  The exact non-Markovian dynamics of a microcavity strongly coupled to a
general reservoir at arbitrary temperature is studied. With the exact master
equation for the reduced density operator of the cavity system, we analytically
solve the time evolution of the cavity state and the associated physical
observables. We show that the non-Markovian dynamics is completely determined
by the propagating (retarded) and correlation Green functions. Compare the
non-Markovian behavior at finite temperature with those at zero-temperature
limit or Born-Markov limit, we find that the non-Markovian memory effect can
dramatically change the coherent and thermal dynamics of the cavity. We also
numerically study the dissipation dynamics of the cavity through the mean mode
amplitude decay and the average photon number decay in the microwave regime. It
is shown that the strong coupling between the cavity and the reservoir results
in a long-time dissipationless evolution to the cavity field amplitude, and its
noise dynamics undergoes a critical transition from the weak to strong coupling
due to the non-Markovian memory effect.
