Dynamic control of the entanglement in the presence of the time-varying field

The interactions between a two-level atom and a field with a time-varying frequency have been investigated. The two typical cases, the frequency of the field varying with time in the forms of sine and rectangle, have been considered. The dynamic behavior of the atom-field entanglement is investigated numerically as function of time. A number of novel phenomena are discovered and discussed. The sine modulation of the field frequency can help to realize and stabilize the degree of the atom-field entanglement at high level. The influence of the rectangular frequency modulated field on the atom-field entanglement indicates that the entanglement is more sensitive to the detuning than the correlation between different Rabi oscillations. Not only the sine field frequency modulation but also the rectangular field frequency modulation is favorable to improve, enhance and stabilize the degree of the atom-field entanglement.