This the text of a proceeding accepted for the 21st International Symposium
on Mathematical Theory of Networks and Systems (MTNS 2014). We present some
results of an ongoing research on the controllability problem of an abstract
bilinear Schrodinger equation. We are interested by approximation of this
equation by finite dimensional systems. Assuming that the uncontrolled term A
has a pure discrete spectrum and the control potential B is in some sense
regular with respect to A we show that such an approximation is possible.
More precisely the solutions are approximated by their projections on finite
dimensional subspaces spanned by the eigenvectors of A. This approximation is
uniform in time and in the control, if this control has bounded variation with
a priori bounded total variation. Hence if these finite dimensional systems are
controllable with a fixed bound on the total variation of the control then the
system is approximatively controllable. The main outcome of our analysis is
that we can build solutions for low regular controls such as bounded variation
ones and even Radon measures
