Abstract
In this communication we examine the field entropy and the degree of entanglement for a time dependent Jaynes–Cummings model. We have allowed the amplitude of the laser field irradiating a trapped ion to be modulated. A sinusoidal modulation depending on a quadratic function in the argument is considered. At exact resonances the analytic solution for the wave function is given, and the density matrix operator is obtained. We show that for a small value of the acceleration the entanglement between the field and the atom would delay, while for a large value of the acceleration the entanglement decreases its value. We have also shown that the effect of the velocity is different from that of the acceleration where the value of the entropy decreases as we increase the value of its parameter.