  Coherent two-dimensional electronic spectroscopy probes ultrafast dynamics
using femtosecond pulses. In case the timescale of the studied dynamics become
comparable to the pulse duration, pulse overlap effects may compromise the
experimental data. Here, we perform one-dimensional coherence scans and study
pulse overlap effects in clean two-level systems. We find parasitic
multiple-quantum coherence signals as a consequence of the arbitrary time
ordering during the temporal pulse overlap. Surprisingly, the signal lifetimes
exceed the temporal pulse overlap by a factor of 1.8. These findings have
important implications for the interpretation of higher-order coherent
two-dimensional and related spectroscopy experiments.
