Communications: Signatures of quasiparticle entanglement in multidimensional nonlinear optical spectroscopy of aggregates.

Excitons represent collective optical excitations in which the motions of electrons belonging to different chromophores are correlated. We discuss the utility of the notion of entanglement commonly used in quantum information processing, in the description of these excitations. A distinction is made between some apparent entanglement effects associated with the linear response that may be removed by a transformation of coordinates and can be handled classically, and genuine entanglement that is fundamentally quantum in nature and shows up only in the nonlinear optical response.