Recently Nekrasov and Shatashvili proposed a remarkable relationship between supersymmetric gauge theories and integrable models. One example is the N=2 super QCD with Nf = 2Nc, whose Seiberg-Witten curve corresponds to the Baxter equation of an integrable spin chain. When the four dimensional theory is subject to Omega deformation in one plane, the supersymmetric vacua is quantized and identified with the eigenstates of the spin chain. I will talk about how to understand the low-energy electromagnetic duality as a particle-hole duality. This is joint work with Nick Dorey and Sungjay Lee.