Tunnelling-Induced Transient Gain in an Asymmetric Double Quantum Well

We investigate the transient behaviour of a weak probe in asymmetric double quantum well structures, where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. There is no external coherent coupling field applied, and we find that probe gain can be achieved during the transient process, which is induced by the coherent coupling of the upper states via the resonant tunnelling. We show that the transient behaviour of the probe depends on the coupling strength and the dephasing rate and can be tuned by changing the width of the tunnelling barrier.