  We consider a three-port single-level quantum dot system with one input and
two output leads. Instead of considering an empty dot, we study the situations
that two input electrons co-tunnel through the quantum dot occupied by one or
two dot electrons. We show that electron entanglement can be generated via the
co-tunneling processes when the dot is occupied by two electrons, yielding
non-local spin-singlet states at the output leads. When the dot is occupied by
a single electron, net spin-singlet final states could be generated by
injecting polarized electrons to the dot system. When the input electrons are
unpolarized, we show that by carefully arranging model parameters non-local
spin-triplet electrons can also be obtained at the output leads if the
dot-electron spin remains unchanged in the final state.
