Ultrafast coherent spectroscopy of one-dimensional magnetoexcitons in semiconductors

We investigate the ultrashort coherent dynamics of one-dimensional Fano and Lorentzian magnetoexcitons in GaAs using temporally and spectrally resolved four-wave mixing (FWM). The dephasing time of a Fano resonance 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 scattering at low temperatures. We find a very fast decay of the time-integrated 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 destructive quantum interference is not observed for purely Lorentzian dynamics. For the simultaneous excitation of Lorentzian and Fano magnetoexciton resonances, destructive quantum interference also quenches the coherent emission from Lorentzian magnetoexcitons due to quantum mechanical coupling between the different resonances.