Quasiparticle representation of coherent nonlinear optical signals of multi-excitons
Abstract
Multi-exciton Green’s functions and scattering matrices in many fermion systems are calculated using a quasiparticle approach based on a generalized Bethe–Salpeter equation. The simulation protocol only requires numerical diagonalization of the single-exciton manifold. Using coboson algebra all many-body effects are recast in terms of two tetradic exciton–exciton interactions: direct Coulomb scattering and Pauli exchange. The tedious equations-of-motion derivations and calculations of multi-exciton manifolds are avoided. The approach is applied to calculate the third- and fifth-order signals generated by sequences of femtosecond optical pulses. Several coherent fifth order optical signals that directly probe three-exciton states and their projections on double and single-exciton states are predicted.