MEASUREMENT OF PHASE AND MAGNITUDE OF THE REFLECTION COEFFICIENT OF AQUANTUM-DOT

We measure the phase and magnitude of the reflection coefficient of a quantum dot (QD) in the integer quantum Hall regime. This was done by coupling the QD under study to a large QD, serving as an interferomete r, and monitoring the phase of the magnetoconductance oscillations of the coupled system. As the Coulomb blockade resonances of the QD are s canned we find two distinct and qualitatively different behaviors of t he phase. Our results agree for the most part with the theoretical pre dictions for resonant tunneling in a noninteracting system.