  We report the experimental realization of a new kind of optical lattice for
ultra-cold atoms where arbitrarily large separation between the sites can be
achieved without renouncing to the stability of ordinary lattices. Two
collinear lasers, with slightly different commensurate wavelengths and
retroreflected on a mirror, generate a superlattice potential with a periodic
"beat-note" profile where the regions with large amplitude modulation provide
the effective potential minima for the atoms. To prove the analogy with a
standard large spacing optical lattice we study Bloch oscillations of a Bose
Einstein condensate with negligible interactions in the presence of a small
force. The observed dynamics between sites separated by ten microns for times
exceeding one second proves the high stability of the potential. This novel
lattice is the ideal candidate for the coherent manipulation of atomic samples
at large spatial separations and might find direct application in atom-based
technologies like trapped atom interferometers and quantum simulators.
