Resonant excitation amidst dephasing: An exact analytic solution
  An exact analytic solution is presented for coherent resonant excitation of a two-state quantum system driven by a time-dependent pulsed external field with a hyperbolic-secant shape in the presence of dephasing. Analytic results are derived for the amplitude and the phase shift of the damped Rabi oscillations. 
E. S. Kyoseva, and N. V. Vitanov