  We report the experimental realization of double quantum dots in
single-walled carbon nanotubes. The device consists of a nanotube with source
and drain contact, and three additional top-gate electrodes in between. We show
that, by energizing these top-gates, it is possible to locally gate a nanotube,
to create a barrier, or to tune the chemical potential of a part of the
nanotube. At low temperatures we find (for three different devices) that in
certain ranges of top-gate voltages our device acts as a double quantum dot,
evidenced by the typical honeycomb charge stability pattern.
