Ciro Santilli
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Quantum entanglement | 🗖 nosplit | ↑ parent "Quantum mechanics" | 510, 5, 557

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Quantum entanglement is often called spooky/surprising/unintuitive, but they key question is to understand why.
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To understand that, you have to understand why it is fundamentally impossible for the entangled particle pair be in a predefined state according to experiments done e.g. where one is deterministically yes and the other deterministically down.
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In other words, why local hidden-variable theory is not valid.
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How to generate entangled particles:
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Video 74. Bell's Theorem: The Quantum Venn Diagram Paradox by minutephysics (2017-09-13) Source.
Contains the clearest Bell test experiment description seen so far.
It clearly describes the photon-based 22.5, 45 degree/85%/15% probability photon polarization experiment and its result conceptually.
It does not mention spontaneous parametric down-conversion but that's what they likely hint at.
Done in Collaboration with 3Blue1Brown.
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Video 75. "Quantum Entanglement & Spooky Action at a Distance" by veritasium (2015-01-12) Source. Gives a clear explanation of a thought Bell test experiments with electron spin of electron pairs from photon decay with three 120-degree separated slits. The downside is that he does not clearly describe an experimental setup, it is quite generic.
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Video 76. "Quantum Mechanics: Animation explaining quantum physics" by Physics Videos by Eugene Khutoryansky (2013) Source. Usual Eugene, good animations, and not too precise explanations :-) https://youtu.be/iVpXrbZ4bnU?t=922 describes a conceptual spin entangled electron-prositro pair production Stern-Gerlach experiment as a Bell test experiments. The 85% is mentioned, but not explained at all.
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Video 77. "Quantum Entanglement: Spooky Action at a Distance" by Don Lincoln (2020-02-12) Source. This only has two merits compared to Video 75. ""Quantum Entanglement & Spooky Action at a Distance" by veritasium (2015-01-12)": it mentions the Aspect et al. (1982) Bell test experiment, and it shows the continuous curve similar to https://en.wikipedia.org/wiki/File:Bell.svg. But it just does not clearly explain the bell test.
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Video 78. Quantum Entanglement Lab by Scientific American (2013-03-20) Source. The hosts interview Professor Enrique Galvez of Colgate University who shows briefly the optical table setup without great details, and then moves to a whiteboard explanation. Treats the audience as stupid, doesn't say the keywords spontaneous parametric down-conversion and Bell's theorem which they clearly allude to. You can even them showing a two second footage of the professor explaining the rotation experiments and the data for it, but that's all you get.
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