Transmission phase shift of a quantum dot with Kondo correlations

We study the effects of Kondo correlations on the transmission phase shift uf a quantum dot in an Aharonov-Bohm ring. We predict in detail how the dev elopment of a Kondo resonance should affect the dependence of the phase shi ft on transport voltage, gate voltage, and temperature. This system should allow the first direct observation of the well-known scattering phase shift of pi/2 expected (but not directly measurable in bulk systems) at zero tem perature for an electron scattering off a spin-1/2 impurity that is screene d into a singlet.