  The large N spectrum of the quantum mechanical hamiltonian of two hermitean
matrices in a harmonic potential is studied in a framework where one of the
matrices is treated exactly and the other is treated as a creation operator
impurity in the background of the first matrix. For the free case, the complete
set of invariant eigenstates and corresponding energies are obtained. When
g_{YM}^2 interactions are added, it is shown that the full string tension
corrected spectrum of BMN loops is obtained.
