Before this interaction can be utilized, a fundamental understanding of how it works must be puzzled out of the menagerie of phenomena there are to observe. In order to get a picture of our research, it is important to understand the basics of atom-light interactions. The prototypical situation is the one shown below. The lines, representing the energy of the atom, show that the atom may be in either of two states. In the real world there's no such thing as a two level atom.
Real atoms have many, many more levels than just two.
To make matters even worse, each level itself may be made up of several sub-levels all with the same energy. Well, like I said, a real atom has many degenerate sub-levels. Well, that's where the polarization of the light comes in. By choosing the polarization of the light just right, namely by making it circular, we can tell the atom which one to go into. This is called optical pumping.