Fig. 5. Comparison of quantum and classical 2D spectra.

(A) 2D spectra obtained by the quantum spectroscopy described in Eq. 8. (B) Absorptive 2D spectrum obtained using the classical pulses in the impulsive limit. (C) SE contribution to the absorptive 2D spectra. In (A), the detection time of the idler photon was set as $t_{\mathrm{I}}=0$. The time resolution of the detector and the frequency resolution of the spectrometer were set to ${\mathrm{\sigma }}_{\mathrm{t}}=400 \text{fs}$ and ${\mathrm{\sigma }}_{\mathrm{f}}=0$, respectively. Normalization of contour plots in (A) to (C) is such that the maximum value of each spectrum at $t_{\mathrm{F}}=0$ (${\mathrm{\tau }}_2=0$) is unity, and equally spaced contour levels ($0,\pm 0.1,\pm 0.2,\dots$) are shown.