  We study the orbital entanglement in a biased Aharonov-Bohm ring connected in
a four-terminal setup. We find that the concurrence achieves a maximum when the
magnetic flux B coincides with an integer number of a half flux quantum 0 /2.
We show that this behavior is a consequence of the existence of degenerate
states of the ring having opposite chirality. We also analyze the behavior of
the noise as a function of and discuss the reliability of this quantity as
evidence of entanglement.
