  The aim of this chapter is to describe two situations where positive noise
correlations can be directly monitored using a transport experiment, either
with a superconductor or with a correlated electron system. To be more precise,
the present text reflects the presentations made by the three authors during
the Delft NATO workshop. Bell inequalities and quantum mechanical non-locality
with electrons injected from a superconductor will be addressed first. Next,
noise correlations will be computed in a carbon nanotube where electrons are
injected in the bulk from a STM tip. The first topic is the result of an
ongoing collaboration with G. Lesovik and G. Blatter over the years. The
unifying theme is that in both branched quantum circuits, entanglement is
explicit and can be illustrated via noise correlations. Entanglement can be
achieved either for pairs of electrons in the case of superconductor sources
connected to Fermi liquid leads, or alternatively for pairs of quasiparticle
excitations of the correlated electron fluid.
