Coherent control and enhancement of refractive index in an asymmetric double quantum well

We propose coherent control and enhancement of the refractive index with ze ro absorption in an n-type asymmetric double quantum well using intersubban d transitions. These effects are caused by quantum coherence and interferen ce whereby a strong infrared laser mixes upper conduction subbands of an in tersubband transition with an auxiliary subband. In the GaAs/AlxGa1-xAs sys tem considered here, an approximately 10% enhancement of the refractive ind ex accompanied with zero absorption occurs at 10.5 mum, when the system is driven by a 6.2-mum laser held with an intensity of similar to1 MW/cm(2). T he interplay between quantum coherence and electron population dynamics not only causes an enhancement of refractive index similar to that in atomic s ystems, but can also induce both low positive and negative group velocities .