I’m a big fan of review articles. For those not in academic science, “review article” means a long (tens of pages) paper collecting together the important results of some field of science, and presenting an overview of the whole thing. These vary somewhat in just how specific they are– some deal with both experiment and theory, others just theoretical approaches– and some are more readable than others, but typically, they’re written in a way that somebody from outside the field can understand.
These are a great boon to lazy authors, or authors facing tight page limits (“Ref.  and references therein” takes up a lot less space than individual citations for the ten most important historical papers), and also to people who would like to get a technical introduction to a new field. They have a slight tendency to overemphasize the particular interests or results of the people writing the review, but that’s not too big a distortion, provided the authors are chosen well.
The journal Reviews of Modern Physics is primarily review articles of this type, and a recent paper there caught my eye as something worth talking about on the blog. Hence this post.
Waitaminute– do you seriously expect us to wade through 51 pages of a physics article? No, not really. Not unless you really want a thorough overview of the field. It’s more that this is an area of work that is generating some interest these days, and this article is a convenient collection of the important results. You don’t need to read the whole thing, though– you can just skim it for the good parts if you like.
All right, then. So, what do loathsome bipedal crustaceans have to do with quantum information? That’s a Zoidberg, not a Rydberg. A “Rydberg atom” is an atom in a highly excited state, very close to the ionization limit– technically, it probably ought to be “quantum information with atoms in Rydberg states,” but “Rydberg atom” is well established jargon and there’s nothing to be done about it now.
The name comes from the Rydberg formula, which was the first really good description of the emission spectrum of hydrogen, which Niels Bohr eventually showed could be interpreted as describing transitions between discrete electronic states of the atom. The Rydberg formula only works well for the low-lying states of hydrogen, because interactions between the electrons in more complicated atoms (i.e., everything else) shift all the energy states. If you take one electron and excite it to a very high level, though, the states up there start to follow something like the Rydberg formula again.