  We present a simple model of transmission across a metallic mesoscopic ring.
In one of its arm an electron interacts with a single magnetic impurity via an
exchange coupling. We show that entanglement between electron and spin impurity
states leads to reduction of Aharonov-Bohm oscillations in the transmission
coefficient. The spin-conductance is asymmetric in the flux reversal as opposed
to the two probe electrical conductance which is symmetric. In the same model
in contradiction to the naive expectation of a current magnification effect, we
observe enhancement as well as the suppression of this effect depending on the
system parameters. The limitations of this model to the general notion of
dephasing or decoherence in quantum systems are pointed out.
