I'm new to quantum mechanics and I was wondering is there a limit on the size and material of objects that can be entangled? And how would one go about entangling these objects? I read that photons are the easiest to entangle, but I've also seen an article where two millimeter wide diamonds were entangled.

  • $\begingroup$ "I've also seen an article where two millimeter wide diamonds were entangled" - don't believe everything you read. The LQE (Large Quantum Entangler) device has not yet been invented. $\endgroup$ – safesphere Jan 29 '18 at 0:39
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    $\begingroup$ @safesphere was published in Science some time ago: nature.com/news/entangled-diamonds-vibrate-together-1.9532 $\endgroup$ – Allure Jan 29 '18 at 1:00
  • $\begingroup$ @Allure Let me clarify my statement. Don't believe everything you read in Science ;) $\endgroup$ – safesphere Jan 29 '18 at 1:08

Yes and no. The "no" part comes from the fact that we know quantum mechanics isn't a complete theory - it fails when gravity becomes important. So it's possible that we cannot entangle Saturn & Jupiter (but it's also possible we can; we just don't have a quantum theory of gravity yet).

Having said the above, in QM, there's no theoretical limit on how large an object is before it cannot be entangled. In practice, we can't use overly large objects because they "decohere" - they interact with the environment, which kills the quantum superposition. The larger the two objects are, the harder it is to insulate them from the environment, and the harder it is to entangle them.

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    $\begingroup$ Can you explain how "quantum mechanics fails when gravity becomes important"? $\endgroup$ – safesphere Jan 29 '18 at 1:12
  • $\begingroup$ Is there a theoretical limit on what materials or structures that can be entangled? $\endgroup$ – AL_1 Jan 29 '18 at 1:39
  • $\begingroup$ @safesphere Now that you mention it I'm actually not so certain, since I'm no expert on quantum gravity. If someone else better in the know wants to edit the answer feel free. AL_1, as far as I know, there's no theoretical limit. $\endgroup$ – Allure Jan 29 '18 at 7:41

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