Entropy for the quantized field in the atom-field interaction: Initial   mixed field
  We study the atom-field interaction when the field is in a mixture of coherent states. We show that in this case it is possible to calculate analytically the field entropy for times of the order of twice the collapse time. Such analytical results are done with the help of numerical analysis. 
A. Zuniga-Segundo, R. Juarez-Amaro, O. Aguilar-Loreto and H.M.   Moya-Cessa
quant-ph