ULTRAFAST COHERENT SPECTROSCOPY OF ONE-DIMENSIONAL MAGNETOEXCITONS INSEMICONDUCTORS

We investigate the ultrashort coherent dynamics of one-dimensional Fan o and Lorentzian magnetoexcitons in GaAs using temporally and spectral ly resolved four-wave mixing (FWM), The dephasing time of a Fano reson ance is intrinsically limited by the coupling between discrete states and continua which is responsible for Fano interference. In contrast, the coherent emission from Lorentzian magnetoexcitons dephases solely due to quasi-particle scattering, dominated by exciton-exciton scatter ing at low temperatures. We find a very fast decay of the time-integra ted FWM signal from Fano magnetoexciton resonances. This decay is not due to dephasing. The quenching of the FWM signal for non-overlapping excitation pulses is the result of quantum interference. This destruct ive quantum interference is not observed for purely Lorentzian dynamic s. For the simultaneous excitation of Lorentzian and Fano magnetoexcit on resonances, destructive quantum interference also quenches the cohe rent emission from Lorentzian magnetoexcitons due to quantum mechanica l coupling between the different resonances.