The theory of resonant tunneling of noninteracting electrons through localized states between two-dimensional reservoirs was developed by Xue and Lee405 (see also Refs.159 and406). If the resonances are well separated in energy, a single localized state will give the dominant contribution to the transmission probability. The maximum conductance on resonance is then e2/h (for one spin direction), regardless of the number of channels N in the reservoirs.405,406 This maximum (which may be interpreted as a contact resistance, similar to that of a quantum point contact) is attained if the localized state has identical leak rates L/¯h and R/¯h to the left and right reservoirs. Provided these leak rates are small (cf. Section IV.D) the conductance G as a function of Fermi energy EF is a Lorentzian centered around the resonance energy E0: