  We report the observation of Coulomb blockade in a quantum dot contacted by
two quantum point contacts each with a single fully-transmitting mode, a system
previously thought to be well described without invoking Coulomb interactions.
At temperatures below 50 mK we observe a periodic oscillation in the
conductance of the dot with gate voltage that corresponds to a residual
quantization of charge. From the temperature and magnetic field dependence, we
infer the oscillations are Mesoscopic Coulomb Blockade, a type of Coulomb
blockade caused by electron interference in an otherwise open system.
