Synthetic spin-orbit coupling in ultracold $\Lambda$-type atoms
  We consider the simulation of non-abelian gauge potentials in ultracold atom systems with atom-field interaction in the $\Lambda$ configuration where two internal states of an atom are coupled to a third common one with a detuning. We find the simulated non-abelian gauge potentials can have the same structures as those simulated in the tripod configuration if we parameterize Rabi frequencies properly, which means we can design spin-orbit coupling simulation schemes based on those proposed in the tripod configuration. We show the simulated spin-orbit coupling in the $\Lambda$ configuration can only be of a form similar to $p_{x}\sigma_{y}$ even when the Rabi frequencies are not much smaller than the detuning. 
Ming-Yong Ye, Xiu-Min Lin
cond-mat.quant-gas