  There is an increasing interest in the role of macroscopic environments to
our understanding of the basics of quantum theory. The knowledge of the
implications of the quantum theory to other theories, especially to the
statistical mechanics and the domain of validity has captivated scientists from
the beginning of quantum description. In such a context, the presence of an
environment is commonly thought as entanglement, decohering and mixing
properties of quantum system. Generically, an environment is assumed to be a
noisy reservoir or a heat bath. Whereas in common interpretation of statistical
mechanics the heat bath is unspecified, in quantum systems a heat bath can also
provide an indirect interaction between otherwise totally decoupled subsystems
and consequently a means to entangle them \cite{cdkl,dvclp,bfp}. In simple
example for the entanglement between two qubits due to the interaction with a
common heat bath has been explicitly shown in \cite{b}. Whereas in that paper
the bath is described by a collection of harmonic oscillators, it seems to be
more reasonable to specify the bath by stochastic forces represented by
stochastic fields. From a more general point of view we expect the bath should
be better described in a stochastic manner and not by deterministic forces. In
the present paper we consider a two level system (qubits) which are able to
perform flip processes by a coupling to classical stochastic fields. Thus we
bridge the gap between quantum and classical probability theory. This problem
is related to many other questions of quantum optics and quantum electronics
where quantum statistical aspects arising from the intrinsic quantum character
of the system while the possible time-dependence of system parameters may be
interpreted as the influence of classical thermal fluctuations.
