  The paper proposes the method to analyze the internal dynamics of nanoscopic
systems by periodic modulation of the electrochemical potentials of the
attached leads and measuring the time-averaged current. The idea is presented
using the example of the a double quantum dot coupled to one nonmagnetic and
one spin-polarized lead. The current flowing through the molecule is shown to
depend on both the frequency of the modulation and the exchange coupling
between the electrons occupying the molecule. In particular, one can observe a
pronounced oscillatory behavior of the current-frequency dependence, which
reveals the coherent oscillations between the spin states of the system.
