Optical Dephasing in Multilevel Systems. Bath-Independent Dephasing and Breakdown of the Two-Level Approximation
A general description of zero-temperature pure dephasing in optical multilevel systems is presented. We derive expressions for the dephasing time due to transition multipole interactions. Specific application of the theory to mixed crystal systems predicts the dependence of the dephasing times on the concentration of guest molecules and transition dipole moments which is observed experimentally. Numerical estimates of the zero-temperature dephasing rates are in good agreement with experiments when the dependence on exciting pulse flip angle is included. Finally, our results suggest new experiments which are briefly discussed.