PHASE RIGIDITY AND H 2E OSCILLATIONS IN A SINGLE-RING AHARONOV-BOHM EXPERIMENT/

We address the results presented recently by Yacoby er al. [Phys. Rev. Lett. 74, 4047 (1995)] on the coherency and phase evolution in a reso nant tunneling quantum dot embedded in an Aharonov-Bohm (AB) ring. The observed phase rigidity of the AB conductance oscillations is theoret ically explained by invoking simple symmetry arguments applicable to t wo terminal measurements, and is corroborated experimentally in generi c experiments. We show that under certain conditions h/2e oscillations dominate completely the conductance of a single AB ring.