PHASE EFFECT FOR ATOMIC DIPOLES IN A JAYNES-CUMMINGS MODEL WITH VARIOUS INITIAL ELECTROMAGNETIC-FIELDS

We investigate the difference between the time dependence of the real and imaginary parts of the expectation value of the complex dipole mom ent ([S(x)] and [S(y)]) of a two-level atom in a Jaynes-Cummings model . We find that this difference is controlled by the phase of the initi al field state as well as by the phase of the initial atomic dipole. W e find that if the two expectation values of the dipole moment are ini tially equal, a different dependence on time is achieved only if the p hase of the initial field is well defined. This is demonstrated by cal culating the real and imaginary parts of the dipole moment with differ ent initial states of the field. The initial electromagnetic states in vestigated are: number state, chaotic field, coherent field, squeezed vacuum (SV) and displaced squeezed states (SS). We associate the phase of SS with two-photon phase operators and in this way we get a well d efined phase for SV and ''displaced phase SS with strong squeezing. Th e difference between SS with a well-defined phase and coherent fields is manifested mainly in the damping of revivals and oscillations for s trong squeezing. For cases in which the phase of SS is well defined a new kind of ''damping'' for the dipole moment occurs which is differen t for the real and imaginary dipole components. We discuss some possib ilities for measuring these effects.