  A general theoretical approach to study the quantum kinetics in a system
coupled to a bath is proposed. Starting with the microscopic interaction, a
Lindblad master equation is established, which goes beyond the common secular
approximation. This allows for the treatment of systems, where coherences are
generated by the bath couplings while avoiding the negative occupations
occurring in the Bloch-Wangsness-Redfield kinetic equations. The versatility
and accuracy of the approach is verified by its application to three entirely
different physical systems: (i) electric transport through a double-dot system
coupled to electronic reservoirs, (ii) exciton kinetics in coupled chromophores
in the presence of a heat bath, and (iii) the simulation of quantum cascade
lasers, where the coherent electron transport is established by scattering with
phonons and impurities.
