Anomalously fast decay of the LH-HH exciton Raman coherence

We perform 3‐pulse transient four‐wave‐mixing on a GaAs/AlGaAs multiple quantum well. This allows us to measure both the decay of the Raman coherence between the heavy‐hole and light‐hole excitons and the decay of the respective optical coherences. We observe that the decay rate of the Raman coherence is greater than the sum of decay rates of the optical coherences. This cannot happen within a Markov approximation for the scattering processes, as verified by simulations. The simulations show that such behavior can occur only in the presence of anti‐correlated scattering processes in a non‐Markovian regime.