arXiv subjects
Publications and source records attributed to Shangqing Gong.
The second-order susceptibility which vanishes in the electric-dipole approximation for an atom is induced by the spontaneously generated coherence. The spontaneously generated coherence considered in a lambda-type atomic system causes an indirect coupling between the lower two levels which acts equivalently as a DC-field and therefore makes possible the existence of second-order susceptibility.
In a Lambda-type system employing a two-photon pump field, a four-wave mixing field can be generated simultaneously and hence a closed-loop system forms. We study theoretically on the effect of the relative phase between the two incident fields on the generated four-wave mixing field and the electromagnetically induced transparency. It is found that the phase of the generated four-wave mixing field is a sum of the incident relative phase and a fixed phase which is irrelative to the incident relative phase. Hence the total phase of the closed-loop system is independent of the incident relative phase. As a result, the incident relative phase has no effect on electromagnetically induced transparency, which is different from the case of a Lambda-type loop system closed by a third incident field.
We propose a scheme for creating atomic coherent superpositions via stimulated Raman adiabatic passage in a Lambda-type system where the final state has twofold levels. In the employ of a control field, the presence of double dark states leads to two arbitrary coherent superposition states with equal amplitude but inverse relative phase without the condition of multi-photon resonance. In particular, two orthogonal maximal coherent superposition states are created when the control field is resonant with the transition of the twofold levels. This scheme can also be extended to manifold Lambda-type systems.