Coherent off-resonant excitation of an infinite series of bound states, not unlike an atomic Rydberg series, is shown to lead to suppression of mixing between the degenerate levels of the Rydberg state that is resonantly excited. The generation of high harmonics that accompanies the mixing is similarly suppressed.

Phys. Rev. Lett.

Muller, H. G., & Noordam, L. D. (1999). Suppression of angular-momentum mixing in photoexcitation of Rydberg states by multistate off-resonant quantum coherence. Phys.Rev.Lett., 82, 5024–5027.