Pumping at resonant transmission and transferred charge quantization

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.