  The wave function of a moderately cold atom in a stationary near-resonant
standing light wave delocalizes very fast due to wave packet splitting.
However, we show that frequency modulation of the field may suppress packet
splitting for some atoms having specific velocities in a narrow range. These
atoms remain localized in a small space for a long time. We demonstrate and
explain this effect numerically and analytically. Also we demonstrate that
modulated field can not only trap, but also cool the atoms. We perform a
numerical experiment with a large atomic ensebmble having wide initial velocity
and energy distribution. During the experiment, most of atoms leave the wave
while trapped atoms have narrow energy distribution

Atomic Physics;Quantum Physics