  In this paper, we carry out a theoretical analysis of the zero-frequency and
finite-frequency shot noise in electron tunneling through a two-level
interacting system connected to two leads, when a coherent coupling between the
two levels is present, by means of recently developed bias-voltage and
temperature dependent quantum rate equations. For this purpose, we generalize
the traditional generation-recombination approach for shot noise of
two-terminal tunneling devices properly to take into account the coherent
superposition of different electronic states (quantum effects). As
applications, analytical and numerical investigations have been given in detail
for two cases: (1) electron tunneling through a quantum dot connected to
ferromagnetic leads with intradot spin-flip scattering, and (2) spinless
fermions tunneling through seriesly coupled quantum dots, focusing on the shot
noise as functions of bias-voltage and frequency.
