The electromagnetically induced transparency in the Y-type four-level atom system at low light levels

In this paper a Y-type four-level atom interacting with external fields system is investigated. It is shown that increasing the control field can reduce the probe absorption, the electromagnetically induced transparency (EIT) and gain can be obtained if the parameters are taken appropriately. An interesting phenomenon is found that the system appears to be probe gain in a large region if the external fields Rabi phases are taken appropriately, too.