  We will show how it is possible to generate entangled states out of
unentangled ones on a bipartite system by means of dynamical boundary
conditions. The auxiliary system is defined by a symmetric but not self-adjoint
Hamiltonian and the space of self-adjoint extensions of the bipartite system is
studied. It is shown that only a small set of them leads to separable dynamics
and they are characterized. Various simple examples illustrating this
phenomenon are discussed, in particular we will analyze the hybrid system
consisting on a planar quantum rotor and a spin system under a wide class of
boundary conditions.
