Double-quantum resonances and exciton-scattering in coherent 2D spectroscopy of photosynthetic complexes.

A simulation study demonstrates how the nonlinear optical response of the Fenna-Matthews-Olson photosynthetic light-harvesting complex may be explored by a sequence of laser pulses specifically designed to probe the correlated dynamics of double excitations. Cross peaks in the 2D correlation plots of the spectra reveal projections of the double-exciton wavefunctions onto a basis of direct products of single excitons. An alternative physical interpretation of these signals in terms of quasiparticle scattering is developed.