  In the framework of the Lindblad theory for open quantum systems, expressions
for the density operator, von Neumann entropy and effective temperature of the
damped harmonic oscillator are obtained. The entropy for a state characterized
by a Wigner distribution function which is Gaussian in form is found to depend
only on the variance of the distribution function. We give a series of
inequalities, relating uncertainty to von Neumann entropy and linear entropy.
We analyze the conditions for purity of states and show that for a special
choice of the diffusion coefficients, the correlated coherent states (squeezed
coherent states) are the only states which remain pure all the time during the
evolution of the considered system. These states are also the most stable under
evolution in the presence of the environment and play an important role in the
description of environment induced decoherence.
