CONTROLLING 2-LEVEL ATOMS WITH A QUANTIZED PI OR PI 2 PULSE/

We discuss the quantum effect of the optical control field such as a p i pulse and a pi/2 pulse on the decoherence of a two-level system to b e controlled in the experiments such as atom interference and quantum computation. A general solution for the Jaynes-Cummings model is obtai ned for this purpose, and the reduced density operator of the controll ed two-level atom after the interaction is calculated. Examining typic al initial quantum states for the control field such as number state, large-amplitude coherent state and small-amplitude coherent state, we can compare these states in the scope of atomic coherence controllabil ity. It became clear that a number state field mostly destroys the pur ity of the two-level atom, and that a large-amplitude coherent state i s ideal (except that large energy is required to control the atomic st ate). Use of a coherent state with considerably small photon number wi ll cause decoherence, but not too much.