Class multilevel::Exact< NL >: MultiLevel Exact not fully implemented, cf. the late 'shift' function. Maybe it's easier with something similar to Tridiagonal::freqs_ in Sigma
Class PumpedLossyMultiLevelSch< NL, VP, VL, AveragingType >: some static sanity checks of VP and VL in view of NL should be done
Class SpinBase: Implement some spherical-coordinates class and use it here
Page The MultiLevel bundle: Describe phase noise.