  The long time accumulation of the \textit{random} actions of a single
particle "reservoir" on its coupled system can transfer some temperature
information of its initial state to the coupled system. This dynamic process
can be referred to as a quantum thermalization in the sense that the coupled
system can reach a stable thermal equilibrium with a temperature equal to that
of the reservoir. We illustrate this idea based on the usual micromaser model,
in which a series of initially prepared two-level atoms randomly pass through
an electromagnetic cavity. It is found that, when the randomly injected atoms
are initially prepared in a thermal equilibrium state with a given temperature,
the cavity field will reach a thermal equilibrium state with the same
temperature as that of the injected atoms. As in two limit cases, the cavity
field can be cooled and "coherently heated" as a maser process, respectively,
when the injected atoms are initially prepared in ground and excited states.
Especially, when the atoms in equilibrium are driven to possess some coherence,
the cavity field may reach a higher temperature in comparison with the injected
atoms. We also point out a possible experimental test for our theoretical
prediction based on a superconducting circuit QED system.
