  We present a novel quantum phenomenon named electromagnetically induced
entanglement in the conventional Lambda-type three-level atomic system driven
by a strong pump field and a relatively weak probe field. Nearly perfect
entanglement between the pump and probe fields can be achieved with a low
coherence decay rate between the two lower levels, high pump-field intensity,
and large optical depth of the atomic ensemble. The physical origin is quantum
coherence between the lower doublet produced by the pump and probe fields,
similar to the well-known electromagnetically induced transparency. This method
would greatly facilitate the generation of nondegenerate narrow-band
continuous-variable entanglement between bright light beams by using only
coherent laser fields, and may find potential and broad applications in
realistic quantum information processing.
