  The stochastic methods in Hilbert space have been used both from a
fundamental and a practical point of view. The result we report here concerns
only the idea of applying these methods to model the evolution of quantum
systems and does not enter into the question of their fundamental or practical
status. It can be easily stated as follows: Once a quantum stochastic evolution
scheme is assumed, the incompatibility between the Markov property and the
notion of quantum jump is rapidly established.
