  Within the imaginary-time theory for nonequilibrium in quantum dot systems
the calculation of dynamical quantities like Green's functions is possible via
a suitable quantum Monte-Carlo algorithm. The challenging task is to
analytically continue the imaginary-time data for both complex voltage and
complex frequency onto the real variables. To this end a function-theoretical
description of dynamical observables is introduced and discussed within the
framework of the mathematical theory of several complex variables. We construct
a feasible maximum-entropy algorithm for the analytical continuation by
imposing a continuity assumption on the analytic structure and provide results
for spectral functions in stationary non-equilibrium and current-voltage
characteristics for different values of the dot charging energy.
