Excitonic quantum beats in semiconductor quantum-well structures Original Research Article

We study quantum beats from excitonic states in semiconductor quantum-well structures. The quantum beats manifest themselves as modulations in transient four-wave mixing (FWM) signals. Using time-integrated, time-resolved, and spectrally resolved detection of the FWM signal, beat phenomena of various origins are studied, including interferences between the bound and unbound (continuum) states of a quantum-well Wannier exciton, and interference between excitonic transitions associated with spatial regions of different quantum-well thickness. An attempt is made to specify in how far excitonic quantum beats can be described as interferences between the states of a multi-level system like in atomic and molecular spectroscopy. We investigate to which extent quantum beats are modified or even generated by Coulomb, disorder, and propagation induced effects characteristic of semiconductors and semiconductor heterostructures.