I just noticed that the question
was closed as off-topic a couple of months ago, and I don't understand why. The topic is basic quantum field theory: the entanglement structure of the vacuum is fundamental to understanding basic things like the interplay between causality and the structure of two-point correlation functions, understanding why a strict position-operator doesn't exist in relativistic QFT, and so on, not to mention its central role in more exotic (but still very much mainstream) things like Hawking radiation, the black-hole information paradox, and the AdS/CFT correspondence. In case the fundamental importance of the vacuum entanglement topic in quantum field theory is unfamiliar, note that Edward Witten wrote a review paper about it (Notes on Some Entanglement Properties of Quantum Field Theory, arXiv:1803.04993). This particular question is about harvesting entanglement from the vacuum, which is not something that has any practical utility, but it does have pedagogical utility.
There is plenty of precedent on this site for regarding theoretical physics as on-topic as long as it's mainstream, even if it is purely a pedagogical thought experiment with no forseeable practical applications. I'm curious to understand why this particular question about basic quantum field theory was deemed to be off-topic. Not complaining, just sincerely curious to know what the reasoning was, in case I'm overlooking a good reason.