  Double-quantum two-dimensional coherent spectroscopy (MDCS) is a powerful
optical method that is used to study optical properties of atomic and complex
molecular systems and semiconductor materials. Double-quantum 2D spectra and
particularly the peak lineshapes on the spectra can also provide information
about many-body interactions. We model 2D spectra by solving the optical Bloch
equations and show the effects of correlation between coupled resonances, which
also explains the discrepancies between the experimental results reported by
multiple groups.
