Two-color optical nonlinearity in an ultracold Rydberg atom gas mixture

We report the experimental observation of strong two-color optical nonlinearity in an ultracold gas $^{85}\mathrm{Rb}$-$^{87}\mathrm{Rb}$ atom mixture. By simultaneously coupling two probe transitions $^{85}$Rb and $^{87}$Rb atoms to Rydberg states electromagnetically induced transparency (EIT) configurations, we observe significant suppression resonance for one field when second is detuned at $\sim1~\mathrm{GHz}$ hitting EIT other isotope. Such a cross-absorption modulation beam propagation dynamics can be described by coupled nonlinear wave equations develope. further demonstrate that tuned varying density ratio different atomic isotopes, which highlights its potential exploring strongly interacting multi-component fluids light.