Mesoscopic scattering in the half plane: Squeezing conductance through a small hole - art. no. 245312

We model the two-probe conductance of a quantum-point contact (QPC), in lin ear response. If the QPC is highly nonadiabatic or near to scatterers in th e open-reservoir regions, then the usual distinction between leads and rese rvoirs breaks down and a technique based on scattering theory in the full t wo-dimensional half plane is more appropriate. Therefore we relate conducta nce to the transmission cross section for incident plane waves. This is equ ivalent to Landauer's formula using a radial partial-wave basis. We derive the result that an arbitrarily small (tunneling) QPC can reach a p-wave cha nnel conductance of 2e(2)/h when coupled to a suitable ref-lector. If two o r more resonances coincide the total conductance can even exceed this. This relates to recent mesoscopic experiments in open geometries. We also discu ss reciprocity of conductance, and the possibility of its breakdown in a pr oposed QPC for atom waves.