Intersubband antipolaritons: Microscopic approach

This paper demonstrates that the coupling between light and intersubband excitations in semiconductors is fundamentally different from the well understood coupling to interband transitions that leads to excitonic polaritons. Numerical results for III-V quantum wells under nonequilibrium conditions are given by direct evaluation of analytical approximations obtained from a Keldysh Green's-function formalism. It is shown that bosonic approximations required for a Hamiltonian theory can be manipulated and turned on and off in the regime of excitations where the signatures of the coupling are stable and well defined. This is in contrast to interband polaritons, whose dispersions lose resolution as the exciton absorption is bleached and the bosonic approximation is violated. Thus, bosonic effects can be, in principle, controlled by manipulating the intersubband carrier injection. Furthermore, the evolution of the quasiparticle with injected carrier density is opposite to that of the conventional polariton. The approach consistently describes dispersions found experimentally if light is absorbed due to intersubband transitions and predicts anomalous dispersions under population inversion conditions. A more appropriate intersubband antipolariton is introduced to describe the light-intersubband excitation coupling. The influence of the dominant many-body effects on the quasiparticle dispersion is also discussed.