  We propose a general method for optical control of magnetic Feshbach
resonances in ultracold atomic gases with more than one molecular state in an
energetically closed channel. Using two optical frequencies to couple two
states in the closed channel, inelastic loss arising from spontaneous emission
is greatly suppressed by destructive quantum interference at the two-photon
resonance, i.e., dark-state formation, while the scattering length is widely
tunable by varying the frequencies and/or intensities of the optical fields.
This technique is of particular interest for a two-component atomic Fermi gas,
which is stable near a Feshbach resonance.
