  We investigate both experimentally and theoretically disorder induced damping
of Bloch oscillations of Bose-Einstein condensates in optical lattices. The
spatially inhomogeneous force responsible for the damping is realised by a
combination of a disordered optical and a magnetic gradient potential. We show
that the inhomogeneity of this force results in a broadening of the
quasimomentum spectrum, which in turn causes damping of the centre-of-mass
oscillation. We quantitatively compare the obtained damping rates to the
simulations using the Gross-Pitaevskii equation. Our results are relevant for
high precision experiments on very small forces, which require the observation
of a large number of oscillation cycles.
