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!