Comment on “Opening Optical Four-Wave Mixing Channels with Giant Enhancement Using Ultraslow Pump Waves

In their recent study [1] on a four-wave mixing (FWM) process, Deng et al. state that ‘‘many orders of magnitude enhancement in the amplitude of the generated wave’’ is obtained when electromagnetically induced transparency (EIT) is present. Here we will show that their claim is deeply misleading. In fact, according to the formulas reported in their paper, it is straightforward to show that the efficiency of the FWM generation process is actually reduced by the presence of EIT, and that the maximum FWM signal is obtained in the absence of EIT.