  We investigate resonant tunneling through molecular states of coupled double
quantum dots embedded in an Aharonov-Bohm (AB) interferometer. The conductance
through the system consists of two resonances associated with the bonding and
the antibonding quantum states. We predict that the two resonances are composed
of a Breit-Wigner resonance and a Fano resonance, those widths and Fano factor
depending on the AB phase very sensitively.
  Further, we point out that the bonding properties, such as the covalent and
the ionic bonding, can be identified by the AB oscillations.
