PHASE MEASUREMENT IN A QUANTUM-DOT VIA A DOUBLE-SLIT INTERFERENCE EXPERIMENT

The transport properties of electronic devices are usually characteriz ed on the basis of conductance measurements. Such measurements are ade quate for devices in which transport occurs incoherently, but for very small devices-such as quantum dots(1,2)-the wave nature of the electr ons plays an important role(3), Because the phase of an electron's wav efunction changes as it passes through such a device, phase measuremen ts are required to characterize the transport properties fully, Here w e report the results of a double-slit interference experiment which pe rmits the measurement of the phase-shift of an electron traversing a q uantum dot, This is accomplished by inserting the quantum dot into one arm of an interferometer, thereby introducing a measurable phase shif t between the arms, We find that the phase evolution within a resonanc e of the quantum dot can be accounted for qualitatively by a model tha t ignores the interactions between the electrons within the dot. Altho ugh these electrons must interact strongly, such interactions apparent ly have no observable effect on the phase. On the other hand, we also find that the phase behaviour is identical for all resonances, and tha t there is a sharp jump of the phase between successive resonance peak s. Adequate explanation of these features may require a model that inc ludes interactions between electrons.