A quantum two-path interferometer allows for direct measurement of the transmission phase shift of an electron, providing useful information on coherent scattering problems. In mesoscopic systems, however, the two-path interference is easily smeared by contributions from other paths, and this makes it difficult to observe the true transmission phase shift. Here we address this problem and discuss the criteria to ensure reliable phase measurements. We compare the criterion used frequently in previous experiments with the one we have recently developed in our original two-path interferometer. We confirm that our criterion indeed ensures reliable phase measurements and on the other hand the other does not. Finally we discuss the phase behavior of the Kondo correlated quantum dot revealed in our original interferometer.

Contact : cecile.naud@neel.cnrs.fr