Use the matrix representation of the rotation operator R^(ϕk) in the ∣x⟩-∣y⟩ basis as given in (2.113) to establish that the photon circular polarization states (2.114), expressed as column vectors in the ∣x⟩-∣y⟩ basis, are eigenstates of the rotation operator with the eigenvalues that appear in (2.116) and (2.119).