In a recent paper [Pham2022], our team has demonstrated the possibility to tune a laser close to the auto-ionizing doubly-excited Rydberg states of ytterbium atoms and obtain a large AC-Stark shift while suppressing the usual auto-ionization:

In a divalent atom like ytterbium, after exciting a first electron to a Rydberg state, the second electron will display optical transitions similar to the ones existing in the corresponding ion. The excitation of these transitions is called Isolated Core Excitation (ICE). Unfortunately, the resulting doubly excited atom will usually auto-ionize quickly. Indeed the total energy is far above the first ionization limit and the Coulomb interaction allows the two electrons to exchange energy. It is known though that many doubly excited states exist and that quantum interferences allow to control the auto-ionization down to zero for the correct destructive interferences. We have thus studied these auto-ionization zeros, with a specific interest to the resulting AC-Stark shift to check if it also vanishes or not. We have demonstrated both theoretically and experimentally that it does not vanish, thus proving the possibility to use ICE light to perform quantum operations on Rydberg qbits in atomic quantum processors.

[Pham2022] K.-L. Pham et al., PRX Quantum 3, 020327 (2022).