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Is it possible that two entangled photons when absorbed by two material particles, say two atoms, lead to the entanglement of these atoms? Is there any published research on this topic?

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    $\begingroup$ For sure. For example, if the polarization states of the photons are entangled, the angular momenta of the atoms will become entangled, because the angular momentum delivered to each atom depends on that of the photon. $\endgroup$ Nov 13, 2021 at 19:16
  • $\begingroup$ Exactly....Could you share some references? $\endgroup$
    – User101
    Nov 14, 2021 at 12:38

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Not quite what you are asking, but (van Enk 2005) is a nice short paper arguing that (certain) single-photon states ought to be considered entangled even if there is a single "particle" involved, based on precisely the fact that the correlation in single-photon states can be transferred into more "standard" entanglement between atoms or other systems. It's a thought experiment though, not really an implementation.

More on point, one example that comes to mind is one of the experimental demonstrations of loophole-free Bell inequality violation that were done a few years ago. E.g. (Hensen et al. 2015, arXiv:1508.05949) showed experimentally nonlocality from measurements of entangled spins. To entangle spatially separated spins, they first generate entangled photons in the usual way, to then send the photons to different "far" laboratories, and transfer their states (and thus their shared entanglement) into spin systems.

I'm sure one can find countless other examples of this sort of thing.

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  • $\begingroup$ I took the question as regarding specifically entanglement transfer between photons' and atomic degrees of freedom. I agree that this probably happens in some form or another in any natural interaction of light with something else, but in the vast majority of the cases it's not controlled enough to be directly measurable, so I gave an example of a paper doing it explicitly. Regarding "heterogeneous entanglement", one should define what it means first. Talking about "entanglement with the observer" gets into interpretations territory though, so I wouldn't go there for this discussion $\endgroup$
    – glS
    Nov 13, 2021 at 22:51

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