  We propose a method to controllably suppress the effect of the four-wave
mixing caused by the coupling of the strong control optical field to both
optical transitions in the $\Lambda$ system under the conditions of
electromagnetically induced transparency. At sufficiently high atomic density,
this process leads to amplification of a weak optical signal field, that is
detrimental for the fidelity of any EIT-based quantum information applications.
Here we show that an additional absorption resonance centered around the idler
field frequency, generated in such a four-wave mixing process, may efficiently
suppress the unwanted signal amplification without affecting properties of the
EIT interaction. We discuss the possibility of creating such tunable absorption
using two-photon Raman absorption resonances in the other Rb isotope, and
present some preliminary experimental results.
