# Evidence for entanglement

1. Nov 30, 2011

### gespex

Hello all,

I know "quantum entanglement" is real, in some sense. I know that if we entangle two particles their spin, for instance, is closely related. Especially spin entanglement has enough evidence, yet it is also easy to explain using a hidden variable.
Hence I wonder: what other experimental evidence is there for entanglement? Which properties have been shown to be entangled, and in what way?

Gespex

2. Dec 1, 2011

### DrChinese

Once you read Bell's Theorem, I would hope you would revise your comment about "easy to explain using a hidden variable". A non-local hidden variable is theoretically feasible, but not with local ones. Are you familiar with Bell?

As to things that can be entangled: there are many things which have been experimentally entangled besides photons. I don't keep track of them specifically, but you can get an idea of papers published this year by scanning some of these:

http://arxiv.org/find/quant-ph/1/abs:+AND+entanglement+experiment/0/1/0/2011/0/1?per_page=100

Here is an older paper you may like:

Hyper-entanglement (more than just spin):
http://arxiv.org/abs/quant-ph/0406148

3. Dec 1, 2011

### gespex

Thank you for your answer. I'm not saying it is easy to introduce a local variable theorem for all of entanglement, only for the entanglement of spin.

I wasn't asking about what kind of particles have been entangled, I know it's not about the particles. But rather, which properties of particles have been tested to be entangled and in what way this test was done.
The only one I am aware of is spin, where the test is "up-spin" or "down-spin" for two distinct axis. But I know others have been tested as well, I just don't know of any such experiments.

Thanks

4. Dec 1, 2011

### DrChinese

Bell's Theorem shows that is not possible. See below for a proof (from my website, and I will be glad to answer any questions).

Bell's Theorem with Easy Math

5. Dec 1, 2011

### gespex

Hmm very interesting link... Maybe I was wrong, but I'm going to have to let it sink in a bit more.