Superluminal two-color light in multiple Raman gain medium
  We investigate theoretically the formation of two-component light with superluminal group velocity in a medium controlled by four Raman pump fields. In such an optical scheme only a particular combination of the probe fields is coupled to the matter and exhibits superluminal propagation, the orthogonal combination is uncoupled. The individual probe fields do not have a definite group velocity in the medium. Calculations demonstrate that this superluminal component experiences an envelope advancement in the medium with respect to the propagation in vacuum. 
V. Kudria\v{s}ov, J. Ruseckas, A. Mekys, A. Ekers, N. Bezuglov and G.   Juzeli\=unas
quant-ph cond-mat.quant-gas physics.optics