Decay of an excited system to its ground state is a ubiquitous phenomenon in all branches of physics. Here we use a photonic simulator to show specific and counterintuitive features of such decay in quantum systems. Significant deviations from the widely accepted exponential decay dynamics are experimentally demonstrated, in particular showing oscillatory behavior at very long decay times. Such oscillation are due to quantum interference effects and mean that in this region the decay process is not monotonic but there is the possibility that the system is re-excited by the interaction with the environment.
