Coherent Population Trapping of a Three-level Atom Interacting with Few Cycle Pulse Train

Abstract

The poulation transfer and coherent population trapping of a three-level atom interacting with few cycle pulse train are studied.The density matrix equation in interation picture is numerical solved without rotating wave approximation.The research indicates that if a three-level atom interacts with a few cycle pulse train,the population transfer of level and the coherence of ground state will be gradual accumulated.When the repetition frequency of pulses is integer points of the ground-state splitting,the three atom interacts with pulse train can be seen as the atom interacts with two tenoning frequency of the frequency comb.So the system will be in the dark state and reach coherent population trapping.If the parameters of few-cycle pulse are appropriately selected,the coherence of three-level system will evolute into stable value in 0.5 nanosecond.The coherent population trapping in the three-level is generated.Comparing with the pulse that the pulse width is 100 femtoseconds,the build-up time of coherent population trapping by few cycle pulse train is shortened two orders of magnitude.When the ground-state splitting is wided enough and the carrier frequency of pulse is ω=(ω1+ω2)/2,where,are the atomic transition frequency,the doppler frequency shift that is aroused by the movement of atom won't destroy the coherent population trapping of atom.The reason is that all tenoning frequencies of the frequency comb have the same frequency shift,so the condition of coherent population trapping is still meeted.