Suppression of the four-wave mixing amplification via Raman absorption

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 $Λ$ 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.

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