In this section we review well-known facts about angular
momentum operators in quantum mechanics1–4 in order to
introduce the notation used in the following. We denote the
Cartesian components of the angular momentum operators
by jˆ i , where i5x,y,z. The commutation relations read as
@jˆ x ,jˆ y#5ijˆ z , ~1!
and cyclic permutations of this equation.