Competition-induced shifts of spectral peaks in photon coincidence spectroscopy

We show that shifts in locations of two-photon coincidence spectral peaks, for a bichromatically driven two-level atom passing through a single-mode cavity, are due to competition between excitation pathways for a Jaynes-Cummings system. We also discuss an analogous shift of (single-photon) spectral peaks for a driven three-level V system, which demonstrates that competition between excitation pathways is also important in this simple system.