This animation shows the variation of the spectral function in the quasi-bound state region as the atomic well depth parameter g varies. The dashed line represents the spectral function without an electric field. In this F=0 case, as g increases and reaches the point where ag=1 a second bound state emerges from the continuum, and then these two bound states decrease in energy, slowly merging to become degenerate at g ® ¥. The solid line shows the situation with the external electric field present, in which case we see the second quasi-bound state emerge from the continuum. Notice that the two quasi-bound states become narrower in width as g increases, as tunneling becomes suppressed. Also note that as g becomes large the separation between the two quasi-bound levels tends to 2Fa, which equals 1.5 for this animation.