The exact solution of the master equation for the case of a high-Q cavity with atomic decay is found. We use
the negativity of the Wigner function (WF) as an indicator of non-classicality. It is found that the negative values of
the field WF are very sensitive to any change in the damping parameter. The atomic spontaneous decay leads to the
simultaneous disappearance of both entanglement and nonclassicality of quantum states. Moreover, the purity of the
field states is lost completely.