APPLICATION OF LOWDIN PROJECTORS TO EVALUATE DENSITY-MATRIX EVOLUTIONS

Projection operators are employed to evaluate functions of operators. In particular, this formalism is used to find polynomial expressions for exponential operators and thence to solve density matrix evolutions in closed analytical form. Problems explicitly treated include pulse rotation of spin-I and spin - 3 2 systems, spin tickling and spin interferometry on a system of two coupled spin- 1 2 nuclei, isotropic mixing in systems of two coupled nuclei (both spins- 1 2 or spins-1), and dipolar evolution in a two-spin- 1 2 system. The method is compared to the BCH approach for operator evolutions. © 1990.