The photon-number-dependent parts in the evolution operator are cancelled with the assistant of a strong classical field, so the scheme is insensitive to the thermal field.

Considering the initial atomic coherence and the detuning, dipole squeezing of a two-level atom interacting with squeezed vacuum field is studied by means of the time-evolution operator method.

For the basic differential evolution algorithm, the increasing quadratic function crossover operator was added to increase the convergence speed.