title was light "sources" that are 150 Million Kilometers apart. I didn't catch that at first.
- abdullahkhalids 7y ago
  > created here is the same/similar enough to one from the sun for this to take place Exactly. They are testing if photons on Earth are the same as those produced in the Sun - a very simple test of the translation invariance of the laws of quantum physics. > If you couldn't entangle them, what would that mean? If such experiments failed despite repeated efforts, then maybe the laws of quantum physics are not invariant under translation as far as 150M kilometers. Note that we communicate with Voyager crafts for instance using classical EM waves, so presumably the laws of classical EM work the same as far as the edge of the solar system.
  - wwarner 7y ago
    I'm not an expert, but I thought the paper was more novel than that, in that it challenges my picture of entanglement. The paper demontrates entangled behavior with photons with no common history. They are "identical" in their conserved properties, rather than "entangled" which to me implies that their conserved properties sum to the values that existed before the event that produced the entangled pair. To me, the surprise is that identical pairs always take the same path.
    - abdullahkhalids 7y ago
      This might challenge your picture of entanglement, but definitely not that of a physicist. Otherwise, I can't make head or tail of your statements.
      - wwarner 7y ago
        I'll try to restate. I was under the impression that entanglement implied what the paper calls "common history", such as when an excited calcium atom decays to its ground state and produces two entangled photons. I also understood entanglement to be particles with some opposite properties, so that the sum of say the angular momentum of the system before and after the decay remains constant. So it was news to me that (a) photons without a common history, and (b) photons indistinguishable in all degrees of freedom could be entangled.
        abdullahkhalids 7y ago
        > So it was news to me that (a) photons without a common history, and (b) photons indistinguishable in all degrees of freedom could be entangled. Oh no. It is definitely possible to entangle two photons from two different sources. Say two hydrogen atoms emit a photon each; then you just need a non-linear crystal to entangle them, or use linear crystals and post-select good results. Here is a recent example for the latter for quantum repeaters [1], though this has been done for decades now. And making two different photon sources indistinguishable (or controllably-distinguishable) is like the first thing you do in a quantum optics lab. > I also understood entanglement... That's not a correct way to think of entanglement. Two particles are (maximally) entangled if (1) you do the same measurement on the two particles, the results are (perfectly) correlated. (2) if you do orthogonal measurements on the two particles, the results are (perfectly) uncorrelated. And all this happens in a way that no local classical theory can explain. [1] https://arxiv.org/pdf/1908.05351.pdf https://arxiv.org/pdf/1908.05351.pdf

bmcooley 7y ago

I have a limited understanding, but I think this is just further reproduction of the same science. I believe there's some controversy over non-locality in that entanglement and spooky action at a distance is still a result of hidden local variables. By increasing the distance between the sources of the photons, you would give more evidence to nonlocality. Please correct me if this is offbase.

longtom 7y ago
Non-locality means that the way the probability of presence (wave function) of a photon is determined is by trying out all possible paths through the entire universe at once rather than only in regions nearby the photons?
- Misdicorl 7y ago
  The path integral formulation is the most prevalent and successful version of quantum physics (this is what you describe in the second half). Non locality is different; it supposes that there are hidden mechanisms we have not uncovered (and may but be able to uncover) instead which describes our world. It must be non local to get the observed experimental results. Non local means data about the universe is teleporting faster than (conventional) causality allows i.e. the speed of light
  - longtom 7y ago
    Either case seems to require faster-than-light or instant communication between alternative paths that are being tried out, so the distinction is whether the combination of different paths is mediated by another faster-than-light (non-local) particle or whether the combination is axiomatic to the laws of the universe without a particle mediating it?
    - Misdicorl 7y ago
      No, the path integral formulation does not require faster than light communication. Time is an explicit parameter

chews 7y ago

Imagine entangled data transmission... having a matrix of entangled particles, using known truths to illuminate what has up until now have been unknowable things. Wow, it’s an amazing time to be alive.