  We measure the quantum speed of the state evolution of the field in a
weakly-driven optical cavity QED system. To this end, the mode of the
electromagnetic field is considered as a quantum system of interest with a
preferential coupling to a tunable environment: the atoms. By controlling the
environment, i.e., changing the number of atoms coupled to the optical cavity
mode, an environment assisted speed-up is realized: the quantum speed of the
state re-population in the optical cavity increases with the coupling strength
between the optical cavity mode and this non-Markovian environment (the number
of atoms).
