Transmission phase of a quantum dot: Testing the role of population switching

We propose a controlled experiment to clarify the physical mechanism 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. It offers a decisive test of “population switching”, one of the leading contenders for an explanation of the phenomenon.