  Weak near-infrared and strong terahertz excitation are applied to study
excitonic Rabi splitting in (GaIn)As/GaAs quantum wells. Pronounced
anticrossing behavior of the split peaks is observed for different terahertz
intensities and detunings relative to the intraexcitonic heavy-hole
1s-2p-transition. At intermediate to high electric fields the splitting becomes
highly asymmetric and exhibits significant broadening. A fully microscopic
theory is needed to explain the experimental results. Comparisons with a
two-level model reveal the increasing importance of higher excitonic states at
elevated excitation levels.
