Coherent properties of a tripod system coupled via a continuum

Coherent interaction between discrete quantum states via a continuum is an intriguing process. Although the continuum is traditionally seen as an incoherent medium, (partial) transfer of coherence can nevertheless occur through a continuum. In particular, much theoretical and experimental attention has been devoted to laserinduced continuum structure (LICS) [1–19], where the interaction between a discrete state ψ2 and a structureless, flat continuum creates a structure in the continuum which affects significantly the interaction of another discrete state ψ1 with this continuum. For example, the ionization probability for state ψ1, when plotted as a function of the frequency of the ionizing laser, exhibits the so-called Fano profile [1]. The physical nature of LICS is closely related to autoionizing states [1,20–26]. It has been suggested by Carroll and Hioe a few years ago [27,28] that a continuum can serve as an intermediary