What Are the Origins of Entangled Particles?

[edguy99]

I would find it helpful to have a list of where entangled particles come from (perhaps there is a good internet site with such a list that someone could post?). Along those lines I would like to start and refine such a list of entangled particles, what is entangled and get some feedback on the correctness of such a list. Here goes:

1/ gamma rays - when close to a nucleon, may produce an entangled electron/positron pair where the spin of the particles is opposite and the direction of motion of the particles is opposite.

2/ photons - when fired at a birefringent crystal, may produce entangled photons where the energy of the 2 photons add up to the original, the spin of both is the same, and the direction depends on the crystal.

3/ electrons - when falling into an energy level, if they have enough energy, may emit 2 photons with the same spin traveling in opposite directions where the energy of one photon minus the other, adds up to the difference in the energy level the electron finds itself in compared to the energy level it was at. (this may be the same as 2, but I am not sure?).

4/ nucleon decay - elements (especially with lots of extra neutrons) may decay and emit entangled electrons, where the spin of the electrons is opposite and direction is opposite.

Others?

 

[DrChinese]

2/ photons - when fired at a birefringent crystal, may produce entangled photons where the energy of the 2 photons add up to the original, the spin of both is the same, and the direction depends on the crystal.

Parametric down conversion is usually classified as the following:

Type I: It takes 2 of these crystals (oriented perpendicular) to get entanglement. The photons are parallel (same) polarization.

Type II: Only need 1 crystal, the photon pair output is perpendicular (opposite).

 

[DrChinese]

Others?

Probably hundreds, based on papers I have seen. Many of which could be called exotic, such as this one: http://arxiv.org/abs/0711.3662

All kinds of atomic structures can display entanglement, which often arises when components of a system are in indistinguishable configurations and there is a conservation rule in effect. Check at arxiv advanced search, variations of entanglement and experiment, such as this one:

http://arxiv.org/find/all/1/abs:+AND+entangled+experimental/0/1/0/all/0/1