To understand how Sisyphus cooling works, we consider a precooled atom (which we refer to as "hot"!), in the presence of a lin perp lin light field (Figure 5). We expect that as a result of optical pumping, atoms located in positions where the polarization is purely will be in the g_1/2  level, and in g_-1/2 where the polarization is purely σ^-.
Consider the atom in Figure 5 located at z = λ/2 (σ^-) and in state g_-1/2. As it moves to the right, it climbs the potential hill (z = 3λ/4) until it reaches the top, where the polarization is now purely σ⁺. At this point, the atom will be optically pumped from the g_-1/2 level to the g_+1/2 level (from g_-1/2  to e_1/2 {red arrow}, and then to g_+1/2  via spontaneous emission {blue arrow}) , where it will be in a lower energy state. Where does the energy, equal to the difference between the two potentials at z = 3λ/4, go? It gets carried off in the spontaneously emitted photon. Thus the atom has lost energy. This process is repeated as the atom moves to the next potential minimum, until the atom has an energy less than the depth of the potential, at which point it remains confined in a potential well.

In steady state, the atoms will come to rest in the minima of the two potentials.