Direct observation of the excitonic ac Stark splitting in a quantum well

Ultrafast pump-probe measurements evidence the dynamical Stark splitting in the exciton absorption spectrum of a single semiconductor quantum well. Th e intensity of the Stark sidebands in the spectrum is comparable to the lin ear absorption and their separation scales as the pump field amplitude. In the time domain the Rabi oscillations are observed. The semiconductor Bloch equations solved in the Hartree-Fock approximation demonstrate that the co herent exciton-light coupling dominates over the many-body dephasing.