COHERENCE AND PHASE-SENSITIVE MEASUREMENTS IN A QUANTUM-DOT

Via a novel interference experiment, which measures magnitude and phas e of the transmission coefficient through a quantum dot in the Coulomb regime, we prove directly, for the first time, that transport through the dot has a coherent component. We find the same phase of the trans mission coefficient at successive Coulomb peaks, each representing a d ifferent number of electrons in the dot, however, as we scan through a single Coulomb peak we find an abrupt phase change of pi. The abrupt phase change can be explained in the framework of a one-dimensional mo del, which we develop.