Comment on "Gain-assisted superluminal propagation and rotary drag of photon and surface polaritons"

International audienceIn their study of superluminal propagation, rotary drag and surface polaritons [Phys. Rev. A 96, 013848 and 049906(E) (2017)], Khan et al. consider a four-level atomic arrangement with transitions in the optical domain. In fact, the values they give to the parameters lead to a probe wavelength lying in the decimeter band and we point out that, in such conditions, all their results are irrelevant