1. The problem statement, all variables and given/known data I have a question related to representation of rotation operator R in the basis spanned by the eigenvectors of J2 and Jz. I am studying from Quantum Mechanics by Zettili. The development of Wigner D-matrix and its elements Dj (Wigner functions) is clear. But the book goes on to say that the Wigner functions are joint eigenfunctions of J2 and Jz. How can the matrix elements be the eigenfunctions?