Facing the challenges of THz quantum cascade laser device development: the relevance of nonequilibrium many body theories

In this review we summarize current challenges for THz quantum cascade laser development as well as recent theoretical results, which indicate the relevance of nonequilibrium many body effects in the complex scattering and correlation microscopic mechanisms underlying the operation of those devices. The strongly nonthermal nature of the electronic wavefunctions, the fact that the energy difference between the subbands relevant for laser action are of the order of many body effects, and of the resulting level broadening, the Coulomb enhanced cross absorption, as well as the need to account for dephasing in the transport, require our advanced nonequilibrium many body approach for predictive simulations.