Optical coherence storage in dark exciton states using spin-dependent three-pulse photon echo

Extension of coherence time is a desired goal in the field of all-optical information processing implemented in both classical and quantum ways. Here we show how the decay time of a coherent signal from localized excitons can be significantly increased utilizing the spin degree of freedom. To experimentally demonstrate this effect, we studied three-pulse photon echoes from excitons in a single InGaAs/GaAs quantum well subject to a transverse magnetic field. Field-induced quantum beats lead to oscillation of the exciton population between short-lived bright and long-lived dark states during the coherence storage period between the second and third excitation pulses. In the aperiodic regime, the echo signal decay time tends to the dark exciton lifetime, which leads to an increase in the photon echo decay time by an order of magnitude.