  Time-resolved electron transport in nano-devices is described by means of a
time-nonlocal quantum master equation for the reduced density operator. Our
formulation allows for arbitrary time dependences of any device or contact
parameter. The quantum master equation and the related expression for the
electron current through the device are derived in fourth order of the coupling
to the contacts. It is shown that a consistent sum up to infinite orders
induces level broadening in the device. To facilitate a numerical propagation
of the equations we propose to use auxiliary density operators. An expansion of
the Fermi function in terms of a sum of simple poles leads to a set of
equations of motion, which can be solved by standard methods. We demonstrate
the viability of the proposed propagation scheme and consider electron
transport through a double quantum dot.

Mesoscale and Nanoscale Physics