What's the highest-$n$ Rydberg state that's been created and detected experimentally?

Question

Rydberg states form an infinite series of electronic states that asymptotically approach the ionization potential of the atom or molecule, usually in good agreement with the simple Rydberg formula.

^{Image source}

Experimentally, it seems that it's relatively workable to produce Rydberg states with principal quantum number $n$ up in the several hundreds. How high does this ladder go? That is, what is the highest $n$ that has been produced and detected in an experiment?

Similarly, what's the record in terms of circular Rydberg states, i.e. for Rydberg states with saturated angular momentum $\ell=n-1$?

Answer 1

Here is a paper from 2009 in which they go up to $n=700$:

• Engineering atomic Rydberg states with pulsed electric fields. FB Dunning et al. J. Phys. B: At. Mol. Opt. Phys. 42, 022001 (2009).

That's the highest I've ever come across. Targeting single Rydberg states spectroscopically becomes extremely difficult above the $n=100$-$200$ range because the spacing between levels becomes too small, scaling with $n^{-3}$ (not to mention that the levels themselves become extremely sensitive to external fields, scaling with $n^7$).

The highest state to which people can coherently excite is much lower. It is routinely done up to about $n=100$, sometimes a bit higher. In our lab we use $n=70$.