  Quantum point contacts (QPCs) are commonly employed to capacitively detect
the charge state of coupled quantum dots (QD). An indirect back-action of a
biased QPC onto a double QD laterally defined in a GaAs/AlGaAs heterostructure
is observed. Energy is emitted by non-equilibrium charge carriers in the leads
of the biased QPC. Part of this energy is absorbed by the double QD where it
causes charge fluctuations that can be observed under certain conditions in its
stability diagram. By investigating the spectrum of the absorbed energy, we
identify both acoustic phonons and Coulomb interaction being involved in the
back-action, depending on the geometry and coupling constants.
