We have developed a quantum jump approach for the one photon micromaser wit
h a Poissonian atomic pumping beam. In our approach we can describe the dyn
amics of the system, completely unravelling the master equation in terms of
stochastic wavefunctions. We have applied the approach to the most general
case in which the atoms enter the cavity in an arbitrary coherent superpos
ition of the atomic states with different initial conditions for the cavity
field. Hence, we are able to study the system dynamics when the atoms ente
r the cavity in the excited state and interacting initially with the field
in a pure state as well as when the atoms enter the cavity in a coherent su
perposition with the field initially in a statistical mixture leading to th
e production of a cotangent state.