Infrared-induced dark states and coherent population trapping of excitons in quantum well structures

Abstract

We study enhancement of the $2s$ state emission intensity of the e1-hh1 excitons via generation of dark states. This process is shown for a ${\mathrm{In}}_{0.43}{\mathrm{Ga}}_{0.57}\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}\mathrm{P}$ quantum well structure interacting with a single infrared laser near resonance with the transition between e1 and e2. Via generation of strong nonparabolic hole dispersion, the tensile strain of this structure enhances the dipole moments of the nonallowed transitions between the $2s$ states of the e1-hh1 and the $1s$ states of e2-hh1 excitons. We show that, due to the simultaneous coupling of these transitions and those between the $1s$ states of the e1-hh1 and e2-hh1 excitons (allowed transitions), the infrared field can generate dark states, coherently pumping the $2s$ states of e1-hh1 excitons and dramatically increasing their emission intensities. We also show that when the allowed and nonallowed transitions are driven by two resonant infrared field beams, coherent population trapping of excitons of the e1-hh1 excitons occurs.