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I get quantum entanglement but I don't quite get how one would go about generating two complementary particles that are entangled (a photon and its entangled sibling, an electron and its entangled sibling, etc.).

Can anyone explain this referencing how this could be achieved in a lab?


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For photons, take a positronium - an electron-positron bound state - and make sure that it's in the singlet, spin-zero, state. When it decays, the total spin has to be zero, so both photons resulting from the annihilation of the positronium have to be right-handed or both left-handed (because both of them go in the opposite direction, the same handedness means the opposite angular momentum, so that the sum cancels). For electrons, you may kick them e.g. out of helium where they're entangled, too. These are not necessarily the most practical ways but they are possible ways. –  Luboš Motl Apr 28 '11 at 5:15
nice - you should have this comment down as an answer! –  JohnIdol Apr 28 '11 at 9:15
just found this article which offers some more info about this (only they are generating 8 entangled photons): technologyreview.com/blog/arxiv/26837/?ref=rss –  JohnIdol Jun 2 '11 at 10:02
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up vote 5 down vote accepted

For photons, the process that immediately comes to mind is Spontaneous Parametric Down Conversion where a single photon is split into two by a nonlinear crystal. I've never actually bothered to look up methods for other qubit systems, but it looks like a search for "generating entangled electrons" without quotes in Google Scholar turns up quite a few results.

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