Transmission phase of quantum dots: Testing the role of population switching

We propose a controlled experiment to clarify the role of "population switching," i.e., filling of one level at the expense of another one, in causing phase lapses of the amplitude for electron transmission through nanoscale devices. Such lapses are generically observed in valleys between adjacent Coulomb-blockade peaks. The experiment involves two quantum dots embedded in the same arm of an Aharonov-Bohm interferometer. By varying independently their gate voltages, one can controllably induce population switchings in consecutive Coulomb-blockade valleys, and test whether the expected phase lapses follow.