What Properties Can Become Entangled When Atoms Interact?

[idea2000]

Hi,

I read this article on quantum entanglement of beryllium atoms:

http://www.physorg.com/news80396930.html

I have read other similar articles on the entanglement of photons and I understand that the spin of two photons can become entangled.

My question is, when two atoms become entangled, what properties of the two atoms are entangled? So far, the only articles that I've read have to do with the spin becoming entangled. In general, what other properties can become entangled? Can any quantum state become entangled?

Another related question
In the article above, it mentions that some pairs can become perfectly entangled, whereas others are not entangled with "high fidelity". It also talks about atoms being entangled with higher purity and the link between the two particles degrading as they move apart. It seems from the reading the article that a pair of particles can be somewhat entangled, but not quite entangled. How can a pair of particles become entangled, but not quite entangled?

Thanks!

 

[DrClaude]

My question is, when two atoms become entangled, what properties of the two atoms are entangled? So far, the only articles that I've read have to do with the spin becoming entangled. In general, what other properties can become entangled? Can any quantum state become entangled?

Yes, any quantum property can be entangled. Entanglement (for two particles) simply means that is is not possible to write a two-particle state as a product of single-particle states. In that way, the state of each particle is dependent on the state of the other.

In the article above, it mentions that some pairs can become perfectly entangled, whereas others are not entangled with "high fidelity". It also talks about atoms being entangled with higher purity and the link between the two particles degrading as they move apart. It seems from the reading the article that a pair of particles can be somewhat entangled, but not quite entangled. How can a pair of particles become entangled, but not quite entangled?

The atoms can not only be in pure states, but also in mixed states, with some statistical uncertainty.
https://en.wikipedia.org/wiki/Quantum_state#Mixed_states