  We calculate the charge susceptibility and the linear and differential
conductances of a double quantum dot coupled to two metallic reservoirs both at
equilibrium and when the system is driven away from equilibrium. This work is
motivated by recent progress in the realization of solid state spin qubits. The
calculations are performed by using the Keldysh nonequilibrium Green function
technique. In the noninteracting case, we give the analytical expression for
the electrical current and deduce from there the linear conductance as a
function of the gate voltages applied to the dots, leading to a characteristic
charge stability diagram. We determine the charge susceptibility which also
exhibits peaks as a function of gate voltages. We show how the study can be
extended to the case of an interacting quantum dot.

Mesoscale and Nanoscale Physics