  Recent interest in the role of quantum mechanics in the primary events of
photosynthetic energy transfer has led to a convergence of nonlinear optical
spectroscopy and quantum optics on the topic of energy-transfer dynamics in
pigment-protein complexes. The convergence of these two communities has
unveiled a mismatch between the background and terminology of the respective
fields. To make connections, we provide a pedagogical guide to understanding
the basics of two-dimensional electronic spectra aimed at researchers with a
background in quantum optics.
