  In this paper we will give a short presentation of the quantum Levy-Khinchin
formula and of the formulation of quantum continual measurements based on
stochastic differential equations, matters which we had the pleasure to work on
in collaboration with Prof. Holevo. Then we will begin the study of various
entropies and relative entropies, which seem to be promising quantities for
measuring the information content of the continual measurement under
consideration and for analysing its asymptotic behaviour.
