The Wigner-Eckart theorem concerns matrix elements of a type that is of frequent occurrence in all areas of quantum physics, especially in perturbation theory and in the theory of the emission and absorption of radiation. This theorem allows one to determine very quickly the selection rules for the matrix element that follow from rotational invariance. In… (More)

@inproceedings{Littlejohn2017IrreducibleTO,
title={Irreducible Tensor Operators and the Wigner - Eckart Theorem},
author={Robert G. Littlejohn},
year={2017}
}