  Extension of coherent response time is a desired goal in the field of
all-optical information processing implemented in classical and quantum ways.
Here we demonstrate how spin-dependent stimulated photon echo can be used to
extend decay time of coherent signal from exciton ensemble. We experimentally
studied photon echoes from excitons in a model single InGaAs/GaAs quantum well
subject to transverse magnetic field. Field-induced quantum beats lead to
oscillation of exciton population between bright and long-lived dark excitons.
As a result, photon echo decays much longer with decay time attaining dark
exciton lifetime in case of non-oscillatory regime.
