= Quantum entanglement
{wiki}
= Entangled particle
{synonym}
= Entanglement
{synonym}
= Entangled
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Quantum entanglement is often called spooky/surprising/unintuitive, but they key question is to understand why.
To understand that, you have to understand why it is fundamentally impossible for the entangled particle pair be in a predefined state <Bell test experiment>[according to experiments done] e.g. where one is deterministically yes and the other deterministically down.
In other words, why <local hidden-variable theory> is not valid.
How to generate entangled particles:
* <particle decay>, notably <pair production>
* for <photons>, notably: <spontaneous parametric down-conversion>, e.g.: https://www.youtube.com/watch?v=tn1sEaw1K2k "Shanni Prutchi Construction of an Entangled Photon Source" by HACKADAY (2015). Estimatd price: 5000 USD.
\Video[https://www.youtube.com/watch?v=zcqZHYo7ONs]
{title=Bell's Theorem: The Quantum Venn Diagram Paradox by <minutephysics> (2017)}
{description=
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>.
Question asking further clarification on why the 100/85/50 thing is surprising: https://physics.stackexchange.com/questions/357039/why-is-the-quantum-venn-diagram-paradox-considered-a-paradox/597982\#597982
}
\Video[https://www.youtube.com/watch?v=sAXxSKifgtU]
{title=Bell's Inequality I by <ViaScience> (2014)}
\Video[https://www.youtube.com/watch?v=ZuvK-od647c]
{title=Quantum Entanglement & Spooky Action at a Distance by <Veritasium> (2015)}
{description=Gives a clear explanation of a thought <Bell test experiments> with <electron> <spin (physics)> 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.}
\Video[https://www.youtube.com/watch?v=iVpXrbZ4bnU]
{title=Quantum Mechanics: Animation explaining quantum physics by <Physics Videos by Eugene Khutoryansky> (2013)}
{description=Usual Eugene, good animations, and not too precise explanations :-) https://youtu.be/iVpXrbZ4bnU?t=922 describes a conceptual spin entangled electron-positron <pair production> <Stern-Gerlach experiment> as a <Bell test experiments>. The 85% is mentioned, but not explained at all.}
\Video[https://www.youtube.com/watch?v=JFozGfxmi8A]
{title=Quantum Entanglement: Spooky Action at a Distance by <Don Lincoln> (2020)}
{description=This only has two merits compared to <video Quantum Entanglement & Spooky Action at a Distance by Veritasium (2015)>: it mentions the <Alain Aspect>[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.}
\Video[https://www.youtube.com/watch?v=Z34ugMy1QaA]
{title=Quantum Entanglement Lab by <Scientific American> (2013)}
{description=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.}