On each orbit W of the
coadjoint representation of a nilpotent, connected and simply connected Lie group G,
there exist ∗ products which are relative quantizations for the Lie algebra
g of G. Choosing one of these ∗ products, we first define a ∗-exponential
for each X in g. These ∗-exponentials are formal power series and, with
the ∗ product, they form a group. Thanks to that, we are able to define a
representation of G in a “ ∗ polarization” and to intertwine it with the unitary
irreducible one associated to W. Finally, we study the uniqueness of our
construction.