  We consider pumping through a small quantum dot separated from the leads by
two point contacts, whose conductances, $G_{1}$ and $G_{2}$, serve as pumping
parameters. When the dot is pincched, we find that there is a "resonance line"
in the parameter plane $\{G_{1}, G_{2}\}$ along which the Fermi energy in the
leads aligns with the energy of the quasi-bound state in the quantum dot. When
$G_{1}$ and $G_{2}$ are modulated periodically and adiabatically such that the
pumping contour defined by $G_{1}=G_{1}(t)$ and $ G_{2}=G_{2}(t)$ encircles the
resonance line, the current is quantized: the charge pumped through the dot
during each period of the modulation is close to a single electronic charge.
